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Published by : INDIAN INSTITUTE OF CERAMICS Care : Central Glass & Ceramic Research Institute Kolkata — 700 032 Vol. 22 No. 1 2013

Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

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Page 1: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

Published by : INDIAN INSTITUTE OF CERAMICS Care : Central Glass & Ceramic Research Institute

Kolkata — 700 032

Vol. 22 No. 1 2013

Page 2: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC BULLETIN

Publication Committee

1. Prof. B.N. Samaddar ….. Chairman2. Prof. G.C. Das ….. Member3. Dr. Kaberi Das ….. Member4. Dr. Ritwik Sarkar ….. Member5. Dr. M.K. Haldar ….. Member6. Dr. Sankar Ghatak ….. Member7. Dr. Amarnath Sen ….. Member8. Prof. Om Prakash ….. Member9. Prof. F. D. Gnanam ….. Member10. Dr. K.G.K. Warrier ….. Member11. Dr. L.N. Satapathy ….. Member12. Dr. A. L. Shashi Mohan ….. Member13. Dr. L. K. Sharma ….. Member14. Prof. S. P. Singh ….. Member15. Dr. Sunanda Mukhopadhyay….. Member16. Dr. Gora Ghosh ….. Member17. Dr. Sanjay Kumar ….. Member18. Dr. Tapas Bhattacharya ….. Member19. Mr. S.N. Laha ….. Member20. Dr. Nibedita Chakraborty….. Member21. Dr. Parag Bhargava ….. Member22. Dr. S. P. Yawale ….. Member23. Prof. Siddhartha Mukherjee….. Convener

Hony Editor :

Editorial Office :Indian Institute of CeramicsCare : Central Glass & Ceramic Research InstituteP.O. Jadavpur UniversityKolkata – 700 032Tel : (033) 2413 - 8879 / 65366714E-mail : [email protected] site : www.iiceram.org

Vol. 22, No.1

CONTENTSEditorial Desk ....... 1

INSTITUTE ACTIVITIES ....... 2

STUDENT SECTION ....... 5

Report on the UGC sponsored ....... 6National Workshop on“Current trend”

TECHNICAL SECTION1. Recent advances in the field ....... 7

of MgO-C Refractories —by Siddhartha Mukherjee,Somdeb Pramanik, Soumya Mukherjee

2. A Brief Description of the ....... 16Processing of Ceramics —by Prof. Saikat Maitra

3. Particulate Composite — ....... 20by Jaydip Chakraborty

Page 3: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 1

Editorial Desk

Modern development vis-à-vis environmentalchallenges. Recently we have faced a series of disastersdue to unplanned development of modern city andrural areas especially in North India. Ruraldevelopment should be taken up with properassessment of critical ecosystem. Environmentalchallenges can lead to resistance to achievedevelopmental goals. The extent of damage isincalculable. In this aspect regeneration / reuse ofnatural resources and conservation of ecosystemsshould be considered on priority basis.Some of the important considerations can besummarized as:-Utilization and reclamation of wastesConservation of natural resourcesSystematic studies on environmental impacts and ecological balanceImproved climatic resilience of communitiesProper planning of rural and urban areasAssessment of hydrological balance vis-à-visdevelopment with respect to water bodiesR & D efforts should be laid on environment friendlyprocesses maximizing utilization of industrial wastesconserving natural resources. Rapid urbanization indeveloping countries responsible for people residesin areas prone to natural disasters. This has lead toloss of life and property.One of the important areas where competentauthorities is lacking is in areas ofDisaster management policies and techniquesComprehensive analysis of ecology of the aresFly ash utilization conserving natural resourcesUtilization of slags of iron and steel plantsUtilization of fines and low grade ore / concentrate/ ceramic raw materials for conservation of mineralsUtilization of secondary resources just like scrap, e-waste conservation and protection of waterProper awareness should be created in the aboveareas to generate better environmental protectionfor future development.

Prof Siddhartha Mukherjee,Editor

Ceramic news and EventsTwo day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science and Technology,6th September , 2013 ICS, Kolkata 033-24138878, email [email protected] Indian Engineering Congress, Chennai, Dec-2013. Tel- 044-25360614, email- ieitamil [email protected] National Convention of Metallurgicaland Material Engineers on Multifunctional andAdaptive Materials, Bangalore- Feb 6-7, 2014 IEI,Karnataka State Centre, 560001080-22264698, [email protected] Seminar on Refractory Raw Materials &Monolithics, 12th-13th November,2013 at CG&CRI, Kolkata. Energy & Efficiency-Key For SustainableDevelopment Outlook of Indian Industries (Minining,Metallurgy, Manufacturing, Power, Oil and GasConstruction, Services, R&D) 20.12,2013 at TajBengal Kolkata organized by IIM-Kolkata Chapter

email: [email protected] NMD & 67th ATM of the IIM, 12-15 November,2013 at IIT BHU e-mail : [email protected]

Page 4: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 2

INSTITUTE ACTIVITIES

Highlights of the 37th Annual Session, January 2013

38th Annual Session of Indian Institute of Ceramics,held on 18th January, 2013.Joint Inaugural SessionThe joint Inaugural Ceremony of the 76th AnnualSession of The Indian Ceramic Society, 64th AnnualSession of All India Pottery Manufacturers’Association and 38th Annual Session of Indian Instituteof Ceramics was held on January 18, 2013 at “TagoreHall”, Paldi, Ahmedabad, Gujarat.

Welcome Song

In the inaugural ceremony, Smt. Monika Shah, aneminent classical vocalist of Gujarat performed a soloclassical vocal recital. This was of very high standard.In the history of Annual Sessions, for the first time theinaugural programme was preceded by a culturalprogramme and everybody enjoyed and appreciatedthe same.

About 200 delegates from all over India and abroadcomprising scientists, technologists, students,equipment manufacturers, raw material suppliers andend-users in the field of glass and ceramics,refractories and allied disciplines, academic institutions,R&D organizations as well as guests and invitedspeakers actively participated in the Session.

Inaugural ProgrammeAfter the inaugural song, Dr. S.N. Misra,Scientist-in-Charge, CSIR-CG&CRI, Naroda Centreand Convener, GTGC-2013 was requested to escortthe Chief Guest, Shri Maheshwar Sahu, IAS, PrincipalSecretary, Govt. of Gujarat and the Guest of Honour,Shri Kamal Dayani, IAS, Industries Commissioner,Govt. of Gujarat and other dignitaries on the dias.Mr. G.G. Trivedi, Executive Director, SomanyCeramics Ltd., Gujarat and Chairman, OrganizingCommittee especially rendered his hearty welcometo Dr. S.N. Misra Scientist-in-Charge, CSIR-CG&CRI, Naroda Centre and Convener, GTGC-2013, Dr. A.K. Chattopadhyay, Vice President,

InCerS, Prof. Arun Kr. Varshneya, Professor of GlassScience, The New York State College of Ceramics,Alfred University, USA, Shri Rupesh C. Shah,Chairman, Gujarat Chapter, InCerS, Shri S.K.Kudaisya, Chief Patron & Managing Director,Sabarmati Gas Ltd., Shri Subhash Dave, Chief Patron& Managing Director, Sabarmati Gas Ltd., ChiefGuest, Shri Maheshwar Sahu, IAS, PrincipalSecretary, Govt. of Gujarat and the Guest of Honour,Shri Kamal Dayani, IAS, Industries Commissioner,Govt. of Gujarat for their gracious presence on theoccasion. Shri Maheshwar Sahu, IAS, PrincipalSecretary, Govt. of Gujarat and Chief Guest, 76thAnnual Session of the Indian Ceramic Society officiallyinaugurated the occasion by lighting the ceremoniallamp.Annual General Meeting :

The 38th Annual General Meeting of Indian Instituteof Ceramics was held at Tagore Hall, Paldi,Ahmedabad, Gujarat. Mr. Anil Chand Lodha,President of the Institute was in the Chair. The meetingwas attended by about 150 members.

Annual Report on the activities of the Instituteduring the year 2012

Prof. Saikat Maitra, Hony Secretary presented a briefsummary of the activities of the Institute during theyear 2012. The report contained informations aboutthe activities of the Institute during the year which wereas follows :

(A) Committee Meetings :

During the period from January to December, 2011aseries of meetings were held as stated below :

Council – One (1 No.), Executive Committee – Four(4 Nos.), Examination Committee – Three (3 Nos.),Publication Committee – One (1 No.), MembershipCommittee – One (1 No.)& Special Meeting – Three(3 Nos.)

(B) Membership

A total of thirty-one (31) candidates wererecommended and approved for membership indifferent categories as detailed below :-

Page 5: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 3

Fresh Membership recommended

Fellows — 4Members — 3

Upgradation recommendedMember to Fellow — 4Associate Member to — 2Member

A.I.I.Ceram. Examination — 2012A total of Two hundred thirty-four (234)

students were enrolled in 2012 for A.I.I.Ceram.Examination, out of which Two hundred eleven (211)of students appeared during October, 2012. Thetheoretical examination was held during the periodfrom 28th October to 4th November, 2012 in threecentres and the practical examination was held from8th November to 11th November, 2012.

Election of Office Bearers and other CouncilMembers for the terms 2013– 2014

Mr. Anil Chand Lodha, President of the In-stitute, announced the results of the election of OfficeBearers and Members of the Council for the terms2013 – 2014. These are as follows :-

Office BearersPresident — Mr. Anil Kumar KavirajVice-President — Dr. L. K. SharmaHony Secretary — Prof. (Dr) Saikat MaitraHony Joint Secretary — Dr. H. S. TripathiHony Treasurer — Dr. Arup Ghosh

Fellows representing the Council

Mr. Sachchidananda ChakrabartiDr. P. ManoharDr. (Mrs.) Nibedita ChakrabartiMr. Gouranga DattaDr. Shankar GhatakDr. Tapas Kumar Mukhopadhyay

Members representing the Council

Prof. P. K. GogoiDr. Subrata Ghosh

Associate Members representing the Council

Mr. Moti Lal RamMr. Shibasish BarikMr. Rana Das Gupta

Different Sub-Committees of the Council andthe composition for the term 2013 & 2014

The newly elected President of the Institute Mr. AnilKumar Kaviraj, presented the recommendations ofthe 67th Executive Committee Meeting held on 23rdMarch, 2013 for the constitution of various sub-committees. The same with some addition andalteration was approved by the 87th Council Meetingheld on 24th April, 2013.

Examination Committee

1. Prof. (Dr) Ram Pyare …… Chairman2. Prof. G. C. Das ….. Co-Chairman3. Prof. Siddhartha Mukherjee….. Member4. Dr. P. Manohar ….. Member5. Mr. J. S. Yadav ….. Member6. Mr. Kala Hasthi Subba Rao …. Member7. Prof. T. K. Parya ….. Member8. Dr. Nibedita Chakrabarty ….. Member9. Dr. C. S. Prasad ….. Member10. Prof. Om Prakash ….. Member11. Dr. Ritwik Sarkar ….. Member12. Dr. C.D. Madhusoodana ….. Member13. Dr. Manas Kamal Halder ….. Member14. Dr. T. K. Bhattacharya ….. Member15. Prof. Rituparno Sen ….. Member16. Prof. Ranjan Roy ….. Member17. Dr. Srimanta Patra ….. Member18. Mr. S. Chakrabarti ….. Member19. Dr. T. K. Mukhopadhyay ….. Member20. Dr. Nandini Das ….. Member21. Dr. Kaberi Das ….. Member22. Dr. L. K. Sharma ….. Member23. Dr. Arup Ghosh ….. Member24. Dr. H. S. Tripathi ….. Member25. Mr. R. C. Das ….. Convener26. Dr. Kausik Dana ….. Co-Convener

Page 6: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 4

Membership Committee

1. Mr. Anil Chand Lodha ..… Chairman2. Dr. A. K. Chatterjee ..… Member3. Dr. F. D. Gnanam ….. Member4. Dr. G. Banerjee ….. Member5. Dr. Arup Kumar Chattopadhyay….. Member6. Mr. Amal Kumar Guha ….. Member7. Mr. Amit Kr. De ….. Member8. Mr. S. K. Ghosh ….. Member9. Prof. B.N. Samaddar ….. Member10.Prof. Om Prakash ….. Member11.Mr. S. Chakrabarti ….. Member12.Dr. Barundeb Mukherjee ….. Member13. Prof. G.C. Das ….. Member14. Mr. Ajay Kumar Das Gupta….. Member15. Dr. Arup Ghosh ….. Member16. Dr. H. S. Tripathi ….. Member17. Dr. Shankar Ghatak ..… Convener

Publication Committee1. Prof. B.N. Samaddar ….. Chairman2. Prof. G.C. Das ….. Member3. Dr. Kaberi Das ….. Member4. Dr. Ritwik Sarkar ….. Member5. Dr. M.K. Haldar ….. Member6. Dr. Sankar Ghatak ….. Member7. Dr. Amarnath Sen ….. Member8. Prof. Om Prakash ….. Member9. Prof. F. D. Gnanam ….. Member10. Dr. K.G.K. Warrier ….. Member11. Dr. L.N. Satapathy ….. Member12. Dr. A. L. Shashi Mohan ….. Member13. Dr. L. K. Sharma ….. Member14. Prof. S. P. Singh ….. Member15. Dr. Sunanda Mukhopadhyay….. Member16. Dr. Gora Ghosh ….. Member17. Dr. Sanjay Kumar ….. Member18. Dr. Tapas Bhattacharya ….. Member19. Mr. S.N. Laha ….. Member20. Dr. Nibedita Chakraborty ….. Member21. Dr. Parag Varghav ….. Member22. Dr. S. P. Yale ….. Member23. Prof. Siddhartha Mukherjee….. Convener

Page 7: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 5

STUDENTS’ SECTION

A.I.I.CERAM. EXAMINATION RESULT — 2012On the recommendations / approval of the Examination Committee the results have been published on 6thFebruary, 2013. An overall analyses of the result is tabulated as below followed by the detailed list ofpass-out candidates (students).

No. of candidates enrolled – 108 (New Syllabus)

No. of candidates enrolled – 126 (Old Syllabus)

No. of candidates appeared in the examination – 103 (New Syllabus)

No. of candidates appeared in the examination – 108 (Old Syllabus)

No. of candidates absent – 05 (New Syllabus)

No. of candidates absent – 18 (Old Syllabus)

No. of candidates appeared for the Final part of the examination – 07 (New Syllabus)

No. of candidates appeared for the Final part of the examination – 50 (Old Syllabus)

No. of successful candidates – 08

Percentage of passed candidates in Final examination – 16%

Grade 1st Class 2nd Class Pass (P)

03 05 Nil

Sl. Name Registration No. Roll No.No.

1. Ms. Suchika Jena IC-081650 121018

2. Mr. Ajeet Singh IC-081659 127019

3. Mr. M. Suresh IC-091747 126043

4. Mr. Thammi Sreenivas IC-091802 126065

5. Mr. Biswarup Das IC-101879 121092

6. Mr. Prakash Kumar Sharma IC-101896 127101

7. Mr. G. Jagadeesh IC-101922 126113

8. Mr. Anil Kumar IC-101931 127116

Page 8: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 6

AWARDS

For the year 2012 Examinations, the ExaminationCommittee has decided to bestow “SAHAJMEMORIAL AWARD” & “AMIC PRIZE” onMr. G. Jagadeesh (Registration No. IC101922 &Roll No. 126113) for the best performance securingthe highest total marks (628) in the part-IIexamination and also securing the highest total marks(126) in Ceramic Science—I & II (Section – A)combined.

Report on the UGC sponsored nationalworkshop on “Current trend”One UGC sponsored National Workshop on“Current Trend and Future Prospects of GlassTechnology” was organized by Govt. College of Engg& Ceramic Technology in Association with IndianInstitute of Ceramics on 25th Aug, 2013 at CollegeAuditorium.12 no Students of B.Tech in Chemical Tech(Ceramic Engg) from University of Calcutta,Department of Chemical Technology, and 17 nostudents of B.Des in Glass & Ceramic from VisvaBharati university and 11 no students of 2nd , 43 nostudents of 3rd and 20 no students of 4th B.Tech inCeramic Tech and M.Tech in Ceramic Tech studentsof the college were actively participated in theworkshop.Four eminent speakers presented and covered fourimportant aspects of Glass Technology. Theworkshop was started at 11:00 am and was dividedinto two sessions with a 1 hr break.The first session was chaired by Prof. P.K.Gangopadhyay, Ex Officer-in –Charge, GCECT,Kolkata. Mr. Ashoke Chakraborty, CEO, DeltaPlus India Ltd, presented one lecture on “Aspects ofattention in manufacturing control and qualityassurance of Float glass process”. The lecturecovered all the important aspects of the glassmanufacturing starting from the selection and handlingof raw materials to the loading through the doghouseto the principle of float process and annealing process.The topic also covered the defects of the glass arisesduring manufacturing. The second lecture wasdelivered by Mr. Dwijen Lal Mudii, Asst Vice

President, HNG Ltd on “Modern Container glassmanufacturing process and modern refractories usedin Glass Tank Furnace”The second session was chaired by Prof. B. N.Samaddar, Ex Principal, GCECT, Kolkata. Dr. B.Karmakar, Senior Principal Scientist, CG&CRI,Kolkata presented a lecture on”Speciality Glasses foradvanced Technology”. The lecture covered mainlythe research & development work on optical, radiationresistance & shielding, glass-ceramics, laser glass,photochromatic glass etc the glass that are going onand the future prospects. The last lecture on “Presentday practice and future challenges in glass Industry”was presented by Mr. Sujay Bhattacharya, consultant.

Page 9: Vol. 22 No. 1 2013Prof Siddhartha Mukherjee,Editor Ceramic news and Events Two day workshop on Ceramic Science 4th and 5th September, 2013 One day National Synposium on Ceramic Science

IIC Bulletin Vol.22, No. 1, 2013 7

Recent advances in the field of MgO-C RefractoriesSomdeb Pramanik, Soumya Mukherjee#, Siddhartha Mukherjee

Department of Metallurgical and Materials EngineeringJadavpur University, Kolkata-700032

# Corresponding author: [email protected], [email protected]

Abstract: Extensive research work has been carried out all over the world on various aspects of Magnesia-Carbon refractories , an integral part for the development high temperature refractories for Steel Industry. Anattempt has been made to review the recent developmental work in this area and their important findings havebeen represented. Emphasis has been laid on the oxidation behaviour of various carbon sources viz. graphite,carbon black, binders such as coal-tar pitch and petroleum pitch. New generation refractory developed cleansteel production is based on low C MgO-C refractory for ladles, converters and EAF applications. It wasfound that the order of reactivity of the carbon sources with oxygen in ascending order is graphite<petroleumpitch<coal tar pitch<carbon black. The roles of additives like Al, Si, SiC and B4C in preventing oxidationtendency of these refractories have been reviewed. The order of effectiveness of antioxidant was observed tobe SiC<Si<Al<B4C. A study regarding the developmental work on nano carbon containing magnesia carbonrefractories was exhibited in an attempt to reduce the total carbon content and hence decrease the deleteriouseffects of carbon. The resultant properties were evaluated and compared against the conventional refractoryprepared under exactly similar conditions. The reported elemental mapping of carbon from the literature wasstudied to find the nature of distribution of the nano carbon in the matrix. The oxidation kinetics of the MgO-C bricks was obtained, along with mathematical modelling to determine the extent of oxidation with time.

Keywords: MgO-C refractories, Nano carbon, oxidation, oxidation resistance, petroleum pitch, antioxidantsetc.

1.IntroductionMagnesia-carbon (MgO-C) refractories findwidespread applications as the lining material in basicoxygen furnaces, electric arc furnaces and steel ladles. They have good thermal shock resistance andexcellent slag-corrosion resistance. These refractoriescontain about 12–18% total carbon. The primarysource of carbon in magnesia-carbon refractories isgraphite [1-9], which offers the following majoradvantages -1. It has a high melting point.2. It improves the corrosion resistance of therefractory, the reason being its lower wettability bymetal and slag.3. Graphite is characterized by low thermal expansion,high thermal conductivity and low modulus of elasticity.As a result of these properties graphite addition leads

to improve thermal shock resistance of therefractoriness.4. Graphite has lubrication property and thus resultsin better packing efficiency.There was a tendency to use more and more carbonin the brick in an attempt to achieve better corrosionresistance and thermal shock resistance. But too higha carbon content may lead to the series of drawbacks:1. Carbon is inherently prone to oxidation and getsoxidized at high temperatures encountered in steelmaking processes especially at the time of oxygenlancing. The structure of the refractory becomes highlyporous with weakened bonds and reduced strengthafter oxidation. Since the porosity is increased andslag try to penetrate easily and corrode the refractory.2. The presence of carbon enhances the conductivity.This entails large heat loss. As a result more energy isused up per unit during steel production. The

Technical Section – Paper – 1

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IIC Bulletin Vol.22, No. 1, 2013 8

production thus becomes less cost effective in termsof energy efficiency.3. Due to high thermal conductivity, there is apossibility for higher temperature in steel shelltemperature leading to damage and deformation ofthe shell/metallurgical vessel, causing thermal stresson the structure which may lead to brittle failure duringcritical hot metal operation.4. Steel making is a decarburization process. But ifthe carbon content in the refractory is high the chancesof carbon pick-up from the refractories by the refinedsteel may increase. This may disturb to obtain therequired specifications of the steel .5. Increase amount of the carbon dioxide or carbonmonoxide gases are released to the atmosphere. Hence to avoid all such drawbacks of theconventional carbon containing refractories,researches have been carried out to develop a newkind of MgO-C refractory with low carbon content ,keeping in mind that this may lead to decline incorrosion and thermal shock resistances of therefractory. The effect of increasing amount of nanocarbon on the properties of MgO-C refractory isstudied keeping total carbon content below half ofthat of the conventional MgO-C refractories. Lowand ultra low carbon steel demand low carbonrefractories to have clean steel. Composition withoptimum nano carbon addition is also compared withconventional composition processed under exactlysimilar conditions. The MgO-C bricks are used inslag line of steel ladles and no carbon containingrefractories on other parts. Use of nano C can reducethe C level to half and increase slar resistance duemore densification. Carbon, in MgO–C refractories, is oxidizedin two ways: direct oxidation and indirect oxidation.Direct oxidation occurs under 1400 0C as per reaction1, when carbon is oxidized directly by the oxygenfrom atmosphere[5]. Indirect oxidation occurs above1400 0C where carbon is oxidized by the oxygen fromMgO from reaction 2 or reduction of FeO from slagphase-reaction 3. The resulting Mg vapor oxidizesagain and formed pure MgO which is called thesecondary oxide phase or the dense layer. It is claimed

that the secondary oxide phase protects the brickagainst oxidation by preventing oxygen ingress.2C(s)+O2(g)=2CO(g)……………………….(1)C(s)+MgO(s)=Mg(g)+CO(g)……………….(2)C(s)+FeO(l)=Fe(l)+CO(g)………………….(3)2Mg(g)+O2(g)=2MgO(s)…………………...(4)Different researchers have studied the oxidationbehavior of antioxidants. The Al, Si and Mg powdersare mostly used antioxidants due to their low costand effective protection and highly stable oxide former.One of the aims of this study was to examine andcompare the effects of different antioxidants on theoxidation resistance of magnesia–carbon refractorybricks.The primary constituents of these refractory materialsare magnesia and graphite. Other importantconstituents present are carbon black and sulphur intheir composition. This necessitates the addition ofan external binder to agglomerate all the solidconstituents. Resin (e.g., phenolic resin)and coal-tar pitch are the most commonly used bindersfor this application. However, these types of binderhave the disadvantage that they emit pollutants duringthe preparation of the magnesia–carbon material.These emissions consist mainly of phenol, in the caseof the resin, and polycyclic aromatic hydrocarbons(PAH), in the case of the coal-tar pitch. It has beenproved that some of the PAH are carcinogenic (e.g.,benzo[a]pyrene). Much effort has been made inrecent years to reduce the emission of thesecompounds. In response to this problem, new carbo-resins containing very low amount of toxic compoundswere specifically developed for refractory industry.However, these resins have the limitation of their highcost in comparison with pitches. In the field of thepitches, new petroleum pitches with a lower pollutantimpact but a similar binder capacity to standard coal-tar pitches have been developed. So from the abovediscussion we come to know that there are multiplesources of carbon in these refractory materials. Oneof the main factors as already discussed, thatdetermine the life span of magnesia–carbon materialsis their oxidation behaviour. These materials areprepared to operate at temperatures above 1000 0C.However, at these temperatures the air reactivity of

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IIC Bulletin Vol.22, No. 1, 2013 9

the carbon sources is extremely high, which makes itdifficult to detect the possible mechanisms at work orto establish the differences between the differentcarbon sources that make up the materials. A studyof the oxidation behavior at low temperaturemagnesia–carbon materials prepared by petroleumpitch and a standard coal-tar pitch as binder has beencompared. Thus the reactivities of the different carbonsources were assessed.

2. ROLE OF ANTIOXIDANTSThe various samples of magnesia carbon bricks with0, 1 and 3% antioxidants as additives werecompared. The rate of losses of the weight percentageof the bricks due to carbon oxidation was used as ameasure of oxidation resistance. The exact expressionfor the above parameter is:Carbon loss (weight%)=(m1-m2)/(m3*%g)*100Where m1=weight of heat treated specimen(gm) m2=weight of oxidised specimen

m3=weight of specimen without heat treatment

g=weight percentage of graphiteThe % carbon loss of the specimen was determinedas a function of temperature (13000C and 15000C)and time (2 hrs, 4 hrs, and 6hrs). The microstructuraland phase modifications of the oxidized areas of thebricks were observed through XRD, SEM and EDS.The oxidation resistance provided by the antioxidantswas due to the formation of secondary phases[1].These phases slowed down the oxygen ingress byfilling up the open pores and creating impermeabledense layers on the brick surface. The oxidationresistance at 15000C was found to be better than thatat 13000 C because of the formation of moresecondary phases at 15000C.B4C was found to be the most effective antioxidant.The secondary phase formed here was Mg3B2O6 .Addition of B4C of about 3% to MgO-C at 13000Crevealed the presence of B2O3 and Mg3B2O6 in theoxidized areas. SEM images of the 3% B4C addedMgO-C at 15000C showed a very thin oxidized layeron the surface. XRD analysis of the thin oxidised layershowed many peaks of Mg3B2O6. No other Boronbased compounds or impurities were found to exist.

Mecahnism of formation of Mg3B2O6 layer on thesurface is as follows:B4C(s)+6CO(g)=2B2O3(l)+7C(s) …………… (5)B2O3(l)+3MgO(s)=Mg3B2O6(s) …….………(6)Melting point of Mg3B2O6 is 13600 C. Mg3B2O6 is avery good oxygen barrier above its melting point. Theliquid Mg3B2O6 fills up the open pores and forms athin film layer on the brick surface at 15000 C, so thatoxygen cannot diffuse into the refractory.The second most effective antioxidant was Aluminium,the secondary phase formed in this case was MgAl2O4which is a spinel phase. Addition of 3% Al to MgO-C specimens at 13000C and 15000C showed spinelphases (MgAl2O4) in the oxidised areas. Smalleramount of spinel was observed at 13000C than at15000C. Graphite from MgO-C was also present.SEM image of 3% Al added MgO-C specimens at15000C revealed the presence of large fused MgOgrains, flake graphite and spinel phase. The mechanismof spinel formation is as follows:Al oxidises rapidly after fabrication to form a thin layerof Al2O3. The melting temperature of Al being 6600C,the thin layer contains liquid Al2O3 for a while until itbreaks and releases molten Al. The released Al reactswith C to form Al4C3. C is oxidised by the air diffusedinto the bricks to form CO. The Al4C3 reacts withCO to form Al2O3, which in turn reacts with MgO toform MgAl2O4. The different chemical equations areas follows:4Al(s)+3O2(g)=2Al2O3(s) ……………….…(7)4Al(l)+3C(s)=Al4C3(s) ……………………(8)Al4C3(s)+6CO(g)=2Al2O3(s)+9C(s) ………… (9)Al2O3(s)+MgO(s)=MgAl2O4(s) ………….(10)The oxidation resistance due to Si as well as SiCaddition was the result of formation of Forsterite phase(Mg2SiO4). The forsterite was found in the oxidisedareas of the specimen treated at both 13000C and15000C. Relatively fewer forsterite peaks wereobserved for SiC than Si at both the temperatures.Metallic Si is less stable than SiC. So the latter hadnegligible effect on the oxidation resistance of MgO-C refractories at either temperature. In fact among allthe four antioxidants mentioned in this study, SiC wasproved to be the least effective, its contribution beingmarginally better than only the specimens without any

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antioxidant. More forsterite formation was observedat 15000C than at 13000C (for both Si and SiC) dueto the formation of more CO gas at 15000C which isfavorable for SiO2 formation. The mechanism offorsterite formation is as follows:Si(s)+C(s)=SiC(s) ……………………. (11)SiC(s)+2CO(g)=SiO2(s)+3C(s) ….………(12)SiO2(s)+2MgO(s)=Mg2SiO4(s) …………..(13)3. OXIDATION BEHAVIOUR OF DIFFERENTCARBON SOURCESThe reactivity of the different carbon sources in air ofmagnesia carbon refractory were compared not onlyin isolated form i.e simply as carbon, but also afterbeing introduced into MgO-C materials. The differentsources of carbon in magnesia carbon refractory aregraphite, carbon black and the requisite bindermaterial. Here two different binder materials viz.conventional coal-tar pitch and petroleum pitch wereused and apart from comparing the reactivity of thedifferent carbon sources in air another fruit of thisinvestigation was on the choice of a suitable bindermaterial. The specimens used for testing wereprepared by using the following raw materials:Four different granulometric fractions ( coarse, 2 medium and fine grained) of electrofused type magnesiaNatural graphite in the form of flakes of particle size 160µmThermal carbon black of paticle size 4.5µmRhombohedric sulphur (S8) for polymerization and hardening of the binder in the cokeTwo pitches as binders viz. coal-tar pitch and petroleum pitch converted to their respective coke forms by carbonization at 50C/min upto 9000C in N2 atmosphere so as to be able to study the oxidation behavior of single carbon sources.

3.1 The reactivity of the carbon sources in airThe carbon samples were ground/sieved to particlesize <0.1mm to mitigate the effect of porosity on thereactivity of the samples in air. The reactivity of thecarbon sources in air was monitored by TGA methodunder both isothermal and non-isothermal conditions.

This was followed by microstructural characterizationof the C sources. EBSD was used for graphite andcarbon black whereas pitch coke (both coal-tar andpetroleum) were characterized using an opticalmicroscope. Let us take the help of the followingfigures to understand and analyze the results.

Fig1. Typical TG oxidation curves of the carbon sources in a non-isothermic regime. (Ref-2)

Fig2. Typical DTG oxidation curves of the carbon sources in a non-isothermic regime. (Ref-2)

Fig3. Oxidation profiles (700 æ%C) of the cokes obtained from the coal-tar pitch and petroleum pitch. (Ref-2)

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Fig4. Oxidation profiles (600 æ%C) of the cokes obtained from the coal-tar pitch and petroleum pitch. (Ref-2)

Fig5. SEM images of the (a and b) carbon black and (c and d) graphite. (Ref-2)

Fig6. Optical microscopy images of the cokes obtained from the (a) coal-tar pitch and (b) petroleum pitch. (Ref-2)

The reason for the difference in behavior is related tothe microcrystalline order of the samples.Carbon black is an amorphous material. It is madeup of small spheres <1µm which tend to agglomerateto form aggregates of about 20-50µm. Due to thepresence of both discrete particles and aggregatesand also due to the diffusion of oxygen observed inthis type of material we get two peaks in DTG. Onthe other hand graphite has a well-ordered structurewhich explains its behavior. The coke from coal tarand petroleum pitch are optically anisotropic. Thedifference in behavior arises (Coal tar pitch andPetroleum pitch) from the fact that the former (Coaltar pitch) consists mainly of anisotropic microstructuresof smaller size due to the presence of primaryQuinoline Insoluble (QI) particles. These particlesoriginate during formation of tar from which the coaltar was formed. These are thermally stable andbecome a part of the coke. During pitch carbonizationthey tend to surround the mesophase spheres, makingit difficult for the mesophase to coalesce and thespheres to grow. This is why coke from coal tar is ofanisotropic microstructures of small size. On thecontrary petroleum pitch coke has no QI particles.So the mesophase growth is not restricted. Nowmicrostructures of small size, i.e mosaic type are moreeasily consumed than microstructures of a large size,i.e domain type.Moreover QI particles are the first coke materials tobe consumed on oxidation. Due to these reasons theoxidation resistance of coal tar pitch coke is lowerthan that of petroleum pitch coke.It was also found that the oxidation behaviours of thetwo pitch cokes are markedly different in thetemperature range 600-7000C. Therefore in order toestablish the difference in oxidation behaviour ofMgO-C materials experiments must be carried out inthis range.

3.2 The reactivity of the MgO-C materials in air

The MgO-C materials were prepared following thedifferent stages viz. blending, moulding and thermaltreatments at temperatures of 3000C followed by oneat 10000C. Samples with similar properties (density,

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porosity, mechanical properties, etc.) were selectedto minimize the textural effects (e.g porosity). Afternecessary pre-oxidation characterization the samplesto be used for oxidation studies were heated at 2.50C/min upto 6000C for periods of 120, 240 and 360mins. Air flow rate was 333ml/min. The representativephotographs of the external appearance of the sampleswere taken with camera.

Fig7. Images of the magnesia–carbon materials obtained from the coal-tar pitch (a and b) before oxidation and (c and d) after oxidation at 600 æ%C for 6 h. (Ref-2)

The macroscopic visual appearance leads to thefollowing differences. Before loss of carbon (i.eoxidation) the material had a black colour, a compactand dense appearance which highlights the gooddistribution and cohesion of particles(homogeneous cross section with no apparent effectsof disintegration). After carbon loss the materials losetheir blackness and acquire a grayish appearance. Thematerial also have a brittle appearance.

Fig8. Oxidation profiles (600æ%C) for the magnesia–carbon materials bound with coal-tar pitch and petroleum pitch.(Ref-2)

Low percentage of binder (5 wt %) is used in thistype of materials. So it is difficult to appreciatedifferences in weight loss except over large periodsof residence time. After 120 and 240 mins of oxidation(residence time) the weight loss suffered by both thesamples were 17% and 21% respectively. It is onlyabove these residence times that the oxidation profilesbegin to diverge[2].4. OXIDATION KINETICSAs already mentioned, the major limitation of MgO-C refractories is the susceptibility of graphite tooxidation which leads to the degradation of brickproperties in service. The oxidation of carbon is oftwo types; direct oxidation (gas phase oxidation)which refers to the consumption of carbon by gaseousoxygen, and indirect( solid phase oxidation ) whichinvolves the reaction of carbon with solid oxygen inMgO. The first one is dominant for temperaturesbelow 14000C and is mostly used for comparison ofoxidation resistance of refractories. A study wasconducted regarding the kinetics/ rate of oxidation/disappearance of graphite (1000 to 12000C) bygaseous oxygen of air, i.e direct oxidation. Amathematical model was used to explain the extent ofoxidation with time. The factors affecting the rate ofdirect oxidation were partial pressure of O2,accessibility of O2 to the graphite flake edges, openporosity, shape and orientation of the products, flowcharacteristics of the gaseous species around theproducts, reactivity of the flakes[4]. The entire processof oxidation was divided into five steps each of whichwas assumed to occur at the same rate. Fromequations of mass transfer related to these a relationwas obtained involving the radius of the unoxidisedarea, oxidation time, physical and kinematicparameters.

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Fig9. Variation of oxidation time with radius of unoxidized area.(Ref-4)

5. REDUCTION OF TOTAL CARBON CONTENT: ROLE OF NANO CARBON

To take care of the limitations of carbon in MgO-Crefractories and to prduce more eco-friendlyrefractories an attempt was made to reduce the totalcarbon content to less than half of the amount presentin conventional refractories by introducing nanocarbon, without sacrificing on the beneficial effects ofcarbon. Different percentages of nano carbon areused in combination with graphite as carbon source.The compositions were processed as per theconventional manufacturing techniques and theproperties were evaluated and compared against theconventional refractory prepared under exactly similarconditions. Also elemental mapping of carbon wasdone to study the distribution of the nano carbon inthe matrix.(Ref-3)

Batch composition

Raw materials/batch 1 2 3 4 5 6 7

MgO (0–6 mm) 96 95.7 95.4 95.1 94.8 94.5 89

Flake graphite 3 3 3 3 3 3 10

Nano carbon 0 0.3 0.6 0.9 1.2 1.5 0

Al metal powder 0.5 0.5 0.5 0.5 0.5 0.5 0.5

B4C powder 0.5 0.5 0.5 0.5 0.5 0.5 0.5

Liquid resin 2.75 2.75 2.75 2.75 2.75 2.75 2.75

Pitch powder 1 1 1 1 1 1 1

In terms of the ascertained properties batch 4 was found to have the optimum properties. Therefore itsproperties were compared with those of the conventional batch 7 (without any nano carbon addition).Propertycomparison of batch 4 and conventional MgO-C refractory (batch 7)

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Property Batch Batch 4 Batch 7

Apparent porosity (%) 4.3 3.8

Bulk density (g/cm3) 3.12 3.05

Cold crushing strength (MPa) 51 37.5

HMOR (MPa) 4.5 3.9

Oxidation loss (%) 21.82 36.95

Slag penetration depth (mm) 2.01 1.98

Thermal shock resistance 12 12 (cycle)

Addition of nano carbon has resulted more evenlydisperse of the matrix phase, thereby filling in a betterway among the tiny spaces between coarse, mediumand fine particles of starting materials and filling ofinterior pores and gaps. This reduces porosity,increases densification, strength, corrosion resistance,etc. Again nano carbon also absorbs and relieves thestress due to thermal expansion and shrinkage of therefractory particles, thereby reduces the detrimentaleffect of thermal stress in the interior portion ofrefractories and improves thermal shock resistance.Thus MgO-C (with nano carbon) refractory withmuch reduced carbon content but superior propertiescompared to conventional MgO-C refractories isobtained [3].

CONCLUSION

In this paper the various important aspects of magnesiacarbon refractories were highlighted. From the studyon the effect of various antioxidants it was found thatB4C was the most effective followed by Al, Si andSiC respectively. The oxidation resistance improvedat higher temperatures for each of these cases due tothe formation of greater amount of secondary phaseswhich were responsible for the prevention of oxygeningress. The various sources of carbon in the aboverefractory material were compared in terms of theiroxidation resistance. Graphite was found to be theleast reactive followed by petroleum pitch, coal tar

pitch and carbon black respectively. In the light ofthis result petroleum pitch has been suggested as analternative binder material instead of coal tar pitch asthe former is less prone to oxidation. The susceptibilityof graphite to oxidation leading to deterioration ofbrick properties in service has been addressed as onemajor problem in these materials. The prospects ofincorporation of nano carbon into the material in anattempt to reduce the total carbon content was seemsto be feasible. The various properties of a samplecontaining an optimum amount of nano carbon andan amount of total carbon less than half of what ispresent in conventional refractories were found to beeither better or same as that of the conventional MgO-C refractories.

REFERENCES

[1] A.S. Gokce, C. Gurcan , S. Ozgen, S. Aydin,The effect of antioxidants on the oxidation behaviourof magnesia–carbon refractory bricks, CeramicsInternational. 34 (2008) 323–330.

[2] V.G. Rocha, R. Menéndez, R. Santamaría, C.Blanco, M. Granda, Oxidation behaviour ofmagnesia–carbon materials prepared with petroleumpitch as binder Journal of Analytical and AppliedPyrolysis. 88 (2010) 207–212.

[3] Mousom Bag , Sukumar Adak , Ritwik Sarkar,Study on low carbon containing MgO-C refractory:Use of nano carbon, Ceramics International. 38 (2012)2339–2346.

[4] Mohammad-Ali Faghihi-Sani, Akira Yamaguchi,Oxidation kinetics of MgO–C refractory bricks,Ceramics International. 28 (2002) 835–839.

[5] S. Zhang, N.J. Marriott , W.E. Lee,Thermochemistry and microstructures of MgO–Crefractories containing various antioxidants, J. Eur.Ceram. Soc. 21 (2001) 1037–1047.

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[6] S. Uchida, K. Niihara, K. Ichikawa, High-temperature properties of unburned MgO–C brickscontaining Al and Si powders, J. Am. Ceram. Soc.81 (1998) 2910–2916.

[7] S. Zhang, W.E. Lee, Influence of additives oncorrosion resistance and corroded microstructures ofMgO–C refractories, J. Eur. Ceram. Soc. 21 (2001)2393–2404.

[8] T. Wang, A. Yamaguchi, Oxidation protection ofMgO–C refractories by means of Al8B4C7, J. Am.Ceram. Soc. 84 (2001) 577–582.

[9] N.K. Ghosh, K.P. Jagannathan, D.N. Ghosh,Oxidation of magnesia–carbon refractories withaddition of aluminium and silicon in air, Interceram 50(2001) 196–202.

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A Brief Description of the Processing of CeramicsPROF. SAIKAT MAITRA

Acting PrincipalGovt. College of Engineering & Ceramic technology

Kolkata -- 700 010E-mail : [email protected] / [email protected]

Introduction

Ceramics basically are compounds of metallic and non-metallic elements,characterized by properties like,high temperature stability, high hardness, brittleness, high mechanical strength, low elongation under applicationof stress, low thermal and electrical conductivities etc.Classification of ceramics can be done in different waysdue to their divergence in composition, properties and applications. Application wise ceramics are classifiedin categories, like, glasses, clay products, refractories, abrasives, cements and advanced ceramics for specialapplications. Based on their composition, ceramics are classified as, oxides, carbides, nitrides, sulphides,fluorides, etc. From the point of engineering applications, ceramics are classified basically into two groups;traditional and engineering ceramics. Traditional ceramics are mostly made up of clay, silica and feldspar.Engineering ceramics are consisted of highly purified aluminium oxide (Al2O3),silicon carbide (SiC) and siliconnitiride (Si3N4). All types of ceramics as mentioned above are processed by following certain techniques. Atthis paper these different techniques for the processing of ceramics have been discussed in brief.

Traditional Processing of Ceramics:

The most important property of ceramics is its hightemperature stability which makes the conventionalfabrication routes unsuitable for ceramic processing.Ceramic powder processing route includes synthesisof powder, followed by fabrication of green product.The green product is consolidated to develop the finalproduct.These forming techniques are well known fordeveloping engineering components with dimensionalstability, surface quality, near theoretical density andmicrostructural uniformity. As the usages and diversityof specialty forms of ceramics are increasing, thediversity of process technologies are also increasing.Synthesis of precursor powder for making traditionalceramics involves crushing, grinding, separatingimpurities and blending of different powdersdepending on the compositional requirement.Sizereduction by crushing and grinding is also known asmilling or comminution. Milling of the raw materials is

followed by batching of the milled materials in definiteproportions. Batching is followed by mixing to ensurehomogeneity and mixing is followed by forming to giveshape to the mass. The shaped mass is subjected todrying which is followed by firing and the fired massis assembled. Let us discuss these stages one afteranother.Milling involves breaking up of cemented materialwhere the individual particles retain their shape. It isalso associated with pulverization where the particlesare ground themselves to a smaller size. In generalmilling is done by mechanical means mostly. Thedifferent forces in milling includes (a) attritionorparticle-to-particle collision resulting in agglomeratebreak up or particle shearing (b) compression whereforces are applied for fracturing, and (c)impactwherea milling medium is used or the particles themselvesare used to cause fracturing.. Mills for primary sizereduction or crushing include the jaw crusher, rollercrusher and cone crusher. Mills for secondary sizereduction or grinding are generally based on the impact

Technical Section – Paper – 2

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action and most popular in this category is the ball milor tube mill. In ball mill the materials are fractured bytumbling action with impact from metallic or ceramicballs.Shaft impactors cause particle-to particle attritionand compression. Attrition milling equipment includesthe wet scrubber. These are also known as planetarymill or wet attrition mill. It contains paddles in waterto create vortexes in which the material collides andbreak upPowders for advanced ceramic materials aresynthesized by chemical routes like, co-precipitation,sol-gel and by spray drying technique. Co-precipitation is a relatively cheaper and easier processfor the generation of powders with unique powderproperties obtained like, small size and homogeneity.It consists of preparing solution containing metalionsthatcontrol chemical reaction by monitoring pH.In sol-gel process stable sol of precursor metal ionsare formed which is then converted to gel undercontrolled condition. Very small sized particle withnarrow size distribution of can be prepared by sol-gel process. Here a stable sol of the precursor is madefirst either from inorganic or organic salts undercontrolled condition and the sol is destabilized to formthe gel. But it is relatively slow and expensive process.Spray pyrolysis process is ideal for production ofceramic powder with precise quality standards like,particle size distribution, residual moisture content,bulk density and particle morphology. Here a saltsolution or slurry of the precursor materials is sprayedin a stream of hot gas for the generation of granules.In batching the starting materials are weighedaccording to recipes, and they are made ready formixing and drying.Mixing is performed with variousmachines like, muller mixers and pug mills. Wet mixinggenerally also involves the same equipment.Forming is making the mixed material into shapes,ranging from sanitary ware to spark plug insulators.Forming can involve: (1) Uniaxial pressing which issuitable for mass production of simple ceramics parts.It is also referred to as Die Pressing. Powder ispressed in closed dies to form the green compact.The processes involve: filling of the die followed bycompaction of powder and finally ejection of theceramic part. (2) Extrusion, such as wire cut brick

block making. Compression of clay through a dieorifice to produce long sections of uniform crosssection, which are then cut to required piece length(3) Slip casting for making sanitary wares, statuesetc.In slip casting, water is removed from the powdersuspension by the water suction of the plaster mouldand a consolidated layer consisting of packed particlesbuilds up. When a desirable thickness has beenreached the excess slip is removed (drain casting), orthe casting proceeds until the casting fronts approacheach other anda solid body has been obtained (solidcasting). Forming produces a workable “green” part, readyfor drying. Dryingis associated with the removal ofwater or binder from the formed material. Spray dryingis widely used to prepare powder for pressingoperations. Other dryers for drying pressed/extrudedor slip cast products are tunnel dryers and periodicdryers. Controlled heat is applied to remove the water.This step needs careful control, as rapid heating causesdevelopment of cracks and surface defects. As wateris removed from the wet mass, inter-particle spacingis also decreased causing shrinkage in the mast. Thedried part is smaller than the green part and requirescareful handling, since a small impact will causecrumbling and breaking.Firing of the dried parts pass through a controlledheating process is carried out to develop strength inthe product. The oxides are chemically changed tocause sintering and bonding. The fired part will besmaller than the dried part.Advanced Forming methodsSuch methods are required for producing advanced,high-temperature structural parts such as heat enginecomponents and turbines. Materials other thanceramics which are used in these processes mayinclude: wood, metal, water, plaster and epoxy—mostof which will be eliminated upon firing.Advanced ceramic forming techniques generallyinclude tape casting, injection molding, dry pressing,isostatic pressing, hot isostatic pressing (HIP) andothers. In tape casting, thin sheets of green ceramicare cast as flexible tape which is used for integratedcircuits and capacitors. A slip of suspended ceramicparticles in organic liquid

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(containing binders, plasticizers) is used for the castingpurpose. In injection molding Ceramic particles aremixed with a thermoplastic polymer, then heated andinjected into a mold cavity. The polymer acts as acarrier and provides flow characteristics for molding.Upon cooling which hardens the polymer, the mold isopened and the part is removed. Iso-static pressinguses hydrostatic pressure to compact the ceramicpowders from all directions. It avoids the problem ofnon-uniform density in the final product that is oftenobserved in conventional uniaxial pressing. Hotisostatic pressing is similar to dry pressing except it iscarried out at elevated temperatures so sintering ofthe product is accomplished simultaneously withpressing. This eliminates the need for a separate firingstep. Higher densities and finer grain size are obtainedby hot pressing, but die life is reduced by the hotabrasive particles against the die surfacesThe reinforcing fibers and filaments in ceramiccomposites are mainly made by sol-gel or CVDprocesses besides common melting and drawingprocess. Tape casting is mostly done for electronicsubstrates and packages of layered structure.Photolithography is another technique for precisepatterning of conductors and other components inelectronic packaging. Tape casting is also of increasinginterest for other applications like fuel cells, ceramiccomposites etc.The other major layer structure for advance applicationis coating, where melt spraying is very important. Butchemical and physical vapor deposition and chemical(e.g., sol-gel and polymer pyrolysis) coating methodsare also increasing. Using advanced forming methodsopen structures such as honeycomb catalyst supportsfrom formed tape and extruded structuresare done.Using advanced forming methods, highly porousstructures, including various foams, like, reticulatedfoam, are also of increasing use.Densification of consolidated powder bodies isachieved predominantly by pressure-less sintering.However, for non-oxides and parts of simple shapeswhere microstructural homogeneity is needed the useof pressure sintering by hot pressing is increasing.The sintering process

Firing of ceramic articles is done at a temperaturebelow its melting point.The gren body, after drying issubjected to firing in a furnace at elevated temperaturewhere atomic and molecular diffusion processes giverise to significant changes in the primarymicrostructural features. It includes (always)strengthening of the micro-structure by neck growthand / or particle gluing by a glass phase, densificationby elimination of porosity accompanied by shrinkageand coarsening of the microstructure by grain growthand possibly pore growth.Thus, as the sinteringprogresses the pores in the object close up, resultingin a denser product of significant thermo-mechanicalproperties.Another major change in the body during the firing orsintering process takes place in the form of thedevelopment of polycrystalline nature of the solid. Thischange introduces a definite pattern of grain sizedistribution, which exhibits a significant impact on theultimate physical properties of the material. The grainsizes remains associated with either the initial particlesize, or possibly the sizes of aggregates or particleclusters develops during the initial stages of processing.Solid state sintering takes place below the melting pointof ceramics and it is a diffusion controlled process.Material transport in solid state sintering dependsinversely on particle diameter and temperature andexcessive diffusion causes rapid grain growth withpore entrapment.In liquid phase sintering presence of liquid phasecauses enhanced sintering resulting more uniformdensification. The role of liquid is to introduce capillarypressure to assist particle rearrangement for efficientpacking.The ultimate microstructure(and thus the physicalproperties) of the final product will be limited by andsubject to the form of the structural template orprecursor which is created in the initial stages ofchemical synthesis and physical forming. Hence theimportance of chemical powder and polymerprocessing as it pertains to the synthesis of industrialceramics, glasses and glass-ceramics.There are numerous possible refinements of thesintering process. Some of the most common involvepressing the green body to give the densification a

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head start and reduce the sintering time needed.Sometimes organic binders such as polyvinyl alcoholare added to hold the green body together; these burnout during the firing (at 200–350 °C). Sometimesorganic lubricants are added during pressing toincrease densification. It is common to combine these,and add binders and lubricants to a powder, then press.(The formulation of these organic chemical additivesis an art in itself. This is particularly important in themanufacture of high performance ceramics such asthose used by the billions for electronics, in capacitors,inductors, sensors, etc.)Parts made of new ceramics sometimes requirefinishing for 1) increased dimensional accuracy 2)improved surface finish and 3) making minor changesin part geometry. Finishing usually involves abrasiveprocesses and diamond abrasives are used to cut thehardened ceramic materials

Summary:Ceramic products for traditional applications arefabricated following certain processes, like crushingof the raw materials, grinding of the crushed productsto fine powders, compaction of the powders, dryingof the compacted powders, sintering of the dried massand post treatment of the sintered mass using differentmachineries. Ceramic products for advancedapplications are synthesized by different chemicalroutes like co-precipitaion, sol-gel, spray pyrolysisetc. All these techniques have been discussed in briefin this paper.

References:

1. M.N.Rahman, Ceramic Processing and Sintering, CRC/Taylor and Francis, 2007.

2. Costas Sikalidis (Ed), Advances in Ceramics - Synthesis and Characterization, Processing and Specific Applications, InTech, 2011.

3. D.W. Richerson, Modern Ceramic Engineering:Properties, Processing, and Use in Design,M.Deker, 1992.

4. J.E. Reed, Principles of Ceramic Processing, John Wiley and Sons, 1995.

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Introduction:Composite materials can be classified into threegroups according to the size of the form of thereinforcement use in it. Reinforcement are classifiedinto three groups,1. Particles : Aspect ratio is less than 12. Fibrous : Aspect ratio is greater than 103. Plate: reinforcement has length, width.According to this classification, there are three kindsof composite materials,a) Particulate composite: Reinforcements are in particle form ( diameter 1o to100 nm).b) Fibrous composite: Reinforcements are in fibrous form (epoxy-glass fiber composite).c) Laminated composite: Reinforcements are in plate form (ply wood).A special group of dispersion strengthened materialscontaining particles 10nm to 250 nm in diameter calledas particulate composite. Particulate composites aremuch less efficient in the way the filler contributes tothe strength. There is a small gain in stiffness, andsometimes in strength and toughness, but it is far lessthan in a fibrous composite. Their attraction lies morein their low cost and in the good wear resistance thathard filler can give. Road surfaces are a good example:they are either macadam (a particulate composite ofgravel in bitumen, a polymer) or concrete. Criteria for a good particulate composite: During processing of composite, the

reinforcement should retain its shape and thetype (structure, nature).

The reinforcement should not react with matrixand the matrix should not react withreinforcement.

The interphases (phases between matrix andreinforcement) should be chemically andphysically compatible with the phases presentin matrix components. These interphases arealso gradually changes in composition and innature as going to close to reinforcement frommatrix. Consequently the properties are alsochanging in this grading. Both interphase andinterface of constituents are responsible forreinforcement matrix bonding (RIM).

Reinforcement sizes are responsible for thecreep resistance of the composite frommicro level to nano level.

The properties of reinforcement should bebetter than matrix.

There must be appropriate temperaturestability so as to suit processing temperature.

There should no thermal and chemicalreactivity between reinforcement and matrix.

There should not very strong bondingbetween matrix and reinforcement ,otherwise it becomes brittle.

Rule of mixture:Certain properties of a particulate composite dependonly on the relative amounts and properties of theindividual constituents. The rule of mixtures canaccurately predict these properties. The density of aparticulate composite, for example,

= = + + + … +

Where is the density of the composite , , …, are the densities of each constituent in the

Particulate CompositeJAYDIP CHAKRABORTY

M. Tech. (2nd Year), Ceramic TechnologyGovt. College of Engineering & Ceramic Technology

Kolkata, Sept. 2013

Technical Section – Paper – 3

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IIC Bulletin Vol.22, No. 1, 2013 21

composite, and , , …., are the volume fractionsof each constituent. From rule of mixture we canpredict the upper bound limit and the lower boundlimit of elastic modulus of particulate composite.

(u)= . + . ……… for upper boundary

(l)= . /( . + .)…… for lower boundaryIn these above equation E & V denote elastic modulusand volume fraction respectively, whereas thesubscript c, m, p represents composite , matrix andparticulate phases.(1)(2)

Dispersion –strengthened composites:It is not as pronounced as with precipitationhardening; however the strengthening is retained atelevated temperatures and for extended time periodsbecause the dispersed particles are chosen to beunreactive with the matrix phase. In aluminum-

aluminum oxide system, a very thin oxide and adherentalumina coating is caused to from on the surface ofextremely small flakes of aluminum, which aredispersed within an aluminum metal matrix; thismaterial is termed sintered aluminum powder. (2)

Methods of fabrication of particulate composite:Fabrication method of composite material dependson the types of both matrix and reinforces materials.Particulate composites are made by blending silicaflour, glass beads, even sand into a polymer duringprocessingHere mainly two methods are discussed in brief.

I. Powder metallurgical process:This method is used to fabricate mainly electricalcomposite material (e.g. silver tungsten compositematerial).

I. Compo-casting:

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IIC Bulletin Vol.22, No. 1, 2013 22

An unusual technique for producing particulatereinforced castings is based on the thixotropicbehaviour of partly liquid partly solid melts. A liquidalloy allowed to cool until about 40% solid haveformed; during solidification , the solid-liquid mixtureis vigorously stirred to break up the dendriticstructure, A particulate material is introduced duringstirring. The resulting solid-liquid slurry displaysthixotropic behavior-the slurry behaves as a solidwhen no stress is applied, but flows like a liquid whenpressure is exerted. Consequently, the thixotropicslurry can be injected into a die under a pressure, aprocess called compocasting. A variety of ceramicparticles and glass beads have been in corporate into aluminium and magnesium alloys by this technique.Aluminium casting dispersed SiC particles forautomotive applications, including pistons andconnecting rods, represent and important commercialapplication for particulate composites. With specialprocessing, the SiC particles can be wet by the liquid,helping to keep the ceramic particles from sinkingduring freezing.

Abrasives:Grinding and cutting wheels are formed from alumina,silicon carbide and cubic boron nitride. To providetoughness, the abrasive particles are bonded by glass

or polymer matrix. Diamond abrasives are typicallybonded with a metal matrix. As the hard particles wear,they fracture or pull out of the matrix, exposing newcutting surfaces.Cemented carbides or cermets:Cermets contain hard ceramic particles dispersed inmetallic matrix. Tungsten carbide inserts used forcutting tools in machining operations are typical ofthis group. WC is a hard, stiff high melting temperatureceramic. Unfortunately, tools conducted from tungstencarbide are extremely brittle.To improve toughness, tungsten carbide particles arecombined with cobalt powder and pressed intopowder compacts. The compacts are heated abovethe melting temperature of the cobalt. The liquid cobaltsurrounds each of the solid WC particles. Aftersolidification, the cobalt serves as the binder fortungsten carbide and provides good impact resistance.Other castables, such as TaC, TiC, may also beincluded in the cermet.

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IIC Bulletin Vol.22, No. 1, 2013 23

References:

1. Donald R. Askheland, Pradeep P. Phule; “The Science and Engineering of Materials”, fifth edition, page no 615 to 618.

2. William D. Callister, Jr. ,”Callister’s Materials Science and Engineering”, seventh edition, page no 542 to544.

3. William F. Smith, “Principles of Materials Science and Engineering “, first edition, page no 700.

4. http://textbooks.elsevier.com/ manualsprotectedtextbooks/9780750663809/ Static/composites/composites1a.htm

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IIC Bulletin Vol.22, No. 1, 2013

Importance of Excess Air Calculations in Oil Fired Tunnel Kilnsin Ceramic Industries

Anil K Goel, Ajit Kumar * & Sagar Maji, **Indian Oil Corporation, Lodhi Road, New Delhi-110 003

[email protected] Air Fuel is one of the very important parameters for obtaining improved fuel economy and betterfuel efficiency. Quantum of Excess Air is measured indirectly from analysis of flue gases. Some of the equationsto calculate excess air are extremely complex. A simple method for calculating excess air has been discussedin this paper.Keywords – Excess Air, Flue Gas, Stoichiometric Air*School of Engineering and Technology, Indira Gandhi National Open University , Delhi- 110 069**Department of Mechanical Engineering, Delhi Technological University, Delhi-110 042

IntroductionEver rising energy prices, limited resources andconcerns about global warming, all have lead toemphasis on fuel efficiency. . Fuel requires oxygen toburn. Fuel gets oxygen from Air. Carbon andHydrogen atoms in fuel need oxygen to burn. Theyproduce carbon dioxide and water respectively. Bothreactions are exothermic reactions and hence energyis produced. Certain specific amount of air is requiredto burn the fuel. This can be calculated by chemicalequation and putting atomicWeights and molecular weights in place. The quantityof air requirement calculated in this manner is calledstoichiometric air. This calculation assumes that alloxygen molecules in air and all atoms of carbon andhydrogen in fuel participate in reaction. But actuallysome molecules of oxygen are not able to combinewith either carbon or hydrogen atoms. Correspondingamount of fuel shall remain un-burnt if stoichiometicair is supplied to the fuel. Unburnt fuel would result inloss of energy and poor fuel efficiency. To enable fuelto burn completely, some extra air is supplied inaddition to the stoichiometric air. This extra air whichis supplied over and above the stoichiometric air iscalled Excess Air. Excess Air is measured as a fractionor percentage of stoichiometric air requirement.Optimisation of excess air in furnaces and boilers is akey measure towards achieving higher fuel efficiency(1). Certain amount of Excess air in combustion is

necessary to facilitate complete combustion or nearcomplete combustion of fuel (2) . But excess of excessair affects fuel efficiency adversely because excessair also requires energy to heat it up to flue gastemperature. Hot Excess Air exits along with Flue Gasthru chimney. Large amount of excess air also requireshigher size of air and flue gas handling equipment(3).These in turn require more space, more capital costand more maintenance cost.Excess Air CalculationsExcess Air is not measured directly. It is indirectlycalculated from carbon dioxide or oxygen componentin flue gas which are obtained from flue gas analysis(4). Various formulae are used for Excess Airpercentage calculation. Some of them are extremelycomplex and some others are quite simple. (5). Mostpopular formulae used for calculation of excess airare:

Excess Air Fraction =Oxygen %age in flue gas / (21– Oxygen %age in flue gas)

EA = O2 / (21 – O2) (6) (1)

Other formula used is more like a thumb rule i.e. EA% = 5* oxygen % in flue gas (7).To arrive at the inherent assumptions in theseformulae, first we need to work out how these formulaehave been arrived at. The theory behind first formulai.e. O2 / (21-O2) is worked out below - Oxygen percentage is measured in flue gas

Technical Section – Paper – 4

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IIC Bulletin Vol.22, No. 1, 2013

Excess air is calculated by the formulaO2 / (21-O2)

Excess Air Formula is derived as given below: Let stoichiometric air required be = 100 moles Let excess air quantity be = x moles Air has 21% oxygen and 79% nitrogen by volume Flue gas formed 100 + x moles Oxygen in flue gas = 0.21x moles (2) Oxygen fraction in flue gas = 0.21x/(100 + x) (3) Oxygen percentage in flue gas= 0.21x *100/(100 + x)

= 21 x / (100 + x) (4) 21x = (100 +x) * oxygen percentage in FG (O2) 21x – x * O2 -= 100 * O2 x = 100*O2 / (21- O2) (5)

Excess air fraction = O2 / (21- O2) (6)Most of the users are unaware of the presumptions inthis formula. The derivation has presumed that x molesof excess air plus 100 moles of required stoichiometricair form 100 + x moles of flue gas. There lies aninherent assumption that 100 moles of stoichiometricair also forms 100 moles of Flue Gas. For fuelcontaining mostly carbon, it would be true but forliquid petroleum fuels, which consist of a very largequantum of hydrogen atoms bonding with carbonatoms, we need to examine in more details. Hereoxygen reacts with carbon and hydrogen in fuel,resulting in change in moles. Relevant reactions areas under:

C + O2 = CO2 (7)2H2 + O2= 2H2 O (8)

Sulphur (which is present in small quantities) in fuelreacts as S + O2= SO2

(8).

It is correct to assume that x moles of Excess Airforms x moles of flue gas, because it does notparticipate in chemical reaction. Equation (7) showsthat one molecule or one mole of oxygen reacts withcarbon to form one molecule or one mole of carbondioxide. So moles in Excess Air remain unchangedwhen air changes into flue gas after reacting withcarbon. Equation (8) shows that one mole of oxygenreacts with hydrogen in fuel to form two moles ofwater vapour or steam. Thus moles in Flue Gas willbe more than moles in air. Understanding of these

facts unravels the implication of the assumption. If fuelcontains only the carbon or almost completely thecarbon and nil or almost nil hydrogen as fuel, theassumption made that is 100 mole of air give 100moles of flue gas would be correct. Nitrogen in airdoes not participate in reaction for producing energy.Negligible quantity of nitrogen oxides that are formedcan be ignored for this analysis without any tangibleeffect on accuracy. Oxygen also reacts with sulphurin the same way as with carbon. This reaction doesnot result in change in moles. Therefore, presence ofsulphur in fuel tends to maintain applicability of theassumption and so the applicability of the formula.Therefore for fuels like coal or pet coke, the formulais perfectly applicable.Ash content in coal does not react with air to formflue gas. (9) Therefore Ash content does not affecteither the assumption or the applicability of formula.This understanding is important because in Indianscenario, coal is the largest source of energy. Othermajor source of energy is petroleum Oil, i.e. fuel Oilor other liquid petroleum fuels. Most part of thesefuels contains molecules which are long chains ofcarbon and hydrogen atoms (10). These are mostly ofnomenclature CnH2n+2 with n being in the range of 15to 30. With n being so large, ratio of carbon andhydrogen atoms can be taken as nearly 1: 2. Nowwhen we come back to our equations:

C + O2= CO2

Or2C + 2 O2 = 2 CO2

and2H2 + O2= 2H2O

2 carbon atoms would carry 4 hydrogen atoms asper the ratio of 1:2 as discussed above. 2 carbonatoms combine with 2 oxygen molecules to form 2molecules of carbon dioxide. 4 Hydrogen atomscombine 2 atoms or one molecule of oxygen to form2 water molecules.

2C + 4 H + 3 O2 = 2 CO2 + 2 H2OThus 3 Oxygen molecules in air combine with 2carbon atoms and 4 hydrogen atoms to form 4

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IIC Bulletin Vol.22, No. 1, 2013

molecules of Flue gas (2 CO2 + 2H2O). Hence 3moles of oxygen in stoichiometric air give 4 moles offlue gas. So moles in Flue Gas increase in comparisonto moles of oxygen in stoichiometric air. Increase isto the extent of 33% of moles in oxygen. Now thequestion arises that with such large change, how far isthe formula EA=O2 / (21-O2) valid which assumesthat moles remain unchanged. It is seen that inaccuracyis creeping in because of oxygen reaction withhydrogen present in fuel. We examine in more detailsas given below - Air contains 79% Nitrogen by volume. Since

nitrogen does not participate in reaction, moles ofN2 remain unchanged. Those moles of O2 that reactwith sulphur also remain unchanged. Sincepetroleum fuels mostly contain carbon andhydrogen, we consider the following :

79 Moles of N2 in air = 79 moles of N2 in FG 21 moles O2 in air = 28moles in FG (14 moles of

CO2 &14 moles of H2O)Thus 100 moles of stoichiometric air give 107 molesof Flue gas. So this leaves inaccuracy to the extent of7% and not 33%. On further analysis, we find - For 100 moles of stoichiometric air, there are also

x moles of excess air present. Excess Air doesnot participate in reaction and therefore moles inExcess Air remain unchanged.

Thus 100 + x moles of air form 107 + x moleof flue gas. Excess air requirement depends on the nature and

condition of fuel being used (11). Solid fuels requiremuch more excess air than liquid and gaseous fuels.Also viscous fluids require more excess air.Requirement of excess air also depends on howwell Excess Air quantity is monitored andmaintained by operating personnel.

Oxygen has been found to be present in Flue Gasfrom 1% to 2% in well managed plants using gaseousand liquid fuel like large Ceramic industries orpetroleum oil refineries (12). On the other end it is alsofound to be to 12 % to 15% in plants which use solidfuels and which are not so well operated andmaintained. Let us see what it means in terms ofExcess Air :

a) 1% O2 results in 1/ (21-1) = 1/(20) = 5% EAb) 2% O2 results in 2/(21-2) = 2 /(19) = 10.5 % EAc) 8% O2 results in = 8/(21-8) = 8/(13) = 1.5% EAd) 12% O2 results in = 12 / (21-12) = 12 / (9)

= 133% EAAbove results are as given in Table-I :

We have tried to examine the effect of 5% EA, 10%EA, 50% EA and 120% EA on assumption made inthis formula and their effect on accuracy of formulaare as given below

a) 5% EA would mean,105 moles in air give 112moles of FG. Adeviation of 6.7%.

b) 10% EA would mean,110moles in air give 117moles of FG, Adeviation of 6.3%

c) 50% EA would mean150 moles of air give 157moles of Fg, Adeviation of 4.5%

d) 120% EA would mean220 moles of air give 227moles of FG. Adeviation of 3.1%

These results can be summarised as under for liquidpetroleum fuels:

Table : 2

Oxygen % in Flue Gas Excess Air %1 52 108 61.512 133

Excess Air % % deviation calculation by formula

5 6.710 6.350 4.5120 3.1

Fuel Liquid Petroleum

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IIC Bulletin Vol.22, No. 1, 2013

Actual deviation in fact is even less. Reasons are thatthese fuels contain some little %age of sulphur. Theyalso contain some complex chains of Carbon-Hydrogen molecules (13). Sulphur combines with 1 molein Oxygen in air to form 1 mole of SO2 in Flue Gas.Thus moles in air that combine with sulphur remainsame when converted to Flue Gas. This has asobering effect on deviation. Similarly complex chainsof carbon hydrogen molecules contain higherpercentage of carbon than the %age of carbon in linearchains. Since 1 mole of oxygen combines with carbonto give 1 mole of carbon dioxide in Flue Gas, suchhigher percentage of carbon also has additionalsobering effect on deviation. So deviation in calculationof EA is between 3% and 6% for liquid petroleumfuels. . Let us take it as 5% for our further discussions.Methane as FuelFor Methane CH4 the calculations shall work out asunder -

C + 4H + 2O2 = CO2 + 2 H2OHere 2 molecules of oxygen combine with 1 carbonatom and 4 hydrogen atoms to form 3 molecules inFlue Gas. If Methane is used as fuel, increase in molesin fuel gas is to the extent of 50% of moles in oxygen.Inthis case: 79 moles of nitrogen = 79 moles in Flue Gas 21 moles of oxygen = 31.5 moles in Flue Gas 100 moles of Stoichiometric Air will give 110.5

moles of Flue Gas.When we analyse its effect on 5% Excess Air, 10%Excess Air, 50% Excess Air and 120% Excess Air asin the case of liquid petroleum fuels, we find : 5% Excess Air would mean

105 moles of air give 115.5 moles of Flue Gas; adeviation of 10%

10% Excess Air would mean110 moles of air give 120.5 moles of Flue Gas; adeviation of 9.5%

50% Excess Air would mean150 moles of air give 160.5 moles of Flue Gas; adeviation of 7%

120% Excess Air would mean220 moles of air give 230.5 moles of Flue Gas; adeviation of 4.8%

Excess Air % % deviation calculation by formula

5 1010 9.550 7120 4.8

Fuel Methane

These results are summarised in Table for MethaneFuel –

Table : 3

Now, Deviation in loss of energy can be calculatedas under - Loss of energy in flue gas depends upon Excess

Air percentage and temperature of flue gas. If weassume 8% O2 in FG, EA works out to be

8 / (21-8) = 8 / (13) = 61.5% (14)

Specific heat of Flue Gas is 0.24 kcal/kg 0 C (14)

1kg of fuel requires 14.1 kg of stoichiometric airto burn completely (15)

Thus Air required to burn 1 kg of fuel is (1 + 0.615)* 14.1 = 22.8 kg.So flue gas generated from 1 kg of fuel =(22.8 +1) = 23.8 kg

In tunnel kilns in industrial clusters for small Ceramicindustries, Excess Air percentage is high but Flue Gastemperatures are not that high (16). Taking average fluegas temperature as 250 0C and ambient temperatureas 30 deg. C, Heat loss works out to be 23.8 * 0.24* (250-30)

= 1250.66 kcal/ kg of fuelConsidering calorific value of fuel to be 10600 kcal/kg; this loss in flue gases works out to be about12%.We had earlier worked out that deviation incalculation of Excess Air is about 5% for liquidpetroleum fuels. Coupled with this typical casewherein flue gas losses are calculated to be 12%,deviation in fuel consumption shall work out to be5% of 12% i.e. 0.6% for liquid petroleum fuels.Thus it can be seen that usage of formula -

EA = O2 / (21-02)

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IIC Bulletin Vol.22, No. 1, 2013

for calculating excess air fraction gives accuracy withdeviation of about 0.6% in fuel consumption.Direction of Deviation:We have seen that Flue Gas contains more moles ofgases than number of moles in air. But formulaassumes that Flue Gas contains same number ofmoles as in Air. Therefore, Oxygen % obtained byFlue Gas measuring instruments is slightly less thanwhat it would have been, if the number of moles inFlue Gas had been equal to number of moles in Airas assumed in the formula. Thus deviation incalculation of Excess Air is on negative side. As aresult deviation in calculation of losses in Flue Gas isalso on the lower side.General Thumb rule in practice in CeramicIndustries:Now let us look at the thumb rule. This is extensivelyused by engineers and managers in large industries.The thumb rule used is

E A% = 5 * Oxygen % in Flue gas.

Well managed large organisations, employprofessionals and qualified engineers in large numbers.In such industries, using liquid and gaseous petroleumfuels, O2 % age in Flue Gas is watched constantlyand very critically. Corrective measures are taken assoon as deviations are noticed. Management is veryalert to O2 % age variation in Flue Gas. Let us examinevarious scenarios in which O2 % is 1%, 2%, 5%,10% and 12% in flue gas When O2 = 1%, Thumb rule gives EA %= 5% as

per formulaEA = 1/ (21-1) = 1(20) = 5%

When oxygen is 2% in FG : thumb rule giveEA % = 10%,Formula givesEA = 2 / (21-2) = 2 / (19) = 10.5%

When oxygen is 5% in Flue Gas, thumb rule giveEA= 25%.Formula givesEA = 5 / (21-5) = 31.25%

When O2 is 10%, thumb rule give ExcessAir = 50%.Formula givesEA = 10/ (21-10) = 10 / (11) = 90.9%

When O2 is 12%, thumb rule give Excess Air= 60%.Formula givesEA = 12 / (21-12) = 12 / (9) = 133%

These results are summarised in a table.

Thus it is seen that when O2 % in flue gas is low say1%, thumb rule gives perfect results. Even with 2%oxygen in flue gas, it gives almost accurate results.However as O2 % increases, this thumb rule giveslower estimation of Excess Air than it actually is. It isseen that with 5% O2, thumb rule show 25% ExcessAir, but actually it is 31.25%. Similarly for 10% O2,thumb rule indicates 50% Excess Air but actually it is90.9%. That is 40.9% more than 50% or actualExcess Air. It is 81.8% more (40.9 *100)/50 thanwhat is indicated by thumb rule. Therefore thumb rulecan be safely used in large well managed organisationswhich are using liquid or gaseous petroleum fuels.

Oxygen % in Flue Gas Excess Air % as calculated by Excess Air as calculatedthumb rule by formula

1 5 52 10 10.55 25 31.2510 50 90.912 60 133

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IIC Bulletin Vol.22, No. 1, 2013

However, it would not be appropriate to use it inindustries which use solid petroleum or agriculturalfuel where O2 % is higher than 5% in Flue Gas.

Conclusions:(i) The formula for calculating Excess Air i.e. Excess

Air = O2 / (21 – O2) is applicable perfectly forthe fuels containing carbon alone. Presence ofsulphur also does not affect accuracy of formula.

(ii) Presence of Hydrogen results in certaininaccuracy in calculation of Excess Air. For liquidpetroleum fuels containing carbon and hydrogen;inaccuracy in results is between 3% and 6%.

(iii) Results obtained from this formula show a littlelower excess air than the actual.

(iv) Thumb rule for calculating Excess Air i.e. ExcessAir % = 5 * oxygen % in Flue gas can be usedwhen oxygen percentage is about 1% to 2% inFlue Gas. For more than 5% oxygen, the thumbrule will give large deviations. These deviationsalso show a lower excess air than the actual.

REFERENCES

1. Training manual on Energy Efficiency for Smalland Medium Enterprises”, APO Japan ISBN92833-7084-8, 2010

2. Importance of Excess Air in process.www.mac.nesu.edu/chapter (Date 4/11/2013)

3. Power Engineer – Boiler draft and flue gashandling equipment www.operating engineers .ca.(Date 4/11/2013)

4. Improving energy efficiency of boiler systemswww.cedeng.neeing.com (Date 4/11/2013)

5. Mass Balance. http://eu.wikipedia.ing/massbalance (Date 4/11/2013)

6. Energy efficiency in Thermal Utilities by Bureauof Energy Efficiency, Ministry of Power, Govt.of India, 2006 Page No.102

7. Principles of combustion http:/uptel.iitm.ac.inplacement (Date 4/11/2013)

8. Sulphur content of certain liquid fuels.www.eurapa.eu. (Date 4/11/2013)

9. Coal combustion and combustion products.www.eolss.net (Date 4/11/2013)

10. World petroleum Ceramaic – Alternate transportfuels www.petroleum.org/knowledge centre(Date 4/11/2013)

11. Fuels and combustion. Thermal equipmentwww.retseveen.net/eeasia.fuel & combustion(Date 4/11/2013)

12. Thermal Utilities - www.pcra.org (Date 4/112013)

13. Chemistry of Petroleumwww.lloydminsterheavyoil.com(Date 4/11/2013)

14. Energy performance and assessment ofequipment, BEE, Ministry of Power, Govt. ofIndia, 2006, Page No.87

15. Combustion of oil www. Productivity.in(Date 4/11/2013)

16. DPR on recuperates in tunnel kiln.www.dcmsme.gov.in/ceremic (Date 4/11/2013)

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