I= STUDIES ON THE SYNTHESIS OF WOLLASTONITE FROM RICE HUSK ASH AND LIMESTONE
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Title of Thesis
STUDIES ON THE SYNTHESIS OF WOLLASTONITE FROM RICE HUSK ASH AND LIMESTONE

Author(s)
Muhammad Sharif Nizami
Institute/University/Department Details
Institute of Chemistry, University of the Punjab, Lahore
Session
1993
Subject
Chemistry
Number of Pages
280
Keywords (Extracted from title, table of contents and abstract of thesis)
wollastonite, rice husk ash, limestone, rha silica

Abstract
Wollastonite (CaSiO3), an important industrial raw material, has been attempted to synthesize from its constituent oxides i.e. CaO and SiO2. Besides its industrial importance. This synthesis was per-for-med on account of insufficient availability of wollastonite in natural for-me Rice husk and limestone were used as source materials for the said oxides. Abundantly available r-ice husk was pyroprocessed under varying time temperature conditions to obtain ash with maximum percentage of silica, having dominant amorphous character Rice husk ash. With highest silica yield i.e. 92.01%, was purified by different physico-chemical methods to eliminate the metallic impurities and residual carbon. Thus prepared silica, being 98.50% pure, was reacted with CaO from limestone. Two routes were adopted to synthesize wollastonite. In first, CaO obtained by proper calcination of limestone was inter-mixed with silica, the mixture pulverized and hydrothermally treated in autoclave under water vapour pressur-e from 30 bars to 80 bars, for one hour. The resulting inter-mediate compounds i.e. calcium silicate hydrates. were investigated employing chemical analysis, SEM and XRD techniques. Hydrothermal runs, carried out under 50 and 70 bars water vapour pressure. resulted in formation of xonotlite and tobermorite respectively. These, being structurally related to wollastonite were calcined at 950oC for three hour-s, to eliminate the chemically combined water molecules. Secondly. prepared silica and limestone powders were mixed in 1:1 molar ratio and a mineralizer having glass like composition was added. Direct solid state synthesis was attempted by heating the raw mixed batches at The products obtained through both. hydrothermal and solid state routes. were evaluated and mutually compared as we 11 . Wollastonite resulting from hydrothermal process showed comparatively low yield and was not as well crystalline as that from the latter route. Batches sintered at 1200oC and 1300oC produced the highest percentage of β-wollastonite and α-wollastonite respectively. The rate of solid state reaction was found proportional to rise in temperature. Reactivity of rice husk ash silica towards CaO was also considered for its comparison with that of the commonly available variety i.e. quartz. Chemical kinetic study of produced wollastonite showed that required energy of activation was 27.48 KCal.mole-1. While on the other hand. this value for the same synthesis, utilizing quartz instead of rice husk ash silica. amounted to 78 KCal.mole-1. Consequently, amorphous form of rice husk SiO2 proved to be many times more reactive than crystalline variety of the same. This was also shown by the results regarding evaluation of synthesized CSH. Utilization of synthesized wollastonite. in ceramic tile bodies. was also tried. Both, natural as well as synthetic wollastonite were separately added (55%) to other batch components with fixed proportions and raw bodies were fired under identical conditions. Fast firing tile technology saves both time and energy simultaneously. It was observed in this regard that produced tile bodies matured within two hours instead of twelve hours. the time required for tiles without wollastonite. Considerable saving in time and heat energy can be made in tile production by using wollastonite. Physical properties i. e. crushing strength. transverse breaking strength and water absorption etc. of these bodies were determined and found comparable.

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1705.16 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
80.82 KB
2 1 Introduction 1-6
41.84 KB
  1.1 Rice Husk 2
  1.2 Rice Husk Ash 2
  1.3 Scope of the study 3
3 2 Literature review 7-28
162.18 KB
  2.1 RHA preparation 7
  2.2 RHA Utilization 10
  2.3 Synthesis of Wollastontie 13
  2.4 Utilization of Wollastontie 26
4 3 Experimental work 19-72
249.72 KB
  3.1 Materials and methods 29
  3.2 Procedures 43
5 4 Results and discussion 73-190
965.51 KB
  4.1 Pyroprocessing of Rice Husk 73
  4.2 Purification of RHA Silica 89
  4.3 Wollastonite Intermediates 99
  4.4 Thermal Decomposition of CaCo 3 In-Situ 130
  4.5 Reaction Potential 133
  4.6 Temperature -ˆ†H Effect 137
  4.7 Phase Rule consideration 138
  4.8 Field strength 141
  4.9 Kinetic model of solid state Reaction 142
  4.10 Quantitative Kinetic analysis of solid state reaction 149
  4.11 Solid state reaction products 156
  4.12 Physico-Chemical characteristics of synthetic wollastonite 172
  4.13 Physical properties of prepared tile bodies 181
6 5 Conclusions and future work 191-195
32.77 KB
  5.1 Conclusions 191
  5.2 Future work 195
7 6 References 196-219
131.34 KB
  6.1 Appendix A: Publications 220