CHEMICAL SOLUTION ROUTES FOR THE SYNTHESIS OF TITANATES, ZIRCONATES, CUPRATES, MOLYBDATES AND VANADATES
by
PRAMOD K. SHARMA
Department of Chemistry
THESIS SUBMITTED
IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY
NEW DELHI - 110016, INDIA MARCH, 1996
5
CERTlli iCATE
This is to certify that the thesis entitled "CHEMICAL SOLUTION ROUTES FOR THE SYNTHESIS OF TITANATES, ZIRCONATES CUPRATES, MOLYBDATES AND VANADATES" being submitted by Mr. Pramod K. Sharma to the Indian Institute of Technology, New Delhi for the award of the degree of Doctor of Philosophy in Chemistry, is a record of bonafide research work carried out by him. Mr.
Pramod K. Sharma has worked under my guidance and supervision, and has fulfilled the rquirements for the submission of this thesis which, to my knowledge, has reached requisite standard.
The results contained in the dissertation have not been submitted, in part or in full, to any other university or institute for the award of any degree or diploma.
March, 1995
(A. RAMANAN) Assistant Professor Department of Chemistry Indian Institute of Technology New Delhi.
VEDIC/9'1ED (113
gt/l9( MOTHER
BEI,OYED FAVIER
ACKNOWLEDGEMENTS
I take pleasure in recording my sincere thanks to Dr. A. Ramanan, Assistant Professor, Department of Chemistry, Indian Institute of Technology, New Delhi, for his inspiring guidance and constant encouragement throughout the course of this investigation.
My sincere thanks are due to Prof G. N. Rao, Head of chemistry Department, for providing me necessary facilities in the department. Thanks are also due to all the faculty members and supporting staff of the department for their kind help and cooperation.
My grateful thanks are due to Mr. G.S. Hegde, Dr. G.N. Subbanna and Dr. N. Y.
Vasantacharya, Bangalore, for help with X-ray, electron diffraction and magnetic suceptibility measurements.
I am thankful to Prof Vankar and Mr. Tiwari, lIT Delhi, for help with x-ray powder diffraction. I am really thankful to Prof B.P. Pichumani, Department of Chemical Engineering for particle size analysis and Dr. Bhattachadee and Mr. Rakesh, Department of Civil Engineering at IIT, Delhi for pore size measurements. It is my privilege to acknowledge the help of Prof N. K. Sandie and Dr. F. V. Varghese for surface area measurements.
I am grateful to all the members of my family for their constant encouragement throughout my academic career which undoubtedly, has added much to my will and vigour to pursue my research work.
I also wish to express my appreciation and warm feelings of gratitude to all my friends including Dr. Sunil, Dr. Kapur, Dr(Mrs). Ranjana, Dr. Sunita, Dr. Rupal, Dr.
Bhardwaj, Dr. E. Rajshakharan, Shivcharanji, Bhatheja, Sandhya, Nidhi, Mr. Dutta, Menakshi, Pradhan, Shashank Deep, Abhishek, Achiruya and Bhasin.
7
,2,-„„Atati, k[PRAMOD K.SHARMA]
ABSTRACT
The motivation for the present study is to explore the potential of solution rout_e_siLsarti icular, sol-gel processu►g, mild hydrothermal reactions and lligh.21kaline media in the preparation of a few electroceramic materials containin transition metal oxides such as lead titanates, zirconates and bismuth cuprates. We also report here the synthesis and characterization of a few new reduced vanadates and molybdates crystallized under hydrothermal conditions from aqueous solution.
Stabilization of sol is one of the critical factors in controlling the structure of the final products and their processing properties. In composition of the sol, the concentration of water plays an important role in determining the chemical make up, morphology and size distribution of alkoxide polymers as it is directly involved in the chemical reaction that form the molecular structure. A serious problem encountered in producing gel monolith through the S-G process from metal alkoxide precursor is fracture and crack formation that takes place during the conversion of wet gel into dry gel. N,N-dimethyl aniline (DMA) has been used both as stabilizing as well as drying control chemical agent (DCCA) for the first time. Xerogels derived from DMA stabilized sol were found to be crack-free with a larger surface area and higher porosity. We also describe our results on the rheological aspects like gelling time, density, fluidity, viscosity and surface tension of the titania sol derived from titanium-tetra-isopropoxide (TTIP), water and isopropanol (i-PrOH) in presence of
( i )
DMA. We employed thermal and infrared studies to examine the drying characteristics of the xerogels. Scanning and transmission electron microscopic [SEM and TEM] studies were used to probe the microstructure of these gels. X-ray powder diffraction [XRD] studies revealed that by varying heat treatments we could synthesize uniform small particles of titania in either a completely amorphous, anatase or rutile form. Titania xerogels obtained in our study could be converted into rutile phase at much lower temperatures than reported so far.
In the preparation of lead based electroceramics such as lead titanate [PT], lead zirconate [PZ] and lead zirconate titanate [PZT], the low diffusion and nonuniform mixing of species such as Zrl+ and TO+ poses a major problem resulting in high sintering temperature, large sintering time and poor homogeneity. Hence it becomes essential to explore alternate chemical routes for the formation of these phases. We used sol-gel and hydrothermal methods in addition to ceramic route to synthesize PT, PZ and PZT. The purity and phase analysis were carried out by XRD.
Particle size distribution of the powders derived from different routes revealed that the largest particle size could be obtained from SG route. The uniformity and surface morphology of the xerogels were studied by SEM.
We also describe the results obtained from low temperature chemical reactions to crystallize unusual bismuth cuprates from high alkaline medium. We succeeded in obtaining highly crystalline Bi2CuO4 (tetragonal) at temperatures around 90 °C. Our studies have shown that this appears to be the only stable phase formed in Bi-M-Cu-O
(iv)
(M =Ca, Sr) as well as Bi-Cu-O systems under these conditions. We also observed that powders obtained in our study were very small, uniform and exhibited spheroidal habits as shown by SEM and particle size measurements. D.C. magnetic susceptibility measurements of the low temperature synthesized Bi2Cu04 showed a different magnetic behaviour at low temperatures in comparison to the material synthesized through ceramic route.
We also report our results on the synthesis and characterization of new layered vanadates and framework molybdates which are obtained during our investigation on the hydrothermal treatment of aqueous solution containing vanadates and molybdates.
The effect of pH, nature of acid, temperature and the oxidation state of metal are discussed in determining the structure, crystallinity and composition of the materials.
Due acknowledgement has been made to other investigators wherever the work described is based on their findings. The author apologizes for any omission or
t.
mistalce5Which might have occurred due to oversight.
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TABLES OF CONTENTS
CERTIFICATE
ACKNOWLEDGEMENTS ABSTRACT
CHAPTER I:
I.1 1.2 1.3 1.4 1.5 1.6
INTRODUCTION BASED ON CHEMICAL SOLUTION ROUTES FOR NOVEL
TRANSITION METAL OXIDES General introduction
Alternate chemical route
Chemical aspects of direct precipitation of oxides from solutionog
Chemistry of sol-gel synthesis Motivation for the present work References
2 6 11 22 26 28 CHAPTER II: SOL-GEL PROCESSING OF TITANIUM
DIOXIDE FROM ALKOXIDE ROUTE
II.1 Introduction 35
11.2 Experimenter 37
11.3 Result'land discussion 40
11.4 Conclusion. 75
11.5 References 76
CHAPTER III: EFFECT OF SYNTHETIC ROUT AND PRECURSOR ON THE MICROSTRUCT'URE
OF LEAD BASED TITANATES AND ZIRCONATES
111.1 Introduction 79
111.2 81
111.3
Experi(inentedt,
Resul and discussion 84
111.4 ConclusionS 103
111.5 References 109
CHAPTER IV: LOW TEMPERATUTRE SYNTHESIS OF BISMUTH CUPRATES
IV . 1 Introduction 112
1V.2 Experimental 114
IV.3 ResulfSand discussion 116
IV.4 Conclusion. 127
IV.5 References 128
CHAPTER V: HYDROTHERMAL SYNTHESIS OF MOLYBDATES AND VANADATES
V.1 Introduction i 130
V.2 Experilient 133
V.3 Result and discussion 135
V.4 Conclusion A 148
V.5 References 150
CONCLUSIONS 151
LIST OF PUBLICATIONS' 153
