IR and thermal studies on lanthanum zirconyl oxalate

Abstract

Lanthanum zirconyl oxalate hydrate (LaZO) was prepared and characterized by chemical analysis and i.r. spectral studies. Its thermal decomposition was investigated by using DTA, TG, X-ray diffraction and i.r. spectral studies. On the basis of the TG and isothermal results, a tentative decomposition scheme was proposed. In the first step the dehydration of LaZO takes place in two steps between room temperature and 498 K, to give the anhydrous compound. The anhydrous oxalate decomposes in a series of steps (498--548 K, 548-673 K and 673--773 K). Finally the decomposition of the carbonate takes place (773--1073 K) to give lanthanum zirconate (La2Zr20~).In view of the wide variety of applications in technology, the preparation of perovskite and pyrochlore type mixed oxides has attracted the attention of chemists and ceramists, with a view to obtaining them in high purity by simpler methods. The zirconates of the alkaline earths and rare earths have found considerable importance in ceramics. The preparation of various mixed oxides in pure and homogeneous form could be achieved by thermal decomposition of mixed metal oxalate salts [1,2]. Zirconium is reported to form anionic oxalato zirconates with bivalent metal cations [3], and the thermal decomposition of such complex salts makes an interesting study. The lack of literature on zirconyl oxalates of trivalent cations led us to prepare and study the thermal decomposition of lanthanum zirconyl oxalate hydrate (LaZO). In its decomposition behaviour, this may show some interesting features different from those of the systems studied earlier [4][5][6][7][8], since the decomposition of the simple lanthanum oxalate is of a complex nature [9]. ExperimentalAll the materials used in the present study were of analytical grade. Lanthanum oxide of 99.99 % purity was obtained from Indian Rare Earths, Ltd. The zirconium oxychloride octahydrate was a product of Fluka AG, Switzerland. Lanthanum zirconyl oxalate hydrate (LaZO) was prepared by adding equimolar (0.IM) solutions of zirconyl chloride and lanthanum oxide (dissolved in HNO3) to warm oxalic acid solution (0.3M). The clear solution so obtained was left in a refrigerator for five to six days, whereupon a white, fine powder solid settled out. The product was filtered, washed with distilled water and acetone, and air-dried. Such a sample

Thermal decomposition of mixed calcium oxalate hydrates – kinetic deconvolution of complex heterogeneous processes

“…(8) (9) Note that each of the above-listed kinetic models includes certain kinetic exponent(s) responsible for the actual shape of the DSC peak.…”

Effect of some organic substances on kinetics of crystallization of calcium oxalate monohydrate and on some bacteria in urine

“…(1)(2)(3) Industrial usage of oxalate hydrates includes e.g. thermochemical energy storage (4) (the reversible chemical reaction anhydride CaOx ↔ COM is utilized), synthesis of superconducting multicomponent oxides , (5,6) preparation of high purity titanates, stannates, ferrites and zirconates (7)(8)(9) or separation of rare earth elements from raw ores by coprecipitation (10) . However, major importance of these minerals lies in the fact that they are the main crystalline components of human urinary stones (11)(12)(13) .…”

Preparation, spectral and thermal studies of neodymium zirconyl oxalate hexahydrate

“…It has been demonstrated by several workers that high purity titanates, stannates, ferrites, zirconates of perfect stoichiometry can be prepared from pyrolysis of mixed metal oxalate systems [1][2][3][4]. Zirconium is reported zo form anionic oxalato zirconates [5] and thermal decomposition of such complex s~lts make up an interesting study.…”