Retention Behaviours Of Carbon In Sol-Gel Derived ZrO 2 Studied By Fourier Transform Infrared Spectroscopy
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H.C. ZENG Department of Chemical Engineering, Faculty of Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 0511
ABSTRACT The carbon retention patterns based on evolution of FT-JR spectra at different calcination temperatures for ZrO2 gels derived from Zr-n-propoxide-acetylacetone-waterisopropanol system are examined in detail. For most captured carbon species, carbon can be depleted at relatively low temperature of about 400'C. However, for lattice-included species, especially those incorporated into lattice during phase transition, a temperature around 9000 C is needed to eliminate carbon in the gels. It is found that water treatment alone does not provide new routes for carbon retention in as-prepared ZrO2 gels. When gels are pre-treated with Ni2 ' and water, new forms of carbon containing species can be observed. This is attributed to an inter-diffusion of Ni 2 ' and ZrO2 matrix and the catalytic effect of resultant solid solution NiO-ZrO2 on the retained carbon. INTRODUCTION The ZrO2 -based ceramics derived by sol-gel method have received increasing attention in recent years due to the prospect of industrial-scale applications of these superior materials. There has been a wide spectrum of these studies, ranging from the important technological research [1-9] to more fundamental research in general sol-gel science [10,11]. One of key factors in sol-gel processing of ZrO 2 is the controlling hydrolysis and polycondensation kinetics. As most reagents and solvents used in the sol-gel processing are organic compounds, the retention of carbon containing species in as-prepared ZrO 2 gels (xerogels) will affect physical and chemical properties of the gels [7,12,13]. In most applications, a ZrO 2 gel with sufficient mechanical and chemical stability is required. And for this reason, the interstitial carbon containing species in the solid network of gel must be removed. A general approach to this is termed drying, or thermal treatment, which is also an important step to obtain a crystalline ZrO 2 With specified crystallographic structural phases [7,12,13]. For the drying of xerogels of ZrO 2 , relatively low temperatures and ordinary pressure are commonly adopted for calcination. In this connection, the chemical composition in ambient may thus play an important role in thermal treatment precess. Water and carbon dioxide, for example, may invite new chemical processes to the gel calcination. Metal contaminants in as-prepared gels, on the other hand, may be incorporated into gel network to form new solid solution during the heat treatment and thus catalytic effect of these impurities on the carbon retention should not be ignored. In this paper, we report a systematic study of carbon retention behaviours on the so)gel derived ZrO2 using FT-JR pellet technique. A detailed carbon retention patten for xerogel ZrO 2 during the calcination will be presented. Also reported will be the effect of water and carbon dioxide on thermal treatment of as-prepared gel. And finally, the interaction of carbon
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