Removal of Organic Phase in Alumina Parts by Thermal Treatment
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Removal of Organic Phase in Alumina Parts by Thermal Treatment José J. Coronel-Hernández, Víctor M. Arellano-Badillo, José Santos-Cruz, Sandra A. MayénHernández, Rocío Quintanar-Hernández Facultad de Química, Universidad Autónoma de Querétaro, Centro Universitario, Cerro de las Campanas, Querétaro 76010, México. ABSTRACT In this work it was conducted a pre heat treatment of a number of samples of alumina with organic binder in order to remove most of the organic phase. The treatment showed no effect on the physical properties of test specimens; green bodies remained stable during sintering process. Preheating at 100 °C for 4 h followed by heating at 300 °C for 4 h were the most favorable conditions to avoid formation of defects in the sintered pieces. INTRODUCTION Advanced ceramic compounds have been arising in importance for manufacturing of parts for automotive, aerospace or appliance use [1-2]. One of the most commonly used materials is alumina due to its excellent physical properties such as resistance to stress, oxidation and hardness of sintered parts, and also for having an accessible cost compared to other advanced ceramics. In spite of some difficulty in forming, machined or extruded green pieces have been successfully reported [4, 8]. Several methods of manufacturing have been developed in which an organic phase is added as a binder to the alumina, forming a suspension or slurry; among others, some of the most used substances are polymers, cellulose, beeswax, paraffin etc. [3, 5, 7]. Part of the organic phase must be removed prior to sintering to prevent distortion or cracking development by sintering. Some defects being reported are caused by not optimal removal of the organic including parts deformation, cracking, instability, voiding, high porosity, etc. [6]. The aim of this work was to optimize the binder thermal removal, relating it with superficial defects in pieces to determine the most favorable thermal treatment prior to sintering. EXPERIMENT DETAILS Experimental Setup Specimens with organic binder containing 58 and 60 vol.% of alumina, were produced by injection. Dimensions of test samples were 5 x 6 x 50 mm3. Specific fabrication conditions of suspensions and injection are given elsewhere [1-2]. The injected samples were cut to 5 x 6 x 10 mm3 pieces in order to have smaller samples of the same material. The pieces underwent heat treatment between 50 and 500 °C; an increment of 50 °C was used for each test (from now on, this heat treatment will be known as “pre heat treatment”). A sand bed was used to remove organics via capillarity, as suggested in previous works [1-2]. Samples that showed no cracking after pre heat treatment underwent an additional heat treatment between 150 and 350 °C, with an increment of 50 °C in each test (from now on, this heat treatment will be known only as “heat treatment”). Before and after treatments, samples were weighed to register the organic eliminated. Samples were then sintered (1 hour at 1700 °C).
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Analytical Methods To determine the amount of alumina remo
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