Investigating slip casting of ceramics based on stabilized ZnO2 obtained by the chemical coprecipitation method

Abstract

Stoichiometric mixture 1200 ~ 3h a-Al20~and I 1250 ~ 3hf m-Al=O~, TiO~-1400 ~ 3h 1400 ~ 3 ,hA}~TiOs.phaseThe results of petrographic and x-ray analyses of the specimens synthesized at 1350~ suggest that phase X may be identified as an intermediate transition state (compound of variable composition) preceding the formation of aluminum titanate. CONCLUSIONSWe studied the synthesis of aluminum titanate in the I000-1600~ range. The synthesis occurs through the formation of an intermediate product of variable composition. We propose a scheme for the formation of aluminum titanate from the original hydroxides of aluminum and titanium. There has been a sharp increase in recent years in the interest shown in ceramics based on ZrO 2 or containing additions of the oxide, which is due mainly to the possibility of realizing the transformation strengthening effect of such materials [I-3]. In the production of ZrO= ceramics for high-duty purposes, special attention is paid to the synthesis of the original material and the technology for making the final product. In this case interest is also attached to obtaining ZrO 2 by the method of chemical coprecipitation from aqueous solutions of chlorides [4][5][6][7]. During the coprecipitation from solutions of zirconium ions and stabilizing additives (most frequently Y203) their homogenization occurs at the molecular level. This contributes to completion of the stabilization up to temperatures of 1000~ [5], which is significantly lower than in the conventional technology and this is connected with high-temperature melting of ZrO 2 with a stabilizing additive. INVESTIGATING SLIP CASTING OF CERAMICS BASED ON STABILIZEDThe characteristic feature of heat processing hydroxides in the synthesis of ZrO 2 is an increase in the particle sizes by 1-2 orders, which, apparently, is explained by the recrystallization sintering of aggregates of particles. The latter makes it necessary to mill the materials before shaping, since the original (after heat treatment) specific surface of the s powder does not exceed 0.25-0.30 m2/g (average surface diameter of particles dmean more than 4 ~m).The process of slip casting ceramics from ZrO 2 has so far been studied only in relation to material obtained by high-temperature melting [8,9]. In regard to ZrO 2 obtained by chemidal coprecipitation, special investigations of slip casting are not known, except for certain statements in [3]. In this work the solid solution ZrO2-Y203 was synthesized by combined precipitation of the components from a water solution of the chlorides. The filtered residue of the hydroxides was dried and heat-treated at 900~ after which wet milling was carried out in a steel ballmill in 80 h. The tramp iron was removed by treatment with HCI containing an addition of hydrogen peroxide, followed by decantation with distilled water. Casting was done with a slip density of 2.5 g/cm 3 (volume proportion of solid phase C v = 0.31) with a pH = 1.6.The castings from the powders obtained with this method are distinguished by a high (up to 3-5%)...

Rheological and technological properties of zirconia suspensions stabilized with various amounts of calcium oxide

“…Originally in studying the conditions for obtaining suspensions of quartz glass [2,3], and then quartz sand [4], the VKVS of other materials in siliceous, aluminosilicate and other compositions [I, 5-10] it was established that the final properties of the suspension and the casting (bond) to a considerable degree depend on the volume concentration C v of VKVS during wet milling. With an increase in C v of the suspension during milling it becomes possible to sharply increase the bonding properties of VKS.…”

Highly concentrated ceramic binder suspensions (HCBS). Raw materials, properties, and classification (Review)

“…For example, an attempt was made [26] to produce a suspension based on Y20s (IP = 3.1) obtained from dissociation of yttrium carbonate. The suspension exhibited distinct thixotropic properties at C V = 0.12-0.15.…”

“…The exceptional role of the technology and the type of the mill in the milling process was shown when obtaining HCBS based on AI20, and Zr02 [15,[25][26][27]. According to the conventional technology, when obtaining casting suspensions from the aforementioned materials and various other materials, milling was carried out in steel mills and this was followed by multiple washing for removing the ground iron contaminant and suspending the washed material [25,28,29].…”