Study On Synthesis Of T-ZrO₂/α-Al₂O₃ Nanosized Composite Ceramic Powders

Because of small size of gains, high ratio of atoms on the surface, and so with the four specific effects: volumetric effect, superficial effect, quantum-size effect and macroscopical tunneling effect, nanosized alumina powders is ideal starting materials for developing new generation of higher strength, higher structure toughness and multifunctional ceramics. Nanosized alumina powders is being applied in many high-tech fields, which includes electronics, machine, aerospace industry, etc. But the brittleness of alumina ceramics hinder severely from its development and application. Recently, many researchers have tried to promote the mechanical performances of alumina ceramics though doping the second phase. So toughening alumina ceramics dispersed with t-ZrO₂ has been paid more attention in the fields of fine ceramics materials today. This paper focus on fabricating of t-ZrO₂/α-Al₂O₃ nano-composite powders by three different ways, comparing the difference of the composite powders fabricated through them, finding out the reasonable conditions though studying the influences of different conditions on making ZrO₂/Al₂O₃ nano-composite powders. The nanosized composite powders t-ZrO₂/Al₂O₃ were fabricated by coprecipitation. 45℃is suitable for the reaction temperature to synthesize the precursor. The influence of the ratio of NH4HCO3/ (Zr+Al) on the precipitation ratio of zirconium is great. After composite precursor powders being calcined at 1100℃, the broaden diffraction peaks of t-ZrO₂ and γ-Al₂O₃ appear, t-ZrO₂ is rather uniformly dispersed in alumina, and the grain sizes of both phases are 10²0nm. Through further being heated to 1200℃, α-Al₂O₃ phase rapidly forms and accompanying with part of crystallites blending. The precursors of alumina were made by room temperature solid reaction with NH4Al(SO4)2·12H2O and NH4HCO3 as raw materials. The precursors with the amorphous structure has the same makeup of ammonium aluminum carbonate hydroxide. Also the composite precursors doping with zirconium were synthesized by the this method. And ZrO2/Al2O3 nano-composite obtained though calcination under 1200℃for 0.5h. The morphologies of both phases are regular. And both phases are dispersed uniformly, and the distribution of grain size is narrow, which is about 20nm. The fact is observed that the being of ZrO2 restrain the growth of Al2O3 crystalline grain. Doped with zirconium polyaluminum chloride sol with basicity of 80% was prepared by uniformly alkalization method. After being dried, and then being calcined under 1200℃for 1h, ZrO2/Al2O3 composite powders was obtained, which has several crystalline phase, such as t-ZrO2, m-ZrO2, α-Al2O3, γ-Al2O3. And the powders agglomerated badly. The average size of the unsintered grain is about 100nm.