Ceramic powder synthesis coprecipitation

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

K. Osseo-Asare, F. J. Arriagada, and J. H. Adair, "Solubility Relationships in the Coprecipitation Synthesis of Barium Titanate Heterogeneous Equihbria in the Ba—Ti—C2O4—H2O System," in G. L. Messing, E. R. Fuller, Jr., and Hans Hausin, eds.. Ceramic Powder Science Vol. 2,1987, pp. 47-53. 

Strength, brittleness, and solvent permeability properties are limited because of lack of control of the ceramic composition on a macro- and microlevel. Even small particle sizes are large compared with the molecular level. There have been a number of attempts to produce uniform ceramic powders including the sol-gel synthesis in which processing involves a stable liquid medium, coprecipitation in which two or more ions are precipitated simultaneously. More recently, Carraher and Xu have used the thermal degradation of metal containing polymers to deposit metal atoms and oxides on a molecular level. 

Huang Z, Guo W, Fei BJ, Li JT, Cao YG (2013) Influence of sulphate on synthesis of Nd Y2O3 powders via coprecipitation route and fabrication of transparent ceramics. Mater Res Innovations 17 73-79... 

The many and varied chemical preparation routes for the production of electronic ceramic powders are too numerous to discuss in detail here. Typical precursors include chlorides organometallics such as oxalates and alcohol-based complexes The processes involved include hydrothermal synthesis coprecipitation precipitation of one component followed by coatings of successive dopants, sol-gel preparation polyiner1sation etc. It will be some time before the benefits of the processes can be assessed. Questions concerning their flexibility for producing different compositions, the quality of results and the problems of cost and scaling up still need to be resolved. What is not in doubt is that chemical methods offer potentially much improved powders compared to those prepared by traditional mixed oxide routes. 

Historically, stabilized (and partially stabilized) zirconia ceramics were prepared from powders in which the component oxides are mechanically blended prior to forming and sintering. Because solid state diffusion is sluggish, firing temperatures in excess of 1800°C are normally required. Furthermore, the dopant was nonuniformly distributed, leading to inferior electrical properties. Trace impurities in the raw materials can also lead to enhancement of electronic conductivity in certain temperature ranges, which is also undesirable. To overcome these problems, several procedures have been developed to prepare reactive (small particle size) and chemically pure and homogeneous precursor powders for both fully stabilized and partially stabilized material. Two of these are alkoxide synthesis and hydroxide coprecipitation. 

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