The effect of pH of precipitation, starting solution concentration, and agitation levels on the particle size of hydrous zirconia precipitates have been investigated. It was found that all three variables affect the particle size of the hydrous zirconia. The smallest particle size is produced by a 0.81 M starting solution, precipitated at pH 12 with a high agitation level. The pH of precipitation was also found to have a significant impact on the type of hydrous zirconia produced. TGA/DTA, micro combustion and TEM / EDS were used to investigate the difference in the powders produced at pH 3 and 12. This work suggests that powders produced at pH 3 will have a structure similar to Zr [OH] . XRD and micro-combustion suggest that the powders produced at pH 3 retained ammonium chloride whilst those produced at pH 12 did not. The filtration rates for the pH 3 product were significantly faster than that of the powders made at pH 12 which is significant in the industrial production of these materials.

In situ and ex situ x-ray diffraction, and transmission electron microscopy were used to investigate the calcination of four samples of zirconia manufactured using two different zirconia reactant solution concentrations (0.81 and 1.62 M) with precipitation carried out at pH 3 and 12. The calcinations were investigated over the temperature range from room temperature to 1000 ºC. It was found that varying the precipitation conditions resulted in differing calcination routes; it is believed that variations in particle size and initial degree of hydration are responsible for these differences. It was also found that the initial phase produced after calcination was tetragonal zirconia, which underwent a process of crystallite growth to a size of ~30 nm before transformation from tetragonal to monoclinic.

a b s t r a c tTwo 3 mol% partially stabilised zirconia (P-SZ) samples suitable for the SOFC market were manufactured from solutions through to ceramics using a method similar to a known industrial process. The only difference in preparation of the two 3 mol% P-SZ samples was the pH of precipitation which was set at pH 3 or 12. Particle size measurements by dynamic light scattering were used to characterise the precipitate and the filtration rates were investigated. Five point N 2 -BET was used to investigate the specific surface area before and after calcination with the response to temperature tracked. Similarly TGA/DTA investigation was used to determine the calcination point during all of these tests and it was found that both powders behaved similarly. XRD-Rietveld analysis incorporating in situ and ex situ calcination revealed that the pH 3 sample had more monoclinic phase present after calcination and sintering as a ceramic. Ceramic testing incorporating hardness (Vickers), toughness (K 1C ), MOR, density and grain sizing was carried out, all determined that the material produced at pH 12 was superior for SOFC applications than the pH 3 sample. Further investigation using TEM-EDS revealed that the processing of the pH 3 powder had allowed a lower concentration of the yttrium which was incorporated at approximately 2 mol% instead of the required 3. ICP-OES of the after filter liquor indicated that high concentrations of yttrium (797 ppm) were found in the solution with the wash solution having 149 ppm yttrium. In contrast the pH 12 samples had 7 ppm in both the after filter liquor and wash indicating that the yttrium is bound within the matrix more completely at the higher pH.

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