Zirconia precipitation methods

The active phase of transition metals (Co, Cr) oxides was deposited by the precipitation method, ionic exchange from nitrate salts solutions and ionic exchange in solid phase as well [8,10], The catalysts were obtained by impregnation of zirconia obtained by both methods with aqueous solutions of the corresponding salts (cobalt or chromium nitrate), subsequent drying at 100 °C, and roasting at 320 °C for 6 h. The McxOy/ZrOz samples containing 5-10 wt% metal oxides on the support (relative to the metal) were prepared by this method. 

M. Z. C. Hu, R. D. Hunt, E, A, Payzant, and C, R, Hubbard, Nanocrystallization and phase transformation in monodispersed ultrafine zirconia particles from various homogeneous precipitation methods. J. Am. Ceramic Soc., 82 2313-2320, 1999... 

Zirconia is usually produced fiom zircon, ZrSi04. The first step is to convert zircon to zirconyl chloride by melting the zircon with sodium hydroxide to form NajZrOj. This compound is then treated with HCl to form zirconyl chloride, ZrOCl2 SHjO. Two methods are used to make zirconia fiom zirconyl chloride thermal decomposition and precipitation. The thermal decomposition method is the less costly of the two, but the resulting material is not usually of as high a purity and fine particle size as that produced by precipitation. The precipitation method uses chemical reactions to obtain the zirconia hydroxides as an intermediate material. A final calcination process results in zirconia powder. By controUmg the precipitation and calcination conditions, it is possible to achieve desired particle size and shape, grain size, and specific surface area. 

Silva, V.V. and Domingues, R.Z. (1997) Hydroxyapatite-zirconia composites prepared by precipitation method. Journal of Materials Science Materials in Medicine, 8, 907-10. 

The co-precipitation technique starts with an aqueous solution of nitrates, carbonates, chlorides, oxychlorides, etc., which is added to a pH-controlled solution of NH4OH, allowing the hydroxides to precipitate immediately. This method requires water-soluble precursors and insoluble hydroxides as a final product. The hydroxides are filtered and rinsed with water when chlorides are employed as starting materials and chlorine is not desired in the final product. After drying the filtrate, it is calcined and sintered. This method is being applied very successfully for oxygen-ion conducting zirconia ceramics [30],... 

Guizard et al. (1986), Cot, Guizard and Larbot (1988) and Larbot et al. (1989) used a sol-gel method to prepare zirconia membrane top layers on an alumina support. The water necessary for the hydrolysis of the Zr-alkoxide was obtained from an esterification reaction. The complete hydrolysis was done at room temperature and resulted in a hydrated oxide. The precipitate was peptized with nitric or hydrochloric acid at pH <1.1 and the final sol... 

Abrasive particles are a key component in CMP slurry. The most commonly used abrasive particles include silica, alumina, ceria, zirconia, titania, and diamond. Table 21.1 listed a set of information on each type of abrasive particles such as density, microhardness, and isoelectric points (lEP). It is important to point out that the specific values for these properties depend highly on the preparation techniques and the specific states of the samples. The values listed in the table represent an average of the most commonly reported data. For example, the isoelectric point for silica is a function of the number of hydroxyl groups, type and level of adsorbed species, metal impurity in the solid matrix, and the treatment history of the materials [1]. There are three major types of silica according to their preparation methods fumed, colloidal, and precipitated. The common sources for obtaining these abrasive particles are listed in Table 21.2. As examples, some of the more specific information on... 

Kaneko et al. employed a coprecipitation method, which involved a base-catalyzed procedure that precipitated irregular particles of zirconia-silica mixed oxides. Specifically, a zirconium salt (zirconyl chloride octahy-drate) was added to an acidified solution of sodium me-tasUicate ennehydrate. The solution was made alkaline... 

Pure zirconia was obtained by precipitation and the sol-gel method. Analysis of the literature data showed that precipitation is the most commonly accepted method. Thus, we prepared a sanqrle of starting zirconia by precipitation of the hydroxide from 0.5 M aqueous solution of zirconium oxychloride by adding 2.5 M aqueous ammonia under vigorous stirring at 20 °C and constant pH 9. After precipitation, Zr(OH)4 was maintained in contact with the mother liquor for five days and the precipitate was then washed with aqueous ammonia with pH 8 until there was a negative test for chloride ioa The sample was then dried at 170 °C for 3-4 h. 

The reactions between cerium trichloride and oxide ions were initially studied in the pure KCl-NaCl equimolar mixture at 1000 K by the method of potentiometric titration using a calcium-stabilized zirconia membrane electrode. The titration curves clearly demonstrated the existence of the soluble cerium oxychloride CeO+ and precipitated cerium oxide ... 

Phosphate and sulphate modifiers were incorporated by the addition of appropriate amounts of 0.01 M sulphuric or phosphoric acid to a pre-calcined aerogel followed by further calcination at 873 K. Samples are labeled as X-SiZr (y) where X refers to either sulphated (S) or phosphated (P) samples, and y refers to the mole ratio of sulphate/phosphate relative to zirconium in the preparation method. For comparison purposes, samples of zirconia and sulphated zirconia were also prepared. This was achieved via precipitation from zirconium isopropoxide (Aldrich 70 wt.%). The same H2O Zr propanol ratios were employed as used during the preparation of the mixed oxides. A sulphated zirconia, prepared by the use of sulphuric acid as hydrolysis catalyst was prepared for comparative purposes and had a nominal S Zr ratio of 0.30 1. A further sample was prepared where segregation of components was induced by thermal treatment by calcination at 1373 K for 6 h.of the non-treated SiZr (0)... 

The preparation of sulphated zirconia designed for catalyst supports was studied by Boutonnet et al. . Zirconia prepared in microemulsion showed a pure tetragonal structure compared with zirconia prepared by an impregnation -precipitation procedure which also contained monoclinic phase. Platinum-promoted sulphated zirconia catalysts were prepared both in anionic and non-ionic microemulsions. Furthermore, the catalytic activity and selectivity for the isomerization of hexanes were tested. The catalysts produced by the microemulsion method showed a higher selectivity towards isomers but a lower activity when compared to catalysts prepared by impregnation technique. More recently, a study of zirconia synthesis from micro and macroemulsion systems has been conducted . Spherical ZrOa particles ranging from tens of nanometers to a few micrometers were produced. 

The two-emulsion (reverse) method has been used recently by Lee etal, [185] in an attempt to synthesize spherical zirconia particles under controlled conditions. In the overall scheme, a non-ionic surfactant (Span 85, Span 80, Span 40 or Arlacel 83, i.e. Sorbitan sesquioleate see below for the choice of surfactant) was dissolved in n-heptane. The HLB values of the surfactants varied in the range 1.8-6.7. Aqueous solutions of zirconium acetate or ammonia were added to two parts of the surfactant-oil phase combination the two had identical volumes. Reverse emulsions were prepared by subjecting the above to ultrasonic agitation, and the two emulsions thus produced were then mixed under stirring. The gel particles that formed in the process were separated by using a modified Dean-Stark moisture trap. Figure 4.4 presents the two-emulsion process in which the two complementary emulsions are mixed to obtain gel precipitates in the spherical droplets. 

To prepare low-hafnium zirconia, the mother liquor from the first fractional precipitation is treated with ammonium hydroxide to precipitate the hydroxides, which are then filtered and redissolved in a calculated amount of moderately concentrated sulfuric acid. This solution is then diluted with the amount of water required to give 2 N sulfuric acid solution that contains 5 per cent RO2. From a fraction containing 0.7 per cent hafnium, one fractionation in which about 60 per cent of the total oxide is precipitated as the phosphate will yield a product containing only 0.2 per cent hafnium. Additional fractionations of the mother liquor will reduce the hafnium content to a concentration below the sensitivity of the arc spectrographic method used (about 0.05 per cent Hf). Because the impurities concentrate in the most soluble fraction, a complete phosphate precipitation is made on the final solution, the precipitate is washed with 2 N sulfuric acid, and then converted to the peroxy compound. For final purification, the acid-soluble peroxy compound is dissolved in hydrochloric acid, and the oxychloride prepared according to the procedure of Young and Arch. The oxychloride may then be used as a starting material for the preparation of any other zirconium compound. 

Kaneko et al. employed a coprecipitation method, which involved a base-catalyzed procedure that precipitated irregular particles of zirconia-sihca mixed oxides. Specifically, a zirconium salt (zirconyl chloride octahy-drate) was added to an acidified solution of sodium metasilicate ennehydrate. The solution was made alkaline (pH 7-9) to allow the precipitation of the mixed oxide gel. The gel was aged for 10 hr, collected by filtration and washed to remove residual chloride ions. The gel was dried at 110°C and then ground to an appropriate mesh size. The resulting precipitate was regarded as an intimate mixture of silica and metal oxide gel (in this case, zirconia). The silica... 

For this purpose, different preparation methods (precipitation, electrolysis, sol-gel process, etc.) and zirconium precursors (chloride, oxychloride, nitrate, and alkoxides) have been used. However, it is widely known that supercritical drying (SCD) of zirconia gels is one of the more promising processes allowing the enhancement of textural and structural properties (Chap. 21) of zirconium oxide phases. 

Many researchers noted that independent of the zirconium precursor and the preparation method (precipitation, sol-gel, etc.), obtained zirconia xerogeis, dried at moderate temperature, were X-ray amorphous and crystallized only after calcination, at least, at 300°C, while the high-temperature SCD led to samples exhibiting tetragonal nanocrystallites. 

---