Oxalate coprecipitation method

In the oxalate coprecipitation method, oxalate acid reacts with metal cations to form the precipitate, which is subsequently calcined to obtain the products. The advantage of oxalate acid as a precipitant is that, unlike hydroxides, oxalates are less sensitive to the treatment conditions, such as washing and drying. In addition, the... 

Nevertheless, the oxalate coprecipitation method has some problems. For example, this method usually results in rodlike doped ceria particles, which are agglomerations of smaller particles with irregular shapes. Hence, the green density of the compact body is relatively low, so it is difficult to fabricate a dense electrolyte film or membrane. In addition, the poor flow of the rodlike powder makes forming difficult. 

Figure 1.23 The fracture strength of Ce02)o.go LnOi 5)0.20 (Ln=Y, Cd, and Sm) ceramics prepared by solid-state reaction ofCe02 and the respective rare earth oxide powder and by an oxalate coprecipitation method [272],...

Park Y-U, Kim J, Gwon H, Seo D-H, Kim S-W, Kang K (2010) Synthesis of multicomponent olivine by a novel mixed transition metal oxalate coprecipitation method and electrochemical characterization. Chem Mater 22 2573-2581... 

FIGURE 1.37 The Arrhenius plot of Ce08Sm0i2Oli9 from different methods (A) solid-state reaction [95] (B) sol-gel process [116] (C) oxalate coprecipitation [91] (D) carbonate coprecipitation, our work and (E) glycine-nitrate process [157]. 

The eflBciency of these methods of co-precipitation was studied for plutonium, only, by comparing the chemical recovery of the original yield monitor with that of a second (and different) plutonium isotope yield monitor added to the acid solution of the co-precipitated hydroxide or oxalate (6). This second monitor shows all losses following the coprecipitation step. The eflBciency of the hydroxide precipitation for plutonium extraction was in the range 70-80%. That for the oxalate coprecipitation was typically 75-85%. 

At these temperatures, not alkoxide catalyst, but conventional Cu/Zn based catalyst could be applied for the process to attain such high CO conversion, because some additives to Cu/Zn based catalyst such as Al, Ga, Zr, and Cr optimized the surface Cu /Cu ratio to give high methanol synthesis activity (5). Furthennore, Cu/Zn based catalysts prepared by an oxalate-ethanol coprecipitation method shows higher activity than those prepared by alkali coprecipitation method (6, 7), and thus, novel synergetic additives are expected using the novel preparation method. Therefore, we focused on the development... 

Cu/Zn/X oxide catalysts were prepared by an oxalate-ethanol coprecipitation method. Ethanol solutions of nitrate of Cu, Zn and one additive were mixed (Cu/Zn/X molar ratio was 65/35/5), and then an ethanol solution of oxalic acid was mixed to precipitate the mixed oxalic salts. Only vanadium acetyl acetone was solved in a mixed solvent (acetone methanol =1 1), and it was used as V source. Ethanol was removed by vaporization followed by calcination in air at 623 K for 4 hours. 

Dang et al. (2000) increased the sensitivity of NAA for Th by separating the indicator radionuclide, Pa, using co-predpitations with manganese dioxide and barium sulfate and determined Th in total diet samples. A similar postirradiation procedure was coupled to the following pre-irradiation separation and concentration of Th (PC-RNAA) by H5llriegl et al. (2005) to increase the sensitivity of the method for the determination of urinary Th excretions. The pre-concentration procedure consisted of phosphate and caldum oxalate coprecipitations. The detection limit of Th in the urine sample was about 10 pg (0.04 jiBq). 

The simplest technique may be coprecipitation. In this method, a reagent is added to the stock solution that is destabilized and precipitated. Better mixing at a microscopic level is then achieved without mechanical grinding and mixing. Insoluble carboxylates such as citrates, oxalates and carbonates or hydroxides are the most suitable reagents. 

The activity of traditional ZnO-based catalysts may be improved by using new preparation methods. Cu-ZnO-Al203 catalysts prepared by a new oxalate gel precipitation exhibited higher activity in C02 reduction than did those made by coprecipitation, which was attributed to the isomorphous substitution of Cu and Zn.47 48... 

The sol-gel method has been conveniently employed for the synthesis of 123 compounds such as YBa2Cu307 and the bismuth cuprates. Materials prepared by such low-temperature methods have to be annealed or heated under suitable conditions to obtain the desired oxygen stoichiometry as well as the characteristic high Tc value. 124 cuprates, lead cuprates and even thallium cuprates have been made by the sol-gel method the first two are particularly difficult to make by the ceramic method. Coprecipitation of all the cations in the form of a sparingly soluble salt such as carbonate in a proper medium (e.g. using tetraethyl-ammonium oxalate), followed by thermal decomposition of the dried precipitate has been employed by many workers to prepare cuprates. 

The classic method for the isolation of the rare earth group which is used for both qualitative and quantitative determination involves three methods. In the first method, rare earths are precipitated as fluorides in acidic medium. The elements precipitated include Mg, Cu, Fe, rare earths Th, Ca and Sr. The second method consists of precipitation as hydroxides resulting in the removal of alkaline-earth elements like calcium from the mineral. In the third method rare earths are precipitated as oxalates from moderately acidic solutions and the elements Ca, Zn, Pb, Cu, Cd, and Ag may be coprecipitated. In early times the above methods were repeated several times to isolate, the rare earth group in a relatively pure form. 

Laboratory tests and a large-scale test in the fuel storage basin showed that strontium-90 can be removed from basin water by coprecipitating strontium with calcium oxalate. At a mole ratio of calcium plus magnesium-to-oxalate of 1.0, ca. 90% of the strontium will coprecipitate as strontium-calcium oxalate. However, the slow settling precipitate creates excessive turbidity in the water for many days, and slow hydrolysis of the strontium oxalate (ca. 10% per month) reduces the effectiveness of this treatment unless a method is available to remove the precipitate. 

Wachowski et al. (42,43) have compared the surface areas of a series of eight perovskites prepared by different methods ceramic (<2.4 m2/g), coprecipitation as oxalates (4.5-11 m2/g), explosion (21-37 m2/g), and freeze-drying (22-39 m2/g). Again, surface areas clearly depended on the minimum temperature necessary for complete reaction. The greatest losses in surface area by sintering were observed in the temperature range 700-930°C. 

The typical purification method for rare earths is coprecipitation with ferric hydroxide, dissolution in dilute acid, precipitation as fluoride in strong mineral acid solution, dissolution in strong nitric acid with boric acid to complex fluoride, and precipitation for counting as the oxalate in dilute acid solution (Stevenson and Nervik 1961). Because Pm has no stable isotope, another rare earth (such as lanthanum) is added as carrier. The " Pm precipitate can be counted with a proportional counter, or can be dissolved and measured with an LS counter because of the low beta-particle energy. If small amounts of the other rare earth radionuclides are detected by gamma-ray spectrometric analysis, the beta-particle count rate of Pm can be calculated by difference. 

Coprecipitation of ferric chloride in excess NaOH and in the presence of barium carbonate forms a mixture of mixed hydroxides and basic carbonates which, upon calcination at 710°C, form the barium ferrite. The magnetic properties are optimized by subsequent heat treament at 950 °C. This method produces plateletshaped particles with an average size of 0.3 pm [110]. Another technique involves oxidation of feirous oxalate by hydrogen peroxide in the presence of excess oxalic acid. The addition of barium carbonate (Ba/Fe = 1/12) forms.mixed complexes of... 

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