Slurry oxidation

Emission Control Catalysts. An appHcation of growing importance for cerium is as one of the catalyticaHy active components used to remove pollutants from vehicle (autoexhaust) emissions (36). The active form of cerium is the oxide that can be formed in situ by calciaation of a soluble salt such as nitrate or by deposition of slurried oxide (see Exhaust control, automotive). 

The slurry solution plays a different role between oxide (as a hydrolizer) and metal (as an oxidizer) slurries. It is more complex in metal than in oxide, because traditionally, oxide slurry is used only for polishing oxide (for ILD, for example), whereas the metal slurry (for tungsten, for example) is used to polish tungsten, titanium nitride, titanium, and oxide. Accordingly, the choice of a metal slurry oxidizer must first satisfy the requirement of the selectivities between each different deposited film. Selection of solution for oxide slurry does not have such constraints. 

Converted starches, also called thin-boiling starches, are produced by degradation of the starch chains into small segments. They can be cooked in water at higher concentrations than native starches. Low-viscosity starches are needed in applications where a high solid starch paste with a pumpable and workable viscosity is required. There are four classes of commercial converted starches dextrins (hydrolysis in solid-state) acid-modified starches (hydrolysis in a slurry) oxidized starches and enzymically depolymerized starches. 

Juta T, Bigman J, Singh RK. Monitoring and control of CMP slurry oxidizer concentration and particle characteristics using NIR absorption spectroscopy. Proceedings of the CAMP s 10th International Symposia on CMP 2005 Aug 14-17 Lake Placid, NY. 

Cobalt- rather than iron-based FT catalysts have been examined, in order to minimize the competing water-gas shift reaction, which would result in a lowered carbon efficiency. Most cobalt FT catalysts have been prepared by coprecipitation of Co salts with various promoters onto a slurried oxide support to afford mixed phase systems (J ). Reduction to the active catalyst was controlled by addition of various promoters (e.g. MgO, Th02, AI2O3) (2). In part, these promoters are necessary to maintain good metal dispersion in the catalyst and resistance to sintering. Dispersion... 

A1 slurry oxidative addition 10.2.4.2 CigHisAuClP (C6H5)3PAuC1... 

A solid-liquid mass transfer coefficient of 0.015 cm/s was found by comparing the predictions of [S(IV)] to experimental results obtained under conditions in which the liquid phase kinetics were fast. The model was then applied to slurry oxidation under more general conditions by using liquid phase reaction rate kinetics obtained in clear solutions. The results of the model agree with experimental findings for the total rate of oxidation. 

Gladkii(16) at the State Scientific Research Institute of Industrial and Sanitary Gas Cleaning at Moscow did work on the three-phase calcium sulfite slurry oxidation system, finding that the liquid phase oxidation (pH 3.6-6) is first order with respect to the sulfite species. He pointed out, on the basis of pH versus time data from his semi-batch reaction, that the slurry oxidation had different periods in which either reaction kinetics or solid-liquid mass transfer controlled the oxidation rate. He also presented an omnibus empirical correlation between pH, temperature, and the liquid phase saturation concentration of calcium sulfite solution for predicting the slurry oxidation rate. The catalytic effect of manganese... 

Modeling of the Slurry Oxidation. In 1969 Ramachandran and Sharma(18) first proposed a film model for gas absorption accompanied by a fast chemical reaction in a slurry containing sparingly soluble, fine particles. A first case assumed that the solid dissolution in the liquid film next to the gas-liquid interface was unimportant. The second case assumed that it was important. Numerical solutions were given for the second case which indicated hat the specific rate of absorption of gas in the presence of fine particles could be considerably higher than in the absence of solids. 

Variable Catalyst Concentration Solutions. Using the mass transfer coefficient of 0.015 cm/sec, the model was then used to simulate the slurry oxidation with three concentrations of added Mn catalyst. Results are presented in Figure 8. The 1.5 order homogeneous reaction rate constants for 0, 6.66, and 200 ppm added Mn reactions were found from the model to be 0.35, 2.25, and 5.5 2,0 5 mol-0 5 sec-1 respectively. The corresponding values of 1.5 order rate constants from the comparable clear solution experiments are 0.162, 0.35, and 0.8 to 5... 

Slurry Density Variations. The model was also used to simulate the slurry oxidations with different initial conditions. Initial pH s of 4.5 and 5.5 were both tested. Results (total concentration and solution phase concentration curves) for the initial pH 4.5 are presented in Figure 9. By using the predicted mass transfer coefficient and rate constants, the computer curves can match these experimental results very well. 

By incorporating the film theory into the mathematical model for the batch slurry oxidation, a mass transfer coefficient of 0.015 cm/sec was obtained by matching the model to highly catalyzed (2000 ppm Mn added) slurry oxidation data. Saturation concentration of sulfite is most important in determining mass transfer coefficient(32). A correlation is given... 

Wang, C. C., "Experiments and Modeling of Calcium Sulfite Slurry Oxidation," M.S. Thesis, University of Virginia... 

Shima S, Fukunaga A, Tsujimura M. Effects of liner metal and CMP slurry oxidizer on copper galvanic corrosion. ECS Trans 2007 11(6) 285—95. 

A third method for the preparation of slurry oxide is the thermal decomposition of thorium formate [28]. In this procedure, thorium nitrate in solution is decomposed on adding it to concentrated formic acid at 95°C [29,30]. The precipitated thorium formate is washed free of excess acid and decomposed by calcination at 500 to 800 C. The oxide from the formate procedure is similar in its slurry behavior to that produced by thorium oxalate thermal decomposition however, less is known about its handling characteristics. Because of this, the oxalate preparation method is preferred at the present time. 

Brief studies made with thorium hydroxide indicated [33] that it is probably not a good source material for the production of slurry oxide. As precipitated from nitrate solution, the hydroxide formed a bulky precipitate which was hard to filter and wash, was amorphous to x-rays, and contained con.siderable nitrate impurity. Drying at 300 to 500°C yielded a crystalline oxide product which was difficult to slurry. Autoclaving a slurry of the hydroxide (without previous drying) at 250°C gave a bulky slurry (settled volume 300 to 500 g Th/liter) exhibiting a characteristic TI1O2 x-ray diffraction pattern. 

Pumping does not affect the average x-ray cry.stallite size of slurry oxides [52]. Also, oxides which have been pumped as slurries, dried, and then calcined, show relatively little crystallite growth. From these considerations it would seem that the crystallite size as measured by x-ray diffraction line broadening represents the ultimate limit of the attrition process due to pumping. 

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