Metal size distribution

Similar to the importance of mechanical stability, physical properties such as surface area, pore size, and pore size distribution, metal dispersion, and surface acidity are important parameters, which the catalytic chemist or engineer considers when developing a catalytic system. The physical properties are optimized to fit the catalytic application. Measurement of these properties, while not all are fully standardized, have been widely published for specific catalytic systems. The most complete review of these procedures with examples for specific catalytic systems and references have been published (7-8). ... 

Only limited work has been done on the bioaccessibility of metals in windborne mine waste and tailings material, and so much must be inferred. Mullins and Norman (1994) analyzed the size distribution, metal content, and metal extraction by simulated biofluids (lung, gastric, intestinal) of surface materials (soils) collected from several mine waste piles in the Butte, Montana, district. They found that the concentrations of arsenic, cadmium, copper, manganese, and lead were commonly greatest in the smallest size fractions (<4.7 pm) of the waste dump material. The percentage of metals leached from the hne fraction was quite variable, but not in any consistent way, between different metals, different dumps, and different extraction fluids. 

Schreiber E, Ziener U, Manzke A, et al. (2009) Preparation of narrowly size distributed metal-containing polymer latexes by miniemulsion and other emulsion techniques applications for nanolithography. Chem Mater 21 1750-1760... 

Fumaric acid is sold as resia-grade and food-grade. The general sales specification under which resia-grade fumaric acid is sold ia the United States specifies white, crystalline granules with a minimum assay of 99.6% and maximum ash content of 0.05%. The moisture specification is 0.3% maximum with < 10 ppm heavy metals. The color of a 5% solution ia methanol is to be less than 10 APHA. Food-grade fumaric acid calls for somewhat lower impurity levels. Particle size and particle size distribution are important ia many appHcations. 

Aluminum chlorohydrate [12359-72-7] Al2(OH) Gl 2H20 is a PAG product of specific composition, having r = 2.5. Aluminum chlorohydrate is used in antiperspirants regulated by the U.S. Food and Dmg Administration (FDA). Solutions sold for FDA-approved use are colorless in appearance, have 23—24% Al as AI2O2, and low levels of iron (<50 ppm), sulfate (<0.025 %), metals (Ga, Mg, Na <10 ppm), and heavy metals (as Pb <10 ppm). The pH of these solutions at 25°G is about 3.8—4.0. Typically, solutions at 25°G have specific gravities from 1.33 to 1.35 and viscosities from 40 to 60 mPa-s(=cps). Aluminum chlorohydrate [12042-91 -0] is also available in dry form with different particle-size distributions. 

Tantalum Compounds. Potassium heptafluorotantalate [16924-00-8] K TaF, is the most important tantalum compound produced at plant scale. This compound is used in large quantities for tantalum metal production. The fluorotantalate is prepared by adding potassium salts such as KCl and KF to the hot aqueous tantalum solution produced by the solvent extraction process. The mixture is then allowed to cool under strictiy controlled conditions to get a crystalline mass having a reproducible particle size distribution. To prevent the formation of oxyfluorides, it is necessary to start with reaction mixtures having an excess of about 5% HF on a wt/wt basis. The acid is added directiy to the reaction mixture or together with the aqueous solution of the potassium compound. Potassium heptafluorotantalate is produced either in a batch process where the quantity of output is about 300—500 kg K TaFy, or by a continuously operated process (28). 

Supports. The principal component of a typical catalyst is the porous support (49,50). Most supports are robust soHds that can be made with wide ranges of surface areas and pore size distributions. The most widely appHed supports are metal oxides others are carbon, kieselguhr, organic polymers, and zeoHtes. 

Strong acids are able to donate protons to a reactant and to take them back. Into this class fall the common acids, aluminum hahdes, and boron trifluoride. Also acid in nature are silica, alumina, alumi-nosihcates, metal sulfates and phosphates, and sulfonated ion exchange resins. They can transfer protons to hydrocarbons acting as weak bases. Zeolites are dehydrated aluminosilicates with small pores of narrow size distribution, to which is due their highly selective action since only molecules small enough to enter the pores can reacl . 

The particle size distribution of ball-milled metals and minerals, and atomized metals, follows approximately the Gaussian or normal distribution, in most cases when the logarithn of die diameter is used rather dran the simple diameter. The normal Gaussian distribution equation is... 

Fig. 6. Size-distribution of metal crystallites on the surface of Co-silica made by precipitalion-ion-exchange method.

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