Surface area, mineral particles

As early as 1940, Sanderson had discussed a number of factors that affected adsorption of hydrocarbon gases by soils. He noted that the ability of the soil to adsorb any gas depends upon the type of gas, the characteristics of the soil and the conditions under which the soil is exposed to the gas. Adsorption will depend upon the type and surface area of particles and their chemical composition. The surface reactivity will be modified considerably by the presence of previously-adsorbed molecules, such as carbon dioxide, water and mineral ions. The condition of adsorption is complicated by temperature and pressure and length of exposure time in addition to concentrations and species of gases present. Adsorbed-gas data can, at best, be only approximations of the original mixture of migrated gases. Another possible problem lies in the quantitative desorption of the gases from the mineral components of the soil. 

Fillers are those materials added to a matrix in order to improve its properties. The filler characteristics that affect the composite s properties are particle size, size distribution, specific surface area and particle shape and interfacial interactions. The shape of most mineral filler particles can be approximated as a sphere, cube, block, plate, needle or fibre. Some fillers contain a mixture of shapes. ... 

The properties of a material that determine its suitability as a filler and the properties it imparts to rubber are its grain-size, surface area of particles and surface activity of particles (i.e. the ability of the particle s surface to bond with the rubber matrix). These properties of clay minerals, especially kaolinite, and their appropriateness as fillers are explained below. 

The characteristics which determine the properties filler that will impart to a composite are particle shape, particle size, surface area, and particle-matrix compatibility (Fig. 1). Particle-matrix compatibility relates to the ability of the polymer to coat and adhere to the filler. The shape of most mineral filler particles can be a sphere, cube, block, plate, needle, or fiber whereas some filler also contain a mixture of shapes. Mineral particles resembling plates, needles, and fibers are further characterized by their aspect ratio (http //www.rtvanderbilt.com/ fillersintroweb.pdf). In rubber/polymer composites, applied stress is transferred from the rubber/polymer matrix to the strong and stiff mineral. It seems reasonable that this stress transfer will be better affected if the mineral particles are smaller, because greater surface is thereby exposed for a given mineral concentration. Moreover, if these particles have a high aspect ratio (are needle-like, fibrous or platy in shape), they will better intercept the stress propagation through the matrix (Fig. 2) (http //www.rtvanderbilt.com/fillersintroweb.pdf). 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Example 4 Calculation of Sample Weight for Surface Moisture Content An example is given with reference to material with minimal internal or pore-retained moisture such as mineral concentrates wherein physically adhering moisture is the sole consideration. With this simphfication, a moisture coefficient K is employed as miiltipher of nominal top-size particle size d taken to the third power to account for surface area. Adapting fundamental sampling theory to moisture sampling, variance is of a minimum sample quantity is expressed as... 

It may be mentioned here that the mode which represents the most commonly occurring size in a given distribution is not of much use in mineral processing since it does not describe fully the characteristics of a group of particles. The arithmetic mean diameter suffers from the same limitation except when the distribution is a normal one. The harmonic mean diameter is related to the specific surface area. It is, therefore, useful in such mineral processing operations where surface area is an important parameter. 

Soil is a relatively thin layer of unconsolidated matter on the surface of the earth, in which there is biological activity. The bulk of most soil consists of a mixture of extremely small, loose particles of minerals and organic matter the mineral particles are derived from the weathering of rocks the organic matter from the dead remains of living organisms (Rowell 1994 Limbrey 1975). The composition and texture of the soil are altered by human habitation humans change the natural flora and fauna of entire areas, their activ-... 

Mineral Median Particle Diameter (microns) Surfac Area (meter /gram)... 

Since sorption is primarily a surface phenomenon, its activity is a direct function of the surface area of the solid as well as the electrical forces active on that surface. Most organic chemicals are nonionic and therefore associate more readily with organic rather than with mineral particles in soils. Dispersed organic carbon found in soils has a very high surface-to-volume ratio. A small percentage of organic carbon can have a larger adsorptive capacity than the total of the mineral components. 

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