Particle size oxide

R.D. Gould, Combustion Instability of Solid Propellants Effect of Oxidizer Particle Size, Oxidizer/Fuel Ratio and Addition of Titanium Dioxide to Plastic Pro pell ants , Rept No RPE-TR-68/1, Westcott (Engl)... 

Pollutant. A pollutant can be defined"as a substance that is brought near a receptor by the atmosphere. A particular pollutant is distinguished from others by its physical and chemical properties. For example, it may be a gas or it may be an aerosol with a certain distribution of particle sizes oxides of sulfur may be present as S02, S03, or H2S04. The pollutant can also be characterized with respect to concentration, the length of time that a certain concentration is present, or the frequency distributions of periods of known duration and concentration (1). The pollutant... 

Granular activated carbons (GAC) are made mainly from coconut she]), peat and bituminous coals. The use of an abundant, cheap source, implies that carbon ex-mineral coals represent more than 60% of GAC production (ref. 11). Details of the manufacturing process have usually been kept as an industrial secret. However, variables like coal rank, particle size, oxidation, flow rate of reactants and yield in the activation step, must be taken into account in tailoring an activated carbon for a specific application. 

Because x-rays are particularly penetrating, they are very usefiil in probing solids, but are not as well suited for the analysis of surfaces. X-ray diffraction (XRD) methods are nevertheless used routinely in the characterization of powders and of supported catalysts to extract infomration about the degree of crystallinity and the nature and crystallographic phases of oxides, nitrides and carbides [, ]. Particle size and dispersion data are often acquired with XRD as well. 

If a dilute acid is added to this solution, a white gelatinous precipitate of the hydrated tin(IV) oxide is obtained. It was once thought that this was an acid and several formulae were suggested. However, it now seems likely that all these are different forms of the hydrated oxide, the differences arising from differences in particle size and degree of hydration. When some varieties of the hydrated tin(IV) oxide dissolve in hydrochloric acid, this is really a breaking up of the particles to form a colloidal solution—a phenomenon known as peptisation. 

Physical Properties. Physical properties of importance include particle size, density, volume fraction of intraparticle and extraparticle voids when packed into adsorbent beds, strength, attrition resistance, and dustiness. These properties can be varied intentionally to tailor adsorbents to specific apphcations (See Adsorption liquid separation Aluminum compounds, aluminum oxide (alumna) Carbon, activated carbon Ion exchange Molecular sieves and Silicon compounds, synthetic inorganic silicates). 

Raw ] Ia.teria.ls. Most of the raw materials are oxides (PbO, Ti02, Zr02) or carbonates (BaCO, SrCO, CaCO ). The levels of certain impurities and particle size are specified by the chemical suppHer. However, particle size and degree of aggregation are more difficult to specify. Because reactivity depends on particle size and the perfection of the crystals comprising the particles, the more detailed the specification, the more expensive the material. Thus raw materials are usually selected to meet appHcation-dependent requirements. 

Mixing. The most widely used mixing method is wet ball milling, which is a slow process, but it can be left unattended for the whole procedure. A ball mill is a barrel that rotates on its axis and is partially filled with a grinding medium (usually of ceramic material) in the form of spheres, cylinders, or rods. It mixes the raw oxides, eliminates aggregates, and can reduce the particle size. 

Formation of a gelatinous precipitate that is difficult to filter can be avoided by addition of magnesium oxide to the acid solution. In order to increase particle size it is often necessary to keep the solution hot for several hours however, this problem is avoided by heating an intimate mixture of ammonium bifluoride with magnesium carbonate to 150—400°C (11). Particles of Mgp2 similar in size to those of the magnesium carbonate are obtained. 

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

Mercuric Oxide. Mercuric oxide[21908-53-2] HgO, is a red or yellow water-insoluble powder, rhombic in shape when viewed microscopically. The color and shade depend on particle size. The finer particles (< 5 -lm) appear yellow the coarser particles (> 8 -lm) appear redder. The product is soluble in most acids, organic and inorganic, but the yellow form, which has greater surface area, is more reactive and dissolves more readily. Mercuric oxide decomposes at 332°C and has a high (11.1) specific gravity. 

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