Powder classification characteristics

This is an on-going project aimed at examining the T/D characteristics of metals and alloys in a marine medium in seven- and twenty eight-day tests. The data obtained to date on seven-day tests of cuprous oxide (Cu20) and nickel metal powder (Ni) provides useful comparisons with those reported earlier for the freshwater OECD 203-based media at pH 6 and 8 (Skeaff Hardy 2005) and insight into the behaviour of metal-bearing substances used in commerce under marine conditions of the T/DP. The data supports an approach directed to the eventual adaptation, validation and application of the OECD T/DP to marine systems for the purposes of marine hazard classification of metals, metal compounds and alloys. 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

Incorporation of Geldart s classification of powders in relation to fluidisation characteristics (Chapter 6). 

Casein can be precipitated from solution by any of several salts. Addition of (NH4)2S04 to milk to a concentration of 260 g 1 1 causes complete precipitation of the casein together with some whey proteins (immunoglobulins, Ig). MgS04 may also be used. Saturation of milk with NaCl at 37°C precipitates the casein and Igs while the major whey proteins remain soluble, provided they are undenatured. This characteristic is the basis of a commercial test used for the heat classification of milk powders which contain variable levels of denatured whey proteins. 

Identification of single substances, and classification of powder photographs. Each crystalline substance has its own set of plane-spacirfgs, which is different from those of other crystalline substances. The relative intensities of the various reflections are also characteristic. Each substance thus gives its own characteristic powder photograph, the scale of which, however, depends on the wavelength of the X-rays used and the diameter of the camera. 

ICM classification (Yang et al, 1985) according to the bed-collapsing curve of a fluidized powder, in which three characteristic stages have been identified ... 

Natural graphite may be divided into three grades in respect to grinding characteristics flake, crystalline, and amorphous. Flake is generally the most difficult to reduce to fine powder, and the ciystalline variety is the most abrasive. Graphite is ground in ball mills, tube mills, ring-roller mills, and jet mills wiui or without air classification. Benefici-ation by flotation is an essential part of most current procedures. 

Bulk powder characteristics are important in understanding the handling properties of an excipient or a granulated product. A classification system to evaluate the flow properties of powders has been introduced by Carr.P A flowable powder is defined as free-flowing and tends to flow steadily and consistently, whereas a floodable powder exhibits an unstable, discontinuous, and gushing type of flow. A number of studies have investigated the bulk powder properties of starch " and granulations made with starch. The starch materials were found to exhibit poor to borderline flow properties. 

Extremely coarse powder gained by classification (to separate any finer particles) exhibits excellent flow characteristics and is used in plasma spraying. 

The classification of powders according to their handling characteristics must, therefore, be done on the basis of direct test results. 

ACs are the most commonly used form of porous carbons for a long time. Typically, they refer to coal and petroleum pitch as well as coconut sheUs-based AC. In most cases, ACs are processed to be filled with rich micropores that increase the surface area available for gas sorption and separation. For this category, to get a definite classification on the basis of pore structure is difficult due to their countless products as well as their complex pore features. Based on the physical characteristics, they can be widely classified into the following types powdered, granular, extruded, bead ACs, etc. For the pore structure of ACs, actually, all the three types of pores (micropore, mesopore, and macropore) are included in one product (Fig. 2.1), with a wide pore size distribution [1, 2]. Up to now, many kinds of ACs have been well commercialized in gas sorption/separation including CO2 capture. For example, the BPL type with specific area of 1,141 m g is able to adsorb 7 mmol g CO2 under the conditions of 25 °C and 35 bar, while under the same conditions MAXSORB-activated carbon with specific area of 3,250 g can capture up to 25 mmol g [3]. 

Chemical vapor deposition refers to the formation of a nonvolatile solid material from the reaction of chemical reactants, called precursors, being in vapor phase in the right constituents. A reaction chamber is used for this process, into which the reactant gases are introduced to decompose and react with the substrate to form thin film or powders There are several main classification schemes for chemical vapor deposition processes. These include classification by the pressure (atmospheric, low-pressure, or ultrahigh vacuum), characteristics of the vapor (aerosol or direct liquid injection), or plasma processing type (microwave plasma-assisted deposition, plasma-enhanced deposition, remote plasma-enhanced deposition)... 

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