Aggregation of powder

There are a number of industrial and technological areas in which nanoscale adhesion is important. One of the earliest fields concerned with adhesion on this scale was colloid science. Colloid particles lie in the intermediate region between macro and nano, with dimensions typically of the order of hundreds of nanometers up to a few microns. This means that their true contact areas he well within the nano-domain and are influenced by interactions on this length scale. Adhesion between such particles is important, due to its influence on mineral separation processes and on the aggregation of powders, for example, on the walls of machinery or in the forming of medical tablets. In an extraterrestrial context, such... 

Thermodynamic principles are important in all aspects of materials science. In this section we introduce some of the fundamentals, but thermodynamics will be used in several other chapters (e.g., point defects. Chapter 11, and surfaces, Chapter 13). The primary role of thermodynamics in ceramics is to indicate whether a system is stable and what conditions (usually changes in temperature or pressure) will cause it to change. Our system may be a crystal structure, a phase, a grain boundary, an aggregate of powder particles, or a concentration of defects. Table 3.7 lists some of the important thermodynamic parameters we meet in ceramics together with their units. 

In the case of powders formed by grinding and particles formed by aggregation, surface roughness can be so extreme that, curiously, it can be treated by mathematical geometry (see Mandelbrot, Ref. 102 also Ref. 103). We can... 

Two classes of grinding equipment are used to prepare dispersions. The first, the coUoid mill, does not effect a particle size reduction but does break down aggregates of fine particles. CoUoid mills are used for such powders as clays, precipitated whiting, etc. Sometimes these mills are used to process zinc oxide but for dipped mbber products that is not satisfactory. 

In the pharmaceutical industry, surface area is becoming more important in the characterization of materials during development, formulation, and manufacturing. The surface area of a solid material provides information about the void spaces on the surfaces of individual particles or aggregates of particles [5], This becomes important because factors such as chemical activity, adsorption, dissolution, and bioavailability of the drug may depend on the surface on the solid [3,5]. Handling properties of materials, such as flowability of a powder, can also be related to particle size and surface area [4],... 

The average structure is defined at the microscopic (near atomic) scale and represented by a unit cell that when repeated over an essentially infinite number of atomic distances generates microscopic crystallites, which in turn comprise macroscopic single crystals, polycrystalline aggregates, or powders. 

Small amounts of surfactants may be used to prevent aggregation of proteins and may enhance the refolding process when the dried protein dissolves. Buffers may also help to prevent aggregation of the dissolved drug. Similarly, polymers may be used as aggregation inhibitors or to form matrices. Chan et al. [86] prepared crystalline powders of recombinant human deoxyribonuclease with high fractions of sodium chloride. These powders were formulated as adhesive mixtures on lactose and mannitol and showed improved aerosolization behaviour compared to the pure protein. 

Microamorphous sihca is made of particles with diameters less than 1pm. They have very high surface areas, usuady greater than 3m2/g. These microamorphous sihca are an aggregation of colloidal ultimate particles that broadly include sols, gels, powder, and porous glass. An important class of... 

For powders, such as Lead Azide (LA), the limiting diam is small and it is possible to have conditions such that each particle of the powder taken separately is able to detonate. In this case the deton wave being propagated represents an aggregate of deton waves being propagated in separate crysts and which are transmitted from one cryst to the next... 

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