Paste particle size, effect

When colored or black systems are reduced with white pigments, an undertone is observed, which is a particle-size effect of the white pigment (see Section 1.3.1). These undertones can be conveniently expressed as CIELAB color differences. The effects can, however, also be measured by using the difference Rz — Rx between the values obtained with the blue and red tristimulus filters. The undertone measured in this way depends on the lightness, and has a maximum at Y = 41.4. The lightness of a gray paste should therefore have this value to ensure that undertone differences between white pigments are comparable [1.32], [1.33]. 

Reviews have appeared in the past on particle size effects (3, 9, 10, 15, 19-24), but in the present one we attempt to give a comprehensive and... 

More advanced insulations are also under development. These insulations, sometimes called superinsulations, have R that exceed 20 fthh-°F/Btu-m. This can be accomplished with encapsulated fine powders in an evacuated space. Superinsulations have been used commercially in the walls of refrigerators and freezers. The encapsulating film, which is usually plastic film, metallized film, or a combination, provides a barrier to the inward diffusion of air and water that would result in loss of the vacuum. The effective life of such insulations depends on the effectiveness of the encapsulating material. A number of powders, including silica, milled perlite, and calcium silicate powder, have been used as filler in evacuated superinsulations. In general, the smaller the particle size, the more effective and durable the insulation packet. Evacuated multilayer reflective insulations have been used in space applications in past years. 

Carbon black is derived from vegetable material, usually peat, by complete combustion to residual carbon. The particle size is very small, usually less than 5 /rm, and consequently is very difficult to handle. It is usually sold to the food industry in the form of a viscous paste in a glucose syrup. Carbon black is very stable and technologically a very effective colorant. It is widely used in Europe and other countries in confectionery. 

Hydration gives rise to effects on pore filling and the consequent enhancement of mechanical performance (low-porosity pastes are stronger than high-porosity ones). The first fast hydration step is followed by a relatively dormant period that may last 6 months or more, depending on temperature, particle size, and aqueous phase composition. In order to control the hydration step, alkyl sulfonate salts surface-active substances (SAS) are used. 

Lanthanides doped into nanocrystalline semiconductors have been the subject of numerous investigations in the past decades. If the size of a semiconductor particle is smaller than the Bohr radius of the excitons, the so-called quantum confinement occurs. As a result, the band gap of the semiconductor increases and discrete energy levels occur at the edges of the valence and conduction bands (Bol et al., 2002 Bras, 1986). These quantum size effects have stimulated extensive interest in both basic and applied research. 

The field of particle size distribution analysis has experienced a renaissance over the past five years and is now a rapidly growing and lively area of scientific and technological activity. This revitalization has been driven by advances in electronics and computer technology in conjunction with the market pull for particle size distribution analysis methods that cover a wide dynamic particle size range and have improved resolution. These technological advances are embodied in computer-aided, user-friendly, reliable, and cost-effective instrumentation. Three activities characterize this renaissance. 

These effects of particle size and shape have all been described in connection with dispersions, pastes, greases or loose powders, in which particles remain separated. The effects of particle dimensions on the formation and properties of films are far less clear. The process of film formation as described in Sections 6.2 and 6.3, would seem likely to benefit from large particle size, for a number of reasons. Large particles would presumably embed more effectively in substrate surfaces. Subsequently large particles would experience higher rotational couples than small ones during the orientation process. Finally, once the surface is fully oriented, a... 

Earlier, in Chapters 2, 4, and 5, it was pointed out that many foods contain solid particles. Thus the role of the size, shape and hardness of particles in oral perception of texture is of interest. For example, in the confectionary industry the minimum particle size that can be comprehended by the palate is said to be about 25 p,m. Further, particle sizes about 10-15 p,m are considered to be the limit of diminishing effect. On the other hand, in tooth paste, the alumina trihydrate particles with an average diameter 5-20 p,m are used and larger particles are known to contribute to gritty sensation in the mouth (Tyle, 1993). 

---