Closing voids

Polyurethane grout supplied shall be water-reactive liquid polyurethane base solutions which when reacted expand by foaming to at least seven (7) times the initial liquid volume and when set produce a flexible, closed void solid resistant to degradation by wet and dry cycles and chemicals found in concrete construction. Specific waterproofing grouts meeting these requirements are marketed by the following manufacturers.... ... 

Other closed voids (cavities) have been found (in addition to small channels along a, b, and c) in the crystals of ewdo-bicyclo[2.2.2]oct-5-ene-2,3-dicarboxyanhydride (P2j/c), the Diels-Alder adduct of 1,3-cyclohexadiene and maleic anhydride [1]. The voids extend as tall three-axis ellipsoids under the skew faces of about (01 10 ) and (118). These crystals include up to 0.4 equivalents of diluted bromine vapor without melting. No addition of bromine to the double bond occurs, as no large channels and no cleavage planes are available for anisotropic migrations in the 3D-interlocked structure. The bromine can be evaporated in a vacuum at 20-50 °C without having attacked the double bond of the host [1]. It can enter into the crystal and exit via the small channels. Numerous crystallographic closed voids are to be expected in various crystals. 

Particles consist of both internal and external surface area. The external surface area represents that caused by exterior topography, whereas the internal surface area measures that caused by microcracks, capillaries, and closed voids inside the particles. Since the chosen surface area technique should relate to the ultimate use of the data, not all techniques are useful for fine powders. The commonly used approaches are permeametry and gas adsorption according to the Brunauer, Emmet, and Teller (BET) equation [9]. Because of simplicity of operation and speed of operation, permeametry methods have received much attention. The permeametry apparatus consists of a chamber for placing the material to be measured and a device to force fluid to flow through the powder bed. The pressure drop and rate of flow across the powder bed are measured and related to an average particle size and surface area. Especially for porous powders, permeametry data include some internal surface area, thus decreasing their value. 

Forceflll (metallization, semiconductor processing) The use of high isostatic pressure ( 60Mpa) and temperature ( 400°C) to close voids in thin film aluminum metallization. 

Local average values of concentrations and partial pressures, rather chan point values, are also used in Che flux relations. However, in this case it is convenient to use interstitial local averages, based on the void volume rather than the total volume, since these are. ore closely related to the properties of bulk gases. 

Although most cakes consist of polydisperse, nonspherical particle systems theoretically capable of producing more closely packed deposits, the practical cakes usually have large voids and are more loosely packed due to the lack of sufficient particle relaxation time available at the time of cake deposition hence the above-derived value of 17.6 pm becomes nearer the 10 pm limit when air pressure dewatering becomes necessary. 

The gas phase in a cellular polymer is distributed in voids, pores, or pockets called cells. If these cells are intercoimected in such a manner that gas can pass from one to another, the material is termed open-ceUed. If the cells are discrete and the gas phase of each is independent of that of the other cells, the material is termed closed-ceUed. 

The manufacture of metal in powder form is a complex and highly engineered operation. It is dominated by the variables of the powder, namely those that are closely connected with an individual powder particle, those that refer to the mass of particles which form the powder, and those that refer to the voids in the particles themselves. In a mass of loosely piled powder, >60% of the volume consists of voids. The primary methods for the manufacture of metal powders are atomization, the reduction of metal oxides, and electrolytic deposition (15,16). Typical metal powder particle shapes are shown in Figure 5. 

Stmcture is usually measured by a void volume test such as the absorption of dibutyl phthalate (DBPA) (15), or by bulk density measurements of the carbon black under compression. In order to eliminate the effects of pelletizing conditions the DBPA test has been modified to use a sample that has been precompressed at a pressure of 165 MPa (24,000 psi) and then broken up four successive times (24M4) (16). This procedure causes some aggregate breakdown and is claimed to more closely approximate the actual breakdown that occurs duting mbber mixing. 

With closely screened material, the percentage of voids (usually 37 percent) is independent of particle size. With unscreened particles showing a wide variation in size, the void volume is decreaseci irregularity in gas flow results. 

The presence of notches or sharp angles or of a few holes, voids, particle inclusions or small inserts tends to concentrate the stress. Different polymers vary in their notch sensitivity and this is presumably a reflection of how close they are to their tough-brittle transitions. The aim of the designer and processor must be to reduce such stress concentration to a minimum. 

The CPVC can be readily identified in Fig. 8 as the point where the filler particles are close packed with just sufficient binder to coat the filler and substrate leaving no interstitial voids. At this point, PVC/CPVC = 1. Below the CPVC, there is excess binder and the filler particles are not close packed. Above the CPVC, interstitial voids exist due to insufficient binder. 

Fluidization may be described as incipient buoyancy because the particles are still so close as to have essentially no mobility, whereas the usual desire in fluidization is to create bed homogeneity. Such homogeneity can be achieved only by violent mixing. This is brought about by increasing the fluid velocity to the point of blowing "bubbles" or voids into the bed, which mix the bed as they rise. The increased fluid velocity at which bubbles form first is referred to as the incipient (or minimum) bubbling velocity. 

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