Compression characteristics, pressure

For the two explosive loading systems used, the initial pressure wave into the powder is relatively low, varying from perhaps 1.5-4 GPa. In such cases the most relevant compression characteristic of the powder compact is its crush strength , i.e., the pressure required to compress the porous compact to solid density. In the simulations, this strength can be varied over a wide range with the P-a model. The wavespeed of the initial waves was modeled on the basis of shock-compression data on rutile at densities from 44% to 61% of solid density [74T02]. 

On the experimental side, one may expect most progress from thermodynamic measurements designed to elucidate the non-configurational aspects of solution. The determination of the change in heat capacity and the change in thermal expansion coefficient, both as a function of temperature, will aid in the distinction between changes in the harmonic and the anharmonic characteristics of the vibrations. Measurement of the variation of heat capacity and of compressibility with pressure of both pure metals and their solutions should give some information on the... 

In a demonstration of the pharmaceutical advantage that can be realized through the use of a cocrystal form of a substance, it was shown that the 1 1 cocrystal of caffeine and methyl gallate exhibited significantly improved powder compaction properties [64], The compression characteristics of the cocrystal were reported to be excellent over the entire pressure range studied, with the tablet tensile strength of the cocrystal being twice that of caffeine at pressures less than 200 MPa. The superior compaction properties of the cocrystal product were attributed to the presence of slip planes in crystal structure. 

Raman spectra for the sample were conducted in a compression-decompression cycle. In this experiment, the crystalline diffraction began to disappear above 7-8 GPa during compression, and pressure-induced amorphization was indicated by the Raman spectra above 13 GPa (Fig. 14). The resultant HDA Si exhibits the Raman spectrum that differs from the spectrum of normal -Si (LDA Si). Rather, the characteristics of the spectrum for HDA Si resemble those of the (3-tin crystal, which indicates that HDA Si has a (locally) analogous structure to the (3-tin structure. The synthesis of the HDA form of Si by Deb et al. [263] has a strong resemblance to that of water (ice) by Mishima et al. [149, 196]. Whereas compression induced amorphization that was almost completed at 13-15 GPa, decompression induced an HDA-LDA transition below 10 GPa, which is clearly shown in the Raman spectra (Fig. 14). This is the first direct observation of an amorphous-amorphous transition in Si. The spectrum at 0 GPa after the pressure release exhibits the characteristic bands of tetrahedrally coordinated -Si (LDA Si). Based on their experimental findings Deb et al. [263] discussed the possible existence of liquid-liquid transition in Si by invoking a bond-excitation model [258, 259]. They have predicted a first-order transition between high-density liquid (HDL) and low-density liquid... 

Fig. 1 shows the surface pressure-area (n-A) isotherms of stearic acid monolayers on pure water and ion-containing subphases, respectively. The presence of bivalent cations in the subphase gives rise to condensation of the monolayers. On the Ag+-containing subphase, the isotherm shows extremely compressed characteristics with a limiting area of 0.12nm2/molecule, much smaller than the cross-sectional area of 0.20 nm2 of a saturated hydrocarbon chain, which suggests the formation of a three-dimensional structure of the compressed monolayer [48]. 

Carless, J.E. Leigh, S. Compression characteristics of powders radial die wall pressure transmission and density changes. J. Pharm. Pharmacol. 1974, 26, 289-297. 

Obiorah, B.A. Possible prediction of compression characteristics from pressure cycle plots. Int. J. Pharm. 1978, 1, 249-255. 

The prediction of miscibility requires knowledge of the parameters T" (the characteristic temperature), p (the characteristic pressure) and V (the characteristic specific volume) of the corresponding equation of state which can be calculated from the density, thermal expansivity and isothermal compressibility. The isobaric thermal expansivity and the isothermal compressibility can be determined experimentally from p-V-Tmeasurements where these values can be calculated from V T) and V(p)j. The characteristic temperature T is a measure of the interaction energy per mer, V is the densely packed mer volume so that p is defined as the interaction energy per... 

These general comments and the theoretical developments provided in Chapter 2 point to the need for information on the effect of pressure differentials on filter c e resistance, porosity, moisture content, etc. Test work must be designed to quantify the compressibility characteristics of the suspension of interest. This information fedlitates the estimation of filter size and productivity in various operating conditions. Quite ofi en, the level of pressure used in plant-scale separations are quite different to those available in the test laboratory. 

In addition to the normal manual valve between a compressor and the common discharge header, there should be a fail-closed remotely actuated globe control valve with Monel trim and an equal percentage flow characteristic (HV-65 on Fig. 11.26). It should handle the full capacity of the compressor with a pressure drop of about lOkPa. When, during startup, the pressure instrument referred to above shows that the compressed gas pressure is equal to the discharge header pressure, the operator can open this valve slowly. 

Many investigators have studied the compression characteristics of bulk materials [3-14] a number of these studies have dealt with polymeric bulk materials. The compaction process is quite complicated for a number of reasons. The distribution of stresses in the material during compaction is rather complex and depends very much on the geometry and surface conditions of the compression apparatus and the detailed characteristics of the bulk material. The effect of pressure on bulk density is often described by an empirical relationship ... 

The principal objective of an expression test is to determine the compression deliquoring characteristics of a cake. However, the nature of the test allows both filtration and compression characteristics to be determined when the starting mixture is a suspension (i.e. where the solids are not networked or they are interacting to a significant extent). Cake formation rate, specific resistance and solids volume fraction data can be determined for the filtration phase while analysis of a subsequent consolidation phase allows the calculation of parameters such as consolidation coefficient, consolidation index and ultimate solids concentration in the cake. Repeated use of the expression test over a range of constant pressures allows the evaluation of scale-up coefficients for filter sizing and simulation as described in Section 4.7. 

Figure 19 Compression characteristics of recipe I. The second v-axis shows the influence of the nitrogen pressure on the porosity. Porosity was calculated by the quotient of upward pressure of the coated granules in silicon oil as a measure of the apparent density and the true density. The three different charts display the compression characteristics for three compression forces (5-15 kN).

Attempts to explain the remarkable fact that a gel, which consists mostly of fluid, behaves as a rigid solid and yet retains many properties characteristic of the fluid component (such as compressibility, vapor pressure, and electrical conductivity, which are but little altered), have resulted in many contributions to the colloid chemical literature and numerous hypotheses concerning the nature of gel structure. Most prominent among these (c/. Goodeve, 1939) have been those based on (a) immobilization of solvent through adsorption by the solute, (6) the presence of a three-dimensional network of solute, and (c) the operation of long-range forces between solute particles. Each of these theories may be applicable to some gel systems but not to others. 

Compressed Ga.s PropeIIa.nts. The compressed gas propellants, so named because they are gaseous in conventional aerosol containers, are nontoxic, nonflammable, low in cost, and very inert. When used in aerosols, however, the pressure in the container drops as the contents are depleted. Although the problem is lessened when the contents are materials in which the propellant is somewhat soluble, this pressure drop may cause changes in the rate and characteristics of the aerosol spray. A compressed gas aerosol system is illustrated in Figure 3. 

On firings the gases from the propellant accelerate the piston that compresses the light gas in front of it. At a preestablished pressure, the projectile is propelled down the launch tube accelerated by the low molecular weight gas which follows the projectile to the mouth of the tube. The target material is placed in front of the launch tube, and appropriate instmmentation used to estabUsh the characteristics of the interface reaction between projectile and target (117-120). 

Other Energy Systems. Chemical plants usually require cooling water, compressed air, and fuel distribution systems. Sometimes also included are refrigeration, pressurized hot water, or specialized heat-transfer fluids such as Therrninol Hquid or condensing vapor. Each of these systems serves the process and reflabiUty is the most important characteristic. Thus a project in any of them that achieves a 10% reduction in energy cost at the expense of a 1% loss of rehabihty loses money for the operation. 

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