Density effective 347, true apparent

Sieve analysis using standard mesh screens is commonly used to determine particle size and size distribution of pellets and the reader is referred to standard texts for further information (61). Several types of densities have been defined for pellets based on interparticulate (void fraction) and intraparticulate pore volumes and include true, apparent, effective, bulk and tapped. The bulk and tapped densities may be obtained using simple devices, such as that used to evaluate granulations in tableting, while the true and apparent densities need more complex techniques based on mercury intrusion, gas flow, powder displacement, imaging or minimum fluidization velocity (62). 

The effective density of a particle is the particle mass divided by the volume of liquid it displaces (Archimedes density). Its true density is the particle mass divided by the volume it would occupy if it were compressed so as to eliminate all the pores and surface fissures. Its apparent density is its mass divided by its volume, excluding open pores but including closed pores. 

In the case of filled systems, the two latter effects provide a substantial contribution to C2 compared with the influence of trapped entanglements [80]. For filled systems, the estimated or apparent crosslinking density can be analyzed with the help of the Mooney-Rivlin equation using the assumption that the hard filler particles do not undergo deformation. This means that the macroscopic strain is lower than the intrinsic strain (local elongation of the polymer matrix). Thus, in the presence of hard particles, the macroscopic strain is usually replaced by a true intrinsic strain ... 

A naphtha is desulfurized by reducing its thiophene content with hydrogen at 660 K and 30 atm.The reaction is apparently first order with k = 0.3 cc thiophene/(g catalyst)(sec). The catalyst particle diameter is 0.35 cm, true density 2.65 g/cc, specific surface 180 m2/g, porosity 40%, In an experiment with very fine particles, conversion was 90%, but with the particles in question it was 70%. Find the effectiveness of the catalyst and the tortuosity of the pores. 

Quoted density values in standard reference works are of the materials true density. If density is determined using a gas pyknometer, the volume measured would include closed pores but exclude open pores i.e. the measured density would be the apparent density. If the suspending liquid penetrates all the cracks and fissures on the particle surface, the measured volume would be the same as that determined by gas pyknometry but the total mass would be greater due to the included liquid that will remain with the particle as it falls in the liquid, hence its sedimentation density will be intermediate between the apparent density and the true density and greater than the effective density. These differences are usually not highly significant for coarse particles unless they are highly porous. 

Under almost all the deposition conditions we have studied, the number density of nuclei first increased approximately linearly to irradiation time with a negligible induction period, and then the rate of increase was gradually slowed down due to a saturation effect (3-5). We have to properly discriminate between a true induction period and only an apparent one. The latter is connected to the detection limit and means a period during which the nuclei are too small to be observed even if they actually exist. Provided that some induction period was detected, one must be very careful in judging its origin. Fortunately, we have not encountered such a situation, which in turn implies that the minimum size of Si nuclei detectable by the chemical amplification is actually very small, though precise size evaluation has not been successful, as stated before. 

To check further on the extent to which electrode reactions on the basal plane may be impeded by semiconductor effects, the Fe(CN)6 -Fe(CN)6 redox couple has been examined and found to have an exchange current on the basal plane which is 1/3 of that on the edge plane. This difference may be caused by a difference in the ratio of true-to-apparent surface area or ionic double-layer effects (different point of zero charge) as well as semiconductor effects but is certainly far less than the two orders of magnitude difference in the exchange current densities for the O2 reduction on the basal and edge planes. 

The apparent density, also called the true density, real density, or absolute density, expressed in kg.m is obtained when the volume measured excludes the pores as well as the void spaces between particles within the bulk sample. Absolute density is determined by pycnometry using water or another Hquid that is expected to fill the pores in the sample, thus removing their volume from the measurement. Sometimes the material is subjected to boiling in the same liquid to ensure pore penetration, and sometimes the sample is evacuated prior to immersion to assist pore filling. However, surface-tension effects and entrapped gases resist the filling of very small pores. Therefore the best method consists in determining the apparent density by hehum pycnometry ... 

The evolution of the piston displacement upon compressing the LDA sample is shown in Figure 5. For comparison, the results obtained upon PIA of ice Ih are included. The LDA-to-HDA transformation occurs at f 0.6 GPa, as indicated by the sudden change in d(/. This pressure is lower than the pressure at which ice Ih transforms to HDA ( 1 GPa). Still, the LDA-to-HDA transition is at least as sharp as the ice Ih-to-HDA transition and, thus, it also resembles a first-order transition in its volume change. We note that the density of HDA at 1 bar and T — 77K is, within error bars, the same density of the HDA samples obtained from PIA of ice Ih, 1.17 g cm . Moreover, the X ray diffraction patterns of HDA, obtained from ice Ih and LDA, are also very similar to each other [62]. Therefore, the HDA form obtained from LDA is apparently the same amorphous ice that results from PIA of Ih at r = 77K [24,62]. If the LDA to HDA transformation is indeed a true first-order transition, then one would expect to observe that HDA transforms back to LDA upon decompression. Otherwise, the LDA to HDA transformation could be interpreted as a simple relaxation effect of LDA. In this case, there would be a single amorphous phase of water (LDA), and HDA, instead of being a new amorphous phase different from LDA, would be a relaxed version of LDA [63]. Figure 5 shows... 

The amount of operating liquid holdup in a packed bed is influenced by the density of the continuous vapor phase. The apparent density of the liquid in the tower is the true liquid density less the actual vapor density, even when there is no aeration of the liquid phase. This buoyancy effect normally is imperceptible at atmospheric pressure because the density of the vapor is only about 0.5% of the liquid density but at higher pressures this effect becomes significant. 

Anodic evolution of chlorine at graphite has been investigated many times mainly for applied value (see, for example, the review articles[308-311]). Ksenzhek and Stender[312-315] were the first to analyze the effect of porosity of a graphite anode on the kinetic parameters of the process. Proceeding from the idea formulated by Ioffe[316] about the relation between the IR drop in electrolyte in the pores of the anode and a decrease in the true current density the authors analyzed the shape of the polarization curve and showed, in particular, that in the Tafel region the true current density on the outer surface of the electrode is proportional to the square of the apparent current density, which results in the doubling of the slope b. This result is valid for any true value of the Tafel slope[317]. 

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