Diffusion processes in the sintering of nickel alloy powders with spherical particles under pressure

Conclusions Hot gasostatic pressing and subsequent annealing at 1200C result in the formation of 160–200-m diffusion zones between particles, which extend over practically the whole particle widths. During sintering under conditions of hot hydrostatic pressing, which is characterized by a shorter period of annealing at any given temperature and pressure, the widths of the diffusion zones after sintering and annealing attain 50–65m. The optimum diffusion zone width in the sintering of particles making good contact with one another (pure and even surfaces) is about 30–40m. However, the presence of oxides, carbide phases, and more complex compounds on the surfaces of particles substantially increases the optimum width of this zone. In such a case the optimum width is determined by the need for diffusion to cross interparticle contacts with diffusion-inhibiting barriers. In view of this, for particles of the nickel alloys investigated the optimum diffusion zone width may be taken to be 100m. At this width there are no areas in which the diffusion zone width is less than 40m, i.e., the minimum thickness at which strong bonds can be expected to form between particles.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 38–41, May, 1982.     

Compaction of an array of spherical particles

The compaction response has been investigated for an array of spherical particles composed of elastic, perfectly plastic material. Numerical simulations have been used to examine the evolution of contact size, contact pressure and macroscopic yield surface with the degree of compaction. It is found that the macroscopic yield surface of a compact has a corner at the loading point, and its shape evolves with increasing strain in a non self-similar fashion.     

Course of porosity in layered beds of spherical particles

Measurements of area porosity of layered beds in the ?interfacial“ region of contact between layers of spheres of unequal diameter. Definition, computational determination and correlation of the ?interfacial excess pressure drop“ associated with the flow across the region of contact.     

Carbidization of spherical titanium particles in a solid-liquid state

Conclusions A mathematical model of the carbidization process of titanium in a solid-liquid state and optimum conditions of carbidization of titanium are proposed. Data yielded by model experiments are in qualitative agreement with results of calculations. An investigation, involving microhardness measurements on specimen sections, was carried out into the carbidization kinetics of spherical titanium specimens at temperatures of 2073–2573°K.Translated from Poroshkovaya Metallurgiya, No. 9(249), pp. 28–33, September, 1983.     

A nonoverlap model for the dispersion of spherical particles

The dispersion of randomly positioned spherical particles can be characterized in terms of probability functions for the center to center spacings to its neighbors. This model is used with a correction procedure for describing the dispersion of nonoverlapping spherical particles. Modification of the random model to account for the bias introduced by excluding overlap is carried out by setting the neighbor probability functions equal to zero for radial distances which cause overlap, and then renormalizing the functions. Comparison of the probability distributions and their moments for the nonoverlap model with Monte Carlo simulation data show that it provides a valid approximation for the dispersion of spherical particles with volume fractions as high as 30 pct. The effects of volume fraction and size distribution of the particles upon the nonoverlap probability functions and their moments are described. Radial density functions are also calculated for both the random and the nonoverlap models. Formerly with Division of Minerals Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA.     

A nonoverlap model for the dispersion of spherical particles

The dispersion of randomly positioned spherical particles can be characterized in terms of probability functions for the center to center spacings to its neighbors. This model is used with a correction procedure for describing the dispersion of nonoverlapping spherical particles. Modification of the random model to account for the bias introduced by excluding overlap is carried out by setting the neighbor probability functions equal to zero for radial distances which cause overlap, and then renormalizing the functions. Comparison of the probability distributions and their moments for the nonoverlap model with Monte Carlo simulation data show that it provides a valid approximation for the dispersion of spherical particles with volume fractions as high as 30 pct. The effects of volume fraction and size distribution of the particles upon the nonoverlap probability functions and their moments are described. Radial density functions are also calculated for both the random and the nonoverlap models.     

An analysis of the capillary forces in liquid-phase sintering of spherical particles

The interparticle force due to capillary action of a liquid contact between two solid spheres is shown rigorously to have two contributions, one the surface tension force itself and the other due to the pressure difference caused by surface curvature. Numerical means are used to solve for the shape of the liquid surface and to evaluate this interparticle force as a function of contact angle, volume of liquid, size of sphere, and surface tension. The rigorous solution is then compared to the often-used circle approximation. We also evaluate the effect of neglecting one of the terms in the force equation, as is sometimes done in the literature. The general force relations are then used to draw several practical conclusions concerning liquid-phase sintering of spherical powders.     

Identification of spherical virus particles in digitized images of entire electron micrographs

Interferon-gamma (IFN-gamma) has the most potent immunomodulatory activity of all the interferons. This phase II-B study was performed to define time- and dose-dependent immunomodulatory effects mediated by IFN-gamma in a subset of patients with melanoma treated in the dose-seeking therapeutic trial conducted by the Eastern Cooperative Oncology Group E4687 (13). The effects of IFN-gamma (Genentech, San Francisco, CA) were evaluated for phenotype and function of peripheral blood lymphocytes obtained twice prestudy, and on days 2, 9, and 29 of IFN-gamma therapy for 50 patients. Early significant increases in CD4/CD8 ratio (p = 0.001) were noted, largely due to a rise in CD4+ and fall in CD8+ T-cell populations sustained through day 29 at only the lowest dosage. Increased natural killer cell (NK) activity (p = 0.001 on day 9; p = 0.01 on day 29) was accompanied by durable increases in circulating activated NK cells (CD56+DR+% p = 0.001, day 9; p = 0.001, day 29). After initial depression of CD56+ and CD16+ cells on day 2, the total percent of CD56+ and CD16+ cells increased significantly by day 29. Increases in NK cell activity were maximal at doses > or =0.1 mg. Monocyte CD14+ expression of DQ+ rose early (p = 0.011 and 0.001 on days 2 and 9), accompanied by elevation in CD14+DR+ cells that was less significant. Immunomodulatory effects of IFN-gamma reported in this trial have major implications for interpretation of past and current clinical trials, and the design of future trials. This is the first trial in which IFN-gamma has been shown to have significant effects on the T-cell compartment of the immune system.