Modification of the surface of very fine iron with polyvinylpyrrolidone

Adsorption of polyvinylpyrrolidone from alcohol solutions on ellipsoidal and dendrite-shaped particles of very fine iron has been studied. The possibility of modifying the surface of iron particles with polyvinylpyrrolidone, which is of interest in creating composites for medical purposes, is demonstrated.Institute of Colloid Chemistry and Water Chemistry, Ukrainin Natural Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, March–April, 1995.     

The role of transport phenomena in the plasma synthesis of fine particles: The production of silicon powder

A mathematical formulation has been developed to describe heat and fluid flow phenomena in a complex nontransferred are plasma jet system, and this information is then used to calculate the rate at which an injected silane stream decomposes. Problems of this type are important in the plasma synthesis of fine ceramic particles. The most important finding of the work is that swirl of the plasma jet plays a key role in determining the intermixing of the various streams and, hence, the overall process kinetics. The theoretical predictions were found to be in good agreement with measurements regarding the temperature fields. Furthermore, the capability of predicting temperature fields, residence times, and process kinetics should provide useful guidelines regarding reactor design such that the formation of monodispersed particles is favored. A.H. DILAWARI, formerly with the Massachusetts Institute of Technology This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

Flow and thermal behavior of the top surface flux/powder layers in continuous casting molds

Steady-state finite-element models have been formulated to investigate the coupled fluid flow and thermal behavior of the top-surface flux layers in continuous casting of steel slabs. The three-dimensional (3-D) FIDAP model includes the shear stresses imposed on the flux/steel interface by flow velocities calculated in the molten steel pool. It also includes different temperature-dependent powder properties for solidification and melting. Good agreement between the 3-D model and experimental measurements was obtained. The shear forces, imposed by the steel surface motion toward the submerged entry nozzle (SEN), create a large recirculation zone in the liquid flux pool. Its depth increases with increasing casting speed, increasing liquid flux conductivity, and decreasing flux viscosity. For typical conditions, this zone contains almost 4 kg of flux, which contributes to an average residence time of about 2 minutes. Additionally, because the shear forces produced by the narrowface consumption and the steel flow oppose each other, the flow in the liquid flux layer separates at a location centered 200 mm from the narrowface wall. This flow separation depletes the liquid flux pool at this location and may contribute to generically poor feeding of the mold-strand gap there. As a further consequence, a relatively cold spot develops at the wideface mold wall near the separation point. This nonuniformity in the temperature distribution may result in nonuniform heat removal, and possibly nonuniform initial shell growth in the meniscus region along the wideface off-corner region. In this way, potential steel quality problems may be linked to flow in the liquid flux pool.     

Structural transformations and properties of 40N2M powder steel in conventional and isothermal quenching

Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 48–52, April, 1991.     

The structure and chemical composition of the surface layers of powder metallurgy copper after friction

Translated from Poroshkovaya Metallurgiya, No. 12, pp. 69–74, December, 1990.     

Kinetics of bonding powder particles with the surface of the component in hot gas spraying of coatings

Translated from Poroshkovaya Metallurgiya, No. 3(315), pp. 50–54, March, 1989.     

High-strength carbon steels with hereditary fine crystal structure I. The effect of vibrogrinding on the parameters of the fine structure of iron powder particles

Conclusions We investigated the dependence of the specific Surface and of the parameters of the fine structure of powdered pure iron on the duration of vibrogrinding and their change in the process of reduction. It was shown that this is accompanied during the first 15–30 h as a result of deformation polygonization by the formation of a block structure. When ground powders are reduced, processes of polygonization occur intensively; however, regardless of that, the defectiveness of the crystal structure of the metal remains high, and this apparently is bound to have a substantial influence on the processes of dissolving carbon and structurization during the sintering of pellets.Deceased.Translated from Poroshkovaya Metallurgiya, No. 6(282), pp. 46–51, June, 1986.