Mechanical Comminution Research Articles

Kinetics of dissolution of mechanically comminuted rock-forming oxides and silicates—II. Deformation and dissolution of oxides and silicates in the laboratory and at the Earth's surface

Comparison of the patterns of fracture under tensile stress, indentation, and scratching of periclase. quartz, and corundum indicates that the properties relevant to dissolution of rock-forming oxides and of rock-forming non-layer silicates should be changed by mechanical comminution in essentially the same way as those of quartz. The changes are accomplished by brittle fracture under the tensile component of the stress field, which does not generate subsurface damage, and by microplastic behavior under local stresses with high net compressive and shear components, which does. Mechanical comminution should therefore affect the apparent rates of dissolution (rates calculated with respect to the initial interface area) of rock-forming oxides and of rock-forming non-layer silicates in essentially the same way in which it affects the apparent rate of dissolution of quartz. This is supported by the available evidence on the effect of dry grinding on the kinetics of dissolution of feldspars, pyroxenes, and olivines in aqueous solutions. Different effects of mechanical comminution on solubilities and dissolution rate constants can be related to certain measured or calculated properties of the considered minerals. Notably, the effect of grain size on the dissolution rate constant can be rigorously related to the Kelvin effect. The available evidence on the mechanical comminution at the bases of dry-based glaciers in highgradient segments of streams, in certain high-energy coastal and epeiric environments, and in sandy deserts indicates that such mechanical comminution should significantly affect the simultaneous or subsequent dissolution of the comminuted material.

Streufall und Streuschwund in einem Caricetum curvulae

This research was part of long term plant production studies in Alpine grass heaths and was performed in the course of the Austrian MaB-6-programme. Different methods were tested to estimate the annual litter fall and litter disappearance of a Caricetum curvulae in the “Hohe Tauern” mountain range: Harvests of the above ground phytomass and litter store from especially prepared litter sample squares: At the start of the experiment, the above ground vegetation was clipped off and removed from 6 representative squares of 30 × 30 cm2 Three years later, the phanerogams on these quadrats had regenerated almost completely, but phytomass of the cryptogams still accounted to only 16 % of the long term mean. Now the entire phytomass of these plots as well as the litter of the last (current) year were harvested. As a result, an amount of 196 g dry substance per m2 was calculated as litter fall of aerial parts of the plant community between May 1977 and May 1978. Morphometric method: Several times throughout the 1979 growing season, the following shoot parameters of Carex curvula were measured: number of living and dead leaves per shoot as well as length and weight of living and dead leaf parts. Each time at least 120 shoots were taken into account to produce reliable data. The loss measured in standing dead material of Carex curvula leaves provided the calculation of litter fall in the 1979 growing season: about 60 g dry substance per m2 Long term phytomass and litter harvestings: By means of the harvesting method (Milner and Hughes 1968) the above ground net production of the Caricetum curvulae was studied. In the course of this research, an annual litter fall of 160 to 230 g dry substance per m2 could be found for the years 1975-1977. Most of the litter loss, especially in winter, is obviously caused by wind, mechanical comminution and leaching. Comparatively little is decomposed in summer. According to the varying weather conditions during the years of sampling, litter production as well as the disappearance of dead material was subject to remarkable variation.

Membranes of Rhodospirillum rubrum: physicochemical properties of chromatophore fractions isolated from osmotically and mechanically disrupted cells.

Isolation of highly purified membrane fractions from phototrophically grown Rhodospirillum rubrum was achieved by velocity and isopyknic sedimentation under carefully controlled ionic conditions. Bacteriochlorophyll-rich and succinic dehydrogenase-rich chromatophores that were essentially devoid of contamination by non-chromatophore protein were separated from a denser fraction in extracts disrupted in a French pressure cell. Highly purified chromatophores and a nearly photopigment-free envelope fraction were also obtained from cells lysed by treatment with ethylenediaminetetraacetate-lysozyme-Brij 58. After lysis with lysozyme and ethylenediaminetetraacetate alone, about 50% of the total photosynthetic pigment was released in chromatophores similar to those isolated by the above procedures. Chromatophores prepared by each method were found to have very similar near-infrared absorption spectra, overall chemical composition, equilibrium buoyant densities in CsCl, and protein patterns in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein profiles of the dense, outer membrane-rich fractions were different from those of the chromatophores. The release of much of the photosynthetic apparatus as discrete chromatophores is osmotically lysed extracts necessitates a reevaluation of the concept that isolated chromatophores arise only from mechanical comminution of a larger membrane structure.

Electron microscopical and electron diffraction investigations of mechanically comminuted boron powders

1. An electron-microscopical and electron-diffraction study was made of mechanically comminuted particles of crystalline boron. 2. It was established that comminution brings about amorphization of crystalline boron particles. The extent of the amorphization is independent of the method of preparation and purity of the starting rhombohedralβ boron, and characterizes the nature of the mechanical comminution process. 3. A model is proposed for the amorphization of crystalline boron during its mechanical comminution. The amorphized structure of the surface layers of particles corresponds to a delocalized state of the valence electrons of boron atoms.

Transformations in crystalline boron induced by mechanical comminution

Transformations in crystalline boron induced by mechanical comminution

Thermal stresses in spheres—A basis for studying the grinding of preheated rocks

It is a well-established fact that heating the mill feed prior to mechanical comminution enhances the grindability of many ores. However, no detailed calculations have been published to date by means of which the severity of the thermal shock, which will initiate fracture in the feed particles, can be estimated. It is the purpose of this paper to do so. Results are presented in a graphical form. They cover the thermal stresses which are induced in spheres and in long cylinders when these are subjected to linear heat transfer at their surface. These two shapes were selected because they provide a fair representation of the multiplicity of irregular shapes found in an actual grinding system, since the thermal stresses induced in spheres and cylinders are believed to be of the same order or magnitude as those which arise in heated mill-feed particles. Therefore the required physical parameters, for the thermal section of a thermal-mechanical comminution system, such as the degree of heating and quench severity can be estimated on the basis of the present results.

Manufacture of powders by the mechanical comminution of sulfur-containing iron-nickel alloys

1. Using 80N2M alloy as an example, it has been shown that mechanical comminution of sulfur-embrittled bulk alloys is a potentially useful method of preparation of iron-nickel alloy powders. 2. The optimum sulfur content of 80N2M alloy has been established ensuring that a fine grain is formed in the course of hot rolling and that the resultant hot-rolled alloy can be effectively comminuted in impact-type mechanical mills. 3. A comparative study was carried out of the physicotechnological properties of iron-nickel alloy powders produced by the techniques of coreduction of oxides, atomization or a molten metal stream, and mechanical communution of a sulfur-embrittled hot-rolled alloy. As a result of experiments on 80N2M alloy, the advantages have been demonstrated of mechanical comminution as a method of preparation of powders possessing high apparent and pyknometric densities. Such powders appear to be suitable for the formulation of high-permeability magnetic materials.

Electrolytic aluminum powder and its properties

1. An electrolysis apparatus and a process for the manufacture of electrolytic aluminum powder have been developed and tested on a large laboratory scale. 2. A study was made of the effect of electrolysis variables on the particle size distribution and particle morphology of electrolytic aluminum powder. It has been demonstrated that: a) lowering the temperature, increasing the initial current density, and reducing the duration of electrolysis decrease the proportion of coarse fractions in electrodeposited powder and narrow the range of particle sizes; b) with decreasing current density, the particle shape changes from elongated, dendritic to compact and, finally, lamellar; c) the powder particles are perfect single crystals. 3. Compared with powders produced by the atomization of liquid aluminum and mechanical comminution of solid aluminum, electrolytic aluminum powder has a larger specific surface, Its gravimetric density and aluminum oxide content per unit surface are less than those of the other powders. 4. The amount of the principal metallic impurities is less in electrolytic aluminum powder than in A99 grade aluminum.

The magnetic and mechanical hardness of the intermetallic compounds SmCo5 and LaCo5

The magnetisation, coercivity, HC, and remanence coercivity, HR, have been measured for the intermetallic compounds SmCo5 and LaCo5. The coercivities HC and HR for SmCo5 are very much greater than those for LaCo5. The differences in these parameters are much greater than would be expected from a simple theoretical model, so that they cannot be accounted for in terms of differences in the magnetocrystalline anisotropy constants. Since the specimens used for the magnetic measurements were produced by mechanical comminution, Knoop hardness measurements were made in an attempt to account for the magnetic behaviour in terms of the crystallographic damage and plastic deformation produced during the grinding process. The hardness results show that, within experimental error, the SmCo5 is very nearly isotropic, whereas the LaCo5 is very anisotropic on the {10¯10} planes with a Knoop hardness of 138 in the 〈0001〉 directions and 511 in the 〈12¯10〉. It is concluded that plastic deformation will occur more easily in LaCo5 and that this could, to some extent, explain the comparatively low coercivities.