Crystallographic preferred orientations may develop in nanocrystalline materials on fault planes due to surface energy interactions
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Abstract A layer of substantially noncrystalline material, composed of partially annealed nanopowder with local melt, was experimentally generated by comminution during ∼1.5 mm total slip at ∼2.5 × 10 −6 m s −1 , P conf ∼ 0.5 GPa, and 450°C or 600°C, on saw cut surfaces in novaculite. The partially annealed nanopowder comprises angular grains mostly 5–200 nm diameter in a variably dense packing arrangement. A sharp transition from wall rock to partially annealed nanopowder illustrates that the nanopowder effectively localizes shear, consistent with generation of nanoparticles during initial fragmentation, not by progressive grain size reduction. Dislocation densities in nanopowder grains or immediate wall rock are not significantly high, but there are planar plastic defects spaced at 5–200 nm parallel to the host quartz grain's basal plane. We propose these plastic defects developed into through‐going fractures to generate nanocrystals. The partially annealed nanopowder has a crystallographic preferred orientation (CPO) that we hypothesize developed due to surface energy interactions to maximize coincident site lattices (CSL) during annealing. This mechanism may also have generated CPOs recently described in micro/nanocrystalline calcite fault gouges.Keywords:
Nanocrystalline material
Comminution
Severe Plastic Deformation
Comminution process can be regarded as an assembly of single fractures, and as a natural result the behaviour of the materials in single fracture an essential role in the performance of the comminution system. In this paper glass spheres and irregular shaped limestone particles with different grain sizes have been comminuted under various impact velocities and the behaviour of these materials in high velocity comminution has been investigated and the results have been analysed for the size distribution of the products. Using these results the authors have tried to estimate a performance of a high velocity impact comminution system by simulation study. A summary of the results is as follows:(1) Size distribution of the product is with a unique function of the impact velocity, and can be normalized in terms of the feed size.(2) The results of simultion indicates that the multistage comminution system of relatively low impact velocity can make the best use of comminution energy.(3) Impact comminution experiments on limestone particles showed that the peak of the size distribution of the products is consistent with the crystalline grain size of the materials.
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Control over the growth and crystallographic orientation of nanocrystals in amorphous alloys is of particular importance for the development of advanced nanocrystalline materials. In the present study, Nd2Fe14B nanocrystals with a strong crystallographic texture along the [410] direction have been produced in Nd-lean amorphous Nd9Fe85B6 under a high pressure of 6 GPa at 923 K. This is attributed to the high pressure inducing the preferential growth of Nd2Fe14B nanocrystals in the alloy. The present study demonstrates the potential application of high-pressure technology in controlling nanocrystalline orientation in amorphous alloys.
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The compressibility of calcite to 40 kbar has been remeasured by using a piston-cylinder apparatus. Calcite 1 is found to transform to calcite 2 at 14.5 kbar with a volume change of 0.00483 cm3/g, and calcite 2 is found to change to calcite 3 at 17.4 kbar with a volume change of 0.01291 cm3/g. The volume compression data for the three phases are described by the following quadratic relations: Calcite 1 Calcite 2 Calcite 3 where P is pressure in kilobars. The compression data for calcite 1 and calcite 3 are in good agreement with those available in the literature. The data exhibiting an abnormally high compression of calcite 2 have been reported for the first time. The compression data for calcite 2 have been used to explain quantitatively the abnormal drop near 15 kbar observed in the ultrasonic sound velocity in calcite.
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ABSTRACT The comminution function is just one in a long chain of value-adding functions that begins with ore in the ground and ends with the sale of metal, concentrate or some other product. The creation of an economic model for comminution is complicated by the fact that it is difficult to identify the exact amount of value added by comminution, and further complicated by the fact that changes in comminution impact on a range of other associated functions such as ore-waste discrimination (cut-offs), mine scheduling and downstream processing. The authors argue that in order for comminution to be modelled effectively, it must be incorporated into a framework which includes many other related functions. In this way, a change in the comminution circuit can be evaluated after taking into account its effect on other related activities. This paper also presents a significant innovation which allows the simultaneous optimization of milling time and processing cut-offs, with the objective of maximising NPV.
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