Value Of Specific Surface Energy Research Articles

The concept of quasi-brittle rock fracture as applied to extraction and processing operations

Research objective is to substantiate the method for calculating the value of specific surface energy as the work irreversibly expended on fracture surfaces formation in the course of rock fracture in mining flow processes. Methods of research. The scheme of a uniformly expanded thin brittle plate with an embedded crack perpendicular to the load (Griffith plate) was taken as the basis for analytical calculations. The statement of the problem was based on building the energy balance of the work irreversibly expended on fracture surfaces formation through crack creation and propagation. The general solution analysis revealed that the well-known Griffith formula refers to a particular case of a perfectly brittle material fracture, when a sample in the form of a plate has specific dimensions with respect to the length of the embedded crack. Griffith theory postulates the presence of embedded structural cracks in a fractured body and does not explain the mechanism of crack creation and propagation up to the critical value. Therefore, it has not yet found practical application in analytical calculations of mining operations. Results. To extend application of the obtained design dependence of the specific surface energy for the tough fracture of rocks as well, a modified Irwin criterion has been proposed that determines the condition for the local fracture of crack-like flaws in the material’s structure. Therefore, by introducing a new constant in the form of an integrated structural-textural constant of the rock material, it has become possible to obtain the final answer to the question of what the value of specific energy consumption is in the flow processes of rock fracture by tensile cracks propagation. The theoretical novelty of the obtained regularity, along with its clear, understandable physical sense, is represented in the specific energy irreversibly spent for through tensile cracks creation by substantiated introduction of energy efficiency in the course of fracture, which substantially increases the value of the design energy consumption.

Boron carbide nanoparticles for high-hardness ceramics: Crystal lattice defects after treatment in a planetary ball mill

Deformation features of the boron carbide lattice treated in a planetary ball mill are studied in our work. It is shown that such treatment causes a decrease in the B4C grain size and cracking along the {202¯1}h planes, whereas the same treatment in the presence of silicon results in the appearance of twins along the {101¯1}h planes. Distorted stacking faults along (101¯4)h are observed. Ab initio simulations shown, that among low-index crystallographic planes {202¯1}h and {101¯1}h have the smallest values of specific surface energy which favors the formation of defects and cracks.

Theoretical Equilibrium Morphology of Gypsum (CaSO4·2H2O). 2. The Stepped Faces of the Main [001] Zone

The athermal equilibrium shape (ES) of gypsum crystal is calculated, in a vacuum, in the zone interval of the stepped {1k0} forms (3 ≤ k ≤ 8). The surface profiles are obtained by applying either the Hartman―Perdok method of the periodic bond chains (PBC) or the method of systematic cuts (SC) generated under the only conditions of stoichiometry, electroneutrality, and annihilation of the dipole moment perpendicular to each d 1k0 slice. The specific surface energy values γ 1k0 have been calculated, both for ideal and relaxed surface profiles, using a semiempirical potential function proposed by Adam. From calculations, it follows that the ES in the [001] zone is characterized not only by the well-known {120} and {010} flat forms and by the stepped {100} pinacoid but also by the {140} and {180} stepped forms. Further, following the PBC method, the stepped {130} and {170} forms also should enter the ES. Finally, an unambiguous analogy arises between our results and the systematic presence of the {1k0} faces on the giant crystals found in the Naica mine, whose growth occurs very near the equilibrium.

Study of adhesion during actual contact area formation at light loads

The present work considers simulation of contact area formation using the contact models of Hertz, DMT and JKR. The purpose of this work was to study development of real contact between rough surfaces taking into account the action of adhesion. The model of the Winkler foundation is used to describe the elastic properties of the rough surface. Solids with thin hard coatings were used as test specimens. The surface topography was measured with typical AFM at different scale levels. The data on the specific surface energy of specimens are obtained with contact adhesion meter developed in MPRI (Gomel, Belarus). The obtained value of specific surface energy was used in computer simulations of real contact using the AFM images.

Coercive properties of Nd 2Fe 14B+αFe nanocrystalline composites exhibiting wide distributions of switching fields in the frame of the Global Nucleation Model

The demagnetization processes in Nd 2F 14B+αFe nanocrystalline composites exhibiting square and two-step hysteresis loops are investigated. In all these microstructures, an expanding nucleus model (Global Model) reasonably describes the experimental results in the entire range of the demagnetization loop, provided different sites acting as inverse nucleus are considered. Nucleation is found to take place in both phases and under different coupling conditions exhibiting, in each case, a different reversion regime. Each regime has associated definite values of specific nucleus surface energy and effective local demagnetizing factor, which are similar in all the specimens, in spite of their different microstructures and compositions. These specific surface energy values are close to those expected for domain wall-like configurations resulting from competing interactions in the particular nucleation site, not always related to the intrinsic properties of the phase itself but largely determined by inter-grain interactions.

Surface Energy of Germanium and Silicon

Surface energy is one of the most fundamental parameters of a solid since it depends directly on the binding forces of the material. Indeed, it is a measure of the work necessary to separate a material into two parts along a plane. Very few measurements have been made of this quantity and these by indirect means, because of difficulties of measurement and interpretation. This report deals with a direct measurement of specific surface energy of Ge and Si made by the cleavage technique. By measuring the force just necessary to move a crack “in reversible fashion” the surface energy can be obtained. The measured value for the {111} planes of Ge and Si are 1060 ergs/cm2 and 1230 ergs/cm2. From these measured values the energy of the planes {100} and {110}can be estimated. They are: Using the measured value of specific surface energy, assuming this is due to the appropriate number of broken , the bond strength of Ge and Si was obtained as ; .