UDC 620.22:621.921
V. I. Kushch
V. M. Bakul Institute of Superhard Materials, NAS of Ukraine, Kyiv, Ukraine
vkushch56@gmail.com
Continuous modeling of elastic behavior of nanosized diamond single crystals (pp. 3-13)
Two continuum models are proposed for predicting elastic fields and properties of nanosized diamond single crystals. The first of them is a boundary value problem of the theory of elasticity for a sphere with a thin shell, which ensures that the effect of free surface energy on the elastic behavior of a nanoparticle is taken into account. In the second model, the surface energy is taken into account by the boundary condition according to the Gurtin-Murdoch theory of material surfaces. The geometric and material parameters of the models are identified by comparison with molecular dynamics data. A parametric analysis of the developed models was carried out, and regularities of the influence of the size of a diamond nanoparticle on the lattice parameter, stress concentration, and bulk elastic modulus were established.
Keywords: diamond, nanocrystal, elasticity, continuum model, molecular dynamics.
UDC 544.344.015.4:539.89:661.883.1/.2
Yahya Al-Khatatbeh1, *, Khaldoun Tarawneh1, Ahmad M. Alsaad2
1Department of Basic Sciences, Princess Sumaya University for Technology, Amman, Jordan
2Department of Physical Sciences, Jordan University of Science and Technology, Irbid, Jordan
*y.alkhatatbeh@psut.edu.jo
Prediction of the behavior of the repeated phase transition of cottonite in zirconium dioxide and hafnium at high pressures (pp. 14-26)
First-principles calculations within the framework of density functional theory are implemented to study the behavior of ultrahigh-pressure phases of zirconium (ZrO2) and hafnium (HfO2) compounds. The phase relationships between the ultrahigh pressure phases of these dioxides were investigated: the previously observed OII phase (cotunnite), the Fe2P-type phases, and the recently predicted Ni2In-type phase. Using the generalized gradient approximation, calculations predicted an unusual OII to Fe2P phase transition. In both dioxides, enthalpy calculations showed that the OII phase transforms to Fe2P at pressures of 96 GPa (122 GPa) for ZrO2 (HfO2), where the Fe2P phase remains stable up to 254 GPa (310 GPa) in ZrO2 (HfO2) before transforming back to the OII phase, indicating a repeated OII phase transition. The calculations showed that the OII ® Fe2P and Fe2P ® OII transitions are associated with a small change in both volume and enthalpy. It is concluded that the transition to the Ni2In phase occurs from the OII phase, rather than the Fe2P phase, and therefore an updated sequence of high-pressure phase transitions is provided for zirconium and hafnium at these extreme pressures. The OII ® Ni2In transition is predicted to occur at pressures of 302 and 372 GPa in zirconium and hafnium, respectively. To gain a deeper understanding of the mechanism of phase transitions in ZrO2 and HfO2, the influence of enthalpy difference components on the predicted phase transitions was carefully investigated.
Keywords: phase transitions, enthalpy difference components, equation of state, first principles, phase stability.
UDC 544.431.7:661.665.3:536.46
Ozan Coban1, 2, *, Mehmet Bugdayci3, 4, Serkan Baslayici1, 4, M. Ercan Acma1
1Istanbul Technical University, Metallurgical and Materials Engineering Dep., Istanbul, Turkey
2Istanbul Gedik University, Faculty of Engineering,Metallurgical and Materials Engineering Dep., Istanbul, Turkey
3Yalova University, Chemical Engineering Dep., Yalova, Turkey
4Istanbul Medipol University, Vocational School, Construction Technology Dep., Istanbul, Turkey
*ozan.coban@gedik.edu.tr
Combustion synthesis of B4C–TiB2 nanocomposite powder: effect of Mg particle size on self-propagating high-temperature synthesis and optimization of acid leaching process (pp. 27-40)
B4C–TiB2 composite nanoparticles obtained by the method self-propagating high-temperature synthesis (SHS) under atmospheric conditions using oxide feedstocks (B2O3, TiO2) and carbon black and magnesium as reducing agents, as well as the effect of Mg particle size on SHS efficiency. To remove unwanted phases from SHS products, one-stage and two-stage leaching processes were carried out. In the first leaching process with HCl acid, the leaching temperature and duration were optimized. As a result of the second leaching process with the addition of carbon dioxide and H2O2, commercial-quality nanoparticles were synthesized. The results showed that increasing the Mg particle size reduces the SHS efficiency, however, the use of very small Mg particles reduces its efficiency due to Mg evaporation and scattering. The optimal Mg particle size was determined to be 75–150 μm. Since the particle size has a significant effect on the removal of Mg borate phases, the optimal leaching temperature was determined to be 90 °C, and the optimal leaching duration was 60 min. As a result of the optimized leaching processes, B4C–TiB2 nanoparticles with a purity of 99.11%, a size of 193.5 nm, and a surface area of 30.65 m2/g were synthesized.
Keywords: high-temperature self-propagating synthesis, boron carbide, titanium diboride, composite powder, nanoparticle synthesis.
UDC 621.763
E. S. Gevorkyan1, *, D. S. Sofron calculate the specific energy intensity of grinding taking into account the volume of material consumed during processing of the working layer of the wheel. A formula for calculating the specific energy intensity in the case of diamond grinding of ceramic materials is given. It is shown that the plastic mode occurs precisely when the specific energy intensity of grinding becomes close to the specific heat capacity of melting of ceramic materials.
Keywords: diamond grinding, specific energy intensity of grinding, specific heat capacity of melting, ceramic materials, plastic mode.
UDC 621.921.34–492.544.023.5:539.215
G. A. Petasyuk
Institute of Superhard Materials named after V.M. Bakul, NAS of Ukraine, Kyiv, Ukraine
petasyuk@ukr.net
Study of the influence of the method of matching the actual geometric parameters of the grain and its adopted 3D model on the error of determining the coating thickness of diamond powders (pp. 91-102)
The methodological components of the indirect-analytical determination of the coating thickness of diamond powders, which is an important characteristic of them, are analyzed. The importance of the method of matching the actual geometric parameters of the grain and its adopted 3D model as a factor of influence on the error of determining the coating thickness is proven. The results of a comparative study of the influence of the method of matching the actual geometric parameters of the test grain (cuboctahedron) and its adopted 3D models (sphere, cube, ellipsoid) on the coating thickness and the error of its determination are presented.
Keywords: coating, thickness, error, grain, 3D model, ellipsoid, sphere, cube, cuboctahedron.