Papers by Keyword: Phase

Abstract: A methodology for analytical stability assessment of individual compressed flexible phases of discretely heterogeneous composite elements of engineering structures is proposed to ensure their reliable safe operation and minimise the consequences of emergencies. Based on the energy balance equation for the proportional forces of a normal resistance of the medium to the phase displacement, expressions are obtained for determining the critical force, taking into account the possible initial curvature (non-rectilinearity) of a single phase in the elastic medium of the matrix for three possible cases of stability loss. The approbation of the results of the study on the example of deformation features of reinforcing bars in a compressed reinforced concrete column is presented.

Abstract: Thermal upgrading is the process for nickel extraction in selective reduction with holding temperature in low (300-500 °C). The effect and type of reductor are the main factor during this process. With those factors, this research will be finding the variation of reductor type. The first step is limonite and reductor characterization. Ni, Fe, Mg, Al, and Si levels in limonite are 1.4 Ni, 50.5 Fe, 1.81 Al, 4.86 Mg, and 16.5 Si weight percent, respectively. The iron oxide/oxyhydroxide content of limonite is 94.4 percent and 5.6 percent silicate. For reductor, those are graphite, palm kernel shell, and anthracite with carbon percentage 98, 77, and 68 %. From XRF, the optimum nickel grade is in the graphite and anthracite with 6.5 and 7 wt%. For phases, the ferronickel is appearing in the high intensity for the optimum reductor type and the microstructure is around 5-10 um for both. Moreover, the optimum reductor type are graphite and anthracite. Keyword: reductor type, limonite, phase, microstructure, thermal upgrading.

Abstract: Using differential scanning calorimetry, phase transitions in polycarbonate-polytetramethylene oxide block copolymers were studied. It is shown that, depending on the ratio of rigid polycarbonate and flexible polytetramethylene oxide units, block copolymers can be two-phase or four-phase. It is shown that phase transitions in copolymers of a polyester-polyether depend on the ability to crystallize the components.

Abstract: In this work, preparation of Fe_1.025Se samples was done using a solid-state reaction. Iron and selenium powder were used as raw materials. The raw materials were milled using a shaker mill for 5 hours after weighed in an atomic ratio of Fe:Se=1.025:1. To find out the formation of polycrystalline Fe_1.025Se, the milled powder was then compacted in a stainless-steel tube and sintered at a temperature of 355°C (for sample 1) and 745°C (for sample 2) for 6 hours. All samples were sintered in the air atmosphere and cooled rapidly in the air. XRD was used to analyze the phase formation. Based on the diffraction pattern calculation, the sintered sample at a temperature of 745°C has a higher mass fraction of the tetragonal phase than the sample sintered at 355°C. The lattice parameters of the sample sintered at a temperature of 745°C are a = 3.7688 Å and c = 5.5236 Å. According to the resistivity measurement results, it appears that the sample sintered at 745°C has a critical temperature onset of ~13.28 K.

Abstract: The relationship between the phase composition and the Young’s modulus in quenched PT-7M, Ti-6Al-7Nb, BT16 titanium alloys has been studied using the structural analysis, thermodynamic calculations in the Thermo-Calc software and micro-indentation. It is found that the nature of the change in the Young’s modulus in the investigated titanium alloys after quenching from the two-phase α+β-region depends on the chemical composition of the alloy, which determines the nature of the observed metastable phases (α', α", ω, β). The correlation between the extreme change in the Young’s modulus from the quenching temperature and the so-called interatomic bonding force (F_b) calculated from the electronic structure parameters of the α, α', β phases was shown for the Ti-6Al-7Nb alloy. The relationship between the limits of the Young’s modulus of the investigated alloys during quenching with the level of their alloying with α-and β-stabilizers is shown.

Abstract: The purpose of the work is the obtaining of magnesium silicate ceramic proppants, based on ultrabasic overburden rocks of Kempirsai deposits of chromite ores (Kazakhstan). The chemical and mineralogical composition of ultrabasic overburden rock was studied by chemical, microscopic and X-ray diffraction analyzes. It is established that the main mineral of ultrabasic overburden rocks is serpentine, present in the form of fibrous chrysotile and lamellar antigorite. In the impurities are iron oxides and hydroxides, chrome spinel, carbonates, quartz. Assessment of the use of overburden rocks as a raw material for the production of ceramic proppants was carried out. The sintering interval of overburden rocks was determined at 1280-1300 °C. The sintering firing optimum temperature of ceramics, based on this type of raw material is 1300 °C. It is established that to harden the structure of magnesium silicate ceramic it is necessary to activate the raw material thermally at a temperature of 1000 °C. The influence of binder type on the properties of magnesium silicate proppants, based on the Kempirsai serpentinites was studied. Magnesium silicate proppants, based on ultrabasic overburden rocks, were obtained with the following properties: apparent density – 1.6 g/cm³, strength resistance (52 MPa) – 14%, sphericity and roundness – 0.8; chemical resistance (hydrochloric acid) – 98%, static strength of the fraction 16/20 - 72–118 N/granule. The field of application is oil and gas production, metallurgy and ceramic industries.

Abstract: The necessity of finding scientifically grounded methods for the development of new heat-resistant, wear-resistant and corrosion-resistant aluminum alloys is presented in the present work. For this purpose, the analysis of modern methods for computer calculation of phase diagrams in multicomponent metal systems using the Thermo-Calc program was carried out. Therefore, a quantitative analysis of the phase diagram the Al-Cu-Mn-Zr system was carried out, as the basis of deformable high-temperature aluminum alloys. Isothermal and polythermal sections of the phase diagram were calculated in this system. The temperatures of phase transformations were calculated. The mass and volume fractions of the phases in the studied alloys were calculated. The range of concentrations and temperatures at which the maximum amount of dispersoids Al₂₀Cu₂Mn₃ may be achieved, was defined. The minimum amount of Al₂Cu phase is calculated, which should correspond to the best heat resistance of alloys. It is substantiated that in the alloys of a new generation of ALTEK type, the use of homogenization and quenching operations is inexpedient, which implies the possibility of a significant reduction in the cost of heat treatment in comparison with industrial alloys, such as 1201.

Abstract: Yttrium aluminum garnet Y₃Al₅O₁₂ (YAG) nanopowders were synthesized from co-crystallized precursors of Y₂(SO₄)₃, Al(NO₃)₃-Al₂(SO₄)₃ and Y(NO₃)₃ with a three-layer core-shell structure. X-ray diffraction (XRD) pattern indicated that too much was detrimental to the synthesis of pure phase YAG because of the serious separation between Y₂(SO₄)₃ and Al(NO₃)₃-Al₂(SO₄)₃. Transmission electron microscopy (TEM) revealed that was beneficial for the dispersion of the powders owing to the high decomposition temperature of . The powders with the n()/n(Y³⁺) mole ratio of 1.5/3 calcined at 1050°C showed good sintering activity.

Abstract: The properties of Ti-43Al-9V-Y alloy powders, which were produced by cold crucible melting and argon gas atomization, were investigated. The results showed that the size of the powders was normal distribution in a range of 10-210μm. The powders possessed a near perfectly spherical shape. The microstructure of the powders was composed of dendritic and cellular crystal grains, and the dendritic crystal grains decreased in finer particles. The X-ray diffraction result indicated that there were two main phases, α2 and B2 in the powders, and the amount of B2 phase increased as the particle size decreased. In addition, the oxygen and nitrogen contents were below 1000ppm and around 140ppm, respectively.

Abstract: The evaluation of heterogeneous materials used in civil engineering on the microscopic level has become important aspect in proper understanding of the macroscopic behavior of the material. This contribution aims at advantages and problems related to the technique of grid indentation and at the evaluation of mechanical properties.