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Using structural analysis methods (metallographic, X-ray diffraction, differential scanning microscopy), a comprehensive study of the structure of Al82Cu7Fe11 alloy, obtained in the form of ribbons by the melt spinning method, was carried out. It is shown that a multiphase amorphous-nanocrystalline structure of high dispersity is formed in the alloy, which includes a solid solution based on aluminum, intermetallic compounds Fe4Al13 and CuAl2, and a small amount of a quasicrystalline phase of the composition Al–Fe–Cu with a tenth order symmetry axis (decagonal). The parameters of crystal lattices of phases and their volumetric content have been certified. It is shown that the main structural component of an alloy is iron aluminide, the content of which varies from 68 to 61 wt % across the ribbon cross section from the contact to the free surface. The temperatures of phase transformations in the alloy upon heating were determined. A comparative analysis of the structures on the basis of the phase composition and morphology of phases formed in rapidly quenched ribbons and an ingot of the same composition crystallized under equilibrium conditions was carried out. A difference in the alloy structure after different methods of crystallization has been established. The microhardness of the main structural components in the ingot was determined. Iron aluminide has a maximum hardness of 780 HV. It has been shown that the high hardness of 615 HV of the alloy after high-speed quenching is ensured by the formed multiphase amorphous-nanocrystalline state of the structure. [ABSTRACT FROM AUTHOR]

We employed contact alloying in the range 1000–1860°С to study the reaction specifics between SiC and Al2O3−(t + m)ZrO2(Y2O3) oxide composition. Real-time experiments with photographic recording of the changing size and shape of the Al2O3−(t + m)ZrO2(Y2O3) sample on a SiC ceramic substrate showed that Al2O3−(t + m)ZrO2(Y2O3) compositions react with the silicon carbide substrate in the range 1720–1860°С to melt and penetrate into (impregnate) the substrate. X-ray powder diffraction patterns were measured for samples taken from the contact area of the oxide composition with SiC directly on the substrate and in a chipped-off <1-mm-deep near-surface layer. ZrС, Al2Y4O9, and Al3.21Si0.47 were formed in the contact area via redox reactions involving oxide melt, in addition to 6H-SiC, Si and Al2O3, t-ZrO2 phases, which are the initial components of the substrate and oxide composition, respectively. [ABSTRACT FROM AUTHOR]

Cerium-containing tricalcium phosphate (TCP, Ca3(PO4)2) nanopowders with the whitlockite structure have been prepared via precipitation from solution. After heat treatment at 1300°C, the materials contained 0, 0.07, 0.18, and 0.39 wt % cerium, which corresponded to х = 0, 0.0025, 0.006, and 0.013 in the general formula Ca3 –хCe2х/3(PO4)2. The thermal stability of β-TCP has been shown to increase with increasing cerium content. The synthesized cerium-containing TCP powders show luminescence properties under excitation at wavelengths from 270 to 320 nm, with a peak emission wavelength from 360 to 390 nm, characteristic of Ce3+ luminescence. Varying the percentage of cerium in the materials and heat treatment temperature causes the emission spectrum to shift. [ABSTRACT FROM AUTHOR]

Si3N4-based ceramics have been produced by hot pressing in the temperature range 1550–1650°C using α-Si3N4 starting powder and CaO–Al2O3 (48 : 52 wt %) sintering aids. The powders and the ceramics have been characterized by dilatometry, scanning electron microscopy, and X-ray diffraction, and we have measured the microhardness and density of the ceramic samples. The results demonstrate that the sintering aid reacted with Si3N4 to form Ca-α-SiAlON. At 40 wt % sintering aids, all of the silicon nitride was converted into Ca-α-SiAlON. We have clarified general trends in the effect of the amount of sintering aids on the properties of the ceramic samples. [ABSTRACT FROM AUTHOR]

The compaction of initial powders, the bending strength, and the microhardness of 21R sialon ceramics obtained by hot pressing have been studied experimentally. It is found that the Sm2O3 sintering additive substantially reduces the annealing temperature and enhances the properties of the ceramics. The samples of 21R sialon ceramics without additives, which are prepared by annealing at 1950°C, have a density of 3.01 g/cm3, a bending strength of 240 ± 15 MPa, and a Vickers microhardness of 16.2 ± 0.4 GPa; the samples of 21R sialon ceramics with 2.5 wt % Sm2O3, which are annealed at 1750°C, are characterized by a density of 3.39 g/cm3, a bending strength of 315 ± 16 MPa, and a Vickers microhardness of 21.9 ± 0.2 GPa. It is shown that Sm2O3 reacts with 21R sialon in the temperature range of 1600–1700°C to form the 27R sialon and SmAlO3 impurity phases. In the samples annealed at 1750°C, the 27R sialon and Sm–sialon (Sm3Si2.5Al3.5O12.5N1.5) impurity phases are detected. [ABSTRACT FROM AUTHOR]

Powders of cerium-containing hydroxyapatites (Ce–HA) with an estimated cerium concentration of up to 0.5 mol % have been synthesized. The phase formation and luminescent properties of the compounds after heat treatment in oxidizing and reducing atmospheres have been investigated. It has been shown that a high HA luminescence intensity can be achieved by preventing the cerium(III) → cerium(IV) transition in a reducing atmosphere at 900–1200°C, as well as by cosubstitution of Ce3+ and Li+ ions for Ca2+ ions to compensate for the excess charge of the additive. The dependence of the luminescence intensity of materials on the heat treatment temperature and cerium concentration is shown. [ABSTRACT FROM AUTHOR]

X-ray amorphous ribbons of aluminum-based alloys doped with transition (Ni, Fe) and rare earth (La) metals in various ratios were obtained by melt spinning. The mechanical characteristics and fracture surfaces of the ribbons under conditions of uniaxial tension with speeds from 0.01 to 10 mm/min were studied. It was shown that, with an increase in the rate in all investigated alloys, the strength limit increases and low plasticity remains. Inhomogeneous deformation is realized by the initiation and spread of shear bands. The mixed fracture surface indicates a brittle-viscous fracture with a high ratio of the viscous component. A significant influence of the scale factor on the strength characteristics of the ribbons was confirmed. The tensile strength of the ribbons increases with rising iron content and decreasing nickel content when the influence of the scale factor is excluded. It is experimentally shown on ribbons with a low-melting tin coating that local heating in shear bands reaches the melting point of tin of 231.9°C. [ABSTRACT FROM AUTHOR]

The elemental mapping of a hard magnetic powder Fe–30Cr–8Co alloy prepared at different charge mixing times allows us to find that a homogeneous distribution of the components is reached upon mixing for 60 min. The dependence of the magnetic hysteretic properties of the powder Fe–30Cr–8Co alloy samples sintered at 1200°C on the mixing time exhibits logarithmic behavior. At the same time, the magnetic hysteretic properties of the same samples sintered at 1400°C are higher because of lower residual porosity and are independent on the charge mixing time. [ABSTRACT FROM AUTHOR]

Abstract—Hydroxyapatite powders containing up to 2.4 mol % Cu (Cu-HA) have been synthesized via precipitation from solution. The synthesized materials have been characterized by X-ray diffraction after heat treatment in the temperature range from 900 to 1400°C and their lattice parameters and crystallite size have been determined. We have studied the bending strength and microstructure of Cu-HA-based ceramics. The results demonstrate that the addition of more than 0.8 mol % copper reduces the thermal stability of HA, leading to its partial decomposition to monoclinic tricalcium phosphate (α-TCP) and its transformation into the hexagonal phase (β-TCP), with possible concentration of the copper in it. Increasing the percentage of copper leads to a decrease in HA sintering rate in combination with an increase in crystallite size and porosity. According to in vitro biological investigations, the ceramic materials are cytocompatible and their surface has marked matrix properties. [ABSTRACT FROM AUTHOR]

We study the effects that the morphology of nickel nanopowders obtained by chemical metallurgy, nickel formate thermal decomposition, and wire electrical explosion has on the properties of porous samples fabricated from these nanopowders using the powder metallurgy method. Porous nickel samples are prepared from a mixture of nickel powder (30 vol %) and ammonium bicarbonate (70 vol %) by sintering in a flow of hydrogen at 700°C and under a pressure of 300 MPa. Samples fabricated from the nickel nanopowder obtained by the wire electrical explosion method have the highest total and open (65.8%) porosities. Samples fabricated from the other two types of nickel nanopowders have lower porosity. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of sintering of nanosized (20 nm) and microsized (0.7-0.9 μm) hydroxyapatite (HA) powders with continuously increasing temperature at a constant rate was studied by dilatometry. The sintering of the HA micropowders within the temperature range 1100-1300°C occurred by the mechanism of diffusion-viscous flow of crystalline particles. The kinetics of the process was described by a power-law function of time; i.e., the process rate depended on current shrinkage. The shrinkage of the nanopowders within the sintering temperature range was directly proportional to temperature, occurred by the law of viscous flow of amorphous particles, and was independent of the temperature increase rate. The apparent sintering activation energies of the studied micro- and nanopowders were 180 and 60 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The high-temperature solid-phase interaction of hydroxyapatite (HA) with magnesium, strontium, and zinc nitrates at the stage of annealing of ceramics was investigated. The phase composition and unit cell parameters of the obtained materials were studied for various metals introduced into the structure to different concentrations. The introduction of Mg led to partial decomposition of HA to tricalcium phosphate and tetracalcium phosphate, the addition of Sr caused partial formation of tetracalcium phosphate from HA, and the doping with Zn gave rise to single-phase HAs. [ABSTRACT FROM AUTHOR]

Abstract—: This paper presents dilatometric analysis data for the sintering of off-the-shelf molybdenum disilicide (MoSi2) powder prepared by magnesiothermic synthesis. We have obtained continuous shrinkage curves for MoSi2 powder compacts with an initial relative density of 70% at different heating rates: 5, 10, 20, and 30°C/min. From a quantitative analysis of densification curves for the compacts, the activation energy for the initial stage of sintering has been determined to be Q = 695 kJ/mol. It has been shown that the dominant process in the initial stage of MoSi2 powder sintering is volume diffusion from grain boundaries and surfaces. [ABSTRACT FROM AUTHOR]

The effect of the content of temporary process binder (paraffin, oleic acid, and beeswax) in the range of 10-18% on the molding of the silicon carbide products using hot slip casting has been studied. It has been determined that the flawless compact blanks based on SiC with Y3Al5O12 can be prepared at the TPB content of 14%. The conditions of four-stage heat treatment of the specimens during removal of TPB have been determined. The bending strength of the ceramic specimens prepared by sintering of the blanks at 1800°C is 437 ± 0.2 MPa. [ABSTRACT FROM AUTHOR]