D. D. Titov

Influence of WSi2 content and additions of magnesium alumosilicates on oxidation and strength properties of MoSi2-WSi2 composites

Samples of MoSi2-WSi2 composite materials with additions of magnesium alumosilicates are obtained by solid phase sintering at 1650–1800°C in an argon atmosphere of powdered mixtures of initial components and disintegrated cast samples of 70% MoSi2–30% WSi2 (Mo0.7W0.3Si2), synthesized in an SHS reactor. The influence of the content of tungsten and oxide additive on oxidation of samples in air at 750°C for 100 h is studied. It is found that 70% MoSi2–30% WSi2 composite materials are less exposed to oxidation than MoSi2 and WSi2, and addition of 20 vol % magnesium alumosilicates decreases the rate of low temperature oxidation.

Effect of mechanical activation of powders on the sintering of calcium carbonate-based ceramic materials containing carbonated hydroxyapatite

79 Calcium carbonate based materials containing carbonated hydroxyapatite are promising as materials for replacing and restoration of bone defects [1]. The key technological drawback of these materials is low temperature thermal decomposition of calcium car bonate, which prevents sintering [2, 3]. This accounts for low strength of materials and precludes using them as implants bearing mechanical load [4]. The activity of ceramic powders toward sintering can be enhanced by mechanical activation (MA) [5].

Effect of thermal treatment on sintering and strength of ceramics from hydroxyapatite nanopowders

The effect of thermal prehistory of hydroxyapatite powders synthesized by precipitation from aqueous solutions on sintering and strength of ceramics produced on their basis was investigated. After synthesis, the initial powders underwent thermal treatment in the temperature range from 400 up to 1000°C, which resulted in the change from a needle-like morphology to a hexagonal one, whereas the individual particle size increased from 15 to 200 nm. Sintering was performed under continuous heating conditions with isothermal soaking at a maximum temperature of 1200°C. It was established that the activity of powders in sintering depends on the temperature of thermal pretreatment. The existence of a maximum at 700°C on the dependence of the ceramic strength on temperature is caused by competing effects of the residual porosity and granule size on the sample strength.

Low-temperature oxidation of MoSi2–Si3N4 composites

Composites in the MoSi2 + Si3N4 system containing 1.0, 2.5, and 5.0 wt % Si3N4 were synthesized by hot pressing at the temperature of 1650°C and the pressure of 30 MPa. Silicon nitride powders of two types of were used as reinforcing additives: one with isometric equiaxed crystals and one with fibrous structure. The samples were characterized by microstructural and phase analyses; the relative density and the flexural strength were determined. Composites with the flexural strength of up to 410 MPa were synthesized. The resistance to low-temperature oxidation of MoSi2 + Si3N4 composites in air at the temperature of 750°C was studied. The increase in the resistance to oxidation of composites with silicon nitride in air compared to pure molybdenum disilicide for both types of silicon nitride powders was established. For all the composites obtained, the parabolic oxidation rate constants were calculated.

Synthesis of aluminum oxynitride (AlON) and study of the properties of ceramics based on it

Aluminum oxynitride Al23O27N5 was synthesized by solid phase synthesis from a stoichiometric mixture of aluminum nitride and aluminum hydroxide at 1850°C in a nitrogen atmosphere. Aluminum oxynitride ceramic was prepared from the synthesized powders by hot pressing without sintering additives. The obtained samples were characterized by scanning electron microscopy and X-ray phase analysis; the mechanical properties of the ceramic samples were measured.

Thermochemical gypsum conversion forming calcium phosphates

A study was carried out on effect of the conditions of physicochemical conversion of a porous gypsum intermediate product to calcium phosphates. Depending on the initial conditions of sample preparation, the materials around hydroxyapatite and dicalcium phosphate were obtained. The conducted thermal analysis and dilatometric studies made it possible to propose the conditions of thermal treatment preventing shrinkage and deformation of samples. After thermal treatment at 1000°C, fine crystalline porous materials were obtained with crystal size between 0.5 and 2 μm and pore size up to 50 μm on the basis of β-tricalcium phosphate with strength up to 2.8 MPa. The developed pore structure and fairly high strength make it possible to use the developed materials based on tricalcium phosphate to obtain biomaterials for the replacement of defects in bone tissue.

Molding Features of Silicon Carbide Products by the Method of Hot Slip Casting

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.

Agglomeration and Properties of Ceramics Based on Partially Stabilized Zirconium Dioxide Containing Oxides of Aluminum and Iron

Agglomeration of ceramics of partially stabilized zirconium dioxide containing 5 wt % of aluminum oxide depending on the amount of additive (iron oxide) was studied. It was shown that introduction of an additive promotes a decrease in agglomeration temperature to 1400–1450°С and formation of a dense structure, as well as acquisition of high strength up to 450 MPa (after agglomeration at 1400°С).

Effect of Reaction Sintering Conditions on Properties of Ceramics Based on Alumina Oxynitride

A comparative analysis of the physicomechanical characteristics and phase composition of Al23O27N5 ceramic obtained by reaction sintering of the mixture of Al2O3 and AlN powders at different temperatures and pressures is carried out. The samples obtained had properties that correlated well with the published data.

Strengthening of composite materials of the fluorohydroxyapatite–zirconia system by titanium nitride

Composite materials of the ZrO2–fluorohydroxyapatite (FHA)–titanium nitride (TiN) system have been synthesized and studied. In the course of sintering even in a protective inert medium, the reaction between the components begins at 700°C to give calcium titanates, titanium oxides, and oxygen-deficient zirconia compounds. As a result of working through the procedure of synthesis of ultrafine powders and selecting sintering regimes, including the hot-pressing method, dense composite materials of the FHA–ZrO2 system containing TiN were obtained with a bending strength of up to 273 MPa and a crack resistance of up to 3.3 MPa m1/2.