Specific Features of the Synthesis of Porous Materials Based on a Magnesium–Aluminum Spinel

Ultrafine powders are synthesized through cocrystallization of magnesium, aluminum, and silicon compounds. Spinel–cordierite two-phase composites are prepared based on these powders. The leaching of a chemically unstable phase in hydrofluoric acid solutions is studied. The optimum conditions are determined for treatment of two-phase materials with the aim of preparing ceramics based on the magnesium–aluminum spinel with an accessible porosity of higher than 50%.     

An Effect of Interelectrode Potentials on an Afterpulse Formation in a Photomultiplier Tube

An effect of the interelectrode potential difference on the intensity of the afterpulse formation in a XP2020 photomultiplier tube is studied; the afterpulses are caused by an ion feedback. It is shown that the photocathode–accelerating-electrode gap plays a decisive role in the process, while the dynode system is of minor importance at pulse currents below a few dozens of milliamperes.     

Wear-Resistant Layered Electrospark Coatings Based on ZrB2

We have studied the composition and tribological parameters (coefficient of friction and wear rate) of coatings obtained in electrospark alloying (ESA) of steel 45 with the composite ceramic ZrB₂ – SiC – B₄C based on zirconium diboride. We have shown that layer-by-layer electrospark alloying using Ti – Al – N composites to form an undercoat reduces the coefficient of friction of the coating down to 0.12-0.20 while maintaining a rather low wear level (7-11 μm/km). We have analyzed the effect of the composition of the secondary structures which are formed during tribo-oxidation under dry friction conditions.     

Tribotechnical characteristics of polymer composites reinforced with fibrous structures

Studies have been made on the effects of the nature, textile structure, and strength characteristics of fibrous reinforcement and on hybrid reinforcement, nature of the polymer matrix, and the addition of ultrafine diamond powder on the coefficient of friction and wear of a polymer composite containing a thermoreactive matrix. The tests were performed in air without lubricant with an insert-shaft pair scheme with counterbody composed of chromed cast iron and with a ceramic counterbody (boron carbide, silicon carbide and nitride) at sliding speeds of 5, 10, and 15 m/sec and pressure 0.5 MPa. Glass plastics show more wear than carbon plastics on reinforcements with woven or knitted structures. The carbon plastics have tribotechnical properties at the level of the best ones. The ultrafine diamond powder substantially reduced the wear. The best tribotechnical properties occurred with the friction pair carbon-glass plastic against silicon nitride.     

The influence of tungsten compounds on the synthesis and properties of polyaniline

Aniline was oxidized in an acidic aqueous medium with ammonium peroxydisulfate in the presence of various concentrations of tungsten compounds. The oxidation has two phases: an induction period followed by the exothermic polymerization. The course of oxidation was monitored by recording the reaction temperature or pH. The introduction of 2 mol% sodium tungstate (relative to aniline) prolonged the induction period from 5 to 30 min. Such molar concentration of tungstosilicic acid delayed the onset of polymerization by 120 min. The effect of sodium molybdate was less pronounced; sodium chromate had no influence on the course of oxidation. The presence of tungsten compounds had not affected the conductivity and molecular weight of the produced polyaniline. FTIR spectra and density determinations have proved that tungstate and tungstosilicate counter‐ions have been incorporated into polyaniline when they were present in the reaction mixture. Copyright © 2005 Society of Chemical Industry     

Effect of hydrogen on improving purity of WC and AlN powders

A method for WC and AlN treatment in hydrogen is discussed. Excellent results were achieved in the purification of WC. It was noticed that the powders treated in hydrogen were moulded without a binder and sintered at much lower temperatures.     

Phase equilibria in vanadium-rich alloys of the V-Ni-Al system

Vanadium-rich alloys of the V-Ni-Al system were studied by the methods of metallographic, x-ray diffraction, and electron beam microprobe analysis. The boundaries of the phases, and the vertices of the conoidal triangle αβσ, in the vanadium corne, of the 1200°C isothermal section were determined. The maximum solubility of aluminum in the σ-phase is 6 at. %. The homogeneity range of the NiAl-based β-phase is very broad; the maximum solubility of vanadium in β reaches 41.5 at. %. The maximum solubility of nickel in the vanadium solid solution is 25 at. %. Alloys containing 15–20 % Al and 20–30% Ni exhibit a tendency to dispersion haraen and, therefore, might serve as a basis for the development of a new generation of radiation-resistant materials. Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 43–47, July–August, 1997.     

Compatibility and biocompatibility study of new HPC/PU blends

BACKGROUND: Polymer blending is one of the most useful methods for the improvement or modification of the physicochemical properties of polymeric materials without altering the structure and function of individual polymers. The blends between biopolymers and synthetic polymers are of particular significance because they can combine biocompatibility with good processability and mechanical resistance and can be used as biomaterials. The aim of the blending of hydroxypropylcellulose (HPC) and polyurethane (PU) is to find applications for newly synthesized PUs and also to create new materials with possible medical applications and enhanced surface properties. RESULTS: Films containing mostly HPC or mostly PU are found to be homogeneous and transparent, while for the intermediate composition range a morphology of a fine dispersion in a continuous matrix is characteristic. The values of the blood–biomaterial interfacial tension (γ_SL) are in the range 1.96–3.27 mN m^?1, which allows us to conclude that these materials have a good haemocompatibility. CONCLUSION: The thermomechanical and morphological behaviour were explored and specific interactions were evident between the PU blocks and the HPC chains especially in the 60% HPC–20% HPC/40% PU–80% PU composition range because of the high degree of compatibility. The blends obtained are not cytotoxic and exhibit good surface properties and haemocompatibility. Therefore they could be candidates for medical and pharmaceutical applications. Copyright © 2008 Society of Chemical Industry     

Sensor composites consisting of a ceramic substrate and thin films of TbOx oxides and (TbOx)0.5(YO1.5)0.5 solid solutions

A porous nanoceramic material based on aluminum magnesium spinel is synthesized. Films based on terbium oxide and the (TbO _x )_0.5(YO_1.5)_0.5 solid solution are prepared by the sol-gel processing and thermal vacuum evaporation onto a MgAl₂O₄ substrate. The temperature dependences of the electrical resistance of the films in air and CO₂ are investigated. The maximum values of the relative sensitivity coefficient of the films under investigation are determined.