Use of Combined Methods of Successive Carburizing and Nitriding of Martensitic Steels in Low-Pressure Atmospheres

Metal Science and Heat Treatment - The paper discusses combined conditions of saturating martensitic steel with carbon and nitrogen using low-pressure atmospheres. The studied conditions include...     

Diffusion potentials and transport numbers in molten alkali chlorides and their binary mixtures

Diffusion potentials at porous asbestos diaphragms separating chloride melts of different cation compositions have been measured as functions of temperature making use of cells with chlorine electrodes. Between individual molten alkali chlorides the diffusion potentials were found to increase with the difference in their cation radii reaching a maximum of ～ 35 mV for

and a minimum of ～ 2 mV for

The melts with smaller alkali cations were more electropositive in all cases. From the experimental data for the systems

where M₁  Cs or K and M_II  Li or Na, transport numbers of those cations were computed as functions of N. They proved to be smaller for Li⁺ and Na⁺ and larger for Cs⁺ and K⁺ as compared with their additive values. The cation mobilities were calculated. For Cs⁺ or K⁺ they are a little higher in the salt mixtures than in their individual chlorides whereas for Li⁺ or Na⁺ they are considerably lower. Such changes in cation transport numbers and mobilities can be explained in terms of autocomplex structure model for molten alkali halides developed recently by M. V. Smirnov.     

Tribological behaviour of a 3Y-TZP/Ta ceramic-metal biocomposite against ultrahigh molecular weight polyethylene (UHMWPE)

This study aims to evaluate the tribological behaviour of 3Y-TZP/Ta (20 vol%) ceramic-metal composites and 3Y-TZP monolithic ceramic prepared by spark plasma sintering (SPS) against ultrahigh molecular weight polyethylene (UHMWPE). According to the results of pin (UHMWPE)-on-flat wear test under dry conditions, the UHMWPE – 3Y-TZP/Ta system exhibited lower volume loss and friction coefficient than the UHMWPE – monolithic ceramic combination due to the presence of an autolubricating layer that provides sufficient lubrication for reducing the friction. Owing to the lubrication of the liquid media, under wet conditions obtained using simulated body fluid (SBF), similar behaviour is observed in both cases. Additionally, the ceramic and biocomposite materials were subjected to a low temperature degradation (LTD) process (often referred to as “ageing”) to evaluate the changes in the tribological behaviour after this treatment. In this particular case, the wear properties of the UHMWPE-biocomposite system were found to be less influenced by ageing in contrast to the case of the UHMWPE-zirconia monolithic material. In addition to their exceptional mechanical performance, 3Y-TZP/Ta composites also showed high resistance to low temperature degradation and good tribological properties, making them promising candidates for biomedical applications, especially for orthopaedic implants.     

Effect of Process Parameters on the Structure and Physicomechanical Properties of Nonwoven Materials Manufactured by Aerodynamic

The optimum design of nozzle devices that provide for maximum aerodynamic drawing and stable web formation in manufacture of fibre nonwovens from polymer solutions is selected. The effect of the specific viscosity of the spinning solution on the diameter of the fibres in the nonwoven material is assessed. The conditions of manufacturing fibre materials of sufficiently high strength consisting of fibres of minimum diameter are determined.     

Thermal Decomposition of Triaminoguanidinium Nitrate

The kinetics of thermal decomposition of triaminoguanidinium nitrate (TAGN) was studied for the solid and liquid (solution) states of aggregation. The decomposition of crystalline powdered TAGN develops with severe self-acceleration. Its formal kinetic characteristics are determined. The main cause of the acceleration is the progressive melting of the solid during its thermal decomposition. The decomposition of TAGN in solution is severalfold faster than that in the solid state and proceeds at a rate decreasing with time. The main gaseous products of TAGN decomposition are N₂, N₂O, and H₂O. The chemistry of the processes involved in TAGN decomposition are discussed. Key words: thermal decomposition, triaminoguanidinium nitrate, oxidizer.