Growing of Tubes with a Small Inner Diameter from the Melt by the Stepanov Method

A mathematical model is suggested for describing the growth of a crystal tube with a small inner diameter from the melt by the modified Stepanov method with the tube being affected by temperature pulses. The behavior of the inner and outer radii of the tube as a function of the amplitude and duration of temperature jumps is studied.     

Starting and operating regimes of vacuum plasmatrons with hollow cathodes

Optimization of starting regimes of industrial plasmatrons is considered. Dependences of the surface temperature in the bath with liquid metal on the inputted specific power are obtained. These dependences may be used for determining the optimal melting conditions and calculating the kinetic regimes for refining metals.     

Determination of the half-life of the spontaneous fission of240PU

Two metallic²⁴⁰Pu sources were certified as reference standards of spontaneous-fission activity and neutron flux. The certification results were used to determine the ratio T_αT_s&f of the alpha-decay and spontaneousfission half-lives of²⁴⁰Pu. The ratio was found to be (5.68+-0.11)·10^−8, which corresponds to T_s&f =(1.16+0.02)·1011 yr for an assumed value T_α=6563+7yr.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 57–58, February, 1995.     

Structure and properties of polyimide‐bonded magnets processed from prepolymers based on diacetyl derivatives of aromatic diamines and dianhydrides

We report a novel method of polyimide (PI) synthesis from prepolymers based on dianhydrides and diacetyl derivatives of aromatic diamines that facilitate the preparation of a melt processable mixture at 300 ± 10°C of the prepolymer and magnetic Nd‐Fe‐B alloy to provide PI‐bonded magnets with enhanced properties. It is shown that chemical structure of the prepolymers strongly influences viscosity behavior via crystallization of the oligoimide in the melt, leading to formation of PI with rigid‐rod like structure. This structural ordering of the prepolymers based on diacetyl derivative of diamine used in this study, if not controlled, leads to exponential increase of melt viscosity with time, making it practically impossible to prepare melt processable mixture of the magnetic particles and the PI prepolymers at elevated temperatures. The results obtained demonstrate that appropriate dianhydrides and diacetyl derivatives of diamines that do not lead to crystallization of oligoimides in prepolymer mixture can be used under controlled processing conditions to prepare melt‐processable PI‐bonded magnets containing rigid‐rod like PI structure that significantly increases thermal stability of the magnets. The temperature dependencies of the magnetic properties of the PI‐bonded magnets under conditions that they are likely to encounter during their service life were found to be remarkably similar to that of commercial thermoplastic magnets such as injection‐molded nylon magnets. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 478–485, 2006     

Acoustic emission data on delayed damage processes in the vicinity of defects in fibre-reinforced plastics

Analysis of the time intervals between acoustic emission (AE) signals in composites makes it possible to study defect mechanisms induced by stress transfer near the previously arisen defect. Unidirectional carbon fibre-reinforced plastics (CFRP) with matrices of different plasticity have been investigated during tensile deformation. There is a characteristic delay time, ₁ between the correlated appearance of defects. For these materials, ₁ ranges from 50–500 s. In the model considered here, ₁ is determined by the time for which the zone of plastic deformation formed at the place of fibre breaking and widening during local stress relaxation, is extended to the neighbouring fibres. Thus, the fibre is overloaded, which may lead to its breaking. The effect of viscoelastic properties on ₁ is discussed. This delay time decreases with the plasticity of the matrix. These data also show that the zone of localized deformation at the broken fibre can cover several layers of neighbouring fibres.