Special features of manufacturing highly porous materials from silicon nitride,silicon oxynitride,and sialons

Results obtained in a study of factors that affect shaping and sintering of highly porous materials are presented. A technology providing highly porous silicon nitride materials that is based on shaping preliminarily fabricated pieces of thermoplastic slip makes it possible to use initial silicon powders of different dispersities. Highly porous materials can also be produced on the basis of sialons and exhibit a diminished thermal conductivity and a heat resistance at the level of similar silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 8 – 13, November, 1996.     

Analysis of the response of piezopolymer pressure gauges to a plane shock wave

We consider a phenomenological model for piezopolymer pressure gauges designed for registration of plane shock-wave pulses. We analyze the response of the gauges taking into account the physical phenomena observed in polarized polymer films upon action of high-intensity shock waves, the thermodynamic state of the material comprising the sensitive element, and the measurement circuit parameters. We compare the numerical calculations with experimental data for gauges made from polyvinylidene fluoride in the dynamic pressure range up to 16 GPa. We show that at such pressures, the electrical response is mainly determined by the change in the residual polarization of the piezofilm as a result of its compression.Institute of Chemical Physics at Chernogolovka. 142432 Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 130–135, May–June 1994.     

Advanced Design of Scanning Infrared Focal Plane Arrays

Modern designs of time delay and integration (TDI) IR linear scanning focal plane arrays (IR FPAs) are analyzed. Advanced designs of linear IR FPAs with increased sensitivity and spatial resolution are proposed. The analysis is based on Monte-Carlo simulation of the diffusion of photogenerated charge carriers in photodiode arrays based on mercury–cadmium–telluride epitaxial layers taking into account the main photoelectric and design parameters of the detectors and optical system.     

Determination of <Emphasis Type="Italic">P</Emphasis>,<Emphasis Type="Italic">T</Emphasis>-conditions developed at high-temperature shock compression of silicon nitride in planar recovery ampoules

We performed experiments on shock compression up to pressures of 36 and 50 GPa of mixed samples of silicon nitride and potassium bromide, placed between copper plates that serve as walls of a recovery ampoule. For comparison, similar experiments were carried out by the conventional compression of a mixture of silicon nitride and copper powder. The loading of the samples was fulfilled by means of aluminum flyers accelerated by products of explosion to a few kilometers per second. The pressure profiles prior to a shock wave entering the sample and after its runout were measured with the use of manganin sensors. It is found that for the configurations of the experimental assembly used, the pressure in the samples, accumulated by circulating the shock wave, reaches the desired value before unloading. Based on estimates of the rate of heat transfer between the components, it is shown that thermal equilibrium can be set during the existence of high pressure in the mixed samples. Within the framework of the single-temperature medium model, the equations of state of the samples are derived, and the temperatures of their shock compression are calculated. Using these equations, we performed numerical simulations that showed good agreement with the experimental data.     

The burst character of thermoelastic shape-memory deformation in crystals of Cu-Al-Ni alloys

We have revealed and investigated the burst character of shape-memory deformation (SMD) in crystals of Cu-13.6 wt % Al-4.0 wt % Ni alloys. We have found that, after giving SMD to 8% when compressed in the direction of the [100] axis and subsequent heating on the solid base with an additional weight of 400 g, the system can rebound up to a height of 55 mm at a speed of ≈1 m/s. The calculations showed that, in the absence of load, a crystal with a weight of 0.8 g (in on absence of air friction) can rebound to a height of 27.5 m with a velocity of 23 m/s when rising from the base. The mechanism of such an unusual behavior of shape-memory deformation in this alloy was studied.     

Assessment of the effect of particle size on the rate of temperature alignment in systems used for shock-wave synthesis of diamond,cubic boron nitride,and γ-silicon nitride,based on a simple model

The change in the spatial distribution of relative temperatures in the system of a spherical particle located in the center of a spherical matrix is simulated. Silicon nitride (Si₃N₄) and boron nitride (BN) are considered in a matrix of potassium bromide (KBr); graphite, diamond, and silicon nitride are studied in a copper matrix. Calculations are performed for the four sizes of particles: 1, 5, 20, and 100 μm. It is shown that the temperature is equalized by approximately 80% in 1 μs in the particles of Si₃N₄ and BN with a size of 5 μm in the KBr matrix. In the system of silicon nitride–copper, such alignment is performed for a particle with a diameter of 20 μm. For a diamond particle in the copper matrix, the particle size may be even greater. The particle sizes for which calculations showed a rather high rate of heat transfer in a time of ~1 μs either match or are somewhat larger than the particles of diamond, cubic boron nitride, and γ-silicon nitride formed during the real shock-wave synthesis of these materials.     

Corrosion of Heating Surfaces of Power Station Boiler Equipment Made of Steel 12X18H10T

The long-term operation of thermal power equipment made of 12X18H10T steel at a temperature of 550°C and higher changes its performance due to the changed composition of inside surfaces and bodies of tubes. To avoid deterioration of service characteristics during the operation, the thermal equipment is recommended to make of low-carbon chrome-nickel stainless steels or niobium-stabilized steels. Preservation of the equipment by octadecylamine should be carried out only at a working temperature below its thermodestruction temperature.     

Cyclic degradation of material in vehicle components

A nonstandard approach to the fatigue strength of materials and structures is proposed, within the framework of the complete-diagram method. The use of the cyclic-degradation model in calculating the life of vehicle components is illustrated. In supercritical cycling, linear summation of the damage is possible in some situations.