Physicomathematical Modeling of Explosive Dispersion of Liquid and Powders

Studies have been conducted with respect to the generation of fine‐disperse aerosols with the use of an explosive disperser model based on hydrodynamic shock tube. The physicomathematical model for the process of explosive dispersion with the aforesaid design is described [1]. The use of elements in the model design to produce cavitation bubbles under the action of shock wave and ensurance of slower outflow process of a water‐steam mixture makes it possible to obtain liquid disperse aerosols. The experimental results for aerosol disperse parameters and the processes of initiation and propagation of an aerosol cloud produced upon explosive dispersion of a variety of liquids and condensed powders are presented. Pressure values in the combustion chamber of the disperser, velocity of aerosol particles, and aerosol disperse parameters were obtained. The design of the explosive disperser with a nozzle, which provides favorable conditions for cavitation processes inside the dispersed liquid, is shown to allow the generation of a high dispersity aerosol (about 1–100 nm), which is essential for many practical problems. The function of distribution of such particles by size cannot be measured reliably and directly by methods available; however, indirect experiments (measurement of humidity when dispersing water) permit estimating the existence of particles in the aerosol with sizes below 1 μm in quantity of approx. 90 %.     

Thermodynamic modeling of BCN chemical vapor deposition from <Emphasis Type="Italic">N</Emphasis>-trimethylborazine + ammonia mixtures

Low-pressure (13.3 and 1.33 Pa) chemical vapor deposition in the B-C-N-H and B-C-N-H-O systems from N-trimethylborazine + ammonia mixtures has been analyzed in a wide range of deposition temperatures, 300–1300 K, using thermodynamic modeling. The results indicate that the presence of oxygen adds significant complexity to the composition of condensed phases. We have examined the feasibility of producing films of various compositions and determined deposition conditions. Oxygen-free deposits can be obtained at high temperatures. At temperatures of 600 and 700 K, the limiting composition of the condensed phase, B: N: C = 1: 1: 1, can be reached at a total pressure in the system of 1.33 and 13.3 Pa, respectively.     

A microchannel avalanche photodiode with a fast recovery time of parameters

The design and operation principle of a novel microchannel avalanche photodiode with the short recovery time of parameters are considered in this Letter. A distinctive feature of the new device is that at the operating potential on it, the n ⁺ regions (pixels) deeply submerged into the epitaxial layer with p-type conductivity are completely depleted; thus, the possibility of accumulation of multiplied charge carriers in them is carried out. This enables attaining the recovery time of pixels in the device of ~50 ns at photocurrent amplification factor equal to 250.     

Sintering of SHS-produced α-Si<Subscript>3</Subscript>N<Subscript>4</Subscript>, α-SiAlON,and β-SiAlON

Explored was the sintering of SHS-produced α-Si₃N₄, α-SiAlON, and β-SiAlON in the presence of sintering aids such as Y₂O₃ and Al₂O₃. Process conditions were optimized to prepare sintered sialon ceramics with a high relative density and good strengths characteristics.     

Properties of powder produced by a high-speed method

A high-speed method of powder production is analyzed. X-ray, chemical, and granulometric analysis indicates that the particle size of the powder obtained depends on the grinding conditions. The properties of the powder are basically the same as those of the initial sample.

     

Phase analysis of new composition of high-strength structural steel

The basic type of carbide for making high-carbon wear-resistant structural steel without using a thermochemical treatment was defined. With consideration of the phase composition of the matrix after tempering, the preliminary intervals of alloying of high-carbon structural steel for gearwheels were recommended.     

Friction forces and plastic strain of plain bearings in airplanes

The paper presents data on the ultimate contact in tribojoints made from aviation antifriction structural materials and lubricants under friction and static loading. The significant influence of the friction force on the plastic strain of collars at heavy-duty contact is shown. For some combinations of structural and lubricating materials, friction decreases the ultimate pressure in the plain bearing by three times relative to static loading, under which collar plastic strain starts. The substitution of the lubricant augments (or decreases) the carrying ability by 2.5 times. The coefficients for calculating the equivalent stresses on the plain bearing friction surface are given in accordance with the results of comparative tests. The underestimation of friction forces may cause the breakdown of tribological components, as well as failures and crashes.     

Application of heat-flow calorimetry for developing mathematical models of reactor processes

The paper discusses the possibility of using heat-flow calorimetry and differential scanning calorimetry to study the kinetics and modeling of industrial multistage reactions. The informativity of the obtained experimental data was studied and the methodology of applying them to solve inverse kinetic problems has been demonstrated. The results of using calorimetry to develop mathematical models of complicated chemical processes and applying them to optimize the operating conditions of industrial processes have been considered.