Investigation into the compaction of nanopowders and micropowders of silicon carbide in high-pressure apparatus

The results of the investigation into the compaction (sintering) of silicon carbide nanopowders and micropowders in a DO-138 high-pressure apparatus are presented. Compaction modes for both types of materials are identical (a pressure of 3.5–4.0 GPa, a temperature of 1600—1700°C, and a holding time of 10 s). The influence of cladding of SiC nanopowders and micropowders with titanium and titanium nitride on the properties of compacts (cakes) formed under the same sintering modes is investigated. It is established that, when compacting the silicon carbide nanopowder, cakes differ in regards to higher density, hardness, and lower porosity compared with the samples made of finely dispersed technical silicon carbide. A higher activity of titanium relative to SiC makes it possible to chemically associate the grains of the latter due to the formation of intermediate layers of titanium carbide between them. The resulting ceramics possesses a higher density, hardness, and wear resistance. The wear resistance of synthesized composites based on nano-SiC is higher than for a polycrystalline material based on silicon carbide micropowder by a factor of 4.5.     

Formation of singular (001) terraces on the surface of single-crystal HPHT diamond substrates

Methods of the experimental diagnostics and control of the misorientation angle for single-crystal HPHT (High Pressure High Temperature) diamond substrates are discussed. Such substrates are used for the homoepitaxial growth of doped and undoped CVD diamond layers. The formation of singular (001) terraces on the surface of HPHT diamond after microwave-discharge-plasma etching in pure hydrogen or a hydrogen–oxygen mixture is observed. This phenomenon can be used for rapid determination of the substrate misorientation and to improve the control precision of the deviation angle during substrate polishing, or for obtaining large singular (001) areas of single-crystal diamond substrates.     

An Energy-Saving Control System for an Orbital Electric Driver of a Press Coupler

A control system for the orbital electric drive of a press coupler capable of reducing energy consumption is considered. Because the stator is not completely overlapped by rotors, it is proposed to reduce the power consumption by means of turning off the power supply from the unused part of the rotor. This requires use of a rotor-positioning sensor as well as an algorithm for determining the overlap area depending on the position of the rotors. A calculation algorithm, which can be applied to orbital electric drives of different configurations, is presented. The algorithm creates rotor and stator maps depending on the angle and the sought overlap area is obtained by overlapping one map on another. This allows applying the optimization methods for finding an optimal control algorithm.     

Effect of synthesis conditions on the impurity composition of STM Almazot diamond single crystals

Diamond single crystals synthesized under various conditions have been characterized by absorption spectroscopy and electron paramagnetic resonance. The results demonstrate that preannealing of the reaction cell materials in an argon-hydrogen mixture and the use of a metal-carbon system containing 3 wt % aluminum allow the concentration of process-related impurities in the single crystals to be reduced. The growing crystal captures more impurities in the initial stages of the process, so the impurities are concentrated in the central part of the crystal, near the seed. The concentration of the process-related impurities near the corners of the crystal is substantially lower.     

Quadrupole lenses on the basis of permanent magnets for a PRIOR proton microscope prototype

Four quadrupole lenses based on permanent magnets of the NdFeB material (PMQ) were developed for the imaging section for forming images of the ion-optical system of the PRIOR proton microscope prototype: the effective length of two of them is 144 mm, and the other two are 288 mm long. The field induction at the radius of the lens aperture is 1.77 Т, and the aperture is 30 mm in size. The modular design of the PMQ makes it possible to vary the length of the lenses, compensate for the offset of the magnetic axis from the ion optical axis of the microscope channel, and decrease the variation of the angular position of the magnetic medians. The PMQ magnetic field was adjusted, scanned, and its main characteristics were determined. The 3D mathematical models of the magnetic-field distribution that are obtained as a result of PMQ measurements are intended for the use in calculations of the beam dynamics during adjustment of the ion-optical system of the proton microscope and for attaining the highest spatial resolution. The developed lenses were used in the first experiments on the PRIOR facility.     

Study of photon statistics using a compound Poisson distribution and quadrature measurements

This paper describes the model of a compound Poisson distribution for photon statistics with regard to their bunching in Fock states, thermal states, and others. The method of generating functions is used to calculate the probability distributions, moments, and correlation functions. The parameters of conditional states arising from the subtraction of photons by splitting the beam are determined. The problem of state reconstruction with regard to quadrature quantum measurements is considered. The study is aimed at developing high-precision methods for generating and controlling optical quantum states.     

Effect of Back-and-Forth Transfer of Iron and Chromium in Formation of Coatings by Iodine Transport

Metal Science and Heat Treatment - Results of a study of transportation of chromium and iron by iodine at various temperatures of diffusion chromizing of armco iron are presented. The phase...     

A criterion of field reversal in a short glow discharge and its dependence on the parameters of the fluid model used

A criterion of field reversal in the near-cathode plasma of short glow discharge is considered. This criterion is shown to be extremely sensitive to the choice of the fluid-discharge model used (in particular, the choice of a Maxwellian or nonequilibrium electron-distribution function).     

Geoceramic Matrices for Immobilization of Nonpartitioned Radioactive Wastes

Immobilization of radioactive wastes (RW) containing large amounts of process alkalis in ceramic matrices based on acid and basic rocks is studied. Immobilizing characteristics of samples with an RW content of 15% are obtained. The best geoceramic matrices are characterized by the forward leaching rates with double-distilled water of 1 × 10^{- 4} and 1 × 10^{- 5} g cm^{- 2} day^{- 1} for Sr and Cs, respectively, and the steady-state leaching rate of about 2 × 10^{- 6} g cm^{- 2} day^{- 1}. Possible fixation mechanisms of the radionuclides in the matrices studied are discussed. Comparative analysis of properties of the geoceramic matrices and borosilicate and some other existing matrices for RW immobilization makes it possible to recommend some kinds of the geoceramics as matrices for immobilization of nonfractionated intermediate- and high-level radioactive wastes.     

Aluminosilicophosphate geoceramics as matrices for the immobilization of partitioned 90Sr and 137Cs wastes

Immobilization of ⁹⁰Sr and ¹³⁷Cs in geoceramic matrices synthesized on the basis of phosphatized calcinate of simulated radioactive wastes and apatite ore dressing tailings is studied. The samples were sintered at 950–1150°C for 1 h. Leaching tests were carried out at 90°C with double-distilled water in the quasiflow and accumulative modes. The leaching was monitored by the conductivity of the liquid phase. To estimate the leaching rates R, the Na, Cs, and Sr concentrations were measured by flame photometry. The best samples of geoceramics are characterized by R of (5–15) × 10^?6 and <0.3 × 10^?6 g cm^?2 day^?1 with respect to Cs and Sr, respectively. Aluminosilicophosphate geoceramics show promise as materials for immobilization of partitioned ⁹⁰Sr and ¹³⁷Cs radioactive wastes.