Chemical Kinetics of the Thermal Decomposition of NTO

The kinetics of thermal decomposition of 3‐nitro‐2,4‐dihydro‐3H‐1,2,4‐triazol‐5‐one (NTO) in the temperature interval from 200 °C to 260 °C was investigated using a glass Bourdon gauge. The overall decomposition reaction includes two distinct stages: the fast first‐order decomposition and the subsequent autocatalytic reaction. The importance of the first stage increases with increasing decomposition temperature and decreasing loading density of the Bourdon gauge (m/V). A period of preliminary heating, at a lower temperature, strongly influences the autocatalytic stage when the decomposition is carried out at a higher temperature. In the temperature domain 200–220 °C, the Arrhenius constants of the decomposition reaction are found to be close to the values usually observed for nitrocompounds: E=173 kJ/mol and log₁₀ k≈12.5 (s⁻¹). It is shown that a simple model of NTO decomposition based on an autocatalytic reaction of the m‐th order can describe the course of the decomposition at high temperature but the m number appears to be excessively high, up to 4. A new model of the decomposition is developed, including an initial monomolecular reaction, decomposition of the crystalline substance, and an autocatalytic reaction of NTO dissolved in liquid decomposition products. This model gives the common order of autocatalysis, m=1.     

Small-angle neutron scattering characterization of the structure of nanoporous carbons for energy-related applications

We used small-angle neutron scattering (SANS) and neutron contrast variation to study the structure of four nanoporous carbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800 °C with pore diameters ranging between ∼4 and ∼11 Å. SANS patterns were obtained from dry samples and samples saturated with deuterium oxide (D₂O) in order to delineate origin of the power law scattering in the low Q domain as well as to evaluate pore accessibility for D₂O molecules. SANS cross section of all samples was fitted to Debye-Anderson-Brumberger (DAB), DAB-Kirste-Porod models as well as to the Guinier and modified Guinier formulae for cylindrical objects, which allowed for evaluating the radii of gyration as well as the radii and lengths of the pores under cylindrical shape approximation. SANS data from D₂O-saturated samples indicate that strong upturn in the low Q limit usually observed in the scattering patterns from microporous carbon powders is due to the scattering from outer surface of the powder particles. Micropores are only partially filled with D₂O molecules due to geometrical constraints and or partial hydrophobicity of the carbon matrix. Structural parameters of the dry carbons obtained using SANS are compared with the results of the gas sorption measurements and the values agree for carbide-derived carbons (CDCs) obtained at high chlorination temperatures (>600 °C). For lower chlorination temperatures, pore radii obtained from gas sorption overestimate the actual pore size as calculated from SANS for two reasons: inaccessible small pores are present and the model-dependent fitting based on density functional theory models assumes non-spherical pores, whereas SANS clearly indicates that the pore shape in microporous CDC obtained at low chlorination temperatures is nearly spherical.     

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.     

Thermogravimetric Analysis of Moisture Desorption from Coal

In coke production, the moisture content of the initial coal is an important parameter. The moisture present in the pores of coal changes the properties of the coking batch. Note also that, together with methane and/or carbon dioxide, water may form gaseous hydrates in the coal bed. In the present work, to study the state of the moisture in coal, attention focuses on eight samples of natural gas saturated to constant moisture content in an atmosphere where the relative partial pressure of water vapor is 91%. The moisture sorbed from the atmosphere has a U-shaped dependence on the metamorphic stage of the coal, with a minimum at coking coal (K coal). In similar conditions, the more mature T and A coal contains twice as much moisture as K coal, while the younger D and G coal contains about four times as much moisture. Thermogravimetric analysis of coal samples saturated to constant moisture content permits calculation of the rate of mass loss and activation energy for the evaporation of moisture in the heating of the given samples. For each coal sample, the temperature range where the evaporation of moisture may be described by a first-order Arrhenius equation is determined. The upper limit of this range is compared with the temperature corresponding to maximum rate of mass loss and also with the temperature corresponding to the maximum thermal effect.     

Nondestructive testing for flaws in the insulation of winding wires

Peculiarities of discharge that is initiated by a flawed section of wire insulation that passes through a primary gas-discharge flaw transducer have been studied. Analysis of the structure of signals has been carried out, and possible mechanism and type of discharge in the sensor have been considered. Informative zones have also been singled out in the signal structure. A technique is described for testing enamel-insulated wires for flaws. The technique makes it possible to determine the number and extent of flawed sections in an enameled wire that is fed through the system at any variable speed. Ways and means are considered for reducing the errors in evaluating the number and extent of flaws. Flow chart of a faultiness-measurement device is suggested, and the principle of its operation is described.     

Problems of the operation of turbocompressors in an internal combustion engine and methods of increasing their reliability

The operating efficiency and reliability of internal combustion engines depends on many factors, including the operation of its components and systems. One of these elements is the turbocompressor of the engine charging system. Extensive statistical data show that the turbocompressor is one of the most frequently failing units of auxiliary engine equipment. The main causes of turbocompressor failures are breakdown of bearings or seals and body or rotor breaking. One of the solutions to increase the reliability and extend the life of turbocompressors is to improve the bearing unit with a gas magnetic support.     

Deactivation of titanium during temperature-induced hydrogen absorption–desorption cycling: I. Effects of water, oxygen and nitrogen traces

The cyclic stability of metallic titanium during absorption–desorption runs in continuous flow system has been studied in the presence of variable level of impurities such as H₂O, O₂ and N₂ in argon and helium flows. Hydrogen absorption–desorption cycles performed in vacuo were reproducible with respect to the absorption rates and uptakes, while absorption–desorption cycles carried out in the flows of carrier gases in the thermoprogrammed mode resulted in the gradual decrease of hydrogen uptakes followed by a shift of absorption maxima from 800 K to 1000 K.

Mass-spectral analysis of the main impurities in a flow of gases revealed that during hydrogen absorption–desorption traces of water, oxygen and nitrogen are consumed by titanium. For the samples subjected to several absorption–desorption cycles in the flow of inert gas XRD revealed the formation of nitrogen-containing titanium compounds, while XPS showed surface enrichment in nitrogen, while oxygen concentration was constant. Nitrogen consumed at higher temperatures during the TPD runs provides better inhibition of hydrogen absorption compared to water and oxygen. Final deactivation state of titanium correlates in general with the overall amount of impurities in the stream.

Although deactivation is controlled mostly by the level of toxic impurities in the feed, certain parameters, i.e., hydrogen absorption/desorption rates are dependent on the nature of neutral media—in contrast to helium, noticeable hydrogen desorption occurs even at room temperature in a flow of pure argon.     

Effect of hardening friction treatment with hard-alloy indenter on microstructure, mechanical properties, and deformation and fracture features of constructional steel under static and cyclic tension

It has been studied how a hardening friction treatment with a sliding hard-alloy indenter influences the chemical composition and roughness of the surface, the structure, the distribution of the microhardness and the density of dislocations in depth of the surface layer, the mechanical properties upon static tension and the features of deformation and fracture upon cyclic tension of the annealed low-carbon (0.17 wt.% C) steel grade 20. It has been found that friction hardening of the steel (an increase in the microhardness up to 4.25 GPa) is due to a considerable dispersion of the ferritic base (with the formation of alpha-phase fragments no less than 100 nm in size) and pearlite colonies (crushing and partial dissolution of cementite plates) under the action of a severe friction deformation; hardening is not connected with the carryover of separate particles of the hard alloy to the steel surface. A finite-element model describing the process of the friction treatment with a sliding cylindrical indenter has been constructed. This model was used to determine how the number of the indenter strokes, the friction coefficient, and the shear component of the deformation affect the value of the accumulated deformation. It has been shown that the friction treatment improves the strength characteristics of the steel upon static tension. The hardened surface layer is susceptible to further considerable hardening (an increase in the microhardness up to 5.6-5.9 GPa) at the initial stages of the cyclic deformation and, therefore, has some margin of plasticity. The plastic flow in the surface-hardened steel under cyclic loading is due to the formation of numerous bands of localized deformation. It has been found that the friction-hardened surface layer is more prone to cracking under cyclic loading. The methods by which cracking of the hardened layer can be diminished have been discussed.     

Identification of contaminants in isophthaloyl chloride by mass-spectrometry,gas chromatography-mass spectrometry,and by liquid chromatography

Conclusions By gas chromatograph-mass spectrometry, mass spectrometry, and liquid chromatography, the following possible contaminants in isophthaloyl chloride have been identified: isophthalic acid, isophthaloyl mono acid chloride, chloroisophthaloyl chloride (a mixture of isomers), chloroisophthalic acid, monochloroisophthaloyl chloride, (3-dichloromethyl)benzoyl chloride, (3-trichloromethyl)benzoyl chloride, 3-formylbenzoyl chloride, isophthalic anhydride bis(acid chloride), isophthalic chloroisophthalic anhydride bis(acid chloride), and chloroisophthalic anhydride bis(acid chloride).A calibration of chromatographic columns for determining 4-monochloroisophthaloyl chloride, 4-chloroisophthaloyl chloride, and 4-chloroisophthalic acid has been carried out.Translated from Khimicheskie Volokna, No. 5, pp. 58–60, September–October, 1988.     

Thermal explosion in mechanoactivated 3Ni + Al mixtures

Explored was thermal explosion in mechanoactivated 3Ni + Al mixtures. Mechanoactivation was found to result in an abnormal decrease in the effective activation energy E and ignition temperature T_ign for thermal explosion. Analysis of reaction thermogram allowed us to find out the kinetic function. Mechanoactivation conditions for synthesis of Ni₃Al in thermal explosion mode have been optimized. SHS reaction in 3Ni + Al mixtures mechanoactivated for 180 s was found to obey the first-order kinetics.