Effect of the mode of combustion on the service life of the combustion chamber material

The effect of the characteristics of intrachamber combustion (the pressure and the temperature of combustion products) on the service life of the material of the combustion chamber of a thermal engine is examined. The problem is studied with the help of the Zhurkov kinetic approach based on model examples of spherical and cylindrical shells subjected to the action of cyclically varying pressure and temperature of the gas in the chamber. An analogy between the influence of stress and temperature on the service life of material is demonstrated. It is shown that periodic variations of the intrachamber characteristics can lead to an appreciable shortening of the service life of the shell in comparison with the service life at a constant pressure and temperature equal to the corresponding mean values. Thus, in the case of pressure and temperature variations (of the harmonic type), small in amplitude, the effect of the accelerated aging of the material per cycle of loading is proportional to the square of the amplitude of variations. In this case, a relative increase in the deterioration of material during one period of loading does not depend on the value of the period of loading. The problem of the effective medium stress with a periodically varying loading of random type is discussed. The theoretical results obtained are illustrated for aluminum shells and other construction materials, as examples.     

Out-diffusion and precipitation of copper in silicon: An electrostatic model

Concentrations of mobile interstitial copper and precipitated copper in silicon were studied after a high temperature intentional contamination and quench to room temperature. It was found that below a critical contamination the copper predominantly diffuses out to the surface, while for higher initial copper concentrations it mainly precipitates in the bulk. The critical copper contamination equals the acceptor concentration plus 10(16) cm (-3). This behavior can be explained by the electrostatic interaction between the positively charged interstitial copper and the forming copper precipitates.     

Solid propellant combustion in the presence of photoirradiation

Previous studies of the nonsteady processes associated with the irradiation of propellants with light have chiefly been devoted to the question of ignition [1–3]. It is also important to consider the effect of such an easily controlled influence as light on the propellant combustion process. We have attempted to estimate the dependence of the propellant burning rate on the intensity of the luminous radiation. Cases of steady-state combustion and combustion in the presence of a light flux varying harmonically with time are considered. It is assumed that the incident light flux is absorbed in the solid phase in accordance with the Bouguer-Lambert exponential law with constant transparency index. Steady-state combustion is considered within the framework of the Zel'dovich theory [4]. It is shown that in the steady state irradiation is equivalent to a certain increase in the initial temperature of the propellant. In the case of combustion with irradiation this makes it possible to use the data on steady-state combustion without irradiation. Nonsteady combustion in the presence of a periodically varying light flux is described with the aid of the Novozhilov model [5]. A correction to the mean burning rate (u °), proportional to the square of the light flux amplitude, is obtained. In the case of an exponential dependence of the burning rate on initial temperature the correction u ° is negative. The effect of irradiation on the stability of the steady-state propellant combustion mode is discussed.Translated from Zhumal Prikladnoi Mekhaniki i Tekhnicneskoi Fiziki, No. 5, pp. 70–77, September–October, 1971.In conclusion the authors thank O. I. Leipunskii and V. B. Librovich for their valuable advice.     

Silatrane-containing poly(β-amino esters)

Russian Chemical Bulletin - A series of poly(β-amino esters) were synthesized using the Michael addition reaction from 1-(3-aminopropyl)silatrane and glycol diacrylates. The structure of the...     

Electrophysics of nanocluster thin-film systems: Achieving superconducting topological states

The possibility of controlling the functional properties of nanostructured thin films deposited on solid substrates using lasers stems from the different topology and elemental composition of the deposited materials. Quantum-correlated states that emerge in the deposited granular nanocluster semiconductor/ metal structures lead to hopping/tunneling conductivity. The possibility of high-temperature superconductivity in such nanocluster structures that are both stable and can give rise to different (nonphonon) electron pairing mechanisms is discussed. An increase in electrical conductivity (by several orders of magnitude) is observed in experiments, depending on the surface and boundary conditions in various topologically organized cluster systems. The problem is to find the optimum numerical relations between the topological parameters in order to obtain the patterns of directivity (such as the Bragg resonance) needed for a sharp increase in electrical conductivity in selective directions.     

Electrical properties and diffusion behavior of hafnium in single crystal silicon

Electrical properties and diffusivity of Hf in single crystal Si have been studied. Several deep level defects were found for Hf in both the upper and lower half of the silicon band gap, and their parameters were measured. Energy levels, concentrations, and capture cross sections were determined for all Hf defects. The DLTS spectra depend on the cooling rate. Analysis of electrical properties yielded a dominant deep level defect at E_C -0.27 eV, which showed field enhanced emission due to Poole–Frenkel effect, confirming its donor nature. This agreed with results obtained using CV and TSCAP. In the lower half of the bandgap, a defect level at E_V +0.24 eV was found to have a capture barrier of 0.04 eV. Diffusivity of Hf was studied using two methods for Hf incorporation in Si – ion implantation and sputtering. Analysis of broadening of the Hf profile in implanted samples, which were annealed for 168 h, allowed us to estimate the diffusivity of Hf as 1.7×10^-15 cm²/s at 1250 °C: the spreading of implanted profiles at lower temperatures was too small. Analysis of Hf depth profiles in the sputtered and annealed samples reveals that Hf appears to have a fast and slow component to its diffusivity whose migration energy was determined to be 3.5±0.3 eV and 4.1±0.3 eV respectively. The fast and slow component are ascribed to interstitial and substitutional Hf with an energy level of E_C -0.27 eV and E_V +0.43 eV respectively. The mechanism for the fast component seems to indicate a direct interstitial diffusion mechanism whereas the diffusion of the substitutional Hf seems most consistent with the concerted exchange diffusion mechanism. In addition, estimates of solubility for both, interstitial and substitutional Hf, are included. PACS 61.72.Tt; 66.30.Jt; 71.55.Cn     

Cellular and Tulip Flame Configurations

Flame propagation in a plane channel with the formation of tulip and cellular configurations of the combustion front is simulated. The near-flame flow structure and the thermal flow structure are determined. An analogy is found between the tulip configuration and flame inflections at cell interfaces.     

Quantifying uncertainty in the measurement of arsenic in suspended particulate matter by Atomic Absorption Spectrometry with hydride generator

Arsenic is the toxic element, which creates several problems in human being specially when inhaled through air. So the accurate and precise measurement of arsenic in suspended particulate matter (SPM) is of prime importance as it gives information about the level of toxicity in the environment, and preventive measures could be taken in the effective areas. Quality assurance is equally important in the measurement of arsenic in SPM samples before making any decision. The quality and reliability of the data of such volatile elements depends upon the measurement of uncertainty of each step involved from sampling to analysis. The analytical results quantifying uncertainty gives a measure of the confidence level of the concerned laboratory. So the main objective of this study was to determine arsenic content in SPM samples with uncertainty budget and to find out various potential sources of uncertainty, which affects the results. Keeping these facts, we have selected seven diverse sites of Delhi (National Capital of India) for quantification of arsenic content in SPM samples with uncertainty budget following sampling by HVS to analysis by Atomic Absorption Spectrometer-Hydride Generator (AAS-HG). In the measurement of arsenic in SPM samples so many steps are involved from sampling to final result and we have considered various potential sources of uncertainties. The calculation of uncertainty is based on ISO/IEC17025: 2005 document and EURACHEM guideline. It has been found that the final results mostly depend on the uncertainty in measurement mainly due to repeatability, final volume prepared for analysis, weighing balance and sampling by HVS. After the analysis of data of seven diverse sites of Delhi, it has been concluded that during the period from 31^st Jan. 2008 to 7^th Feb. 2008 the arsenic concentration varies from 1.44 ± 0.25 to 5.58 ± 0.55 ng/m³ with 95% confidence level (k = 2).     

Theory of the combustion of small drops of metal

The article discusses the combustion of small drops of metal. It is postulated that the formation of an oxide in the liquid phase starts with the origin of a condensed phase and continues as the result of a reaction between the vapors of the drop and the oxidizer at the surface of the forming particles of the condensed phase. It is shown that the process of the formation of particles of condensed oxide in the gas, for very small drops, has an essentially unsteady-state character. Under these circumstances, a considerable fraction of the vaporization products of a drop does not succeed in condensing after the complete gasification of the drop and remains in the gaseous state.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 47–53, March–April, 1976.