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1.
The synthesis process of solid SiC in thermal plasma was investigated theoretically by computing the equilibrium composition
of the gas mixtures involving silicon and carbon in the presence of argon and hydrogen at various silicon/carbon amounts and
at two different total pressures in the system, in the temperature range between 1000 and 6000 K. Use is made of the fact
that a thermal plasma, by definition, is a plasma in (local) thermodynamical equilibrium, which makes possible the theoretical
determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds
present in the system. From the calculated compositions of the investigated gas systems the temperature-composition phase
diagrams were obtained. Using these data the temperature zones with saturated and/or oversaturated vapour of SiC as well as
of Si and C were determined and the possibility of the formation of SiC in the solid state via different reaction routes was
analyzed
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
J. Réffy 《Journal of organometallic chemistry》1975,96(2):187-193
CNDO/2 calculations with an spd basis set have been carried out on methyl-phenylsilane anion radicals, and the calculated spin density values compared with the experimental hyperfine coupling constants. The CNDO method overestimates the role of d orbitals and the partial charges on hydrogen atoms attached to silicon atom. The partial charge distribution and the carbonsilicon bond order in the anion radicals and the corresponding neutral molecules are discussed. The equilibrium carbonsilicon bond distance in the trimethylphenylsilane molecule and corresponding anion radical have also been investigated. 相似文献
3.
N. A. Arutyunyan A. I. Zaitsev N. G. Shaposhnikov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(3):339-341
An interally consistent analysis of the available data on the conditions of the equilibrium of phases and thermodynamic properties
of Si-B alloys based on silicon is performed. Phase equilibria in the Si-B-Ti system in the temperature and concentration
regions of the existence of solid solution based on silicon are calculated using the obtained data. Conditions for the precipitation
of titanium diboride from Si-B-Ti solid solution at 1523 K are found. 相似文献
4.
《Comptes Rendus Chimie》2007,10(7):658-665
A comprehensive thermodynamic assessment has been carried out on the Au–Si–O system involved in the growth mechanism of Silicon NanoWires (SiNW) via the solid–liquid–solid process. The driving force needed to trigger the SiNW precipitation is supersaturation of liquid alloy Au–Si. Our model demonstrates, for the first time, how and from where supersaturation is reached. Supersaturation is not due to the migration of silicon from the wafer as claimed by many researchers, but to the existence of SiO volatile species resulting from the metastable equilibrium SiO2, amorphous/Siwafer. More interesting is that the partial pressure PSiO does impose an initial minimum radius of the first generation of nanowires in the range of 10 nm. After that, other generations of nanowires will grow due to the new metastable equilibrium SiO2, amorphous/Sinanowire. 相似文献
5.
Alexander Ya. Potemkin Vladimir B. Koltsov Maria G. Vahrameeva 《Monatshefte für Chemie / Chemical Monthly》2005,31(9):1877-1883
The main reason of the degradation of silicon monocrystals at heating is a structural transformation connected with a partial
transition of the diamond-like structure into the structure of white tin. The reason for this transformation being observed
under high pressures is the appearance of stress zones at the boundaries of variously oriented crystal microvolumes due to
heat expansion anisotropy. The high stress concentration in the microvolumes provides sufficient pressure for the indicated
phase transformation which results in the observed degradation of the electrophysical properties of silicon. The prevention
of the structural transformation is considered to be possible by doping of Si by transition or rare-earth metals which increases
the interatomic energy and decreases the thermal expansion coefficient. The choice of the doping additions is based on the
bonding energy and the charge density calculated for a system of non-polarised ionic radii. The technology to increase the
thermal stability of silicon has been patented#. 相似文献
6.
Summary. The main reason of the degradation of silicon monocrystals at heating is a structural transformation connected with a partial
transition of the diamond-like structure into the structure of white tin. The reason for this transformation being observed
under high pressures is the appearance of stress zones at the boundaries of variously oriented crystal microvolumes due to
heat expansion anisotropy. The high stress concentration in the microvolumes provides sufficient pressure for the indicated
phase transformation which results in the observed degradation of the electrophysical properties of silicon. The prevention
of the structural transformation is considered to be possible by doping of Si by transition or rare-earth metals which increases
the interatomic energy and decreases the thermal expansion coefficient. The choice of the doping additions is based on the
bonding energy and the charge density calculated for a system of non-polarised ionic radii. The technology to increase the
thermal stability of silicon has been patented#.
Patent of Russia, No 2094904, 13/10/1995 相似文献
7.
Tang M Ramos AV Jud E Chung SY Gautier-Soyer M Cannon RM Carter WC Chiang YM 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):1891-1896
Despite the extremely broad technical applications of the Si/SiO2 structure, the equilibrium wetting properties of silicon oxide on silicon are poorly understood. Here, we produce new results in which a solid-state buffer method is used to systematically titrate oxygen activity about the Si/SiO2 coexistence value. The equilibrium morphology at the Si(001) surface over >8 decades of PO2 about coexistence is revealed to be a uniform sub-stoichiometric SiOx film of sub-nanometer thickness, coexisting with secondary island structures which coarsen with annealing time. A new thermodynamic method using chemical potential to stabilize and control surficial oxides in nanoscale devices is suggested. 相似文献
8.
Fedorova N. A. Tsymbulov L. B. Tsemekhman L. Sh. 《Russian Journal of Applied Chemistry》2003,76(4):526-530
The equilibrium between a copper-nickel alloy and an oxide melt in the Cu2O-NiO-SiO2 system was studied experimentally. The distribution coefficients of nickel were determined as a function of the content of silicon dioxide, and the ratio of activity coefficients of nickel and copper oxides at 1300°C was found. 相似文献
9.
Kinetics and rate-limiting mechanisms of dolomite dissolution at various CO_2 partial pressures 总被引:1,自引:0,他引:1
Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite dissolution in flowing CO2-H2O system. Experiments run in the solutions equilibrated with various CO2 partial pressures (PCO2) from 30 to 100000 Pa. It shows that dissolution rates of
dolomite are related with rotating speeds at conditions far from equilibrium. This was explained by modified diffusion boundary layer (DBL) model. In addition, the dissolution rates increase after addition of carbonic anhydrase (CA) to solutions, where the CA catalyzes CO2 conversion. However, great differences occur among various CO2 partial pressures. The experimental observations give a conclusion that the modified DBL model enables one to predict dissolution rates and their behaviour at various PCO2 with satisfactory precision at least far from equilibrium. 相似文献
10.
V. N. Volodin S. A. Trebukhov B. K. Kenzhaliyev A. V. Nitsenko N. M. Burabaeva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(3):407-410
The values of partial pressure of saturated vapor of the constituents of the Те–S system are determined from boiling points. The boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor–liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation–condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium. 相似文献
11.
Zhang Shimin 《Journal of mathematical chemistry》2006,39(1):187-199
A generalized formula to predict the direction of an equilibrium shift,
, is presented, where ξ is the extent of the reaction, t is the characteristic variable to affect an equilibrium and f is the characteristic function whose partial differential with respect to ξ can be used as an equilibrium criterion. When
the stable equilibrium of a thermodynamic system is disturbed on condition that f exhibits a minimum with respect to ξ, the equilibrium will shift in the direction to resist the increase of f if the disturbance make f increase; however, the equilibrium will shift in the direction to accelerate the decrease of f if the disturbance make f decrease to minimize f. On condition that f exhibits a maximum with respect to ξ, the equilibrium will shift in the direction to resist the decrease of f if the disturbance make f decrease; however, the equilibrium will shift in the direction to accelerate the increase of f if the disturbance make f increase to maximize f. On the other hand, Le Chatalier’s Principle is not consistent with the real situations under certain circumstances 相似文献
12.
Ž. D. Živković D. Živković J. Šesták 《Journal of Thermal Analysis and Calorimetry》1995,43(2):417-426
Results of the comparative thermodynamic analysis of the binary system Bi?Sb obtained by DTA measurements and predicting are presented in this paper. Activities, activity coefficients, partial and integral molar quantities for Bi and Sb at temperatures 973, 1073 and 1173 K in the investigated binary system Bi?Sb determined by DTA measurements and thermodynamic predicting are given. An excellent agreement between the experimental and predicted results is reached. Also, a phase diagram of the investigated system Bi?Sb obtained by DTA shows good agreement with literature and it can be concluded that DTA could be satisfactorily used for quantitative thermodynamic analysis of any binary system containing equilibrium between solid and liquid solutions. It was also determined that conclusion about linear dependence ofgKs constant for binary eutectic systems and systems with phase transformation is valid for binary system containing equilibrium between solid and liquid solutions too. 相似文献
13.
The behavior of methane hydrate was investigated after it was pressurized with helium or nitrogen gas in a test system by monitoring the gas compositions. The results obtained indicate that even when the partial pressure of methane gas in such a system is lower than the equilibrium pressure at a certain temperature, the dissociation rate of methane hydrate is greatly depressed by pressurization with helium or nitrogen gas. This phenomenon is only observed when the total pressure of methane and helium (or nitrogen) gas in the system is greater than the equilibrium pressure required to stabilize methane hydrate with just methane gas. The following model has been proposed to explain the observed phenomenon: (1) Gas bubbles develop at the hydrate surface during hydrate dissociation, and there is a pressure balance between the methane gas inside the gas bubbles and the external pressurizing gas (methane and helium or nitrogen), as transmitted through the water film; as a result the methane gas in the gas bubbles stabilizes the hydrate surface covered with bubbles when the total gas pressure is greater than the equilibrium pressure of the methane hydrate at that temperature; this situation persists until the gas in the bubbles becomes sufficiently dilute in methane or until the surface becomes bubble-free. (2) In case of direct contact of methane hydrate with water, the water surrounding the hydrate is supersaturated with methane released upon hydrate dissociation; consequently, methane hydrate is stabilized when the hydrostatic pressure is above the equilibrium pressure of methane hydrate at a certain temperature, again until the dissolved gas at the surface becomes sufficiently dilute in methane. In essence, the phenomenon is due to the presence of a nonequilibrium state where there is a chemical potential gradient from the solid hydrate particles to the bulk solution that exists as long as solid hydrate remains. 相似文献
14.
《Physics and Chemistry of Liquids》2012,50(3):296-301
The solubility of CO2 in dimethyl sulfoxide has been determined from 293.15 K to 313.15 K and partial pressure of CO2 from 5.56 kPa to 18.2 kPa. Based on the data obtained from the CO2 solubility experiments, a gas–liquid phase equilibrium model for CO2–DMSO system was proposed. The average relative deviation between the experimental data of equilibrium partial pressure of CO2 in DMSO and the corresponding data predicted by the model proposed is 4.85%, it shows that the agreement is satisfactory. 相似文献
15.
A generalization of the method of calculating the state of equilibrium of a multicomponent system, using a hill-climbing minimization procedure, is proposed. Moreover, an original method of calculating values for partial free energies from the state of equilibrium has been made an essential part of the general schedule. 相似文献
16.
The effect of antimony concentration (C(Sb)/mass%) on the surface tension of molten silicon has been determined with the sessile drop method in the temperature range from 1693 to 1773 K and in the range of the oxygen partial pressure, Po(2), in an Ar atmosphere from 10(-23) to 10(-21) MPa. The results show that the surface tension of molten silicon decreases with increasing Sb concentration in the range of C(Sb)<0.9 mass%, which indicates positive adsorption of Sb in molten silicon and can be fairly described with the Szyszkowski's equation. The maximum decrease rate of surface tension is about 65 mN m(-1) (mass% C(Sb))(-1), and the temperature coefficient of surface tension, (partial differential sigma/ partial differential T)C(Sb), increases with increasing C(Sb). The evaporation of the systems was only observed between the melting points of antimony (904 K) and silicon (1683 K), and the surface tension presents no dependence on measuring time above the melting point of silicon. 相似文献
17.
Spectroscopic and callorimetric measurements of temperature arid number density have been made using a 50-kW radio-frequency inductively coupled plasma (RFICP) torch operated at atmospheric pressure with maximum temperatures and electron densities near 8,1000 K and 2 x 1021 m3, respectively These measurements enabled the determination o/ the stale o/ equilibrium and of the corresponding applicability of rarious diagnostic techniques in hoth a recombining argon plasma and a recombining plasma with hydrogen or nitrogen. Results indicate that the Pure argon plasma is well described by u partial equilibrium model in which the free and bound-excited electrons are in mutual equilibrium irespective of possible departures from equilibrium with the ground state. The addition of just tenths of a percent of either atomic Hydrogen or nitrogen, however, disturbs this partial equilibrium hr argon plasmas with electron densities roughly less than 1021 m3 such that only diagnostic techniques which are independent o/ partial equilibrium assumptions can be reliably implemented. 相似文献
18.
The system water–caprolactam–polymer at equilibrium is regarded as a solution consisting of two solvents (water and caprolactam) and one solute (polymer). The activities of water and caprolactam in equilibrium at 270°C in the range of 2–10 wt-% total water content have been determined by vapor-pressure measurements. Water shows large negative deviations from Raoult's law, as a consequence of the different size of water and polymer molecules. The partial molar free energies of mixing are compared with the expressions derived from the Flory-Huggins theory of polymer solutions; the results are not conclusive, but seem to indicate a qualitative agreement with the theory. The increase in vapor pressure during polymerization in sealed systems and the water dependence of the polycondensation equilibrium are discussed and explained in terms of water activity changes. 相似文献
19.
Pranay Jairam Darda Kees Hogendoorn Tjaart Molenkamp Geert Versteeg 《Macromolecular Symposia》2004,206(1):275-290
The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m - cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 equation/tex2gif-stack-1.gif). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory - Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics. 相似文献
20.
L. P. Krul' A. M. Nikiforov A. P. Polikarpov O. I. Shadyro 《High Energy Chemistry》2000,34(6):361-365
The dependence of the concentration of network junction points, as determined by equilibrium swelling ratio, in an SKTV-shch siloxane rubber and siloxane rubber–silicon dioxide formulations on the dose of ionizing radiation was investigated. The radiation-chemical yield of crosslinking was shown to increase with increasing the filler content. This result was tentatively explained by reducing the molecular mobility of the rubber chains adsorbed at the surface of silicon dioxide particles. 相似文献