Silicon vapor pressure

The values of A, and B, for different systems are presented in Table 2. This equation describes vapor pressure with good accuracy for the system SiC-Si. When approaching the temperature of peritectic transformation Tp the curves deviate from linear ones in the coordinates Ig p = f(llT) (Fig. 3f). The silicon vapor pressure data presented are approximately two times higher than the most reliable experimental data. Vapor pressures over other polytypes can be calculated using the expression... 

The values of fli are shown in Table 3. Vapor pressures of Si2C and SiC2 according to the constants of dissociative evaporation reactions depend on silicon vapor pressure. In order to control the vapor composition over silicon carbide, it is extremely important to know the equations... 

Fig.3.1.9 (a) The adsorption-desorption isotherm (circles, right axis) and the self-diffusion coefficients D (triangles, left axis) for cyclohexane in porous silicon with 3.6-nm pore diameter as a function of the relative vapor pressure z = P/PS1 where Ps is the saturated vapor pressure, (b) The self-diffusion coefficients D for acetone (squares) and cyclohexane (triangles) as a function of the concentration 0 of molecules in pores measured on the adsorption (open symbols) and the desorption (filled symbols) branches. 

In freeze-drying, a solution is filled into vials, a special slotted stopper is partially inserted into the neck of the vial (Fig. 3), and trays of filled vials are transferred to the freeze-dryer. The solution is frozen by circulation of a fluid, such as silicone oil, at a temperature in the range of — 35 to about — 45°C through internal channels in the shelf assembly. When the product has solidified sufficiently, the pressure in the freeze-dry chamber is reduced to a pressure less that the vapor pressure of ice at the temperature of the product, and heat is applied to the... 

The vapor pressure at 0° (43 mm.) is generally a sufficient criterion for purity. (The checkers also used infrared spectroscopy and noted a trace of impurity of silicon tetrachloride.) Elemental analysis is readily accomplished by heating a weighed sample at 160° for 18 hours with a slight excess of water in a sealed glass tube. A 15 to 20% excess of water over that required by the equation ... 

A. Tseplyaeva, Y. Priselkov, and V. Karelin, The Measurement of the saturated vapor pressure of silicon, Vestmik Moskovskogo Universiteta. Ser 11 15, 36-38 (1960). 

Phosphoric Acid Fuel Cell (PAFC) Phosphoric acid concentrated to 100% is used for the electrolyte in this fuel cell, which operates at 150 to 220°C. At lower temperatures, phosphoric acid is a poor ionic conductor, and CO poisoning of the Pt electrocatalyst in the anode becomes severe. The relative stability of concentrated phosphoric acid is high compared to other common acids consequently the PAFC is capable of operating at the high end of the acid temperature range (100 to 220°C). In addition, the use of concentrated acid (100%) minimizes the water vapor pressure so water management in the cell is not difficult. The matrix universally used to retain the acid is silicon carbide (1), and the electrocatalyst in both the anode and cathode is Pt. 

Results for vapor pressure as a function of temperature are presented for major organic chemical compounds. The coefficients are displayed in an easy-to-use table which is especially applicable for rapid engineering usage with the personal computer or hand calculator. The organic chemicals encompass hydrocarbon, oxygen, nitrogen, halogen, silicon, sulfur and other chemical type compounds. 

Exists in two adotropic modifications. Crystalline sihcon is made up of grayish-black lustrous needle-hke crystals or octahedral platelets cubic structure Amorphous sdicon is a brown powder. Other physical properties are density 2.33g/cm3 at 25°C melts at 1,414°C high purity liquid silicon has density 2.533 g/cm at its melting point vaporizes at 3,265°C vapor pressure 0.76 torr at 2,067°C Mohs hardness 6.5. Brinell hardness 250 poor conductor of electricity dielectiric constant 13 critical temperature 4°C calculated critical pressure 530 atm magnetic susceptibility (containing 0.085%Fe) 0.13x10 insoluble in water dissolves in hydrofluoric acid or a mixture of hydrofluoric and nitric acids soluble in molten alkalies. 

Fig. 9.14 Vapor pressure of nonmetallic sealing materials (the vapor pressure curve forfluoro rubber lies between the curves for silicone rubber and Teflon).

Diffusion pumps operate at very low pressures. The ultimate vacuum attainable depends somewhat upon the vapor pressure of the pump liquid at the temperature of the condensing surfaces. By providing a cold trap between the diffusion pump and the region being evacuated, pressures as low as 10" mmHg absolute are achieved in this manner. Liquids used for diffusion pumps are mercury and oils of low vapor pressure. Silicone oils have excellent characteristics for this... 

Deposition was performed using a vacuum system [1]. Before deposition of the alkoxlde, the sample was evacuated at 673 K for 2 hr, and the temperature was then lowered to 593 - 293 K for the deposition of silicon methoxlde. S1(0CH3)4 vapor was then admitted to the dried zeolite at a vapor pressure of 2.5 Torr. The resultant Increase of weight was measured by the quartz microbalance. After the deposition, the decatlonlzed zeolite was calcined Iji situ by oxygen at 673 K to remove the coke residue, while the Na-type mordenlte was treated with water vapor at 593 K. The amount of SI deposited was... 

If a barometer were filled with a silicone fluid whose vapor pressure is very low but whose density is 1 15 g/ml, what would be. the barometer reading when the atmospheric pressure is 710 torr7 density of mercury S 56... 

This situation may represent the diffusion of a high-vapor-pressure dopant out of a thin film (thickness L, initial dopant concentration c0) of silicon when placed in a vacuum. Assume that the variables are separable.7 Letting c(x,t) = X(x)T(t) and substituting into the diffusion equation gives... 

The best results were obtained with compound 21 that exhibited high vapor pressure and low decomposition temperature (<523 K). Various CVD conditions were applied and gave in all cases shiny, dark-brown deposits.43 XRD and XPS analyses of the deposits indicated the presence of a vanadium carbonitride phase with little contamination from oxygen and free carbon. The films were less adherent on steel substrates than on silicon ones. The steel substrates seemed to suffer corrosion due to the presence of Cl-containing species. We had noticed the same feature in the case of Cl-containing precursors to vanadium carbide. Therefore, in order to increase the volatility of compound 23 and to reduce the Cl content of the molecule, we prepared compounds 24 and 25. Unfortunately, the yields obtained in their syntheses were much too low to permit TG and CVD experiments. 

Reactants should be weighed in the atomic ratio of 1 Si/ 2.0-2.5P. The presence of excess phosphorus has been found to enhance reaction and impede the formation of silicon monophosphide. Since a large excess of phosphorus increases the chance of explosion from its vapor pressure, an optimum ratio is... 

Si (g). von Wartenberg2 considered the vapor to be polyatomic and gave —44 as the heat of sublimation. Recently Ruff and Konschak1 measured what they believed to be the vapor pressure of silicon, and deduced the heat of sublimation to be —85 at 18°. The heat of sublimation of silicon can also be computed by utilizing the lattice energy of SiC>2, which is 3247 according to Hylleraas,2 but the value obtained is a small difference of very large numbers and the uncertainty may be as much as 200. 

Figure 9.10 Adsorbed amount of water on a silicon oxide surfaces versus relative vapor pressure at 20°C. The continuous line was calculated with the theory of Polanyi and assuming van der Waals forces only (Eq. 9.57). Experimental results as measured on Aerosil 200 were adapted from Ref. [379] (see also Fig. 9.9). The deviation at high pressure is partially due to the porosity of the adsorbent. The equilibrium vapor pressure is P0 = 3.17 kPa.

Vanadium oxytrichloride is a lemon-yellow liquid. Its boiling point is 124.5°C. at 736 mm. and 127.16°C. at 760 mm. It remains liquid at —77°. The vapor pressure at —77° is 4.1 mm. at 0°, 21 mm. and at 85°C., 270 mm. Its density in grams per milliliter is 1.854 at 0° and 1.811 at 32°C. At ordinary temperatures, it neither dissolves nor reacts with carbon, hydrogen, nitrogen, oxygen, silicon, tellurium, or metals except the alkali metals and antimony. The reactions with the alkali metals are explosive at characteristic temperatures, varying from 30°C. for cesium to 180°C. for sodium (lithium not determined). Small... 

Equation (2.79) expresses the driving force in pervaporation in terms of the vapor pressure. The driving force could equally well have been expressed in terms of concentration differences, as in Equation (2.83). However, in practice, the vapor pressure expression provides much more useful results and clearly shows the connection between pervaporation and gas separation, Equation (2.60). Also, the gas phase coefficient, is much less dependent on temperature than P L. The reliability of Equation (2.79) has been amply demonstrated experimentally [17,18], Figure 2.13, for example, shows data for the pervaporation of water as a function of permeate pressure. As the permeate pressure (p,e) increases, the water flux falls, reaching zero flux when the permeate pressure is equal to the feed-liquid vapor pressure (pIsal) at the temperature of the experiment. The straight lines in Figure 2.13 indicate that the permeability coefficient d f ) of water in silicone rubber is constant, as expected in this and similar systems in which the membrane material is a rubbery polymer and the permeant swells the polymer only moderately. 

Figure 2.13 The effect of permeate pressure on the water flux through a silicone rubber pervaporation membrane. The arrows on the lower axis represent the saturation vapor pressures of the feed solution at the temperature of these experiments as predicted by Equation (2.79) [15]...

Consequently such a microvaporizer uses a glass-silicon-glass stack with a microstructured silicon evaporator. This evaporator is heated up by a pulsed NIR-laser diode. Thus, the liquids which are in contact with the evaporator within a very short period of time are heated beyond their evaporation temperature. This arrangement not only requires a low energy to evaporate in comparison to the commonly used resistive heating, but the very rapid heating of the silicon vaporizer also allows for simultaneous evaporation of sample mixtures with components of different evaporation temperatures and partial pressures, respectively. Furthermore,... 

Table 1.1. Abundance of the metal in the earths s crust, optical band gap Es (d direct i indirect) [23,24], crystal structure and lattice parameters a and c [23,24], density, thermal conductivity k, thermal expansion coefficient at room temperature a [25-27], piezoelectric stress ea, e3i, eis and strain d33, dn, dig coefficients [28], electromechanical coupling factors IC33, ksi, fcis [29], static e(0) and optical e(oo) dielectric constants [23,30,31] (see also Sect. 3.3, Table 3.3), melting temperature of the compound Tm and of the metal Tm(metal), temperature Tvp at which the metal has a vapor pressure of 10 3 Pa, heat of formation AH per formula unit [32] of zinc oxide in comparison to other TCOs and to silicon...

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