Chromium vapor pressure

The gases used in the CVD reactor may be either commercially available gases in tanks, such as Ar, N2, WF, SiH, B2H, H2, and NH Hquids such as chlorides and carbonyls or soflds such as Mo carbonyl, which has a vapor pressure of 10 Pa (75 mtorr) at 20°C and decomposes at >150° C. Vapor may also come from reactive-bed sources where a flowing haUde, such as chlorine, reacts with a hot-bed material, such as chromium or tantalum, to give a gaseous species. 

The behavior of materials, particularly steel, in cavitating fluids results in an erosion mechanism, including mechanical erosion and electrochemical corrosion. The straightforward way to fight cavitation is to use hardened materials, chromium, chrome-nickel compounds, or elastomeric plastics. Other cures are to reduce the vapor pressure with additives, reduce the turbulence, change the liquid s temperature, or add air to act as a cushion for the collapsing bubbles. 

Next, let the example of vanadium, which, in the as-reduced condition, may contain a variety of impurities (including aluminum, calcium, chromium, copper, iron, molybdenum, nickel, lead, titanium, and zinc) be considered. Vanadium melts at 1910 °C, and at this temperature it is considerably less volatile than many of the impurity metals present in it. The vapor pressure of pure vanadium at this temperature is 0.02 torr, whereas those of the impurity elements in their pure states are the following aluminum 22 torr calcium 1 atm, chromium 6 torr copper 23 torr iron 2 torr molybdenum 6 1CT6 torr nickel 1 torr lead 1 torr titanium 0.1 torr and zinc 1 atm. However, since most of these impurities form a dilute solution in vanadium, their actual partial pressures over vanadium are considerably lower than the values indicated. Taking this into account, the vaporization rate, mA, of an element A (the evaporating species) can be approximated by the following free evaporation equation (Langmuir equation) ... 

If you require metal components on your vacuum system, select metals with low gas permeation, such as 300 series stainless steel. It is nonmagnetic and, like glass, is a poor conductor of heat and electricity. Stainless steel, also like glass, is relatively nonreactive, and therefore is less likely to rust or be affected by chemicals. If welding the stainless steel is required, select 304L stainless steel, which is low in carbon. Otherwise, at welding temperatures the carbon will combine with the chromium (within the stainless steel) to form chromium carbide and the corrosion protection of the chromium will be lost. Type 303 stainless steel should not be used for vacuum work because it contains selenium, which has a high vapor pressure. 

Table 1(d) on vapor pressure of the metals shows the results of the calculations for the metals tungsten, chromium, iron, and magnesium. 

With the exception of tungsten and zirconium (not calculated) the metals are volatile at elevated temperatures in vacua of the order of 10-10 atm. At 1000°C. the vapor pressure of chromium is 10-8-61 atm., that of iron 10-8-8 atm., and that of magnesium 10-1-5 atm. Thus at 1000°C. the vaporization of chromium and iron is appreciable. 

The vacuum microbalance can be applied to the study of vapor pressures of metals and in particular to the effect on the vapor pressure of films of oxide, nitride, and other protective layers on the metal surfaces. We studied the vapor pressure of several metals including beryllium and chromium and in this section will discuss the work on beryllium (43). 

The hexacarbonyls of chromium, molybdenum, and tungsten are mononuclear the internal bonding parameters are presented in Table 3. The coordination geometry is that of a regular octahedron of idealized Oh syuunetry. The crystal packing is due to weak van der Waals interactions see van der Waals Forces), which explains the volatility of these compounds (the vapor pressures of Cr(CO)6, Mo(CO)6, and W(CO)6 at 30 °C are 0.28, 0.27, and 0.06 mmHg, respectively), and their solubility in organic solvents. 

Mixed carbide fuels eliminate undesirable second phases or render them harmless. Alloying UC with ZrC increases the melting point and lowers the vapor pressure. Chromium and vanadium improve the compatibility of the carbide fuel with stainless steel cladding. 

Chromium difluoride dioxide is a violet-red crystalline solid that at 29.6° has a vapor pressure of 760 mm. It melts to an orange-red liquid at 31.6°, and its vapor pressure at the triple point is 885 mm. Although the fluoride is thermally stable,° care should be exercised in its handling because it is water-sensitive and is also a very strong oxidizing agent. 

Flammable solid flash point (closed cup) 65.6°C (150°F) vapor pressure 0.18 torr at 20°C (68°F) vapor density 5.2 autoignition temperature 466°C (871°F) fire-extinguishing agent none reported water or foam may cause frothing water spray may be applied carefully on the surface to blanket and extinguish a fire. i//-Camphor forms explosive mixtures with air the LEL and UEL values are 0.6 and 3.5% by volume of air, respectively. It may react violently with chromium trioxide and other strong oxidizers. 

HEAT CAPACITY AND VAPOR PRESSURE OF CRYSTALLINE BIS/BENZENE/CHROMIUM. THIRD-LAW ENTROPY COMPARISON AND THERMODYNAMIC EVIDENCE CONCERNING THE STRUCTURE OF BIS/BENZENE/CHROMIUM. 

Chromium hexacarbonyl forms large, highly refractive crystals that can be sublimed in vacuum without change but decompose on heating above about 100°. The vapor pressure of chromium hexacarbonyl has been measured up to 125°. On exposure to light and air at room temperature... 

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