Cadmium vapor

Mercury Vapor Lamp Zinc Vapor Lamp Cadmium Vapor Lamp... 

Cadmium oxide is prepared by the reaction of cadmium vapor with oxygen. The metal is first melted in a steel retort and transported into a heated chamber where it is vaporized. The vapor is reacted with air, and the cadmium oxide formed is collected in a bag house. The particle size of the product depends on the ratio of air to cadmium vapor. The oxide may be further purified and particles of uniform size may be obtained by calcination at low red heat. 

Cadmium sulfide also may be obtained by treatment of sodium or other alkali metal sulfide solution with that of a soluble cadmium salt. The compound also may be prepared by heating a mixture of cadmium or its oxide with sulfur at 800°C or by the reaction of H2S with cadmium vapor at 800°C. 

Assume that the system is being used to deposit cadmium onto the wafers. The inlet gas is primarily He, which carries a 1% trace of monatomic Cd vapor. The inlet mixture temperature is at the nominal wall temperature of T — 800°C. The cadmium vapor reacts to form a film on the lower-temperature deposition zone with a sticking coefficient of Y =0.8. All other sections of the reactor walls are presumed to be chemically inert. The process is intended to run at a nominal reduced pressure of p = 0.05 bar. 

Determine the needed bulk gas properties for this problem, including any important temperature dependencies. Determine the diffusion coefficient between the helium carrier and the cadmium vapor. 

At a temperature of about 1050K and a pressure of 1 bar, the cadmium vaporizes, thus in the reduction process of CdO,... 

The work of this laboratory extends the defect treatment to intermetallie compounds. The experiments measure simultaneously both the cadmium vapor pressure and the composition at equilibrium for a series of only slightly different alloy compositions. The precision and the relative accuracy of the measurements are high the absolute values suffer from any starting composition uncertainty and from errors in the absolute vapor pressure of cadmium as determined by other techniques. The experimental method is described elsewhere in this symposium (6). It has proved possible to infer the concentration and identity of lattice defects by analyzing the experimental data following the analytical techniques described below. 

The technique requires the measurement of some property which is proportional to a product concentration—e.g., pH, color, or electrical conductivity. In the cerium-cadmium system the cadmium vapor pressure is one such measurable property. 

Once the principal net reaction and equilibrium constant are established, standard total free energies, entropies, and heat contents become corollary. In the case of the cadmium vapor pressure one can therefore calculate total thermodynamic quantities from the established reactions as well as partial thermodynamic quantities from the vapor pressures directly. 

Initial measurements on CeCd 4 r), as expected, indicated a continuous variation of cadmium vapor pressure with composition as is shown in the upper curve of Figure 1. However, the system soon demonstrated distinct, discontinuous vapor pressure-composition relationships, as illustrated by the remaining curves of Figure 1 and as shown in greater detail and with additional data in the remaining figures. We have designated these secondary structures as microphases. ... 

Table I. Cadmium Vapor Pressures for CeCd 45 Structures in Equilibrium with Other Phases at 639° C.

If two vapor pressures are indicated for a single composition, the structures must be different. Any total composition is made up of parent structure plus defects. If the lines cross, the total compositions and cadmium vapor pressures have become equal, but the cerium vapor pressures, total free energies, and structures in the two microphases are different. 

Thermodynamics. Although we have very accurate relative data for the cadmium vapor pressures, we cannot present equally accurate thermodynamics values for the commonly used standard formation reactions. There are four main sources of difficulty ... 

Since we do not have cadmium vapor pressure across the whole cerium-cadmium system, some standard state other than the pure metal would have to be used for cerium. 

Photosensitized reactions make up an important class of photochemical reactions. In these reactions the reactants are mixed with a foreign gas mercury or cadmium vapor are often used. The primary photochemical act is the absorption of the quantum by the foreign atom or molecule. 

Barium carbonate Carbon Copper oxide (ic) Dimercury dichloride electrodes, cadmium-vapor lamps Cadmium... 

Goebel D, Hohm U (1995) Dispersion of the refractive-index of cadmium vapor and the dipole polarizability of the atomic cadmium state. Phys Rev A 52 3691-3694 Braun A, Holeman P (1936) The temperature dependence of the reftaction of iodine and the refraction of atomic iodine. Z phys Chem B 34 357-380... 

Note to the definition of immediately dangerous to life or health Some materials—hydrogen fluoride gas and cadmium vapor, for example—may produce immediate transient effects that, even if severe, may pass without medical attention, but are followed by sudden, possibly fatal collapse 12-72 hours after exposure. The victim feels normal from recovery from transient effects until collapse. Such materials in hazardous quantities are considered to be immediately dangerous to life or health. 

Cadmium vapor is a toxic substance whose diffusivity in air is not readily available in the literature. It is desired to calculate its diffusivity at its boiling point of 1038 K and a pressure of 1 atm. Because an empirical atomic volume is not available, we use the reported value for its liquid volume of 14 cm / mol for an atomic weight of 112.4. We obtain, using Equation 3.2 ... 

Applying this procedure to the cadmium vapor of Illustration 3.1, we obtain... 

A reasonable order of magnitude estimate can therefore be arrived at in most cases by starting with a value of D b = 0.1 cm /s and applying temperature or pressure correction factors in accordance with Equation 3.2. Applying this procedure to tiie cadmium vapor of Illustration 3.1, we obtain a value of... 

Cadmium vapors are known to induce metal-fume fever and may lead to a characteristic pneumonitis (Barnhart andRosENSTocK 1984). Their association with HP is not supported (Kelleher et al. 2000). 

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