Metal Vapor Condensation

The evaporators are heated resistively to approximately 1500 °C. A wire made from the material to be vaporized is brought into contact with each boat at which point it instantly melts and becomes gaseous. The metal vapor condenses on the cooled film passing by, and forms a thin metal coating on the film surface. This is the most commonly used method of evaporation. 

Some stages of this multistep process (especially the particle growth) are similar to the mechanism of the metal vapor condensation on the polymer [1]. The thermolysis in the presence of polymers was in greater extent studied for carbonyls of cobalt (see, for example, references 56 and 57) and iron [53, 56-58] (Table 3.7) when the process proceeds by a direct Ma(CO) vaporization over polymers or by a preliminary adsorption on them. 

In principle, the kinetics of metal vapor condensation is analogous to the coagulation kinetics of an ideal suspension. There are unstable states, which can be described by the Smoluchowski equation for fast coagulation. 

The effect of a boiling-condensing liquid metal on its container material is most easily studied in a refluxing capsule experiment. The capsule design illustrated in Fig. 11 was used for evaluating the effect of refluxing potassium on refractory metals. A 300 mm capsule containing machined insert specimens in the condenser section was half filled with potassium and heated. Liquid metal vaporizes, condenses in the water-cooled upper section of the capsule, and... 

Metal-bis-arene sandwich complexes, accessible by reactions of the Fischer type (MCI3 -1- arene -1- AICI3 -I- Al) or by the metal-vapor condensation technique, have electronic structures and redox properties close to those of the metallocenes. 

Because they have low vapor pressures, transition metals cannot be loaded by direct adsorption, but their adsorption can be mediated by transient organo-metallic complexes formed between zerovalent metal atoms and solvent molecules. This is the basis of the solvated metal atom dispersion (SMAD) method developed by Klabunde and Tanaka [72]. Metal vapors condensed in Hquid hydrocarbons at low temperatures form weak complexes that are easily decomposed even below room temperature. Microporous supports impregnated with solutions of metal complexes at low temperatures are warmed up to decompose the complex and liberate zerovalent metal atoms which nucleate into clusters. Preparation of Ni- and Co-clusters in HY and HZSM-5 was reported [72]. In the same way, Nazar et al. [64] condensed iron and cobalt vapors in a slurry of dehydrated NaY zeolite in toluene at -120 °C, then the mixture was rotated at-78°C. The bis-toluene complex thus formed and adsorbed in the zeoUte was decomposed by warming to room temperature yielding clusters small enough to fit into supercages. 

Condensation of metal vapors followed by deposition on cooler surfaces yields metal powders as does decomposition of metal hydrides. Vacuum treatment of metal hydrides gives powders of fine particle size. Reaction of a metal haHde and molten magnesium, known as the KroU process, is used for titanium and zirconium. This results in a sponge-like product. 

Heat gains and losses for heating or cooling raw materials and parts brought into or taken out of the building, melted metal solidification, vapor condensation, or liquid evaporation... 

The metal-vapor synthesis, involving co-condensation of nickel vapors, r-BuC = P, and 1,2,4-triphospholyl system leads to the mixed-ligand species 178 (94AGE2330). 

Co-condensation of Hf and Zr atoms from an electron-gun evaporation device, with P(Me)3 and arenes at 77K gave good yields of the species [M(arene)2P(Me3)]. Metal vapor synthesis led to Fe(i7 -arene)L2 and Fe(i7 -arene)-(i7 -diene), where L is a phosphorus ligand. In addition, complexes of stoichiometry Fe(T) -diene)L3 (where L is again a... 

Briquettes of CaO with 5-20% excess powdered A1 are heated under vacuum to 1170°C in a Ni-Cr steel (15/28) retort in which the Ca vapor, produced by reduction of solid CaO by A1 vapor, is condensed in a zone at 680-740 C. Any Mg impurity is condensed in a zone at 275-350°C a mixture of the two metals condenses in an intermediate zone. The A1 content of the product can be reduced by passing the metal vapor, before it condenses, through a vessel filled with solid CaO. The adaptation of the FeSi thermal reduction process for Mg production (see 7.2.3.2.1) to Ca manufacture has also been described but is not economically viable in comparison with the above process. The thermal reduction of CaO with carbon has been proposed as for Mg production, however, the reversibility of the equilibrium ... 

Figure 1. Schematic illustration of the laser-vaporization supersonic cluster source. Just before the peak of an intense He pulse from the nozzle (at left), a weakly focused laser pulse strikes from the rotating metal rod. The hot metal vapor sputtered from the surface is swept down the condensation channel in dense He, where cluster formation occurs through nucleation. The gas pulse expands into vacuum, with a skinned portion to serve as a collimated cluster bean. The deflection magnet is used to measure magnetic properties, while the final chaiber at right is for measurement of the cluster distribution by laser photoionization time-of-flight mass spectroscopy.

Many metals can be deposited on glass in a vacuum, by vaporizing the metal and condensing it on the glass. J. Yarwood (1955) has given a general account of this method. 

Another thin film technology based nanoparticle preparation route is gas condensation, in which metal vapor is cooled to high levels of supersaturation in an inert gas ambient [126-128]. In these experiments particles necessarily nucleate in the gas phase. In a promising extension of this technique a pulsed laser beam replaces the conventionally used thermal metal vapor source [120,121,129-134]. 

The co-condensation at low temperature of a metal vapor (commonly produced by resistance or electron-beam heating of metals) with a vapor of weakly stabilizing organic ligands (such as -pentane, toluene, tetrahydrofu-ran, acetone, or acetonitrile), using commercially available reactors, affords solid matrices, where reactions between the ligand molecules and metal atoms can take place (Scheme 1(A) Figure 1) [5]. 

Figure 1. Condensation of solvent vapor (A) and co-condensation of metal vapor with solvent vapor (B).

Vacuum metalizing is the process of coating a workpiece with metal by flash heating metal vapor in a high-vacuum chamber containing the workpiece. The vapor condenses on all exposed surfaces. 

The simplest case of M-M bonds was observed in Mj+ dimers without surrounding coordinate ligands. These compounds (with n = 0) were synthesized for a number of metals by fast condensation of metal vapors in inert-gas matrices at low temperatures [130-135]. 

---