Tungsten film, evaporated

Fig. 11. Sorption isobars at 0.1 mm. pressure of hydrogen on an evaporated tungsten film sintered at 23°C. (upper curves) and at 500°C. (lower curves).

Fig. 18. Heats of adsorption of hydrogen on evaporated tungsten films at 23°C. as a function of surface covered.

Not only the hydrogen adsorption but also the nitrogen adsorption as observed by Davis (17a), as well as by Beeck and coworkers fits well into this picture. It was observed by Beeck et al. that 60 % of the surface of evaporated tungsten films could be covered by nitrogen at room temperature, 50% being adsorbed instantaneously with a constant heat... 

Hydrogen Isobars on Evaporated Tungsten Films and on Tungsten Powder ... 

The data of Rideal and Trapnell (7) for the adsorption of hydrogen on an evaporated tungsten film are fitted by (18), or rather by a limiting form of (18). When (1 — 8)Ax/kT is large, equation (18) becomes... 

Volumetric studies on low area filaments are very inaccurate and because of its high refractivity tungsten does not lend itself so easily to the production of large area powders, or evaporated metal films, as do many other softer metals. Consequently, the first systematic study on the CO-tungsten system was carried out only in 1950 when Rideal and Trapnell (9), using evaporated tungsten films, measured the CO pressure isotherms between 77 and 300°K (Fig. 2). Using these isotherms, they... 

Fig. 2. Isotherms for CO adsorption on evaporated tungsten films. [Redrawn from Rideal and Trapnell (9).]...

Quite similar equations are found for the B—K, C—K, and D—K bonds. Langmuir has found that the oxygen film adsorbed on tungsten has evaporated as WO3 before the W evaporation, from which Aw > Aow.w. This gives an idea of the order of magnitude of A. 

Other uses are in thin film technology where coatings are applied by vacuum deposition. Tungsten boats, or coils fabricated from wire are heated by direct resistance heating and used to evaporate Ag, Al, Au, B, Ba, Ce, Cr, Fe, In, Mg, Mn, Ni, Pa, Pt, SiO, Te, V, Zn and Zr. 

The following experimental details apply both to the determination of tungsten with bromine as internal standard, and to the experiments of Table 7-2. The solutions filled a 3-ml container made by sectioning a 10-ml beaker. To prevent" evaporation and to maintain a fixed distance between x-ray tube window and sample surface, the beaker-section was covered with Mylar film, 0.0025 cm thick, placed in a plastic sample holder and pressed firmly against the sample drawer. The Mylar film attenuated the x-rays uniformly enough so as not to affect the precision of the results. 

Anderson and Kemball (35) examined the reaction between gaseous deuterium and benzene catalyzed by evaporated films of iron, nickel, palladium, silver, tungsten, and platinum. The order of reactivity (estimated from the temperature at which the addition reaction achieved an initial rate of 1% per minute for a 10 mg film at certain specified reactant... 

In one of the earliest reports of the use of clean evaporated alloy films in surface studies, Stephens described the preparation and characterization of Pd-Au films and presented some results for the adsorption of oxygen on them 46). Films of pure Pd and 60% Au were evaporated directly from wires, while films of 80% Au and pure Au were evaporated from a pre-outgassed tungsten support wire. The films were evaporated in a UHV system and the pressure was kept below PC8 Torr during evaporation. After evaporation, the films were stabilized by cycling between —195° and 30°C four times. They w ere characterized by X-ray diffraction and chemical analysis surface areas were measured by the BET method using krypton adsorption. 

The decomposition of formic acid over evaporated Pd-Au alloy films has been studied by Clarke and Rafter (69) the same reaction on Pd-Au alloy wires was studied by Eley and Luetic (128). The alloy films were prepared in a conventional high vacuum system by simultaneous evaporation of the component metals from tungsten hairpins. The alloy films were characterized by X-ray diffraction and electron microscopy. The X-ray diffractometer peaks were analyzed by a method first used by Moss and Thomas (SO). It was found that alloys deposited at a substrate temperature of 450°C followed by annealing for one hour at the same temperature were substantially homogeneous. Electron microscopy revealed that all compositions were subject to preferred orientation (Section III). 

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