Glowing promotion

Adhesion or printability of polymeric surfaces, including films, is often promoted by plasma or glow discharge treatment. In particular for apolar (low surface energy) surfaces such as polyolefins this is a commonly applied procedure. As a practical industrial example, the adhesion behaviour of polypropylenes after... 

A wide spectrum of heterogeneous processes can occur at solid surfaces exposed to a glow discharge (5,25,27). The primary processes of interest in plasma etching (and in plasma deposition) are summarized in Table II i20). These interactions result from the bombardment of surfaces by particles. Although vacuum UV photons and soft x-rays present in the plasma are sufficiently energetic to break chemical bonds, electron and particularly ion bombardment has been found to be the most effective method of promoting surface reactions (25). 

The original C.P.D. determinations of Oatley (44) were made with Ha and Oa on a Pt anode. The gases were ionized, and the work function of the anode increased by 1.2 v. with Oa and decreased by 1.15 v. with Ha. Similarly, Weissler and Wilson (46) obtained C.P.D. values of —1.2 v. and up to —1.4 V. for the adsorption of Oa on W and Ag films which were evaporated on to the inside of a cylindrical Ta anode. Adsorption was promoted by means of a glow discharge. Less reliable positive S.P. values were obtained for the adsorption of Ha and Na. The results were not always reproducible, and it is possible that the anode was a source of contamination. 

Effect of Additives. One of the first attempts to solve the preignition problem by additives was the use of tributyl phosphite, claimed in a patent by Campbell (14) This compound inhibited the catalytic activity of lead compounds in promoting the glowing of carbon. A later patent issued to Withrow claimed that trimethyl phosphate and trimethyl phosphite also are effective as fuel additives in inhibiting surface ignition due to leaded deposits (94). Street, in 1952, ran tests with tricresyl phosphate as an additive in leaded fuel and reported that the phosphorus compound affected the occurrence of lead compounds in the end-gas region of the combustion chamber (80). 

Glow discharges or plasmas have been used extensively to promote chemical reactions for thin-film etching and deposition in a variety of technologically important areas. The reactive chemical atmosphere and complex discharge-surface interactions in these systems permit the attainment of unique etch profiles and film properties. 

Preservative formulations that contain copper and chromium salts reportedly promote afterglow in treated wood subjected to fire. Once the treated wood starts to burn or glow, the wood may continue to glow until the entire member is consumed, even when no flame is present (38, 39). This characteristic can cause serious problems in utility poles, fenceposts, and highway signs, structures that might be... 

This study resulted in a series of reports on a comprehensive evaluation of fire-retardant treatments for wood (2-6). One hundred and thirty single chemicals or combinations of chemicals in the form of various salts were evaluated for flame-spread reduction, smoke, and corrosivity. Diammonium phosphate ranked first in reducing flame spread, followed by monoammonium phosphate, ammonium chloride, ammonium sulfate, borax, and zinc chloride. Zinc chloride, although excellent as a flame retardant, promoted smoke and glowing. Ammonium sulfate was the least expensive, but under certain environmental conditions it was corrosive to metals. None of the 130 compositions tested was considered ideal because of the adverse effects on some of the properties of wood. Several reviews of the subject are available and provide additional background material (J, 7-JO). 

An increase in the boron trichloride-to-hydrogen ratio tends to concentrate the glow around the substrate, promoting efficiency and minimizing the extraneous deposition. 

Electrons, ions, atoms, radicals and excited species are typically those promoting such reactions. In intense glow discharges, their concentrations reach significant values changing the overall reaction stoichiometry and, consequently, the steady-state concentrations of reactants and products. Thus, purely catalytic effects of the plasmas are observed only in weak discharges... 

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