Glow discharge polymerization

The increasing application of SF6 as an insulating gas has led to many studies on SF6 decomposition in gas-insulated equipment. In the presence-of an electric arc, spark or corona, SF6 decomposes to a wide variety of chemically active products which possess completely different properties from SF6. The accumulation of these decomposition products in the equipment has caused concerns regarding personnel safety and material compatibility problems. This paper reviews previous research in SF6 decomposition relating to the operation of gas-insulated switchgears, gas-insulated transmission lines, and electrostatic accelerators. Results on the qualitative and quantitative determination of the by-products and their formation ion rates in various modes of electrical discharges are summarized. The mechanisms leading to the formation of transient and stable products are described. In particular, the influence of discharge energies and impurities on the formation of SOF2 and SO2F2, the two dominant stable by-products, is discussed. The effects of the by-products on personnel safety and equipment ent dielectric integrity are presented. The application of SF6 gas analysis as a tool for diagnosing the internal condition of gas-insulated equipment is assessed. Based on the results of many phenomenological observations, future research activities are suggested to address the issues of safety, compatibility and equipment aging. More fundamental studies on electron, ion, and neutral reaction rates in an SF6 discharge are required to gain a better understanding of the decompositon mechanisms and the influence of the products on equipment operation.

SF6 Decomposition in Gas-Insulated Equipment

3 – Plasma-Polymerized Organosilicones and Organometallics

For pt.I see ibid., vol.26, no.6, p.1163-76, Dec. 1991. In order to define the origin and the production rate of the CF/sub 4/ formed under the effect of arcing in circuit breakers containing SF/sub 6/ as a gaseous insulator, a series of measurements was taken in two Alsthom circuit breakers in which the gaseous insulator (SF/sub 6/, N/sub 2/), the material from which the nozzle is made (PTFE+CaF/sub 2/, pure PTFE, RPS Ryton R4) and the electrode metal (Cu/W alloy, copper) were changed. Moreover, with the aim of refining the results concerning the influence of the chemical composition of the insulator used to make the nozzle, several insulators (Megelite, PPS Ryton R4, Kel'F, Teflon, polypropylene and nylon) were exposed to sparking in an SF/sub 6/ atmosphere. >

SF/sub 6/ decomposition under power arcs. II. Chemical aspects

This article will describe some of the recent progress in the area of plasma polymerization and plasma treatment. It is not intended to be an exhaustive overview of the field, but instead a summary of the highlights of research studies in this field selected by the authors according to the importance.

Plasma chemistry of polymers

The influence of various parameters on the polymerization reaction of benzene in a capacitively coupled rf plasma has been investigated, with particular emphasis on coatings structure and quality. Molecular weight distribution studies by gel permeation chromatography indicate that the degree of polymerization is mainly influenced by pressure and power. A two-stage mechanism of polymer formation is proposed on the basis of experimental data: oligomers or polymers are first formed in the gas phase and then diffuse to the electrodes and reactor walls, where they may undergo an emulsiontype polymerization. Sputtering and pyrolysis effects are suggested to explain the additional observations on the lowest-and highest-pressure films.

Polymerization of benzene in a capacitively coupled RF plasma

Propriétés électriques de minces films de polyméres formés dans une décharge r.f. à partir de monoméres organiques semi-conducteurs

An investigation has been made of the degradation reactions due to the application of an electric are at the polymeric insulating material/SF 6 interface. Polyethylene, Teflon, epoxy and phenolic resins were used as the solid insulating materials in the study. The degradation process was observed to occur in two separate steps. In the first step, the polymeric materials are pyrolyzed by the are (are degradation). The second step involves a gas-phase reaction between the SF 6 and the volatile products generated by the are degradation. Analysis of the arc-degradation products by gas chromatography, mass spectrometry and infrared spectrophotometry indicates a significant difference between the composition of the various reaction products and the corresponding products of a degradation reaction carried out thermally. The principal reaction products of the gas-phase reactions between SF 6 and the volatile degradation products were identified as CF 4 , SOF 2 , SF 4 , SiF 4 , HF and also CO in the cases of epoxy and phenolic resins. General reaction mechanisms for the formation of these products are proposed. The implications of these results regarding the use of such insulating systems in electrical apparatus are discussed.

Arc degradation of SF 6 in the presence of polymeric insulating materials

Studies were conducted on the degradation reaction of polyethylene, poly(tetrafluoroethylene), and an expoxy resin resulting from the action of a 13.56-MHz radio-frequency (rf) discharge in SF6. The curves showing the temperature variations of the samples during the experiment suggest that this degradation process occurs in two distinct stages: in the first, the heat released by the electric discharge causes the thermal degradation of the polymers, whereas in the second, the volatile degradation products react in the gas phase with the excited SF6. Analysis of the reaction products shows consistency with this two-step degradation model. The main degradation products have been identified as C2H2, C2H4, SOF2, and CS2 in the case of polyethylene; as CF4, C2F4, and SOF2 in the case of poly(tetrafluorethylene); and finally as CO2 and SOF2 in the case of the epoxy resin. Furthermore, it is interesting to note the formation of polymers of the di(trifluoromethyl) polysulfane type, CF3-Sn-CF3, among the reaction products. The more volatile members, n = 2, 3, and 4, were identified by mass spectrometry, whereas the heavier members, identified by infrared spectrophotometry, often took the form of a whitish powder deposited on the walls of the reactor.

Antoine Théorêt

Papers

Polymerization of benzene in a capacitively coupled RF plasma

Propriétés électriques de minces films de polyméres formés dans une décharge r.f. à partir de monoméres organiques semi-conducteurs

Arc degradation of SF 6 in the presence of polymeric insulating materials

Degradation of polymers subjected to radio‐frequency discharges in SF6