Corona or Plasma Discharge

Atmospheric corona discharge has been used to increase the surface energy of wood surfaces by oxidative activation (Back and Danielsson, 1987). Improved bonding of a water-based acrylate lacquer was found following corona treatment of the wood surface, with no improvement found when a solvent-based alkyd system was used. 

Mahlberg etal. (1998) modified the surface of birch veneer with a hexamethyldisi-loxane (HMDSO) plasma in order to improve the compatibility between the wood surface 

A disadvantage with conventional plasma treatment techniques is the requirement for treatments to take place in a vacuum, adding to the equipment costs. However, if a dielectric material is placed between the electrodes of the plasma equipment, then treatment can be performed at atmospheric pressure. This method is known as a dielctric barrier discharge treatment and has been the subject of some recently reported studies. 

To be effective, it is essential that the impregnant is nonleachable in service conditions. However, it is not a primary requirement that the impregnant be chemically bonded to the cell wall polymeric constituents, although this may occur in some circumstances. It is essential that the frxed impregnant is nontoxic whilst in the cell wall and under any circumstances in which it is released from the cell waU, such as disposal by incineration or composting, or due to any recycling process. 

Wood Modification Chemical, Thermal and Other Processes C. Hill 2006 John Wiley Sons, Ltd 

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The various surfactants/treatments use include, but are not limited to, corona or plasma discharge, surface derivatization, graft copolymerization, acetylation. 

All three types of discharge involve the formation of ions as part of the process. For various reasons, most of the ions are positive. The ions can be examined by mass spectrometry. If small amounts of a sample substance are introduced into a corona or plasma or arc, ions are formed by the electrons present in the discharge or by collision with ions of the discharge gas. 

Several fiber treatments are reported in literature [9], namely (a) physical treatments, such as solvent extraction (b) physico-chemical treatments, like the use of corona and plasma discharges or laser, y-ray and UV bombardment and (c) chemical modifications, both by the direct condensation of the coupling agents onto the cellulose surface and by various grafting strategies calling upon polycondensations and free-radical or ionic polymerizations. 

In the laboratory, it has been found that similar effects can be produced if a voltage is applied between two electrodes immersed in a gas. The nature of the laboratory or instrumental discharge depends critically on the type of gas used, the gas pressure, and the magnitude of the applied voltage. The actual electrical and gas pressure conditions determine whether or not the discharge is called a corona, a plasma, or an arc. 

Particularly in mass spectrometry, where discharges are used to enhance or produce ions from sample materials, mostly coronas, plasmas, and arcs are used. The gas pressure is normally atmospheric, and the electrodes are arranged to give nonuniform electric fields. Usually, coronas and plasmas are struck between electrodes that are not of similar shapes, complicating any description of the discharge because the resulting electric-field gradients are not uniform between the electrodes. 

The various stages of this process depend critically on the type of gas, its pressure, and the configuration of the electrodes. (Their distance apart and their shapes control the size and shape of the applied electric field.) By controlling the various parameters, the discharge can be made to operate as a corona, a plasma, or an arc at atmospheric pressure. All three discharges can be used as ion sources in mass spectrometry. 

The exact conditions of gas pressure, current flow, and applied voltage under which the discharge occurs determine if it is of the corona, plasma, or arc type. The color of the emitted light may also change, depending not only on the type of gas used but also on whether it is a corona, plasma, or arc discharge. 

Printing and coating need pre-treatment such as corona discharge or plasma treatments. The exposure must be brief and superficial and the original and aged properties must be tested. 

Of all the reactions studied, only the synthesis of nitrogen oxides and acetylene in arcs or plasma torches and that of ozone in glow and corona discharges are of major importance. In addition, a few small-scale preparations of inorganic compounds have been developed, e.g. synthesis of hydrazine and of hydrides and halides of silicon, germanium, tin, lead, phosphorus or arsenic 3> ... 

These factors lead to an inferior barrier and a more rapid reduction of the barrier effect. For a good barrier effect, co-extrusion or coating of the substrate, corona discharge, or plasma pretreatment, are, therefore, usually necessary. Vacuum metallization conditions, thermal stress of the substrate, and mechanical stress of the metal layer also play a fundamental role ... 

The use of static SIMS for the characterization of surfaces of polypropylene (PP), PTFE and a PMDA-ODA type poly-imide is described. Interfaces between evaporated copper or chromium films onto PTFE and polyimide were also analyzed. Some of the polymer substrates were modified by ion beams, corona discharge in air or plasma treatments in air, At and H2. It is demonstrated that SIMS is highly complementary to XPS for the analysis of such modified surfaces, in that effects such as crosslinking, unsaturation and formation of low-molecular weight material at surfaces can be detected. 

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