Gas penetration

A high yield chemical pulp, eg, 52—53% bleached yield from softwoods, can be obtained, but strength properties ate inferior to those obtained from the kraft process. If a protector, eg, potassium iodide, is added, an additional 2—3% yield is obtained, as is an improvement in all strength properties. The gas penetration problem can be minimized if ftbetization is accompHshed before treatment with oxygen. Oxygen treatment of virtually all types of semichemical and mechanical pulps has been explored (55). Caustic, sodium bicarbonate, and sodium carbonate have been used as the source of base (56,57). In all cases, the replacement of the kraft by these other processes has not been justified over the alternative of pollution abatement procedures. 

Through circulation. The gas penetrates and flows through interstices among the solids, circulating more or less freely around the individual particles (Fig. 12-32). This may occur when solids are in static, moving, fluidized, or dilute conditions. 

Line S.J. Pickerell J.K. (1973) Testing a steam-formaldehyde sterilizer for gas penetration efficiency. J Clin Pathol, 26, 716-720. 

As mentioned above, gas has been widely used and it is a powerful vesicant agent. In the form of vapor, it damages the respiratory tract. Eyes become temporarily blind and the skin in contact with the substance becomes inflammatory. The sweaty zones of skin are the most damaged as well as sensitive mucous membranes. If no treatment is applied, the cutaneous reaction provokes blisters full of liquid after 4-8 h. Spread in the form of particles, the gas penetrates the respiratory tract and destroys the mucous membranes with a respiration distress syndrome. Lungs suffer from emphysemae and edema due to the presence of fluids, which may cause a death similar to a drowning if the dose is too strong. 

Natural gas is assuming a preponderant role in world energy supplies. Gas penetration in the energy sector is very large, reaching about 23 % world-wide in 2001 and with a forecast increase up to 28 % by 2025 Due to heating requirements, this sector has to deal with wide seasonal variations in consumption. 

The problem of gas-assisted displacement of Newtonian fluids along capillaries was first examined by Fairbrother and Stubbs (60). Later, Marchessault and Mason (61) measured the coating thickness after gas penetration (Rq — Rf) as well as the fractional... 

Fig. 13.36 The fractional coverage during nonisothermal gas-penetration experiments in PB-300, where the gas was injected after different F0 = at/R, that is, dimensionless delay times, following the step bath temperature switchover from 60° to 0°C. [Reprinted by permission from K. W. Koelling, V. Gauri, M. Tendulkar, R. Kaminski, and O. Becker, Understanding the Controlling Mechanisms of Gas-assisted Injection Molding through Visualization, SPE ANTEC Tech Papers, 43, 3697 (1997).]...

A. J. Poslinski and D. J. Coyle, Steady Gas Penetration through Non-Newtonian Liquids in Tube and Slit Geometries Isothermal Shear-Thinning Effects, Proc. Polymer Processing Society, 10th Annu. Meet., Akron, Ohio (1994), pp. 219-220. 

Helium pycnometry can also be used to obtain an estimate of porosity providing that the porous sample is sealed to prevent gas penetration. There are experimental problems that need to be addressed to ensure that the seal is effective and that it doesn t significantly alter the volume or weight of the sample which are beyond the scope of this study. 

Phillips (19) formed a reference electrode by coating a noble metal with a Langmuir-Blodgett multilayer of calcium palmitate and used it to detect the presence of a polar vapor in dry atmospheres by its adsorption on an uncoated metal electrode. Water vapor and oxygen were carefully excluded from the surrounding atmosphere, since either gas penetrated the multilayer coating on the reference electrode. This report describes the preparation, properties, and several applications of a more general and useful type of reference electrode. 

Fig. 10.14 Non-emissive defects in a polymer LED visual appearance (a), gas penetration at grain boundaries (b) and dust particles (c) in the cathode. Reproduced with permission of Wiley-VCH from Kim et al. (2002).

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