Barrier physical

The most common and traditional approach for controlling AMD is to establish a physical barrier that comprises a wet or dry cover (Kleinmann 1990 Evangelou and Zhang 1995). Such dry or wet covers work because they create an oxygen barrier that prevents pyrite oxidation (Belzile et al. 1997 Peppas et al. 2000 Vigneault et al. 2001). 

In addition to using soil as a dry cover material, synthetic materials such as polyethylene and plastic liners can be used to control AMD under field conditions. Caruccio (1983) used a plastic cover to completely cover a site in West Virginia and found that AMD was significantly reduced. However, covering a large volume of waste with a synthetic liner is usually too expensive, which may preclude its routine field use (Skousen and Foreman 2000). Additionally, plastic or polymer liners are prone to cracking, and repair costs are prohibitive. 

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A third method of contact known as an anaerobic filter also uses upward flow but keeps the sludge in the digester by a physical barrier such as a grid. 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Eig. 1. The relation between physical barriers and levels of protection in defense-in-depth design of a nuclear faciUty (12). Courtesy of IAEA. 

Oil Repellent. Fluorochemicals are the only class of material that can provide oil repeUency without altering the porosity of the paper or paperboard. Physical barriers to oil penetration are used primarily for their moisture- or gas-barrier properties, with retarded oil penetration as a secondary benefit. The most common od-repeUent additives are long-chain perfluoroalkyl phosphate salts of ammonia or diethanol amine. Commercial sources include Scotchban (3M), Zonyl (DuPont), and Lodyne (Ciba Specialties). There are also a fluorochemical carboxylate salt, Lodyne (Ciba Specialties), and fluorochemical copolymers, eg, Scotchban (3M). The widest range of oily fluid holdout is provided by the fluorochemical copolymers. 

The Kit Test (T-559 pm-96) can be used to measure oU repeUency when there is no physical barrier to oU penetration such as that provided by a film, foU, or waterproof coating (71). Another measure of oU repeUency is the Turpentine Test (T-454 om-89) (71). If a physical barrier is present, tests that measure the weight of oU pick-up or show-through under conditions that simulate the end use are appropriate. 

Waxes are one of the two general classes of commercial antiozonants. Waxes are derived from petroleum and are of two common types, paraffin and microcrystalline (20—23). Typical carbon numbers are n = 20 50 for paraffin waxes and n = 30 70 for microcrystalline materials. If a wax is present ia a vulcanizate at a concentration exceeding its solubiUty, some of it will migrate to the mbber surface where it can form a physical barrier to prevent the penetration of ozone. Waxes, of course, are essentially unreactive towards ozone so that there is no appreciable chemical protection. Commercial waxes are... 

Separator s a physical barrier between the positive and negative electrodes incorporated into most cell designs to prevent electrical shorting. The separator can be a gelled electrolyte or a microporous plastic film or other porous inert material filled with electrolyte. Separators must be permeable to ions and inert in the battery environment. 

Various physical barrier devices are available for contraceptive use by men and women. Modem barrier methods such as diaphragms, condoms, and cervical caps were made possible by the discovery of the vulcanisation of mbber. 

A skin woundprotectant is a nonirritating antimicrobial-containing preparation appHed to small cleansed wounds it provides a protective physical barrier and a chemical (antimicrobial) barrier that neither delays healing nor favors the growth of microorganisms. 

Sites made suitable for use by human-made physical barriers shall not be located where improper operations or maintenance of such structures could permit the waste, leachate, or gases to contact usable groundwater or surface water. 

Separate the metal from the environment with a physical barrier. Many corrosion inhibitors make use of this principal to protect metals. Proper use of an appropriate inhibitor may reduce or eliminate pitting. Pits are frequently initiation sites for corrosion-fatigue cracks. The effectiveness of inhibitors depends upon their application to clean metal surfaces. An example of this method is the use of zinc coatings on steel to stifle pit formation. 

The security system can be considered as layers of protection. Physical barriers and deterrents constitute not only the building stmcture itself, made up of walls, doors, windows, floor and a roof, but the yard around the building and probably a perimeter fence or wall. 

These systems are used in conjunction with some form of physical barrier (e.g. door, gate, turnstile) and comprise ... 

For size analyses of particles larger than Vte y, the geometric properties of uniformly constructed physical barriers such as sieves are commonly used. Though this technique of finished product size control dates back to at least 2500 BC when the Egyptians constructed woven cloth sieves for preparation of foodstuffs, it is only within the... 

General adsorption inhibitors form a physical barrier over the entire metal surface. Examples are diphenylamine and furfuraldehyde. 

Physical barriers, e.g. splashguards, screens, or use of separate rooms. 

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