Layer multiple

Another limitation of tire Langmuir model is that it does not account for multilayer adsorption. The Braunauer, Ennnett and Teller (BET) model is a refinement of Langmuir adsorption in which multiple layers of adsorbates are allowed [29, 31]. In the BET model, the particles in each layer act as the adsorption sites for the subsequent layers. There are many refinements to this approach, in which parameters such as sticking coefficient, activation energy, etc, are considered to be different for each layer. 

One type of thick hardwood plywood stiU available is imported from the northern Scandinavian countries and is generally known as Finnish birch. Characteristically, these plywoods are manufactured using multiple layers of veneer of the same thickness, about 1.5 mm (1 /16 in.), and bonded with a urea—formaldehyde or melamine—urea—formaldehyde adhesive. 

Tables 2—5 Hst some typical properties or ranges of properties for the more common film and sheet products. Although these values are good for comparative purposes, actual performance tests are best to determine suitabiHty for use. Properties of multiple-layer films or sheets in laminar stmctures cannot always be predicted from values for the individual polymer layers. Use conditions of stress, temperature, humidity, and light exposure all strongly influence performance. Film and sheet manufacturers can recommend product combinations or variations that may provide significant performance advantages to the user.

All laminated glass iacreases the level of secutity to some extent. However, depending on the appHcation, secutity glass is constmcted of multiple layers of glass, PVB, polycarbonate, polyurethane, or other polymer matenals. Laminated glass permits the same visual observation as normal glass but prevents or delays unauthorized entry (or exit) until the attempt can be detected. It complies with test UL 972 (38). 

Die cut metal lamiaates are also appHed to plastics for decorative effects, or for radio frequeacy iaterfereace shielding. These lamiaates are formed by vacuum depositioa, or by attachmeat of foil to a plastic layer for easier handling. Multiple layer composites of plastic and aluminum are used for specialized packagiag, especially for moisture or gas barriers. 

Metal powder—glass powder—binder mixtures are used to apply conductive (or resistive) coatings to ceramics or metals, especially for printed circuits and electronics parts on ceramic substrates, such as multichip modules. Multiple layers of aluminum nitride [24304-00-5] AIN, or aluminay ceramic are fused with copper sheet and other metals in powdered form. The mixtures are appHed as a paste, paint, or slurry, then fired to fuse the metal and glass to the surface while burning off the binder. Copper, palladium, gold, silver, and many alloys are commonly used. 

Fig. 4. Integrated vault technology for low level waste disposal where A represents waste containers that are placed in concrete overpacks and sealed with grout B, closed modules covered with a multiple-layer earthen cover, to direct water away from modules, and short rooted vegetation for erosion control and C, overpacks placed in reinforced concrete modules which are closed with a reinforced concrete roof Courtesy of Chem-Nuclear Systems, Inc.

StiU another method used to produce PV cells is provided by thin-fiLm technologies. Thin films ate made by depositing semiconductor materials on a sohd substrate such as glass or metal sheet. Among the wide variety of thin-fiLm materials under development ate amorphous siUcon, polycrystaUine sUicon, copper indium diselenide, and cadmium teUuride. Additionally, development of multijunction thin-film PV cells is being explored. These cells use multiple layers of thin-film sUicon alloys or other semiconductors tailored to respond to specific portions of the light spectmm. 

A large amount of information can be provided on a technical service Internet site by means of hyperlinks, ie, cHckable terms or addresses that allow the reader to access multiple layers of information by a simple cHck of a control device. Some companies have provided their entire Hbrary of open Hterature on their products ia the form of material stored within a hypedinked page. The reader can either browse this information directly on the site or download it to their own computer to be read at their convenience. 

SBS membrane systems are generally installed in hot asphalt but can be installed using a torch like APP products or in some cold apphcation cement systems. Like APP systems, they are generally installed in multiple layers. The undedayment layers are generally standard BUR felts or basesheets. SBS membrane sheets can also be formulated to be self-adhering. These products are no longer used in membrane appHcations but are used as ice and water dam matedals on the eaves under shingle roofs in cold climates. 

In most coatiag operatioas a single layer is coated. Whea more than one layer must be appHed one can make multiple passes, or use tandem coaters where the next layer is appHed at another coatiag statioa ioimediately foUowiag the dryer sectioa for the previous layer, or a multilayer coatiag statioa can be used. Slot, extmsion, sHde, and curtain coaters are used to apply multiple layers simultaneously. SHde and curtain coaters can apply an unlimited number of layers simultaneously, whereas slot and extmsion coaters are limited by the complexity of the die internals. 

Extmsion coating lines operate at speeds up to 1000 m /min and can apply 10—30 g/m of coating. Additionally, multiple layers can be extmded from one die. Multiple extmders feeding one die provide the unique capabiUty of producing layers of different resins to give superior functional properties. For example, an inexpensive resin can be used as the core of a three-ply extmdate, the outer pHes being more expensive but also much thinner than if extmded alone. 

Habitrol (102), co-developed by Lohmarin Therapie Systeme and Ciba-Geigy Ltd., and marketed by Ciba-Geigy, consists of an impermeable backiag laminate with a layer of adhesive and a nonwoven pad to which a nicotine solution is appHed (103). Multiple layers of adhesive on a release liner are then laminated on the patch. The systems come ia 10, 20, and 30 cm sizes corresponding to 7, 14, and 21 mg/day, respectively, deUvered over 24 hours. 

Fig. 2. Multilayer printed circuit board composite. Constmction is multiple layers of epoxy—glass and foil copper. Foil copper outermost layer and drilled through-holes are sequentially plated with electroless copper, electrolytic copper, electroless nickel, and electroless gold.

In a third process, a loose liner is fastened to a carbon steel shell by welds spaced so as to prevent collapse of the hner. A fourth method is weld overlay, which involves depositing multiple layers of alloy weld metal to cover the steel surface. 

Cables with multiple-layer sheathing have plastic-insulated cores. Solid PE or sintered PE is used as the plastic. Sintered PE is a foamed polyethylene material that has different electrical properties than solid PE. Under certain circumstances the core region is filled with a petrolatum material to give protection against... 

In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiate a specimen, and the emitted fluorescent X rays are analyzed with a crystal spectrometer and scintillation or proportional counter. The fluorescent radiation normally is diffracted by a crystal at different angles to separate the X-ray wavelengths and therefore to identify the elements concentrations are determined from the peak intensities. For thin films XRF intensity-composition-thickness equations derived from first principles are used for the precision determination of composition and thickness. This can be done also for each individual layer of multiple-layer films. 

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