Contact epoxy-resin

Aqueous dispersions are used in fiber bonding, paper coating, friction and abrasive appHcations, and laminates and wood bonding. PhenoHc dispersions improve the strength of latex-contact adhesive appHcations. Epoxy-modified phenoHc dispersions are prepared by dispersion of the phenoHc epoxy resin. The systems are used for baked primer appHcations and bonding requirements. Minimum baking conditions are 20 min at 150°C (25). 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forrning tools, and foundry patterns, as weU as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a Hquid bisphenol A epoxy resin with an aHphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

The metal film is then electroplated with copper, and the metal part brazed to the copper plating. Adhesives, usually epoxy resins, are used to join parts at low temperatures. Finally, ceramic parts can be clamped together, provided the clamps avoid stress concentrations, and are provided with soft (e.g. rubber) packing to avoid contact stresses. 

Polymeric materials are commonly used for bonding materials. Impact or contact adhesives are mainly based on highly crystalline polychloroprene (Neoprene), NR latex is used as a flexible adhesive very suitable for use with fabrics. Rigid adhesives based on materials such as polystyrene cement, epoxy resin or cyanoacrylates are suitable for bonding of rigid materials. The bond is provided by intramolecular forces between the adhesive and the adherend. Adiabatic... 

In the case of contact between metals and epoxy resins, a sandwich of the epoxy between two flat and well-cleaned metal (copper or gold) surfaces was realized. A steady-state technique was used in most cases. 

The most frequent causes of allergic contact dermatitis in the United States include plants (poison ivy, poison oak, and poison sumac), metallic salts, organic dyes, plastic resins, rubber additives, and germicides.74 The most common skin patch test allergens found to be positive in patients along with potential sources of exposure are shown in Table 32.1.75 In patients with occupational contact dermatitis who were skin patch tested, the common allergens included carba mix, thiuram mix, formaldehyde, epoxy resin, and nickel.76... 

Figure 9.2 Schematic diagram showing how an electrical contact is fixed with silver paint to the conductive side of an optically transparent electrode. The outer layer of epoxy resin is necessary to impart strength, to insulate the silver paint from the analyte solution and to stop analyte solution seeping between the paint and the conductive layer.

Bisphenol F (BPF) is a mixture of three isomers 2,2 -, 2,4 -, and 4,4 -dihydroxydiphenylmethane, in the ratio 15%, 50% and 35%, respectively. It has also found application in the manufacture of epoxy resins, but as a fully crosslinked polymer it is rarely used in food-contact materials. Residues of... 

Persistent photosensitivity developed in eight men after occupational exposure to hot epoxy resin fiimes. The condition was limited to sites contacted by the resin. Small doses of ultraviolet-A light evoked abnormal reactions consisting of erythema, edema, and papules in the clinically involved skin. Positive photopatch tests were observed to epoxy resin in four subjects and to bisphenol A in all subjects. Another study showed that bisphenol A can be released during the thermal decomposition of epoxy resin in the temperature range of 250-350°C. Photosensitizing activity was explained by the formation of ftee radicals during exposure to ultraviolet-B radiation of bisphenol A vapor, to form a semiquinone derivative of bisphenol A ... 

Cements that harden by the loss of solvent generally are to be avoided because the solvent can be lost only be diffusion thru the expl. Diffusion may be slow and the solvent may modify the properties of the expl. Two types of cement that have been used for this purpose are catalytic setting cements, like epoxy resins, and contact cements. Compatibility of the materials to be used should be checked. Compatibility of epoxy resins with most explosives depends upon the catalyst or hardener used (Ref 8). Data regarding bond strengths and other pertinent properties also have been compiled (Refs 5 6)... 

When introducing binders or plasticizers into intimate contact with explosives, it is critical that there is no chemical incompatibility either initially or later on, as munitions are expected to have in-service life-spans of up to 30 years. Nitramines for example, have been found to be chemically incompatible with amines which are used for fast-curing epoxy resins. Therefore, all materials that might be used as part of an explosive formulation are carefully tested for their chemical compatibility with each other and also with the explosive, prior to their use for explosive formulations. 

The value of the epoxy resins lies in their reactivity with a variety of chemical groups. This enhanced reactivity also means that the surface chemistry of the reinforcement which the epoxies are cured against, can alter the local structure in the interphase regionJl). The most common reinforcement surfaces cured in contact with the epoxies are carbon/graphite fibers, glass fibers, aramid fibers and metal oxides. The surface chemistry of these reinforcement surfaces is quite diverse and in many cases can be the reason for alteration of the interphase epoxy structure as compared to the bulk. 

Bisphenol A diglycidyl ether is a contact allergen among people who have worked with low-molecular-weight epoxy resins (lARC, 1989). 

G-17216, and in Victoria Land by John Mulligan, also on an NSF grant to the Bureau of Mines. Each sample was crushed by hand with a mortar and pestle to approximately 0.625 by 0.25 inch. A split of each crushed sample was embeaaed in epoxy resin, polished, examined microscopically, photographed, and then its reflectance was determined. Knoop indention hardnesses were also determined by using a 20-gram load on the diamond indenter. The indenter was kept in contact with the sample for 15 seconds. Additional splits of each sample were crushed to minus 60 mesh, dried at 100°C. for 24 horns, and their electrical resistivity was determined at 20,000 p.s.i. The sample locations, chemistry, petrography, reflectance, electrical resistivity, and hardness of the 36 Antarctic coal samples studied are included in Table I. 

Connection between the electrode material and lead or shaft is made in one of four ways soldering, with silver-loaded epoxy resin, spot welding, or by spring-loaded contacts. 

The n-type GaP used was a single crystal in the form of wafers, 99.999%pure and doped with sulfur to the concentration of 2 to 3 x 1017 cm-3 (Yamanaka Chemical Industries Ltd.). The p-type GaP used was doped with zinc to 3.7 x 10 cm 3 (Sanyo Electric Co., Ltd.). Both were cut perpendicular to the [lll]-axis. The ohmic contact was made by vacuum deposition of indium on one face of the crystal, followed by heating at ca. 500 °C for 10 min. The side connected with a wire was covered with epoxy resin. Before the experiment, the crystals were polished and etched with warm aqua regia. The (lll)-face (Ga face) and the (lll)-face (P face) were distinguishable by microscopic inspection of the etched surfaces, the former very rough and the latter smooth. 

Modification of the sensor structure. The above amperometric sensor has a rather complicated construction, because the sample gas (H2 + air) is separated from the reference air. So, we tried to simplify the sensor structure as shown in Figure 9. As proton conductor we used a thin antimonic acid membrane (mixed with Teflon powder) of 0.2 mm thickness. This membrane is thin and porous enough to allow a part of the sample gas to permeate. On the other hand, the counter Pt electrode was covered with Teflon and Epoxy resin in order to avoid a direct contact with the sample gas. 

UMEs used in our laboratory were constructed by sealing of carbon fibre into low viscosity epoxy resin (see Fig. 32.4) [118]. This method is simple, rapid and no specialised instrumentation is required. Firstly, the fibres are cleaned with this aim. They are immersed in dilute nitric acid (10%), rinsed with distilled water, soaked in acetone, rinsed again with distilled water and dried in an oven at 70°C. A single fibre is then inserted into a 100- iL standard micropipette tip to a distance of 2 cm. A small drop of low-viscosity epoxy resin (A. R. Spurr, California) is carefully applied to the tip of the micropipette. Capillary action pulls the epoxy resin, producing an adequate sealing. The assembly is placed horizontally in a rack and cured at 70°C for 8h to ensure complete polymerization of the resin. After that, the electric contact between the carbon fibre and a metallic wire or rod is made by back-filling the pipette with mercury or conductive epoxy resin. Finally, the micropipette tip is totally filled with epoxy resin to avoid the mobility of the external connection. Then, the carbon fibre UME is ready. An optional protective sheath can be incorporated to prevent electrode damage. 

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