Resistance of glass

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La203 improves the alkali resistance of glass, and is used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron. 

The constmction of the E-111 windshield shown in Eigure 8 replaced a glass—silicone laminate previously used. The all-plastic windshield has improved impact resistance so that it is birdproof to 250 m/s (33). In this instance, the scratch resistance of glass was waived to obtain the impact performance at the allowed weight. 

The introduction of divalent calcium and barium oxides into frits in preference to monovalent sodium and potassium generally increases water resistance. Furthermore, oxides of tetravalent and pentavalent metals have a favourable effect on the resistance of glasses and enamels to water. The influence of B2O3 and fluorine in the frit upon chemical resistance is variable and is dependent upon the content of them and the balance of the frit constituents, but they usually cause a diminution in resistance. In general, mill-added clay, silica and opaciher increase water resistance provided the firing or fusing of the enamel is at the optimum. 

The effects of corrosion on other properties need similar direct assessment in many cases. However, in the absence of accepted standard tests the BS, DIN, ISO tests for laboratory glassware are often used. At the present time, the British Standard BS 3473 Methods of testing and classification of the chemical resistance of glass used in the production of laboratory glassware is being re-issued in six parts, of which the first five parts are identical to recently revised ISO test procedures. There are also corresponding DIN tests in some cases which are very similar. The current situation is ... 

Standard Methods of Test for Resistance of Glass Containers to Chemical A Hack, ASTM Method C 225-68... 

Method of Testing Chemical Resistance of Glass Used in the Production of Laboratory Glassware, BS 3473 1962... 

Determination of resistance of Glass to Attack by Boiling Aqueous Solution of Mixed Alkali, ISO R695 1968 ... 

Determination of Hydrolytic Resistance of Glass Grains at 98°C, ISO R719 1968... 

Alkali ions in solution increase the pH, with two consequences. The rate of silica extraction increases with the rise in pH value above 9 and the rate of alkali exchange is reduced. However, since the higher alkalinity favours solution (of silica) further alkali is released by the lattice. The quantity of alkali extracted can be used as a measure of the resistance of glass to attack... 

How does chemistry increase the resistance of glass to impact and shattering ... 

The resistance to moisture and hot water is good without hydrolysis but the resistances of glass fibre reinforced compounds can decrease significantly because of polymer/fibre interface alterations. For example, after 1 year in water at 120°C, tensile strength retention is 50% for a given compound. However, special grades with improved hot-water resistance are marketed and are successfully used in hot-water pumps. 

The chemical nature of the experimental methacrylate functional silanes on silica was studied by FTIR, and the performance of the silanes in improving the chemical resistance of glass fiber/polyester composites was evaluated. 

Whenever there is a chemical erosion of glass, water or its dissociation products, H+ or OH ions will be involved. Because of this, a distinction is made between the resistance of glass to water (its hydrolytic resistance) and to alkali or acid. Under attack from water or acids, small numbers of cations, particularly monovalent and divalent, are released. On resistant types of glass, a very thin layer of silica gel forms in this way on the glass surface and usually inhibits further erosion. In contrast, hydrofluoric acid, alkaline solutions and, under certain circumstances, phosphoric acid will slowly remove the inhibitor layer and thus the entire surface. Nonaqueous solutions (organic solutions), however, are practically nonreactive with glass. 

Assumptions 1 Steady operating conditions exist. 2 Heat transfer through the v/indow is one-dimensional. 3 Ifie thermal resistance of glass sheets is negligible. Piopeities The emissivity of clear glass is 0.84. 

Determine the CZ-faclors for the center-of-glass section of a double-pane window and a triple-pane window, fhe heat transfer coefficients on the inside and outside surfaces are 6 and 25 W/ni °C, respectively. The thickness of the air layer is 1.5 cm and there are two such air layers in tiiple-pane window. The Nu.sselt number across an air layer is estimated to be 1.2- Take the thermal conductivity of air to be 0.025 W/m C and neglect the thermal resistance of glass sheets. Also, assume that the effect of radiation through the air space is of the same magnitude as the convection. 

Specific resistance of glasses decreases with temperature, or in other words, electrical conductivity increases according to the exponential relationship... 

Because of the similarity between the mechanisms of viscous flow, diffusion and electrical conductivity, which are all activated processes, a relationship between these phenomena was sought. It has been established empirically that the temperature dependence of viscosity and resistivity of glass melts are often mutually dependent according to the relationship log t/ 3 log 2, or log = a log — b (cf. Morey, 1954). However, it should be borne in mind that mobility of cations is critical for transfer of electric charges while mobility of anionic structural units (network formers) is involved in the case of vi.scous flow. This is why the relation between the two quantities is difficult to interpret. 

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