Alloys amalgams

The high mobility and tendency to dispersion exhibited by mercury, and the ease with which it forms alloys (amalgams) with many laboratory and electrical contact metals, can cause severe corrosion problems in laboratories. A filter-cyclone trap is described to contain completely mercury ejected accidentally by overpressuring of mercury manometers and similar items. 

Ooourrcnoe—Early History—Preparation—Physical Properties—Spectrum— Chemical Propertie.s—Uses—Atomic Weight—Alloys—Amalgams. 

Solid solutions can form in metals if the atoms of which they are composed.are similar also, compounds can form. In such cases, expressions for the excess Gibbs energy of solid mixtures should contain a strain or mechanical energy term (which results from distorting the crystal structure to accommodate an atom of different size), a valence or coiilombic term to account for the difference in charge between the solute atom and the atoms of the host crystal, the noncoulombic interactions of the type we considered in discussing molecular fluids in Sec. 9.5, and perhaps a chemical reaction term to account for compound formation. Alloys, amalgams, and intermetallic compounds can occur in solids these more complicated situations will not be considered here. 

For these reasons, potential measurements of alloys are frequently made at higher temperatures with solid electrolytes or by using molten salt electrolytes. Measurements in aqueous electrolytes and at room temperatures were mostly restricted to mercury alloy (amalgam) electrodes. 

Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group and is the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium, and potassium. It colors a flame yellowish violet. Rubidium metal can be prepared by reducing rubidium chloride with calcium, and by a number of other methods. It must be kept under a dry mineral oil or in a vacuum or inert atmosphere. 

Density gradient Dental alloys Dental amalgam Dental amalgams Dental caries... 

Silver-mercury amalgams [SILVER AND SILVER ALLOYS] (Vol 22)... 

Metal acetylides Metal-air cells Metal alcoholates Metal alkoxides Metal alloys Metal amalgams... 

Aluminum, although highly electropositive, does not react with water under ordinary conditions because it is protected by a thin (2—3 nm) impervious oxide film that rapidly forms even at room temperature on nascent aluminum surfaces exposed to oxygen. If the protective film is overcome by amalgamation or scratching, water rapidly attacks to form hydrous aluminum oxide. Because of the tendency to amalgamate, aluminum and its alloys... 

Sodium amalgam is employed ia the manufacture of sodium hydroxide sodium—potassium alloy, NaK, is used ia heat-transfer appHcations and sodium—lead alloy is used ia the manufacture of tetraethyllead and tetramethyUead, and methylcyclopentadienylmanganesetricarbonyl, a gasoline additive growing ia importance for improving refining efficiency and octane contribution. 

Dental amalgams, mainly silver—tin—mercury alloys, have been used as fillings for many years (see Dental MATERIALS). The most common alloy contains 12 wt % tin. 

Composition. The composition of powdered alloys used in preparing dental amalgams usually includes 66.7—75.5% silver 25.3—27.0% tin ... 

The copper-rich amalgams have performed well in clinical trials in which they were compared with alloys having lower copper content. An improved marginal stability was observed, which may be associated with a longer clinical lifetime (136). These amalgams have also been called non-y2 amalgams, where refers to the compound Sn Hg comprised of Sn Hg [11092-12-9] and Sn Hg [11092-11-8]. 

In the dispersed-phase amalgam an additional phase of an eutectic of the Ag—Cu system and a reaction ring (2one) of Cu Sn [12019-69-1] around the residual silver alloy particles has been detected. If 10% gold is added to conventional alloys at the expense of the silver content, non-y2 amalgams are... 

The phases and their proportions present ia hardened amalgam are controlled by many factors. The composition of the alloy the size, shape, and size distribution of the particles the thermal history of the cast ingot and the comminuted alloy and the surface treatment of the particles are some of the factors for which the manufacturer is responsible. The tooth cavity preparation and the mixing, compacting, and finishing techniques of the dentist can make the difference between satisfactory and unsatisfactory restorations, even with the best of alloys. A minimal amount of residual mercury and porosity are needed to obtain the most serviceable restorations (138). 

Amalgam restorations are prepared by mixing a powdered alloy with mercury to form a plastic moldable mass that is packed or condensed iato the prepared cavity. The cavity is designed to provide mechanical retention, maximum marginal mass, support to absorb the functional stresses transmitted through the restoration, and maximum protection to the remaining tooth stmcture. The restoration reestabUshes the normal tooth anatomical form and function. 

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