Amalgams mixed alloys

The result of the amalgamization is a microstructure consisting of unreacted Ag3Sn and Ag-Cu surrounded by a layer of Cu6Sn5 and the y matrix. The microstructure of the one-component non-gamma-2 amalgams is similar to that of the mixed alloy except that the Cu6Sn5 particles are decomposed in the 7j phase and form no layer. 

Amalgam An alloy obtained by mixing silver tin alloy with mercury. 

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. 

Alloys are metallic materials prepared by mixing two or more molten metals. They are used for many purposes, such as construction, and are central to the transportation and electronics industries. Some common alloys are listed in Table 5.5. In homogeneous alloys, atoms of the different elements are distributed uniformly. Examples include brass, bronze, and the coinage alloys. Heterogeneous alloys, such as tin-lead solder and the mercury amalgam sometimes used to fill teeth, consist of a mixture of crystalline phases with different compositions. 

Most substances expand when heated and contract when cooled, but liquid mercury shows an especially large variation of volume with temperature. That is why it is so often used in thermometers and barometers. Mercury also mixes with a number of metals to form alloys called amalgams. Amalgam is a special name given to alloys of mercury. With silver it forms a silver amalgam, which quickly hardens. This is the silver filling used by dentists. 

In 1787 William Cruikshank (1745-1795) isolated, but did not identify, strontium from the mineral strontianite he examined. In 1790 Dr. Adair Crawford (1748—1794), an Irish chemist, discovered strontium by accident as he was examining barium chloride. He found a substance other than what he expected and considered it a new mineral. He named the new element strontium and its mineral strontianite after a village in Scotland. In 1808 Sir Humphry Davy treated the ore with hydrochloric acid, which produced strontium chloride. He then mixed mercury oxide with the strontium chloride to form an amalgam alloy of the two metals that collected at the cathode of his electrolysis apparatus. He heated the resulting substance to vaporize the mercury, leaving the strontium metal as a deposit. 

This methodology has been applied for determining the relative composition of alloys [225], amalgams [226], and mixed crystals [227], among others [74-78], based on peak current measurements. The essential requisite is that both electroactive components behave independently—i.e., that the components of a mechanical mixture do not influence each other with respect to their thermodynamic activities in electrochemical reactions [77]. In Fig. 4.4, theoretical calibration plots for the absolute peak current, when the amount of mixture is constant for each measurement (left) and for the percentage peak current (right), are shown [77, 228]. 

One silver alloy containing about 70% silver. 26% tin. 3% copper, and 1% zinc is unique in that it is used extensively by dentists in combination with mercury to fill cavities in teeth. The amalgam manufacturers supply dentists with the alloy in the form of powder (filed, or more recently, atomized). This is mixed with mercury, using from 8 to 5 parts of mercury to 5 of alloy, and the cavity is packed. In the cavity, a metallurgical reaction takes place in which the silver-tin compound in the alloy becomes a durable silver-tm-mercury compound. 

Dental amalgam (SEDA-10,210) (SEDA-15,233) (14,15) is still used for about 75-80% of single-tooth restorations. The modern amalgam consists of a metalhc alloy (silver, tin, and copper, sometimes with small amounts of zinc, indium, and/or palladium) mixed with mercury in a percentage of 40-54% mercury by weight. The resultant plastic mass sets and hardens over a period of 8-24 hours. 

The electron g-factors for mixed AgCli j.Br and AgBrj- I (y <0.4) crystals have been measured by EPR. The g-factors in these amalgam alloys generally exhibit a linear relationship with concentration [84,109,110]. Thus the observed g-factor decreases linearly from about 1.88 in AgCl to about 1.49 in AgBr. Almost identical results have been found in ODMR measure-... 

Hydrogen Antimonid—Stibin—Antimoniuretted hydrogen— Stibamin—Stibonia—SbHi—138.—It has not been obtained in a condi tion of purity, but is prod need, mixed with H, when a reducible compound of Sb is in presence of nascent H. It is obtained in larger amount, by decomposing an alloy of 400 parts of a 3 sodium amalgam, and 8 parts of freshly reduced, and dried Sb, by HaO, in a current of COa. 

By definition amalgam is an alloy of mercury with one or more other metals. Dental amalgams are produced by mixing an alloy powder with... 

Since this implies the absence of any free energy of mixing, few alloys follow this relationship. Some dilute amalgams in aqueous solutions of corresponding ions at temperatures at which they are liquid do show linear relation-... 

Dental amalgam is an alloy made of liquid mercury and other solid metal particulate alloys made of silver, tin, copper, etc. The solid alloy is mixed with (Hquid) mercury in a mechanical vibrating mixer and the resulting material is packed into the prepared cavity. One of the soHd alloys is composed of at least 65% silver, and not more than 29% tin, 6% copper, 2% zinc, and 3% mercury. The reaction during setting is thought to be... 

The term alloy can also apply to certain heterogeneous mixtures, such as the common two-phase solid mixture of lead and tin known as solder, or to intermetallic compounds, such as the silver-tin compound Ag3Sn that, in the past, was mixed with mercury in dmtal amalgam. 

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