Alloying elements single-phase

Above the solution treatment temperature (ca 1250°C), the alloy is single phase with a bcc crystal stmcture. During cooling to ca 750—850°C, the sohd solution decomposes spinodally into two other bcc phases a and lattice parameter composition. The matrix a-phase is rich in Ni and Al and weakly magnetic as compared with which is rich in Fe and Co. The a -phase tends to be rod-like in the (100) dkection and ca 10 nm in diameter and ca 100 nm long. As the temperature is decreased, segregation of the elements becomes mote pronounced and the difference between the saturation polarizations of the two phases increases. 

Rudenauer and coworkers [78, 79] use metallic glasses as standards for several reasons 1) the metallic glasses are single phase systems and are homogeneous at the micron scale 2) metallic glasses can be prepared in a broader concentration range than alloying components, and even insoluble elements can form an amorphous phase under suitable conditions 3) the ion yields of elements in isotopic amorphous alloys are not-dependent on the orientation of the bombardment surface and 4) amorphous alloys have metallic character. 

Very pure single crystals have defects that can effect corrosion, but impurities and alloying elements, grain boundaries, second phases, and inclusions often have serious effects. Welded structures invariably corrode first at the welds because of metallurgical heterogeneities that exist in and near welds. The most susceptible site or defect in a metal will be the first to be attacked on exposure to a corrosive environment. Sometimes such attack simply results in innocuous removal of the susceptible material, leaving a surface with improved corrosion resistance. (Frankel)5... 

Amorphous materials have properties that are of interest in terms of catalysis. Amorphous alloys can be produced with wide composition ranges not available in crystalline form, which permits the continuous control of their electronic properties. Their single-phase character and possible lack of surface segregation of the alloying elements ensure that the active species are in a uniform dispersion in a chemically homoge-... 

Beside the beneficial effect of the addition alloying metallic elements that contribute to the increased corrosion resistance, the amorphous structure itself is also responsible for the very low corrosion. For example, crystalline alloys with the same composition exhibit high rates of dissolution. The chemically homogeneous, single-phase nature of amorphous alloys is believed to account for their corrosion resistance (8, 100, 101). This also allows for the formation of a uniform, protective film on the surface of amorphous alloy electrodes. 

One additional method used to study single phase /3-Ce is by alloying with an element which stabilized the /3-phase field such as lanthanum (Roberts and Lock, 1957) or yttrium (Panousis and Gschneidner, 1972). The properties of the pure /3-phase may be estimated by extrapolation of data measured at several alloy compositions to 100% /3-Ce. 

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