Type II alloys

An alloy is said to be of Type II if neither the AC nor the BC component has the structure a as its stable crystal form at the temperature range T]. Instead, another phase (P) is stable at T, whereas the a-phase does exist in the phase diagram of the constituents at some different temperature range. It then appears that the alloy environment stabilizes the high-temperature phase of the constituent binary systems. Type II alloys exhibit a a P phase transition at some critical composition Xc, which generally depends on the preparation conditions and temperature. Correspondingly, the alloy properties (e.g., lattice constant, band gaps) often show a derivative discontinuity at Xc. 

A smaller class of type II alloys of II-VI binaries also exists, including the (CdS) ,(ZnSe)i (CdS) ,(ZnTe)i (CdSe) ,(ZnSe)i (CdS) ,(CdTe)i-. (CdSe)x(CdTe)i i , and (CdS) c(ZnS)i i systems, which transform at some critical composition from the W to the ZB structure. Importantly, the transition temperatures are usually well below those required to attain a thermodynamically stable wurtzite form for the binary constituents (e.g., 700-800 °C for pure CdS and > 1,020 "C for pure ZnS). The type 11 pseudobinary CdxZni jcSe is of considerable interest in thin film form for the development of tandem solar cells as well as for the fabrication of superlattices and phosphor materials for monitors. The CdSe Tei-x alloy is one of the most investigated semiconductors in photoelectrochemical applications. 

The US military specification covering powdered Zr-Ni alloy is MIL-Z-11410B (12 Feb 1968) (Ref 4). The following requirements, shown in Table 1, apply to 70/30 Zr—Ni (Type I) and 30/70 Zr—Ni (Type II) alloys "Refs 1) Anon, Engrg Des Hndbk, Military Pyrotechnics Series, Part Three—Properties of Materials Used in Pyrotechnic Compositions , AMCP 706-187 (1963), 337 2) D. Zauder et... 

In general, for a mixture of two or more pure elements, there are two types of solid-solution alloys that may be obtained. Type I alloys are completely miscible with one another in both liquid and solid states. As long as the Hume-Rothery rules are satisfied, a random substitutional alloy will be produced. We will see many examples of these alloys in this section for a variety of metal dopants in stainless steels. By comparison, type II alloys are only miscible in the molten state, and will separate from... 

As regards type II alloys (type C in Allgaier s notation) Allgaier regards the situation as a good deal less clear cut. In Table 7.7, a list of Hall mobilities is given for a variety of hquids of the three main types. Allgaier points out that there is considerable overlap between 11 values for each class of liquid. For example, the Hall mobility of liquid Bi, which is... 

One field which deserves special attention concerns the structure of liquid semiconductors — particularly those which we have regarded as type II alloys. It is still a matter of dispute whether an ionic or a covalent model is the most appropriate starting point. Carefully planned experiments involving the techniques of neutron diffraction seem to offer the most promising line of attack. Fortunately, sufficient isotopes of different neutron scattering cross-sections, but of interest in connection with liquid semiconductors, exist studies involving a range of Type II liquids are at present underway at the University of Leicester. 

Type II, medium-hard alloys, are harder, stronger, and have lower elongation than type I alloys. They are used for moderate stress appHcation, eg, three-quarter crowns, abutments, pontics, full crowns, and saddles. The type II gold alloys are difficult to burnish, and can usually be heat-treated. 

GoldJilloys, Wrought Type. Two types of wrought gold alloys were formerly recognized by the ADA specification no. 7 for the fabrication of orthodontic and prosthetic dental appHances, ie, type I, high-precious-metal alloys, and type II, low-precious-metal alloys (gold color). Alloys of this type are seldom used in the United States they have been replaced by stainless steels and nickel—titanium alloys. 

Alloy component (wt%) ASTM B4I8-88 Type I ASTM B4I8-88 Type II US Mil Spec. A I800I J DnV Recomm for elevated temp. 

High performance sealants, 22 28 High phosphorus alloys, corrosion performance of, 9 710-711 High pinning Type II superconductors, 23 High pressure apparatus, 13 413 High pressure applications, 13 436-448 in commercial products, 13 436-438 in inorganic chemistry reactions, 13 440—448... 

Specification Requirements for Type I and Type II Zirconium-Nickel Alloys. Z 25... 

Zirconium-Nickel Alloys. Zr/Ni 70/30 (Type I) and 30/70 (Type II) silvery white to grey cubic crystn pdrs d, 7.20g/cc (Type I), 8.10g/cc... 

The range of coherence follows naturally from the BCS theory, and we see now why it becomes short in alloys. The electron mean free path is much shorter in an alloy than in a pure metal, and electron scattering tends to break up the correlated pairs, so dial for very short mean free paths one would expect die coherence length to become comparable to the mean free path. Then the ratio k i/f (called the Ginzburg-Landau order parameter) becomes greater than unity, and the observed magnetic properties of alloy superconductors can be derived. The two kinds of superconductors, namely those with k < 1/-/(2T and those with k > l/,/(2j (the inequalities follow from the detailed theory) are called respectively type I and type II superconductors. 

Soft metallic elements such as Al, In, Pb, Hg, Sn, Zn, Tl, Ga, Cd, V and Nb are type I superconductors. Alloys and chemical compounds such as Nb3Sn, V3Ga, and lZa3In, and some transition elements, are type II superconductors. Type II substances generally have a higher Tc than do type I superconductors. The recently discovered transition metal oxide superconductors have generated intense interest because they are type II superconductors with very high transition temperatures. Table 13.1 summarizes Tc for selected superconductors. 

The preceding chapters have shown that the majority of metals can now be electrodeposited from ambient-temperature ionic liquids. However, this does not necessarily mean that the liquid with the widest potential window will negate the use of all other ionic liquids. Rather, it is most likely that ionic liquids will be task-specific with discrete anions being used for metals that cannot be electrodeposited from aqueous solutions such as Al, Li, Ti, V and W. Type I eutectics will probably be the most suitable for Al, Ga and Ge. Type II eutectics are most suitable for Cr and Type III are most suited to Zn, Cu, Ag and associated alloys. Type III will also find application in metal winning, oxide recycling and electropolishing. To date most practically important metals have been electrodeposited from ionic liquids and a comprehensive review is given in articles by Abbott [99] and Endres [100-102],... 

Fig. 4.10 A range of metal and metal alloy coatings deposited elec-trolytically from type II (Cr) and type III (Ni, Cu Zn Sn, Ag) choline chloride-based ionic liquids.

Binary and ternary alloys and oxides of these elements, as well as pure V, Nb, Gd, and Tc are referred to as Type II or high-field superconductors. In contrast to Type I, these materials exhibit conductive characteristics varying from normal metallic to superconductive, depending on the magnitude of the external magnetic field. It is noteworthy to point out that metals with the highest electrical conductivity (e.g., Cu, Au) do not naturally possess superconductivity. Although this behavior was first discovered in 1911 for supercooled liquid mercury, it was not until 1957 that a theory was developed for this phenomenon. 

This treatment without reanneal is, therefore, of value only regards Shock Resistance for alloys of Type II, the Shock ssistance being 12 kg. m. per sq. cm. instead of 4-5, as in the ged state, but the other properties remain approximately e same. 

The Photographs 38 and 39, Plate XI, refer to the alloy of Type II, as forged, and Photographs 40 and 41 refer to the same alloy as annealed after forging. They show the same two constituents as do the preceding bronzes. 

Scientists have been interested in bimetallic systems as catalysts for many years. For a decade or longer beginning shortly after World War II, much attention was devoted to the use of metal alloys as catalysts to probe the relationship between the catalytic activity of a metal and its electronic structure (1-4). One type of alloy which was investigated extensively consisted of a Croup VIII and a Group IB metal, for instance, nickel-copper or palladium-gold. 

The positions of the vague maxima were not reproducible. In our opinion this type of behaviour is due to small amounts of Si and/or B subsurface impurities, which were not detectable in our AES analysis. Small amounts of these elements are known to form stable oxides at the surface (15-19). Type I and type II, however, were fully reproducible. Type I (fig.3d) is a Pt-like behaviour comparable to those of pure Pt (fig.3a) and the Pt-rich alloy (fig.3b). Type II (fig.3e), which shows a maximum for the oxygen intensity likewise at 800 K, is a Rh-like behaviour (compare fig.3c). The maximum relative intensity is lower than that observed for pure Rh. The figures also show that for the Rh-rich alloy the dashed line is much lower relative to the solid line than for pure Rh. This might indicate that the surface oxygen is more easily removed by the residual gas on the alloy than on the pure Rh. It was shown earlier that on a Pt-Rh alloy surface oxygen preferentially occupies the Rh sites leaving the Pt sites initially free (10). If many free Pt sites are present at the surface... 

A new DSC cell, based on the DTA principle (as is the Du Pont DSC cell previously discussed) has been described by David (HO). The calorimeter cell, as shown in Figure 6.36, contains a differential thermocouple of a new thin-form design that is isolated from the cell wall and bottom to provide greater sensitivity. This thermocouple consists of a sheet of negative Platinel II type thermocouple alloy coupled to a positive Platinel II alloy. Flat shallow containers are employed for the sample and reference materials. Two addi-... 

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