Alloy resistivity

Copper and copper alloys resist corrosion by most food products. Traces of copper may be dissolved and affect taste or metals are often tin coated. 

Aluminium-base alloys resist the action of many molten salts which are nearly neutral in reaction. Molten sodium nitrate or mixtures of sodium nitrate and potassium nitrate are used for salt bath heat treatment of some aluminium alloys. 

Details of jet impingement tests will be found in Section 19.1. Alloys resistant to impingement attack will be considered subsequently. 

In early times 70/30 brass condenser tubes failed by dezincification and Admiralty brass (70Cu-29Zn-lSn) was brought into use. This proved little better, but some time later the addition of arsenic was found to inhibit dezincification. Failures of Admiralty brass by impingement attack became a serious problem, particularly as cooling water speeds increased with the development of the steam turbine. The introduction of alloys resistant to this type of attack was a great step forward and immediately reduced the incidences of failure. 

The relative susceptibility of metals to atmospheric corrosion varies widely with the type of contaminant, e.g. zinc and cadmium, two metals that are used for the protection of steel in exposed environments, are both rapidly attacked by organic acidson the other hand, aluminium alloys resist attack by organic acids but may be rapidly corroded by chlorides, especially at crevices or areas of contact. 

Pd-Ni alloy Resistance H2 scan Corporation 0.5-100% No No interference from CO (30%), H2S ... 

Two kinds of alloys resistant to hydrogen embrittlement can be used for hydrogen containers FeNiCr stainless steel and FeNiCr stainless steels strengthened with N. Mn and nanosize /-precipitates strengthened superallovs. 

A dilatometer is used to measure the intrusion and extrusion volumes and several methods are used to measure the change in mercury level within the dilatometer stem as intrusion and extrusion take place. One method involves the use of platinum or platinum-alloy resistance wire placed coaxially in the stem of dilatometer tube. As the mercury level decreases, the amount of resistance wire exposed increases, thereby providing a voltage which increases linearly with decreasing mercury level. Very small current is used to minimize resistive heating of the mercury. Platinum or platinum-iridium alloy may be employed as the resistance wire because they do not amalgamate with mercury. 

Resistivity in Metals and Alloys. Resistivity is the reciprocal of conductivity. We will find if useful fo momentarily concentrate on resistivity instead of conductivity to explain some important electrical phenomena. If the metal crystal lattice were perfect and there were no lattice vibrations, the electrons would pass through... 

The variation of resistivity with composition is also expressed in an empirical fashion. For two-phase alloys consisting of phases a and P, the rnle of mixtnres can be nsed to approximate the alloy resistivity from the individnal metal resistivities ... 

Houston, B. "Cohalt-Free Alloys Resist Wear." Client. Eng. Progress, 9 (December 1990)... 

The aluminum content of these alloys ranges from 4 to 10%. They are moderately hard, very ductile, and lough. The alloys resist scaling and oxidation at high temperatures because of the aluminum comenl. They perform well in both acids and alkalis. 

Over the years many alloys have been developed for applications in which the alloys resist oxidation and give good performance without failure. Table 1.11 gives the nominal compositions of some alloys for use in industrial environments. The performance of alloys in various industrial environments is summarized in Table 1.12. 

If the alloy resists the action of aqua regia, fuse it with sodium hydroxide pellets in a silver dish or crucible (CAUTION). When decomposition is complete, allow to cool, transfer the silver vessel to a beaker and extract the melt with water remove the silver vessel from the beaker. Strongly acidify the contents of the beaker with nitric acid, evaporate to dryness on a water bath, and proceed as above. 

One important use of ruthenium is in the manufacture of alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals. Ruthenium adds two properties to an alloy. First, it makes the alloy hard. Second, it makes the alloy resistant to attack by oxygen and other materials. 

Polypur (A. Schulman, Inc. USA) Thermoplastic polyurethane alloys Resistant to oils, gasoline and alkalis... 

With this knowledge available, two approaches to the problem of making lithium a usable coolant could be made to develop alloys resistant to lithium with known amoimts of impurities, and to develop techniques of manufacturing and handling lithium in order to maintain the degree of purity required. 

The Pd-Au and Pd-Cu alloys retained their metallic luster upon exposure to hydrogen sulfide and recovered their activity after removal of H2S [74], implying that both alloys were resistant to formation of bulk sulfides. The unalloyed Pd and Pd-Ag membranes were much changed in appearance, according to McKinley, indicative of the formation of bulk sulfides. X-ray diffraction analysis at Eltron Research Inc. shows that unalloyed Pd forms the bulk sulfide, Pd4S, and that Pd-Ag alloys form bulk palladium-silver sulfides, leading to failure of membranes exposed to under 20 ppmv H2S in the range 593-713 K (320-440 °C) [75]. The Pd 60-Cu 40 (wt%) alloys resist formation of bulk sulfides, but were not completely satisfactory for use with H2S [75], in accord with the work of McKinley [74]. 

Type 304 stainless steel (containing 18%-20% chromium and 8%-10.5% nickel) is used in the tritium production reactor tanks, process water piping, and original process heat exchangers. This alloy resists most types of corrosion. 

Figure 5.35 shows the impedance response of a bare and a cobalt-coated metal-hydride electrode. Two semicircles are seen in the Nyquist plot initially for the bare alloy and Co-coated alloy. After 50 charge/discharge cycles of the electrode for the bare alloy, the two semicircles merge and a significant increase in the alloy resistance is observed. The increase in resistance for the Co-coated alloy is comparatively less even after 120 cycles [76]. AUoy oxidation is responsible for the increase of the parti cle-to-particle resistance observed in the bare alloy in Fig. 5.35. 

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