Chromium electrical resistivity

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

The non-ferrous alloys include the misleadingly named nickel silver (or German silver) which contains 10-30% Ni, 55-65% Cu and the rest Zn when electroplated with silver (electroplated nickel silver) it is familiar as EPNS tableware. Monel (68% Ni, 32% Cu, traces of Mn and Fe) is used in apparatus for handling corrosive materials such as F2 cupro-nickels (up to 80% Cu) are used for silver coinage Nichrome (60% Ni, 40% Cr), which has a very small temperature coefficient of electrical resistance, and Invar, which has a very small coefficient of expansion are other well-known Ni alloys. Electroplated nickel is an ideal undercoat for electroplated chromium, and smaller amounts of nickel are used as catalysts in the hydrogenation of unsaturated vegetable oils and in storage batteries such as the Ni/Fe batteries. 

Chromium plating from hexavalent baths is carried out with insoluble lead-lead peroxide anodes, since chromium anodes would be insoluble (passive). There are three main anode reactions oxidation of water, reoxidation of Cr ions (or more probably complex polychromate compounds) produced at the cathode and gradual thickening of the PbOj film. The anode current density must balance the reduction and reoxidation of trivalent chromium so that the concentration reaches a steady state. From time to time the PbOj film is removed as it increases electrical resistance. 

Acid copper sulphate test t 16 wt.% H2SO4 -1-100 g/l CuSO, (-1- metallic copper) 72 h exposure to boiling solution 1. Appearance of sample upon bending 2. Electrical resistivity change 3. Change in tensile properties -1- 0-30 to -1- 0-58 Chromium-depleted area... 

Electric detonators are also used for detonation of high explosive charges. They are similar in design to other types of detonators except for the presence of an electric fusehead consisting of a bridgewire made of chromium and nickel. The bridgewire is covered by a heat-sensitive pyrotechnic mixture protected by varnish insulation. Standard fuseheads have electrical resistance of 1.2 to 1.4 ohms and... 

A large fraction of the iron and steel produced today is recycled scrap. Since scrap does not require reduction, it can be melted down directly in an electric arc furnace, in which the charge is heated through its own electrical resistance to arcs struck from graphite electrodes above it. The main problem with this process is the presence of tramps (i.e., copper from electrical wiring, chromium, nickel, and various other metals) that accompany scrap steel such as crushed automobile bodies and that lead to brittleness in the product. Tin in combination with sulfur is the most troublesome tramp. Only the highest quality recycled steel—specifically, steel with no more than 0.13% tramps—can be used for new automobile bodies, and usually reprocessed scrap has to be mixed with new steel to meet these requirements. 

Belertser et al (1988) have observed that the electrical resistivity of amorphous chromium films at liquid-helium temperatures jumps from a value (10 3 O cm) characteristic of a poor metal by a factor 103, when the hydrogen content is increased sufficiently to increase the lattice constant by 10%. The transition is not abrupt, and is thought by these authors to be of Anderson type. They claim that it is the first time such a transition has been observed in a solid, and that it is similar to that in expanded mercury vapour (Section 4). 

In addilion to ferrous ulluys, chromium also is added to cupper, vanadium, zirconium, and other metals to form several hundred chromium-bearing alloys. Nickel-chromium-iron alloys have high electrical resistance and are used widely as electrical heating elements. Niclirttme and ChromeI are examples. 

The control of electrical resistivity in these ceramics is, as noted above, very desirable. There has been considerable success in the use of uranium as a dopant for this function in a variety of compositions [36-38], Recently, chromium has also been shown to exhibit some promise for this [39],... 

In another high-pressure detector, Manganin, gold-chromium, platinum, or lead wire sensors are wound helically on a core. The electrical resistance of these wire materials will change in proportion to the pressure experienced on their surfaces. The pressure-resistance relationship of Manganin... 

Furnaces for thermal analysis instruments are nearly always electric resistance heated. Wound furnaces consist of a refractory metal wire wrapped around or within4 an alumina or other refractory tube. Nichrome (nickel/chromium alloy) or Kanthal (a trade name for an iron/chromium alloy 72% Fe, 5% Al, 22% Cr,. 5% Co) windings may be used inexpensively for heating to a maximum temperature of 1300°C. More expensive plat-... 

Finally, no mention of the subject of alloys would be complete without mentioning the Marsh Nichrome case (13). Marsh admitted that the alloy itself was old his discovery was for a new use—namely, as an electric heating element. Therefore he was allowed to claim an electric resistance element formed of a metal alloy consisting of nickel and chromium. Present practice no longer permits claiming a new use for old materials in this fashion rather a new use must be claimed, if at all, as a process in which the new use of the known material is recited, all as set forth in Section 100(b) of the Patent Law. 

Solid chromium adopts a body-centered cnbic stracture and crystallizes in the space gronp Imim with a = 288.46pm its density is 7.19 gcm (at 293 K). The metal melts at 2130 ( 20) K and boils at 2945 K the corresponding enthalpies are A//fusion = 15.3kJmoP and A//vap = 348.78 kJ moU. Values of various thermodynamic functions are listed in Table 2. Some other values are thermal conductivity 93.7 W m (at300 K), electrical resistivity ... 

Metallic materials for be used as interconnects in SOFCs should fulfil a number of specific requirements [1, 2], Crucial properties of the materials are high oxidation resistance in both air and anode environment, low electrical resistance of the oxide scales formed on the alloy surface as well as good compatibility with the contact materials. Additionally, the value of the coefficient of thermal expansion (CTE) should match with those of the other cell components [3], These requirements can potentially be achieved with high chromium ferritic steels [4], however, previous studies [5] have shown that none of the commercially available ferritic steels seems to possess the suitable combination of properties required for long term reliable cell performance. 

Nichrome /nf-krohm/ Trademark) Any of a group of nickel-chromium-iron alloys, containing 60-80% nickel and about 16% chromium small amounts of other elements, such as carbon or silicon, may be added. They can withstand very high temperatures and their high electrical resistivity makes them suitable for use in heating elements. 

The interconnect material s function is to connect the single cells to provide higher output. They are in contact with both the anode and the cathode. Therefore, they must be stable with both electrode materials and in oxidizing and reducing environments. To reduce the ohmic losses and increase efficiency, the interconnect material must also maintain a low electrical resistance. Basically, two materials are used as interconnect materials metallic and ceramic materials, in which chromium are present, such as CoCr204, YCrOj, and LaCrOj. Glass composite interconnects have also been considered. 

The measurement results of electrical resistance of irradiated films (Figure 24.19) speak in favor of the offered mechanism. At irradiation doses of up to 10 cm" both materials manifest an increase in resistance provoked by the accumulation of helium at boundaries, which results in enlargement of electron scattering centers. Further, chromium nitride experiences a catastrophic growth of resistance, which results in collapse. The vanadium nitride forms a stable system of opened channels, through which the excess helium escapes. The value of electrical resistance remains unchanged. 

The apparatus employed for the reduction is showm in Fig. 28. A pyrex reaction tube 2.5 X 50 cm., previously heated in vacuo at 500°, is fitted with a two-hole rubber stopper carrying an outlet tube A and the longer tube B, 8 mm. in diameter, for leading the gases to the closed end this tube should slip rather easily into the rubber stopper. The sublimed chromium(III) chloride is spread out toward the closed end of the reaction tube and the latter is placed in an electric resistance furnace, the temperature of which can be measured with a thermocouple. Dry oxygen-free hydrogen and hydrogen chloride, each at the rate of 50 ml. per minute, are passed first into a T-tube where they mix, and then led to the closed end of the... 

Pou] Poubeau, J.J., Bigot, J., Determination of Carbon Solubihty in Chromium with Measurement of Electrical Resistivity at Low Temperature (in French), Acta Metall., 33(6), 1137-1141 (1985) (Crys. Stmcture, Phase Diagram, Experimental, 20)... 

Because of their low thermal conductivity and higher electrical resistance stainless steels require 20-30% less heat input than carbon steels during resistance welding. The resulting slow cooling rate may lead to a lower corrosion resistance because of the precipitation of chromium carbides. 

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