Ni-Cr alloys

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). 

Cobalt—Chromium Alloys. Co—Cr and Ni—Cr alloys are used predominately for the casting of removable partial dentures fixed partial dentures (bridges), crowns, and inlays are also cast. Because of high hardness, corrosion resistance, and wear resistance cobalt-chromium alloys are used for bite adjustments and as serrated inserts in plastic teeth used in fliU dentures. These alloys are well tolerated by the body and also are used for dental implants and orthopedic implant alloys. 

Ni—Cr alloys primarily contain nickel with ca 12% or more of chromium. They are used mainly for the casting of fixed partial dentures (bridges), crowns, or inlays, either with or without aesthetic porcelain or plastic veneers (Table 10). However, some of them are used for removable partial dentures. 

Because the melting temperature range of Ni—Cr alloy is 1220—1345°C, it is necessary to heat the investment molds to 800—935°C. The castings should not be pickled in acid because of their high nickel content and should be cleaned by sandblasting. The alloys are generally hard and are difficult to finish and to abrade for clinical adjustment in the mouth. 

Nickel alloys include monels (Ni-Cu alloys), nichromes (Ni-Cr alloys), nimonics and nickel-based super-alloys (Ni-Fe-Cr-Al-Co-Mo alloys). 

Sarkar, N. K., Graves, R. A. and Park, J. R. (b) Electrochemical Behaviour of Ni-Cr Alloys in Chloride Solutions containing Amino Acids , Journal of Dental Research, 66, 206 (Abstr. 795) (1987)... 

Fig. 4.22 Effect of chromium content on the anodic behaviour of Ni-Cr alloys in 0-5 M H2SO4 (de-aerated with H2) at 25°C the potential was increased incrementally by 0-025 V every 3 min (after Hodge and Wilde...

Fig. 4.37 Influence of the chromium content of Ni-Cr alloys on the breakdown potential in 0-1 M NaCI at 25°C de-aerated with N2 (after Horvath and Uhlig )...

Nickel and Ni-Cr alloys are among the most resistant metallic materials to corrosion and oxidation at high temperatures and are widely used to resist corrosion by gases and molten salts at elevated temperatures (see Sections 7.1 and 7.5). 

Intergranular corrosion of Fe-Ni-Cr alloys has been the subject of a comprehensive review by Cowan and Tedmon who summarised the various tests used for determining susceptibility (Table 19.3). Of these tests. Nos. 1-5, which are regarded as reliable test procedures by the ASTM, have been incorporated into ASTM A262 1986 Recommended Practice for Detecting Susceptibility to Intergranular Attack in Stainless Steel as follows ... 

Chromium compounds Cr203 surface scale Nickel- chromium—iron alloys Nickel-chromium— molybdenum (tungsten) alloys Ni-Cr alloys analytical methods, 6 502-514 composition of metal compared to chromium ferroalloys, 6 501t dispersoid former, 2 325, 327 disposal, 6 519-521 economic aspects, 6 496—500 effect on cobalt alloys, 7 220 effect on stainless steel corrosion resistance, 7 809... 

Nicotine adenine dinucleotide phosphate (NADP+), 24 147 Nicotinic acid, 9 477-478 26 291 alkaloid precursor, 2 78 Ni-Cr alloys, 23 499. See also Nickel-chromium entries NiCrAlY coatings, 13 508 nido designation boranes, 4 184-186 boron hydrides, 4 170, 172-176 Nidrel, molecular formula and structure, 5 129t... 

The reformer tubes typically operate at maximum temperatures of 1,600°F to 1,700°F and are designed for a minimum stress-to-rupture life of 100,000 operating hours. A 35/25 Ni/Cr alloy is used that is modified with niobium and microalloyed with trace elements such as titanium and zirconium. Smaller tube diameters provide better heat transfer and cooler walls. This reduces tube and fuel costs and increases tube life. But more tubes increases the pressure drop. The optimum inside tube diameter is 4 to 5 in. The wall thickness may be as low as 0.25 inch with a length of 40 to 45 ft. The lane spacing between tube rows must be enough to avoid flame impingement from the burners. Typical spacing is 6 to 8 feet. 

In another study, Chen and Zhao [55] demonstrated that by using a Ni-Cr alloy metal foam as the cathode DL (and current collector), instead of a CFP or CC, the performance of a DMFC can be enhanced significantly due to the improvement of the mass transfer of oxygen and overall water removal on the cathode side. Fly and Brady [56] designed a fuel cell stack in which the distribution layers were made out of metal foams (open cell foams). In addition, more than one foam (with different porosity) could be sandwiched together in order to form a DL with variable porosity. 

Figure 6.10. Comparison of the extiqralated liquidus/solidus lines relating to the f.c.c. phase in Ni-Cr alloys, derived by (a) using the van Laar method and (b) the trajectory obtained using the modified FP qiproach used by Chang et al. (l S).

Te, Mg, Se or Zr, or a mixture of smokeless powders. It is suitable for electric squibs. Tire mixture is heated by means of a bridge wire of Ni-Cr alloy with a diam of at least 0.00225 , whereby certainty of firing is assured under conditions prevailing in series firing USP 2228339... 

B) Bridge Type Electric Cap consisted of a cylindrical casing Ni-plated brass or Ni-plated steel). See Fig E19, contg the following items a)Bridge wire ( . fuse ) (such as of 80/20-Ni/Cr alloy was soldered to two leads consisting of two metal foil strips separated by a mill-board, serving as an insulator b) Fusehead c) Molded Plastic insulator d) Brass contact... 

The activity of chromium in liquid Ni-Cr alloys was measured using the following cell ... 

Copper, low brasses or bronze silver solder Ni-Cr alloys austenitic corrosion-resistant steels -0.20 0.35 ... 

Praliaud and Martin (77) proposed the formation of Ni-Si and Ni-Cr alloys on silica and chromia supports, respectively, under H2 at sufficiently high temperatures. They suggested that hydrogen spilt over from Ni to the Cr203 carrier and partially reduced it to Cr°, which was then alloyed with Ni as indicated by magnetic measurements. The same technique in conjunction with IR spectroscopy and volumetric adsorption of H2 was applied to partially reduced Ni-on-alumina and Ni-on-zeolite catalysts by Dalmon et al. (78). These supported Ni systems contained Ni° and Ni+. H2 was found to be activated only when the couple Ni°/Ni+ was present according to... 

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