Refractory alloys

Argon, helium, and their mixtures with other gases are used as the working fluids in plasma arc devices for producing plasma jets with temperatures in excess of 50,000 K. These devices are used for cutting metals and for spray coating of refractory alloys and ceramics (qv) (see Plasma technology). 

So far, few of the commercially operated diffusion processes have been applied to the lower-melting-point metals. While they are being used to an increasing extent for protection of nickel, cobalt and refractory alloys, the bulk of present-day applications is still concerned with the treatment of ferrous materials. 

Because sulfuric acid and halogen are very corrosive, selection of the structural materials is an important issue. Screening tests have been carried out using test pieces of commercially available materials at GA [29], JAEA [30,31], etc. As for the gas-phase environment of the H2S04 decomposition step, some refractory alloys that have been used in conventional chemical plants showed good corrosion resistance. Figure 4.13 shows one of the experimental results of Alloys 800 and —600 obtained under gas-phase sulfuric acid decomposition environments at 850°C. Gas compositions in the upstream and downstream... 

Adiabatic calorimeters have also been used for direct-reaction calorimetry. Kubaschewski and Walter (1939) designed a calorimeter to study intermetallic compoimds up to 700°C. The procedure involved dropping compressed powders of two metals into the calorimeter and maintaining an equal temperature between the main calorimetric block and a surrounding jacket of refractory alloy. Any rise in temperature due to the reaction of the metal powders in the calorimeter was compensated by electrically heating the surrounding jacket so that its temperature remained the same as the calorimeter. The heat of reaction was then directly a function of the electrical energy needed to maintain the jacket at the same temperature as the calorimeter. One of the main problems with this calorimeter was the low thermal conductivity of the refractory alloy which meant that it was very difficult to maintain true adiabatic conditions. 

When the powder is isostatically compacted at elevated temperatnres, the process is called hot isostatic pressing (HIP). In this case, the flexible dies are often made of thin metals, and high-pressnre gases snch as argon are nsed to heat the part rapidly and rednce thermal losses. Pressnre np to 100 MPa and temperatnres in excess of 2000°C are possible nsing HIP, and parts up to 600 kg can be fabricated. A schematic diagram of a typical HIP apparatus is shown in Figure 7.18. Metals that are processed commercially by HIP include various specialty steels, superalloys, hard metals, refractory alloys, and beryllium. We will see in Section 7.2 that HIP is also particularly useful for the densification of ceramic components. 

Two different kinds of metals are found in chondrites. Small nuggets composed of highly refractory siderophile elements (iridium, osmium, ruthenium, molybdenum, tungsten, rhenium) occur within CAIs. These refractory alloys are predicted to condense at temperatures above 1600 from a gas of solar composition. Except for tungsten, they are also the expected residues of CAI oxidation. 

Gadolinium 64 Gd Electronic materials, high-temperature refractories, alloys, cryogenic refrigerant, thermal neutron absorber, superconductor, magnetic materials, bubble memory substrates... 

The thiocyanate method has been utilised for determination of tungsten in ores and concentrates [7], molybdenum and its compounds [128], steels [6,129,131,134,178], refractory alloys [131] titanium, zirconium, and their alloys [136], nickel alloys [179], and ferromolybdenum [135]. 

The indophenol method has been applied for determination of nitrogen (as ammonia) in biological materials [31,32], plant materials [33,34], foods [1,2,35], air [36], boiler water [37], and other waters [38-40], organic substances [17,41], refractory alloys [42], tantalum alloys [43], vanadium, titanium, and uranium [21], alkali and alkaline earth metals [22],... 

The Xylenol Orange method has been used for the determination of Zr in silicates [36], table salt [93], steel [94], nickel alloys [47,54], and refractory alloys [7,47]. A sorbent modified with Xylenol Orange has been used for preconcentration of Zr in mineral waters [95], and in basalt and granite rocks [96]. 

Key words Refractory alloys, rhenium effect, Cr-Re alloys, mechanical properties, high temperature, oxidation resistance, thermal shock resistance. 

Hafnium metal is used in refractory alloys and in photo flashbulbs where especially high light output is wanted. 

Such carbon exchange can be observed between alkali metals and ferritic or austenitic steels as well as alloys based on vanadium, niobium, or other refractory alloys. Carbon dissolved in alkali metals also has the ability to react with other dissolved nonmetallic elements. In some cases, rather surprising reaction products have been observed. 

F. S. Pettit and G. H., Meier, The effects of refractory elements on the high temperature oxidation and hot corrosion properties of superalloys. In Refractory Alloying Elements in Superalloys, eds. J. K Tien and S. Reichman, Metals Park, OH, ASM, 1984, p. 165. 

C. E. Ramberg, P. Beatrice, K. Kurokawa, W.L. Worrell, High temperature oxidation behavior of stmctural silicides, in in C.L. Briant, J.J. Petrovic, B.P. Bewlay, A.K. Vasudevan, H.H. Lipsitt (Eds.), High Temperature Silicides and Refractory Alloys, vol. 332, Martials Research Society, Pittsburgh, 1994, pp. 243-254. 

Lanthanides in silicate rocks, commercial phosphoric acid, geological materials, refractory alloys, steel alloys, minerals, ores, monazite, and luminescent phosphors have been determined by HPLC. Determination of trace lanthanide impurities in nuclear grade uranium has been studied." An HPLC technique using the dynamic ion-exchange approach was also employed for the determination of Pm in urine. A typical application of lanthanide assay in nuclear industry is described next. 

Phosphorous. The presence of trace amounts of phosphorus in metals and semiconductors is known to affect material properties. The produced in the (n,y) reaction is a pure emitter and has to be separated and rigorously purified. Paul (1998,2000) developed a method for P determination in steels and other high-temperature refractory alloys of interest to the aircraft industry. Irradiated samples were dissolved passed through cation-exchange columns to remove Co, Ni, and Cr followed by repeated precipitations of magnesium ammonium phosphate and ammonium phosphomolybdate. One of the major advantages of this technique is the determination of the chemical yield by gravimetry. Phosphorus was determined by INAA in matrices other than metals, e.g., polymers. In this case, the beta spectrum was corrected for interferences and self-absorption (St-Pierre and Kennedy 1998). A modified version of this procedure has been used to certify implanted phosphorus in silicon (Paul et al. 2003). 

High-temperature refractory alloy based on depleted uranium (U-i-Mo) for gammashielding. The operating temperature is 700-800° C, lifetime is 10 years, density >17 g/cm ... 

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