Temperature iron-rhodium

Among the sulfides of molybdenum, cobalt, nickel, iron, rhodium, rhenium, osmium, and ruthenium, only the polysulfide of cobalt153 and the sulfide of ruthenium showed good selectivities. Optimum conditions over cobalt polysulfide included temperatures of 85-120°C, hydrogen pressures of 2.8-6.9 MPa, substrate concentrations of up to 25%, and substrate catalyst ratios of 50-80 1 (g of feed/g of Co). A typical run is shown in eq. 9.64. The hydrogenation over ruthenium disulfide was successful... 

TPR and TPO patterns of silica-supported rhodium, iron, and iron-rhodium catalysts are shown in Fig. 11.5 [14]. These catalysts were prepared by pore volume impregnation from aqueous solutions of iron nitrate and rhodium chloride. Note the difference in reduction temperature between the noble metal rhodium and the non-noble metal iron. The bimetallic combination reduces largely in the same temperature range as the rhodium catalyst does, indicating that rhodium catalyzes the reduction of the iron. This forms evidence that rhodium and iron are well mixed in the fresh catalyst. The TPR patterns of the freshly prepared catalysts consist of two peaks, one coincides with that of the TPR pattern of the fully oxidized catalyst (right panel of Fig. 11.5) and can thus be... 

Alloys suitable for castings that ate to be bonded to porcelain must have expansion coefficients matching those of porcelain as well as soHdus temperatures above that at which the ceramic is fired. These ate composed of gold and palladium and small quantities of other constituents silver, calcium, iron, indium, tin, iridium, rhenium, and rhodium. The readily oxidi2able components increase the bond strength with the porcelain by chemical interaction of the oxidi2ed species with the oxide system of the enamel (see Dental materials). 

Thermocouples Temperature measurements using thermocouples are based on the discovery by Seebeck in 1821 that an electric current flows in a continuous circuit of two different metalhc wires if the two junctions are at different temperatures. The thermocouple may be represented diagrammaticaUy as shown in Fig. 8-60. A and B are the two metals, and T and To are the temperatures of the junctions. Let T and To be the reference junction (cold junction) and the measuring junc tion, respectively. If the thermoelectric current i flows in the direc tion indicated in Fig. 8-60, metal A is customarily referred to as thermoelectricaUy positive to metal B. Metal pairs used for thermocouples include platinum-rhodium (the most popular and accurate), cmromel-alumel, copper-constantan, and iron-constantan. The thermal emf is a measure of the difference in temperature between To and T. In control systems the reference junction is usually located at... 

Thermocouples are primarily based on the Seebeck effect In an open circuit, consisting of two wires of different materials joined together at one end, an electromotive force (voltage) is generated between the free wire ends when subject to a temperature gradient. Because the voltage is dependent on the temperature difference between the wires (measurement) junction and the free (reference) ends, the system can be used for temperature measurement. Before modern electronic developments, a real reference temperature, for example, a water-ice bath, was used for the reference end of the thermocouple circuit. This is not necessary today, as the reference can be obtained electronically. Thermocouple material pairs, their temperature-electromotive forces, and tolerances are standardized. The standards are close to each other but not identical. The most common base-metal pairs are iron-constantan (type J), chomel-alumel (type K), and copper-constantan (type T). Noble-metal thermocouples (types S, R, and B) are made of platinum and rhodium in different mixing ratios. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

The behaviour of iridium is closely analogous to that of rhodium its corrosion diagram is very similar and it is, with rhodium, one of the least corrodible of metals. It is unattacked by alkalis, acids or oxidising agents in aqueous solution, although a fused mixture of caustic potash and potassium nitrate will attack it. The metal has an excellent resistance to fused lead oxide, silicates, molten copper and iron at temperatures up to 1 500°C. Additions of iridium to platinum considerably raise the corrosion resistance of the latter to a very wide range of reagents. 

Catalysts. The methanation of CO and C02 is catalyzed by metals of Group VIII, by molybdenum (Group VI), and by silver (Group I). These catalysts were identified by Fischer, Tropsch, and Dilthey (18) who studied the methanation properties of various metals at temperatures up to 800°C. They found that methanation activity varied with the metal as follows ruthenium > iridium > rhodium > nickel > cobalt > osmium > platinum > iron > molybdenum > palladium > silver. 

Rhodium and cobalt carbonyls have long been known as thermally active hydroformylation catalysts. With thermal activation alone, however, they require higher temperatures and pressures than in the photocatalytic reaction. Iron carbonyl, on the other hand, is a poor hydroformylation catalyst at all temperatures under thermal activation. When irradiated under synthesis gas at 100 atm, the iron carbonyl catalyzes the hydroformylation of terminal olefins even at room temperatures, as was first discovered by P. Krusic. ESR studies suggested the formation of HFe9(C0) radicals as the active catalyst, /25, 26/. Our own results support this idea, 111,28/. Light is necessary to start the hydroformylation of 1-octene with the iron carbonyl catalyst. Once initiated, the reaction proceeds even in the... 

Figure 3 shows the Mossbauer spectra for an alloy of 75% iron and 25% rhodium after two different heat treatments. Since absorption rather than transmission is plotted, these curves are right side up. The upper spectrum is taken from an alloy which was annealed in the low temperature field (cesium chloride structure), and there are two six-hne patterns... 

Mention has been made variously that the rate of adsorption of hydrogen on nickel and iron is very fast at room temperature. In fact, the rate is so fast that the limiting factor appears to be the rate at which gases enter the reaction chamber through the stopcock from the reservoir. This essentially instantaneous adsorption has been observed for many other metals, including platinum, rhodium, palladium, tungsten, tanta-... 

Nonsteroidal antiinflammatory drugs, interaction with lithium, 36 66 No-phonon transition, 35 324 Norbomadiene complexes with cobalt, 12 286 with copper, 12 328, 330, 331 with gold, 12 348, 349 with group VIB metals, 12 231 with group VnB metals, 12 241 with iron, 12 265 with palladium, 12 314 with platinum, 12 319 with rhodium, 12 300-302 with ruthenium, 12 278, 279 with silver, 12 340-342, 344, 346 Norbomylsiloxane, 42 226, 228 Notch receptor proteins, 46 473, 475 h (N)" oxime complexes, osmium, 37 260 h (N,0) oxime complexes, osmium, 37 260 (NPr ljiFeCfrdto),], magnetization versus temperature, 43 230... 

To measure temperatures not exceeding 800 °C, one should use thermocouples made from copper and constantan (the latter is an alloy of 45-60% copper, 40-55% nickel, and 0-1.4% manganese it usually also contains about 0.1% carbon), Alumel (an alloy of 95% nickel, 2 % aluminium, 2% manganese, and 1% silicon), and Chromel (90% nickel and 10% chromium), or iron and constantan. Platinum-platinum/rhodium thermocouples are generally used for measuring high temperatures (up to 1600 °C). 

In a logical continuation of this work, carbene addition to an iron-iron double bond has also been exploited for the simple synthesis of the first /. -methylene complex in the nitrosyl series. The readily available /x-nitrosyliron complex [(Tj5-C5H5)Fe(/u.-NO)]2 (26) exhibits the same structural features as the rhodium dimer 21 (157) and reacts with diazomethane in the temperature range -80-25°C to give the expected /z-methylene derivative 27 (Scheme 14) as a black, air-stable compound in... 

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