Chromium metal

Not all ligands use just two electrons to bond to transition metals Chromium has the electron configuration [Ar]4s 3rf (6 valence electrons) and needs 12 more to satisfy the 18 electron rule In the compound (benzene)tricarbonylchromium 6 of these 12 are the tt elec Irons of the benzene ring the remammg 6 are from the three carbonyl ligands... 

Fig. 1. Simplified flow chart for the production of metallic chromium and chromium compounds from chromite.

In the many reports on photoelectron spectroscopy, studies on the interface formation between PPVs and metals, focus mainly on the two most commonly used top electrode metals in polymer light emitting device structures, namely aluminum [55-62] and calcium [62-67]. Other metals studied include chromium [55, 68], gold [69], nickel [69], sodium [70, 71], and rubidium [72], For the cases of nickel, gold, and chromium deposited on top of the polymer surfaces, interactions with the polymers are reported [55, 68]. In the case of the interface between PPV on top of metallic chromium, however, no interaction with the polymer was detected [55]. The results concerning the interaction between chromium and PPV indicates two different effects, namely the polymer-on-metal versus the metal-on-polymer interface formation. Next, the PPV interface formation with aluminum and calcium will be discussed in more detail. 

Metallic chromium is an ingredient of several important alloys. Some forms of stainless steel, for example, contain about 12% Cr. Nichrome, which is commonly used for heating coils, has about 15% Cr in addition to 60% Ni and 25% iron. Both these alloys are quite resistant to chemical oxidation. 

Tin Free Steel—Electrolytic Chromium-Coated. A less expensive substitute for tinplate, electrolytic chromium coated-steel, has been developed and is designated TFS-CT (tin free steel-chromium type) or TFS-CCO (tin free steel-chromium-chromium oxide) (19). This material can be used for many products where the cathodic protection usually supplied by tin is not needed. A schematic cross section is shown in Figure 2. Electrolytic, chromium-coated steel is made by electro-lytically depositing a thin layer of metallic chromium on the basic tin mill steel, which is in turn covered by a thin passive coherent layer of chromium oxide. 

Cr03 As a transition metal, chromium forms more than one stable cation. Name the metal first, using a Roman numeral to designate chromium s charge. Each of the three oxide anions has a -2 charge. To maintain net charge neutrality, Cr must be +6, so the name of the compound is chromium(VI) oxide. 

FSM Sosnowiec manufactures automobile lamps, door locks, and window winders for the Polish-manufactured Fiat cars. The lamp bodies are made of zinc-aluminum alloy and then copper-nickel-chromium plated. The door locks and window winders are made of steel and then zinc plated. The wastestreams contain cyanide and the heavy metals chromium (VI), copper, zinc, and nickel. The company carries out the traditional treatments of detoxification, neutralization, and dewatering.29... 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

Acetic anhydride, Organic materials, Transition metals Hikita, T. et al., J. Chem. Soc. Japan, Ind. Chem. Sect., 1951, 54, 253-255 The stability ranges of mixtures of the acid, anhydride and organic materials (ethanol, gelatine) used in electropolishing were studied. Presence of transition metals (chromium, iron, nickel) increases the possibility of explosion. (This is why such mixtures must not be stored after use for etching metals.)... 

Chlorine trifluoride Metals Chromium trioxide Alkali metals Dichlorine oxide Oxidisable materials Nitryl fluoride Metals... 

Chromium (II) chloride solutions can be prepared by any one of several different procedures. If pure electrolytic chromium is available, the procedure of Holah-Fackler (see synthesis 4) is recommended. Some modification as noted at the end of this procedure may be desirable. If metallic chromium is not available, commercial chromium(III) chloride may be reduced electrolytically (a suitable divided cell is needed), or the reduction may be effected by zinc and hydrochloric acid. The latter procedure, which starts with the most commonly available reagents and apparatus, is described here. 

Methyl methacrylate 4-Methylnitrobenzene 2- Methylpyridine Methylsodium Molybdenum trioxide Naphthalene 2-Naphthol Air, benzoyl peroxide Sulfuric acid, tetranitromethane Hydrogen peroxide, iron(II) sulfate, sulfuric acid 4-Chloronitrobenzene Chlorine trifluoride, interhalogens, metals Chromium trioxide, dinitrogen pentaoxide Antipyrine, camphor, phenol, iron(III) salts, menthol, oxidizing materials, permanganates, urethane... 

The contact between the aluminium layers and the ceramic substrate requires a joining material which will wet both metal and ceramic, and solders such as the conventional Pb-Sn alloy have been used which are molten during the annealing process. The contact between the solder and the aluminium layer is frequently unsatisfactory because of the intervention of the A1203 layer, and a practical solution appears to be to place three layers of metal chromium in contact with the aluminium, copper in contact with the chromium, and gold between the copper layer and the solder. 

Valkov and Zhabina [109] reduced elemental sulphur in marine sediments to hydrogen sulphide using metallic chromium. The liberated hydrogen sulphide was absorbed in cadmium solution and estimated iodometrically. 

Main uses of the metal. Chromium can serve as a protective coating of alloys to prevent oxidation. It is an important component of several ferrous alloys, mainly stainless steels. 

Molybdenum oxidizes at high temperatures but not at room temperatures. It is insoluble in acids and hydroxides at room temperatures. At room temperatures, all three metals (chromium, molybdenum, and tungsten) resist atmospheric corrosion, which is one reason chromium is used to plate other metals. They also resist attacks from acids and strong alkalis, with the exception of chromium, which, unless in very pure form, will dissolve in hydrochloric acid (HCl). 

Chromite ore roast mixed with sheep fat implanted intrapleurally in rats produced sarcomas coexisting with squamous cell carcinomas of the lungs the same material implanted in the thigh of rats produced fibrosarcomas/ However, the lARC concluded that these studies were inadequate to fully evaluate the carcinogenicity of this compound/ Other animal studies have found no increase in the incidence of tumors with chromium metal and chromite ore/ The lARC has determined that there is inadequate evidence in humans and animals for the carcinogenicity of metallic chromium and chromium(III) compounds. 

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

As this table suggests, the environmental hazard posed by heavy metals varies significantly. Some of the elements listed in that chart are among the most hazardous substances released to the environment. The EPA has classified four of the heavy metals—arsenic, lead, mercury, and cadmium—among the top 25 most hazardous chemicals present in the environment in the United States. (Of the remaining substances on that list 18 are toxic organic chemicals one is another heavy metal, chromium one is white phosphorus and the last is creosote produced from coal tar.)... 

Nicolas-Louis Vauquelin, the discoverer of the metal chromium, was bom on May 16, 1763, in a little Normany village called St. Andre... 

Since the properties of erythronium closely resembled those which Fourcroy had ascribed to the recently discovered metal chromium, del Rio lost confidence in the importance of his discovery and concluded that his supposed new element was, after all, nothing but chromium (11). In a note to his translation of Kars ten s Mineralogical Tables he wrote (7, 9,12) .. . but, knowing that chromium also gives by evaporation red or yellow salts, I believe that the brown lead is a yellow oxide of chromium, combined with excess lead also in the form of the yellow oxide. ... 

Preparation of Chromium(II) Chloride. (Perform one of the following two experiments.) 1. Put several pieces of metallic chromium into a test tube, pour in 2-3 ml of a 20% hydrochloric acid solution, and insert a stopper with a gas-discharge tube. Connect to the latter a rubber tube with a slot closed by a glass rod (a Bunsen valve. Fig. 125). What is the role of the slot in the rubber tube Identify the substance in the solution. Write the equation of the reaction. 

Chromate op Potassa.—This salt, though much more important as a compound of chromium than of potassium, yet requires to be noticod under this head. The metal, chromium, so called from its tendency to produce colored salts, the name being derived from the Greek word signifying color, was discovered by VaUQUElin in 1797, in the examination of red chromate of lead from Siberia. The most important native compound... 

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