Nitric surface resistance

Plastic solid of milky transperency. d 0.92. Tough and flexible at room temps, mp 85-1KT. Breaks with cryst fracture at — 50°. Oood electrical insulator. Surface resistivity 10H ohms. Will burn, but hardly supports combustion. Stable to water, non-oxidizing acids and alkalies, alcohols, ethers, ketones, esters at ordinary temps. Attacked by oxidizing acids such as nitric acid and perchloric acid, free halogens, bsnzene, petr ether, gasoline and lubricating oils, aromatic and chlorinated hydrocarbons. 

The corrosion behavior of tantalum is weU-documented (46). Technically, the excellent corrosion resistance of the metal reflects the chemical properties of the thermal oxide always present on the surface of the metal. This very adherent oxide layer makes tantalum one of the most corrosion-resistant metals to many chemicals at temperatures below 150°C. Tantalum is not attacked by most mineral acids, including aqua regia, perchloric acid, nitric acid, and concentrated sulfuric acid below 175°C. Tantalum is inert to most organic compounds organic acids, alcohols, ketones, esters, and phenols do not attack tantalum. 

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

Many optical glasses are much less resistant to attack than are container and window glasses, and less severe tests are necessary. A commonly used method is to immerse specimens in either dilute nitric acid or standard acetate solution of pH 4-6 for specified periods at room temperature, then to examine the surfaces either visually or by interferometry. 

The bluish white, hard, yet ductile, metal is inert to all acids and highly non-abrasive. Used for heavy-duty parts in electrical contacts and spinning jets. Reflectors are prepared from the mirror-smooth surfaces (e.g. head mirrors in medicine). Thin coatings provide a corrosion-resistant protective layer, for example, for jewelry, watches, and spectacle frames. The metal is a constituent of three-way catalysts. Rhodium complexes are used with great success in carbonylations (reactions with CO) and oxidations (nitric acid) in industry. Platinum-rhodium alloys are suitable thermocouples. 

Grayish, soft metal with a white luster on polished surfaces ductile and very malleable at room temperature also highly ductile at cryogenic temperatures body-centered cubic crystals density 8.66 g/cm at 20°C melts at 2,468+10°C vaporizes at 5,127°C electrical resistivity 13.2 microhm-cm at 20°C becomes superconducting at 9.15K thermal neutron-capture cross section 1.1 barns insoluble in water insoluble in hydrochloric acid, nitric acid and aquaregia soluble in hydrofluoric acid soluble in fused alkah hydroxide. 

The electrochemical reduction behavior of 1102 was also studied in a nitric acid-hydrazine solution at a titanium electrode because of its resistance to corrosion in nitric acid [59]. It was necessary to pretreat the titanium electrode, to remove surface oxide, through cathodic... 

Nearly all cells express kinin receptors that mediate the activities of both bradykinin and kallidin. The activation of these G-protein coupled receptors causes relaxation of venular smooth muscle and hypotension, increased vascular permeability, contraction of smooth muscle of the gut and airway leading to increased airway resistance, stimulation of sensory neurons, alteration of ion secretion of epithelial cells, production of nitric oxide, release of cytokines from leukocytes, and the production of eicosanoids from various cell types [11,12]. Because of this broad spectrum of activity, kinins have been implicated as an important mediator in many pathophysiologies including pain, sepsis, asthma, rheumatoid arthritis, pancreatitis, and a wide variety of other inflammatory diseases. Moreover, a recent report demonstrated that bradykinin B2 receptors on the surface of human fibroblasts were upregulated three-fold beyond normal in patients with Alzheimer s disease, implicating bradykinin as a participant in the peripheral inflammatory processes associated with that disease [13]. 

Anodizing employs electrochemical means to develop a surface oxide film on the workpiece, enhancing its corrosion resistance. Passivation is a process by which protective films are formed through immersion in an acid solution. In stainless steel passivation, embedded ion particles are dissolved and a thin oxide coat is formed by immersion in nitric acid, sometimes containing sodium dichromate. 

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