Iridium dioxide

Iridium Oxide. Iridium dioxide [12030 9-8] coatings, typically used in combination with valve metal oxides, are quite similar in stmcture to those of mthenium dioxide coatings. X-ray diffraction shows the mtile crystal stmcture of the iridium dioxide scanning electron micrographs show the micro-cracked surface typical of these thermally prepared oxide coatings. 

The second form consists of Pt metal but the iridium is present as iridium dioxide. Iridium metal may or may not be present, depending on the baking temperature (14). Titanium dioxide is present in amounts of only a few weight percent. The analysis of these coatings suggests that the platinum metal acts as a binder for the iridium oxide, which in turn acts as the electrocatalyst for chlorine discharge (14). In the case of thermally deposited platinum—iridium metal coatings, these may actually form an intermetallic. Both the electrocatalytic properties and wear rates are expected to differ for these two forms of platinum—iridium-coated anodes. 

Insoluble iridium dioxide from the sodium peroxide fusion is dissolved in aqua regia, oxidized with nitric acid, and precipitated with ammonium chloride as impure ammonium hexachloroiridate(IV), To purify this salt, it is necessary to redissolve the compound and precipitate out the... 

Miscellaneous. Iridium dioxide, like RUO2, is useful as an electrode material for dimensionally stable anodes (DSA) (189). SoHd-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) ofIr02 ate stable electrochromic materials (191). 

Fig. 7.67 Conversion electron Mossbauer spectra of the 73 keV y-rays in Ir recored at 4.2 K using a metal source, (a, b) metallic iridium, 5 mg cm, (c, d) iridium dioxide, 5 and 1 mg cm , respectively. Measuring time about 10 h for spectra a-c and 20 h for spectrum d (from [308])...

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

Iridium dioxide, 79 608-609, 650 Iridium oxides, electrochromic materials, 6 579-580, 580t... 

Iridium Oxide, Iridium dioxide comings, typically used in combination with valve metal oxides, arc quite similar in structure to those of ruthenium dioxide comings. 

Metals or Metal Oxides. Explosions result on contact with Ni powder, Hg, colloidal Ag, thallium powder, Zn powder, PbO, Pb304, and Na202 violent decomposition occurs with barium peroxide, CuO, impure Cr03, iridium dioxide, Pb02, Mn02, and V205 and with Fe powder contaminated with a trace of Mn02.3... 

Direct electrooxidation is theoretically possible at low potentials, before oxygen evolution, but the reaction rate usually has low kinetics that depends on the electro-catalytic activity of the anode. High electrochemical rates have been observed using noble metals such as Pt and Pd, and metal-oxide anodes such as iridium dioxide, ruthenium-titanium dioxide, and iridium-titanium dioxide (Foti et al. 1997). 

Iridium dioxide — Iridium oxide crystallizes in the rutile structure and is the best conductor among the transition metal oxides, exhibiting metallic conductivity at room temperature. This material has established itself as a well-known - pH sensing [i] and electrochromic [ii] material (- electrochromism) as well as a catalytic electrode in the production of chlorine and caustic [iii]. The oxide may be prepared thermally [iv] (e.g., by thermal decomposition of suitable precursors at temperatures between 300 and 500 °C to form a film on a substrate such as titanium) or by anodic electrodeposition [v]. 

Iridium Oxybromide has been obtained by heating iridium dioxide to 800° C. in a closed vessel with bromine. It yields black needles, soluble in water, for which the formula (IrBr4)2Ir02 has been suggested.2... 

Iridium Dioxide, IrOs, is obtained when potassium iridate, Ir03.2KaO.H20, is heated with excess of potassium bromide and chloride. The melt is extracted with water, the insoluble residue treated with aqua regia to dissolve any unchanged iridate, and finally dried at 100° C. The product thus obtained is pure, crystalline iridium dioxide.5... 

When heated, iridium dioxide decomposes into oxygen and the... 

Iridium dioxide is readily reduced to the metal by heating in hydrogen. 

Hydrated Iridium Dioxide, Ir02.2H20, results (1) when excess of caustic alkali is added to a solution of chloriridate or of iridium tetrachloride. Any sesquioxide simultaneously produced passes into solution, but is converted into the dioxide by boiling in air, by addition of hydrogen peroxide, or by passing a current of oxgen through the solution. 

The colour of iridium dioxide depends to a large extent upon the hydration. Dried over concentrated sulphuric acid it contains two molecules of water and is black in colour. When heated to 760° C. it becomes anhydrous. 

Iridium dioxide also exists in colloidal form in solutions obtained by dissolving the amorphous oxide in hydrochloric acid. 

Iridium is unreactive at room temperatures. When exposed to air, it reacts with oxygen to form a thin layer of iridium dioxide (Ir02). 

At high temperatures, the metal becomes more reactive. Then it reacts with oxygen and halogens to form iridium dioxide and iridium trihalides. For example ... 

The DSA-type anodes are inert , coated anodes made of a valve metal (titanium, niobium, or tantalum) base coated with an electrochemically active coating. The active coating is made either of noble metals or of mixed metal oxides. Noble metals in active coatings are usually platinum or platinum alloys. Mixed metal-oxide coatings contain active oxides and inert oxides the active components are usually ruthenium dioxide (R.UO2) and iridium dioxide (IrC>2) and the inert components are mostly titanium dioxide (TiC>2) and other oxides such as tantalum... 

Ardizzone, S., Lettieri, D., and Trasatti, S., Effect of ionic adsorption on the point of zero charge of iridium dioxide, J. Electroanal. Chem., 146,431, 1983. 

Vitins, A. et al.. Model description of the adsorption properties of iridium dioxide in aqueous solutions, Sov. Electrochem., 28, 328, 1992. 

While the majority of enzyme electrodes fabricated have been rather large devices, there have been some recent reports concerning the development of miniaturized and even microsensors. For example, MeyerhoflF (M5) prepared an essentially disposable urea sensor (tip diameter 3 mm) by immobilizing urease at the surface of a new type of polymer-membrane electrode-based ammonia sensor (see Fig. 4). Alexander and Joseph (Al) have also prepared a new miniature urea sensor by immobilizing urease at the surface of pH-sensitive antimony wire. Similarly, lannello and Ycynych (II) immobilized urease on a pH-sensitive iridium dioxide electrode. In these latter investigations, ammonia liberated from the enzyme-catalyzed reaction alters the pH in the thin film of enzyme adjacent to the pH-sensitive wire. 

II. lanniello, R. M., and Yacynych, A. M., Urea sensor based on iridium dioxide electrodes with immobilized urease. Anal. Chhn. Acta 146, 249-253 (1983). 

Ir02 IRIDIUM DIOXIDE 877 K2SI409 POTASSIUM TETRASILICATE 920... 

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