Iridium electrical resistivity

The most important use of iridium is as an alloying metal for platinum and palladium. Such alloys are used for jewelry, decorative purposes, electrical contacts, thermocouples, crucibles, electrodes, hypodermic needles, and medical accessories. Iridium enhances resistance of platinum to chemical attack and corrosion. It also enhances hardness and tensile strength. The radioisotope Ir-192 is used in examination of ferrous welds and in other radiographic applications. 

Rhodium melts at 1907° C.4 and boils at about 2500° C. It is less volatile than platinum,5 and when alloyed with that metal not only stiffens it, but, unlike iridium, reduces its volatility at all temperatures above 900° C. It has been suggested,6 therefore, that a useful alloy for best quality crucibles would consist of platinum 95 to 97 per cent., and rhodium 3 to 5 per cent., and containing no other detectable impurities. Below 900° C. the presence of rhodium appears to exert a negligible effect. When cooled to — 80° C. rhodium appears to undergo a molecular transformation of some kind, analogous to that evidenced by copper. At this temperature the electrical resistance is considerably below the calculated value.7 The most intense lines in the spectrum of rhodium are as follow 8 ... 

An exceptionally pure form of reduced iron has been obtained by Lambert and Thomson 4 by reduction of pure, colourless crystals of ferric nitrate.5 The crystals were first converted into oxide or basic nitrate by ignition in an iridium boat.6 The whole was then introduced into a silica tube and heated in an electric resistance furnace to just above 1000° C. in a current of pure hydrogen gas, obtained by the electrolysis of barium hydroxide solution. 

Use Jewelry ( medium platinum is 95% platinum, 5% iridium and hard platinum is 90% platinum, 10% iridium), electrical contacts (10-25% iridium), fuse wire (10-20% iridium), hypodermic needles (20-30% iridium), and in general where high corrosion resistance is needed. 

In the case of dynamic random access memory (DRAM), the top electrode used in capacitor for a device s high speed raises the necessity of noble mefals like rufhenium (Ru), platinum (Pt), and iridium (Ir), which have low electric resistance and are mechanically and thermally stable. These noble metals are also chemically very stable and it is not easy to form capacitors by fhe efch back process. That is why noble metal CMP is compulsory. However, Ru is divided during the CMP process as a consequence of poor adhesion of leakage of cap oxide, grain growth of Ru, and cap oxide. To protect this phenomenon, the application of new functional slurry is essential. 

The electrical resistivities (initial geometry and including volume expansion) for iridium were calculated using the respective formulae, and volume expansion values from the literature (see Figure in volume expansion section) were used to obtain pvE- Unfortunately, the volume expansion data taken from [62] are limited to a maximum temperature of 3000 K, but show a linear behaviour, which was assumed for higher temperatures too and used to extrapolate the data. The plotted literature data can be found in [121 ( ), 122... 

Figure 5. Iridium Set of thermophysical properties obtained from a single pulse-calorimetric experiment on an iridium sample a) basic electrical quantities and the pyrometer signal as a function of experimental duration b) specific enthalpy as a function of temperature c) electrical resistivity, at initial geometry and with volume expansion, as a function of temperature d) thermal conductivity as a function of temperature e) thermal diffusivity as a frmction of temperature f)...

For the thermophysical data of solid and liquid iridium, the following uncertainties should be applied temperatures below 2400 K, 4%, temperatures above 2400 K, 1.7 %, normal spectral emittance, 6%, enthalpy in tfie solid state, 4%, enthalpy in the liquid state, 2.5%, heat of fusion, 8%, isobaric heat capacity, 8%, electrical resistivity at initial geometry solid, 4%, liquid, 3.5%, electrical resistivity including volume expansion solid and liquid, 6%, thermal conductivity, 12%, and finally thermal difliisivity, 16%. 

The heater material is a crucial point for the stability of this type of device during operation. Driven by CMOS compatibility, Poly-Si was first used but it suffers from an inappropriate drift of its electrical resistivity at high temperature (Ehmann et al, 2001). Platinum is the material that has been implemented for the heater for improved reliability. It is used in most micromachined metal-oxide sensors on the market at the time of writing, not only for the heater, but also for the electrodes. Courbat et al (2008) showed that adding a small amount of another refractory metal (such as iridium) to the platinum can improve its resistance to electromigration. However, Mo exhibited superior performances to platinum, allowing higher operational temperatures (Mele et a/., 2012). 

VFB electrode materials currently adapted can be divided into two types (1) metal and (2) carbon materials. A range of metal electrode materials such as Pb, Au, Pt, platinised titanium (Pt-Ti) and iridium oxide dimensionally stable electrodes (DSAs) have been evaluated for their suitability as positive electrodes in VFBs [41]. It was foimd that the electrochemical reversibility for the VO /V02 redox couple was not sufficient on the Au electrode. The Pb and Ti electrodes were easily passivated in the potential range, where the /V02 redox couple reactions occur. The passivation film formed on the surface would increase the electric resistance. The growth of the passivation... 

A dimensionally stable anode consisting of an electrically conducting ceramic substrate coated with a noble metal oxide has been developed (55). Iridium oxide, for example, resists anode wear experienced ia the Downs and similar electrolytic cells (see Metal anodes). 

Copper is another transition metal that does not corrode easily, which makes it useful for water pipes. Copper is also an excellent conductor of heat, which explains why copper-bottomed cooking pans have been used for centuries. Today, most copper is used in electrical wiring, since it conducts electricity so well and can be stretched into thin shapes. Other transition metals that resist corrosion include platinum, osmium, and iridium. These last two elements are often used in metal pen nibs (the tip of a fountain ink pen) and the tip of spark plugs for cars. 

Uses.—Rhodium is used, both alone but generally alloyed with platinum, in the construction of scientific apparatus such as crucibles. A rhodium crucible is, for all practical purposes, as resistant as one of iridium, and is both cheaper and lighter.7 It has also found application in the manufacture of thermo-electric couples.8 Rhodium black has been used for producing a black colour in the decoration of poree lain.9... 

A very convenient form of measuring temperatures is now at our disposal in the form of electrical thermometers., These are of twofold construction they may be either resistance or contact thermometers. In the resistance thermometers, use is made of the fact that the resistance of a metal to the passage of a current depends upon the temperature, so that if, for instance, a platinum wire is exposed to the heat of a furnace and a weak current is passed through it, that current will affect the needle of a galvanometer according to the temperature of the wire. The contact thermometer, on the other hand, depends upon the fact that if two pieces of different metals, as, for instance, an iridium and a platinum wire, are placed in contact,... 

Iridium is highly resistant to corrosion making it desirable for alloys for high-precision instruments and bearings. It is also used in electrical contacts, in pen points, in spark plugs, and in jewelry. 

Rhodium has the highest electrical conductivity, thermal conductivity, and reflectivity of any PGM. It is similar to iridium. It is difflcult to fabricate and is resistant to corrosion. The major corrosive agents are moist iodine, NaClO, hot H2SO4, and hot HBr. 

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