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The major use of Platinum is in catalytic converters (∼50%), an automobile emission control device, that converts the toxic pollutants as exhaust gas to less toxic pollutants by catalyzing redox (reduction–oxidation) reaction. Catalytic converters are used in internal combustion engine fueled by either gasoline or diesel. The PGEs are highly resistant to wear and tarnishing, making them well suited internationally for fine jewelry (30%). The other uses are in chemical and petroleum refining plants, laboratory equipment, platinum resistance thermometers, currency, and investment. The chemical inertness and refractory properties of these metals find applications in electrical contacts, electronics, electrodes, and dental and medical fields.
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Palladium is used as a substitute for silver in dentistry and jewelry. The pure metal is used as the delicate mainsprings in analog wristwatches. Palladium is used as catalytic converters, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide) into less-harmful substances (nitrogen, carbon dioxide, and water vapor). The metal is also used in surgical instruments, electronics, hydrogen storage, coinage, photography, jewelry, and investment.
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The most important compounds of Iridium in use are the salts and acids it forms with chlorine. Iridium is an extremely hard and too brittle an element to be used in the pure state. Therefore, it is often used as an alloy. Platinum–iridium alloys are used in the manufacturing industries for the production of machine parts, containers (crucibles), fountain-pen nib heads, and electric contacts that may be exposed to high temperatures and chemicals. The other uses include jewelry and electrodes of spark plugs.
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Osmium is rarely used in its pure state. The metal is used as alloys with platinum, iridium, and other platinum group metals in electrical circuit components, fountain-pen tips, and other applications in which extreme durability and hardness are necessary.
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Most Ruthenium produced is converted to hard platinum–palladium alloy and used for wear-resistant electrical contacts and the manufacture of thick-film resistors.
Including Actinides
Mikiya Tanaka, … Tetsuo Oishi, in Handbook on the Physics and Chemistry of Rare Earths, 2013
5.3 Catalysts
Three-way catalysts used in exhaust-gas catalytic converters of automobiles contain platinum, palladium, rhodium, zirconium, and cerium. Oki et al. have developed a method which concentrates these metals by means of a two-step crushing procedure (Kim et al., 2010; Oki et al. 2010). The process makes it possible to increase concentration of rare-earth metals by a factor of five by first demolishing the honeycomb structure, and then peeling off the surface. To date, no process leading to recovery of individual rare-earth metals has been described.
Reserves Base
S.K. Haldar, in Platinum-Nickel-Chromium Deposits, 2017
11.6.1 Platinum Group of Metals
PGMs are used in a wide range of technologies, including catalytic converters, electronics, and jewelry. Platinum market fundamentals are complex, and face very different issues than those of other strategic metals. The demand for jewelry, automobiles, and coin are all expected to rise, whereas the supply is from extremely limited locations. Very few significant platinum–palladium mining operations exist in the world. These two metals have the highest economic importance and are found in the largest quantities among the PGEs. The Bushveld Complex has the resources to supply world demand for platinum for the next century. However, miners’ strikes complicate the economic stability of the noble metals, and the prices have skyrocketed due to strikes at South African mines.
South Africa is the largest producer of platinum from the Bushveld Complex since 1925, with palladium and rhodium as byproducts. Platinum was discovered in the rocks of The Great Dyke, Zimbabwe, in 1918, but significant output from this extensive resource only began in the 1990s. The fresh supply of platinum in decreasing order is contributed by South Africa, Russia, North America (including Canada), and other countries. In addition, a bulk amount is received from the recycling of scrap which is about 25% of the fresh supply. Global demand and supply of platinum between 1990 and 2015 is provided in Fig. 11.14. The overall average demand of platinum is expected to rise by exceeding 3.5% per annum due to increasing need for catalytic converters, autocatalysts, jewelry, and coins.
Figure 11.14. The global gross demand and supply trend of platinum is continuously increasing at a rate exceeding 3.5%. The gap between demand and supply is partially compensated by metal recovery from scraps.
Russia is the largest producer of palladium. The Stillwater Complex, United States, is a palladium-rich mine producing since 1987. Palladium demand is expected to rise by 3.5% per annum, and the supply is likely to drop in the future. This gap in demand and supply may result increase in the price of palladium over platinum. The global demand and supply trend of palladium between 1990 and 2015 is similar to that of platinum.
The average global supply of PGEs is shared by Bushveld (∼78% Pt, and ∼40% Pd), Noril’sk (∼11% Pt, and ∼44% Pd), Stillwater (∼2% Pt, and ∼6% Pd), and The Great Dyke (∼3% Pt and ∼2% Pd). The other four metals (rhodium, ruthenium, iridium, and osmium) are produced as co-products of platinum and palladium. The annual production of these metals depends on production of the primary metals.
Fuel Cells
Aldo Vieira da Rosa, Juan Carlos Ordóñez, in Fundamentals of Renewable Energy Processes (Fourth Edition), 2022
9.5.2.1 A Fuel Cell Battery (Engelhard)
Engelhardg made an attempt to commercially implement the technology exemplified by the demonstration fuel cell of the previous section. It offered a completely autonomous 750 W battery which included a fuel supply and all the control devices. The knotty problem of providing the hydrogen for the cell was solved by an integrated ammonia-cracking subunit. Ammonia, NH3, is, indeed, a convenient way of storing hydrogen because, at room temperature under moderate pressures, it is a liquid and can, therefore, be easily handled.
The electrolyte was phosphoric acid. The cell construction can be seen in Fig. 9.8.
Figure 9.8. One element of the Engelhard PAFC.
Since fuel cells are low voltage, high current devices, they must be connected in series. The simplest way of doing so is to use a bipolar configuration: a given electrode acts as anode for one cell and (on the other face) as cathode for the next. The bipolar electrode was made of either aluminum or carbon. Gold was plated on aluminum for protection and flashed on carbon to reduce contact resistance.
The plate was 3 mm thick and had grooves or channels machined on both faces. The oxidant channels ran perpendicular to those for hydrogen on the opposite face. The plate was rectangular with its smaller dimension along the air flow direction to minimize pressure drop. The channels, in addition to leading in the gases, served also to increase the active surface of the electrodes.
The electrolyte soaked a “cell laminate” held in place by a rubber gasket. It can be seen that this type of construction does not differ fundamentally from that used in the demonstration cell described before.
The cell operated at 125∘C. The oxidant was air, which entered at ambient temperature and left hot and moist, carrying away excess heat and water (formed by the oxidation of the fuel in the cell). The air flow was adjusted to provide sufficient oxygen and to ensure proper heat and water removal.
Apparently, no catalysts were used. This, combined with the relatively low operating temperature (phosphoric acid cells frequently operate at temperatures above 150∘C), resulted in somewhat adverse kinetics and, consequently, in low voltage efficiency.
The system consisted of an ammonia source (a pressure cylinder), a dissociator or cracker, a scrubber, the fuel cells, and ancillary pumping and control mechanisms.