Industrial Applications of Minor Metals
The MMs in recent years have played a significant role in providing a major breakthrough in engineering industries which has resulted in new product development worldwide. The social amenities like miniaturized/movable products, their rising sales and rapid obsolescence is creating an inordinate demand of MMs. The important uses are in ferrous (military vehicles, aerospace marine etc.), in nonferrous and other industries (battery alloys for hybrid vehicles, permanent magnets, phosphors, laptops, mobile phones, ceramics, catalysts, polishing powders & glass additives etc.) which are briefly explained below.
1) Pharmaceutical & Medical - The MMs like Pd, Rh, Os, Ir, Mo, Ni, Cr, V, Mn etc as metal or their compounds are used in pharmaceutical products related to the preparation of drugs, medicines, dentistry, micro-nutrients etc. The Ce, Bi, Hg, Li & Pt & their compounds are used in the above industries e.g., Ce2 (C2O4)3 is an antiemetic drug. Bi-subsalicylate is used for ulcer treatment. Hg is used as dental amalgams. Biocompatible materials are used in orthopedic, cardiovascular and dental applications. Pt, Pd, Ti and stainless alloys are used for making human body parts.
2) Magnetic refrigeration - A cooling technology based on magnetic energy derived from the magneto-caloric effect (this is a phenomenon in which a reversible change in temperature of magnetic materials takes place i.e. materials heat up when they are subjected to a magnetic field & cool down on its removal). This energy is used to maintain a low temperature in refrigerators and other cooling devices. The important magnetic materials are Gd- alloy Gd5 (Si2Ge2), Pr-Ni alloy, Ni (PrNi5) etc.
3) Super alloys - High performance alloys mainly consists of various proportions of Fe, Ni, Co, and Cr, and minor amounts of W, Mo, Ta, Nb, Ti, Re, Zr, and Al. These alloys capable of sustaining at & above 1000°C and also exhibit high mechanical and creep strength, corrosion resistance, good surface stability at high temperatures and are traded as Monel, Wasp alloy, Incoloy etc. suitable for applications in gas turbine, pressure vessels, aero engines and electron beam welding.
4) Specialty alloys - Possessing special physical properties (magnetic, electric, thermal, or elastic) or a rare combination of physical, physicochemical, and mechanical properties and corresponding structure of the alloy such as specialty dies & tools, stainless steels, titanium alloys. Normally used in plate, sheet; strip, bar, pipe, fittings and welding materials. Re-Pt alloys are used as catalyst for catalytic reforming, Cr-Co, Co-Mo, Ga-In-Zn Oxide. Al-Li alloys are used in aircrafts. Te, Se, Si, Re etc are also used both for ferrous & non- ferrous alloys.
5) Super Magnets - The NdFeB magnet is an extremely powerful versatile magnetic alloy resistant against demagnetization, and is stable and magnetic energy efficient (45MGOe) in comparison to conventional magnets. Small, lightweight, high-strength magnets produced with Nd, Sm, Gd, Dy, or Pr have allowed miniaturization of numerous electrical and electronic components used in appliances like disc drive, MRI, high efficiency D.C. motors etc.
6) Metallurgical Applications - In process metallurgy, Re, Ti, W etc are used for high temperature alloys. Nuclear weapons and reactors use Si, Ge, Zr. In HSLA steels with Nb, Ti, V being used as micro alloying elements. In extractive metallurgy, Li is used in primary aluminum production. Bi is used to substitute toxic Pb in machinable alloys. In powder metallurgy, wear-resistant materials, like carbides of W and Ti, and borides, with binder metals like Co, Ni, and Ni-Mo alloys are used for making machine tools & machine parts.
7) Glass/Ceramics/Pigments - CeO2 is used as a glass polishing agent, for mirrors, eye-glasses, precision lenses etc. The chief commercial uses for selenium today is in glassmaking and in pigments. The Zirconia &, Ceria fine powders are used in glass polishing and TiO2 pigments are used for making paints. Fiber amplifier based on glass fibers, doped with laser-active RE ions, with the most important being Er-doped & Yb-doped fibers for high powered laser amplifiers.
8) Photovoltaic - A method of power generation employing solar panels composed of a number of solar cells containing a photovoltaic material. This method of converting solar radiation into d.c. electricity using semiconductors, that exhibit photovoltaic effects, which acts as a source of emf. CdTe, CIGS, amorphous Si, microcrystalline Si, Ga, Ge, In, Se, Te, Ru etc. are used in thin-film solar cells Cu-Telluride is used in solar energy and advanced optical applications.
9) Super Batteries - REE, Li, In, Co etc. are used in advanced super charge ion batteries. The Li-ion batteries reduce recharging time and have a long life. The NiMH (Ni-metal hydride) batteries are eco-friendly and convenient to recycle after EoL. The nickel- oxy-hydroxide (NiOx) batteries (Duracell & Panasonic) with graphite cathodes are also in use. Li-Mn batteries are expected to be low cost energy storage devices enable the cheaper LiMn2O4 to be used instead of the expensive LiCoO2.
10) Fuel cells - Fuel cells combine hydrogen and oxygen, separated by a proton-conductive membrane impermeable to gas, which results in the generation of energy and production of water. A more efficient solid oxide fuel cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material and the SOFC have a solid oxide or ceramic. Yttria stabilized zirconia (YSZ), Samaria doped ceria, Porous NiO-YSZ which convert hydrogen, natural gas or another fuel into electricity through an electrochemical process, where chemical energy from a fuel into electricity through a chemical reaction employ MMs like PGM ( Pd, Pt, Rb, Ru) & REE (Li Y &Zr).
11) Catalysts - Co, Ge, Re, Se, Te is extensively used as catalysts. Ce2O3 is a catalytic converter for the reduction of CO. The REE is used to produce catalysts for the cracking of crude petroleum and hydration of ketones to form secondary alcohols and for hydrogenation of olefins to form alkanes (parafins).
12) Nuclear - The elements like Eu, Gd, Dy have large thermal neutron capture cross sections and are suitable for incorporation in control rods used to regulate reactor operation. REE are also used as burnable neutron absorbers to maintain the reactor flux density. Li-6 deuteride (6LiD) is used in nuclear weapons.
13) Solder - Joining material made up of fusible metals/alloys having an m.p. lower than the job or work piece which is required to be joined. Solder Indalloy -13 (In70 Sn15 Pb9.6 Cd5.4), indium lowers the m.p. & improves the ductility.
14) Electronic - The elements such as Li, Cs, Ta, REE, PGM, Co, Cd, In, Bi, W are the key MMs of the electronic industries. Cd Telluride is used in thin film solar cells (TFSC-and is made by depositing a thin layer of PV materials over a substrate). Ga is used in Laser-diodes, LEDs, Solar cells high capacity transistors etc. Ta is used in capacitors.
15) Opto-electronics - Electronic devices that source all types of light irrespective to visible & invisible i.e. these are either optical to electrical or electrical to optical transducers (which convert one form of energy to another) the technology of the inter-conversion of electrical & optical signals. CRT - phosphors, laser reader of CD, light sensors of camera are the examples. The opto electronic devices employ many MMs like Te, Se, Si, REE, In, Ga, Ge etc. Coloured CRT & LCD used in monitors employ Eu-red phosphor.
16) Grease & Lubricants - Lubricant is a substance introduced between moving surfaces to reduce friction (Liquid lubricants 90% oil + 10% additives). Non-liquid lubricants are grease, powders of graphite, Mo & W disulphides (sustainable up to 350°C). The Li-sterate and Li-12 hydroxy stearate can be used up to 120°C.
17) CFL - Eu-doped Yttrium oxide (Y2O3), a white powder material which emits red light excited by UV light at 253.7nm, known as luminophore (manifests luminescence, a blend of different chemical components to create the desired color) used for manufacturing conventional fluorescent lamps. The function of these chemicals is to convert the energy of the ultraviolet light (created by the electric discharge in the tube) into visible light. The CFL uses the UV-light which transfers the energy to the luminophore coated on the inner wall of the CFL tube which stimulates it to emit blue, green and red light, which appears white light to human eyes.