A substance with a positive temperature resistivity is usually defined as a metal. Metals have good conductivity because their electrons tend to decompose, and their valences are only 0 and positive. The bond between metal molecules is a metal bond, which can be reestablished by changing the position at will, so the metal has good ductility. In terms of atomic structure, the outermost electron number of most metal atoms is less than or equal to 4 except for a few metals such as tin, antimony and bismuth. The outermost electrons in the atomic structure of metals are easy to lose, so most metals are chemically active. Therefore, most metals in nature exist in a combined state, while only a few metals such as gold, silver, platinum and bismuth exist in a free state.
Due to its rich variety and unique physical and chemical properties, metals are widely used in many fields such as organic chemistry, biomedicine and environmental protection.
- Organic chemistry: Metals are widely used in organic chemistry. In addition to being raw materials for some reactions, the application of metals in organic chemistry is more focused on catalyzing many types of reactions. For example, metal-organic framework materials (MOFs) are a class of porous crystalline solid materials formed by the self-assembly of metal ions or ion clusters with organic ligands through weak coordination bonds. MOFs have unique structural characteristics, such as large specific surface area, regular pore size, high porosity, and abundant catalytic active sites, so they can be used as catalysts or as carriers for multifunctional catalysts. In the field of chemistry, metal-organic framework materials are often used to catalyze reactions such as photocatalytic decomposition of water to produce hydrogen, electrocatalytic CO2 reduction, and selective hydrogenation.
Figure 1. Metal-organic framework materials
- Biomedicine: Metals used in the field of biomedicine are generally called biomedical metal materials, which belong to a class of inert materials. Biomedical metal materials have high fatigue resistance and mechanical strength, and are widely used in clinical auxiliary equipment, artificial organs, hard tissues, soft tissues, etc. The medical metal materials that have been used clinically mainly include cobalt-based alloys, titanium-based alloys, stainless steels, shape memory alloys, precious metals, pure metals niobium, zirconium, titanium, tantalum, and the like. For example, medical precious metal platinum has unique biocompatibility, good ductility, and is non-toxic to the human body, so it is often used as an important dental implant material in medicine. In addition, silver nanoparticles can cross blood vessels to reach target organs and can be attached to single DNA strands, thereby making it useful in biomedical fields such as biosensing, biomarkers, bioimaging, medical diagnosis and treatment. At the same time, nano-silver has good broad-spectrum antibacterial ability and can be used in salves and creams to treat burns.
Figure 2. Tooth with metal platinum as raw material
- Environmental protection: Metals have very important applications in environmental protection. For example, copper-based alloys, 304 stainless steel, 316 stainless steel, GH3030 high nickel alloy and GH4 superalloy metal fiber products, Fe-Al sintered powder and 310S sintered metal wire mesh are widely used for high-temperature dust removal. In addition, porous supports made of Fe-Cr-AI alloy materials have begun to replace porous ceramics, thereby achieving efficient automotive exhaust purification.
According to whether the chemical properties are active, metals can be divided into active metals and inert metals. According to the density, metals can be divided into heavy metals and light metals. According to the amount in the earth's crust and the difficulty of extraction from raw materials, metals can be divided into common metals and rare metals.
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