Is antimony a metalloid?

Antimony is a metalloid element, the English name Antimony, the element symbol: Sb, belongs to the VA group, the atomic number is 51, the relative atomic weight is 121.75, the density is 6.684g/cm³, the melting point is 630.74 ° C, and the boiling point is 1750 ° C. Antimony is a brittle and lustrous silver-white solid, which is poisonous, has unique heat shrinkage and cold expansion, and has no ductility.

Antimony is not oxidized by air at room temperature, but can react with concentrated nitric acid. The content of antimony in the earth's crust is 0.0001%. There are as many as 120 kinds of antimony-containing minerals known at present, but only 10 kinds have industrial value. With the development of science and technology, antimony has been widely used in the production of various flame retardants, alloys, ceramics, glass, pigments, semiconductor components, medicine and chemical industry.

Antimony is a metalloid, also known as a semimetal, a substance between metals and non-metals. A metalloid is an element that exhibits the properties of a metal in appearance, but exhibits both metallic and non-metallic properties in chemical properties. Arsenic and antimony, for example, are hard crystalline solids that are apparently metallic in appearance, but exhibit two distinct properties, metallic and non-metallic, when chemically reacted. 

Some of their oxides are soluble in both acids and bases, which is called amphoteric because they behave like both bases and acids. There are many elements that can also form amphoteric compounds. However, the element can only be called a metalloid when the duality of the chemical properties is evident and at the same time shows the appearance of a metal.

Chemical properties of antimony metal 

Antimony is a nitrogen group element (group 15) with an electronegativity of 2.05 (Pauling scale). According to the periodic law of elements, its electronegativity is greater than that of tin and bismuth, and less than that of tellurium and arsenic. Antimony is stable in air at room temperature, but can react with oxygen to form antimony trioxide when heated. Antimony does not react with acid under normal conditions.

There are four known allotropes of antimony: one stable metallic antimony and three metastable antimony (explosive antimony, black antimony, yellow antimony). Antimony metal is a brittle silver-white lustrous metal. When the molten antimony is slowly cooled, the metal antimony will form a trigonal crystal, which is isomorphous to the gray allotrope of arsenic. Antimony in a rare explosive shape can be made by electrolysis of antimony trichloride, and scratching it with a sharp tool will cause an exothermic chemical reaction that emits white smoke and produces metallic antimony. 

If you grind it with a pestle in a mortar, it will explode violently. Black antimony is formed by the rapid cooling of metal antimony vapor. Its crystal structure is the same as that of red phosphorus and black arsenic. It is easily oxidized and even spontaneously ignited in oxygen. When the temperature dropped to 100 °C, it gradually transformed into a stable crystal form. Antimony yellow is the most unstable one and can only be obtained by oxidation of antimony hydrogen at -90°C. Under the action of this temperature and ambient light, the metastable allotropes are transformed into the more stable black antimony.

The structure of antimony metal is a layered structure (space group: R3m), and each layer contains an interconnected folded six-membered ring structure. The nearest and next closest antimony atoms form deformed octahedra, with three antimony atoms in the same bilayer being slightly closer together than the other three. This relative closeness in distance results in a density of 6.697 g/cm3 for antimony metal, but the weak bonding between layers also makes it soft and brittle.

Application of pure antimony

60% of antimony is used to produce flame retardants, while 20% of antimony is used to make alloy materials in batteries, sliding bearings and soldering agents.

Flame retardant

The main use of antimony is its oxide antimony trioxide used in the manufacture of refractory materials. With the exception of halogen-containing polymeric flame retardants, it is almost always used with halogenated flame retardants. The process of antimony trioxide forming antimony halide can slow down combustion, which is the reason for its flame retardant effect. These compounds react with hydrogen atoms, oxygen atoms, and hydroxyl radicals, eventually extinguishing the fire. Commercially these flame retardants are used in children's clothing, toys, aircraft and car seat covers. It is also used as an additive for polyester resins in the fiberglass composite (commonly known as FRP) industry, such as engine covers for light aircraft. Resin burns in a fire but it stops burning on its own when the fire is extinguished.

Alloy

Antimony forms a versatile alloy with lead that increases the hardness and mechanical strength of antimony. In most cases where lead is used, varying amounts of antimony are added to make the alloy. In lead-acid batteries, the additive alters electrode properties and reduces the formation of by-product hydrogen gas during discharge. Antimony is also used in anti-friction alloys (eg Babbitt), bullets, lead bullets, wire jackets, type alloys (eg Linotype), solders (some lead-free solders contain 5% antimony), lead-tin-antimony alloys, As well as hardening the less tin-containing alloys used to make pipe organs.

Other applications

Almost all other antimony are used in the three areas described below. The first application is the production of stabilizers and catalysts for polyethylene terephthalate. The second application is a clarifying agent to remove microscopic bubbles in glass, mainly used in the manufacture of TV screens; this is because antimony ions prevent the continued formation of bubbles when they come into contact with oxygen. The third application is pigments. Antimony's use in the semiconductor industry is growing, primarily as a dopant in ultra-high-conductivity n-type silicon wafers, which are used in the production of diodes, infrared detectors, and Hall-effect elements. In the 1950s, beaded lead-antimony alloys were used to paint the transmitters and receivers of NPN-type alloy junction transistors. Indium antimonide is a material used to make infrared detectors.

Antimony has few biological or medical applications. The medicine whose main component is antimony is called antimony-containing medicine, which is a kind of emetic. Antimony compounds are also used as antiprotozoal agents. Since 1919, potassium antimony tartrate (commonly known as spit tartar) has been used as a drug for the treatment of schistosomiasis. It was later gradually replaced by praziquantel. Antimony and its compounds are used in a variety of veterinary medicines, for example, anthomaline (lithium antimony thiomalate) is used as a skin conditioner in ruminants. Antimony nourishes and regulates keratinized tissues, at least in animals.

Antimony-containing drugs are also used as one of the options for the treatment of leishmaniasis in livestock, such as meglumine antimonate. Unfortunately, it not only has a low therapeutic index, but it also has difficulty entering the bone marrow, where some Leishmania amastigotes are located, and cannot cure diseases that affect the internal organs. Antimony pills made of metal antimony were used as medicine. But it can cause poisoning when ingested from the air by others.

Antimony trisulfide is used in the heads of some safety matches. Antimony-124 is used together with beryllium in a neutron source: Antimony-124 emits gamma rays that initiate photodisintegration of beryllium. The neutrons thus released have an average energy of 24 keV. Antimony sulfides have been shown to stabilize the coefficient of friction of automotive brake pad materials. Antimony is also used in the manufacture of bullets and bullet tracers. This element is also used in traditional decoration, such as brush painting and artistic glass craftsmanship. It was used as a sunscreen for tooth enamel before the 1930s, but was discontinued after repeated poisonings.