Strontium metal

Strontium metal (98% pure) in January 1990 cost about 5/oz. 

This reaction occurs in a vacuum and the gaseous metal is condensed in a cooler part of the apparatus. AH strontium metal is produced commercially by the thermal reduction process in aUoy steel retorts. 

Historically, strontium metal was produced only in very small quantities. Rapid growth of metal production occurred during the late 1980s, however, owing to use as a eutectic modifier in aluminum—silicon casting alloys. The addition of strontium changes the microstmcture of the alloy so that the siUcon is present as a fibrous stmcture, rather than as hard acicular particles. This results in improved ductility and strength in cast aluminum automotive parts such as wheels, intake manifolds, and cylinder heads. 

Annual consumption of strontium metal has increased from a few kilograms to several hundred metric tons. The largest single producer worldwide of strontium metal is Timminco Metals, a division of Timminco Ltd. (Toronto, Canada), which commissioned a faciUty in 1987 in Westmeath, Ontario, for production of high purity strontium metal. Other producers of strontium metal include Calstron Corporation (Memphis, Teimessee) and Pechiney ElectrometaHurgie (Erance). 

Prior to its addition to the aluminum casting alloys, the strontium metal is usually alloyed into the form of a master alloy. These master alloys are typically 10% Sr—90% A1 or 90% Sr—10% Al, and improve the dissolution and handling characteristics of strontium in the foundry. 

A second, more recently developed use for strontium metal is as an inoculant in ductile iron castings. Inoculants provide nuclei upon which graphite forms during the sohdification of cast iron, thus preventing the formation of white cast iron. Elkem Metals Company has commercialized a range of fine-sized foundry inoculants for iron castings. These inoculants, called superseed, are ferrosiUcon alloys containing 50 or 75% Si, 0.8% Sr. Most of the balance is iron. 

Strontium metal is responsible for the red color in fireworks. Fireworks manufacturers use strontium carbonate, which can be produced by combining strontium metal, graphite (C), and oxygen gas. The formation of one mole of SrC03 releases 1220 X 103 k) of energy. 

Preparation. Strontium metal can be obtained by electrolysis of the fused chlorides or by reduction of the oxide by aluminium. 

When strontium metal is exposed to water, it releases hydrogen, as do the other earth metals (Sr + 2HjO —> Sr(OH)2 + H T). Strontium can ignite when heated above its melting point. When in a fine powder form, it will burn spontaneously in air. It must be stored in an inert atmosphere or in naphtha. Several of its salts burn with a bright red flame, making it useful in signal flares and fireworks. 

Strontium metal is not found in its elemental state in nature. Its salts and oxide compounds constitute only 0.025% of the Earths crust. Strontium is found in Mexico and Spain in the mineral ores of strontianite (SrCO ) and celestite (SrSO ). As these ores are treated with hydrochloric acid (HCl), they produce strontium chloride (SrCy that is then used, along with potassium chloride (KCl), to form a eutectic mixture to reduce the melting point of the SrCl, as a molten electrolyte in a graphite dish-shaped electrolysis apparatus. This process produces Sr cations collected at the cathode, where they acquire electrons to form strontium metal. At the same time, Cl anions give up electrons at the anode and are released as chlorine gas Cl T. 

In 1787 William Cruikshank (1745-1795) isolated, but did not identify, strontium from the mineral strontianite he examined. In 1790 Dr. Adair Crawford (1748—1794), an Irish chemist, discovered strontium by accident as he was examining barium chloride. He found a substance other than what he expected and considered it a new mineral. He named the new element strontium and its mineral strontianite after a village in Scotland. In 1808 Sir Humphry Davy treated the ore with hydrochloric acid, which produced strontium chloride. He then mixed mercury oxide with the strontium chloride to form an amalgam alloy of the two metals that collected at the cathode of his electrolysis apparatus. He heated the resulting substance to vaporize the mercury, leaving the strontium metal as a deposit. 

As a powder, strontium metal may spontaneously burst into flames. Both its metal and some of its compounds will explode when heated. Some of the compounds will explode if struck with a hammer. 

MetaUic strontium is produced by electrolysis of a mixed melt of strontium chloride and potassium chloride in a graphite crucible using an iron rod as cathode. The upper cathodic space is cooled and the strontium metal coUects over the cooled cathode and forms a stick. 

Strontium metal also can be prepared by thermal reduction of its oxide with aluminum. Strontium oxide-aluminum mixture is heated at high temperature in vacuum. Strontium is collected by distillation in vacuum. Strontium also is obtained by reduction of its amalgam, hydride, and other salts. The amalgam is heated and the mercury is separated by distillation. If hydride is used, it is heated at 1,000°C in vacuum for decomposition and removal of hydrogen. Such thermal reductions yield high—purity metal. 

Strontium chloride is used to produce strontium metal by electrolysis. It also is used to prepare other strontium salts, as a desensitizer in dentistry, and in pyrotechnics. 

Strontium sulfate occurs in nature as mineral celestite, which is the principal ore of strontium. The sulfate is the starting material for producing strontium metal and practically all its salts. The sulfate also is used in pyrotechnics and in ceramics. 

Strontium occurs chiefly as sulfate (celestite, SrSO,i) and carbonate (strontianite. SrCO ) although widely distributed in small concentration. The commercially exploited deposits are mainly in England. The sulfate or carbonate is transformed into chloride, and the electrolysis of die fused chloride yields strontium metal,... 

Strontium hydride, SrH2, white solid, formed by heating strontium metal or amalgam in hydrogen gas at 250oC. Is reactive with H20, yielding strontium hydroxide and hydrogen gas. 

Barbier-type C-alkylation of imines can be carried out with alkylstrontium halides generated from strontium metal and alkyl halide.38 IV-Alkylation competes, and RSrI is strongly nucleophilic, as shown by a-alkylation of imines derived from enolizable... 

The other compounds of strontium are similar to the corresponding compounds of calcium. Strontium, metal has no practical uses. 

Strontia was later found to be a compound of strontium and oxygen. In 1808, Davy found a way to produce pure strontium metal. He passed an electric current through molten (melted) strontium chloride. The electric current broke the compound into its two elements ... 

Most strontium metal is still obtained by the method used by Davy. An electric current is passed through molten (melted) strontium chloride. 

The name comes from the town of Strontian in Scotland and was given to the element by Thomas Hope (1766-1844). There are many claims for the original discovery of strontium. William Cruikshank, in 1787, and Adair Crawford, in 1790, both examined strontianite (SrC03) and recognized that it had unique properties. Thomas Hope noted an unknown earth in 1791. Martin Klaproth presented a paper on a number of strontium compounds in 1793 and 1794. Richard Kirwan (1733-1812) examined a number of strontium compounds and presented his findings in 1794. It was Davy who isolated strontium metal, in 1808. Strontium does not occur in pure form in nature but is found in small quantities in many places. Some forms of strontium are radioactive, particularly 90Sr, which has been found in nuclear fallout. It can also be used in SNAP devices (Systems for Nuclear Auxiliary Power) as a power source. The main commercial use of strontium is in the glass of color television picture tubes. 

The physical properties of strontium metal and selected strontium compounds are listed in Table 4-2. The percent occurrence of strontium isotopes and radiologic properties of strontium isotopes is listed in Table 4-3. 

PHENYL BROMIDE (108-86-1) Forms explosive mixture with air (flash point 124°F/51°C). Incompatible with strong oxidizers, alkaline earth metals (e.g., barium, calcium, magnesium, strontium), metallic salts, with risk of violent reactions. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

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