Barium

Description

Barium is a silvery-white metal. It exists in nature only in ores containing mixtures of elements. The important combinations are the peroxide, chloride, sulphate, carbonate, nitrate, and chlorate. The pure metal oxidises readily and reacts with water emitting hydrogen. It combines with other chemicals such as sulphur or carbon and oxygen to form barium compounds. Barium compounds are used by the oil and gas industries to make drilling muds. Barium attacks most metals with the formation of alloys; iron is the most resistant to alloy formation. Barium forms alloys and intermetallic compounds with lead, potassium, platinum, magnesium, silicon, zinc, aluminium, and mercury. Barium compounds exhibit close relationships with the compounds of calcium and strontium, which are also alkaline earth metals. Twenty-five barium isotopes have been identified, 138Ba being the most abundant, and the others are unstable isotopes with half-lives ranging from 12.8 days for 140Ba to 12 s for 143Ba. Two of these isotopes, 131Ba and 139Ba, are used in research as radioactive tracers. The general population is exposed to barium through air, drinking water, and food.

Description

Barium is a flammable, silver white or yellowish metal in various forms including powder. Barium mayignite spontaneously in air in the presence of moisture,evolving hydrogen. Molecular weight=137.34; Boilingpoint=1640℃; Freezing/Melting point=725℃; Vaporpressure=10 mmHg at 1049℃. Hazard Identification(based on NFPA-704 M Rating System): Health 2,Flammability 4, Reactivity 3 (water reactive).

Chemical properties

Barium is a silvery-white metal. It exists in nature only in ores containing mixtures of elements. The important combinations are peroxide, chloride, sulfate, carbonate, nitrate, and chlorate. The pure metal oxidizes readily and reacts with water, emitting hydrogen. It combines with other chemicals such as sulfur or carbon and oxygen to form barium compounds. Barium compounds are used by the oil and gas industries to make drilling muds. Barium attacks most metals with the formation of alloys; iron is the most resistant to alloy formation. Barium forms alloys and intermetallic compounds with lead, potassium, platinum, magnesium, silicon, zinc, aluminum, and mercury. Barium compounds exhibit close relation-ships with the compounds of calcium and strontium, which are also alkaline earth metals. Doctors sometimes use barium sulfate to perform medical tests and to take x-rays of the gastrointestinal tract. Twentyive barium isotopes have been identii ed. 138Ba is the most abundant; the others are unstable isotopes with half-lives ranging from 12.8 days for 140Ba to 12 sec for 143Ba. Two of these isotopes, 131Ba and 139Ba, are used in research as radioactive tracers. The general population is exposed to barium through air, drinking water, and food.

Chemical properties

The chemical process of Barium is similar to Ca and Sr, but it is stronger. The single crystal of oxide BaO is easy to grow, and the absorption coefficient and the reflectance spectrum show the peaks at 3.77, 3.9, 4.0, 4.3 and 6 eV.

Physical properties

Barium is the fifth element in group 2 (IIA) of the alkali earth metals and has most of theproperties and characteristics of the other alkali earth metals in this group. For example, theyall are called alkaline earths because, when first discovered, they exhibited both characteristicsof alkaline (basic) substances and characteristics of the earth from which they came. Ancienthumans did not know they were metals because their metallic forms do not exist in nature.Barium is a silvery metal that is somewhat malleable and machineable (can be worked on alathe, stretched and pounded). Its melting point is 725°C, its boiling point is about 1640°C,and its density is 3.51 g/cm³. (The accurate figures for its properties are difficult to determinebecause of barium’s extreme activity—the pure metal will ignite when exposed to air, water,ammonia, oxygen, and the halogens.

Isotopes

Naturally occurring barium is a mixture of seven stable isotopes: barium-138 (71.66%), barium-137 (11.32%), barium-136 (7.81%), barium-135 (6.59%), barium-134 (2.42%), barium-130 (0.101%), and barium- 132 (0.097%). About six times this many radioactive isotopes have been prepared with mass numbers ranging from 114 to 153. Of the 40 isotopes known, most are highly radioactive and have half-lives in the several milliseconds to a few days range. The only notable exceptions are ¹³³Ba with a half-life of 10.51 years, ¹²⁸Ba (2.43 days), ¹⁴¹Ba (11.50 days) and ¹⁴⁰Ba (12.75 days).

Origin of Name

The name barium is derived from the Latin word barys, which means “heavy.

Occurrence

Barium is the 17th most abundant element in the Earth’s crust, making up about 0.05%of the crust. It is found in the minerals witherite, which is barium carbonate (BaCO₃), andbarite, known as barium sulfate (BaSO₄). Pure barium metal does not exist on Earth—only ascompounds or in minerals and ores. Barium ores are found in Missouri, Arkansas, Georgia,Kentucky, Nevada, California, Canada, and Mexico.It is produced by the reduction of barium oxide (BaO), using aluminum or silicon ina high-temperature vacuum. It is also commercially produced by the electrolysis of moltenbarium chloride (BaCl₂) at about 950oC, wherein the barium metal is collected at the cathodeand chlorine gas is emitted at the anode.

History

Baryta was distinguished from lime by Scheele in 1774; Barium was discovered by Sir Humphrey Davy in 1808. It is found only in combination with other elements, chiefly in barite or heavy spar (sulfate) and witherite (carbonate) and is prepared by electrolysis of the chloride. Large deposits of barite are found in China, Germany, India, Morocco, and in the U.S. Barium is a metallic element, soft, and when pure is silvery white like lead; it belongs to the alkaline earth group, resembling calcium chemically. The metal oxidizes very easily and should be kept under petroleum or other suitable oxygen-free liquids to exclude air. It is decomposed by water or alcohol. The metal is used as a “getter” in vacuum tubes. The most important compounds are the peroxide (BaO2), chloride, sulfate, carbonate, nitrate, and chlorate. Lithopone, a pigment containing barium sulfate and zinc sulfide, has good covering power, and does not darken in the presence of sulfides. The sulfate, as permanent white or blanc fixe, is also used in paint, in X-ray diagnostic work, and in glassmaking. Barite is extensively used as a weighting agent in oilwell drilling fluids, and also in making rubber. The carbonate has been used as a rat poison, while the nitrate and chlorate give green colors in pyrotechny. The impure sulfide phosphoresces after exposure to the light. The compounds and the metal are not expensive. Barium metal (99.2 + % pure) costs about $3/g. All barium compounds that are water or acid soluble are poisonous. Naturally occurring barium is a mixture of seven stable isotopes. Thirty-six other radioactive isotopes and isomers are known to exist.

Characteristics

When barium burns in air, it produces barium oxide (2Ba + O₂ → 2BaO). When metallicbarium burns in water, it forms barium hydroxide [Ba + 2H₂O → Ba(OH)₂ + H₂↑]. Severalbarium compounds burn with a bright green flame, which make them useful for fireworks.Barium is more reactive with water than are calcium and strontium. This is a result of thevalence electrons’ being further from the positive nucleus. Therefore, barium is more electronegative than the alkali earth metals with smaller nuclei.In powdered form, it will burst into a bright green flame at room temperature.

The Uses of Barium

Pure barium metal has few commercial uses because of it reactivity with air and water.Nevertheless, this property makes it useful as a “getter” or scavenger to remove the last tracesof gas from vacuum tubes. Barium metal is used to form alloys with other metals. One alloy isused to make sparkplugs that easily emit electrons when heated, thus improving the efficiencyof internal combustion engines.Its compounds have many practical uses. For example, when the mineral barite is groundup into a fine powder, it can be used as a filler and brightener for writing and computer paper.It is also used (along with zinc sulfide) as a pigment, called lithopone, for white paint. Bariumcompounds are also used in the manufacture of plastics, rubber, resins, ceramics, rocket fuel,fireworks, insecticides, and fungicides and to refine vegetable oils.A major medical use is a solution of barium sulfide (with flavoring) that is ingested bypatients undergoing stomach and intestinal X-ray and CT scan examinations. Barium sulfideis opaque to X-rays, and thus it blocks the transmission of the rays. The organs appear in contrast against a background, which highlights any problems with the digestive system.

The Uses of Barium

The element barium (Ba) has the atomic number 56 and is classified as a heavy metal. Barium metal is highly reactive and therefore no elemental barium exists in nature. Natural sources of barium are the water-insoluble minerals barite (barium sulfate) and whiterite (barium carbonate). In order to obtain pure barium compounds, the mineral barite is reacted with carbon, and barium sulfide is formed.

The Uses of Barium

The element is used in metallurgy, and its compounds in pyrotechnics, petroleum mining, and radiology. Metallic barium has few industrial uses. It has been historically used to scavenge air in vacuumtubes. There, the metal is used as a getter in electron tubes to perfect the vacuum by combining with final traces of gases. It is also used as a deoxidizer in copper refining, and as a constituent in certain alloys. The alloy with nickel readily emits electrons when heated and, for this reason, is used in electron tubes and in spark plug electrodes. The presence of barium (atomic number 56), observed after uranium (atomic number 92) had been bombarded by neutrons, was the clue that led to the recognition of nuclear fission (1939).
The most important use of elemental barium is as a scavenger removing last traces of oxygen and other gases in television and other electronic tubes. Additionally, an isotope of barium, 133Ba, is routinely used as a standard source in the calibration of gamma ray detectors in nuclear physics studies.

Definition

A dense, low-melting reactive metal; the fifth member of group 2 (formerly IIA) of the periodic table and a typical alkaline-earth element. The electronic configuration is that of xenon with two additional outer 6s electrons. Barium is of low abundance; it is found as witherite (BaCO3) and barytes (BaSO4). The metal is obtained by the electrolysis of the fused chloride using a cooled cathode which is slowly withdrawn from the melt. Because of its low melting point barium is readily purified by vacuum distillation. Barium metal is used as a ‘getter’, i.e., a compound added to a system to seek out the last traces of oxygen; and as an alloy constituent for certain bearing metals.
Barium has a low ionization potential and a large radius. It is therefore strongly electropositive and its properties, and those of its compounds, are very similar to those of the other alkaline-earth elements calcium and strontium.

Definition

barium: Symbol Ba. A silvery-whitereactive element belonging to group2 (formerly IIA) of the periodic table;a.n. 56; r.a.m. 137.34; r.d. 3.51; m.p.725°C; b.p. 1640°C. It occurs as theminerals barytes (BaSO₄) andwitherite (BaCO₃). Extraction is byhigh-temperature reduction of bariumoxide with aluminium or siliconin a vacuum, or by electrolysis offused barium chloride. The metal isused as a getter in vacuum systems.It oxidizes readily in air and reactswith ethanol and water. Soluble bariumcompounds are extremely poisonous.It was first identified in 1774 byKarl Scheele, and was extracted byHumphry Davy in 1808.

Production Methods

The minerals are BaSO4 and BaCO3. Metal barium is obtained by reducing the barium oxide at a high temperature in vacuum with Al or Si or by doing electrolysis with the Hg cathode and evaporating Hg of amalgam formed at the process slowly to segregate Ba. To obtain vacuum evaporated films, direct heating with the conical basket of W, Ta, Mo, Nb, Ni, Fe, chromel, etc., or with the boat of Ta, Mo is used. Ba reacts with alumina. The rate of evaporation is 2.28×10^-4 g/cm² s with the evaporation temperature of 629 ℃.

General Description

Barium alloy, pyrophoric is mixture of barium and other metals or nonmetallic elements to improve the specific usefulness of barium. Barium alloys are a solid and can ignite spontaneously in contact with air. Barium is toxic and products given off in fire could be very toxic.

Air & Water Reactions

Finely divided metal powder is pyrophoric, ignites spontaneously in air [Bretherick 1979 p. 170-171]. Alloys containing a substantial proportion of barium rapidly decomposed water. The heat of the reaction is sufficient that the evolved hydrogen may ignite [Lab. Govt. Chemist 1965].

Reactivity Profile

Alloys containing a substantial amount of barium react violently with acids [Lab. Gov. Chemist 1965].

Hazard

Barium metal, in powder form, is flammable at room temperature. It must be stored in anoxygen-free atmosphere or in petroleum.
Many of barium’s compounds are toxic, especially barium chloride, which affects the functioningof the heart, causing ventricular fibrillation, an erratic heartbeat that can lead to death.Several of barium’s compounds are explosive as well as toxic if ingested or inhaled. Care shouldbe used when working with barium and other alkali metals in the laboratory or in industry.

Health Hazard

The health effects of barium compounds depend on how well the compound dissolves in water or in the stomach contents. Barium compounds that do not dissolve well, such as barium sulfate, are considered not harmful. Barium carbonate dust and barium oxide dust have been reported to be a bronchial irritant. While barium carbonate is a dermal irritant, barium oxide is a nasal irritant. Occupational workers exposed to barium dust, usually in the form of barium sulfate or carbonate, often develop a benign pneumoco- niosis also called “baritosis.” The effect of baritosis has been shown to be reversible and has not caused any kind of severe pulmonary adverse effect. Barium compounds that do not dissolve in water are considered safe. However, the health effects of the different barium compounds depend on the degree of their water solubility. The compounds that dissolve well in water are known to cause harmful health effects when ingested in high levels. Symptoms of poisoning include stomach irritation, brain swelling, muscle weak- ness, liver and kidney damage, adverse effects to the heart, increased blood pressure, changes in heart rhythm, effects on the spleen, difi culties in breathing, and swelling of the brain. Exposures to high concentrations of barium through food and drinking water cause gastrointestinal disturbances. Barium causes vomiting, abdominal cramps, diar- rhea, difi culties in breathing, increased or decreased blood pressure, numbness around the face, and muscle weakness, changes in heart rhythm or paralysis, and possibly death. Animals exposed to barium over long periods showed kidney damage, decreased body weight, and fatal injury. Ingestion of large amounts of barium chloride (2 and 4 g) causes fatal injury, because barium ions paralyze the heart. Acute poisoning with barium causes nausea and diarrhea, cardiac problems, and muscular spasms, as well as cardiac arrest. Thus, barium, at concentrations normally found in our environment, does not pose any signii cant risk for the general population. However, for specii c subpopulations and under conditions of high barium exposure, the potential for adverse health effects should be taken into account.

Fire Hazard

Flammable/combustible material. May ignite on contact with moist air or moisture. May burn rapidly with flare-burning effect. Some react vigorously or explosively on contact with water. Some may decompose explosively when heated or involved in a fire. May re-ignite after fire is extinguished. Runoff may create fire or explosion hazard. Containers may explode when heated.

Industrial uses

Barium (symbol Ba) is a metallic element thatoccurs in combination in the minerals witheriteand barite, which are widely distributed. Themetal is silvery white in color and can beobtained by electrolysis from the chloride, butit oxidizes so easily that it is difficult to obtainin the metallic state. Its melting point is 850°C,and its specific gravity 3.78. The most extensiveuse of barium is in the form of its compounds.The salts that are soluble, such as sulfide andchloride, are toxic. An insoluble, nontoxic bariumsulfate salt is used in radiography. Bariumcompounds are used as pigments, in chemicalmanufacturing, and in deoxidizing alloys of tin, copper, lead, and zinc. Barium is introducedinto lead-bearing metals by electrolysis toharden the lead.Barium is also a key ingredient in ceramicsuperconductors.

Safety Profile

Water and stomach acids solubilize barium salts and can cause poisoning. Symptoms are vomiting, colic, diarrhea, slow irregular pulse, transient hypertension, and convulsive tremors and muscular paralysis. Death may occur in a few hours to a few days. Half-life of barium in bone has been estimated at 50 days. Dust is dangerous and explosive when exposed to heat, flame, or chemical reaction. Violent or explosive reaction with water, CCh, fluorotrichloromethane, trichloroethylene, and C2Cl4. Incompatible with acids, C2CLF3, C2H2FCl3, C2HCl3 and water, 1,1,2- trichlorotrifluoroethane, and fluorotrichloroethane. The powder may ignite or explode in air or other oxidizing gases. See also BARIUM COMPOUNDS.

Potential Exposure

Metallic barium is used for removal of residual gas in vacuum tubes and in alloys with nickel, lead, calcium, magnesium, sodium, and lithium. Barium compounds are used in the manufacture of lithopone (a white pigment in paints), chlorine, sodium hydroxide, valves, and green flares; in synthetic rubber vulcanization; X-ray diagnostic work, glassmaking, papermaking, beet-sugar purification; animal and vegetable oil refining. They are used in the brick and tile, pyrotechnics, and electronics industries. They are found in lubricants, pesticides, glazes, textile dyes and finishes; pharmaceuticals; in cements which will be exposed to saltwater; and barium is used as a rodenticide, a flux for magnesium alloys, a stabilizer and mold lubricant in the rubber and plastics industries, an extender in paints; a loader for paper, soap, rubber, and linoleum; and as a fire extinguisher for uranium or plutonium fires.

First aid

If a soluble barium compound gets into the eyes,ing. Do not make an unconscious person vomit.Note to physician (poisoning from barium compounds):If ingested, there are treatment considerations availableincluding the following: Gastric emptying, a warm aqueoussolution of 1
3% soluble sulfates of magnesium sulfateor sodium sulfate administered orally as a gastric lavage(forms insoluble barium sulfate). Atropine sulfate,0.5
1.0 mg, to decrease colic. Small doses of morphinemay be necessary to control abdominal pain. If low potasremove any contact lenses at once and irrigate immediately.If a soluble barium compound contacts the skin, flush withwater immediately. If a person breathes in large amounts ofa soluble barium compound, move the exposed person tofresh air at once and perform artificial respiration. When asoluble barium compound has been swallowed, get medicalattention. Give large quantities of water and induce vomit

Environmental Fate

Ingestion of toxic doses of barium affects the muscles, especially the heart. Barium has a digitalis-type effect on the heart. Ventricular fibrillation and slowed pulse rate are noted. This may be related to barium’s tendency to displace potassium; the resulting potassium deficiency causes muscle weakness.

storage

Color Code—Yellow Stripe (strong reducingagent): Reactivity Hazard; Store separately in an area isolated from flammables, combustibles, or other yellow codedmaterials. Barium metal should be stored in a dry area, separated from halogenated solvents, strong oxidants, acids, intightly-closed containers under an inert gas blanket, petroleum, or oxygen-free liquid. Rubber gloves, rubber protective clothing and apron, goggles and gas-filter mask shouldbe worn when working in a barium storage area.

Shipping

UN1400 Barium, Hazard Class: 4.3; Labels: 4.3—Dangerous when wet material. UN1854 Barium alloys, pyrophoric, Hazard Class: 4.2; Labels: 4.2—Spontaneously combustible material. UN1564 Barium compound, n.o.s., Hazard Class: 6.1; Labels: 6.1—Poisonous materials.

Purification Methods

Barium is cleaned by washing with diethyl ether to remove adhering paraffin, then filed in an argon-filled glove box, washed first with ethanol containing 2% conc HCl, then with dry ethanol. It is dried in a vacuum and stored under argon [Addison et al. J Chem Soc 3868 1962]. It has also been purified by double distillation under 10mm of argon pressure.

Toxicity evaluation

Barium is a highly reactive metal that occurs naturally only in a combined state. The element is released to environmental media by both natural processes and anthropogenic sources.
Barium is released primarily to the atmosphere as a result of industrial emissions during the mining, refining, and production of barium and barium chemicals, fossil fuel combustion, and entrainment of soil and rock dust into the air. In addition, coal ash, containing widely variable amounts of barium, is also a source of airborne barium particulates. Most barium released to the environment from industrial sources is in forms that do not become widely dispersed. In the atmosphere, barium is likely to be present in particulate form. Although chemical reactions may cause changes in speciation of barium in air, the main mechanisms for the removal of barium compounds from the atmosphere are likely to be wet and dry depositions.

Structure and conformation

The space lattice of Barium belongs to the cubic system, and its body-centered cubic lattice has a lattice constant of a=0.5009 nm.

Incompatibilities

Barium powder may spontaneously ignite on contact with air. It is a strong reducing agent and Barium 337 reacts violently with oxidizers and acids. Reacts with water, forming combustible hydrogen gas and barium hydroxide. Reacts violently with halogenated hydrocarbon solvents, causing a fire and explosion hazard.

Waste Disposal

Barium in solution (see spill handling) may be precipitated with soda ash and the sludge may be landfilled.