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| Names | |
|---|---|
| Other names barium diborate, barium boron oxide, barium metaborate | |
| Identifiers | |
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3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.033.824 |
| EC Number |
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| UNII | |
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| Properties | |
| BaB2O4 or Ba(BO2)2 | |
| Molar mass | 222.95 |
| Appearance | white powder or colorless crystals |
| Odor | odorless |
| Density | 3.85 g/cm3[1] |
| Melting point | 1,095 °C (2,003 °F; 1,368 K)[2] |
| Solubility inhydrochloric acid | soluble |
Refractive index (nD) | ne = 1.5534, no = 1.6776 |
| Structure | |
| Rhombohedral,hR126[3] | |
| R3c, No. 161 | |
a = 1.2529 nm,c = 1.274 nm | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H302 | |
| P264,P270,P301+P312,P330,P501 | |
| Flash point | Non-flammable |
| Safety data sheet (SDS) | MSDS |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Barium borate is aninorganic compound, aborate ofbarium with a chemical formula BaB2O4 or Ba(BO2)2. It is available as ahydrate or dehydrated form, as white powder or colorless crystals. The crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated asBBO; both phases arebirefringent, and BBO is a commonnonlinear optical material.
Barium borate was discovered and developed byChen Chuangtian and others of the Fujian Institute of Research on the Structure of Matter,Chinese Academy of Sciences.
Barium borate exists in three major crystalline forms: alpha, beta, and gamma. The low-temperature beta phase converts into the alpha phase upon heating to 925 °C. β-Barium borate (BBO) differs from the α form by the positions of the barium ions within the crystal. Both phases are birefringent, however the α phase possesses centric symmetry and thus does not have the same nonlinear properties as the β phase.[4]
Alpha barium borate, α-BaB2O4 is an optical material with a very wide optical transmission window from about 190 nm to 3500 nm. It has good mechanical properties and is a suitable material for high-powerultravioletpolarizationoptics.[5] It can replacecalcite,titanium dioxide orlithium niobate inGlan–Taylor prisms,Glan–Thompson prisms, walk-offbeam splitters and other optical components. It has lowhygroscopicity, and itsMohs hardness is 4.5. Itsdamage threshold is 1 GW/cm2 at 1064 nm and 500 MW/cm2 at 355 nm.[1]
Beta barium borate, β-BaB2O4, is anonlinear optical material transparent in the range ~190–3300 nm. It can be used forspontaneous parametric down-conversion. ItsMohs hardness is also 4.5.[1][2] The material exhibits a melting temperature of 1268 K,[6] with anisotropicthermal expansion coefficients: and α₃₃ = 36 × 10⁻⁶ K⁻¹.[7]
Gamma barium borate, γ-BaB2O4, discovered recently, was produced by heating beta barium borate 900 °C under 3 GPa of pressure. It was found to have a monoclinic crystal structure.[8]
Barium borate has strong negative uniaxialbirefringence and can be phase-matched for type I (ooe)second-harmonic generation from 409.6 to 3500 nm. The temperature sensitivity of the indices of refraction is low, leading to an unusually large (55 °C) temperature phase-matching bandwidth.[2]
Although the ambient-pressure α and β crystal phases contain only trigonal, sp2 hybridized, boron, BBO glass has around 40% of the boron on tetrahedral, sp3 hybridized, sites. In the liquid state the relative fractions of sp2 and sp3 boron are temperature-dependent, with the trigonal planar coordination favored at higher temperatures.[9]
Barium borate can be prepared by reaction of anaqueous solution ofboric acid withbarium hydroxide. The prepared γ-barium borate containswater of crystallization that can not be completely removed by drying at 120 °C. Dehydrated γ-barium borate can be prepared by heating to 300–400 °C.Calcination at about 600–800 °C causes complete conversion to the β form. BBO prepared by this method does not contain trace amounts of BaB2O2[10]
BBO crystals for nonlinear optics can be grown from fluxed melt of barium borate,sodium oxide andsodium chloride.[11]
Thin films of barium borate can be prepared byMOCVD from barium(II) hydro-tri(1-pyrazolyl)borate. Different phases can be obtained depending on deposition temperatures.[12] Thin films of beta-barium borate can be prepared bysol-gel synthesis.[13]
Barium borate monohydrate is prepared from the solution ofbarium sulfide andsodium tetraborate. It is a white powder. It is used as an additive to e.g. paints asflame retardant,mold inhibitor, andcorrosion inhibitor. It is also used as a whitepigment.
Barium borate dihydrate is prepared from the solution ofsodium metaborate andbarium chloride at 90–95 °C. After cooling to room temperature, white powder is precipitated. Barium borate dihydrate loses water at above 140 °C. It is used as aflame retardant for paints, textiles, and paper.[14]
BBO is a popular nonlinear optical crystal.Quantum linked photons are producible with beta barium borate. Barium borate is abactericide andfungicide.[15] It is added to paints, coatings, adhesives, plastics, and paper products.
Barium borate is resistant toultraviolet radiation. It can act asUV stabilizer forpolyvinyl chloride.[16]
The solubility of barium borate is a disadvantage when used as a pigment.Silica-coated powders are available. The alkaline properties and the anodicpassivation properties of the borate ion enhance the anticorrosion performance. Commonly available barium metaborate pigment comes in three grades; Grade I is a barium metaborate itself, grade II is compounded with 27%zinc oxide, and grade III is compounded with 18% ofzinc oxide and 29%calcium sulfate. Barium borate shows synergistic performance withzinc borate.[17]
Barium borate is used as aflux in somebarium titanate andlead zirconateEIA Class 2 dielectricceramic formulations forceramic capacitors, in amount of about 2%. The barium-boron ratio is critical for flux performance; BaB2O2 content adversely affects the performance of the flux.[10][18]
Barium borate-fly ashglass can be used asradiation shielding. Such glasses are superior in performance toconcrete and to other barium borate glasses.[19]
