Barium borate

Crystal structure
Crystal structure of β-barium borate __ Ba 2+      __ B 3+      __ O 2−
General
Surname	Barium borate
other names	Barium metaborate Barium diborotetraoxide
Ratio formula	Ba (BO 2 ) 2
Brief description	white odorless solid (monohydrate)
External identifiers / databases
CAS number 13701-59-2 26124-86-7 (monohydrate) 23436-05-7 (dihydrate) EC number 237-222-4 ECHA InfoCard 100,033,824 PubChem 6101043 ChemSpider 3642855 Wikidata Q830818
properties
Molar mass	222.95 g mol −1
Physical state	firmly
density	3.85 g cm −3 (α) 3.35 g cm −3 (monohydrate)
Melting point	1051 ° C > 900 ° C (monohydrate)
solubility	poorly soluble in water (monohydrate) insoluble in organic solvents (monohydrate)
Refractive index	1.55-1.60 (monohydrate)
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302-360 P: 201-270-280-301 + 310-308 + 313-330-391-501
Toxicological data	850 mg kg −1 ( LD 50 ,  rat ,  oral , monohydrate) > 2000 mg kg −1 ( LD 50 ,  rat ,  transdermal , monohydrate)
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Barium borate (more precisely barium metaborate ) is a chemical compound of barium from the group of borates . It occurs in various modifications that are characterized by unusual properties such as optical birefringence and optical non-linearity .

Extraction and presentation

Barium borate can be obtained by reacting a boric acid solution with barium hydroxide . The γ-barium borate formed contains water of crystallization that can be removed by heating to 300-400 ° C. When heated to 600 to 800 ° C, this is completely converted to β-barium borate. Barium borate monohydrate is made from a solution of barium sulfide and sodium tetraborate . The dihydrate is formed by precipitation from a barium chloride solution by adding a sodium metaborate solution at 90 to 95 ° C. The tetrahydrate precipitates at room temperature.

properties

Crystal structure of β-barium borate seen almost perpendicular to the c-axis.
Colors: green - barium, pink - boron, red - oxygen

Crystal structure of β-barium borate along the c axis.

Barium borate monohydrate is a white solid that is not very soluble in water. The dihydrate, which is also white, loses water of crystallization at 140 ° C. The high-temperature form α-barium borate has good mechanical properties (Mohs hardness of 4.5), high birefringence and is transparent in a very wide range between 189 and 3500 nm. It crystallizes trigonal , space group R 3 c (space group no. 167) with the lattice parameters a = 7.235 Å and c = 39.19 Å. Similar to the α-form, the low-temperature form β-barium borate (BBO) has a trigonal crystal structure with the space group R 3 c (No. 161) and the lattice parameters a = 8.380 Å and α = 96.65 °. The structure contains almost planar trimeric ions (BO ₂ ) ₃ ^- . Each barium atom is coordinated by eight oxygen atoms from neighboring anions. The low temperature phase exhibits non-linear optical properties. Compared to potassium dihydrogen phosphate (KDP), the compound has almost six times as high a non-linearity and a wide range of wavelengths (approx. 210 to 2100 nm ) in which the crystal is transparent. Similar to KDP, BBO can also be used for laser pulses with a very high energy density (high damage threshold: approx. 5  GW / cm ² at 1064 nm wavelength and 10  ns pulse duration).

The refractive indices n _o and n _e of BBO are given by the Sellmeier equation

${\displaystyle n^{2}(\lambda )=A+{\frac {B}{\lambda ^{2}+C}}+D\lambda ^{2}}$

described. Different values ​​are given in publications for the experimentally determined Sellmeier coefficients ( A , B , C , D ). Exemplary the values ​​of Kato:

	A.	B / µm 2	C / µm 2	D / µm −2
n o	2.7359	0.01878	−0.01822	−0.01354
n e	2.3753	0.01224	−0.01667	−0.01516

use

Barium borate monohydrate is used as a pigment , corrosion inhibitor (due to its alkaline properties), flame retardant , tannin discoloration blocking agent for paints and others. The dihydrate is used as a flame retardant in paint, paper, textiles and plastic. Barium borate has been approved as a bactericide and fungicide in the United States since the 1960s . α-barium borate is a useful material for high-performance UV light polarization optics and acousto-optics . β-barium borate is used for:

• Frequency doubling and mixing (generation of the sum and difference frequency ) of the light from (pulsed) lasers
• Correlation for measuring the pulse duration and shape of ultra-short laser pulses
• optical parametric oscillators
• Pockels cells
• to generate UV light

Related links

• Barium orthoborate Ba ₃ (BO ₃ ) ₂

Individual evidence

1. ↑ ^{a b c d} data sheet Barium metaborate monohydrate from AlfaAesar, accessed on June 8, 2014 ( PDF )(JavaScript required) .
2. ↑ ^{a b c d e} Richard C. Ropp: Encyclopedia of the Alkaline Earth Compounds . Newnes, 2012, p. 511 ( limited preview in Google Book search).
3. ↑ ^{a b c d e} W. Paulus: Microbicides for the Protection of Materials: A Handbook . Springer, 1993, p. 429 ( limited preview in Google Book search).
4. ↑ ^{a b} Entry on barium metaborate in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
5. ↑ ^{a b} Govindhan Dhanaraj, Kullaiah Byrappa, Vishwanath Prasad, Michael Dudley: Springer Handbook of Crystal Growth . Springer, 2010, p. 729 ff . ( limited preview in Google Book search).
6. ^ ^{A b c} Dale L. Perry: Handbook of Inorganic Compounds, Second Edition . CRC Press, 2011, pp. 498 ( limited preview in Google Book search).
7. ^ William M. Haynes: CRC Handbook of Chemistry and Physics, 93rd Edition . CRC Press, 2012, p. 50 ( limited preview in Google Book search).
8. ↑ The designation of the low and high temperature forms as β and α forms is handled inconsistently in the literature. In the more recent literature, the designation α-form has established itself for the high-temperature form.
9. ↑ A. Perloff, S. Block, AD Mighell: The crystal structure of the high temperature form of barium borate. In: Acta Crystallographica , 20, 1966, pp. 819-823, doi: 10.1107 / S0365110X66001920 .
10. ↑ ^{a b} R. Fröhlich: Crystal structure of the low-temperature form of BaB ₂ O ₄ . In: Zeitschrift für Kristallographie , 168, 1984, pp. 109–112, doi: 10.1524 / zkri.1984.168.14.109 .
11. ↑ K. Kato: "Second-Harmonic Generation to 2048 Å in β-BaB ₂ O ₄ ", IEEE Journal of Quantum Electronics , 1986, 22  (7), pp. 1013-1014, doi : 10.1109 / JQE.1986.1073097 .
12. ^ Amy Forsgren: Corrosion Control Through Organic Coatings . CRC Press, 2006, pp. 42 ( limited preview in Google Book search).
13. ↑ Michael Ash, Irene Ash: Handbook of Green Chemicals . Synapse Info Resources, 2004, p. 132 ( limited preview in Google Book search).
14. ↑ I. Martynyuk-Lototska: Highly efficient acoustooptic diffraction in alpha-BaB2O4 crystals: improving of geometry of acoustooptic interaction. In: Ukrainian Journal of Physical Optics. 13, 2012, p. 28, doi : 10.3116 / 16091833/13/1/28/2012 .
15. ↑ Mark Peltz: Characterization of new nonlinear crystals for frequency conversion ... Tenea Verlag Ltd., 2004, p. 148 ( limited preview in Google Book search).