Strontium oxide

Crystal structure
__ Sr 2+      __ O 2−
Crystal system	cubic
Space group	Fm 3 m (No. 225)
Coordination numbers	Sr [6], O [6]
General
Surname	Strontium oxide
other names	Ätzstrontian
Ratio formula	SrO
Brief description	colorless or white
External identifiers / databases
CAS number 1314-11-0 EC number 215-219-9 ECHA InfoCard 100,013,837 PubChem 73975 ChemSpider 66603 Wikidata Q418413
properties
Molar mass	103.62 g mol −1
Physical state	firmly
density	5.0 g cm −3
Melting point	2460 ° C
boiling point	3200 ° C
solubility	Decomposes in water
Refractive index	1.8710
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 314 EUH: 014 P: 280-305 + 351 + 338-310
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

Strontium oxide is the oxide of the alkaline earth metal strontium . In the pure state it is a white powder, in technical quality it is often colored gray by foreign admixtures, which are created, for example, by the oxidation of the very reactive strontium.

Extraction and presentation

Strontium oxide can be obtained from strontium carbonate , which is found in nature as the mineral strontianite . At 1268 ° C under normal atmospheric pressure , strontium carbonate breaks down into strontium oxide and carbon dioxide :

${\displaystyle \mathrm {SrCO_{3}\ _{\overrightarrow {1268\,^{\circ }\mathrm {C} }}\ SrO+CO_{2}\uparrow } }$

properties

Strontium oxide crystallizes in the sodium chloride structure. At high pressures of> 36 GPa a phase change to a cesium chloride structure is observed. This is accompanied by a volume reduction of 13%, the density of the crystal increases to over 7.1 g / cm ³ .

With water strontium oxide reacts with evolution of heat to strontium :

${\displaystyle \mathrm {SrO+H_{2}O\rightarrow Sr(OH)_{2}} }$

With the help of aluminum powder , strontium oxide can be reduced to strontium ( aluminothermics ):

${\displaystyle \mathrm {3\,SrO+2\,Al\rightarrow Al_{2}O_{3}+3\,Sr} }$

use

Strontium oxide is used in the glass industry for the production of special glasses, for example the oxide is added to the glass of screen tubes to reduce radiation . In the past, strontium oxide was used in the production of beet sugar (Strontian process).

Furthermore, due to its high melting temperature and its low electron work function of 1.0 eV, it is used as a coating material on cathodes, for example made of tungsten. This makes it an oxide cathode . See work function . However, because it is water soluble, other materials are preferred in applications where the vacuum must be broken for maintenance work and humid atmospheric air can enter the system. Therefore, the use in practice is limited to systems that are continuously operated in a vacuum. In these permanently closed diodes, they allow glow emissions at as low as 800 ° K.

Individual evidence

1. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Inorganic Compounds, pp. 5-92.
2. ↑ ^{a b} Yosiko Sato, Raymond Jeanloz: Phase Transition in SrO. In: Journal of Geophysical Research . 86, 1981, pp. 11773-11778, doi : 10.1029 / JB086iB12p11773 .
3. ↑ ^{a b c d e} Entry on strontium oxide in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
4. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Crystals, pp. 10-248.
5. ^ H. Ost: Textbook of Technical Chemistry , published by Robert Oppenheim, Berlin, 1890, p. 369ff.