TY - JOUR

T1 - Thermal behaviour of NaBH4-sodalites with alumosilicate framework

T2 - Influence of cage water content and the surrounding conditions

AU - Hoefs, T. K.

AU - Buhl, J. C.

PY - 2011/11

Y1 - 2011/11

N2 - Sodalites Na8[AlSiO4]6(BH 4)1.8(H3O2)0.2 and Na8[AlSiO4]6(BH4)(H 3O2)0.5(CO3)0.25(H 2O) were examined to characterize the influence of the mixed cage fillings and the surroundings on the thermal behaviour of enclathrated BH 4- and the stability of the alumosilicate framework. The samples were investigated in a NaCl matrix during temperature dependent IR-measurements (TIR) and by thermal analysis in inert atmosphere (helium) and in synthetic air. The thermal products were further characterized by XRD and SEM/EDS. It could be shown that the extent of the BH4- decomposition strongly depends on the cage-fillings of the individual sodalite phase and on the environmental experimental conditions. At low to medium temperatures hydrolysis of BH4- by water molecules from decomposition of H3O2- and H 2O/CO32- templates leads to B(OH) 4-/BH3OH- and via subsequent dehydration to BO(OH)2- and finally BO2 -. At elevated temperatures direct oxidation of BH4 - to BO2- occurs inside the sodalite cages. Further heating results in sodalite framework destruction and finally formation of nepheline with some boron in its structure besides some unknown polymeric borates outside the alumosilicate phase. Framework stability of the sodalites was found to decrease in the direction → heating in NaCl → heating in He-atmosphere → heating in air.

AB - Sodalites Na8[AlSiO4]6(BH 4)1.8(H3O2)0.2 and Na8[AlSiO4]6(BH4)(H 3O2)0.5(CO3)0.25(H 2O) were examined to characterize the influence of the mixed cage fillings and the surroundings on the thermal behaviour of enclathrated BH 4- and the stability of the alumosilicate framework. The samples were investigated in a NaCl matrix during temperature dependent IR-measurements (TIR) and by thermal analysis in inert atmosphere (helium) and in synthetic air. The thermal products were further characterized by XRD and SEM/EDS. It could be shown that the extent of the BH4- decomposition strongly depends on the cage-fillings of the individual sodalite phase and on the environmental experimental conditions. At low to medium temperatures hydrolysis of BH4- by water molecules from decomposition of H3O2- and H 2O/CO32- templates leads to B(OH) 4-/BH3OH- and via subsequent dehydration to BO(OH)2- and finally BO2 -. At elevated temperatures direct oxidation of BH4 - to BO2- occurs inside the sodalite cages. Further heating results in sodalite framework destruction and finally formation of nepheline with some boron in its structure besides some unknown polymeric borates outside the alumosilicate phase. Framework stability of the sodalites was found to decrease in the direction → heating in NaCl → heating in He-atmosphere → heating in air.

KW - A. Hydrides

KW - A. Microporous materials

KW - C. Infrared spectroscopy

KW - C. X-ray diffraction

UR - http://www.scopus.com/inward/record.url?scp=80052844882&partnerID=8YFLogxK

U2 - 10.1016/j.materresbull.2010.12.029

DO - 10.1016/j.materresbull.2010.12.029

M3 - Article

AN - SCOPUS:80052844882

VL - 46

SP - 2173

EP - 2178

JO - Materials research bulletin

JF - Materials research bulletin

SN - 0025-5408

IS - 11

ER -