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The SRC AOPWIN program (v1.92) has been used to obtain values of the rate constantkOHfor reaction of triethoxysilane and silanetriol with hydroxyl radicals. This prediction method has not been validated to assess applicability to silanes and silanols; therefore, there is uncertainty associated with the calculated values obtained.

The overall half-life in air under default conditions of hydroxyl radical concentration was calculated using the following expressions:

kdegair(d-1) = kOH(cm3/molecule.sec) x OH Concair(molecules/cm3) x 24 x 3600

DT50(d) = ln 2/ kdegair(d-1)

Where:

kdegair= total rate constant for degradation in air

kOH= rate constant for reaction with hydroxyl radicals

OH Concair= concentration of hydroxyl radicals in air =5 x 105OH molecules/ cm3

DT50= half-life

The results are given inTable4.1.2.

 

Table4.1.2Results of photodegradation in air calculations

Parameter

Result: Triethoxysilane

Result: Silanetriol

Result: Ethanol

kOH(cm3/ molecule.sec)

18.5 x 10-12

10.4 x10-12

3.6 x10-12

kdegair (d-1)

0.8

0.5

0.2

DT50(days)

0.9

1.5

4.5