| The Air Liquide Balazs lab in Dallas, TX uses wide spectrum electromagnetic radiation to bake down samples under an argon purge. This method is a form of direct heating which enables otherwise corrosive acid samples to be reduced to a form that can be reconstituted into a solution that can be safely introduced into the lab's analysis equipment without the thermally induced loss of critical analytes. Direct heating by irradiation with light shows a decrease in the temperature of the bake-down solution, as heat is lost due to evaporation and the amount of energy absorbed decreases due to the reduction in mass. We show that reduction of UV light can help prevent the onset of "hot-plate" indirect conductive heating conditions that can lead to the loss of volatile elements. The bake-down bottle is constructed from perfluoroalkoxy polytetrafluoroethylene (PFA), which absorbs strongly in the UV range, while water can absorb both in the UV and the IR, the latter of which PFA is largely transparent to.; The second portion of the study focused on investigating the composition of the bake-down residue via XPS, to find why elements of concern are lost---boron most markedly---when the sample is over-baked. Germanium, titanium, tin and zinc all formed oxides, which explains why they are present at room temperature. Specifically, Ge was in the form of GeO2, Zn was in the form of ZnO, while the oxides of Ti and Sn are a mixture of various stoichiometries and oxidation states. Antimony could not be detected because the photoelectron peak was masked by interferences from other elements.; We speculate that boron can form one of two species that are stable at room temperature, but can be volatilized either in high vacuum or at "hot-plate" temperatures. The two boron compounds of interest are: boron trifluoride dihydrate (BF3-(H2O)2) and decaborane (B10H 14), the latter forming only when an agent for what may be reduction, substitution or perhaps even catalysis, is present. In the case of this study, we believe this agent is lithium. Part of the evidence for this postulation is that the compound of lithium found was LiF---the only fluoride compound present. |
