Investigation of hydrolysed TaCl5-graphite intercalation compounds with PIXE

Graphite intercalation compounds combine low density with high electrical conductivity. These physical properties makes these compounds interesting as components of carbon epoxy composites, but the high reactivity of graphite intercalation compounds to moisture is an obstacle for practical applications.Earlier investigations showed that tantalum chloride forms with graphite flakes an intercalation compound, which is stable against humidity for a few days. We studied the stability against moisture of a stage-2 tantalum chloride intercalation compound after one year. A fresh tantalum chloride intercalation compound was exposed for 2 h in water and afterwards stored at room humidity for ca. 1 year. Some of the flakes were embedded in epoxy resin after a few months. After 1 year all flakes were highly altered. The non-embedded flakes showed coatings of tantalum oxide on the surface. The epoxy-resin-mounted flakes showed an irregular surface with many cracks. The edges of the flakes were sealed by epoxy resin, whereas the basal planes of the flakes are not coated. With particle-induced X-ray emission (PIXE) we performed Ta and Cl analyses across the flakes. The ClTa ratios varied over a wide range and, especially near the cracks, were very low. In other regions of the flake we found that tantalum oxychloride or a mixture of tantalum chloride and tantalum oxide had been formed. In a few regions we found evidence that tantalum chloride was encapsulated in the interior of the flakes.