Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its (...) preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe3O4) and haematite (α-Fe2O3), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides. (shrink)

It is now more than twenty years since Knight (1987) first presented his paradigm-shifting theory of how and why the ‘human revolution’ occurred — and had to occur — in modern humans who, as climates dried under ice age conditions and African rainforests shrank, found themselves surrounded by vast prairies and savannahs, with rich herds of game animals roaming across them. The temptation for male hunters, far from any home base, to eat the best portions of meat at the kill (...) site — as do other social carnivores — called for strong measures from human females, who were paying the heavy metabolic and physical costs of bearing large-brained but helpless children. Even in the modern west, with well stocked supermarkets, a pregnant or lactating woman can lose ten percent of the dry weight of her brain, because developing babies demand dietary lipids for brain growth (Horrobin, 1998). Hence the idea of the menstrual sex strike, designed to force males to deliver their kills entirely into the hands of women for cooking and distribution—a practice common in foraging communities to this day. (shrink)