Unraveling the mystery of “tech red” – a volatile technetium oxide

A molecular Tc2O5 species is the likely identity of a volatile oxide which has remained uncharacterized for 50+ years.

Thermochemistry and the Oxidation of Refractory Metals at High Temperature

Recent developments in the thermochemical data for the condensed oxide phases and volatile oxide species for the refractory metals has made possible an analysis of the several types of high temperature oxidation processes. The analyses show the following factors to be important: (1) the presence or absence of oxide films or scales on the metals, (2) the melting points of the one or more oxide phases, (3) the equilibrium pressures of the several volatile oxides, and (4) the flow rate of reactant gases. The thermochemical predictions are compared to experimental observations for molybdenum and tungsten.

Smokes: Part II.— A method of determining the size of the particles in smokes

In Part I (1) an ultra-microscopic method of counting the particles in dilute and highly disperse solid-gas systems was described, and whilst the number was found to decrease as the cloud aged, a concurrent growth in size of the individual units was observed to take place. These changes in the case of non-volatile oxide smokes were proved to be caused by the aggregating of the smaller particles to form larger complexes. Now, in order to follow this process in a quantitative manner, it is necessary to determine the average mass of a particle at different periods in the age of the smoke. That is to say, some method must be used which can be carried out quickly, so that the particles have not time to increase appreciably in size. Now, none of the usual methods which deal with the movement of individual particles are suitable, because, apart from the validity of the Stokes-Cunningham equation (2), on which the majority of them are based, they are in practice too slow, and require the mean of a large number of observations if a representative value for the average size is to be obtained. This objection applies even more strongly to methods based on Einstein’s (3) equation of the mean displacement of a particle by molecular bombardment along a given axis in a definite time.

Note on the continuous rays observed in the spark spectra of metalloids and some metals

In a paper published in the ‘Proceedings of the Royal Society,’ reasons were given for believing that the back-ground of continuous rays in the spark spectra of the metalloids, for instance, tellurium, arsenic, antimony, and bismuth, was caused by the light emitted by an incandescent oxide, whether in a state of vapour or solid, having its origin in the cooling of the dense vapour of the element in an atmosphere containing oxygen. The spectra of metals which are not oxidisable did not show it, namely, gold, silver, and platinum, neither did those of the easily volatile metals such as mercury, indium, thallium, zinc, and cadmium. It was visible on photographed spectra of metals belonging to the iron group, but at the points of the electrodes only, where a non-volatile oxide is formed. As the original explanation has not been accepted as satisfactory I have recently submitted the question to a special examination.