Reactivity, Stored Energy, and Dislocations in Solid-Solid Reacting Systems

Abstract

ABSTRACT Strong neutron bombardment of graphite can displace many atoms from their lattice positions; many of the dislocated atoms do not anneal during the irradiation process and the net result is an increase of internal energy of the graphite. This increase is usually referred to as stored energy, or in the older literature this phenomenon is sometimes called the total Wigner energy. In addition to irradiation, mechanical milling, decomposition, precipitation, reduction of chemical compounds, and condensation of metal vapors can also produce stored energy in powders. The stored energy associated with defects in solids is an important aspect of the nature of the defects and the processes that produce them. It has been shown experimentally that stored energy results in a large increase of reactivity of the solid materials, and the spontaneous release of the energy in an inert atmosphere can lead to a large temperature rise. This short communication reports on several typical features of stored energy and illustrates the problem with a few experimental examples. Since stored energy substantially increases the reaction rate we can carry out many reactions at much lower temperatures. Consequently, in technical applications for specific reactions high-temperature furnaces can be replaced by high-performance mills operating at room temperatures or by cheap low-temperature furnaces. Non-catalytic reactions, in spite of their importance, have not received as much attention as catalysis in the past. Major developments and working plants erected at the end of the last century without participation of the chemical engineering community, as, for example, cement manufacturing, steel production, and ore processing, did not encourage chemical engineers to study the governing phenomena in a systematic way. Consequently, modeling and experimental studies have been relatively few, and applied physics or metallurgy propelled development in the field. Reactions, that take place in gaseous or liquid systems can usually be well reproduced if the external conditions of the experiment are identical and the experiment is carried out with precursors of identical concentration. The situation is rather different in systems where solid precursors participate in the reaction scheme. In this short note we will report on some phenomena, that are not well known in the realm of chemical reaction engineering and that might play a very important role in experimental investigation and optimization of a particular solid reaction system.