Hedvall Effect in Cement Chemistry
THE increased reactivity of a solid during and as a consequence of a crystalline transformation is commonly known as the Hedvall effect1–3. In a wider sense this effect may include increased reactivity near a transition point. The typical data quoted in support of the Hedvall effect refer to reactions in the binary systems containing silver salts with BaO, SrO and CaO yielding the reciprocal pairs4–7.
Differential reaction analysis ( DRA )-a technique for obtaining difrerential thermal analysis data from inert substances
Many substances, including some common minerals, do not undergo thermal reactions of suff icient magnitude to provide useful dif ferential thermal analyis data. The purpose of this study was to consider possible new techniques by which dif ferential thermal data could be obtained from such relat ively inert substances. The technique explored was to react two substances (the non-reactive material with some chemical agent) and to determine the thermal effects that occur as the mixture is heated. Several reactants were considered including alkali hydroxides, carbonates, and fluorides, microcosmic salt, VrOu, and LLWOT. Of the reactants considered, LirWOn was found to be most satisfactory. Heating curves were obtained using heating rates of approximately 14oC per minute. Cooling curves were obtained by turning off the furnace power and the cool ing rates were nonlinear. Eight si l icate minerals, wollastonite, grossular, bytownite, albite, microcl ine, enstat i te, ol ivine, and zircon were studied. Differential curves for wollastonite, grossular, bytownite, albite, and microcl ine showed detectable reactions and characterist ic dif ferences. The reaction temperatures for enstat i te, ol ivine, and zircon were apparently too high for the furnaces used ( 1000'C l imit) to detect any reactions. X-ray and optical examination revealed the presence of CaWO., NarWOa, and LiAlSiOn in the reaction end products. I t was concluded that this method is feasible and i f further developed might broaden the scope of presently exist ing differential thermal techniques. I t is proposed that this method be cal led dif ferential reaction
The Italian Renaissance: Culture and Society in Italy
In this newly revised edition of his widely acclaimed work, Peter Burke presents a social and cultural history of the Italian Renaissance. He discusses the social and political institutions that existed in Italy during the fifteenth and sixteenth centuries, and he analyzes the ways of thinking and seeing that characterized this period of extraordinary artistic creativity. Developing a distinctive approach, the author is concerned not only with the finished works of Michelangelo, Raphael, Leonardo da Vinci, and others, but also with the social background, patterns of recruitment, and means of subsistence of this "cultural elite." He thus makes a major contribution both to our understanding of the Italian Renaissance and to our comprehension of the complex relations between culture and society. An excellent social history of the lives and culture of the artists and artisans which made it possible for the arts to flourish.