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.
Compositions of Solutions in Contact with Hydrating Tricalcium Silicate Pastes
The concentration of ionic species in the solution in contact with hydrating tricalcium silicate (C3S) has been studied as a function of time and in the presence of admixtures. The ionic product for calcium hydroxide (CH) was calculated as a function of time and correlated with calorimetric measurements and crystal growth data. The results support the hypothesis that nucleation of CH crystals controls the induction period and that their subsequent growth controls the second heat peak. The influence of admixtures can be predicted from their influence on CH crystal growth. However, solution data indicate that the system cannot properly be compared with the growth of pure CH; the combined role of C-S-H and CH must be considered. Some implications for C3S hydration are discussed.
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.