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.
Estimation of tricalcium silicate through polymorphic transformation
Tricalcium silicate characteristically exhibits the most intense reversible transition at a temperature of about 915‡. The intensity of this effect can be used to estimate the amount of C3S in mixtures and to calculate the degree of hydration of C3S. Low sensitivity forδT up to 800‡ and higher sensitivity between 800‡ and 1000‡ enable estimation of both Ca(OH)2 and C3S. Interference effects at higher temperatures owing to decarbonation, recrystallization toΒ-wollastonite, and dehydration of the calcium silicate hydrate can be overcome by heating to 1000‡, cooling to 800‡, and reheating. A determination of the degree of hydration of C3S obtained at different periods by DTA correlates well with that using the X-ray method.RésuméLe silicate tricalcique montre une transition réversible, intense et caractéristique à 915‡ environ. On peut utiliser l'intensité de cet effet pour estimer la teneur en C3S des mélanges et pour calculer le taux d'hydratation. La sensibilité du signalδT, faible jusqu'à 800‡ et plus élevée entre 800 et 1000‡ permet d'estimer à la fois Ca(OH)2 et C3S. Les effets d'interférence aux températures élevées dus à la décarbonatation, à la recristallisation en Β-wollastonite, et à la déshydratation du silicate calcium hydraté peuvent Être évités par chauffage à 1000‡, refroidissement à 800‡ et nouvel échauffement. La détermination du taux d'hydratation de C3S par ATD recoupe bien les résultats de l'étude aux rayons X.ZusammenfassungTrikalziumsilikat zeigt einen charakteristischen übergang bei einer Temperatur von ungefÄhr 915‡. Die IntensitÄt dieses Effektes kann zur Bestimmung der Mengen von C3S in Gemischen und zur Errechnung seines Hydratationsgrades herangezogen werden. Die niedrige Empfindlichkeit fürδT bis 800‡ und die höhere zwischen 800–1000‡ ermöglicht die Bestimmung von Ca(OH)2 und C3S. Interferenzeffekte bei höherer Temperatur, verursacht durch Entkohlung, Rekristallisation von Β-Wollastonit und Dehydratation von Kalziumsilikathydrat, können durch Glühen auf 1000‡, Abkühlen auf 800‡ und erneutes Glühen behoben werden. Die durch DTA erhaltenen Hydratationswerte von C3S stimmten gut mit den röntgenographisch erhaltenen Ergebnissen überein.РЕжУМЕДль тРИкАльцИИсИлИк АтА хАРАктЕРНО пРОьВлЕНИЕ НАИБОлЕЕ ИНтЕНсИВНОгО пРЕВРА ЩЕНИь пРИ тЕМпЕРАтУРЕ ОкОл О 915‡. ИНтЕНсИВНОсть ЁтОгО ЁФФЕктА МОжЕт Б ыть ИспОльжОВАНА Дль ОцЕНкИ кОлИЧЕстВ А C3S В сМЕсИ И РАсЧЕтА стЕпЕНИ гИДРАтАцИИ C3S. НИжкАь ЧУВстВИтЕльН Остьδт ДО 800‡ И БОлЕЕ ВысОкА ь ЧУВстВИтЕльНОсть МЕ жДУ 800 И 1000‡ ДАУт ВОжМОжНОсть ОцЕНИть кАк Ca(OH)2, тАк И C3S. ЁФФЕкты, МЕшАУЩИЕ пРИ БОлЕЕ Вы сОкИх тЕМпЕРАтУРАх И ОБУслОВлЕННыЕ ДЕкА РБОНИжАцИЕИ, РЕкРИстАллИжАцИЕИ Д ОΒ-ВОллАстОНИтА И ДЕгИДРАтАцИЕИ гИДРА тА сИлИкАтА кАльцИь, М ОгУт Быть пРЕОДОлЕНы пУтЕМ НАг РЕВАНИь ДО 1000‡, ОхлАжДЕНИь ДО 800‡ И пО ВтОРНОгО НАгРЕВАНИь. стЕпЕНь гИДРАтАцИИ C3S, ОпРЕДЕл ьЕМАь пРИ РАжлИЧНых пЕРИОД Ах МЕтОДОМ ДтА, хОРОшО кОРРЕлИРУЕтсь с ДАНН ыМИ, пОлУЧЕННыМИ пРИ ИспОльжОВАНИИ МЕ тОДА РЕНтгЕНОстРУкт УРНОгО АНАлИжА.
Further studies on fire retardant polystyrene by Friedel–Crafts chemistry
Abstract The combination of a copolymer of 4-vinylbenzyl alcohol and styrene with 2-ethylhexyldiphenylphosphate (DPP) and with metal chlorides has been studied by TGA, radiative gasification, Cone Calorimetry, and oxygen index measurements. Evidence is presented in support of a cross-linking reaction with the additives and the copolymer, which proceeds through a Friedel–Crafts mechanism. This approach reduces the peak heat release rate (HRR) by 60% as measured in the Cone Calorimeter. There is a significant reduction in the mass loss rate during the thermal degradation, and evidence of char formation is observed in the radiative gasification experiments.