, soffermandoci in particolare su due questioni: (a) se, e in caso affermativo, come facio incrementa la sua produttivitâ, e (b) che tipo di evoluzione semantica esso subisce. 3.2 Frequenza e distribuzione di facio nel latino tardo Vari studi si riferiscono a un
To improve the separation of the dihydrate and hemihydrate phases, different sample masses, heating rates and crucibles were used. A TG-DTA method was developed for the determination of water evolved from CaSO4·xH2O. The new crucible introduced for the Q-1500D MOM derivatograph gives a possibility for the evolved water to be determined independently from the TG and DTA curves.
Authors:G. Ingo, C. Riccucci, G. Bultrini, and G. Chiozzini
By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron
spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition
of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight
into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related
to the thermal decomposition of CaSO4 that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close
to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is
induced by the presence of silica and is related to the surface acid-base interaction between SiO2 and CaSO4. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides
characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties
measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO4 thermal decomposition is observed.
Authors:C. A. Strydom, E. M. Groenewald, and J. H. Potgieter
Using a heating rate of 2°C min−1, CaS reacts with oxygen in air from 700°C to form CaSO4, with a complete conversion at 1100°C. Synthesis of CaS from the reaction between CaSO4 containing compounds and carbon compounds in air would not be possible, as the carbon reacts from 600°C with oxygen in the air to give CO2. Heating stoichiometric amounts of carbon and pure CaSO4, synthetic gypsum or phosphogypsum in a nitrogen atmosphere, results in the formation of CaS from 850°C. Using a heating rate of 10°C min−1, the formation of CaS is completed at 1080°C. Addition of 5% Fe2O3 as a catalyst lowers the starting temperature of the reaction to 750°C. Activation energy values at different fraction reaction values (α) differ between 340 and 400 kJ mol−1. The relationship between the activation energy values and conversion (α) indicates that the reaction proceeds via multiple steps.
The effect of various temperature treatments on TL response characteristics of CaSO4: Dy has been investigated for its reusability when the phosphor has been previously irradiated to increasingly higher gamma doses. In practice, annealing at a standard temperature, namely 400 °C, usually precedes the use or reuse of the phosphor. However, the study demonstrates that the phosphor with a previous history of high accumulated doses does not completely retain its original TL response characteristics with 400 °C treatment unless the phosphor is treated at an elevated temperature, namely 650 °C.
The dehydration of Ca(H2PO4)2·H2O was examined with simultaneous DTA and TG. This dehydration permitted clearly the apparation of the following phases: Ca(H2PO4)2·0.5H2O, Ca(H2PO4)2, Ca3(HP2O7)2, Ca2HP3O10 et Ca(PO3)2.
The reaction of Ca(H2PO4)2·H2O and CaSO4 was also examined with the same technics. It was found that the decomposition of CaSO4 takes place for relatively low temperature (between 600°C and 800°C).
The third-law method has been applied to the results of kinetic studies reported in the literature and obtained in this work
to determine the E parameters of the Arrhenius equation and investigate the impact of self-cooling on the dehydration kinetics
of Li2SO4H2O, CaSO42H2O and CuSO45H2O. The values obtained (104, 98 and 88 kJ mol-1, respectively) are about 20% higher compared to the literature data calculated by the Arrhenius-plots method. This discrepancy
is connected with the severe effect of self-cooling, which can reach several ten degrees at maximum temperatures of experiments.
Differential calorimetry was used to determine the heat evolution and kinetics of hydration processes of the calciumsulphatealuminate phase Ca4(Al6O12)(SO4) with gypsum CaSO4 · 2H2O at room temperature with one mole of water added to the solid phase. An increasing content of sulphate ions in the sytem results in substitution of the monosulphate Ca4(Al2O6)(SO4) · 12H2O in the reaction products by ettringite, Ca6(Al2O6)(SO4)3 · 32H2O. Higher contents of ettringite influence the rates of hydration reactions and the values of the evolved heat.
Linking the tradition of antiquity (fatum, fortuna, casus) with Christian doctrine (deus, providentia), Petrarch tries to interpret fortune as an important and unpredictable force originating partly from God, partly from the talents and actiones (virtues, sins) of man, crucially influencing the lives of individuals and peoples. Fortune being essentially changing, unpredictable, it would be erroneous to found one's life on it, but it must be taken into account: one should reduce its possibilities, and learn to handle its favours and blows. One can best limit its effects by avoiding mortal sin, developing activity-related virtues (fortitudo, iustitita), and handling consciously its interference with one's life: not overestimating its favours, and developing our virtues in connection with moderation and constancy (prudentia, temperantia, patientia). If one can, to some extent, handle fortune, one can become more independent, can significantly influence one's own destiny: instead of forfeiting happiness in the afterlife, one can live a life in harmony with that.