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Sara Sarig - One of the best experts on this subject based on the ideXlab platform.
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Thermogravimetric evaluation of the kinetics of the gypsum-Hemihydrate-soluble anhydrite transitions
Journal of Thermal Analysis and Calorimetry, 1994Co-Authors: Y. Deutsch, Y Nathan, Sara SarigAbstract:Study of the gypsum-Hemihydrate-soluble anhydrite transitions by thermal, X-ray and IR methods showed differences in the intensity of the ∼3493 cm−1 IR absorption peak of the gypsum samples and differences in the peak ratios of the DTA curve at the gypsum-Hemihydrate transition. There were also differences in the temperature and rate of the γ−β anhydrite transition. This suggests that different gypsum species occur, specially among synthetic gypsum.
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Thermogravimetric evaluation of the kinetics of the gypsum-Hemihydrate-soluble anhydrite transitions
Journal of thermal analysis, 1994Co-Authors: Y. Deutsch, Y Nathan, Sara SarigAbstract:Die mittels thermischen, Röntgen- und IR-Methoden untersuchte Umwandlung Gips/Halbhydrat/lösliches Anhydrat zeigte Unterschiede in der Intensität des Absorptionspeaks bei ∼3493 cm^−1 der Gipsprobe und Unterschiede bei den Peakverhältnissen der DTA-Kurve bei der Gips/Halbhydratumwandlung. Es gab auch Unterschiede bei der Temperatur und der Geschwindigkeit der γ−β-Anhydrit-Umwandlung. Dies weist darauf hin, daß—besonders bei synthetischem Gips—verschiedene Gipsarten vorkommen. Um das geeignete Modell für die Gips/Halbhydrat- bzw. die Halbhydrat/Anhydrat-Umwandlung zu finden, wurden fünfzehn Gleichungen getestet. Keines der Modelle entsprach allen Proben. Die beste Gleichung für die Gips/Halbhydratumwandlung von drei Proben war eine Reaktionsordnungsgleichung, während sich für die Halbhydrat/Anhydratumwandlung von vier Proben als beste Gleichung ein Potenzgesetz ergab. Unterschiede in der Kristallitcharakteristik scheinen eine der Hauptgründe für die unterschiedliche Kinetik der einzelnen Proben zu sein. Study of the gypsum-Hemihydrate-soluble anhydrite transitions by thermal, X-ray and IR methods showed differences in the intensity of the ∼3493 cm^−1 IR absorption peak of the gypsum samples and differences in the peak ratios of the DTA curve at the gypsum-Hemihydrate transition. There were also differences in the temperature and rate of the γ−β anhydrite transition. This suggests that different gypsum species occur, specially among synthetic gypsum. Fifteen equations were tested in order to find models which fitted the gypsum-Hemihydrate and the Hemihydrate-anhydrite transitions. No model fitted all the samples. The best fit for the gypsum-Hemihydrate transition in three samples was an order of reaction equation while for the Hemihydrate-anhydrite transition the best fit in four samples was a power law. Differences in crystallite characteristics appear to be one of the main reasons for the differences in kinetics between the samples.
David J.w. Grant - One of the best experts on this subject based on the ideXlab platform.
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Hydration and dehydration behavior of aspartame Hemihydrate
Journal of pharmaceutical sciences, 1998Co-Authors: Suzanne S. Leung, Brian E. Padden, Eric J. Munson, David J.w. GrantAbstract:□ Previous studies have shown that aspartame in the solid state can exist as a Hemihydrate which occurs in two different polymorphic forms (I and II). The present work shows that equilibration of either Hemihydrate at 25 °C with water vapor at relative humidities ≥ 58% or with liquid water produces a 2.5-hydrate. Upon subjecting each of these crystalline hydrates to increasing temperature, the same crystalline anhydrate is formed which thermally cyclizes at a higher temperature to form the known compound 3-(carboxymethyl)-6-benzyl- 2,5-dioxopiperazine. The activation energy of the cyclization reaction appears to depend on the degree of crystallinity of the anhydrate that is formed at a lower temperature. On increasing the temperature of the 2.5-hydrate, a Hemihydrate intervenes before the anhydrate is formed. This intervening Hemihydrate is similar to the commercial form (II) of aspartame Hemihydrate but exhibits greater amorphous character. The techniques employed were Karl Fischer titrimetry, powder X-ray diffractometry, differential scanning calorimetry, thermogravimetric analysis, solid-state 13C nuclear magnetic resonance spectroscopy, and Fourier transform infrared absorption spectroscopy.
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Solid-State Characterization of Two Polymorphs of Aspartame Hemihydrate
Journal of pharmaceutical sciences, 1998Co-Authors: Suzanne S. Leung, Brian E. Padden, Eric J. Munson, David J.w. GrantAbstract:□ From the known crystal structure of aspartame Hemihydrate, designated form I, the theoretical powder X-ray diffraction (PXRD) pattern was calculated. This PXRD pattern differs significantly from that of the commercially available aspartame Hemihydrate, which is therefore a different polymorph, designated form II. Form II transforms to form I during ball-milling or on heating for 30 min at 160 °C in the presence of steam. The two polymorphs were compared by PXRD, differential scanning calorimetry, thermogravimetric analysis, Karl Fischer titrimetry, Fourier transform infrared (FTIR) absorption spectroscopy, 13C solid-state nuclear magnetic resonance (SSNMR) spectroscopy, scanning electron microscopy, particle size analysis, and measurements of true density and intrinsic dissolution rate. Comparison of the 13C SSNMR and FTIR spectra of the two polymorphs suggests that the crystal structure of form II is less symmetric, with the side chains located in multiple environments. Although both Hemihydrate polymorphs on heating in the absence of moisture dehydrate to a crystalline anhydrate, form I does so at a lower temperature, suggesting weaker interactions of water with aspartame molecules. At higher temperatures the anhydrate from both Hemihydrate polymorphs yields 3-(carboxymethyl)-6-benzyl-2,5- dioxopiperazine (DKP) by a cyclization reaction for which the temperature, reaction enthalpy, and activation energy are very similar. Both Hemihydrate forms, when in contact with liquid water, yield the 2.5-hydrate.
Y. Deutsch - One of the best experts on this subject based on the ideXlab platform.
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Thermogravimetric evaluation of the kinetics of the gypsum-Hemihydrate-soluble anhydrite transitions
Journal of Thermal Analysis and Calorimetry, 1994Co-Authors: Y. Deutsch, Y Nathan, Sara SarigAbstract:Study of the gypsum-Hemihydrate-soluble anhydrite transitions by thermal, X-ray and IR methods showed differences in the intensity of the ∼3493 cm−1 IR absorption peak of the gypsum samples and differences in the peak ratios of the DTA curve at the gypsum-Hemihydrate transition. There were also differences in the temperature and rate of the γ−β anhydrite transition. This suggests that different gypsum species occur, specially among synthetic gypsum.
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Thermogravimetric evaluation of the kinetics of the gypsum-Hemihydrate-soluble anhydrite transitions
Journal of thermal analysis, 1994Co-Authors: Y. Deutsch, Y Nathan, Sara SarigAbstract:Die mittels thermischen, Röntgen- und IR-Methoden untersuchte Umwandlung Gips/Halbhydrat/lösliches Anhydrat zeigte Unterschiede in der Intensität des Absorptionspeaks bei ∼3493 cm^−1 der Gipsprobe und Unterschiede bei den Peakverhältnissen der DTA-Kurve bei der Gips/Halbhydratumwandlung. Es gab auch Unterschiede bei der Temperatur und der Geschwindigkeit der γ−β-Anhydrit-Umwandlung. Dies weist darauf hin, daß—besonders bei synthetischem Gips—verschiedene Gipsarten vorkommen. Um das geeignete Modell für die Gips/Halbhydrat- bzw. die Halbhydrat/Anhydrat-Umwandlung zu finden, wurden fünfzehn Gleichungen getestet. Keines der Modelle entsprach allen Proben. Die beste Gleichung für die Gips/Halbhydratumwandlung von drei Proben war eine Reaktionsordnungsgleichung, während sich für die Halbhydrat/Anhydratumwandlung von vier Proben als beste Gleichung ein Potenzgesetz ergab. Unterschiede in der Kristallitcharakteristik scheinen eine der Hauptgründe für die unterschiedliche Kinetik der einzelnen Proben zu sein. Study of the gypsum-Hemihydrate-soluble anhydrite transitions by thermal, X-ray and IR methods showed differences in the intensity of the ∼3493 cm^−1 IR absorption peak of the gypsum samples and differences in the peak ratios of the DTA curve at the gypsum-Hemihydrate transition. There were also differences in the temperature and rate of the γ−β anhydrite transition. This suggests that different gypsum species occur, specially among synthetic gypsum. Fifteen equations were tested in order to find models which fitted the gypsum-Hemihydrate and the Hemihydrate-anhydrite transitions. No model fitted all the samples. The best fit for the gypsum-Hemihydrate transition in three samples was an order of reaction equation while for the Hemihydrate-anhydrite transition the best fit in four samples was a power law. Differences in crystallite characteristics appear to be one of the main reasons for the differences in kinetics between the samples.
George P. Demopoulos - One of the best experts on this subject based on the ideXlab platform.
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Model-Based Construction of Calcium Sulfate Phase-Transition Diagrams in the HCl−CaCl2−H2O System between 0 and 100 °C
Industrial & Engineering Chemistry Research, 2006Co-Authors: George P. DemopoulosAbstract:Phase-transition diagrams of three CaSO4 phases, namely, dihydrate, Hemihydrate, and anhydrate, in the HCl−CaCl2−H2O system are successfully constructed making use of a recently developed OLI-based chemical model. After initial validation of the model by comparison to experimentally determined CaSO4 phase-transition points in H2O or pure HCl solutions, the phase-transition border between dihydrate and anhydrite and that between dihydrate and Hemihydrate was obtained by calculating the solution supersaturation (or scaling tendency according to OLI). The constructed phase-transition diagrams show three main regions, namely, regions I, II, and III. In region I, dihydrate is stable, while anhydrite is stable in regions II and III. Dihydrate is metastable in region II, while Hemihydrate is metastable in region III. An increase in HCl and/or CaCl2 concentration causes the metastable region of HH to expand at the expense of DH. This has the result of lowering the corresponding transition temperatures.
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preparation of α calcium sulfate Hemihydrate by reaction of sulfuric acid with lime
Industrial & Engineering Chemistry Research, 2005Co-Authors: Yuanbing Ling, George P. DemopoulosAbstract:Direct preparation of α-calcium sulfate Hemihydrate out of sulfuric acid solution by reaction with lime under atmospheric pressure conditions is systematically investigated. Two preparation methods are investigated: one involving addition of dry lime to sulfuric acid solution (standard procedure) and the other involving addition of sulfuric acid solution to slaked lime (reverse procedure). On the basis of the standard procedure, the operating window is first determined, followed by thorough examination of preparation conditions such as acidity, retention time and CaO/H2SO4 molar ratio. Dihydrate was found to form as intermediate phase that converts to Hemihydrate under all tested conditions. The typical morphology of α-Hemihydrate crystals produced by the standard procedure is needle-shaped with 50−100 μm length and 1−3 μm thickness. However, when the reverse procedure was used, a different growth mechanism apparently applied yielding shorter (∼60 μm) but thicker (5−10 μm) column-shaped crystals within o...
Suzanne S. Leung - One of the best experts on this subject based on the ideXlab platform.
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Hydration and dehydration behavior of aspartame Hemihydrate
Journal of pharmaceutical sciences, 1998Co-Authors: Suzanne S. Leung, Brian E. Padden, Eric J. Munson, David J.w. GrantAbstract:□ Previous studies have shown that aspartame in the solid state can exist as a Hemihydrate which occurs in two different polymorphic forms (I and II). The present work shows that equilibration of either Hemihydrate at 25 °C with water vapor at relative humidities ≥ 58% or with liquid water produces a 2.5-hydrate. Upon subjecting each of these crystalline hydrates to increasing temperature, the same crystalline anhydrate is formed which thermally cyclizes at a higher temperature to form the known compound 3-(carboxymethyl)-6-benzyl- 2,5-dioxopiperazine. The activation energy of the cyclization reaction appears to depend on the degree of crystallinity of the anhydrate that is formed at a lower temperature. On increasing the temperature of the 2.5-hydrate, a Hemihydrate intervenes before the anhydrate is formed. This intervening Hemihydrate is similar to the commercial form (II) of aspartame Hemihydrate but exhibits greater amorphous character. The techniques employed were Karl Fischer titrimetry, powder X-ray diffractometry, differential scanning calorimetry, thermogravimetric analysis, solid-state 13C nuclear magnetic resonance spectroscopy, and Fourier transform infrared absorption spectroscopy.
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Solid-State Characterization of Two Polymorphs of Aspartame Hemihydrate
Journal of pharmaceutical sciences, 1998Co-Authors: Suzanne S. Leung, Brian E. Padden, Eric J. Munson, David J.w. GrantAbstract:□ From the known crystal structure of aspartame Hemihydrate, designated form I, the theoretical powder X-ray diffraction (PXRD) pattern was calculated. This PXRD pattern differs significantly from that of the commercially available aspartame Hemihydrate, which is therefore a different polymorph, designated form II. Form II transforms to form I during ball-milling or on heating for 30 min at 160 °C in the presence of steam. The two polymorphs were compared by PXRD, differential scanning calorimetry, thermogravimetric analysis, Karl Fischer titrimetry, Fourier transform infrared (FTIR) absorption spectroscopy, 13C solid-state nuclear magnetic resonance (SSNMR) spectroscopy, scanning electron microscopy, particle size analysis, and measurements of true density and intrinsic dissolution rate. Comparison of the 13C SSNMR and FTIR spectra of the two polymorphs suggests that the crystal structure of form II is less symmetric, with the side chains located in multiple environments. Although both Hemihydrate polymorphs on heating in the absence of moisture dehydrate to a crystalline anhydrate, form I does so at a lower temperature, suggesting weaker interactions of water with aspartame molecules. At higher temperatures the anhydrate from both Hemihydrate polymorphs yields 3-(carboxymethyl)-6-benzyl-2,5- dioxopiperazine (DKP) by a cyclization reaction for which the temperature, reaction enthalpy, and activation energy are very similar. Both Hemihydrate forms, when in contact with liquid water, yield the 2.5-hydrate.