Examining Hydrated Minerals Using Optically Stimulated X-Ray Diffraction, an Inexpensive Modification of Traditional Diffractometers

García-Guinea, Javier; Abella, Rafael; Sánchez‐Moral, Sergio; Benito, Raúl; Martín-Ramos, Daniel

doi:10.1306/2dc40944-0e47-11d7-8643000102c1865d

Cited by 12 publications

(7 citation statements)

References 11 publications

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“…The heating system includes a Pt temperature probe, a precision T controller, and a thyristor power regulator firing a halogen lamp (75 W, 220 V) that provides up to 200 °C to the sample. A detailed description of the heating device can be found elsewhere. , A water cooling system was used to prevent overheating. Diffraction patterns were collected in air (30% RH) from 4.5 min scans (10−35° 2θ explored area) at 1 °C intervals (i.e., heating rate of 0.22 K·min -1 ), upon warming from 20 to 198 °C.…”

Section: Methodsmentioning

confidence: 99%

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Mechanism and Kinetics of Dehydration of Epsomite Crystals Formed in the Presence of Organic Additives

2006

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The thermal dehydration of epsomite (MgSO4*7H2O) crystals grown in the presence and absence of organic additives (phosphonates, carboxylic acids, and polyacrylic acid derivatives) was studied by means of thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray thermodiffraction (XRTD), and environmental scanning electron microscopy (ESEM). In situ XRTD analyses (in air, 30% relative humidity) show an -->epsomite hexahydrite (MgSO4*6H2O) transition at 25-38 degrees C, followed by formation of amorphous phase(s) at T > 43-48 degrees C, and MgSO4 crystallization at approximately 300 degrees C. Kinetic parameters (E(alpha) and A) were determined for the main dehydration step (25-160 degrees C), which corresponds to a MgSO4*7H2O-->MgSO4*H2O transition, by applying two isoconversional methods to nonisothermal TG data obtained at different heating rates (beta= 1, 3, and 5 K*min-1). In situ, hot-stage ESEM observations of the thermal dehydration of epsomite crystals are consistent with the nonisothermal kinetic study and, along with XRTD results, allow us to propose a dehydration mechanism which includes an early nucleation and growth event, followed by the advancement of the reaction interface (3D phase boundary reaction). Both E(alpha) and A values increase in the presence of the most effective crystallization inhibitors tested. H-bonding between additives and epsomite crystal surfaces is consistent with Fourier transform infrared spectroscopy (FTIR) and may account for this effect. The increase of E(alpha) values can be related to the excess energy required to break additive-water bonds in the reactant. These results are likely to further our understanding of the interaction mechanisms between salt hydrates and organic additives which act as growth inhibitors/modifiers.

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Section: Methodsmentioning

confidence: 99%

“…A detailed description of the heating device can be found elsewhere. 43,44 A water cooling system was used to prevent overheating. Diffraction patterns were collected in air (30% RH) from 4.5 min scans (10-35°2θ explored area) at 1 °C intervals (i.e., heating rate of 0.22 K‚min -1 ), upon warming from 20 to 198 °C.…”

Section: Methodsmentioning

confidence: 99%

Mechanism and Kinetics of Dehydration of Epsomite Crystals Formed in the Presence of Organic Additives

2006

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“…This device is a chamber where the radiation beam passes through a Mylar window and the heating system is just under the sample support controlled by two thermocouples where the temperature deviation is less than 1 °C. An additional similar device was used with a halogen lamp as heating system with thyristor power regulator and a proportional-integral-derivative (PID) temperature controller as reported elsewhere . Analysis of the relative proportion of polymorphs was performed with the Xpowder program…”

Section: Experimental Methodsmentioning

confidence: 99%

Crystalline Polymorphism and Molecular Structure of Sodium Pravastatin

et al. 2006

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In this work different crystallization processes of sodium pravastatin are explored and a new polymorph is obtained. The analytical results of powder X-ray diffraction (PXRD) and thermal analysis for this new polymorph indicate that it is different from the polymorphs previously reported. This new crystal form shows different physical-chemical properties than the previous forms, such as crystallographic structure, thermal behavior, and melting point, 181.5 degrees C. Besides, all crystallization processes previously reported use an aprotic solvent as antisolvent. However, we propose a new crystallization process for sodium pravastatin that uses only protic solvents, overcoming industrial scaling and environmental problems. Variable-temperature PXRD experiments show a transformation between different crystal forms in the range of 80-120 degrees C. Solid-state 13C NMR, reported in this work for the first time, and Fourier transform infrared (FT-IR) studies of some polymorphs show some differences in intermolecular interactions, especially with carboxylate and hydroxyl groups. Quantum mechanical calculations of the pravastatin molecule are also presented for the first time, obtaining a molecular structure similar to the experimental structure existing within the crystal lattice of the tert-octylamonium salt of pravastatin.

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“…Powder X-ray Thermodiffraction. Temperature-dependent powder X-ray diffraction was performed by fine-tuning an optically stimulated X-ray diffractometer (OSXRD) prototype described elsewhere . The halogen lamp (heating system; Philips Capsuleline Pro 75 W, 220 V) provides up to 210 °C for the sample.…”

Section: Methodsmentioning

confidence: 99%

“…Thermodiffraction (XRTD) is a powerful tool used in many research fields of materials science, as well as in the chemical and pharmaceutical industries, metallurgy, geology, archeometry, or planetary science. − Very different scientific areas such as planetary science, civil engineering, and cultural heritage conservation − are showing great interest in mineralogical and phase transition of hydrated salts, especially magnesium and sodium sulfates.…”

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confidence: 99%

Powder X-ray Thermodiffraction Study of Mirabilite and Epsomite Dehydration. Effects of Direct IR-Irradiation on Samples

et al. 2007

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This paper investigates the thermal and irradiation-dependent dehydration and kinetics occurring in Na2SO4.10H2O (mirabilite) and MgSO4.7H2O (epsomite) at room conditions by using powder X-ray thermodiffraction. An improved version of a first optically stimulated X-ray diffractometer prototype was used. Specific software for the thermodiffraction study was developed (XPowder PLUS) and a filter inserted between the lamp (heating system) and the sample. The results show that these salts are thermal and irradiation sensitive. The temperature and kinetic rates of the salt conversions differed depending on direct exposure to high-intensity radiation (photodehydration) or whether the radiation was blocked by the filter (thermodehydration). In general, radiation-induced dehydration triggers the transformation at lower temperature and accelerates the kinetic reaction more than when the filter is used. Mirabilite dehydration starts with the initial radiation impacts, unlike epsomite. Thermodehydration and photodehydration of mirabilite is a non-isothermal reaction occurring through an amorphous-mediated step. Radiation damage in epsomite leads to isothermal dehydration, whereas non-isothermal dehydration occurs when epsomite is thermally damaged. In both cases, no amorphous material was observed. Because of the weaker bond between cation and oxygen atom in mirabilite, its thermal and radiation stability is lower than in epsomite. These results have important implications for the prevention of salt weathering of porous materials found in the cultural heritage.

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Examining Hydrated Minerals Using Optically Stimulated X-Ray Diffraction, an Inexpensive Modification of Traditional Diffractometers

Cited by 12 publications

References 11 publications

Mechanism and Kinetics of Dehydration of Epsomite Crystals Formed in the Presence of Organic Additives

Mechanism and Kinetics of Dehydration of Epsomite Crystals Formed in the Presence of Organic Additives

Crystalline Polymorphism and Molecular Structure of Sodium Pravastatin

Powder X-ray Thermodiffraction Study of Mirabilite and Epsomite Dehydration. Effects of Direct IR-Irradiation on Samples

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