Temperature-resolved X-ray Diffraction Research Articles

Crystal structure of a new form of Cs[B 5O 6(OH) 4].2H 2O and thermal behavior of M[B 5O 6(OH) 4].2H 2O ( M=Cs, Rb, Tl)

The crystal structure of a new synthetic borate, β-Cs[B 5O 6(OH) 4].2H 2O, was determined from single crystal X-ray diffraction data. The compound is monoclinic, space group C2/c; the unit cell parameters are a=8.160(2) Å, b=12.140(2) Å, c=11.860(2) Å, β=93.00(3)°; Z=4. The crystal structure was resolved from 1188 reflections until R 1=0.0408; it contains isolated [B 5O 6(OH) 4] − polyanions separated by free water molecules and Cs + cations. The cohesion of the structure comes from the hydrogen bonds existing between the water molecules and the polyborate anions. The dehydration of three M[B 5O 6(OH) 4].2H 2O borates ( M=Cs, Rb, Tl) and the transitions of anhydrous MB 5O 8 compounds ( M=Cs, Rb, Tl) were investigated by temperature-resolved X-ray diffraction and thermal analysis. Whatever M + ions ( M=Cs, Rb, Tl), the thermal behavior of M[B 5O 6(OH) 4].2H 2O compounds can be summarized in two steps. The first step corresponds to a loss of four water molecules and leads to an amorphous phase due to the collapsing of the hydrated pentaborate structure. In a second step, the amorphous phase crystallizes and transforms into two ( M=Tl), three ( M=Rb) or four ( M=Cs) anhydrous phases. All these phases are characterized by X-ray powder diffraction; unit cell parameters were determined for almost all of them.

Temperature Resolved X-Ray Diffraction as a Tool for Studying the Recrystallization Process in Cold-Rolled Steels

Temperature Resolved X-Ray Diffraction as a Tool for Studying the Recrystallization Process in Cold-Rolled Steels

Effect of Crystalline Structure and Impurity Content of C60 Thin Films on the Order/Disorder Phase Transition

ABSTRACTNear the temperature of 260 K, C60 crystal is known to undergo a first order phase transition, associated with changes in molecular rotations. The present paper reports the effect of the crystalline structure and impurity content of C60 thin films on their structural behavior near this phase transition. Polycrystalline C60 films with different grain sizes and oxygen content were obtained by varying the conditions of their vacuum deposition and post-grown exposure. Temperature-resolved X-ray diffraction in the range 300 – 15 K was used to determine the lattice parameter and its changes near the phase transition temperature. Decrease in grain sizes and increase in oxygen content of the films are found to lead to a gradual reduction in the discontinuity in lattice parameter and the transition temperature.

In situ study of the scale formation on γ-TiAl during isothermal oxidation at 700°C and on heating

Time and temperature resolved X-ray diffraction as an in situ method and electron microprobe analysis for post oxidation studies were used for the investigation of the oxide scale formation on γ-TiAl at 700°C and during stepwise heating from room temperature to 950°C in air and in He with 19 vol% O2.The formation of alumina in the form of α-Al2O3 and of TiO2 in the form of rutile was observed in both atmospheres and additionally, TiN was found during oxidation in air. Furthermore, diffraction peaks of two phases were detected, which do not exist in the data base for X-ray diffraction JCPDS-ICDD, and are different in air (X′- and X-phase) and in He with 19vol% O2 (Z-phase).In air, TiO2 grows faster than the α-Al2O3 and the growth of TiO2 is not parabolic in the first 50 hours. An oxide scale of 5 μm thickness consisting of a mixture of α-Al2O3 and TiO2 is observed. In He with 19vol% O2 the formation of TiO2 is slower than of α-Al2O3 resulting in a thinner oxide scale.

Melting and crystallization of poly(ethylene- co-octene) measured by modulated d.s.c. and temperature-resolved X-ray diffraction

The melting and crystallization behaviour of metallocene-catalysed commercial poly(ethylene- co-octene) was investigated by conventional and temperature-modulated differential scanning calorimetry (d.s.c. and TMd.s.c.) and by temperature-resolved wide angle X-ray scattering. The thermal behaviour of the copolymer is characterized by a very broad melting and crystallization range. Both the melting and the crystallization are complex transitions of at least two processes with different kinetics. On decreasing the temperature, crystallization starts with the formation of a separate crystalline phase and continues gradually with development of an amorphous–crystalline mesophase until the glass transition is reached. In TMd.s.c., the formation of the crystalline phase is seen as an irreversible, non-reversing process, whereas the glass transition gives a reversing heat flow signal. Similarly, on heating, the melting process is initiated after traversing the glass transition as a largely reversing process, followed by melting of the crystalline phase with non-reversing character in a narrower temperature range.

Thermal Analysis, Microcalorimetry and Combined Techniques for the Study of the Polymorphic Behaviour of a Purine Derivative

The polymorphic behaviour of the purine derivative MKS 492 was studied with investigations of suspensions of selected samples in different solvents and of samples obtained by crystallizations. The samples were analyzed by DSC, TG and X-ray diffraction. Six different crystalline modifications called A, B, B’, C, D and E and an amorphous form were identified. Four pure crystalline modifications, A, B, C and D have been manufactured and characterized by DSC, X-ray, IR, solubilities, densities, hygroscopicity and dissolution measurements. The four forms A, C, D and E are monotrop to the form B. The form B is enantiotrop to the form B’, which revealed the highest melting point of all known polymorphs. This form B’ is only stable at high temperature. Temperature resolved X-ray diffraction was very helpful for proper interpretation of the thermal events. The melting peaks of the forms A and C and the endothermic peak corresponding to the enantiotropic transition B into B’ occur in a narrow range of temperature. The form B which is the most stable one at room temperature has been chosen for further development. Quantitative methods to determine the content of the forms A, C and D in samples of form B or to determine the content of form A, B and D in form C have been developed by using X-ray diffraction. Limits of detection are 1 or 2%. For the quantitative determination of the amorphous fraction, X-ray diffraction and microcalorimetry are compared. For high amounts of the amorphous fraction, the X-ray diffraction method is preferred because it is faster. Microcalorimetry is very attractive for levels below 10% amorphous content. The lowest limit of detection is obtained by microcalorimetry, about 1%.

Temperature resolved X-ray diffraction as a tool of thermal analysis

Time and temperature resolved X-ray diffraction was used for thermal analysis. Series of diffraction patterns were measured, while the samples are heated/cooled stepwise or isothermally with freely selectable temperature programs.

Use of sub-ambient DSC to complement conventional DSC and TG

Several drug substances or excipients are hygroscopic. The uptake or loss of water of such substances is generally difficult to control during processing or storage of drug products. DSC instruments with sub-ambient temperature equipment allow the determination of the amount of freezable water by measuring the corresponding melting enthalpy. The determination of freezable water adds valuable information complementary to TG analysis for understanding the processing and storage of raw materials and drug products. Several substances were tested as is, without treatment, after storage at 92% r.h. and after equilibration with water. The results of these experiments showed that it was possible to demonstrate defined hydrate formation, to determine the upper level of binding of water in amorphous substances and to confirm reversible hydrate formations demonstrated by temperature resolved X-ray diffraction.

Study of the polymorphic behaviour of some local anesthetic drugs

The local anesthetic drug tetracaine hydrochloride is described in the Europ. Pharmacopea with a melting point of 148°C or with a range of 134 to 147°C due to the melting points of two other forms. The polymorphic behaviour of tetracaine hydrochloride has been studied by using thermal treatments, storage at 92% r.h., crystallizations and equilibrations with saturated solutions. Samples were characterized by X-ray diffraction, IR, thermal analysis and elemental analysis. Since some findings were difficult to interpret, temperature resolved X-ray diffraction was used additionally for the understanding of the thermal behaviour of tetracaine hydrochloride. In this study the polymorphic behaviour of some other local anesthetic drugs is compared.

Temperature Resolved X-Ray Diffraction of Ammonium Nitrate Evaluated with Rietveld Analysis

Temperature Resolved X-Ray Diffraction of Ammonium Nitrate Evaluated with Rietveld Analysis

Substitution of Co into the system YBaFeCuO5+δ

In the system of the oxygen deficient perovskite YBaFeCuO5+δ Co was substituted systematically for Cu or Fe. The powder X-ray diffraction pattern of the products revealed a linear change of the cell parameters with increasing fraction of substitution. Further investigations of physical and chemical properties were focused mainly on the sample with composition YBaFeCu0.4Co0.6O5+δ. The magnetic susceptibility of the semiconductive specimen revealed an antiferromagnetic transition at TN1 = 330 K, which can be correlated to a step of ca in temperature resolved X-ray diffraction, and a second minor effect of ordering at TN2 = 190 K. In addition, temperature dependent X-ray diffraction exhibited structural distortions at 413 and 633 K. The application of thermoanalysis demonstrated reversible thermochemical reactivity in different gas atmospheres.

Time and temperature resolved X-ray diffraction for studies of solid state reactions and phase transitions

Three examples for the application of time and temperature resolved X-ray diffraction for the investigation of solid state reactions and phase transitions are given. Samples were submitted to an isothermal temperature program or to stepwise heating/cooling, while diffraction patterns were measured continuously. The applications include the in situ identification of reaction products or phases, the determination of kinetic parameters, the observation of thermal expansion and the formation of layers.

Application of time and temperature resolved x-ray diffraction (TRXRD) to thermal analysis

The application of TRXRD for thermal analysis is demonstrated using examples of phase transitions, solid-state reactions and high-temperature corrosion. The measuring system produces a series of diffraction patterns, which are evaluated by a difference procedure that a reduces the data to curves comparable to DSC and TG curves and thus suited to kinetic evaluation.

Phase transitions of ammonium nitrate doped with alkali nitrates studied with fast X-ray diffraction

Dried samples of ammonium nitrate (AN) containing 1, 3, 5 mol% KNO3, RbNO3 and CsNO3 were investigated with temperature resolved X-ray diffraction. The samples were cycled with 2 temperature programs from −70° to 100° and −70° to 150°C, resp. DSC measurements were made for comparison.KNO3 extends the stability range of phase III. The supercooling observed with the transitions II/III and III/IV was so severe that the phases III and IV could be skipped leading to the transitions II/IV and III/V. No hindered nucleation was observed on heating.RbNO3 gives dried AN the properties of the humid nitrate. Phase III appeared on heating but was skipped on cooling, when the sample had been heated to 150°C. Hindered nucleation was observed.CsNO3 stabilizes the phases II and V. No strong hysteresis or supercooling was observed.

Non-isothermal kinetics of high temperature oxidation studied by a fast X-ray diffraction method

Temperature resolved X-ray diffraction using a diffractometer equipped with a high temperature device was applied to the study of the oxidation of Fe-ARMCO below 570°C. The oxidation products are identified in situ and the difference method yields curvesY(T) showing the global changes. These curves were calibrated to the microscopically measured end thickness of the oxide layer obtaining the growthx(T). A calculated curve including the Arrhenius relation was fitted to thex(T) curve yielding activation energy and values of the oxidation rate constant as a function of temperature.