Increase In Lattice Strain Research Articles

Effects of crystallization in the presence of the opposite enantiomer on the crystal properties of (ss)-( + )-pseudoephedrinium salicylate

Previous work ( Int. J. Pharm., 94 (1993) 171–179) with (RS)-(-)-ephedrinium 2-naphthalenesulfonate, which forms a racemic compound with its opposite enantiomer, has shown that crystallization of the homochiral crystal (host) from aqueous solution containing traces of the opposite enantiomer (guest) leads to uptake of the guest with significant changes in various thermodynamic properties, including an increase in the intrinsic dissolution rate (IDR), perhaps through lattice disruption. The present work tests this possibility with a different but related chiral drug, (SS)-( + )-pseudoephedrinium salicylate, which forms a racemic conglomerate, instead of a racemic compound, with its opposite enantiomer. Increasing concentrations of the guest in the aqueous crystallization solution led to its increasing incorporation into the host crystals, corresponding to a segregation coefficient of 0.24. With increasing mole fraction, x 2, of the guest in the crystals, the IDR of the compacts increased to a maximum (12% increase at x 2 = 0.0076) and then decreased. Meanwhile, with increasing x 2, the enthalpy of fusion, ΔH f, entropy of fusion, ΔS f, and enthalpy of solution, ΔH s, decreased to minima (4–5% decreases at x 2 = 0.0028), suggesting disruption of the crystal lattice of the host and an increase in lattice strain, and then increased, suggesting a release of lattice strain. The water content (0.006 mole fraction) and melting point (405.2 ± 1.2 K) were not significantly affected. The change in the free energy of solution, estimated from the IDR, was approximately linearly related to the calorimetric ΔH s, suggesting enthalpy-entropy compensation. ΔS f and ΔS s decreased linearly with increasing ideal entropy of mixing, corresponding to values of 24.7 and 21.4, respectively, for the ‘disruption index’ ( Int. J. Pharm., 25 (1985) 57–72, 28 (1986) 103–112). These relatively high values indicate significant disruption of the crystal lattice of the host, suggesting potentiation of crystal defects by the incorporated guest.

Mechanically induced structural and magnetic changes in the GdAl2 Laves phase.

Changes of the structure and magnetic behavior of the ${\mathrm{GdAl}}_{2}$ Laves phase by high-energy ball milling were followed by x-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The starting compound crystallizes in the cubic ${\mathrm{MgCu}}_{2}$ structure and is a ferromagnet at lower temperatures with a Curie temperature of about 170 K. Upon mechanical milling, the ordered ${\mathrm{GdAl}}_{2}$ compound is found to become atomically disordered nanocrystalline material. Atomic disorder in ${\mathrm{GdAl}}_{2}$ is evidenced by the disappearance of a number of x-ray diffraction peaks, the decrease of lattice parameter, the increase of lattice strain, and the drastic changes of high-field magnetization curve at 4.2 K and of the nature of magnetic ordering upon milling. On the basis of experimental observations, a special type of atomic disorder namely quadruple-defect disorder is suggested. A constant average-crystallite size of about 21 nm is found after relatively short periods of milling. The material remains in the same crystalline structure as the starting compound even after prolonged periods of milling. While the Curie temperature of ${\mathrm{GdAl}}_{2}$ is slightly decreased by milling, another magnetic phase is detected with a magnetic ordering temperature of about 45 K during the intermediate stage of milling. This magnetic phase has been proved to be a spin-glass phase [Zhou and Bakker, Phys. Rev. Lett. 73, 344 (1994)]. With increasing milling time, both the fraction of the spin-glass phase and its freezing temperature ${\mathit{T}}_{\mathit{f}}$ increase, while the amount of ferromagnetic phase decreases. After long-period milling the original ferromagnetic phase disappears and the material completely becomes the spin-glass phase with a final ${\mathit{T}}_{\mathit{f}}$ of 65 K. Therefore, by mechanical milling well-defined nanocrystalline spin glass is created. The appearance of this spin-glass phase is due to accumulation of quadruple-defect disordering in the lattice of the ${\mathrm{GdAl}}_{2}$ Laves phase. The importance of using magnetic measurements as a structural probe is emphasized.

Ball milling of ductile metals

Pure copper powder was employed to study the effects of ball milling on the development of the structure and properties of ductile metals. The results indicate that larger spheres with diameters of about 2–2.5 mm are created after 20 h of ball milling. The formation of such spheres is mainly due to sphere-to-flake or sphere-to-sphere welding. This welding is not complete, leaving large pores and curved voids in the spheres. The average grain size of such spheres in 10–100 nm. The increase in lattice strain is about 0.2%. The microhardness increases from 45 MPa (unmilled) to 220 MPa (milled for 20 h). High-resolution transmission electron microscopy (HRTEM) investigations show the following: (a) the deformation of hall-milled copper proceeds by [112](111) twinning or high-order twinning: (b) the [112](111) twins are thickned by passage of (a/6)[112] twinning partial dislocations; (c) subgrains tend to form in the twins. In addition to twinning, dislocation slip plays an important role in the deformation process; the mobility of 60° dislocations and their pile-up in the crystals can lead to the formation of subgrains. Crystal refinement leads to an increase in the number of grain boundaries; both low-angle and high-angle grain boundaries with local strain and a high density of dislocations are observed. The estimated mean dislocation density is more than 1014 m−2, which is hardly even reached in plastically deformed metals. The different kinds of structural defects which exists in the grain boundaries and within the crystals may result in increased strength and microhardness, increased free energy and changes in other properties of ball-milled materials.

Study of the surface layer of lead titanate thin film by x-ray diffraction

Lead titanate ferroelectric thin films are prepared by a modified sol-gel process and the differences between the surface and bulk structure are studied. It is experimentally investigated with glancing angle x-ray diffraction (GAXRD) that the lattice constants of the surface layer of lead titanate thin film are differing from those of the inner part, crystallite size and lattice strain increase towards the substrate.

Anomalous X-Ray Diffuse Scattering in a Fe–Pd Invar Alloy

Measurements of X-ray diffuse scattering have been made on a disordered Fe-34.2 at% Pd Invar alloy in a temperature range from 18 K to room temperature, where no abnormal change in lattice parameters other than the Invar effect has been observed and the fcc state has been reported to be preserved. Strong diffuse scatterings were observed at the lower temperatures in the plane perpendicular to the a axis around the 200 lattice point. This result indicates an increase in lattice strain induced by a shear stress with decreasing temperature, suggesting the existence of a very early stage of the premartensitic transformation.

Mechanochemical effects for some Al2O3 powders of dry grinding

Three kinds of Al2O3 powders, i.e. two kinds of low-soda Al2O3 with average particle sizes of 3.9 and 0.6 μm and an electrofused Al2O3 with an average particle size of 21.8 μm, were ground for up to 300 h in a dry vibration ball mill. Variations in particle-size distribution, specific surface area, crystallite size, lattice strain, effective temperature factor and lattice constant were examined against milling time. The mechanism of grinding was found to differ between low-soda Al2O3 and electrofused Al2O3. The mechanochemical effects on these Al2O3 powders occurred in the order decrease of crystallite size → increase of effective temperature factor → increase of lattice strain. The length of the a-axis was clearly increased by a prolonged grinding. The difference in the ground state of three specimens was attributed to differences in the physical state of particles originating from the preparation methods, and also to particle size.

Strain variation in the {100} growth sectors of potash alum single crystals and its relationship to growth rate dispersion

X-ray topographic studies of growth sector geometry in {110} sections of large potash alum crystals confirm the occurrence of growth rate dispersion of the {100} growth fronts. Contrary to previous speculations that this variation arises as a consequence of the refraction of screw dislocations in and out of these sectors we show that the dispersion occurs even in the absence of this effect and despite the presence of continuously propagating edge dislocations in the sectors. Strain mapping using double crystal diffractometry yields a strong correlation between increase of lattice strain along the sector and cessation of growth. This leads to the speculation that the potential cause of the growth rate dispersion is the absorption of undetectable amounts of impurities at the growth interface to generate the observed strain which in turn influences the growth rate (or vice versa). This speculation is in agreement with other observations of the influence of lattice strain on crystal growth.

Quartz in Pottery Stones from Various Localities and Its Cristobalitization

Some characteristics of quartz in pottery stones from various localities and its cristobalitization by firing have been examined by various methods. Specimens were prepared from the pottery stones by crushing, classifying to 10-37μm, and purifying by hot phosphoric acid and fluoric acid. Substitution of Al ion in quartz was confirmed from ESR and EPMA analyses. With the increase in the amount of Al2O3 substitution in quartz, following correlations were observed: (1) increase of unit cell volume, (2) increase of lattice strain, (3) lowering of α-β inversion temperature. Some specimens were found to be mixtures of quartz substituting different amounts of Al2O3. Cristobalitization from quartz in the pottery stones by firing was found to be correlated with the amount of Al2O3 substituted in quartz and a temperature at which quartz convert to cristobalite was lowered with the increase in the amount of substituted Al2O3. Larger amount of cristobalite was formed from the pottery stones with increasing the amount of Al2O3 substituted in quartz and with decreasing the amount of flux components in the pottery stones.

Modification of adipic acid crystals. II. Influence of growth in the presence of oleic acid on crystal properties

Adipic acid (AA) was crystallized under defined conditions from water containing 0–110 μmol · dm −3 oleic acid (OA). With increasing concentration of OA, the water content of the crystals was constant (0.047 ± 0.005 mole fraction), while the uptake of OA increased linearly, and the dissolution rate (DR) and specific surface area (SSA) of a defined sieve fraction decreased. The decrease in DR exceeded the decrease in SSA. Washing the crystals with chloroform removed an appreciable proportion of the poorly water-soluble OA from the surface of the crystals and produced a marked increase in DR. OA at 15 μmol · dm −3 caused a doubling of DR, whereas higher concentrations reduced DR of the washed crystals to the original value. Increasing incorporation of OA into the AA crystals reduced their density, indicating a decrease in crystallinity. Increasing incorporation of OA also reduced the melting point, T m, the enthalpy of fusion, ΔH f, and the enthalpy of solution, ΔH s, of the crystals, indicating an increase in energy of the crystalline bulk, corresponding to an increase of lattice strain. Higher concentrations of OA reversed the energetic effects. The reduction in the entropy of fusion by small amounts of OA was greater than the increase in the sum of the ideal partial molar entropies of the components of the crystals by a factor approaching 1000. This indicates that OA greatly disrupts the order of the crystal lattice of AA.

振動ボールミル粉砕による窒化ケイ素表面の活性化

Silicon nitride powders of α- and β-types were activated by vibration ball milling, and the mechanochemical activation has been investigated by means of X-ray diffractometry and calorimetry. The specific surface area of two types of ground Si3N4 powders increased monotonically with the increase of grinding time. The fine grinding promoted the fragmentation of crystallites and an increase of lattice strain particularly in β-type. The surface energy of ground Si3N4 powders increased remarkably.

X-Ray Investigation on Fatigue Fracture of Notched Steel Specimen : Observation of Fatigue Phenomena of Annealed Low-Carbon Steel by X-Ray Microbeam Technique

It was successful to apply the X-ray microbeam technique for observing fatigue phenomena of annealed low-carbon steel. The following conclusions were obtained : (1) Misorientation and lattice strain increase quickly in the early period of fatigue process, and subsequently they continue to increase till initiation of a crack. Formation of subgrains proceeds relatively slowly in the early period, and it becomes thereafter a main process of fatigue. Formation of subgrains is not observed for fatigue below fatigue limit. (2) Density of excess dislocation of one sign in subboundaries for fatigue is much smaller than those for uniaxial tension and rolling. (3) It is considered that the reason why the half-value breadth increases during fatigue is not the formation of subgrains but is mainly the increase of lattice strain. (4) Schematic diagram of deformation in a grain for fatigue is suggested. The formation of subgrains is closely related to fatigue fracture.