Search

ABSTRACT Epsomite and hexahydrate occur in the form of efflorescence on the church walls made of pure calcium carbonate--tufa stone. A few sources of magnesium are responsible for the precipitation [...]

ABSTRACTThrough international placements, student occupational therapists (SOTs) provide direct services and consultation with communities, organisations and local governments. SOTs work with international partners to assess needs, develop new programs, and adopt new practices. SOTs support individuals and groups to build and sustain capacity in health, function and rehabilitation. However, more comprehensive preparation of SOTs for international involvement is required. The objectives of this paper are: (a) to develop recommendations for best practice for the educational preparation of globally bound SOTs; (b) to disseminate findings that reflect global and culturally sensitive perspectives; and (c) to provide recommendations that support engagement in international placement learning. The World Federation of Occupational Therapists (WFOT) assisted in connecting the investigators and participating countries. Data analyses outlined clear trends related to strengths and gaps in student preparation. Ongoing development of international clinical education resources and partnerships is needed to support dynamic and sustainable global learning in occupational therapy.

Evolution of the structural and magnetic properties of ZnFe1.95Yb0.05O4nanoparticles, prepared via a high-energy ball milling route and exposed to further thermal annealing/heating, was assessed in detail and correlation of these properties explored. While as-prepared spinel nanoparticles possess a high degree of inversion, heating of the sample to ∼500 °C is found to rapidly alter the cation distribution from mixed to normal, in agreement with the known cation preferences. Under the same conditions the crystallite size only slowly grows. By further thermal treatment at higher temperatures, the crystallite size is changed more appreciably. An interrelationship among the lattice parameter, octahedral site occupancy, and crystallite size has been established. The observations are (a) both the site occupancy of Fe3+at octahedral 16d spinel sites (N16d(Fe3+)) and the cubic lattice parameter rapidly increase with an initial increase of the crystallite size, (b) the lattice parameter increases with increasing occupancy, N16d(Fe3+), and (c) there appears to be a critical nanoparticle diameter (approximately 15 nm) above which both the site occupancy and lattice parameter values are saturated. The magnetic behavior of the annealed samples appears to be correlated to the evolution of both the cation distribution and crystallite size, as follows. As-prepared samples and those annealed at lower temperatures show superparamagnetic behavior at room temperature, presumably as a consequence of the Fe3+distribution and strong Fe3+(8a)–O–Fe3+(16d) superexchange interactions. Samples with a nanoparticle diameter greater than 12 nm and with almost normal distributions exhibit the paramagnetic state. The coercive field is found to decrease with an increase of the crystallite size. Partial Yb3+/Fe3+substitution is found to increase the inversion parameter and saturation magnetization. Detailed knowledge of the thermal evolution of structural/microstructural parameters allows control over the cation distribution and crystallite size and hence the magnetic properties of nanoferrites.

Single crystals of ammonium chromium(III) dioxalate dihydrate (or ammonium diaquo bis(μ‐oxalato)chromate(III)) have been obtained from aqueous solution of oxalic acid and ammonium dichromate. A pale violet crystal of good optical quality was used for the structure determination at −100(2) and 25(2) °C, respectively. The basic crystallographic data for the low temperature data set are as follows: monoclinic, space group C2/m, a = 6.597(2) Å, b = 7.301(2) Å, c = 9.983(3) Å, β = 92.32(2)°, V = 480.5(2) Å3. The structure was solved by direct methods and refined (using anisotropic displacement parameters for all non‐hydrogen atoms) to a final residual of R1 = 0.032 for 503 independent observed reflections (I>2σ(I)). The compound is isotypic with the corresponding rubidium salt. The structure is built up from alternating layers parallel to (001) containing (NH4)+ions or Cr(C2O4)2(H2O)2octahedra, respectively. The corners of the octahedra consist of four O atoms from two oxalate groups and two additional water molecules. The ammonium cations (occupying Wyckoff‐site 2a) are disordered among two possible orientations. They provide linkage between different octahedral layers by hydrogen bridging. The water molecules in turn form hydrogen bridges with adjacent octahedra within the same layer. Further structural characterization included infrared spectroscopy. According to DTA/TG experiments the present compound shows several thermal processes in the range between room temperature and 900 °C.

In this paper we present the results of the synthesis, crystal structure investigations and in situ X-ray diffraction studies of the order–disorder phase transition in cobalt substituted lithium titanate oxide spinels, Li1.33xCo2–2xTi1+0.67xO4 (0 ≤ x ≤ 1). Depending on the chemical composition the samples crystallize in two space groups (S.G.): $ \rm Fd\bar 3 m $ (0 ≤ x ≤ 0.40 and x = 1) and P4332 (0.50 ≤ x ≤ 0.875). Samples crystallizing in the S.G. P4332 are ordered spinels with a cation ordering of the 1–3 type at octahedral 4b and 12d sites. The cation ordering in octahedral sites is full in the sample with x = 0.75 (Li and Ti occupy 4b and 12d sites, respectively) and decreases for samples with higher/smaller x. Changes of the extinction conditions and nonlinearities in the concentration dependence of the lattice parameter in the regions 0.40 < x < 0.50 and 0.875 < x < 1 indicate changes of the crystal symmetry ($ \rm Fd\bar 3 m $  P4332). The partially ordered spinel x = 0.50 has a convergent, reversible, order–disorder phase transition at TC = (1083 ± 10) K. Samples with x = 0.875 and 0.75 have an order–disorder phase transition out of our experimental ranges with TC(x = 0.875) < 973 K and TC(x = 0.75) > 1173 K. The mechanism of the phase transition is based on cation migration.

For the protection against the side effects and the improvement of the pharmacological activity of nonsteroidal antiinflammatory drugs (NSAID's), one alternative way is to design a metal complex of these agents. In this context, we have investigated the electrostatic properties of the zinc−aspirinate dihydrate (Zn[C9H7O4]2(H2O)2) complex to characterize and to mimic the activity of this potent pharmaceutical compound. A high-resolution X-ray diffraction experiment at 100 K has been performed on the Zn[C9H7O4]2(H2O)2 complex which crystallizes in the C2/c space group displaying a tetrahedrally coordinated zinc atom. The Hansen−Coppens multipole model was used to derive the experimental electron density to study the chemical bonding and the metal−ligand charge transfer. The investigation of the electron density has revealed that only the Zn 4s orbital participates in the metal−ligand interaction whereas the metal 3d full valence shell remains unperturbated. The κ-model refinement yielded a zinc net charge of +1.3 e with a highly contracted 4s electronic shell. The most positive charge of the aspirinate ligand was found on the acetyl carbon (+0.8 e), in agreement with the previously observed nucleophilic attack on the aspirin drug in the inhibited cyclooxygenase (COX) enzyme channel. The electrostatic potential was calculated from the multipole populations and the net atomic charges derived from the X-ray diffraction data. This fundamental property was carefully analyzed through the 3D isopotential and molecular surface representations to highlight the active sites of the zinc−aspirinate complex.

The structure of stoichiometric celsian glass was investigated by ²⁹Si MAS NMR and IR spectroscopies and reverse Monte Carlo (RMC) simulation of X-ray diffraction data. The glass was prepared by thermally induced phase transformation of Ba²⁺-exchanged LTA (Linde Type A) zeolite, under annealing conditions prior to hexacelsian crystallization. NMR and IR measurements have shown that the local silicon–aluminium ordering of the starting zeolite framework, as well as the framework fragments in the form of deformed tetrahedral rings, is retained in the glass structure. Interatomic distances and mean coordination numbers were calculated from the three-dimensional RMC derived structure model. The local Ba²⁺ environment in the glass was compared with the corresponding crystalline polymorphs. Ba–O distances in the glass are longer than the distances in hexacelsian but the coordination number 12.00 and the increase in the Ba–T distance, compared to zeolite, indicate the establishment of hexacelsian-like coordination. Inspection of the three-dimensional RMC model of the glass showed a layered structure, with Ba²⁺ cations between the layers.

The application of pressure as a technique for obtaining dense and mechanically strengthen materials has been investigated from the structural aspect by the use of X‐Ray Powder Diffraction (XRPD) and Scanning Tunneling Microscopy (STM).

AbstractHigh-temperature investigations of thermal expansion, strain and microstructure of the α ↔ β-hexacelsian reversible phase transition are reported. HexacelsianLTA and hexa-celsianFAUwere synthesised from LTA and FAU zeolites, respectively. Only the former show discontinuities near the transition temperature, ∼ 580 K. The discontinuity in the thermal expansion near the transition temperature for the α ↔ β-hexacelsianLTAsuggest a co-elastic character for the phase transition. A distortion of the co-ordination polyhedra and ordering of framework cations induce this phase transition. The absence of discontinuities for hexacelsianpFAUsuggests non-existence of a phase transition. The similarities in the measured and calculated values for α-hexacelsianLTAand hexacelsianPAUsuggest that hexacelsianFAUcrystallise exclusively as the β-form.

Sm x Y 2− x O 3 solid solutions are semimagnetic semiconducting materials with wide energy gaps. Magnetic properties of these materials are coupled with their structural and microstructural parameters. Evidently, it is of interest to investigate these parameters in order to explain magnetic properties of diluted magnets. All mixed sesquioxides Sm x Y 2− x O 3 ( x = 0.2, 0.5, 0.7, 1.0, 1.4 and 1.7) crystallize in C-M 2 O 3 crystaltype in space group Ia3 with Y and Sm cations in 24(d) and 8(b) Wyckoff positions, respectively. The X-ray diffraction data were used to establish the distribution of magnetic ions over crystallographic positions 8(b) and 24(d). A random distribution was found. The same data were used for evaluation of the crystal size, microstrain and paracrystallinity. The concentration dependence of these values was concluded. Results show that unit cell parameters obey Vegard's rule. That fact leads to indirect information about well mixing of Y 2 O 3 and Sm 2 O 3 . Agreement of the unit cell parameters with Vegard's rule is connected with the difference between cationic radii and electronegativity. The Sm&z.sbnd;O&z.sbnd;Sm bond geometry, important for the superexchange interaction, strongly depends on Sm concentration. By comparing difference of unit cell parameters of the constitutive components Y 2 O 3 and Sm 2 O 3 and values of microstrains of their solid solutions it can be concluded that clusters are randomly formed.

Stoichiometric α-hexacelsian LTA and non-stoichiometric α-hexacelsian FAU phases were synthesized by the method of high-temperature induced transformation of Ba-exchanged LTA and FAU zeolites. The unit cell thermal expansion properties were followed using synchrotron X-ray Powder Diffraction (XRPD) data in the temperature range between 25°C and 700°C. Both samples exhibit normal thermal behavior with all unit cell axes expanding upon heating. The expansion properties of the unit cell volumes are similar in the temperature range between 25°C and 325°C. At 325°C the unit cell volume of the α-hexacelsian LTA phase increases. This is caused by structural inversion to the β-hexacelsian LTA phase. The thermal expansion of the unit cell of the α-hexacelsian FAU phase does not show any discontinuities. The distinct unit cell volume properties observed upon heating at 325/dgC, are consistent with results of DSC measurements of α-hexacelsian LTA and α-hexacelsian FAU samples. The crystal structures of the α- (at 25°C) and β-forms (at 362°C) of Si, Al ordered hexacelsian LTA and disordered hexacelsian FAU phases, were refined in the trigonal space group P-3 (147), from synchrotron XRPD data by the Rietveld method. These structures were refined with agreement factors: R wp = 6.19, R p = 4.29, R Bragg = 6.68 for α-hexacelsian LTA ; R wp = 5.11, R p = 3.53, R Bragg = 5.42 for α-hexacelsian FAU ; R twp = 7.002, R p =4.98, R Bragg = 6.68 for β-hexacelsian LTA ; and R wp = 5.05, R p = 3.58, R Bragg = 4.50 for β-hexacelsian FAU , respectively.

The thermal behavior of fully Sr-exchanged LTA- and FAU-framework zeolites was followed in the temperature range from ambient to 1500 °C. Both zeolite frameworks collapsed into amorphous intermediate substances after heating between 780 and 950 °C. Prolonged annealing of these products above 950 °C induces their recrystallization to ordered hexagonal SrAl2Si2O8, [a0 = 5.1970(2) Å, c0 = 15.200(1) Å] and disordered hexagonal Sr0.85▭0.15Al1.71Si2.29O8 [a0 = 5.2039(2) Å, c0 = 15.158(1) Å], diphyllosilicate phases, respectively. These phases are unstable under prolonged heating, and near 1100 °C, they can be polymorphously transformed into corresponding Sr-feldsparLTA [a0 = 8.358(2) Å, b0 = 12.941(3) Å, c0 = 7.114(1) Å, β = 115.26(2)°] and Sr-feldsparFAU [a0 = 8.354(2) Å, b0 = 12.957(3) Å, c0 = 7.128(2) Å, β = 115.27(2)°] phases, maintaining framework cation-ordering characteristics. The phase conversions in the temperature range investigated were followed by thermal (DTA, TGA, and DSC), XRPD, and SEM analyses. The structural mechanism for M1-xAl2-2xSi2+2xO8 (M = Ca, Sr, Ba, Pb) polymorphous transformation from diphyllosilicate to feldspar topology is discussed.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.