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PubMed2006

X-ray diffraction analysis of mineral trioxide aggregate and Portland cement.

AIM: To compare the major constituents present in ProRoot mineral trioxide aggregate (MTA), ProRoot MTA (tooth coloured formula), ordinary Portland cement and white Portland cement using powder X-ray diffractometery. METHODOLOGY: X-ray diffractometery of the four materials was carried out with the divergence and scatter slits set at 1 degree and the receiving slit at 0.10 mm. The scan range was set at 5-70 degrees and continuous scans for the theta-2theta range were run with a scan speed of 2 degrees min(-1). The patterns obtained were then compared with the Powder Diffraction Files (PDF) found in the International Centre for Diffraction Data database. The three strongest peaks were used for the identification of the constituents. The relative intensities were plotted against the angle 2theta and compared with the plots in the PDF. RESULTS: The main constituents were found to be tricalcium silicate, tricalcium aluminate, calcium silicate, and tetracalcium aluminoferrite in all the four cements with the additional presence of Bi2O3 in ProRoot MTA and ProRoot MTA (tooth coloured formula). CONCLUSIONS: The four cements had similar major constituents. Data on Portland cement may be used for the further development or modification of ProRoot MTA in order to improve its physical characteristics and expand its scope of clinical applications.

Aluminum Compounds↗
PubMed1998

Solid state characterization of spray-dried powders of recombinant human deoxyribonuclease (rhDNase).

rhDNase is a recombinant human protein approved as an aqueous solution for human use by inhalation. To study the feasibility of preparation of dry powders for inhalation, spray-dried powders of pure rhDNase and co-spray-dried mixtures of rhDNase with an excipient approved for inhalation products, lactose, were prepared. Both types of powders were initially amorphous. The lactose, however, was found to crystallize after exposure to a humid environment. The crystals in the powder were identified as the alpha-monohydrate polymorph of lactose by hot-stage optical and scanning electron microscopy, differential scanning calorimetry and thermogravimetry, FTIR spectroscopy, and X-ray powder diffraction. Moisture sorption isotherms indicated that crystallization occurred at high relative humidities (70-85%), depending on the temperature of the environment (5-40 degreesC). The practical implications for the manufacturing and storage of protein powders for inhalation are discussed.

Administration, Inhalation↗
PubMed2004

Role of the lattice in the gamma-->alpha phase transition of Ce: a high-pressure neutron and x-ray diffraction study.

The temperature and pressure dependence of the thermal displacements and lattice parameters were obtained across the gamma-->alpha phase transition of Ce using high-pressure, high-resolution neutron and synchrotron x-ray powder diffraction. The estimated vibrational entropy change per atom in the gamma-->alpha phase transition, DeltaS(gamma-alpha)(vib) approximately (0.75+/-0.15)k(B), is about half of the total entropy change. The bulk modulus follows a power-law pressure dependence that is well described using the framework of electron-phonon coupling. These results clearly demonstrate the importance of lattice vibrations, in addition to the spin and charge degrees of freedom, for a complete description of the gamma-->alpha phase transition in elemental Ce.

Journal Article↗
PubMed1997

Stabilization by Hydrogen. Synthetic and Structural Studies of the Zintl Phase Ba(5)Ga(6)H(2).

Synthesis of the phase formerly reported as Ba(5)Ga(6) succeeds only in the presence of hydrogen. The heavy atom structure of Ba(5)Ga(6)H(2) has been redetermined by single-crystal X-ray diffraction (trigonal P3c1, Z = 2, a = 7.7698(2) Å, c = 14.3902(7) Å), and the hydrogen positions have been elucidated by time-of-flight neutron powder diffraction. The unit cell contains isolated slightly distorted octahedra Ga(6)(8)(-) with barium cations over all edges. Hydride is bound in two types of barium tetrahedra [d(Ba-H) = 2.61-2.62 Å]. The stoichiometry is appropriate for a Zintl phase: (Ba(2+))(5)Ga(6)(8)(-)(H(-))(2).

Journal Article↗
PubMed1976

An X-ray diffraction investigation of age-related changes in the crystal structure of bone apatite.

Evidence relating to the existence of crystalline bone mineral in vivo is considered, and bone apatite crystal structure investigated using an x-ray powder diffraction technique. Specimens of femoral compacta excised post-mortem from male and female subjects ranging from 3 1/2 years to 87 years of age have been studied. Values of the ratio c/a of bone apatite crystal cell axes for females are significantly higher (p less than 0.05) than for males. Moreover, significant change of c/a with age is observed for males (p = 0.0005) but not for females (p = 0.30). Differences in c/a are interpreted as indicating substitution of constituent ions in the bone apatite crystals.

Adolescent↗
PubMed1999

The dissolution and complexing properties of ibuprofen and ketoprofen when mixed with N-methylglucamine.

The objectives of this study were to improve the aqueous dissolution properties of the poorly soluble nonsteroidal anti-inflammatory drugs ibuprofen and ketoprofen and to explore the use of N-methylglucamine (meglumine) to enhance the dissolution properties of poorly water-soluble drug powders. Changes in both differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) results indicate that possibly complexes were produced between ibuprofen and N-methylglucamine. Similar changes were not observed for equivalent ketoprofen and N-methylglucamine mixtures. The results of solubility and dissolution studies in water at 25 degrees C and 37 degrees C showed that N-methylglucamine, in mixtures and coprecipitates, increased the solubility, intrinsic dissolution, and powder dissolution of ketoprofen and ibuprofen. N-Methylglucamine significantly improved the solubility and dissolution properties of both ibuprofen and ketoprofen even when DSC and XRD behavior did not indicate the formation of complexes.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Formation of isomorphic desolvates: creating a molecular vacuum.

The objective of this work was to investigate a common but poorly understood category of crystalline organic substances: isomorphic desolvates. When solvent is lost from a crystal lattice but the lattice retains its three-dimensional order, a lattice is created which is in a high-energy state relative to the original solvate structure. The desolvated lattice can reduce its internal energy by either resorbing solvent or by relaxation processes which increase the packing efficiency of the solid by reducing the unit cell volume. In the following paper, solid-state properties of isomorphic desolvates of cephalexin, cefaclor, erythromycin A, and spirapril hydrochloride hydrates are investigated. The hygroscopicity of the compounds are evaluated using a vacuum moisture balance, and structural relaxation is measured using a combination of X-ray powder diffraction and isothermal microcalorimetry. The study results are explained in terms of Kitaigorodski's close packing principle.

Absorption↗
PubMed2005

Comparison of powder produced by evaporative precipitation into aqueous solution (EPAS) and spray freezing into liquid (SFL) technologies using novel Z-contrast STEM and complimentary techniques.

The objective of this study was to compare the properties of particles formed by nucleation and polymer stabilization (e.g. evaporative precipitation into aqueous solution (EPAS)) versus rapid freezing (e.g. spray freezing into liquid (SFL)). Powders formed by EPAS and SFL, composed of danazol and PVP K-15 in a 1:1 ratio, were characterized using X-ray powder diffraction, modulated differential scanning calorimetry (MDSC), contact angle determination, dissolution, scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), BET specific surface area, and Z-contrast scanning transmission electron microscopy (STEM). Large differences in particle morphologies and properties were observed and explained in terms of the particle formation mechanisms. Both techniques produced amorphous powders with high T(g) and low contact angle values. However, STEM analysis showed highly porous bicontinuous nanostructured 30nm particles connected by narrow bridges for SFL versus aggregated 500 nm primary particles for EPAS. The combination of STEM and other characterization techniques indicates solid solutions were formed for the SFL powders consistent with rapid freezing. In contrast, the EPAS particle cores are enriched in hydrophobic API and the outer surface is enriched in the hydrophilic polymer, with less miscibility than in the SFL powders. Consequently, dissolution rates are faster for the SFL particles, although both techniques enhanced dissolution rates of the API.

Algorithms↗
PubMed2004

Synthesis of nano-sized hydroxyapatite.

In this work, nanometer HA crystals have been synthesized via wet chemical precipitation and characterized. This research studies how key synthesis parameters affect the size and phase purity of the produced HA. Characterization work was carried out using X-ray powder diffraction method and scanning electron microscopy for phase identification and particle sizing, respectively.

Biocompatible Materials↗
PubMed2006

Surfactant-free hydrothermal synthesis of highly tetragonal barium titanate nanowires: a structural investigation.

Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), synchrotron X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM and SEM analyses show the uniform cylindrical nanowires. The Rietveld refinement with synchrotron X-ray powder diffraction showed that the lattice parameters of cubic and tetragonal phases were a (= b = c) = 4.0134 A and a (= b) = 3.9998 A, c = 4.0303 A, respectively. The final weighted R-factor, R(wp), was 6.75% and the goodness of fit indicator was 1.30. The mass fraction of tetragonal and cubic phases based on the refined scale factor for the two phases were 98.4% and 1.6%, respectively, which clearly show the nanowires are tetragonal. The XPS analysis has shown that as-obtained BaTiO3 nanowires were phase pure. The Raman spectra confirm the tetragonal phase of the BaTiO3 nanowires. The dielectric constant measurement shows the shift in the transition temperature (Tc = 105 degrees C) compared to the bulk transition temperature (Tc = 132 degrees C). The dielectric constant at Tc was 174 measured at 1 kHz frequency.

Journal Article↗
PubMed2006

High-pressure neutron diffraction study of L-serine-I and L-serine-II, and the structure of L-serine-III at 8.1 GPa.

The hydrostatic compression of L-serine-d(7) has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, yielding L-serine-II, and the second between 7.3 and 8.1 GPa, yielding L-serine-III. All three polymorphs are orthorhombic, P2(1)2(1)2(1), and feature chains of serine molecules connected via head-to-tail ND...O hydrogen bonds formed between ammonium and carboxylate groups. The chains are linked into a ribbon by a second set of ND...O hydrogen bonds. The hydroxyl moieties are distributed along the outer edges of the ribbon and in phase I they connect the ribbons into a layer by chains of OD...OD hydrogen bonds. The layers are connected together by a third set of ND...O hydrogen bonds, forming R;3_4(14) rings with substantial voids at their centres. In the transition from phase I to II these voids begin to close up, but at the cost of breaking the OD...OD chains. The OD...OD hydrogen bonds are replaced by shorter OD...O hydrogen bonds to carboxylate groups. At 7.3 GPa the O...O distance in the OD...O hydrogen bonds measures only 2.516 (17) A, which is short, and we propose that the phase transition to phase III that occurs between 7.3 and 8.1 GPa relieves the strain that has built up in this region of the structure. The hydroxyl D atom now bifurcates between the OD...O contact that had been present in phase II and a new OD...O contact formed to a carboxylate in another layer. Hirshfeld surface fingerprint plots show that D...D interactions become more numerous, while hydrogen bonds actually begin to lengthen in the transition from phase II to III.

Hydrogen Bonding↗
PubMed2003

The effect of spray drying solutions of bendroflumethiazide/polyethylene glycol on the physicochemical properties of the resultant materials.

The physicochemical properties of co-spray dried bendroflumethiazide (BFMT)/polyethylene glycol (PEG) 4000 composites were investigated. The co-spray dried composites produced from all BFMT/polymer solutions were amorphous. BFMT/PEG 4000 10 and 20% systems consisted of smooth spherical particles approximately 0.5-4mm in diameter. Spray drying resulted in no significant production of the main BFMT degradant, 5-trifluoromethyl-2,4-disulphamoylaniline (TFSA), and for composites consisting of 90% PEG 4000 by weight of total solids, spray drying appeared a superior method of production than the melt method which resulted in significant BFMT degradation. All BFMT/PEG compressed discs showed initial increased release of BFMT compared to discs of micronised BFMT alone, with the spray dried BFMT/PEG 4000 10% system showing initial rates two to three times that of BFMT alone. The physical stability of amorphous BFMT was reduced on inclusion of PEG 4000, recrystallisation occurring more quickly with increasing amount of PEG 4000 in the composites. PEG in the co-spray dried systems appeared to degrade on storage and recrystallised samples failed to show the presence of PEG by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) or GPC. DSC results were consistent with BFMT/PEG forming a eutectic combination rather than a monotectic system.

Bendroflumethiazide↗
PubMed2006

Effect of milling conditions on the solid-state conversion of ranitidine hydrochloride form 1.

Powder samples of ranitidine hydrochloride forms 1 and 2 were milled using a vibrational ball mill (Retsch MM301) for periods up to 240min at 4, 12 and 35 degrees C. X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) were used to monitor solid-state properties of the milled samples. Milling of form 1 at 4 degrees C led to a powder temperature of 36 degrees C in the milling chamber and produced only amorphous drug; at 12 degrees C (powder temperature 45 degrees C) and at 35 degrees C (powder temperature 62 degrees C) progressive transformation of form 1 via amorphous drug to form 2 occurred. DSC of the milled samples showed a glass transition at 13-30 degrees C and a crystallization exotherm (T(c)) between 30 and 65 degrees C if the sample contained amorphous drug. The behaviour of the solid was speculated to be influenced by the relationship between powder temperature and T(c); at powder temperatures below T(c), amorphous drug is formed but no crystallization of form 2 occurs; at temperatures close to T(c), amorphous content initially increases with transformation to form 2 on continued milling. At temperatures much higher than T(c), at intermediate stages, less amorphous drug but both form 1 and form 2 are recovered, but continued milling gives only form 2. Form 2 did not transform to form 1 under any conditions used in this study.

Calorimetry, Differential Scanning↗
PubMed2001

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites.

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100-300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P112(1) using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P2(1)3 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) A, gamma = 90.01 (1) degrees ]. A precise analysis of the BeF(4) tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K(2)Mn(2)(BeF(4))(3) and also of a new type of low-temperature structure for langbeinite compounds.

Journal Article↗
PubMed2003

Characterisation and deposition studies of engineered lactose crystals with potential for use as a carrier for aerosolised salbutamol sulfate from dry powder inhalers.

Lactose particles with different elongation ratio, roundness, polymorphic form and crystallinity were prepared by a one-step crystallisation process using varying ratios of acetone/water. The crystals were characterised using image analysis optical microscopy, scanning electron microscopy, differential scanning calorimetry and X-ray powder diffraction. The elongation ratio was found to increase with increasing acetone ratio which therefore, appears to accelerate the growth in length rather than width and/or thickness. The crystallinity and polymorphic forms were also acetone-concentration dependent. For example, the crystals formed using 65-80% v/v acetone were almost all of the alpha-form whereas at 85% v/v a small amount of beta-form was precipitated, as detected by a peak at the reflection angle 2 theta=10.4 in the X-ray diffractogram. When 90% v/v acetone was incorporated a mixture of alpha- and beta-forms were produced in almost equal quantity, whereas, with 95% v/v acetone the beta-form predominated. At high acetone concentration (90 and 95% v/v), the crystallisation proceeded rapidly leading to the creation of some amorphous content. The 63-90-microm sieve cut of either commercial grade lactose (CL) or crystallised lactose was mixed with salbutamol sulfate and dispersibility was determined using the twin stage liquid impinger. All the formulations containing carrier particles generated by crystallization from solvent showed higher dispersibility and fine particle fraction (FPF) of the drug compared to the formulation made containing CL. The carrier that showed the highest elongation ratio (produced from an 85% acetone 15% water solution), when mixed with salbutamol sulfate produced the highest dispersibility (38.5%) and highest FPF (29.24%). These parameters were six times higher than the values obtained with the formulation containing CL.

Acetone↗
PubMed1997

Compressibility, Phase Transitions, and Oxygen Migration in Zirconium Tungstate, ZrW2O8

In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin. The relative thermal expansion and compressibilities of the cubic and orthorhombic forms can be explained in terms of the "cross-bracing" between polyhedra that occurs as a result of the phase transition.

Journal Article↗
PubMed1994

Crystal structures of synthetic 7 angstrom and 10 angstrom manganates substituted by mono- and divalent cations.

The crystal structures of synthetic 7 angstrom and 10 angstrom manganates, synthetic birnessite and buserite, substituted by mono- and divalent cations were investigated by X-ray and electron diffractions. The monoclinic unit cell parameters of the subcell of lithium 7 angstrom manganate, which is one of the best ordered manganates, were obtained by computing the X-ray powder diffraction data: a = 5.152 angstroms, b = 2.845 angstroms, c = 7.196 angstroms, beta = 103.08 degrees. On the basis of the indices obtained by computing the X-ray diffraction data of Li 7 angstrom manganate, monovalent Na, K and Cs and divalent Be, Sr and Ba 7 angstrom manganates were interpreted as the same monoclinic structure with beta = 100-103 degrees as that of Li 7 angstrom manganate, from their X-ray diffraction data. In addition, divalent Mg, Ca and Ni 10 angstrom manganates were also interpreted as the same monoclinic crystal system with beta=90-94 degrees. The unit cell parameters, especially a, c and beta change possibly with the type of substituent cation probably because of the different ionic radius, hydration energy and molar ratio of substituent cation to manganese. However, these diffraction data, except for those of Sr and Ba 7 angstrom and Ca and Ni 10 angstrom manganates, reveal only some parts of the host manganese structure with the edge-shared [MnO6] octahedral layer. On the other hand, one of the superlattice reflections observed in the electron diffractions was found in the X-ray diffraction lines for heavier divalent cations Sr and Ba 7 angstrom and Ca and Ni 10 angtrom manganates. The reflection presumably results from the substituent cation position in the interlayer which is associated with the vacancies in the edge-shared [MnO6] layer and indicates that the essential vacancies are linearly arranged parallel to the b-axis. Furthermore, the characteristic superlattice reflection patterns for several cations, Li, Mg, Ca, Sr, Ba and Ni, manganates were interpreted that the substituent cations are regularly distributed in the interlayer according to the exchange percentage of substituent cation to Na+. In contrast, the streaking in the a-direction observed strongly in the electron diffractions for heavier monovalent cations, K and Cs, manganates probably results from the disordering of their cations in the a-direction in the interlayer.

Cations↗
PubMed2001

Ordering of nitrogen in nickel nitride Ni(3)N determined by neutron diffraction.

The metallic interstitial nitride Ni(3)N was prepared from Ni(NH(3))(6)Cl(2) and NaNH(2) in supercritical ammonia (p(NH(3)) approximately 2 kbar) at 523 K. Its previously reported crystal structure, as determined from X-ray powder data, was confirmed by neutron powder diffraction: Ni(3)N crystallizes in the hexagonal epsilon-Fe(3)N-type structure (P6(3)22, Z = 2, a = 4.6224 A and c = 4.3059 A at room temperature). The N atoms on the octahedral sites of an hcp arrangement of Ni show virtually complete occupational order at ambient temperatures, which is preserved up to its thermal decomposition at T approximately 600 K. This behavior is in marked contrast to that of the isotypic iron nitride, epsilon-Fe(3)N, which shows reversible partial disordering within the same range of temperatures. Possible reasons for the different behaviors of the two nitrides epsilon-Fe(3)N and Ni(3)N are discussed.

Journal Article↗