J. Neubauer

Synthesis and structural characterization of strontium- and magnesium-co-substituted β-tricalcium phosphate

The synthesis of five different Sr(2+)- and Mg(2+)-co-substituted beta-tricalcium phosphate (beta-TCP) has been obtained by heating the calcium-deficient apatites above 800 degrees C. With the investigated concentrations of Sr(2+) and Mg(2+) from the present study, no additional phases other than beta-TCP have been detected. The synthesized powders have been characterized by X-ray diffraction, Fourier transform infrared spectrometry, elemental analysis and Rietveld refinement studies. The co-substitution of Sr(2+) and Mg(2+) in the beta-TCP has resulted in the formation of crystalline beta-TCP at hexagonal setting (space group R3c). The reduction of lattice a- and c-axis parameters with the combined substitution of Sr(2+) and Mg(2+) in the beta-TCP has been found evident from the present results. Sr(2+) has been found occupying the Ca(1,2,3,4) sites and Mg(2+) was found at the sixfold coordinated Ca(5) site of beta-TCP structure.

Newly developed Sr-substituted α-TCP bone cements

New bone cements made of Sr-substituted brushite-forming alpha-tricalcium phosphate (alpha-TCP) were prepared and characterized in the present work. The quantitative phase analysis and structural refinement of the starting powders and of hardened cements were performed by X-ray powder diffraction and the Rietveld refinement technique. Isothermal calorimetry along with setting time analysis allowed a precise tracing of the setting process of the pastes. The pastes showed exothermic reactions within the first 10-15 min after mixing and further release of heat after about 1h. An apatitic phase formed upon immersion of the hardened cements in simulated body fluid for 15 and 30 days due to the conversion of brushite into apatite confirming their in vitro mineralization capability. The compressive strength of the wet cement specimens decreased with increasing curing time, being higher in the case of Sr-substituted CPC. The results suggest that the newly developed Sr-substituted brushite-forming alpha-TCP cements show promise for uses in orthopaedic and trauma surgery such as in filling bone defects.

QUANTITATIVE IN-SITU X-RAY DIFFRACTION ANALYSIS OF EARLY HYDRATION OF PORTLAND CEMENT AT DEFINED TEMPERATURES

Investigation into the early hydration of Portland cement was performed by in-situ X-ray diffraction (XRD). Technical white cement was used for the XRD analysis on a D5000 diffractometer (Siemens). All diffraction patterns of the in-situ measurement which were recorded up to 22 hours of hydration at defined temperatures were analyzed by Rietveld refinement. The resulting phase composition was transformed with respect to free water and C-SH leading to the total composition of the cement paste. The hydration reactions can be observed by dissolution of clinker phases as well as by the formation of the hydrate phases ettringite and portlandite. With increasing temperatures the reactions proceed faster. The formation of ettringite is directly influenced by the rate of dissolution of anhydrite and tricalcium aluminate (C 3A). The beginning of the main period of hydration is marked by the start of portlandite formation. The experiments point out that a quantitative phase analysis of the cement hydration is feasible with standard lab diffractometers.

In Vitro performance assessment of new brushite-forming Zn- and ZnSr-substituted β-TCP bone cements

The present study investigated the in vitro performance of brushite-forming Zn- and ZnSr-substituted beta-TCP bone cements in terms of wet mechanical strength and biological response. Quantitative phase analysis and structural refinement of the powdered samples were performed by X-ray powder diffraction and Rietveld refinement technique. Initial and final setting times of the cement pastes, measured using Gilmore needles technique, showed that ZnSrCPC sets faster than ZnCPC. The measured values of the wet strength after 48 h of immersion in PBS solution at 37 degrees C showed that ZnSrCPC cements are stronger than ZnCPC cements. Human osteosarcoma-derived MG63 cell line proved the nontoxicity of the cement powders, using the resazurin metabolic assay.

Rietveld structure and in vitro analysis on the influence of magnesium in biphasic (hydroxyapatite and β-tricalcium phosphate) mixtures

The structure of two different Mg-substituted biphasic (HAP and beta-TCP) mixtures along with the biphasic mixtures without substituted Mg(2+) was investigated using Rietveld refinement technique. The substituted Mg(2+) was found in the beta-TCP phase and its influence on the composition has led to an increase in HAP content of Mg-containing biphasic mixtures when compared with the HAP content detected in pure biphasic mixtures. The refined structural parameters of Ca(10)(PO(4))(6)(OH)(2) and beta-Ca(3)(PO(4))(2) confirmed that all the investigated compositions have crystallized in the corresponding hexagonal (space group P6(3)/m) and rhombohedral (space group R3c) structures. The substitution of lower sized magnesium was found preferentially incorporated at the sixfold-coordinated Ca (5) site of beta-TCP, which is due to the strong Ca (5).O interaction among all the five different Ca sites of beta-Ca(3)(PO(4))(2). The in vitro tests using primary culture of osteoblasts showed that all the tested samples are biocompatible and promising materials for in vivo studies.

Alinite — Chemical composition, solid solution and hydration behaviour

Abstract The chemical composition of alinite was investigated in the system CaO SiO2Al2O3MgOCaCl2. Solid solution was observed. The formula should be written as Ca10Mg1−x/2□x/2[(SiO4)3+x(AlO4)1−x/O2Cl] with 0.35 alinite + H 2 O → C 3 A · CaY 2 ·10 H 2 O + Ca(OH) 2 + CSH(Cl?)-gel ⇒ Y = Cl − , OH − , 1 2 CO 3 2− .

A generalized geometric approach to anisotropic peak broadening due to domain morphology

This article reports the derivation of a physically based geometric description of the mean diameter of orthogonal shapes and provides an efficient formalism to relate these to reciprocal lattices and corresponding apparent crystallite sizes. The following descriptions provide a reasonable approximation for the simulation and refinement of anisotropic domain morphology in powder diffraction techniques.

Investigations on introducing Si and Mg into Brownmillerite : A Rietveld refinement

Abstract Brownmillerite (commonly C 4 AF) was synthesized in a laboratory furnace. The product was examined by X-ray powder diffraction and the structure was refined by the Rietveld method. Further syntheses were made under various conditions by substituting Fe 2 O 3 by MgO + SiO 2 according to the formula C 4 AF 1−x M x S x . All samples were examined by X-ray diffraction and quantified by Rietveld method due to their content of Brownmillerite, C 2 S and MgO. All results show that the whole SiO 2 content could be calculated as C 2 S. MgO could be partially found as periclase. Brownmillerite shows a shift of lattice parameters according to the solid solution series C 6 A 2 F − C 2 F.

Domain size anisotropy in the double-Voigt approach: an extended model

An efficient geometric approach to refine anisotropic domain morphology in the double-Voigt approach based on the variance-slope apparent crystallite size was recently described. In this way, the Lorentzian part of the Voigt size contribution can be directly linked to an effective area- or surface-weighted morphology. The size contribution in the Voigt approach is, however, rarely pure Lorentzian. In this article, the previously considered models are extended for the Gaussian part of the size broadening, also taking into account size distributions. The limits of the validity of the Voigt approach are also discussed.

A CHAETETID SPONGE ASSEMBLAGE FROM THE DESMOINESIAN (UPPER MOSCOVIAN) BUCKHORN ASPHALT QUARRY LAGERSTÄTTE IN OKLAHOMA, USA

The first detailed study on chaetetids from the Buckhorn Asphalt Quarry Lagerstatte is presented. Among the investigated specimens we found two samples (chaetetid specimens 2 and 6) that are different from all others in the quarry. Thin sections of these display a complex fragmentation of these Buckhorn chaetetids. Additionally, one of these samples contains two chaetetid morphotypes growing side by side, thus, in the same paleoenvironment. These specimens differ in their mode of growth (laminar and domical), which suggests that chaetetid growth was most likely influenced by genetic factors rather than by the paleoenvironment. We observed a feature, not hitherto reported as far as we are aware, on the surface of chaetetids; namely a regular clustering of seven tubules surrounding a central tubule. This feature could have had an exhalant function. Mineralogical analyses of the skeleton indicate primary high magnesian-calcite mineralogy, which is in accordance with reports in the literature. Cements precipitated during diagenesis are either calcite or dolomite and, where associated with microbial mats, they may contain a distinct amount of manganese. The comparison of the chaetetid skeletons from the Buckhorn Asphalt Quarry leads to the impression, that they represent various morphotypes or even species. Because of the lack of unique features, we have refrained however, from describing new species.