Frank Brink

Chemical Differences Between White and Gray Mineral Trioxide Aggregate

The purpose of this research was to determine and compare the composition of white mineral trioxide aggregate and gray mineral trioxide aggregate. Electron probe microanalysis results indicated that lime (CaO), silica (SiO2), and bismuth oxide (Bi2O3) were the dominant compounds in each case and were present at comparable levels in either of the types of mineral trioxide aggregate analyzed. It was concluded that the most significant differences observed were between the measured concentrations of Al2O3 (+122%), MgO (+130%), and especially FeO (+1000%) when gray mineral trioxide aggregate was compared with white mineral trioxide aggregate.

Comparison of Mineral Trioxide Aggregate's Composition with Portland Cements and a New Endodontic Cement

The aim of this study was to compare the compositions of mineral trioxide aggregates (MTAs), Portland cements (PCs), and a new endodontic cement (NEC). Our study also investigated the surface characteristics of MTA and NEC root-end fillings when immersed in normal saline. For part I, we prepared samples of 9 brands of MTAs, PCs, and NEC. The materials were imaged and analyzed by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA). In part II, 3-mm-deep root-end preparations were filled with MTA or NEC and stored in normal saline for 1 week. Samples were imaged and analyzed by SEM and electron probe microanalysis (EPMA). EDXA investigations revealed differences in the dominant compounds of NEC, PCs, and MTAs. The major components of MTA and PC are the same except for bismuth. The most significant difference was the presence of higher concentrations of Fe (minor element) in gray MTA and PC when compared with white ones. EPMA results revealed remarkably different elements in MTA compared with surrounding dentin, whereas in the NEC group the distribution patterns of calcium, phosphorous, and oxygen were comparable. NEC differs chemically from MTAs and PCs and demonstrates comparable surface composition with adjacent dentin as a root-end filling material.

The chiral structure of porous chitin within the wing-scales of Callophrys rubi

The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4₁32, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable example of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid-protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.

Ferroelectric and non-linear dielectric characteristics of Bi0.5Na0.5TiO3 thin films deposited via a metallorganic decomposition process

J.X. acknowledges financial support from the Department of Education, Science and Training DEST in the form of an Endeavor Australian Research Fellowship Award. J.X., Y.L., and R.L.W. acknowledge financial support from the Australian Research Council ARC in the form of ARC Discovery Grants.

Cryo-scanning electron microscopy (CSEM) in the advancement of functional plant biology: energy dispersive X-ray microanalysis (CEDX) applications.

The capacity to make measurements of elemental concentrations at the level of single cells by energy dispersive X-ray microanalysis of cryo-fixed, inherently-hydrated plant parts (CEDX) is changing or extending our understanding of many plant functions. We include in this review a wide-ranging catalogue of studies that have used CEDX which provides access to the literature on elements measured, plants and tissues studied, techniques used, level of quantitation and the significant findings. These findings include new perspectives on the following areas: salt tolerance; xylem maturation and solute content, root pressure and embolism refilling; the contents of intercellular spaces; sequestration of toxic elements; biomineralisation with silicon; movement of tracer homologues of native cations; indirect localisation of molecules with a distinctive element component; transfer of nutrients from vesicular-arbuscular (VA) mycorrhizas; the role of mucilages in protection and in generating mechanical force. In an Appendix we discuss the procedures involved in CEDX: cryo-fixation, specimen planing, etching, elemental quantitation and mapping. Limitations on sample numbers, elements measurable, spatial resolution, sensitivity and threshold concentrations quantifiable are outlined. A brief discussion of the potential of emerging technologies for cell-specific analysis of cryo-fixed, hydrated specimens is included. In the Accessory Publication we list our standard protocol for CEDX.

Oxygen/fluorine ordering, structured diffuse scattering and the local crystal chemistry of K3MoO3F3

Abstract Bond valence sum calculations are used to investigate the crystal chemistry of the elpasolite-related oxyfluoride K3MoO3F3 in order to obtain insight into the type/s of structural distortion (away from an ideal, high symmetry, elpasolite type parent structure) responsible for a characteristic, highly structured, three-dimensional diffuse intensity distribution. The first required type of local structural distortion corresponds to large amplitude MoO3F3 octahedral rotations while the second is associated with O/F ordering and associated induced Mo ion shifts. Monte Carlo modelling is used to show how the latter when coupled with an appropriate local crystal chemical constraint can give rise to the observed structured diffuse scattering. The study is part of a wider search for diffraction evidence of oxygen/fluorine ordering in metal oxyfluoride systems.

A combined diffraction (XRD, electron and neutron) and electrical study of Na3MoO3F3

Abstract Na3MoO3F3, a member of the A2BMVIO3F3 family of elpasolite-related oxyfluorides, has been prepared by the reaction of NaF with MoO3 at 650°C. It is shown by a combined X-ray, electron and neutron diffraction study, that the true symmetry of Na3MoO3F3 is not monoclinic (pseudo-orthorhombic) as previously reported but instead triclinic (metrically rhombohedral) P1. The superstructure unit cell is given by a=−aR+bR, b=cR, c=(aR+bR+cR), when expressed with respect to the underlying rhombohedral parent structure. Neutron diffraction refinement of the rhombohedral sub-structure shows O and F to be fully ordered with alternate (111)R planes being occupied by O and then F. The nature of the distortion away from the high temperature Fm 3 m parent structure is consistent with a combination of φφφ type rotations of the octahedral framework together with ppp type displacements of the octahedral cations, which is not observed in any of the closely related A2BMVIO3F3 family members. Bond valence arguments are used to give a plausible explanation for this difference in behavior.

Synthesis, electron diffraction, XRD and DSC study of the new elpasolite-related oxyfluoride, Tl3MoO3F3

Abstract Tl3MoO3F3, a previously unreported member of the A2BMVIO3F3 family of elpasolite-related oxyfluorides, has been prepared by the reaction of TlF with MoO3 at 655°C. DSC shows two major polymorphic phase transitions at 42°C and 130°C, respectively. Electron diffraction and XRD studies of the complex room temperature polymorphic form of this material indicate that the spacegroup symmetry is monoclinic P1a1 with a superstructure unit cell given by a =3 a p + c p , b =3 b p , c = 1 2 (− a p +3 c p ) , when expressed with respect to the underlying ideal elpasolite-type parent structure. This superstructure, while related, is not isomorphous to that recently reported for K3MoO3F3. The existence of a shared subset of strong G p ±J/5[204] p * type satellite reflections suggests the existence of a common intermediate superstructure. A highly structured, three-dimensional continuous diffuse intensity distribution is observed in Tl3MoO3F3 and Rb2KMoO3F3. This suggests that a particular pattern of local O/F ordering and associated Mo ion shifts, recently shown to be responsible for the existence of this diffuse distribution in the case of K3MoO3F3, may be common to the entire family of elpasolite-related A2BMVIO3F3 compounds.

Hydrothermal synthesis, structure investigation, and oxide ion conductivity of mixed Si/Ge-based apatite-type phases

Apatite-type oxides ([A(I)4][A(II)6][(BO4)6]O2), particularly those of the rare-earth silicate and germanate systems, are among the more promising materials being considered as alternative solid oxide fuel cell electrolytes. Nonstoichiometric lanthanum silicate and germanate apatites display pure ionic conductivities exceeding those of yttria-stabilized zirconia at moderate temperatures (500-700 °C). In this study, mixed Si/Ge-based apatites were prepared by hydrothermal synthesis under mild conditions rather than the conventional solid-state method at high temperatures. Single-phase and highly crystalline nanosized apatite powders were obtained with the morphology changing across the series from spheres for the Si-based end member to hexagonal rods for the Ge-based end member. Powder X-ray and neutron analysis found all of these apatites to be hexagonal (P63/m). Quantitative X-ray microanalysis established the partial (<15 at%) substitution of La(3+) by Na(+) (introduced from the NaOH hydrothermal reagent), which showed a slight preference to enter the A(I) 4f framework position over the A(II) 6h tunnel site. Moreover, retention of hydroxide (OH(-)) was confirmed by IR spectroscopy and thermogravimetric analysis, and these apatites are best described as oxyhydroxyapatites. To prepare dense pellets for conductivity measurements, both conventional heat treatment and spark plasma sintering methods were compared, with the peculiar features of hydrothermally synthesized apatites and the influence of sodium on the ionic conductivity considered.

Secondary Electron Microscopy Dopant Contrast Image (SEMDCI) for Laser Doping

Laser doping has been the subject of intense research over the past decade, due to its potential to enable high-efficiency, low-cost silicon solar cell fabrication. Information about the doping profile that is created by the process is critical for process optimization but is generally difficult to obtain. We apply the technique of secondary electron image (SEI) contrast to the characterization of the cross sections of laser-doped lines. We demonstrate that this technique can be used for a large range of different dopant sources and different laser doping methods and that good dopant contrast can be obtained under a relatively wide range of microscope parameters. Comparison of dopant contrast and doping density profiles shows that the substrate doping is an important parameter that can significantly influence the dopant contrast, particularly at low (~1018 cm-3) and high (~10 20 cm-3 ) dopant densities. When suitable calibration samples are used, the technique can be employed to obtain quantitative dopant density images for p-type laser-doped regions, albeit currently over a limited range of dopant densities and with relatively large error. Furthermore, the technique can be used to evaluate the risk of metallization shunts near the edges of dielectric film windows that are opened by the laser.