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At least 1,081 records · Page 60Linked to original sources
PubMed2003

Effects of pressure on the fragile nature of fluorozirconates studied by molecular dynamics simulations.

Molecular dynamics simulations for a multicomponent zirconium fluoride, ZBEN (55ZrF(4)-17BaF(2)-5EuF(3)-23NaF) have been carried out at various temperatures and pressures including those of the molten and glassy states. The effect of pressure on the fragile nature of ZBEN was investigated. The relaxation times were calculated from the decay curves of the intermediate scattering function. The fragile nature of ZBEN was reflected by the obvious non-Arrhenius behavior in the temperature dependence of the relaxation time. The so-called "Angell plot" of the relaxation time was represented by a single curve irrespective of applied pressure; the fragile nature changes negligibly with pressure. This seems to contradict the enhancement of the connectivity of ZrF(n) polyhedra under high pressure. The origin of the pressure effects is discussed in comparison with those for molecular liquids and covalent-network glasses.

Journal Article↗
PubMed2006

Experimental detection of the optical Pendellösung effect.

We report observations of periodic oscillatory behavior of the angular selectivity, near the Bragg angle, in volume holographic gratings recorded in a new photopolymerizable glass with high refractive index modulation. We have detected the presence of overmodulation in the intensity distribution of the first diffraction order. The results reported here were achieved by incorporating in the photopolymerizable sol-gel glass zirconium-based high refractive index species at the molecular level. This is the first time that this effect is observed for light diffraction in an amorphous material.

Journal Article↗
PubMed2000

[{Me(4)C(2)(C(5)H(4))(2)}Zr(BH(4))(2)], a bis(tetrahydroborate) complex of a bridged zirconocene.

Bis(tetrahydroborato)[1,1,2,2-tetramethyl-1,2-ethylenebis(eta(5)-cyclopentadienyl)]zirconium, (I), was synthesized by the reaction of the zirconocene dichloride with lithium tetrahydroborate. Crystals suitable for X-ray structure analysis were obtained by recrystallization from toluene. The molecule adopts an appproximate C(2v) symmetry. Both tetrahydroborate ligands are eta(2)-coordinated and tilted by 18-19 degrees out of the equatorial plane; the angle B1-Zr1-B2 is 104.7 degrees. The cyclopentadienyl rings show a normal eta(5)-coordinaton, with a centroid-Zr-centroid angle of 124.3 degrees.

Journal Article↗
PubMed2003

ansa-[(tert-Butylamino)(isodicyclopentadienyl)dimethylsilane]Zr(NMe2)2 prepared by an amine-elimination reaction.

An amine-elimination reaction was used to obtain the title compound, i.e. (N-tert-butyl-N-[[(1,2,3,3a,7a-eta)-4,5,6,7-tetrahydro-4,7-methano-1H-inden-2-yl]dimethylsilyl]amido-kappaN)bis(N-methylmethanaminato-kappaN)zirconium(IV) or [isodiCpSiMe(2)N-tert-butyl]Zr(NMe(2))(2) (Cp is cyclopentadienyl), [Zr(C(16)H(25)NSi)(C(2)H(6)N)(2)], in very good yield. Treatment of isodiCpHSiMe(2)NH-tert-butyl with Zr(NMe(2))(4) leads to the formation of a yellow solid that can be purified by sublimation. The single-crystal structure of the product shows the exo complexation of the isodicyclopentadienyl ligand to the Zr atom. The Cp portion of this ligand is bonded to the Zr atom in a eta(5) manner, with a Zr-Cg (Cg is the ring centroid) distance of 2.2352 (10) A. The isodiCpSiMe(2)N-tert-butyl ligand has a constrained geometry, which is exhibited by the small angle of 95.55 (10) degrees for N-Si-C(Cp).

Journal Article↗
PubMed2004

Tetrakis(tetrahydrofuran-kappaO)lithium mer-tris(carbazolyl-kappaN)-trans-dichloro(tetrahydrofuran-kappaO)zirconate.

In the title compound, [Li(C(4)H(8)O)(4)][ZrCl(2)(C(12)H(8)N)(3)(C(4)H(8)O)], the environment of the Zr atom is pseudo-octahedral, with the three carbazolyl ligands in a mer configuration. The counter-ion of the zirconium complex is composed of an Li atom surrounded by four tetrahydrofuran (THF) molecules. The THF molecule attached to the Zr atom is disordered over two sites, as are two of the THF molecules in the lithium moiety. All bond distances and angles are consistent with those in complexes with similar structural entities. The Zr-N bond distances are 2.2185 (18) and 2.167 (3) A.

Journal Article↗
PubMed2006

A disordered cerium(IV) phosphate with a tunnel structure, K4CeZr(PO4)4.

Tetrapotassium cerium(IV) zirconium tetrakis(monophosphate) crystallizes in the tetragonal system (space group I4(1)/amd). A complex disorder in K4CeZr(PO4)4 involves the mixing of Ce and Zr atoms on a single site with -4m2 symmetry and the splitting of P- and O-atom positions, equivalent to a rotation of the phosphate groups, to yield eight- and sixfold coordination environments around Ce and Zr, respectively. The K atoms are located in tunnels running parallel to the a and b axes.

Journal Article↗
PubMed2001

High-pressure structures of alpha- and delta-ZrMo2O8.

In situ high-pressure synchrotron X-ray powder diffraction studies of trigonal alpha-ZrMo(2)O(8), zirconium molybdate, have been performed from ambient conditions to 1.9 GPa, over the alpha-delta phase transition at 1.06-1.11 GPa. The monoclinic structure of delta-ZrMo(2)O(8), stable between 1.1 and 2.5 GPa at 298 K, has been solved by direct methods and refined using the Rietveld method. Significant distortions of the ZrO(6) and MoO(4) polyhedral elements are observed for delta-ZrMo(2)O(8), as compared to the ambient conditions of the alpha-phase, while the packing of anions becomes more symmetric at high pressure.

Journal Article↗
PubMed2001

In situ XAFS study at the Zr K-edge for SiO2/ZrO2 nano-sol.

The structural characterisation of SiO2/ZrO2 nano-sol particles, prepared by mixing SiO2 sol and aqueous solution of ZrOCl2 8H2O, has been carried out by in-situ XAS measurement at the Zr K-edge during condensation reaction. The detailed XANES features at the Zr K-edge of the mixed sol of SiO2/ZrO2 are compared with those of other references such as ZrO2, ZrOCl2 8H2O. BaZrO3, and ZrSiO4, and it becomes obvious that the Zr4+ ions are stabilised in an octahedral symmetry. The EXAFS result also indicates that each Zr atom is coordinated with six oxygen ones as the first nearest neighbour, where two oxygen atoms are from the linkage of (Si-O-Zr) at short distance, and four ones are from water molecules at long distance. As the condensation reaction proceeds, it is found that the number of oxygen atoms due to the formation of (Si-O-Zr) bond at short distance and the second neighbour of silicon atoms increase simultaneously. From the above EXAFS and XANES results, the structural and gelating models could be proposed, which is based on the octahedrally coordinated but distorted zirconium species attaching on the SiO2 sol surface.

Journal Article↗
PubMed2001

X-ray magnetic circular dichroism in FeZrB amorphous alloys: the influence of the tensile stress.

We present X-ray Magnetic Circular Dichroism experiments (XMCD) on the Fe K edge of FeZrB metallic glasses performed under tensile stress. In these compounds the application of tensile stresses produces a large increase of the Curie Temperature. The XMCD signal presents the features expected for a weak ferromagnet but a gradual enhancement of the ferromagnetism is observed as boron and zirconium concentrations increase. The main effect of the tensile stress is to increase the density of states at the Fermi level as deduced from the increment of the amplitude of the XMCD signal with the stress.

Journal Article↗
PubMed1998

Structure changes in the sol-gel systems of hydrated oxides.

This work was undertaken partly with financial support of the RBRF of the Ministry of Science of the Russian Government (N95-03-09682a) and partly with financial support of the Ministry of Education, Science, Sports and Culture (MONBUSHO) of the Government of Japan.Sols of hydrated aluminium oxide, hydrated zirconium oxide and their mixtures were investigated during the xerogel-amorphous-product-crystalline-product transition by SAXS using synchrotron radiation. In the different temperature regions certain changes in structure and morphology were observed. Some correlation between the characteristics of the initial sols and their mixtures (the size and shape of the pores) was observed. In the temperature region 298-1173 K the characteristics of the mixed sol are defined by the characteristics of the initial sols.

Journal Article↗
PubMed2004

A torsional transducer through in-plane shearing of paired planar piezoelectric elements.

A torsional microtransducer for high-power applications was developed using standard bulk lead zirconium titantate (PZT) placed upon a small rectangular prism made from phosphor bronze, with a tapered conical end serving as a horn and a machined interior to improve the actuator's response. Torsion was obtained from a prototype at the design frequency of 192 kHz as well as over a wide range of frequencies from 136 kHz to 1.02 MHz. Torsional vibration velocities of 335 mm/s at 192 kHz were measured at 27.3 V(RMS) on the 1.5-mm diameter output tip, amounting to 25,600 degree/s vibration velocity along the outer circumference of the tip. At 1.02 MHz, a torsional vibration velocity of 1750 mm/s (134,000 degree/s) at 17.8 V(RMS) was obtained through use of the thickness mode of the PZT elements. Using the design described in this study, high-power torsional transducers with diameters of 5 mm and below are now possible.

Journal Article↗
PubMed2004

Fabrication and modeling of high-frequency PZT composite thick film membrane resonators.

High-frequency, thickness mode resonators were fabricated using a 7 microm piezoelectric transducer (PZT) thick film that was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Zirconium oxide (ZrO2) was selected as a diffusion barrier layer and gave good results when used in conjunction with silicon oxide (SiO2) as an etch stop layer. Using these conditions, devices were produced and the acoustic properties measured and modeled. The resonators showed a resonant frequency of about 200 MHz, an effective electromechanical coupling coefficient of 0.34, and a Q factor of 22. Modeling was based on a Mason-type model that gave good agreement between the experimental data and the simulations. The latter showed, for the PZT thick film, an electromechanical coupling coefficient of 0.35, a stiffness of 8.65 x 10(10) N x m(-2) and an e33,f piezoelectric coefficient of 9 C x m(-2).

Journal Article↗
PubMed2005

Platinum and palladium high-temperature transducers on langasite.

There is a pressing need for the fabrication of surface acoustic wave (SAW) devices capable of operating in harsh environments, at elevated temperature and pressure, or under high-power conditions. These SAW devices operate as frequency-control elements, signal-processing filters, and pressure, temperature, and gas sensors. Applications include gas and oil wells, high-power duplexers in communication systems, and automobile and aerospace combustion engines. Under these high-temperature and power-operating conditions, which can reach several hundred degrees Centigrade, the typically fabricated aluminum (A1) thin film interdigital transducer (IDT) fails due to electro and stress migration. This work reports on high temperature SAW transducers that have been designed, fabricated, and tested on langasite (LGS) piezoelectric substrates. Platinum (Pt) and palladium (Pd) (melting points at 1769 degrees C and 1554.9 degrees C, respectively) have been used as thin metallic films for the SAW IDTs fabricated. Zirconium (Zr) was originally used as an adhesion layer on the fabricated SAW transducers to avoid migration into the Pt or Pd metallic films. The piezoelectric LGS crystal, used as the substrate upon which the SAW devices were fabricated, does not exhibit any phase transition up to its melting point at 1470 degrees C. A radio frequency (RF) test and characterization system capable of withstanding 1000 degrees C has been designed and constructed. The LGS SAW devices with Pt and Pd electrodes and the test system have been exposed to temperatures in the range of 250 degrees C to 750 degrees C over periods up to 6 weeks, with the SAW devices showing a reduced degradation better than 7 dB in the magnitude of transmission coefficient, /S21/, with respect to room temperature. These results qualify the Pt and Pd LGS SAW IDTs fabricated for the above listed modern applications in harsh environments.

Journal Article↗
PubMed1980

Immunologic and nonimmunologic activation of macrophages.

Cells of the mononuclear phagocyte system take on different morphological features and appear to have different functions in immunological and nonimmunological granulomas. In immunological granulomas the appearance is of epitheliod cells. Epitheliod cells are of 2 types. In borderline tuberculoid leprosy granulomas, the appearance is of activated macrophages. Similar activation can be induced by lymphokine which increases respiratory enzyme activity. Other types of epithelioid cell are found in experimental zirconium granulomas. These cells contained rough endoplasmic reticulum, indicating that they may play a secretory role. It is suggested that these cells could play a part in stimulating fibrosis. Other substances that produce nonimmunological granulomas, such as aluminum containing compounds, are directly toxic to macrophages in vitro resulting in the rapid release of cytoplasmic enzymes. These compounds also activate complement, causing C3 conversion and anaphylatoxin production. C3 conversion may be through pathways other than the classical and alternative pathways and does not occur in the absence of plasminogen. Mycobacteria can activate complement through the alternative pathway, suggesting a mechanism for granuloma formation in lepromatous leprosy. Loss of C3 membrane receptors from macrophages in lepromatous leprosy could be produced by feeding peritoneal exudate macrophages with mycobacteria in vitro. This was not just due to phagocytosis, as a similar receptor loss was not obtained when the cells were fed latex particles or zymosan. Epithelioid cells in tuberculoid leprosy and sarcoidosis lose Fc membrane receptors but retain C3 receptors. Thus epithelioid cells can be readily distinguished from other cells of the mononuclear phagocyte series.

Animals↗
PubMed1985

The mononuclear phagocyte system in granulomas.

A comparison is made between immunologically induced and non-immunologically induced granulomas in guinea-pigs injected with metals (zirconium and aluminum) or with mycobacteria (BCG vaccine and Mycobacterium leprae). Immunological granulomas were characterized by epithelioid cells and fibrosis, whereas non-immunological granulomas contained phagocytosing macrophages with little evidence of fibroblast activation. Epithelioid cells carry the same specific macrophage antigen as phagocytosing macrophages and this can be detected by the use of a specific monoclonal antibody. However, they differ from phagocytosing macrophages in that they are poorly phagocytic, not glass adherent and lack Ia antigen. They are however secretory cells with rough endoplasmic reticulum. A relation between the presence of these cells and increased collagen synthesis is indicated. A study of accessory cell function showed that the epithelioid cells of BCG granulomas were able to support mitogen-induced but not antigen-induced proliferation of T lymphocytes. The macrophages of M. leprae granulomas did not support either a mitogen- or antigen-induced proliferative response.

Animals↗
PubMed2006

Focal adhesion contact formation by fibroblasts cultured on surface-modified dental implants: an in vitro study.

A major consideration in designing dental implants is to create a surface that provides strong attachment of the implant to bone, connective tissue and epithelium. The aim of the present study was to examine the influence of different treatments of titanium (Ti) implant surfaces on focal adhesion contact (FAC) formation in fibroblast cultures. Human gingival fibroblasts were cultured on glass sheets and polished Ti discs with different surface coatings (applied by physical vapor deposition (PVD): Ti, titanium nitride (TiN), zirconium nitride (ZrN)) or on Ti discs with different surface topographies. For characterization of all surfaces, modified estimation of surface roughness and spacing parameter was carried out using a contact stylus profilometer. Contact angle measurements were carried out to calculate surface energy. Fibroblasts were prepared for transmission electron microscopy at day 3 after seeding, and the number of FACs and the ratio FAC/cellular cross-sections was determined at a length of 300 microm in ultrathin sections. To visualize the extracellular fibronectin and vitronectin molecules and the intracellular actin and vinculin in FAC areas, immunogold labeling was performed. The results revealed a strong correlation between the number of FACs and the surface roughness. The highest number of FACs and the majority of the immunogold-labeled intra- and extracellular matrix molecules were counted on surfaces with the lowest surface roughness: glass sheets coated with either Ti, TiN or ZrN (roughness average=0.03-0.1 microm). These surfaces appear to favor cellular attachment of human gingival fibroblasts and moreover in previous studies the hard coatings have been shown to reduce bacterial adhesion.

Analysis of Variance↗
PubMed1979

Toxic elements in silicate cements.

Six brands of silicate cements have been characterized by means of optical emission spectrography with respect to the contents of elements in minor or trace quantities in a search for presence of possible toxic elements. Beryllium was observed in two powders at levels of 1.3 and 1.6% Cadmium was found in two powders at levels of 0.02 and 0.03%. Lead was measured in three powders at levels of 0.001-0.003%. Bismuth, boron, copper, gallium, iron, manganese, titanium, tin and zirconium were found in various brands in either powder or liquid at levels of 0.001-0.1%. Upper limits of the amounts of the various elements that might be transferred to the gastrointestinal tract after dissolution of the cement matrix in the oral cavity have been calculated.

Beryllium↗
PubMed2005

Silver-containing alginate fibres and dressings.

Silver is a broad-spectrum antimicrobial agent that is gaining more and more importance in the wound-management industry. By incorporating silver ions into alginate fibres, highly absorbent alginate wound dressings with antimicrobial properties can be made. Laboratory studies have shown that by incorporating fine particles of silver sodium hydrogen zirconium phosphate, the silver-containing alginate fibres can maintain the white physical appearances while providing a sustained release of silver ions when in contact with wound exudates. Test results have proven that these fibres are highly effective against bacteria.

Alginates↗