XRD Analysis (xrd + analysis)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Selected Abstracts

Single-Crystalline Gallium Nitride Microspindles: Synthesis, Characterization, and Thermal Stability ,

F. Xu
Abstract This paper describes a facile procedure for synthesizing high-quality gallium nitride microspindles on a large scale using a solid-state reaction of GaI3, NaNH2, and NH4Cl in a sealed system at 500,C for 6,h. The structures, compositions, and morphologies of the as-synthesized products are derived from X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images show that the as-synthesized GaN spindles are composed of many single-crystalline platelets. The GaN microspindles show different optical properties depending on their shape (e.g., nanowires or nanoparticles) in photoluminescence (PL) emission spectroscopy and Raman spectroscopy. The possible growth mechanism of GaN microspindles is controlled by linear kinetics with a driving force proportional to the difference between a local supersaturation and an equilibrium chemical potential. Furthermore, the thermal stability of the GaN microspindles is investigated under various annealing conditions and discussed on the basis of additional TEM and XRD analyses. [source]

Synthesis and characterization of zwitterionic organogels based on Schiff base chemistry

Nazia Tarannum
Abstract Poly(sulfobetaine)s and poly(carboxybetaine)s have been extensively studied for their zwitterionic and biocompatible nature. The specific features that make such zwitterionic structures technologically important are their chemical structure, a straight forward synthetic route, high ionic contents with interesting dilute solution, and solid state properties. The objective of this work is to synthesize novel zwitterionic polymers having gel characteristics. Here, p- phenylene diamine/melamine react as nucleophiles with glutaraldehyde to produce poly(schiff base)s. In the subsequent step, the poly(sulfobetaine)s and poly(carboxybetaine)s were produced on treatment with 1,3-propane sultone/,-butyrolactone. Hence, a catalyst free facile approach to novel zwitterionic polymers was obtained. The polymers were characterized by elemental analyses, FTIR, XRD analyses, SEM, pH metric titrations, conductometric titrations, and thermal analyses (TGA/DTA). The polymeric samples carry the gel characteristics, showing lamellar structure with porous network. XRD pattern shows Bragg peaks indicative of superstructures. Thermal analysis indicates the Hoffman elimination of , hydrogen and subsequent release of sulfopropyl/carboxybutyl group. One of the gel polymers shows fluorescence also. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Microstructural and crystallographic surface changes after grinding zirconia-based dental ceramics

I. L. Denry
Abstract The purpose of this study was to evaluate microstructural and crystallographic phase changes after grinding 3Y-TZP dental ceramics. Ceramic blanks were sintered according to manufacturer's recommendations and divided into four groups: (A) as-sintered control, (B) diamond-ground manually under water, (C) ground and polished, and (D) ground and annealed at 1000C for 1 h. Bulk specimens were analyzed by X-ray diffraction to characterize the crystalline phases. The microstructure was investigated by SEM. XRD analyses showed that the control group and the group that was ground and annealed contained only tetragonal zirconia. However, after grinding or after grinding followed by polishing, rhombohedral zirconia and strained tetragonal zirconia were present, without any detectable amount of monoclinic zirconia. Annealing led to the disappearance of both residual lattice strain and the rhombohedral phase. The microstructure of the ground and polished specimens was characterized by significant residual surface damage associated with grain pullout to a depth of about 20 ,m. This type of damage could have an impact on the long-term fatigue behavior of 3Y-TZP. 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

Synthesis and liquid crystalline properties of poly(1-alkyne)s carrying triphenylene discogens

Changmin Xing
Abstract Triphenylene-containing 1-decynes with different alkyl chain lengths and their polymers are synthesized and the effects of the structural variables on their mesomorphic properties are investigated. The monomers [HCC(CH2)8CO2C18H6 (OCmH2m+1)5; m = 4,9] are prepared by consecutive etherization, coupling, and esterification reactions. The monomers form columnar phases at room temperature. The polymerizations of the monomers are effected by [Rh(nbd)Cl]2, producing soluble polymers in high yields (up to 84%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, DSC, POM, and XRD analyses. All the polymers are thermally stable, losing little of their weights when heated to 300 C. The isotropization temperature of the polymers increases initially with the length of alkyl chain but decreases on further extension. Although the polymers with shorter and longer alkyl chain lengths adopt a homogeneous hexagonal columnar structure, those with intermediate ones form mesophases with mixed structures. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2960,2974, 2008 [source]

Synthesis of liquid crystalline poly(1-pentyne)s and fabrication of polyacetylene,perovskite hybrids

Jianli Hua
Abstract Poly(1-pentyne)s containing biphenyl and phthalimido pendant groups with different spacer lengths {P1(m); [HCC(CH2)3OBiphOCO(CH2)mN(CO)2C6H4]n, Biph4,4,biphenylyl; m = 7, 10} are synthesized in satisfactory yields by WCl6 -Ph4Sn catalyst in toluene at elevated temperatures. The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, DSC, POM, and XRD analyses. Both of the polymers are thermally stable (Td , 300 C) and exhibit nematicity at high temperatures. Their phthalimido groups are converted into amino groups by hydrolysis, which can, after acidification, complex with lead(II) bromide to furnish polyacetylene,perovskite hybrids in high yields. The organic components contribute good solubility to the hybrids, while the perovskite framework induces the polyacetylene chains to align within the inorganic sheets. The hybrids emit a strong UV light of 374 nm upon photoexcitation, whose quantum yield increases with an increase in the spacer length. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3538,3550, 2006 [source]

Influence of the stacking order on structural features of the Cu-In-Ga-Se precursors for formation of Cu(In,Ga)Se2 thin films prepared by thermal reaction of InSe/Cu/GaSe alloys to elemental Se vapor and diethylselenide gas

F.B. Dejene
Abstract A novel partway for the fabrication of copper-indium (gallium) diselenide has been developed. This two-stage process consists of the formation of Cu-In-(Ga)-Se precursors and subsequent selenization to form CuIn(Ga)Se2. In this work, we have investigated and compared the possible interactions in Cu-In-Ga-Se systems, using sequentially stacked precursors premixed with Se, in order to get a better understanding of the Cu(In,Ga)Se2 thin film formation. Comparison of these SEM micrographs clearly revealed that the surface morphologies and hence surface roughness of the resulting Cu(In,Ga)Se2 absorber films were significantly influenced by the structure of the precursor films prior to selenization. XRD analyses revealed the presence of a graded CuIn1-xGaxSe structure, irrespective of the stacking order during the precursor formation step for samples selenized using elemental Se vapor. It was established that distinct from the case of using Se vapor, a single-phase Cu(In,Ga)Se2 films were obtained by diethylselenide (DESe) selenization from Cu-In-Ga metal precursors premixed Se irrespective of the stacking order during the precursor formation step. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


ARCHAEOMETRY, Issue 5 2009
A series of prehistoric pottery samples excavated from Rahmatabad, south-west Iran, were investigated using XRF and XRD analyses to determine their chemical and mineralogical compositions. The sample microstructures were also studied by SEM/EDX. The relative similarity of compositions, the fine, dense and homogeneous microstructures and the presence of high-temperature phases such as diopside and mullite showed the use of high firing temperatures, in the range 950,1050C. This, along with the homogeneity in shape, decoration and size ranges of the ware, all indicate the adoption of specialized pottery-making techniques by the potters of Rahmatabad in the fifth to fourth millennia bc. [source]

Adsorption properties of microwave synthesized inorgano,organo montmorillonite

Miray Emreol
Abstract The aim of this study is to determine the adsorption properties of microwave synthesized inorgano,organo montmorillonites. Microwave irradiation is preferred because of its low time and energy consumption properties, forming an advantage in industrial applications. In addition to the intercalation of Keggin and hexadecyltrimethylammonium (HDTMA+) cations, the aging process of pillaring solution was also carried out through the microwave irradiation. Both inorgano clays, namely the parents, and their inorgano,organo derivatives, were prepared by using the same amounts of aluminum by keeping the OH,/Al3+ and Al3+/clay ratios constant. The HDTMA+/clay ratio was changed in inorgano-organo clays (IOCs) during the preparation. The effects of these parameters on the surface properties and adsorption behaviors of the samples were investigated by conducting X-ray diffraction (XRD), Fourier transform infrared (FTIR) and simultaneous thermal analyses (STA), as well as batch adsorption experiments, in which phenol was used as a model pollutant. The results of XRD analyses reveal that the intercalation is successfully achieved. The existence of the Keggin and HDTMA+ cations was observed in FTIR spectra of the samples. Through the STA, it was determined that the existence of organic layer increases the dehydroxylation temperature and the thermal behavior of inorgano-organo montmorillonites strongly depends on the structure of the parent clay. An increase in the adsorption efficiencies with increasing HDTMA+/clay ratio was observed, except with the highest ratio. The behavior of this sample was explained by the formation of the second HDTMA+ layer leading to the hydrophilic surface formation. Copyright 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Iridium Metal Thin Films and Patterned IrO2 Nanowires Deposited Using Iridium(I) Carbonyl Precursors

Y.-L. Chen
Abstract Highly volatile iridium(I) carbonyl complexes (1,5) with three anionic fluorinated chelates, namely ketoiminate, aminoalkoxide, or iminoalkoxide, have been synthesized and their physical properties relevant to CVD are evaluated. A single-crystal X-ray diffraction (XRD) study on Ir(CO)2(amakNMe2) (3) confirms a square-planar geometry with two cis-orientated carbonyl ligands. Metallic iridium, polycrystalline IrO2 thin films, or even patterned IrO2 nanowires are deposited using Ir(CO)2(hfdaNnPr) (5) as the CVD precursor. A systematic investigation of the deposition of IrO2 nanowires is conducted, showing a close correlation of observed crystallite morphology with applied system pressure, underlying growth surface, and deposition temperature. Of particular importance, tilted and vertically aligned IrO2 nanowires are obtained on LiTaO3(012) and LiNbO3(100) surfaces under a pressure of 30,Torr of oxygen at 425,C. The morphology and structural composition of the IrO2 are confirmed by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and XRD analyses. [source]

Syntheses, Phase Behavior, Supramolecular Chirality, and Field-Effect Carrier Mobility of Asymmetrically End-Capped Mesogenic Oligothiophenes

Qingwei Meng Dr.
Abstract Supramolecular chirality and liquid crystalline OFET: Achiral end-capped oligothiophenes can be tuned to exhibit supramolecular chirality with unique striped textures showing distinct circular dichroism signals as well as a highly ordered SmE phase that leads to high hole carrier mobility. A novel series of asymmetrically end-capped mesogenic oligothiophenes, with various oligothiophene core lengths, alkoxy tail lengths, and molecular polarities through introducing alkylsulfanyl or alkylsulfonyl functionalities as the terminal group, have been synthesized by palladium-catalyzed Suzuki cross-coupling and Kumada cross-coupling reactions as key steps. For the single end-capped oligothiophenes, CmO-Ar-OT(4)-H in which m=10, 12, 14, 16, and 18, all of these oligomers exhibited a broad temperature range of highly ordered smectic E and enantiotropic nematic phases, apart from the one with the longest octadecyloxy tail. For the double end-capped series C10O-Ar-OT(n)-R, R=Ph-SC6 or Ph-SO2C6 in which n=1, 2, 3, and 4, oligomers with more than one thiophene ring exhibited smectic A and smectic C phases, various crystal polymorphs and/or unusual low-temperature condensed phases. In the nonpolar, alkylsulfanylphenyl-substituted oligothiophene series, both the crystal/solid melting point and mesogenic clear point increased significantly with an increasing oligothiophene conjugation length. In the polar, alkylsulfonylphenyl-substituted oligothiophene series, all the oligomers showed increased melting points, but decreased mesogenic temperature intervals than those of their corresponding alkylsulfanyl counterparts. Remarkably, two different helical structures showing distinct striated textures or striped patterns were observed with a pitch of several to tens of micrometers under a polarized optical microscope upon cooling from their preceding fluidic smectic phases. The unusual twisted smectic layer structures in the thin solid films exhibiting distinct supramolecular chirality of both handednesses, revealed by circular dichroism measurements, were further confirmed by XRD analyses characterized by a sharp layer reflection together with its higher orders and diffuse wide-angle scatterings. In addition, initial studies showed that the highly ordered smectic phase of the single end-capped oligothiophenes can be utilized to improve field-effect charge mobility. C10O-Ar-OT(4)-H showed a hole mobility of 0.07,cm2,V,1,s,1 when deposited on octyltrichlorosilane-treated substrates at 140,C and the on/off current ratios reached 5105; on the other hand, its mobility was only 810,3,cm2,V,1,s,1 on the same substrate when deposited at room temperature. [source]

Properties of InAs co-doped ZnO thin films prepared by pulsed laser deposition

J. Elanchezhiyan
Abstract InAs co-doped ZnO films were grown on sapphire substrates by pulsed laser deposition. The grown films have been characterized using X-ray diffraction (XRD), Hall effect measurements, Atomic force microscope (AFM) and Field emission scanning electron microscope (FESEM) in order to investigate the structural, electrical, morphological and elemental properties of the films respectively. XRD analysis showed that all the films were highly orientated along the c-axis. It was observed from Hall effect measurements that InAs co-doped ZnO films were of n-type conductivity. In addition, the presence of In and As has been confirmed by Energy dispersive X-ray analysis. AFM images revealed that the surface roughness of the films was decreased upon the co-doping. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Formation of Metastable Na2CrO4 -Type LiNiPO4 from a Phosphate,Formate Precursor

Violeta Koleva
Abstract High-pressure modification of LiNiPO4 with a Na2CrO4 -type structure was obtained at ambient pressure and low temperature from a mixed LiNi,phosphate,formate precursor, LiNiPO4Hx(HCOO)xyH2O (where x , 1.2 and y , 2.5). The structural and thermal characterization of the precursor and the LiNiPO4 compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4Hx(HCOO)xyH2O precursors between 450 and 650 C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4 type and the olivine type. It was established that the obtained Na2CrO4 -type LiNiPO4 is a metastable phase, which completely transforms at 700 C into the olivine-type phase. The enthalpy of the phase transition is ,H = ,43.40 kJ,mol,1. The mechanism of formation of the two forms of LiNiPO4 from the LiNi,phosphate,formate precursor is discussed. [source]

Assessing the Potential of Zwitterionic NHCCS2 Adducts for Probing the Stereoelectronic Parameters of N-Heterocyclic Carbenes

Lionel Delaude
Abstract Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and electronic properties of NHC ligands. Because of their outstanding ability to crystallize, the five NHCCS2 betaines were found to be highly suitable for probing the steric influence of nitrogen atom substituents on imidazolylidene-based ligand precursors via XRD analysis, while the corresponding NHCCO2 adducts were deemed more appropriate for evaluating the ,-donating properties of carbene ligands.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Size- and Shape-Controlled Synthesis and Assembly of a Silver Nanocomplex in UV-Irradiated TSA Solution

Liangbao Yang
Abstract In this paper we describe the size-controlled synthesis ofa silver nanocomplex based on the reduction of silvernitrate (AgNO3) by UV-irradiated tungstosilicate acid [H4(SiW12O40), TSA] solution. This method allows the synthesis of ellipsoidal particles with an average size that is tunable between 2.4 and 84 nm by varying the molar ratio of silver nitrate to TSA, the pH of the reaction solution, and the reaction temperature. Silver nanorods can be formed from the ellipsoidal nanoparticles by controlling the aging time. The formation mechanism of these nanorods is also discussed. The nanoparticles are characterized by UV/Vis spectroscopy, FTIR spectroscopy, XRD analysis, XPS, electron diffraction (ED), TEM, and with a Zetasizer instrument. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

K-feldspar alteration to gel material and crystallization of glauconitic peloids with berthierine in Cretaceous marine sediments,sedimentary implications (Prebetic Zone, Betic Cordillera, SE Spain)

Juan Jimnez-Milln
Abstract Glauconitic peloids from a Hauterivian condensed level in a hemipelagic unit of the Internal Prebetic (Los Villares Formation, eastern Betic Cordillera) have been studied by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). The sediments forming the condensed level are characterized by abundant spherical to ovoid green glauconite peloids with radial cracks. Quartz, feldspar and muscovite are also abundant, whereas calcium phosphate is rarely detected. XRD analysis of the peloids reveals glauconite and small amounts of berthierine. SEM and HRTEM data show feldspar dissolution features, a Si,Al-rich gel-like substance filling K-feldspar micropores and interlayering of well-crystallized glauconite and berthierine packets. The last stage of the glauconitization process resulted in conversion of the smectitic precursor. Sedimentary and mineralogical features indicate an autochthonous origin for the glauconite. The depositional environment was a distal, hemipelagic ramp on the Southern Iberian Continental Palaeomargin. Low sedimentation rates lead to sediment condensation in a general transgressive context. The margin was affected by extensional tectonics, creating tilted blocks, resulting in lateral facies changes. The dissolution of K-feldspars probably occurred after their deposition in the marine environment but predating the glauconitization. An influx of meteoric water is therefore required, probably related to subsurface fluxes from adjacent emergent areas (the higher parts of tilted blocks). Copyright 2007 John Wiley & Sons, Ltd. [source]

UV-vis-Induced Vitrification of a Molecular Crystal,

T. Naito
Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source]

Magnetically Anisotropic Cobalt and Iron Nanofibers via Electrospinning

M. Graeser
Magnetically anisotropic cobalt and iron nanofibers (see figure) are obtained via oriented polymer-supported electrospinning and subsequent reduction and thermal treatment. The cobalt and iron nature of the fibers is confirmed by XRD analysis. Fibers of both metals show ferromagnetic behavior. Parallel aligned iron nanofibers revealed anisotropic hysteresis loops depending on field-fiber orientation. [source]

A study of the mechanisms of divalent copper binding to a modified cellulose adsorbent

David William O'Connell
Abstract A modified cellulose material was prepared by grafting glycidyl methacrylate to cellulose (Cell- g -GMA) with subsequent functionalization with imidazole (Cell- g -GMA-imidazole). This latter compound was used in the adsorption of copper from aqueous solution. The mechanism of Cu(II) binding onto the cell- g -GMA-imidazole was investigated at the molecular level using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) and X-ray diffraction (XRD). FTIR and Raman spectroscopy provided an insight into the extent to which perturbation of the imidazole ring occurred following adsorption of the metal while XPS spectra indicated the binding of Cu(II) ions to nitrogen atoms by the appearance of additional binding energy peaks for nitrogen on the cellulose- g -GMA-imidazole sample post adsorption. The EDX technique provided clear evidence of the physical presence of both the copper and sulfate on the cellulose- g -GMA-imidazole material post adsorption. XRD analysis further confirmed the presence of a copper species in the adsorbent material as copper sulfate hydroxide (Cu3(OH)4SO4 - antlerite). The XRD studies further suggest that the overall extent of Cu(II) adsorption is not alone a combination of true metal chelation as suggested by FTIR, Raman and XPS, but also a function of surface precipitation of the polynuclear copper species. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Effect of neutron irradiation on the structural, mechanical, and thermal properties of jute fiber

E. Sinha
Abstract This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 109 to 2 1013 n/cm2. An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Production of B4C coatings by CVD method in a dual impinging-jet reactor: Chemical yield, morphology, and hardness analysis

AICHE JOURNAL, Issue 11 2009
Mustafa Karaman
Abstract ,-rhombohedral boron carbide (B4C) was deposited on a tungsten substrate from a BCl3H2CH4 gas mixture in a dual impinging-jet chemical vapor deposition reactor. On-line FTIR analysis of the product stream proved the formation of BHCl2 and HCl as by products, in a competing parallel reaction. A maximum of 13% chemical yield of boron carbide was observed, and the yield was found to have increasing trend with an increase in temperature. XRD analysis proved the existence of rhombohedral B4C phase at 1300C without any other B4C phases or impurities. At this temperature, the formation of 5-fold icosahedral boron carbide crystals up to 30 micron sizes was observed. Such highly symmetric crystalline regions were observed to have a very high hardness value of 4750 kg/mm2 as revealed from the microhardness analysis. The change in product morphology at low substrate temperatures resulted in a decrease in the hardness values. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Metal-Ceramic Interface Evaluation of a Gold-Infiltrated Alloy

Rupal Vasani BDS
Abstract Purpose: The success of metal-ceramic systems partially depends on the formation of a stable bond between metal and porcelain. The purpose of this study was to investigate the porcelain/metal interface and the mechanism of interfacial bonding in a gold-infiltrated alloy (Captek). Materials and Methods: Captek specimens with feldspathic porcelain were evaluated by optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and the Schwickerath crack initiation test for metal-ceramic bond compatibility. Specimens were processed with or without Capbond, a bonding agent. A traditional metal-ceramic alloy was also analyzed with microscopy for comparative purposes. Results: Optical and scanning electron micrographs of Captek specimens processed with Capbond revealed close adaptation of porcelain to the surface of the metal with sporadic nodules extending from the Captek surface. In contrast, the specimens of Captek without Capbond showed a much flatter porcelain/metal interface. Comparatively, the porcelain/metal interface of the traditional metal-ceramic crown showed greater surface roughness than the Captek specimens. No metal oxides were observed at the porcelain/metal interface of the Captek specimens with XRD. During the Schwickerath test, the Captek specimens permanently deformed, not allowing for crack initiation at the porcelain/metal interface. Conclusions: Microscopy and XRD analysis showed that micromechanical interlocking is the primary mechanism of porcelain adherence to Captek metal. The use of Capbond prior to porcelain application to Captek results in gold nodules on the surface to aid retention. Existing metal-ceramic bond compatibility standardized tests are not sufficient for evaluating Captek, primarily due to the flexibility of the material. [source]

Fabrication of NiO Nanoparticle-Coated Lead Zirconate Titanate Powders by the Heterogeneous Precipitation Method

Ping-Hua Xiang
NiO nanoparticle-coated lead zirconate titanate (PZT) powders are successfully fabricated by the heterogeneous precipitation method using PZT, Ni(NO3)26H2O, and NH4HCO3 as the starting materials. The amorphous NiCO32Ni(OH)22H2O are uniformly coated on the surface of PZT particles. XRD analysis and the selected-area diffraction (SAD) pattern indicate that the amorphous coating layer is crystallized to NiO after being calcined at 400C for 2 h. TEM images show that the NiO particles of ,8 nm are spherical and weakly agglomerated. The thickness of the nanocrystalline NiO coating layer on the surface of PZT particle is ,30 nm. [source]

Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X-ray Diffraction

Shin-ichi Nakashima
Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X-ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics. [source]

Titanium Diboride,Tungsten Diboride Solid Solutions Formed by Induction-Field-Activated Combustion Synthesis

Masachika Shibuya
Solid solutions of titanium diboride,tungsten diboride (TiB2,WB2) were synthesized by induction-field-activated combustion synthesis (IFACS) using elemental reactants. In sharp contrast to conventional methods, solid solutions could be formed by the IFACS method within a very short time, ,2 min. Solutions with compositions ranging from 40,60 mol% WB2 were synthesized with a stoichiometric ratio (Ti + W)/B =; however, samples with excess boron were also made to counter the loss of boron by evaporation. The dependence of the lattice constants of the resulting solid solutions on composition was determined. The "a" parameter decreased only slightly with an increase in the WB2 content, whereas the "c" parameter exhibited a significant decrease over the range 40,60 mol% WB2. Solid-solution powders formed by the IFACS method were subsequently sintered in a spark plasma sintering (SPS) apparatus. After 10 min at 1800C, the samples densified to relative density 86%. XRD analysis showed the presence of only the solid-solution phase. [source]

Zirconia-Based Metastable Solid Solutions through Self-Propagating High-Temperature Synthesis: Synthesis, Characterization, and Mechanistic Investigations

Filippo Maglia
Cubic Zr1,xMexOy(Me = Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe2O3, CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal. [source]

Mullite Decomposition Kinetics and Melt Stabilization in the Temperature Range 1900,2000C

Zhijun Xiao
An investigation of the mullite decomposition mechanism and kinetics in the temperature range 1900,2000C was conducted. SEM-EDS and XRD analysis showed that the decomposition of mullite in this temperature range was primarily caused by the presence of carbon from furnace components. A reaction mechanism, in which gas-phase SiO2 reacts with carbon to form SiO and CO, is proposed; both IR analysis and kinetic studies support the proposed mechanism. The decomposition was completely suppressed by the introduction of a modified crucible assembly and the addition of excess SiO2 to the reaction system. A mullite melt of stable composition was thus obtained, setting the groundwork for inviscid melt spinning mullite fiber making process development. [source]

Inhibition of corrosion of AZ91 magnesium alloy in ethylene glycol solution in presence of chloride anions

E. Slavcheva
Abstract The influence of chloride ions on the corrosion of AZ91 magnesium alloy in water/ethylene glycol solutions and the inhibiting effect of lactobiono-tallowamide (LTA) were investigated using electrochemical and surface analysis methods. Potentiodynamic polarization curves in aqueous solution of ethylene glycol (50:50w%) containing 0.1 g.L,1 chloride and up to 0.5 g.L,1 LBT were obtained at room and at elevated temperatures. The chloride anions showed a distinct deteriorating effect as they caused pit initiation and accelerated the dissolution of the tested alloy. The selected organic compound demonstrated good protective properties against corrosion of AZ91 magnesium alloy and behaved as inhibitor of mixed type hindering both the cathodic and the anodic partial reactions. It showed inhibition efficiency of 77% at relatively low concentration of 0.2 g.L,1 and was considered as a promising corrosion inhibitor. The mechanism of inhibition was discussed on the basis of the electrochemical impedance spectroscopy (EIS) and XRD analysis of the surface. [source]

The electronic and electrochemical properties of the TiFe1,xNix alloys

A. Szajek
Abstract Mechanical alloying (MA) process was introduced to produce nanocrystalline TiFe1,xNix alloys (0 , x , 1). XRD analysis showed that, firstly, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase and, secondly, the annealing in high purity argon at 750 C for 0.5 h led to formation of the CsCl-type (B2) structures with a crystallite sizes of about 30 nm. These materials, used as negative electrodes for Ni,MH batteries, showed an increase in discharge capacity with a maximum for x = 3/4. The band structure has been studied by the Tight Binding version of the Linear Muffin-Tin method in the Atomic Sphere Approximation (TB LMTO ASA). Increasing content of Ni atoms intensified charge transfer from Ti atoms, extended valence bands and increased the values of the densities of electronic states at the Fermi level. [source]

Preparation and characterization of polypropylene/solid-state organomodified montmorillonite nanocomposites

Sun Yu-hai
A novel organomodified montmorillonite prepared by solid-state method and its nanocomposites with polypropylene were studied. The interaction between modifying agent and montmorillonite was investigated by X-ray diffraction (XRD) analysis, contact angle determination, and Fourier-transform infrared spectroscopy. The results showed that the modifying agent behaves as an effective intercalating agent, enlarging the interlayer spacing of montmorillonite and making montmorillonite more hydrophobic. Polypropylene/solid-state organomodified montmorillonite composites were prepared by melt-mixing method. The dispersion of the silicates was investigated by XRD analysis and transmission electron microscopy. It was found that the nanocomposites are formed with solid-state organomodified montmorillonite and polypropylene. The thermogravimetric analysis and differential scanning calorimetry results showed that the organoclay could enhance the thermal stability and decrease the relative crystallinity of polypropylene. Mechanical and rheological tests indicated that the organoclay improves the mechanical properties but has no obvious effect on rheological properties of polypropylene. POLYM. COMPOS., 2008. 2008 Society of Plastics Engineers [source]

Morphology and properties of SAN-clay nanocomposites prepared principally by water-assisted extrusion

Michal Mainil
An efficient extrusion process involving the injection of water while processing was used to prepare poly (styrene- co -acrylonitrile) (SAN)/clay nanocomposites with a high degree of nanoclay delamination. The usefulness of water-assisted extrusion is highlighted here, in comparison with classical extrusion and roll mill processes. Cloisite 30B (C30B), a montmorillonite clay organomodified with alkylammonium cations bearing 2-hydroxyethyl chains, and pristine montmorillonite were melt blended with SAN (25 wt% AN) in a semi-industrial scale extruder specially designed to allow water injection. XRD analysis, visual and TEM observations were used to evaluate the quality of clay dispersion. The relationship between the nanocomposite morphology and its mechanical and thermal properties was then investigated. The superiority of the SAN/C30B nanocomposite extruded with water has been evidenced by cone calorimetry tests and thermogravimetric measurements (TGA). These analyses showed a substantial improvement of the fire behavior and the thermal properties, while a 20% increase of the Young modulus was recorded. POLYM. ENG. SCI., 2010. 2009 Society of Plastics Engineers [source]