Intergranular Sites Research Articles

Assessment of the superior photocatalytic properties of Sn2+-containing SnO2 microrods on the photodegradation of methyl orange

A microporous Sn2+-containing SnO2 material presenting microrod morphology and a surface area of 93.0 m2 g–1 was synthesized via a simple hydrothermal route. Sn2+ ions were detected in the interior of the material (15.8 at.%) after the corrosion of a sample through sputtering. The material’s optical properties have demonstrated the absorption of a considerable fraction of visible light up to wavelengths of 671 nm, due to the presence of Sn2+ states in the material’s band structure. The analysis of the internal crystalline structure of a single microrod was carried out with the aid of a focused ion beam microscope and indicated that the material is mesocrystalline down to nanoscale level. It was proposed that the Sn2+ ions occupy intergranular sites in the highly defective crystalline structure of the material and that Sn2+ states, as well as its relatively large surface area, are responsible for the material’s superior photoactivity. The synthesized material was tested as a photocatalyst to decompose hazardous contaminants in water. The photocatalytic performance of the material was much higher than those of commercial TiO2 and SnO2 materials, decomposing nearly all methyl orange (an azo-dye model) content in water (10 mg L–1) in 6 min under UV irradiation for a photocatalyst dose of 5.33 g L–1. The photodegradation of methyl orange was also verified under visible light.

Roughened gold electrode for in situ SERS analysis of structural changes accompanying the doping process of polyaniline in acidic aqueous media

Electropolymerization of aniline on suitably roughened gold electrodes enabled us to record in situ surface-enhanced Raman scattering (SERS) spectra of polyaniline (PAni) during the doping-undoping process. Indeed, SERS-activation pretreatment of gold working electrode, using a specific electrochemical oxidation-reduction procedure, leads to the formation of countless surface asperities. The intergranular sites, known as “hot spots”, thus generated by the surface roughness are the seat of a strong electromagnetic coupling which leads to a huge SERS effect. Contrary to the case of platinum or mirror-polished gold electrodes, the use of roughened gold leads to high quality in situ SERS spectra of PAni, allowing the observation of important changes in the spectral features of its different oxidation states. In this study, we relied on spectral decomposition procedures to monitor and try to quantify these transformations accompanying the variation in the oxidation state of the polymer in different acidic aqueous solutions. In particular, the transition between the different forms of PAni (leucoemeraldine → emeraldine → pernigraniline), the drastic passage from benzenoid to quinoid structures of some aniline nuclei and the evolution of the charge-carrying structural defects are investigated despite the limitations imposed by the challenging conditions of the in situ analysis.

Graphene oxide modified superconducting and elastic parameters of YBCO superconductor

In the present work, (1-x) YBa2Cu3O7-δ + x Graphene Oxide (GO) {x = 0.0, 0.2, 0.4, 0.6 and 0.8 wt %} composite samples were prepared by standard solid state reaction route. The phase purity, structural and morphological analyses of the composite samples were observed through the X-ray powder diffraction and Field emission scanning electron microscopy respectively. The variations of superconducting parameters were observed through the resistivity vs. temperature and electric field vs. current density measurement. The onset of the superconducting transition temperature (TCon) enhances with increasing wt. % of graphene oxide and the maximum value was found to be 97.02 K for 0.8 wt % graphene oxide added YBCO sample. This may be attributed to the improved inter-linking among the superconducting grains and enhancing the transport of carrier density between the inter-granular sites. As a consequence of the superconducting volume fraction of the composite samples increases, hence critical current density is enhanced with increasing wt. % of graphene oxide. The Ultrasonic measurement has been utilized to observe the elastic parameters of the composite materials.

Microstructure and mechanical behavior of 316L liquid phase sintered stainless steel with boron addition

This work focuses on the role of boron as a sintering additive in powder metallurgy processing of the AISI 316L austenitic stainless steel. Boron effect was investigated regarding densification, microstructure, hardness and micro-scale abrasion resistance. Samples were prepared with 0.6 wt% and 0.8 wt% of boron and sintered at 1240 °C. The microstructure of the sintered bodies was characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and Rietveld refinement of X-ray diffraction (XRD) patterns. Differential scanning calorimetry (DSC) was used to study the behavior of both the free and boron-containing 316L samples at solid and liquid states. The hardness of austenitic matrix and precipitated borides was determined by instrumented indentation tests. EDS and XRD results revealed the formation of M23(B,C)6 carboboride and hard M2B borides, which were concentrated mainly in intergranular sites. The formation of M2B borides favored material densification through the development of a liquid phase during sintering, promoting an increase in density, hardness and micro-scale abrasion resistance of the AISI 316L steel.

Magneto-transport properties of Co3O4 nanoparticles added (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting phase

Solid-state reaction method was used to synthesize Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase and sol-gel method was used to prepare cobalt oxide (Co3O4) magnetic nanoparticles. These Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223; x = 0–2.00 wt.% nanoparticles-superconductor composites. The effects of Co3O4 nanoparticles on crystal structure, phase formation, phase purity and infield superconducting transport properties of CuTl-1223 phase were investigated at different operating temperatures and external applied magnetic fields. The crystal structure and phase formation of Co3O4 nanoparticles and CuTl-1223 superconductor were determined by X-ray diffraction (XRD) technique. XRD peaks of Co3O4 nanoparticles were well indexed according to FCC crystal structure and the average particle size of 70 nm was calculated by using Debye-Scherer's formula. The unaltered crystal structure of host CuTl-1223 superconducting phase (i.e. Tetragonal) with the addition of Co3O4 nanoparticles indicated the dispersion of nanoparticles at inter-granular sites. Temperature dependent magneto-transport superconducting properties of (Co3O4)x/CuTl-1223 composites were investigated by zero field cooled (ZFC) and field cooled (FC) magnetic moment versus temperature (M-T) measurements. The onset transition temperatures {TcOnset (K)} was decreased along with the suppression of diamagnetic amplitude of CuTl-1223 superconducting phase with the addition of magnetic Co3O4 nanoparticles. Temperature dependent magnetic hysteresis (M-H loops) measurements of (Co3O4)x/CuTl-1223 composites were carried out at different operating temperatures from 5 K to 150 K. Critical current density (Jc) was calculated from M-H loops measurements by using Bean's model. Like the suppression of TcOnset (K) values, Jc was also decreased with the inclusion of Co3O4 nanoparticles. It was also observed that variation of Jc with H followed the power law Jc = βH−α at low operating temperatures 5 K and 20 K only.

Highly coercive cobalt ferrite nanoparticles-CuTl-1223 superconductor composites

We explored the effects of highly coercive cobalt ferrite (CoFe2O4) nanoparticles addition on structural, morphological, and superconducting properties of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223} matrix. Series of (CoFe2O4)x/CuTl-1223 (x=0 ~2.0 wt%) composites samples were synthesized and were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) absorption spectroscopy, and dc-resistivity versus temperature measurements. The magnetic behavior of CoFe2O4 nanoparticles was determined by MH-loops with the help of superconducting quantum interference device (SQUID). MH-loops analysis showed that these nanoparticles exhibit high saturation magnetization (86 emu/g) and high coercivity (3350 Oe) at 50 K. The tetragonal structure of host CuTl-1223 superconducting matrix was not altered after the addition of CoFe2O4 nanoparticles, which gave us a clue that these nanoparticles had occupied the inter-granular sites (grain-boundaries) and had filled the pores. The increase of mass density with increasing content of these nanoparticles in composites can also be an evidence of filling up the voids in the matrix. The resistivity versus temperature measurements showed an increase in zero resistivity critical {Tc(0)}, which could be most probably due to improvement of weak-links by the addition of these nanoparticles. But the addition of these nanoparticles beyond an optimum level caused the agglomeration and produced additional stresses in material and suppressed the superconductivity.

Excess conductivity analysis and infrared absorption spectroscopy of Mg-doped TlBa2Ca2Cu3O10-δsuperconductor

Fluctuation induced conductivity (FIC) analysis on dc resistivity versus temperature data of as-prepared and oxygen post-annealed TlBa2(Ca2-yMgy)Cu3O10-δ (y = 0, 0.25, 0.5, 0.75, 1.0) superconductor samples are carried out by using Aslamazov–Larkin model for excess conductivity. The microscopic parameters such as zero temperature coherence length along c axis {ξc(0)}, interlayer coupling (J), intergrain coupling (α), critical exponent (λ) and dimensionality of superconducting fluctuations are calculated with the help of aforementioned model. The crossover temperature (To) is shifted towards higher temperature values with the increase of Mg contents up to y = 0.5 and then start to decrease but still remains greater than those values of undoped samples. The increase in ξc(0) and J after Mg-doping at Ca sites shows the improvement of interplane coupling in TlBa2(Ca2-yMgy)Cu3O10-δ samples. The appreciable change in all the microscopic parameters extracted from the FIC analysis indicates the optimization of oxygen in all the oxygen post-annealed samples. The increase in relative intensity of almost all the oxygen modes indicates the oxygen diffusion in the unit cell after oxygen post-annealing. The diffusion of oxygen can take place at intergranular sites along with intragranular sites, which increases the grains size, intergrain connectivity and carrier density in CuO2 planes.

Effects of constituent particles and sensitization on surface spreading of intergranular corrosion on a sensitized AA5083 alloy

Surface spreading of intergranular corrosion (IGC) on Al–4.4Mg alloys in NaCl solution was modeled at the micrometer scale, using a continuum granular scale model as a function of the degree of sensitization (DoS). The model utilizes electrochemical, metallurgical, and physical inputs. Al–4.4Mg alloys become susceptible to IGC after precipitation of highly anodic β-phase precipitates along the grain boundaries. In addition, cathodic constituent particles form a galvanic couple with the matrix. Local corrosion is triggered at anodic β-phase precipitates proximate to the constituent particles, which subsequently triggers the corrosion of un-attacked β-phase precipitates often aligned on grain boundaries. The fraction of surface intergranular sites corroded and intergranular surface cluster length increased sharply at a certain degree of sensitization. Specifically, IGC spreading was extensive when the DoS level was greater than 24mg/cm2 and was linked to a decrease in the spacing between the nearest β-phase precipitates below a threshold distance.

Intergranular effects on the local electronic properties of the passive film on nickel

The electronic properties of the granular and intergranular sites of passive films grown on Ni(111) single-crystal surfaces in alkaline solution have been studied with scanning tunnelling spectroscopy. The results show no effect of the grain boundaries on the intrinsic semiconductive properties of the single layer hydroxide passive film. In contrast the local properties of the duplex oxide/hydroxide passive film are changed from nearly intrinsic on the grains to p-type at the grain boundaries. The implications of these local modifications of the electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed.

Local Electronic Properties of the Passive Film on Nickel Studied by Scanning Tunneling Spectroscopy

Scanning tunneling spectroscopy has been applied to characterize the electronic properties of the granular and intergranular sites of the passive film grown on Ni(111) single-crystal surfaces in acid solution. The passive film, essentially consisting of NiO, shows p-type grains (valence band edge at 0.54 ± 0.03 eV below Fermi level) with unoccupied Ni 3d surface states at 0.5–1.5 eV above Fermi level in the bandgap. At grain boundaries, the p-type semiconductivity is attenuated as evidenced by a downward shift of 0.12 ± 0.06 eV of the valence band edge, and the density of surface states is markedly reduced, both effects indicating the presence of oxygen vacancies in these sites. The dominant point defect in the film is metallic vacancies but oxygen vacancies attenuate locally the resulting p-type property at the grain boundaries. The implications of these local electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed. The oxygen vacancies at intergranular boundaries imply local changes of the properties of anionic mass transport through the passive film and enhancement of Cl− adsorption and/or penetration, which is consistent with the view of passive film grain boundaries playing a key role in passivity breakdown.

Novel polyaniline/PVDF/BaTiO 3 hybrid composites with high piezo-sensitivity

Polyvinylidene fluoride (PVDF)–barium titanate (BaTiO 3)–polyaniline (PANI) hybrid composites were prepared by conventional powder processing technique which exhibited remarkably high piezo-sensitivity. The effect of poling of these semi-insulating composites on their piezo-response was quite dramatic. Sensitivity factors of 3000 could be achieved for even small poling voltages as low as 180 V/mm. The synergistic effect was obtained only when all three components, viz. PANI, PVDF and BaTiO 3 were present at certain proportion below percolation threshold in the composite. The results have been explained on the basis of charge storage in the piezo components due to the high fields generated, even for low external applied field, at the inter-granular sites between the semi-conducting polyaniline phase dispersed in the insulating matrix.

Microstructural characterization of simulated heat affected zone in a nitrogen-containing 2205 duplex stainless steel

In order to investigate the microstructural evolution in a nitrogen-bearing 2205 duplex stainless steels (DSS) during welding, a simulated weld thermal cycle with 5 kJ cm −1 heat input followed by exposure at 700 °C for different time intervals was performed. The microstructure of high-temperature heat affected zone (HTHAZ) developed with the thermal experience was characterized via optical metallography and transmission electron microscopy (TEM). The duplex structure with equivalent phase components was drastically destroyed by the rapid thermal cycle. In the simulated HTHAZ structure, three different morphologies of newly formed austenite were observed in the coarse-grained δ-ferrite matrix; i.e. allotriomorphic austenite, Widmanstäten autenite and intragranularly nucleated autenite. During the exposure at 700 °C, the intragranularly nucleated austenite got coarse and the Widmanstäten austenite grew progressively. TEM revealed that several variants of rod-like Cr 2N were precipitated selectively at intragranular and intergranular sites. From the analyses of diffraction patterns of TEM, Kurdjumov–Sachs orientation relationship was found to describe the interface between intragranularly nucleated autenite and δ-ferrite, while Pitch–Schrader orientation relationship to describe the disposition between hexagonal Cr 2N precipitates and δ-ferrite matrix.

Pressureless Sintering of Al 2O 3/Ni Nanocomposites

In the present study, an Al 2O 3/Ni nanocomposite containing 5 vol% Ni is prepared by pressureless sintering at 1400°C for 2 h. Most nickel inclusions, around 70% in the sintered nanocomposite, locate at the intergranular sites, the triple junctions and Al 2O 3/Al 2O 3 grain boundaries. The average size of the nickel inclusions at the triple junctions, grain boundaries and intragranular locations is 145, 131 and 73 nm, respectively. The average size of all nickel inclusions is 118 nm. The presence of nickel inclusions can prohibit the grain growth of matrix grains. The size of Al 2O 3 grains in the sintered nanocomposite is only 490 nm. The strength of the nanocomposite is thus high for the refined microstructure. The matrix Al 2O 3 grains and Ni inclusions at triple junctions underwent considerable coarsening during a post-annealing treatment at 1300°C for 2 h. The strength of the annealed composites is thus reduced significantly after annealing.

The characterization of ZrO 2 engineering ceramics by A.C. impedance spectroscopy

The correlation between ionic conductivity as determined by a.c. complex plane analysis and ceramic alloy microstructure as evidenced by transmission electron microscopy and analysed by X-ray diffraction is explored for different compositions within the Y 2O 3ZrO 2 system. It is shown that conductivity data can be interpreted readily in terms of the microstructural characteristics both at intergranular sites and at intragranular sites, yielding information useful to the development of ZrO 2 ceramics for structural applications.

Le comportement du composant sulfur� du manteau sup�rieur pendant les premiers stades de serpentinisation des p�ridotites de type ?alpin?; une discussion a partir de l'exemple des massifs ultramafiques de Beni Bousera (Maroc) et de Ronda (Espagne)

A volumetrically minor Cu−Fe−Ni−S component derived from the uppermost mantle is found within the Beni Bousera (northern Morocco) and Ronda (southern Spain) “Alpine”-type peridotites; it occurs today as inclusions within primary silicates or as assemblages disseminated in the intergranular sites of the host rocks. Detailed microtextural and microprobe data indicate that inclusions and intergranular assemblages behaved as two contrasting systems during the low temperature, incipient serpentinization of the host rocks. The former were equilibrated in closed systems whereas the latter behaved as open systems with respect to hydrothermal fluids; as a result, intergranular assemblages were controlled by redox conditions generated by serpentinization. An early stage of alteration is characterized by a slight decrease of the sulfur content and would be due to the first influx of water inside peridotites; a further transformation was produced by anomalous highly reducing conditions responsible for the crystallization of native iron-bearing alloy assemblages as well as for a preferential partioning of Fe from silicate into pentlandite. The production of anomalous, reducing conditions during incipient serpentinization is ascribed to a low permeability of the host rocks with respect to the diffusion of hydrogen out of the sites of serpentinization. Because of its low temperature behaviour, the intergranular sulfide component would not be of use reconstructing the initial composition of the upper mantle sulfide component; thus, it is concluded that only the sulfide inclusions would provide such informations.

Effect of Heat Treatment on Photoconductivity and Electrophotographic Properties of Lead Monoxide

AbstractThe effect of heat treatment on the photosensitivity and electrophotographic properties of lead monoxide powder has been investigated. There appears to be a critical temperature of annealing at which photosensitivity is maximum and the darkconductivity is minimum. The electrophotographic behaviour characterized by acceptance potential, dark discharge rate, contrast potential, etc. improved considerably on thermal treatment. The results have been explained mainly on the basis of barrier layer formation at the intergranular sites.

The effect of strain rate on the tensile flow and fracture of α-uranium

Tensile stress-strain curves have been obtained for two grades of uranium (total impurity content 240 and 400 ppm) in the vacuum-annealed condition and one grade (total impurity content 240 ppm) in the as-received condition at strain rates from 10 −4 to > 10 +3/s. The effect of strain rate on the flow stress at constant strain has been determined and the results have been analysed in terms of the theory of thermally-activated flow. A ductility transition, decreasing ductility with increasing strain rate, was observed in the vacuum-annealed specimens but not in those of as-received material. Metallographic examinations of the deformed specimens were carried out using optical and scanning electron microscopy. Many voids were observed at intergranular sites, the number of such voids increasing with strain rate. The fracture mode, however, remained unaffected by strain rate.

Occurrence, distribution, and composition of sulfide minerals, Boulder batholith, montana

Sulfide minerals in the Boulder batholith occur 1. as disseminated grains, visible in hand specimens; 2. in aplitic-pegmatitic pods and masses; 3. along joint and shear surfaces; 4. in hydrothermal veins; and 5. as minute masses within pyrite and silicate minerals and along intergranular sites. Hydrothermally altered rocks have an average sulfide content of 0.8 weight per cent, compared to an average of 0.01 per cent for unaltered rocks. Unaltered rock of the batholith may contain as much as 0.7 weight per cent sulfide. Sulfide inclusions in pyrite, the most abundant sulfide of the batholith, are common and represent a captured iss-phase which later changed to chalcopyrite plus pyrrhotite or mackinawite. Inclusions are most abundant, and more complex, in pyrites of hydrothermally altered and ore rocks. Electron-probe analyses show that pyrites of the Boulder batholith have very similar compositions to those found for pyrites from other ore deposits around the world.

Nucleation of recrystallization in aluminium containing dispersions of alumina

A study has been made of the recrystallization process in a series of samples of aluminium containing dispersions of oxide particles. The effect of varying the volume fraction of oxide and the initial grain size has been investigated. Both the macroscopic and microscopic aspects of the recrystallization processes have been evaluated. The results from measurements of hardness and observation by light microscopy and by transmission electron microscopy are in accord. Nucleation events both within the grains and at intergranular sites have been found. The effect of an increasing volume fraction of oxide particles is to slow down both the formation and growth of viable nuclei.