Gamma Phase Research Articles

Parametric optimization in wire electric discharge machining of DC53 steel using gamma phase coated wire

DC53 is considered as superior steel grade by die and mold making industries as compared to D2 and D3 steel due to its excellent mechanical characteristics like high hardness, wear resistance and strength. DC53 steel finds applications in making stamping dies, punches and cutting tools. In wire electric discharge machining (WEDM) process, gamma phase coated wire offers superior machining performance over uncoated brass and zinc coated electrode wires. This work was performed to study the effect of machining variables like sparks on duration, sparks off duration, arc-on time, and servo voltage on response variables, namely kerf width (KW), cutting speed (CS), material removal rate (MRR), and surface roughness (Ra) for WEDM of DC53 steel. Taguchi L18 orthogonal array was used for experimental design. Analysis of variance showed that sparks on duration is the most significant factor affecting KW, CS, and MRR with percentage contribution of 48.25 %, 80.21 %, and 45.21 %, respectively. Optimal set of machining parameters resulted in 14.02 % improvement in MRR and 19.24 % reduction in workpiece surface roughness. Moreover, gamma phase coated wire was found to have 30–35 % faster cutting rate as compared to uncoated brass wire.

Enhancing combustion performance of nano-Al/PVDF composites with β-PVDF

Solid energetic nanocomposites, consisting of reactive metal particles and oxidizers, find broad applications ranging from pyrotechnics to solid rocket propellants and solid ramjet fuels. In particular, nano-aluminum (n-Al) and polyvinylidene fluoride (PVDF) are attractive fuel and oxidizer materials, due to the high energy density of n-Al, and the high oxidizing potential and excellent mechanical properties of PVDF. PVDF is a semi-crystalline polymer and has three common crystalline phases, alpha (α), gamma (γ), and beta (β) phases. Many research works have focused on the chemical reactions between Al and PVDF, yet the effect of PVDF crystallinity on the Al/PVDF reaction is unknown. Here, we experimentally and computationally demonstrate that increasing the mass fraction of β-phase PVDF from 2.5 to 25% in Al/PVDF composites substantially improves peak pressure by 90% (from ~34 to ~64 psi) and pressure rise rates by 300% (from 2.5 psi/ms to 10 psi/ms). This stems from the alignment of F atoms along one side of the β-PVDF polymer chain, making it structurally conducive to reacting with Al particles to form strong Al-F interactions. This strong interaction leads to higher binding energy between, and hence higher reactivity in, β-PVDF and Al. Our research provides a new method for enhancing the reactive performance of Al/PVDF composites by increasing the content of β-PVDF.

Modulation of auditory gamma-band responses using transcranial electrical stimulation.

Auditory gamma-band (>30 Hz) activity is a biomarker of cortical excitation/inhibition (E/I) balance in autism, schizophrenia, and bipolar disorder. We provide a comprehensive account of the effects of transcranial alternating current stimulation (tACS) and transcranial direct current stimulation (tDCS) on gamma responses. Forty-five healthy young adults listened to 40-Hz auditory click trains while electroencephalography (EEG) data were collected to measure stimulus-related gamma activity immediately before and after 10 min of 1 mA tACS (40 Hz), tDCS, or sham stimulation to left auditory cortex. tACS, but not tDCS, increased gamma power and phase locking to the auditory stimulus. However, both tACS and tDCS strengthened the gamma phase connectome, and effects persisted beyond the stimulus. Finally, tDCS strengthened the coupling of gamma activity to alpha oscillations after termination of the stimulus. No effects were observed in prestimulus gamma power, the gamma amplitude connectome, or any band-limited alpha measure. Whereas both stimulation techniques synchronize gamma responses between regions, tACS also tunes the magnitude and timing of gamma responses to the stimulus. Results reveal dissociable neurophysiological changes following tACS and tDCS and demonstrate that clinical biomarkers can be altered with noninvasive neurostimulation, especially frequency-tuned tACS.NEW & NOTEWORTHY Gamma frequency-tuned transcranial alternating current stimulation (tACS) adjusts the magnitude and timing of auditory gamma responses, as compared with both sham stimulation and transcranial direct current stimulation (tDCS). However, both tACS and tDCS strengthen the gamma phase connectome, which is disrupted in numerous neurological and psychiatric disorders. These findings reveal dissociable neurophysiological changes following two noninvasive neurostimulation techniques commonly applied in clinical and research settings.

Influence of milling parameters on the structural and phase formation in Ti-20%Al alloy through mechanical milling

Titanium aluminides are considered the choice material for next generation propulsion systems due to their high specific strength and high temperature performance coupled with good oxidation resistance. They are considered best materials for specific applications in the aerospace and automobile industry. Their production process, however, determines the final phase in the alloy, which greatly affects their mechanical properties. The effect of the milling parameters on the particle size and the formation of phases were studied on mechanically alloyed Ti-Al powder. A high-energy ball mill (HEBM) was used to mill a mixture of CP Ti and Al to produce titanium aluminide. The alloy was produced at a fixed ball-to-powder weight ratio of 10:1 whilst varying the milling speed and milling time. The mechanically produced powders were analysed using SEM with EDX and XRD to investigate the chemical homogeneity and the formation of phases after the mechanical alloying technique. The analysis of the mechanically alloyed powders from the mill are reported in terms of the morphology evolution during different milling speed, milling time, elemental composition and the phases formed. Alloys milled at a speed of 500 rpm for a milling time range of 5–20 h revealed the formation of Ti alpha (α-Ti) and gamma phase (γ-TiAl).

Sub-Micron Surface Structured Stainless Steel As an Anode for Microbial Fuel Cell

Fossil foil depletion and their environmental impact make it inevitable to find alternative energy resources. One of the promising energy sources is to generate electricity through degrading organic compounds, using biofuel cells. Microbial fuel cells (MFCs) are biofuel cells that produce electricity while treating wastewater, allowing for more sustainable wastewater treatment and energy production1. For MFC to be a real-life application, the material of its components should be efficient, cost-effective, and commercially available. MFCs anodes are the interface where the bio-electrochemical reaction takes place through electron transfer from the bacteria to the electrode to produce an electrical current2. Herein we test a 3D nanostructured 316L stainless steel (SS) anode to provide a high specific surface area for the bacteria to adhere to the surface, and in turn, enhances the bacterial catalytic behavior. Furthermore, the SS nanostructured samples were annealed in various gaseous atmospheres to identify the effect of different surface oxidation states on MFC anodes performance. The surface of the bare SS and the nanostructured anodes were imaged using the field emission scanning electron microscopy (FESEM), before and after using them in the MFCs. The as anodized SS had a 3D nanostructured surface of interconnected nanorods that kept its morphology upon annealing. X-ray diffraction (XRD) was performed at a glancing angle (θ <5°), which interpreted that 316 L as received SS had a face-centered cubic structure that has gamma phase iron with the γ(111), γ (200), γ (220), γ (311), and γ (222) facets 3, while the film formed on the as anodized SS had amorphous regions that were transferred to crystalline film upon annealing for one hour in 450 C temperature. X-ray photoelectron spectroscopy (XPS) was used to characterize the composition of the fabricated SS anodes that interpreted that the film formed on SS was iron-chromium oxyhydroxide film4 and upon annealing the ratio of metal oxides especially Fe2O3 and Fe3O4 increased which increased the metal surface conductivity. The surface conductivity of annealed anodes was tested using cyclic voltammetry (CVs) in the ferricyanide solution. The annealed samples had enhanced to electron transfer kinetics on its surface relative to both the as-received and as anodized samples that showed nearly no redox activity. The fabricated SS samples were tested using a dual-chamber MFCs inoculated with sludge, using acetate as a substrate and potassium ferricyanide as the oxidant in the cathode. The power output of the MFCs with different anodes was observed using a data acquisition system for 20 days. CVs were done on the anodes on the 10th day. The results emphasized that the nanostructured SS samples highly increased cell voltage (≈ 80 times). This enhancement in the MFCs power performance is explained by the enhanced biofilm growth offered by the high specific area for the nanostructured SS. The FESEM images taken after the end of the experiment showed an obvious biomass growth on the surface of the as anodized SS relative to the biofilm on the as-received one. In addition, the annealed samples showed an enhanced activity after annealing. Annealing, especially in O2, increased the surface content of the more biocompatible Fe2O3 component, as interpreted by the XPS, which in turn increased the voltage production (≈ 120 times) relative to the as-received sample. The enhancement of the power generation was further supported using the CVs, with the anodized anode annealed in O2 showing an enhancement anodic current in comparison to smooth SS samples.

Diamond/γ-alumina band offset determination by XPS

γ-Alumina is a promising candidate for fabricating the gate of the diamond metal oxide semiconductor field effect transistor based on oxygen termination due to its high bandgap of 6.7 eV and high static dielectric constant of 9. Besides these properties, having a sufficient barrier for holes is mandatory to avoid carriers leakage through the gate. However, the band offset of the diamond/alumina heterojunction can be affected by the alumina crystallinity and interface bonds, which depend on multiple factors such as deposition and annealing temperature or diamond surface treatment prior to deposition.In this work, the heterojunction of atomic layer deposited alumina and (1 0 0) p-diamond is studied using X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy studies reveal that the deposited alumina layer is 35 nm thick and present the gamma phase. The valence band offset between diamond and γ-alumina is evaluated on a single sample with a new methodology based on an ion etching XPS depth profile. The obtained value for the valence band offset of diamond and γ-alumina is 3.4 eV.

Antagonistic muscle prefatigue weakens the functional corticomuscular coupling during isometric elbow extension contraction.

During muscle fatigue, acute changes in the interaction between the sensorimotor cortex and peripheral neurons have been widely studied. However, it is still unclear about the effect of antagonist muscle prefatigue on corticomuscular coupling and central modulation. The purpose of this study was to investigate the changes in the magnitude of electroencephalogram-electromyography (EEG-EMG) coherence and phase synchronization index (PSI) induced by antagonistic muscle prefatigue. Twelve young male volunteers conducted a 30-s long, nonfatiguing isometric elbow extension with a target force level of 20% maximum voluntary contraction (MVC) before and after a fatiguing sustained elbow flexion contraction at 20% MVC until task failure. Coherence and PSI between the EEG recorded over the sensorimotor cortex and the surface EMG of the triceps brachii (TB) muscle were quantified for the pre- and post-fatigue elbow extension contractions. Coherence and PSI in the gamma frequency band (35-60 Hz) were found significantly decreased in the postfatigue elbow extension contraction than the prefatigue contraction. The power of the EEG in the beta and gamma band were significantly increased, while the EMG power showed no significant changes when the antagonistic muscle was prefatigued. PSI in the gamma frequency band between the EMG of the TB muscle and the EEG were found significantly decreased during postfatigue elbow extension contraction compared with prefatigue contraction. Antagonistic muscle prefatigue led to significantly lower gamma band corticomuscular coherence and phase coupling during an isometric elbow extension position task. The lower corticomuscular coupling may indicate a central modulation mechanism of antagonist muscle prefatigue that related to decreased descending common drive or joint instability compensation modulation mechanism.

Movement-related coupling of human subthalamic nucleus spikes to cortical gamma.

Cortico-basal ganglia interactions continuously shape the way we move. Ideas about how this circuit works are based largely on models those consider only firing rate as the mechanism of information transfer. A distinct feature of neural activity accompanying movement, however, is increased motor cortical and basal ganglia gamma synchrony. To investigate the relationship between neuronal firing in the basal ganglia and cortical gamma activity during movement, we analysed human ECoG and subthalamic nucleus (STN) unit activity during hand gripping. We found that fast reaction times were preceded by enhanced STN spike-to-cortical gamma phase coupling, indicating a role in motor preparation. Importantly, increased gamma phase coupling occurred independent of changes in mean STN firing rates, and the relative timing of STN spikes was offset by half a gamma cycle for ipsilateral vs. contralateral movements, indicating that relative spike timing is as relevant as firing rate for understanding cortico-basal ganglia information transfer.

Auditory evoked potentials might have the potential to serve as early indicators related to amyloid beta peptide toxicity

PurposeAccumulation of amyloid beta (Aβ) is thought to be the major cause of the development and progression of Alzheimer's disease (AD). The aim of this study is to elucidate the effects of Aβ1-42 at increasing concentrations on auditory evoked potentials (AEPs) and to determine possible changes relevant to the accumulation of Aβ1-42. Materials and methodsIn this study, rats were randomized to following groups (n = 10 per group): sham (0.9% NaCl), Aβ-1 (1 μg/μl), Aβ-2 (2 μg/μl), Aβ-3 (3 μg/μl), Aβ-4 (4 μg/μl), Aβ-5 (6 μg/μl), Aβ-6 (8 μg/μl) and Aβ-7 (10 μg/μl) groups obtained by injection of 5 μl per ventricle. Then, AEPs were recorded in freely-moving rats. Latencies and amplitudes of AEPs, evoked power, inter-trial phase synchronization, and auditory evoked gamma responses were obtained in response to auditory stimulus. Furthermore, Aβ1-42 levels were determined in the temporal cortex. ResultsAβ1-42 levels were significantly higher in the temporal cortex in Aβ groups compared to the sham. In frontal and parietal regions, P1N1 amplitudes were significantly decreased in Aβ-3, 4, 5 and 6 groups, and N1P2 amplitudes were significantly decreased in all Aβ groups, whereas in temporal regions, P1N1 and N1P2 amplitudes were decreased in Aβ-2,3,4,5,6 and 7 compared to the sham. In the evoked gamma power and phase synchronization of gamma responses, we detected significant decrease after Aβ-4 group, whereas a significant decrease in the filtered gamma responses was observed in Aβ groups compared to the sham. ConclusionsAEPs might be used as a biomarker to determine the Aβ1-42 related neuronal degeneration in the auditory networks.

Effect of Al on phase evolution in Prior-Ni coated galvanized steel: Thermodynamic and kinetic assessment

Coating of advanced high strength steel and ultra-high strength steel is a burning issue due to the problem of surface oxidation of alloying elements and liquid metal induced embrittlement (LMIE). In last decade, prior coating of Ni before galvanizing has gained much interest as it has the potential to suppress the surface oxidation of advanced high strength steel with added benefits. Recently, the galvanized ultra-high strength steel with a prior-Ni coating also has been proved as a solution for hot stamping application. It has been observed that prior-Ni reacts with Zn at the stage of galvanizing and forms different Ni–Zn alloy phases with high melting temperatures and resist the LMIE at the time of hot stamping. Al is one of the most important alloying element in commercial galvanizing bath. However, effect of Al on the Ni–Zn phase formation in such coating has not been researched in detail. In the present study, phase formation in prior-Ni coated galvanized steel in the presence of Al in Zn bath has been thoroughly investigated. The influence of Al on the Ni–Zn phase formation has been assessed by thermodynamic and kinetic calculation and then validated by experiments. Al3Ni2 with dissolved Zn precipitated in the Zn overlay and of Ni–Zn alloy phases such as NiZn8 and gamma phase formed on prior-Ni layer in a Zn–Al bath up to 0.01 mass fraction of Al. However, Ni–Zn alloy phases such as NiZn8 and gamma phases were absent in coating achieved by Zn–Al bath above 0.01 mass fraction of Al. Instead a thin compact layer consisting high amount of Ni, Al and Zn formed on prior-Ni layer and hindered the formation of Ni–Zn alloy phase in coating. The mechanism of the phase formation in the prior-Ni coated galvanized steel in presence of Al has been described with the help dissolution, phase fraction, driving force calculations and experimental observations.

Analytical models of austenite transformation in steels taking into account internal stresses

Analytical models of the transformation of austenite into steel are considered taking into account the influence of the stress state on structural transitions during heat treatment of steels A simple theoretical expression is proposed for calculating the amount of martensite formed as a function of the stresses in the gamma phase

Polyvinylidene fluoride (PVDF)-poly(methyl methacrylate) (PMMA)-expanded graphite (ExGr) conducting polymer blends: Analysis of electrical and thermal behavior

Polyvinylidene fluoride (PVDF)-20 wt% poly (methyl methacrylate) blend has been synthesized by solution blending method. Expanded graphite has been synthesized by microwave irradiation of commercial expandable graphite. With varying concentration of expanded graphite (ExGr) in PVDF-20 wt% PMMA, series of blends are synthesized. The electrical percolation threshold has been observed to be less than 1 wt% ExGr which is due to the formation of graphite nanosheets. The conducting blend system exhibits typical percolation behavior. The thermogravimetric analysis shows two step degradation in PVDF-20 wt% PMMA blend system. This is due to the individual degradation of PMMA and PVDF main chains respectively. The thermal stability of the blend system with 1 wt% ExGr incorporation in PVDF-20 wt% PMMA is increased by 11 °C corresponding to main chain degradation of PVDF. The result proves existence of strong interaction between ExGr particles and the polymer. The DSC analysis shows very clearly the existence of electroactive gamma phase both in PVDF-20 wt% PMMA with and without ExGr particles as there is an additional high temperature melting peak apart from that of the melting peak at 167 °C. This result is confirmed through XRD also. The blend system is characterized by XRD, TGA, DSC and FTIR.

Biosynthesis of iron oxide nanoparticles using ethyl acetate extract of Chaetomium cupreum and their anticancer activity

Background: The biosynthesis of iron oxide nanoparticle (NP) formation was carried out using ethyl acetate extract of fungus Chaetomium cupreum as reducing agents. The C. cupreum contains azaphilones pigments which poses various biological activities. Objectives: The synthesis of iron oxide NP and their anticancer potential was investigated. Materials and Methods: The anticancer activities of biosynthesized iron oxide NP were evaluated using tetrazolium bromide assay, measurement of reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and inhibition of tumorsphere formation. Results: In the present study, the X-ray diffraction shows the presence of gamma phase iron oxide NP withe the type of Fe2O3. The anticancer potential of iron oxide NP was investigated against human breast cancer cell line. The anticancer activity of biosynthesized iron oxide NP against MCF-7 was 20.5, 30.5, 41.1, 55.3 67.5, and 75.25 at 50 μg/ml after 1, 5, 10, 15, 20, and 24 h of treatment, respectively. The results showed that Fe2O3NP induced ROS generation to 68.22% at the concentration of 25 μg/ml and 83.66% at 50 μg/ml as compared to 48.22 in control after 15 h of treatment. The results showed that Fe2O3NP treatment increased depolarization MMP to 8.52% at 25 μg/ml and 10.74% at 50 μg/ml as compared to 6.35% in untreated cells after 24 h. Thus, treatment with Fe2O3NPs showed significant inhibition of MCF-7 tumorsphere formation at higher concentration. Conclusion: The biosynthesized iron oxide NP using ethyl acetate extract of C. cupreum exhibit significant anticancer activity.

Fabrication and characterization of porous biomedical Vitallium alloy with 58S bioglass coating prepared by sol-gel method

Cobalt-based alloys are used as medical implants due to their excellent mechanical properties and suitable biocompatibility. However, its application in the body is restricted due to mechanical mismatch and bio neutrality. This study aimed to fabricate a porous Vitallium alloy and apply 58S bioglass coating on this substrate to improve its mechanical and bioactivity behavior. Porous scaffold with porosity about 36% was fabricated and then, the 58S bioglass coated by sol-gel method on the porous substrate. After drying the coating, it stabilized at a temperature of 600 °C for 1 h. The results showed that all of the formed cobalt phases after sintering were gamma phase with an FCC crystalline structure. The results also showed that the compressive strength and modulus were about 80 MPa and 0.40 GPa, respectively. The porosity percentage of sintered porous Vitallium decreased by about 2% after coating, and the size distribution of the porosities was in the range of 100–400 μm. The coated sample showed significantly higher bioactivity than that of the uncoated sample. According to the collected results, it can be pointed out that the Vitallium porous scaffold with bioglass coating could be chosen for the bone implants.

The hydrogen embrittlement sensitivity of duplex stainless steel with different phase fractions evaluated by in-situ mechanical testing

The influence of the austenite (gamma) phase fraction on the hydrogen embrittlement of duplex stainless steel is investigated. Heat treatments are performed to create two duplex stainless steel specimens, containing 50% and 44% of austenite, respectively. Mechanical testing with and without hydrogen charging reveals that significant embrittlement occurs regardless of the austenite fraction. A higher austenite fraction results in a reduced ductility loss under the presence of hydrogen. Samples with a higher ferrite fraction are embrittled more due to their higher hydrogen diffusivity. In-situ tensile tests, interrupted at the ultimate tensile strength, show hydrogen-assisted cracks on the specimen surface both in austenite and ferrite and across the alpha/gamma interface.

Alterations in sleep, sleep spindle, and EEG power in mGluR5 knockout mice.

The type 5 metabotropic glutamate receptor (mGluR5) represents a novel therapeutic target for schizophrenia and other disorders. Schizophrenia is associated with progressive abnormalities in cortical oscillatory processes including reduced spindles (8-15 Hz) during sleep and increased delta (0.5-4 Hz)- and gamma-band activity (30-80 Hz) during wakefulness. mGluR5 knockout (KO) mice demonstrate many schizophrenia-like behaviors, including abnormal sleep. To examine the effects of mGluR5 on the maintenance of the neocortical circuitry responsible for such neural oscillations, we analyzed sleep/wake electroencephalographic (EEG) activity of mGluR5 KO mice at baseline, after 6 h of sleep deprivation, and during a visual method of cortical entrainment (visual steady state response). We hypothesized mGluR5-KO mice would exhibit translationally relevant abnormalities in sleep and neural oscillations that mimic schizophrenia. Power spectral and spindle density analyses were performed across 24-h EEG recordings in mGluR5-KO mice and wild-type (WT) controls. Novel findings in mGluR5 KO mice include deficits in sleep spindle density, wake alpha power, and 40-Hz visual task-evoked gamma power and phase locking. Sigma power (10-15 Hz), an approximation of spindle activity, was also reduced during non-rapid eye movement sleep transitions. Our observations on abnormal sleep/wake are generally in agreement with previous reports, although we did not replicate changes in rapid eye movement sleep. The timing of these phenotypes may suggest an impaired circadian process in mGluR5 KO mice. In conclusion, EEG phenotypes in mGluR5 KO mice resemble deficits observed in patients with schizophrenia. These findings implicate mGluR5-mediated pathways in several translationally relevant phenotypes associated with schizophrenia, and suggest that agents targeting this receptor may have harmful consequences on sleep health and daily patterns of EEG power.NEW & NOTEWORTHY Metabotropic glutamate receptor type 5 (mGluR5) knockout (KO) mice show several translationally relevant abnormalities in neural oscillatory activity associated with schizophrenia. These include deficits in sleep spindle density, sigma and alpha power, and 40-Hz task-evoked gamma power. The timing of these phenotypes suggests an impaired circadian process in these mice. Previously reported rapid eye movement sleep deficits in this model were not observed. These findings suggest mGluR5-enhancing drugs may improve sleep stability and sleep spindle density, which could impact memory and cognition.

Local ferroelectric studies on interconnected PVDF nano-dot thin films using piezo force microscopy

The local ferroelectric domain structure of interconnected PVDF nano-dots with applied DC voltages of ± 10 V to ± 100 V is evaluated using various Piezo force microscopy (PFM) methods such as conventional PFM and Dynamic contact electrostatic force microscopy (DC-EFM). The self-assembled PVDF nano-dots are fabricated by using a spin coater method with 2 wt% of PVDF-DMSO solution. The polar gamma phase is found to be induced by the microstructural confinement of PVDF monomers and also reveals a strong ferroelectric nature after poling at different DC bias voltages. Poling with altered directions of the voltages renders a 180° phase reversal of PVDF domains. The local domain study depicts that each nano-dot is functioning as a single domain and switches as a whole. The single nano-dot switching signifies the potential of using the nano-dots for organic ferroelectric memory devices.

Microstructural and Mechanical Investigation of WC-TiC-Co Cemented Carbides Obtained by Conventional Powder Metallurgy

WC-Co cemented carbide is one of the widely hard materials used for cutting in machining industry, due to its microstructural and mechanical stability even at high temperature. However, diffusion wear is the most serious problem that WC-Co suffers from. One of the most applied approaches to improve the WC–Co cemented carbide performances is the addition of transition metal carbides such as: TiC, TaC and NbC which prevents diffusion wear thanks to the gamma phase (Ti,Ta,Nb,W)C which is formed during sintering. Therefore, and in order to understand the thermal metallurgical reactions occurred between WC-Co cemented carbide and (Ti, Ta, Nb)C transition carbides and theirs effects on the microstructural and mechanical properties. The WC–TiC– TaC– NbC–Co cemented carbide was elaborated by conventional powder metallurgy then thermal, microstructural and mechanical investigations were performed on the elaborated carbide. A temperature of sintering was determined to be more than 1347 oC by differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Scanning electronic microscopy (SEM) coupled with energy dispersive spectrometer (EDS) observations showed that the microstructure consists in a mixture of angular WC grains and (W,Ti)C rounded grains embedded in the Co-rich binder. X-ray diffraction analysis confirmed the presence of these three phases with free carbon. The results of EDS analysis highlight the solution-reprecipitation phenomena caused by liquid phase sintering and clearly revealed the presence of small amount of free carbon. The mechanical characterizations showed that the WC–TiC– TaC– NbC–Co cemented carbide exhibits excellent hardness-fracture toughness combination.

Experimental and ab initio study of the Ag–Li system for energy storage and high-temperature solders

The standard enthalpies of formation of the Ag30Li70 and Ag20Li80 gamma phases (cubic, sg. I-43 m) were measured using the solution calorimetry method; the standard enthalpy of formation of the Ag10Li90 alloy, corresponding to a hypothetical γ phase, was determined using the same method. All the measured and literature values of the standard enthalpies of formation of the Ag–Li intermetallic phases were compared with the data calculated using ab initio for stable and unstable phases and Miedema’s model. The XRD pattern for a sample with Ag30Li70 was obtained and it was verified that it contained the γ phase, as expected. Moreover, the structure of the γ-phase for the Ag4Li9 disordered phase was minimized and the vibrational heat capacity at constant volume and the thermal coefficient of linear expansion were calculated using ab initio methods. The simulated XRD pattern of the latter phase was compared with the experimental pattern. It was determined that only one gamma phase, with a homogeneity range not wider than 0.69 ≤ x(Li) ≤ 0.73, is stable for T ≥ 298 K. Furthermore, besides AgLi-β with a homogeneity range of 0.50 ≤ x(Li) ≤ 0.60 at 298 K, a cubic Ag15Li49-β is stable for x(Li) = 0.77. The entropy term stabilizes the cubic structure of the AgLi-β which can be tetragonal at 298 K. The enthalpies and Gibbs energies of formation were calculated at 298, 320, 425, and 600 K. A new “map” of the phases in equilibrium at different temperatures is proposed.

A new approach for the fabrication of porous alumina beads using acid leachate of kaolin

Abstract In the present study, alumina beads; both in the α (alpha) phase and γ (gamma) phase; were prepared using the acid leachate of kaolinite as a starting solution by an oil-drop method. Size of the alumina beads prepared by this method was 6 mm–8 mm. The effect of different parameters on the formation, morphology and stability of the alumina beads were studied. Both α phase and γ phase were characterized by powder X-ray diffractometer (XRD), thermogravimetry (TG), differential scanning calorimeter (DSC), Fourier transforms infrared spectrophotometer (FTIR), field emission scanning electron microscope (FESEM), N2 adsorption-desorption surface area analyser and a pore size analyser. The porous nature of the beads was confirmed by the pore size distribution study as per the Barrett, Joyner, and Halenda (BJH) method and FESEM images. The γ alumina beads were found to have a higher surface area and porosity than α alumina beads. The unimodal distribution of pores in the mesoporous region of γ alumina beads suggests the possible application of these beads in the adsorption process.