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The energy band structure is crucial for solid insulation research. The traditional thermally stimulated current is used mostly for direct trap estimation but has some limitations, which can be overcome by the space charge decay method. With the help of a modified pulsed-electro acoustic system, we perform the test under different low temperatures and obtain a more comprehensive band spectrum including shallow traps and different polarities. This study chooses isotactic polypropylene (PP) to investigate in a temperature range of −120 to 20 °C. Signal processing and recovery are considered. Two basic trap estimation methods are compared and the one based on the modified isothermal relaxation current theory is used here. The electron and hole trap densities near different electrode interfaces are considered in the experiment. In the preliminary results, it is found that the traps tend to move toward a shallow direction with a decrease in temperature. A model of the retrapping process caused by phonon scattering is put forward to explain the results. The retrapping possibility is, therefore, assumed to follow a power relation with temperature. An attempt to rectify the trap depth is performed on such a model by numerical approximation and reaches the result that the retrapping possibility may be dependent upon the second power of temperature. Finally, the broadband energy spectrum is calculated after correction. In the normalized coordinate system, the traps in PP are mainly distributed in a deep range; few shallow traps are found maybe because the space charge density is low. [ABSTRACT FROM AUTHOR]

In the whole power system, the importance of the transformer is self-evident, if its fault is bound to cause adverse effects on the whole power system. However, the previous fault diagnosis method is not only time-consuming and laborious, but also has great danger, once it is not handled properly, it may also pose a threat to the life safety of operators. At this time, the transformer fault diagnosis mode based on voice print follows and becomes a big tool for fault diagnosis. However, the surrounding environment of the transformer is changeable and noisy, which will cause interference to the voice print signal and affect the fault diagnosis result. In this regard, this paper will start from this key point and solve this unfavorable factor by using different denoising technologies and feature extraction technologies. The final empirical results show that the improved wavelet threshold technology has the best denoising ability, and the feature parameters obtained under the transformer sound frequency cepstrum coefficient (TFCC) feature extraction technology can better improve the fault diagnosis accuracy. It can solve the problem of low fault diagnosis rate of transformer in different environments, and can be used in practical engineering. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting offers a most promising pathway for "green hydrogen" generation. Even so, it remains a struggle to improve the electrocatalytic performance of non‐noble metal catalysts, especially bifunctional electrocatalysts. Herein, aiming to accelerate the hydrogen and oxygen evolution reactions, an oxygen‐bridged cobalt–chromium (Co‐O‐Cr) dual‐sites catalyst anchored on cobalt phosphide synthesized through MOF‐mediation are proposed. By utilizing the filling characteristics of 3d orbitals and modulated local electronic structure of the catalytic active site, the well‐designed catalyst requires only an external voltage of 1.53 V to deliver the current density of 20 mA cm−2 during the process of water splitting apart from the superb HER and OER activity with a low overpotential of 87 and 203 mV at a current density of 10 mA cm−2, respectively. Moreover, density functional theory (DFT) calculations are utilized to unravel mechanistic investigations, including the accelerated adsorption and dissociation process of H2O on the Co‐O‐Cr moiety surface, the down‐shifted d‐band center, a lowered energy barrier for the OER and so on. This work offers a design direction for optimizing catalytic activity toward energy conversion. [ABSTRACT FROM AUTHOR]

Space charge accumulation in polymer is a key problem for the electrical aging of insulation under DC condition. Space charge accumulation is strongly determined by the charge injection rate. The estimation of charge injection with steady state current contains the extraction current and is not accurate. This paper proposes a quantitative estimation method of the charge injection at the metal/polymer interface with space charge and current simultaneous measurement. A double-layer sample with a blocking layer is employed to make a quasi-unipolar condition to remove the extraction current. In addition, the displacement current is removed by considering the change in electric field on the electrode. The relationship between the electrode electric field and the pure injection current is analyzed. It is found that the square root of electric field intensity and the logarithm of injection current at the Al/LDPE (low density polyethylene) interface are linear with each other. The coefficients β for negative and positive charge injection at Al/LDPE interface are about 8.44 × 10−24 and 8.32 × 10−24, respectively. It indicates that both negative and positive charge injection at Al/LDPE interface fit the mathematical relationship of the Poole–Frenkel effect, rather than the Schottky effect which is mostly used in the study on the charge transport at polymer/metal. The negative and positive charge injection barriers are 1.23 and 1.24 eV, respectively. [ABSTRACT FROM AUTHOR]

A polypropylene (PP) film is usually employed as the main insulation of the peaking capacitor, which is important in an electromagnetic pulse simulator to generate high-amplitude nanosecond pulse. The flashover voltage of PP films under nanosecond pulse limits the highest working voltage of a peaking capacitor. Surface fluorination was employed to increase the flashover voltage of PP. The flashover voltages of PP samples with different fluorination times (0, 4, and 6 h) were tested in an oven with nanosecond pulse voltage. The results showed that the flashover voltage of the PP film with 6-h surface fluorination was increased about 15% than the untreated film in the air. To clarify the influential mechanism, the physicochemical properties of PP film samples were tested and characterized. The results of thermally stimulated depolarization current (TSDC) showed that the trap density of the PP film increased obviously after fluorination treatment. With the increase in treatment time, the trap depth and density were increased obviously. The surface conductivity of PP films slightly decreased with the increase in fluorination time. The mechanism of surface fluorination on the influence of the flashover performance of the PP film under nanosecond pulse is discussed. It is concluded that surface fluorination significantly increases the carbon–fluorine (C–F) bond of the PP film, resulting in the increase in the depth and density of the surface trap, and then, a large amount of homocharges trapped in the surface trap reduces the electric field near the electrode. [ABSTRACT FROM AUTHOR]

• Power networks can use inexpensive liquid metal batteries for large-scale energy storage. • Liquid metal batteries' special structure can prevent dendritic development and minimize safety risks. • The study of liquid metal electrolytes is less than that of liquid electrodes, hence the focus must be shifted to electrolyte research. • Liquid metal batteries' electrolyte issue must be resolved for them to function in low-temperature conditions. Liquid metal batteries possess stable safety performance, high rate performance, and thermal stability. The liquid metal battery stores a large amount of electrical energy producing from wind energy or solar energy. The remarkable performance of the liquid metal batteries is partly attributed to electrolyte, which is an important component of the battery. In this paper, the important research progress of liquid metal batteries electrolyte are reviewed and the electrolyte types which have an influence on energy efficiency are discussed in detail. Then, the limitations and challenges of existing electrolytes are also pointed out. On this basis, the key development directions of liquid metal electrolytes are discussed and clarified. [Display omitted] [ABSTRACT FROM AUTHOR]

• The electrochemical behavior of molybdenum ions and their electrodeposition mechanism in molten salts were systematically investigated. • The variation of Mo element concentration and the valence state of the molten salt bottom product was tested by in situ salt extraction during electrolysis. • The causes of current fluctuation during constant voltage electrolysis were revealed, culminating in the successful electrolysis of molybdenum. The electrochemical behaviors of molybdenum ions in NaCl-KCl molten salt at 750 °C were studied in detail, and pure metallic molybdenum was collected on the cathode. The reduction and diffusion processes of molybdenum ions in NaCl-KCl molten salt were also identified using cyclic voltammetry and square wave voltammetry. The diffusion coefficient and nucleation mode of molybdenum ions were analyzed. Electrodeposition was performed at a constant voltage and the variation of current with time was recorded. The variation of Mo element concentration and the valence state of the molten salt bottom product was tested by in situ salt extraction during electrolysis. The result demonstrated that the electrode reduction process of molybdenum ion in NaCl-KCl molten salt at 750 °C was a two-step reaction, Mo(V) → Mo(III) → Mo, all of which was reversible and controlled by diffusion. Meanwhile, the nucleation mode of molybdenum ions was found to be progressive nucleation. It was determined by XRD, SEM and EDS that the primary component of the cathode deposition product was molybdenum. [ABSTRACT FROM AUTHOR]

Electrocatalysis is a potential method for sustainable hydrogen production, and the development of non‐noble metal‐based effective electrocatalysts for electrochemical water splitting is the core of exploiting and utilizing renewable energy. Herein, a stupendous electrocatalyst with multiheterostructure interfaces and 3D porous structure is synthesized, and the mechanisms of enhanced electrocatalytic activity combining multicharacterizations and density functional calculations are clarified. Especially, the fabricated Co2P/N@Ti3C2Tx@NF (denoted as CPN@TC) exhibits an ultralow overpotential of 15 mV to arrive at a current density of 10 mA cm−2 with the long‐term durability and a small Tafel slope of 30 mV dec−1 in 1 m KOH, which even compares with noble metal catalysts favorably. The outstanding HER activity is ascribed to multiheterointerfaces for adsorbing H2O and H*, fine conductivity for the electronic transmission, and well‐designed structure for rapid transport of ions and gases. It is reasonable to think that the synthetic strategy of CPN@TC can be extended to the preparation of transition‐metal‐based phosphides for enhanced catalytic performance. [ABSTRACT FROM AUTHOR]

A surface streamer is a ubiquitous discharge in electric equipment and surface dielectric barrier discharge. It is expected to suppress this kind of surface discharge in the insulation system, but on the other hand, the surface streamer is also utilized for the generation of active ions and the control of a gas kinetic distribution. As a product of the surface streamer, surface charge influences and characterizes the streamer's behavior. This study observed the two-dimensional transient evolution of the surface charge and the tangential electric field in a single individual surface streamer at the nanosecond level. Using a reflective Pockels effect system and a framing camera system, the surface streamer propagation under a sub-microsecond pulse voltage was measured in real time and in situ. The inception, propagation, and deceleration of a surface streamer are observed. The measurement exhibits an electrode-charge equipotential region that equivalently extends the electrode boundary. Under an anode field with a weak tangential component, the interior of the surface streamer channel exhibits local deviations from the quasi-neutrality, and a reversed tangential electric field is observed. The lateral movement of the positive charge may be responsible for this reverse electric field. The diagnostic technique presented in this study can describe the surface charge transient behavior in pulsed surface discharges, which complements the streamer model. [ABSTRACT FROM AUTHOR]

As an interface between the different insulating polymers exists in the joints of High Voltage Direct Current (HVDC) cables, the differences in the field-and-temperature dependence of the conductivities of the materials is regarded as a problem leading to interface charge accumulation and field distortion. In this report, using blocking materials to prevent charge injection from one or both sides of the electrodes, the contributions of charge injection and ionization in low-density polyethylene (LDPE), cross-linked polyethylene with nanoparticles (nano-XLPE) and ethylene propylene diene monomer (EPDM) are distinguished and evaluated based on the results from pulsed electro-acoustic (PEA) method. It is found that the contributions of charge injection and ionization behave differently in different materials. The mechanism behind the field-and-temperature dependences of the conductivities of the three materials is explained successfully. This study helps to clarify the charge transfer mechanism, and thus supports the quantitative calculation of the space charge and electric field distribution in cable joints. [ABSTRACT FROM AUTHOR]

The development of a system to measure simultaneously the current and space charge in a dielectric is described. The results obtained for low density polyethylene samples show that the relationship between space charge accumulation and the time-dependent current is not straightforward. In accord with previous work on space charge limited currents, the transient currents initially decreased, but after a while an increment or peak appeared. Additionally, the generation and extraction of space charge packets caused an impulse-like current peak such as previously observed. By comparing the electric field and current at the anode, it was found that the increment and the peak of the anode current are determined by injected negative carriers reaching the anode rather than the increase of electric field at the anode. It is shown that the dynamical evolution of the current can be divided into three stages similar to transient space charge limited current theory. [ABSTRACT FROM AUTHOR]

It still remains a great challenge to develop alternative electrocatalysts with low cost, high efficiency and good stability for the hydrogen evolution reaction (HER). In this study, effectively conductive rGO (reduced graphene oxide) was used as the support both to promote charge transfer and to refine the particle size of WC, to realize efficient and stable HER performance. The facile in situ method can make highly dispersed WC nanoparticles firmly anchor onto the rGO substrate. Benefiting from its unique morphology and strong synergistic effect, the designed WC@rGO achieves a giant improvement in HER activity in both acidic and alkaline solutions compared with pristine WC. The overpotentials of WC@rGO are 2.82 and 2.30 times smaller than those of pristine WC to achieve 10 mA cm−2 in acid and alkaline solutions. More specifically, the Pt-modified WC electrocatalyst with negligible accumulation of Pt (4 wt%) even exhibits superior electrocatalytic performance (η10 and Tafel slope of 54 mV and 21 mV dec−1 in acid solution and 61 mV and 28 mV dec−1 in alkaline solution) to commercial 10 wt% Pt@C. The method reported in this study enables eco-friendly preparation of cheap, stable and effective HER electrodes. [ABSTRACT FROM AUTHOR]

Epoxy resin is widely deployed as a high voltage electrical insulation material when compounded with inorganic fillers. However, in the laboratory, the filler prevents visual observation of the long-term degradation known as electrical treeing. To date therefore, much laboratory testing has been conducted on unrepresentative unfilled materials. Here, the impact of micro-sized fillers on the treeing phenomenon in an epoxy system has been explored. Sub-micrometre resolution 3D reconstructions of electrical trees are reported from X-ray computed tomography (XCT) using an advanced ‘pink beam’ synchrotron light source imaging system. The role of filler particles between 1 and 10 μm in size on tree channel propagation is reported. In highly filled materials (30% by weight) a radical change in tree growth behavior is seen, leading to bush tree rather than branch tree growth. The dielectric breakdown time at constant stress was also found to increase as the square root of the filler level. The change in geometry of tree growth may explain the extended life of filled materials in high voltage applications. [ABSTRACT FROM AUTHOR]

This paper reports observations of electrical tree growth by X-ray computed tomography (XCT) in multiple steps. Growth between times of observation has been obtained by subtraction of an image from the subsequent one. Partial discharge (PD) signals were also recorded during tree growth. It is determined that not all PDs support tree extension. By comparing the energy released by PD and the vaporization energy of newly grown tree channels, it is found that only the PDs that reach the tree tips can contribute to the growth of tree length. In such cases, the efficiency of energy conversion was very high, whereas PD resulting in increases in tree channel diameter had a much lower conversion efficiency. Nano XCT images reveal many finer branches along the trunk of the main tree and in the front of the main channel tree tips. It seems that those finer branches led to tree growth, but were not directly associated with local PD. The new imaging techniques have shown great value in resolving the relationship between partial discharge activity and electrical tree growth, providing a platform for deeper understanding of the tree growth process, and interpretation of partial discharge measurements. [ABSTRACT FROM AUTHOR]

• Shape-controlled synthesis of W particles via salt-assisted reduction was proposed. • Large powders disappeared and were degraded under the influence of Y(NO 3) 3. • Temperature and additive greatly affected the morphology and size of W particles. • The added salt improved the crystallization of particles. • The reaction mechanism was discussed as well. Tungsten, one of the refractory metals, has lots of excellent properties, making tungsten powders become a choice of raw material for many applications. This work reported a simple method (the salt-assisted hydrogen reduction of WO 3 powders) for preparing tungsten powders with desired morphologies and size. By adjusting the amount of additive (Y(NO 3) 3) and reduction temperature, metallic tungsten particles with different morphologies and size were obtained. It was found that both temperature and additive had apparent effects on the morphology and size of metallic W particles, and the large parallelepiped-shaped powders disappeared and large irregular blocky-shaped powders were degraded under the influence of additive. With the increase of temperature and amount of salt, particles became more dispersed and the size increased at higher temperatures, and the shape of particles was changed from spherical to polyhedral as well. On the contrary, the size of sub-particles became smaller as increasing amount of Y(NO 3) 3 at lower temperatures. Based on the results, the reaction and refining mechanisms for preparing tungsten were proposed as well. [ABSTRACT FROM AUTHOR]

Electric tree growth is a key ageing mechanism leading to breakdown of high voltage electrical insulation. Partial discharges (PDs) are invariably associated with electrical tree inception and propagation. In turn, the physical structure of an electrical tree influences the characteristics of partial discharge activity. Interpretation of PD patterns is therefore central to developing an understanding of the tree propagation process, and also to the use of PD patterns as an asset management tool. Our previous research indicates that the phase resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns evolve with tree propagation. A method was proposed to estimate the point-on-wave inception and extinction voltages of PDs in tree channels within each power cycle. It was shown that the evolution of PD patterns is a consequence of changes to PD inception and extinction voltages as a tree develops. This paper provides a deterministic model of partial discharge in tree channels. Simulations of PDs in a straight non-conductive tree channel are based on experimental PD inception, extinction and residual voltages. The quantitative simulations reproduce almost all the characteristics of observed PRPD and PSA patterns. It is concluded that PD events are determined by five key parameters: tree structure, applied voltage, PD inception voltage, PD extinction voltage and PD residual voltage. Key parameters estimated by the method, and the models proposed explain PD activity in non-conductive trees. It is suggested that the PSA and PRPD patterns should be discussed together to fully understand the PD events. This model forms a platform for generating robust information for asset managers using PD measurements from high voltage equipment in service. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) characteristics are inherently linked to associated electrical tree growth characteristics. This paper employs both phase-resolved patterns and pulse-sequence analysis (PSA) to study PDs in a short branch-tree grown from a metallic needle tip. It is found that the shape of PSA dV-dV patterns vary with applied voltage; in particular the values of characteristic voltage difference increase with applied voltage. At 10 kV the value of characteristic voltage difference decreases with tree growth, the average number of PDs per cycle increases, the PD magnitudes decrease, and the characteristic wing-like phase-resolved pattern evolves into a turtle-like pattern. This paper proposes a physical model relating PD activity to tree development, considering space charge accumulation inside the tree channel. All key features of experimental results are explained by the model. It is shown that the characteristic voltage differences are determined by the local PD inception and extinction electric fields. These key parameters determining the PD events can be calculated giving a clear physical interpretation of PD measurements, which is invaluable to those using PD as a condition monitoring or asset management tool. [ABSTRACT FROM AUTHOR]

Molybdenum hemicarbide (Mo2C) can be widely used in the fields of steel, metal ceramics, and catalyst of hydrogen-involved reactions. This work reported a new and simple method for preparing molybdenum hemicarbide by reducing and carbonizing MoO2 with methanol, and both thermodynamic and experimental studies were carried out. Based on the results, the reduction and carbonization routes are obtained: MoO2 was reduced and carburized directly to Mo2C in one step at lower temperatures, and first reduced to metallic Mo and then carburized to Mo2C at higher temperatures. The reduction mechanisms at low and high temperatures were proposed as well: The pseudomorphic transformation mechanism dominated the reaction at low temperatures, but at high temperatures, the reaction obeyed the chemical vapor transport mechanism. [ABSTRACT FROM AUTHOR]

Electrical tree growth is a precursor to dielectric breakdown in high voltage polymeric insulation. Partial discharge (PD) has a close relationship with electrical tree propagation and can be both used to understand the aging process, and as a diagnostic tool for asset management. In this paper it is shown that PD patterns change through the early stages of tree growth, and consideration of these changes gives insight into the processes of tree growth. Here, trees have been grown in epoxy resin in needle-plane geometries with 2 mm gaps, at 15 kV peak AC. The PD phase-resolved pattern can be regarded as a combination of the well-known turtle-like and wing-like PD patterns. As a tree extends its length, a wing-like pattern is seen and the maximum discharge magnitude has an almost linear relationship with the maximum length of the growing branch. Comparison of the energy released by discharges and the vaporization energy needed for tree growth supports the proposal that the wing-like pattern corresponds to PDs responsible for growth in length of the trees. Implications for mechanisms for tree growth are considered. Results suggest that asset managers may be able to use partial discharge analysis to distinguish different stages of tree growth, providing a valuable prognostic tool for optimising high voltage plant management and replacement. [ABSTRACT FROM PUBLISHER]

In recent years, MOF-based materials, including pristine metal-organic frameworks (MOFs) and their derivatives, are one kind of the most popular materials, and have been widely used in biomedicine, sensing, energy storage, and catalysis due to their unique pore structures, abundantly accessible metal nodes, large specific surface areas, tailorable function, and morphology. Most of them have shown satisfactory performances in specific fields. However, there are still some urgent problems need to be solved in the application of MOF-based materials in electrocatalytic water splitting, especially the facile and controllable synthesis, and limited activity and stability. Herein, first this article mainly reviewed the applications and challenges of MOF-based materials in electrocatalytic water splitting. Then, typical development strategies (e.g., construction of multi-metallic site of MOF-based materials, structural morphology designing and controlling, engineering of doping, defect, vacancy, coupling with conductive carrier or constructing heterostructures) were highlighted in this review. Finally, perspectives on the development of MOF-based materials were provided for fabricating more efficient water splitting electrocatalysts. [Display omitted] • Different strategies to enhance the electrocatalytic performances of MOF-based materials are summarized. • Advantages of MOF-based materials in electrochemical water splitting are summarized. • The mechanisms of the enhanced catalytic activity are explored. • Some challenges and views for the future development of MOF-based materials are highlighted. [ABSTRACT FROM AUTHOR]

XLPE and its nanocomposites have been subjected to a progressive step voltage until failure occurred, and the results analyzed in terms of an inverse power law ageing expression. The step-stress tests have been conducted at three temperature 20°C,40°C and 60°C, and the exponent n of the inverse power law ageing expression has been estimated for the two materials by a new method, which fully considers the contribution to the failure of the whole sequence of voltage steps, including ageing processes at the lower voltages, the final step and the process of voltage increase. It was found that the value of exponent n increases slightly with increasing temperature for both XLPE and its nano-composites. More importantly the value of n for the nano-composites was found to be substantially lower than that for XLPE at all temperatures. A complementary experiment in which the space charge distribution was measured under the same step-stress protocol as the breakdown tests has also been carried out and the results of both experiments are discussed. [ABSTRACT FROM AUTHOR]

A bipolar charge transport model is used to simulate the formation of space charge in XLPE plaques placed under a temperature gradient. The model is used to assess the relative importance of charge migration and blocked extraction for three possible effects of the temperature gradient. The simulations were carried out for samples with different thicknesses and the results verified by comparison with experiment. In this way it has been shown that not only does the temperature gradient influence space charge accumulation through its introduction of a conductivity gradient, but also through differences in the injecting and extracting processes at electrodes of different temperature. [ABSTRACT FROM AUTHOR]

Two mechanisms have been proposed to explain the suppression of space charge in polyethylene by the addition of nano-fillers, i.e. an interface change that reduces charge injection and a bulk modification that affects charge migration and recombination. The relative importance of each mechanism in Low Density Polyethylene (LDPE) nanocomposites is investigated by the measurement of space charge in samples of doublelayer and triple-layer structures. The experimental results show that the nano-fillers reduce charge injection, but do not entirely eliminate the space charge. Bulk changes also play an important role in space charge suppression. The space charge near the interface between the unfilled LDPE and nanocomposites shows a surface charge at 20 °C, but at 60 °C a bipolar blocking phenomenon is observed in some circumstances. It is shown that these space charge distributions can be reproduced using a band theory approach with the assumption that the introduction of deep traps by nano-fillers raises the Fermi level of the nanocomposite towards the conduction level. [ABSTRACT FROM AUTHOR]

The effect on space charge accumulation of the introduction of nano-filler into polyethylene is usually studied using thin 100 ?m samples in electric fields reaching 100 kV/mm. However, the insulation thickness in an actual HVDC cable is usually some centimeters. Thus there is a great thickness difference between the experiment sample and the insulation application. Here we investigate the thickness dependence of space charge accumulation in unfilled and LDPE doped with nano-SiO2 over a range of temperatures in a field of 50 kV/mm. It is found that the space charge in LDPE/SiO2 nanocomposites exhibits marked thickness dependence whereas in the unfilled LDPE it shows very little thickness dependence. A simulation based on the bipolar injection model and Takada?s trapping potential model has been carried out in order to explain the differences. It is found that when the simulation included the effects of charge injection, extraction, trapping, recombination, mobility and diffusion, it is able to explain the heterocharge formation in the unfilled LDPE, and the thickness dependence in the two kinds of materials. [ABSTRACT FROM AUTHOR]

Although the circulating flow of insulating oil can enhance heat dissipation in converter transformers, it can also influence the space charge distribution in oil–paper composite insulation. In this article, the oil–paper composite insulation between flat electrodes was used as the experimental model. Based on the pulsed electroacoustic (PEA) method, we investigated the effect of uncharged flowing oil on the space charge distribution in composite insulation under a dc electric field and polarity reversal. Under a dc electric field, as the oil flow velocity increased, the amount of interface charge between the oil and paper first increased and then decreased. During the polarity reversal process, the field distortion was aggravated at slower oil flows. These experimental results were explained in terms of the effect of oil flow on ionized charges in the oil. [ABSTRACT FROM AUTHOR]

It is known that 1,2,3 benzotriazole (BTA) can effectively limit the oil flow electrification in oil–paper insulation used in HVAC transformers, but it is still unclear whether BTA is applicable to converter transformers. Thus, the effects of BTA on interface charge behaviors and charge migration in oil–paper system under dc stress are investigated in this article. The experimental results show that BTA reduces the interface barrier between oil and oil-immersed paper by altering the charge distribution of the electric double layer (EDL) at the oil–paper interface, which is beneficial to the operation stability of converter transformers in the condition of polarity inversion. However, it is also found that the BTA additive promotes the charge accumulation at oil–paper interface and enhances the local electric field by increasing the carrier mobility of oil–paper insulation. The experimental results in this article provide references for the selection of insulating oil additives for converter transformers. [ABSTRACT FROM AUTHOR]

Titanium oxycarbide can be used as a soluble anode to produce sponge titanium in USTB or MER molten salt electrolysis process. However, the key factor of these two processes is to prepare oxycarbide with appropriate C/O ratio and at a low cost as well. This work reported a simple method of preparing titanium oxycarbide from TiO 2 in C-H 2 system. Based on the prediction of thermodynamic calculations, titanium oxycarbide was prepared successfully at 1400 °C with the molar ratio of TiO 2 to carbon exceeding 1:2, and the ideal electrolytic anode (TiC 0.5 O 0.5) was produced at 1400 °C (with a ratio of 1:3 of TiO 2 to carbon). Number of parameters (carbon content, temperature, sample's mass, additive (Fe element), and with ball milling treatment) were considered and discussed in the current study. Furthermore, this method can reduce not only the reaction temperature and time, but also the emission of carbon dioxide. • Titanium Oxycarbide with controllable C/O ratio was produced by considering number of parameters in TiO 2 -C-H 2 System. • The ideal electrolytic anode (TiC 0.5 O 0.5) can be produced when the ratio of TiO 2 to carbon is 1:3 at 1400 °C. • The reaction temperature, the usage and emission of carbon were reduced by introducing clean energy (H 2). • The reaction mechanism was discussed as well. [ABSTRACT FROM AUTHOR]

In this research, the equivalence of space charge for coaxial cables and plane samples are analyzed through simulation. Bipolar charge transport models of coaxial cables and plane samples are established with the same material-dependent parameters, the bulk charge and total space charge distributions are simulated and comparatively researched under isothermal and temperature gradient conditions. The presented results indicate that the space charge behavior shows a basic equivalence in terms of charge variation laws and distribution. In addition, few discrepancies in the heterocharge amount and charge waveform amplitude are observed and mainly ascribed to the sample geometry, mobility gradient distribution and the spatial resolution of the measuring system, respectively. Investigations of space charge characteristics with a plane pulsed electro-acoustic measurement system may be accepted as a practice for providing the space charge characteristics of coaxial cable insulation, unless it is necessary to investigate the cable space charge distribution under actual operating conditions. [ABSTRACT FROM AUTHOR]

Abstract The reduction of metal oxides by hydrogen is a very significant reaction in metallurgical industries. Particularly, hydrogen reduction is one of the effective methods to reduce CO 2 emission in iron and steel industry. The mathematical modeling of H 2 reduction process would help to define the operating parameters and to get a better control of the reduction process. In this study, a new kinetic model regarding hydrogen reduction of metal oxides controlled by external gas diffusion has been proposed. The model has incorporated numbers of parameters such as temperature, size of the metal oxides, diffusion coefficient constant, hydrogen partial pressure, density of metal oxides and time. Furthermore, the shape of metal oxides (spherical, cylindrical, lamellar particles) was considered as well, and the models for the reduction of metal oxides with different shapes were combined to a formula. Also, the developed model can be applied to describe the reduction kinetics under both isothermal and non-isothermal conditions. Because the model is in the analytic function, therefore, it is convenient for usage and theoretical analysis. Application of the developed model to practical systems validated that its predicted values agreed very well with the experimental data. Highlights • Kinetic model for the external gas diffusion controlling reduction was proposed. • The model is in the analytic function and is convenient for theoretical analysis. • The shape of metal oxides was considered. • The models for different shapes were combined to a formula. [ABSTRACT FROM AUTHOR]

In the present study, a new and simple method to prepare tungsten and tungsten carbides powders was proposed by using WO 3 powders as the raw material and CH 3 OH vapor as the reduction and carbonization agent. Both thermodynamic and experimental studies were carried out, and based on the results, the reaction routes were obtained. It was found that at low and moderate temperatures, the final product of WC was formed via intermediates of W 18 O 49 , WO 2 , partial metallic W and W 2 C; while at high temperature, WO 3 was first reduced to WO 2 with the intermediate phase of W 18 O 49 , and then reduced to W. The morphology of final products almost retained the same shape as that of raw materials WO 3 at low temperature, however, the large particles with blocky shape disappeared and the products were all small W particles with polyhedral shape at high temperature. Furthermore, the reaction mechanisms were proposed: the pseudomorphic transformation mechanism dominated the reaction at low temperature, but at high temperature, the reduction obeyed the chemical vapor transport mechanism, which is beneficial for grain refining of final product. [ABSTRACT FROM AUTHOR]

• It is a novel process for the separation and preparation of molybdenum and zinc from MoS 2 and ZnS in magnetic separation tailings. • The electrochemical behaviors of MoS 2 , ZnS and MoS 2 -ZnS was investigated in detail, and the mechanism of desulfurization of MoS 2 -ZnS was proposed. • Zn/ZnS played a role of a reducing agent in the process of MoS 2 -ZnS co-desulfurization, which facilitated the process of desulfurization and the semiproduct of zinc could be reused. • It enabled the reduction of MoS 2 at a lower voltage while ZnS presenting in the desulfurization process. The main form of molybdenum in nature is molybdenum sulfide. It also exists in iron ore magnetic separation tailings together with zinc sulfide. Considering separating and extracting molybdenum and zinc, a large amount of SO 2 is released and environmental pollution is caused by high energy consumption for the traditional pyrometallurgy process. This research proposes a novel process to achieve efficient extraction and separation of molybdenum and zinc through co-desulfurization of MoS 2 -ZnS in molten salt. It was found that the sulfur in MoS 2 and ZnS could be effectively removed and collected as solid sulfur by constant potential electrolysis in molten NaCl-KCl at 750 °C. Furthermore, electrochemical testing showed that the decomposition of MoS 2 was carried out in two steps, ZnS was reduced in one step, and the decomposition voltage of ZnS was smaller than that of MoS 2. Zinc was obtained at the first stage, and the MoS 2 or its intermediate compounds were wrapped around by liquid zinc. The substitution reaction, 2Zn + MoS 2 = Mo + 2ZnS, was able to promote the decomposition of MoS 2 in the electrolysis process. Zinc sulfide was then formed in the second stage, and it can be electrolyzed to metallic zinc again for reduction of MoS 2. Zn/ZnS played the role of a reducing agent in the process of MoS 2 -ZnS co-desulfurization, which facilitated the process of desulfurization, and enabled the reduction of MoS 2 at a smaller voltage while zinc could be reused. In this work, molybdenum metal containing zinc was extracted at a cell voltage of 2.7 V. Metallic zinc and molybdenum were separated and purified in the final stage by vacuum distillation. [ABSTRACT FROM AUTHOR]

A review emphasized on the electro-desulfurization mechanism of sulfides as cathodes or anodes in molten salts. [Display omitted] • The research advance of metal or alloy prepared by molten salt electro-desulfurization is reviewed for the first time in this paper. • This review provides a comprehensive insight into the electrode reaction mechanism of various metal sulphides in molten salts. • The challenges in molten salt electro-desulfurization technology are summarized and the future research direction is pointed out. Sulfide is one of the most abundant minerals in the earth's crust and a major raw material for metal extraction. The traditional pyrometallurgy or hydrometallurgy process is relatively lengthy, and will produce CO 2 and SO 2 with greater hazards for environment. Electro-desulfurization is a metal extraction method developed in the past 20 to 30 years, which is considered to be an environmentally friendly and simple process. In electro-desulfurization process, sulfide is used as electrode and raw material, and molten salt is used as electrolyte. Metal and elemental sulfur are extracted at the cathode and anode respectively after current is introduced, meanwhile CO 2 and SO 2 are not produced. In this paper, the recent research of electro-desulfurization in molten salts is summarized, including the electrode reaction process when sulfide is used as cathode or anode, electrolytic products and factors affecting current efficiency and energy consumption. It is expected to provide suggestions for future direction and enhance the theoretical support for the clean development of sulfides through the comprehensive analysis of molten salt electro-desulfurization process. [ABSTRACT FROM AUTHOR]

Tungsten carbides, which can be widely used as cutting and drilling tools, chemical catalysts and aerospace coatings, have attracted widespread attentions. The present work reported a simple method to prepare tungsten carbides by using WO 2 as the raw materials and CO as the reduction and carbonization agent. It was found that at lower and moderate temperatures, all the final product was WC, while at higher temperatures, the final products were W 2 C or W. The reduction and carbonization mechanism was also studied theoretically and experimentally. WO 2 was reduced and carburized to WC in one step at lower temperatures; WO 2 was first reduced and carburized to W 2 C and then to WC at moderate temperatures; while at higher temperatures, WO 2 was first reduced to metallic W and then carbonized to WC or W 2 C, but with the temperature increasing, the carbonization became difficult and required much higher CO content. [ABSTRACT FROM AUTHOR]

The effects of charge carrier injection and intrinsic ionic carriers on the conduction process in superclean low-density polyethylene and cross-linked polyethylene (LDPE and XLPE) and the associated development of space charge are investigated. The carrier mobility is measured directly by space charge measurements in a double- and triple-layer structure. It is shown that the difference between superclean LDPE and XLPE in the field-dependence of the current density results from the dominance of ions in XLPE introduced by cross-linking as compared to injected carriers in the case of superclean LDPE. [ABSTRACT FROM AUTHOR]

Space charge accumulation greatly influences the dielectric performance of epoxy composites under high voltage. It has been reported that nano-fillers can suppress the charge accumulation in the bulk of insulation materials. However, it is still unclear how the nano-fillers influence the charge distribution at the interface between the filler and polymeric matrix. In this work, the dielectric properties and the local dynamic charge mobility behavior at the interface of barium titanate/epoxy resin (BTO/EP) composites were investigated from both bulk and local perspectives based on the macroscopic test techniques and in-situ Kelvin probe force microscopy (KPFM) methods. Charge injection and dissipation behavior exhibited significant discrepancies at different interfaces. The interface between BTO and epoxy is easy to accumulates a negative charge, and nanoscale BTO (n-BTO) particles introduces deeper traps than microscale BTO (m-BTO) to inhibit charge migration. Under the same bias condition, the carriers are more likely to accumulate near the n-BTO than the m-BTO particles. The charge dissipation rate at the interface region in m-BTO/EP is about one order of magnitude higher than that of n-BTO/EP. This work offers experimental support for understanding the mechanism of charge transport in dielectric composites. [ABSTRACT FROM AUTHOR]

For the assembly of electrochromic devices (ECDs) with generally multilayer structures, supportive components usually are needed to be incorporated with EC materials. Herein, we reviewed several impressive methods to design and fabricate ECDs with high performance and versatility based on recent frontier research. The first part of the review is centered on the desirability and strengthening mechanism of nanostructured inorganic EC materials. The second part illustrates the recent advances in transparent conductors. We then summarize the demands and means to modify the formation of electrolytes for practicable ECDs. Moreover, efforts to increase the compatibility with the EC layer and ion capacity are delineated. At the end, the application prospects of inorganic ECDs are further explored, which offers a guideline for the industrialization process of ECDs. [ABSTRACT FROM AUTHOR]

This paper proposes a method of distinguishing the contributions of ionized and injected charges to the charge transport in oil immersed paper in triple-layer and double-layer samples. With the double-layer sample, the apparent mobility including the ions contribution is obtained by the calculation according to the speed of accumulated charge density at the interface. The contribution of ions is excluded by subtracting the accumulated charge density in the triple-layer sample from that in the double-layer sample. It is found that the interface charge mainly comes from the ionization charges under a low field, and the contribution of injected charge takes a more important part at higher electric field. [ABSTRACT FROM AUTHOR]

• A novel process for extraction titanium from high Ti-BF slag has been proposed. • The effects of Fe 2 O 3 , urea and sawdust additives on the reaction have been studied. • The proposed novel recycling process has been assessed. • The novel recycling process showed many potential advantages and great feasibility. The recycling of high-titanium-bearing blast furnace slag (TiO 2 > 23 wt.%) is an urgent problem that has attracted global research attention. To achieve high-efficiency, low-consumption, clean, and high value-added recycling utilization, a new process is proposed herein, which entails reacting a CH 4 -H 2 -N 2 gas mixture with the titanium-bearing blast furnace slag to initially produce Ti(C, N, O) at a low temperature, whereafter the product is purified and chlorinated. The effects of Fe 2 O 3 , urea, and sawdust on the reduction and carbonitriding characteristics are also investigated. The results indicate that the Fe 2 O 3 additive can promote the formation of Ti(C, N, O), while urea and sawdust are instrumental for enhancing gas diffusion in solid powders. The proposed novel recycling process was assessed and it evinced many advantages and great feasibility. [ABSTRACT FROM AUTHOR]

Electrical trees are widely grown in laboratories from metallic needle electrodes to enable the degradation process to proceed rapidly at voltages of ∼10 kV AC. Here it is shown that cone-shaped air gaps may form at a needle tip, even when they are not visible optically. Using X-ray imaging techniques, samples with and without air gaps up to 55 μm long have been characterized. The presence of air gaps led to partial discharge (PD) patterns resembling void-discharges. Prior to tree initiation, discharge characteristics evolved with increased voltage increments and increased phase lag behind the applied voltage. These changes to PD characteristics reflect a change in the physical state of the air gap. Although samples with air gaps generally initiated trees quicker than those with no gap, PD activities did not appear to play a decisive role in tree initiation times. However, initial voids were found to have major impact on the subsequent tree growth. In samples with persistent pre-tree air-gap PDs, trees grew larger branchy structures with higher PD magnitudes. In addition, the PDs became more asymmetric between positive and negative half-cycles than occurred in samples with no air gaps. It is shown that understanding the interface between the needle and polymer at a micron scale is critical to interpretation of laboratory tree growth experiments. [ABSTRACT FROM AUTHOR]

Summary The clean and effective utilization of titanium‐bearing minerals has challenged the titanium industry all over the world. In order to realize the high‐efficiency, clean, and high value‐added comprehensive utilization of ilmenite concentrate, a novel process has been proposed in this study by reducing and carbonitriding ilmenite with the CH4‐N2‐H2 gas mixture at low temperature. Carbonitride performance and mechanism have been investigated experimentally and theoretically. The obtained results showed that the reaction process could be divided into three stages: formation of metallic iron, reduction of titanium oxide to titanium suboxides, and formation of Ti(C, O, N). The metallic iron congregated at the first two stages, but dispersed once the Ti(C, O, N) formed. The effects of both reaction temperature and preoxidation treatment on the reaction have been studied as well. It was found that the increase of temperature was conducive to the formation of Ti(C,O), and the ilmenite could be reduced completely to Ti(C,O) at 1170°C for 8 hours. The preoxidation treatment could improve the kinetics of reduction. At 1170°C, the introduction of N2 could apparently increase the reduction rate, with the complete reduction time decreasing from 8 hours in CH4‐H2 gas mixture to 3 hours in CH4‐N2‐H2 gas mixture. The proposed novel process has been assessed and it showed many potential advantages and feasibility. [ABSTRACT FROM AUTHOR]

The mobility of positive and negative charge carriers has been separately measured independently of carrier concentration in low-density polyethylene (LDPE) and its nanocomposites using space charge measurements in a bilayer system. It was found that the carrier mobility of positive charge carriers was larger than that of negative charge carriers for both LDPE and its nanocomposites and that the carrier mobility was one to two orders of magnitude less in the nanocomposite than unfilled LDPE under the same conditions. The mobility is interpreted in terms of a field-assisted hopping model whose estimated activation energies were verified by measurements at different temperatures. The form of the charge traps and carrier transport is interpreted in terms of known features and electron and hole traps and the effect of nano-particles upon these features is discussed. [ABSTRACT FROM AUTHOR]

The effect of DC bias on electrical tree growth and partial discharge (PD) characteristics in epoxy resin (Araldite LY® 5052/Aradur® HY 5052 supplied by Huntsman) is investigated using three waveforms: AC, AC with positive DC bias, and AC with negative DC bias. Needle-plane samples are used. Tree growth is shown to be accelerated by the combined effect of DC and 50 Hz AC, beyond the AC growth rate. Positive and negative DC biased tests result in 62% and 54% reductions in average time to breakdown, respectively. Different tree structures and stages of development are associated with different partial discharge characteristics, with thick dark tree branches associated with high PD magnitudes, whereas fine tree channel growth is linked with PD magnitudes below 1 pC. AC tests showed five distinct stages of tree growth compared to four stages seen in DC biased tests. In particular, trees growing in the 'reverse direction' from the planar to the point electrode, which is observed in the latter stages of AC tests, is not seen in the DC biased tests. It is concluded that for composite voltages, the AC component is the essential driver of tree growth but the DC component can accelerate propagation. AC noise may therefore compromise the reliability of insulation in HVDC networks. [ABSTRACT FROM AUTHOR]

An electrical treeing process is presented which consists of two types of electrical tree structures that coexist in the same epoxy resin: these have been termed as ‘filamentary trees’ and ‘reverse trees’. In samples with needle-plane electrode geometries, a filamentary tree that consists of fine tree channels propagates from the needle electrode to the plane ground electrode under an applied AC voltage. It is observed that once the filamentary tree has crossed the insulation, trees then grow from the planar electrode towards the needle electrode as reverse trees, eventually leading to dielectric breakdown. The characteristics of the treeing processes have been obtained for a range of samples through optical observations. In addition, partial discharge (PD) activity associated with the growth of a reverse tree is thoroughly characterized. The prior existence of a filamentary tree is a prerequisite for the development of a reverse tree. PD does not appear to be a driving force for the growth of the filamentary trees, whereas high levels of PD are associated with the growth of a reverse tree. This distinction shows that aging can occur undetected by PD, but asset management of the more aggressive treeing stages can use PD analytics. [ABSTRACT FROM AUTHOR]

The effect of temperature gradient on space charge behavior is necessary to investigate for HVDC insulation. In this paper, space charge distributions in neat epoxy resin (EP) and EP/SiO2 nanocomposites (NC) were measured under different DC stresses and temperature gradients. We found that different temperature conditions applied to the electrodes had a great impact on space charge distributions: Only homocharge accumulated near anode at isothermal conditions, on the contrast, at temperature gradient of 60 °C, negative charge injected from cathode (high temperature side) and accumulated in the bulk, heterocharge appeared near anode (low temperature side). Moreover, SiO2 nano-fillers added to NC could suppress the space charge accumulation significantly, and the pattern of space charge distribution in NC at temperature gradient of 60 °C also shows differently from that of EP. Numerical simulation based on the bipolar charge transport model was employed to study the experimental results. It shows that under temperature gradient, charge extraction plays an important role in heterocharge accumulation near the low temperature side. Moreover, it indicates that unlike the apparently measured conductivity, the charge mobility of NC does not increase rapidly with temperature in the range from 20 °C to 80 °C. [ABSTRACT FROM PUBLISHER]

As the temperature gradient always exists in the insulation of power equipment, the influence of temperature gradient on oil-impregnated paper insulation is studied by experiments and simulation. It's found that in the both single-layer and double-layer structures, the heterocharges always appear near the lower temperature electrode, and increase with the enhancement of temperature gradient and field stress, resulting in more considerable field distortion. However, there are more heterocharges in the single-layer samples while the field distortion is more severe in double-layer samples. Numerical simulations were carried out to investigate the mechanism of temperature gradient effect. It is indicated that the space charge accumulation is mainly due to the temperature dependence of the charge injection and conduction. The behavior of interface charges can be well described by assuming an energy barrier for charge transportation at the interface. [ABSTRACT FROM AUTHOR]

The present study investigated the reduction and carbonization behavior of perovskite-geikielite by using CH 4 –H 2 gas mixture, which aimed to recycle the titanium resource in titanium-bearing blast furnace slag. Thermodynamic phase equilibrium analysis in the CaTiO 3 –CH 4 –H 2 , MgTiO 3 –CH 4 –H 2 and CaTiO 3 –MgTiO 3 –CH 4 –H 2 systems was performed by FactSage. The analysis indicated that CaTiO 3 could be ultimately reduced and carbonized to TiC x O y by CH 4 –H 2 gas mixture at temperature above 1300 °C, while the temperature for reduction of MgTiO 3 was above 1200 °C. MgTiO 3 is found to be reduced prior to CaTiO 3 in the CaTiO 3 –MgTiO 3 –CH 4 –H 2 systems. The reduction experiments of perovskite-geikielite were carried out in a temperature range of 1300 °C to 1450 °C in a flowing CH 4 –H 2 atmosphere. Experimental results showed that perovskite-geikielite could be reduced completely to TiC x O y at 1400 °C and above after 8 h reduction, while geikielite was reduced prior to perovskite. The reduction and carbonization extent of samples increased with increasing time and temperature when in a low temperature range (below 1400 °C). However, a much higher temperature (above 1400 °C) would hinder further carbonization of TiC x O y for the production of deposited carbon. Addition of iron oxides to sample strongly facilitated the reduction reaction, and even promoted the reduction of titanium to be completed at only 1300 °C after 8 h reduction. The gas-solid reaction provided a low temperature method to reduce and carbonize perovskite and geikielite, and thus it provided a possible way to use titanium-bearing blast furnace slag. Unlabelled Image • A novel method to reduce and carbonize perovskite and geikielite was proposed. • Thermodynamic and experimental study on the reduction by CH 4 -H 2 was performed. • The ratio of TiC/TiO in TiC x O y reduced from CaTiO 3 and MgTiO 3 has been estimated. • The reduction mechanism of gas-solid reaction with CH 4 -H 2 was discussed. [ABSTRACT FROM AUTHOR]