Search

To accurately measure electrostatic discharge energy, a resistive-capacitive voltage discharge approach was used to measure the parasitic capacitance in a circuit. As a result, an output-stage parasitic capacitance in the circuit during the discharge process and a non-negligible storage-stage parasitic capacitance during the charging process were identified. By comparing the data obtained from the resistive-capacitive discharge voltage model and spark current RCL circuit model, the maximum relative deviation from the total circuit capacitance was 5.4% for both approaches. A model based on graded-stage parasitic capacitance was established to analyze the effect of this capacitance on discharge energy. The energy stored in the charging process increased because of the storage-stage parasitic capacitance, and the discharge energy decreased because of the output-stage parasitic capacitance. The energy calculated by the graded parasitic capacitance model was larger than that calculated by the single-stage parasitic capacitance model, with a maximum relative deviation of 36.7% under the test conditions. The smaller the charging capacitor, the more evident the effect of the parasitic capacitance on the discharge energy. • An equivalent model for analyzing parasitic capacitance of the charging and the discharging circuits. • A method for measuring the parasitic capacitance component of the circuit in the resistive-capacitive discharge. • The availability of the proposed procedure is verified by comparison with spark current RCL model. • The method is discussed to produce small energy sparks accurately in MIE test. [ABSTRACT FROM AUTHOR]

A series of electrostatic sparks at different energies are triggered by different methods in testing the minimum ignition energy (MIE) of dust clouds. It is necessary to investigate the difference between actual spark energies and MIEs under different triggering methods. A multi-energy spark generating circuit combined with high-voltage relay (HVR) triggering and electrode movement (EM) triggering was set up to study the effects of triggering types and inductance loads. The first current peak was proposed together with damping ratio and angular frequency of spark current to evaluate the reliability of the experimental results. Results showed that the deviation of spark energy release efficiency between the two triggering types is about 5%–25% when the storage energy was 34 mJ, 110 mJ, 340 mJ and 1100 mJ, which was not enough to cause the difference in the magnitude of MIE. The MIEs of clouds of lemon powder and sea buckthorn powder are consistent using the two triggering types. But the MIE of clouds of lycopodium triggered by EM without inductance is higher than that triggered by HVR. It indicates different triggering types may lead to different MIE results when testing fine dust even if the actual released energy is almost the same. The spark energy release efficiency without inductance is greater than or equal to that with inductance. However, the MIE of lycopodium clouds dropped from 75–90 mJ with no inductance, to 8–10 mJ with a 1 mH inductance. The MIEs of clouds of lemon powder and sea buckthorn powder showed similar trends. • First current peak is proposed to evaluate spark current together with attenuation factor and angular frequency. • The deviation of discharge efficiency of triggering types is not enough to cause the difference in the magnitude of MIE. • Different triggering types may lead to different MIE results when testing fine dust. [ABSTRACT FROM AUTHOR]

This work has presented gas sensors based on indium tin oxide (ITO) for the detection of SO2 and NO2. The ITO gas-sensing material was deposited by radio frequency (RF) magnetron sputtering. The properties of gas sensing could be improved by increasing the ratio of SnO2. The response characteristics of the gas sensor for detecting different concentrations of NO2 and SO2 were investigated. In the detection of NO2, the sensitivity was significantly improved by increasing the SnO2 ratio in ITO by 5%, and the response and recovery time were reduced significantly. However, the sensitivity of the sensor decreased with increasing SO2 concentration. From X-ray photoelectron spectroscopy (XPS) analysis, the gas-sensitive response mechanisms were different in the atmosphere of NO2 and SO2. The NO2 was adsorbed by ITO via physisorption but the SO2 had a chemical reaction with the ITO surface. The gas selectivity, temperature dependence, and environmental humidity of ITO-based gas sensors were systematically analyzed. The high detection sensitivity for acidic gas of the prepared sensor presented great potential for acid rain monitoring. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SiO 2 /graphene combinations are used as water based lubricant additives for magnesium alloy rolling. • SiO 2 /graphene nanofluids contribute better lubrication effect compared to pure nanofluids. • Experiment indicates that 0.1:0.4 is the optimum SiO 2 /graphene mixing ratio. Abstract The tribological performances and rolling lubrication properties of SiO 2 /graphene combinations as water-based lubricant additives were evaluated using a reciprocating ball-on-plate tribometer and two-high rolling mill. The results obtained therein revealed that dispersion of the SiO 2 /graphene combinations in water is conducive to the reduction of the friction coefficient and wear volume and the increase in the load-bearing capacity, which were superior to the results obtained for the graphene nanofluids or SiO 2 nanofluids separately. In the best case, the addition of 0.1 wt% nano-SiO 2 mixed with 0.4 wt% graphene in water reduced the friction coefficient by 48.5% and the wear volume by 79% compared with the addition of 0.5 wt% graphene. Transmission electron microscopy images of the SiO 2 /graphene combinations additives after friction testing showed that nano-SiO 2 supports the graphene layers as pillars and prevent assembly between the graphene layers. The synergistic effect of the components considerably enhanced the SiO 2 /graphene combination. Additionally, the preliminary application of the SiO 2 /graphene combination nanofluids in magnesium alloy rolling effectively decreased the rolling force and improved the surface quality of sheets. [ABSTRACT FROM AUTHOR]

We combine pre-compressive test, annealing, re-compressive test, quasi-in-situ optical microscopy (OM), electron backscattered diffraction (EBSD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to systematically investigate the macroscopic yield strength differences (Δ ASs) of Mg-1.5Al-1.0Zn-0.3Mn (AZM110, wt.%) sheets with different pre-compressive strains 2%, 4% and 6% after re-compression with annealing, respectively. We observe that with increasing the annealing time, Δ AS firstly increased and then decreased. Moreover, with the increase of pre-compressive strains, Δ AS peak value gradually decreased. Quasi-in-situ OM images reveal that the contribution of new twin nucleation increased and initial twin growth decreased for pre-compressed AZM110 sheets after re-compression with annealing. With the pre-compressive strains, the contribution of new twin nucleation gradually is weakened and initial twin growth is enhanced, which leads to the alteration of Δ AS. By the observation of HAADF-STEM, twin boundaries are stabilized by the segregation of Al and Zn solutes and nano-Al 8 Mn 5 phases pinning, creating pre-compressive annealing strengthening (PCAS). With the annealing time, the disappearance of back stress and dislocation tangle decreases the PCAS effect. Pre-compressive strain also strongly influences the PCAS effect. The increasing volume fraction and width of twins observed from EBSD accelerate twin boundary motion (TBM) with pre-compressive strains from 2% to 4%, decreasing the PCAS effect after re-compression with annealing. Although increasing pre-compressive strain to 6% can put off TBM, low new twin nucleation rate still gives rise to the decreasing PCAS effect. Image 1 • The increasing twin nucleation and the decreasing twin growth created PCAS effect. • Solute segregation and nano-Al 8 Mn 5 phases pinning impeded twin boundary motion. • Twin volume fraction and width influenced twinning behavior during re-compression. • With the pre-compressive strains, PCAS effect decreased. [ABSTRACT FROM AUTHOR]

Microstructures, tensile properties and work-hardening behavior of extruded Mg-1Gd- x Zn (x = 0, 0.5, 1.0, 1.5, wt.%) alloy sheets were investigated in the present work. All the extruded sheets exhibit a fully-recrystallized microstructure and a weak extrusion-direction (ED)-split texture. The average grain sizes of Mg-1Gd sheets slightly decrease with the increase of Zn content up to 1.0 wt%, while a sharp decrease of the grain size occurs in Mg-1Gd-1.5Zn sheet attributed to the existence of abundant fine W-phase precipitates. Zn addition is found to cause a weak ED-split texture and to gradually form new transverse direction (TD)-split texture component. The combination of Zn solute, fine W-phase precipitate and weakening texture induced by Zn addition simultaneously improve the strengths and ductility of Mg-1Gd- x Zn sheets. However, excessive Zn addition leads to larger Mg 5 Gd precipitates and thus decreases the ductility. With the increment of Zn content from 0 to 1.5 wt%, work-hardening exponents of Mg-1Gd- x Zn sheets gradually increase from 0.34 to 0.39 along ED, and from 0.23 to 0.29 along TD, respectively. Meanwhile, hardening capacities increase from 1.73 to 1.84 along ED, and from 0.73 to 1.07 along TD, respectively. • The effect of adding Zn on the microstructures of Mg-1Gd alloy was studied. • The work-hardening mechanism of Zn in Mg-1Gd alloy was analyzed in detail. • Dense W-phase precipitates are homogeneously dispersed in the Mg-1Gd-1.5Zn alloy. [ABSTRACT FROM AUTHOR]

Deformation behavior and texture evolution of an extruded Mg 3Li sheet with a weak transverse direction (TD)-split texture during tension along different directions were systematically examined. Prismatic 〈a〉 slip was the dominant deformation mode along the extrusion direction (ED), while basal 〈a〉 slip and {10−12} twinning played key roles at the initial stage of deformation and prismatic 〈a〉 slip was also activated at the middle stage of deformation along the TD. The activation of prismatic 〈a〉 slip contributed to the enhanced 〈10−10〉 // ED component along the ED. However, the {10−12} twinning and basal 〈a〉 slip led to the formation of a new ED-texture component and a gradual rotation of c-axes towards the normal direction (ND) along the TD, respectively. Additionally, the cooperative activation of the {10−12} twinning and prismatic 〈a〉 slip were responsible for the decreased 〈10−10〉 // ED component along the TD. Unlabelled Image • Extruded Mg 3Li sheet exhibited a weak TD-split texture. • The room-temperature deformation modes of Mg 3Li sheet were investigated. • Prismatic 〈a〉 slip played a dominant role during tension along the ED. • Li additions improved the activation of prismatic 〈a〉 slip, under a lower strain. [ABSTRACT FROM AUTHOR]

A remarkable yield asymmetry at room temperature (RT), all the time, severely influenced the wide industrial applications of Mg alloys. Here, we report a novel approach entitled as bimetal casting-co-extrusion to reduce the yield asymmetry of Mg–3Al–1Zn (wt.%) alloy. The results show that when casting temperature is set as 760 °C, Mg–3Al–1Zn/Mg–1Y (AZ31/W1, wt.%) alloy with the sleeve-core structure can achieve a well metallurgical bonding. While casting temperature is below 760 °C, the contact surface of AZ31 and W1 billets takes place massive cracks, and even two alloys are unable to well connect. After co-extrusion, the interface zone of AZ31/W1 rod never has any cracks and holes. By TEM observation, the interface zone of ~ 1 μm is composed of only α-Mg. With increasing the proportion of W1 core, the tensile and compressive elongation-to-failure values of AZ31/W1 rod apparently enhance, and the decrease in tensile strength and the consistence in compressive strength give rise to the improved yield asymmetry from 0.57 to 0.84 at RT. This is mainly attributed to the more activity of slip deformation in tension and the restriction of {10 1 ‾ 2 } extension twinning in compression. Therefore, this work offers an insightful opinion to improve the mechanical properties of Mg alloys, especially the yield asymmetry, by bimetal casting-co-extrusion method. [ABSTRACT FROM AUTHOR]