Gate Plate Research Articles

Enhancing the thermal shock and corrosion resistance of low‐carbon Al2O3–C refractories: The role of h‐BN composite powder

AbstractDeveloping low‐carbon and high‐performance Al2O3–C refractories is vital for extending the service life of slide gate plate refractories and reducing carbon emissions. In this study, hexagonal boron nitride (h‐BN) composite powder was prepared using the magnesiothermic reduction combustion synthesis route and introduced into low‐carbon Al2O3–C refractories. The phases composition, microstructure, mechanical properties, thermal shock, and slag corrosion resistance of low‐carbon Al2O3–C refractories were investigated. The results show that the thermal shock and slag corrosion resistance of low‐carbon Al2O3–C refractories enhanced by adding h‐BN composite powder. Due to the introduced h‐BN, consequent in situ formed spinel and AlN whiskers, the crack propagation in the refractories was deflected, branched forming more fine cracks, then the thermal shock resistance was enhanced. In addition to the chemical inertness of h‐BN, in situ formed spinel and AlN whiskers, the consequent decrease in pore size plays an important role in enhancing the slag corrosion resistance of the refractories. The h‐BN composite powder synthesized via the combustion synthesis in this study demonstrated potential application in high‐performance Al2O3–C slide gate plates used in continuous casting technology.

Effectiveness of gait plate insole and lateral sole wedged shoes on foot progression angle in children with in-toeing gait: A prospective randomized control trial

BackgroundIn-toeing gait is defined as the internal rotation of the long axis of the foot to the line of progression. Although most of the time it is corrected spontaneously but sometimes causes torsional misalignment syndrome and maybe patellofemoral instability and arthritis of the knee. Research questionWhat is the effect of gait plate insoles and lateral sole wedged shoes on foot progression angle (FPA) in children with in-toeing? MethodIn this study, a randomized control trial was conducted with 11 participants (18 feet) who were girls aged between seven and ten years old. They were randomly assigned to either the gait plate group (6 girls, 11 feet) or the lateral sole wedge group (5 girls, 11 feet). The foot progression angle was measured using the RS scanner pressure platform before and after four weeks of intervention, both with and without interventions. The interaction effects of time and group on outcomes were analyzed using Mixed ANOVA and post-hoc complementary tests with a confidence interval of 95%. ResultsIt was observed that none of the interventions had an immediate impact on the FPA (P > 0.05). However, after four weeks, the FPA increased by 9.96 degrees with the lateral sole wedge and by 3.51 degrees with the gate plate insole. During the immediate and short-term evaluation, no significant difference was noticed between the two groups (P > 0.05). However, there was a large effect size (eta square = 0.269) observed in the time group interaction between the two groups (P = 0.028). SignificanceConservative methods like using a gait plate insole or modifying shoes with a lateral sole wedge can improve the foot progression angle in children with in-toeing gait. However, longer studies with larger sample sizes are needed to reach a conclusion.

(Invited) Switching Characteristics of GaN Power Transistors

A shorter switching time is one of the key advantages of GaN power devices over Si IGBTs. [1] In this paper, we report on the simulation of GaN power transistor switching and investigate the effect on the switching time novel design approaches ranging from the gate edge engineering (beyond just using field plates [2] for optimizing the voltage distribution in the drain-to-gate spacing to using the quantum well channel designs [3] that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of high mobility in the device channel. We also report on the effect of a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges on switching time.[4] Additional contacts in the drain-to-gate spacing for the field control and variable doping implants could also decrease the switching time. Further optimization could be achieved with the perforated channel designs [5] decreasing the parasitic series resistance and improving the heat dissipation.[1] A. Tüysüz, R. Bosshard, and J. W. Kolar, erformance Comparison of a GaN GIT and a Si IGBT for High-Speed Drive Applications, Proceedings of the International Power Electronics Conference - ECCE Asia (IPEC 2014), Hiroshima, Japan, May 18-21, 2014[2] S. Karmalkar, M. S. Shur, G. Simin and M. A. Khan, Field-Plate Engineering for Heterostructure Field Effect Transistors, IEEE Trans. ED, 52, 12, pp. 2516- 2532, December (2005)[3] M. Dyakonov and M. S. Shur, Consequences of Space Dependence of Effective Mass in Heterostructures, J. Appl. Phys. Vol. 84, No. 7, pp. 3726-3730, October 1 (1998)[4] G. Simin, M. Shur and R. Gaska, SETI-0070: Semiconductor device with low-conducting field-controlling element App. No 13/396,059, November 19, 2013 as US Patent No. 8,586,997[5] G. Simin, M. Gaevski, M. Shur, R. Gaska, Perforated Channel Field Effect Transistor, US patent 9,467,105, October 11, 2016

(Invited) Switching Characteristics of GaN Power Transistors

A shorter switching time and smaller conduction and switching losses are the key advantages of GaN power devices over Si technology. Further improvements of GaN HEMT technology will require new design approaches including SiC and even, possibly, diamond substrates, gate and drain edge engineering (beyond just using field plates) for optimizing the voltage distribution in the drain-to-gate spacing to using perforated channel design and a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges on switching time.

Failure analysis of Al2O3–C–SiO2 slide gate plates during continuous casting based on numerical simulation

The thermo-mechanical and failure behavior of the burning-free Al2O3 –C–SiO2 slide gate plate materials during the steel casting process are investigated. Firstly, the instantaneous coefficient of thermal expansion and the Young's modulus of the slide gate plate materials with different component contents at high temperature are measured. Secondly, a material constitutive model and a concrete damage plasticity mode are established based on the experiments, and adopted to simulate the failure behavior of the burning-free Al2O3–C–SiO2 slide gate plate during casting based on Finite Element Method (FEM) analysis. Results show that temperature gradient in the slide gate plate near the casting hole increased significantly and had a significant influence on cracking. The area near the casting hole of the slide gate plate is under tensile stress conditions, and then changes towards compressive stress conditions. Under those severe thermal stress conditions, crack formation is evaluated and an optimized composite structure of the slide gate plate combining advantages of reducing the risk of cracking and extending the service life is proposed. Moreover, the thermal shock test further verified that the microcrack extension was significantly alleviated due to the SiC distributed in whisker form and formed an interlocking structure in material. This work provides a reliable theoretical and experimental basis for the design and optimization of high performance Al2O3–C–SiO2 slide gate plates.

Design study of reflection time-of-flight mass spectrometer for EBIS charge breeder

In this study, a time-of-flight mass spectrometer is developed to analyze the mass-to-charge ratio of ion beams generated from an electron beam ion source (EBIS) at the RAON heavy ion accelerator facility. The time-of-flight mass spectrometer comprises a Bradbury–Nielson gate, steerer, mirror electrode, and microchannel plate detector. The Bradbury–Nielson gate is applied to generate a bunch beam with a 5-ns pulse width at the front end of the time-of-flight system. A double-stage reflector is employed to obtain a beam chromatic correction from the energy spread of the ion beam generated from the EBIS. The design is created through optics simulation using the SIMION code, with 133Cs as the reference ion. Consequently, the charge state of 27+ separated from neighboring states at a maximum voltage of 20 kV is obtained. By utilizing ion sources of Cs1+ (m/z 133) and Rb1+ (m/z 85 and m/z 87) to perform the performance test on the designed TOFMS system, the spectral peak of the ion sources and a relatively high mass resolution are obtained. This paper introduces the development process and test results of the time-of-flight mass spectrometer in detail.

Investigation of transient gas-solid flow characteristics and particle erosion in a square gate valve

As an important component in industrial pneumatic conveying pipelines, gate valves are seriously affected by gas–solid two-phase flow. Solid matter not only affects the flow resistance characteristics and flow field distribution of the gate valve, but also collides with the gate cavity and the gate plate surface, sliding friction and other effects, leading to serious wear and tear of the internal valve body, resulting in the fall off of the gate valve wall material, affecting the sealing performance of the gate valve, reducing its service life, and affecting the safety and reliability of the pipeline transportation system. Based on the consideration of gas–solid two-phase flow and particle–wall collision, combined with wear prediction model, the flow field, particle trajectory, flow resistance characteristics and wear distribution of main wall in gate valve pipeline system are studied in this paper. The accuracy of this method is verified by flow resistance experiment. The results show that the existence of groove structure at the bottom of gate valve has an important influence on the distribution of flow field inside gate valve and the wear of main wall in the flow field of pneumatic conveying pipeline. At the bottom of the groove, there is a low pressure zone, which makes the gas pressure decrease and increases the cost of pneumatic conveying when the fluid passes through the gate valve; the distribution of velocity and flow field is not uniform, resulting in swirling flow; there are different sizes of swirling flow and secondary flow, resulting in unstable flow; at the groove, particles impact on the groove perpendicular to the flow direction at a larger speed under the action of swirling flow. On the wall, the wear is the most serious here, which reduces the sealing performance of the gate valve. In the groove, the velocity distribution decreases, resulting in the accumulation of triangular particles.

(Invited) New Approaches for Shrinking the Performance Gap for GaN Power Devices

The expected performance of GaN and SiC based power devices far exceeds that of Si power transistors, but the gap between the expected and achieved performance is much larger for these wide band gap materials. In these paper, we discuss new approaches for shrinking this performance gap for GaN power devices. They include using the quantum well channel designs that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of a high mobility in the device channel. The gate edge engineering (beyond just using field plates) that optimizes the voltage distribution in the drain-to-gate spacing could be combined with a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges. Additional contacts in the drain-to-gate spacing for the field control and variable doping implants should allow for further optimization. The perforated channel designs could alleviate both the parasitic series resistance problem and the heat dissipation problem. Extending the gate perforations into the drain-to-gate region allows for a considerable reduction of the switching RC constant with a commensurate decrease in power dissipation. The ultimate design should use the lateral-vertical structures. The AlInN/AlN/GaN technology is uniquely poised for the breakthrough in high temperature performance. We predict that the combination of these approaches will dramatically shrink the performance gap firmly establishing GaN as a superb material for power applications.

(Invited) New Approaches for Shrinking the Performance Gap for GaN Power Devices

The expected performance of GaN and SiC based power devices far exceeds that of Si power transistors, but the gap between the expected and achieved performance is much larger for GaN transistors. In this paper, we discuss new approaches for shrinking the performance gap for GaN power devices. They include using the quantum well channel designs that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of a high mobility in the device channel. The gate edge engineering (beyond just using field plates) optimizes the voltage distribution in the drain-to-gate spacing. It could be combined with a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges. Additional contacts in the drain-to-gate spacing for the field control and variable doping implants should allow for further optimization. The perforated channel designs could alleviate both the parasitic series resistance problem and the heat dissipation problem. Extending the gate perforations into the drain-to-gate region allows for a considerable reduction of the switching RC constant with a commensurate decrease in power dissipation. The ultimate design could use the lateral-vertical structures. The AlInN/AlN/GaN technology is uniquely poised for the breakthrough in high temperature performance. We predict that the combination of these approaches will dramatically shrink the performance gap firmly establishing GaN as a superb material for power applications.

Strengthening of Al2O3-C slide gate plate refractories with microcrystalline graphite

Abstract The novel carbon sources (including nano-carbon black, carbon nanotubes and graphene oxide nanosheets, etc.) have been extensively researched in low carbon Al 2 O 3 -C refractory systems. In the present work, ultrafine microcrystalline graphite (UMCG) and nickel-loaded ultrafine microcrystalline graphite (NMCG) were added into low carbon Al 2 O 3 -C slide gate plate refractories to partially replace graphite flake (GF), respectively. The mechanical properties, phase compositions and microstructures were investigated by three-point bending test, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. Also, the reaction mechanisms of in-situ formed ceramic phases were discussed by thermodynamic analysis. The results indicate that the existence of UMCG powders can facilitate the in-situ formation of intertwined ceramic whiskers, leading to increased densification and mechanical properties of low carbon Al 2 O 3 -C slide gate plate. Moreover, multi-walled carbon nanotubes and ceramic phases intensively interlock with each other in the Al 2 O 3 -C refractories containing NMCG powders, which results in their better mechanical properties; the cold modulus of rupture are 36.03±0.12 MPa and 32.14±0.17 MPa for the specimens after coking at 1200 °C and 1350 °C, respectively. This work puts forward a practical application for the microcrystalline graphite as a candidate carbon source in Al 2 O 3 -C slide gate plate refractories.

A novel uncooled thermal imaging sensor using MEMS transistor

In this paper a new uncooled thermal imaging sensor using MEMS transistor with movable gate is presented. The novelty of this work is making moveable polysilicon gate by two minder bi-materials arms on silicon substrate using MEMS technology. The arms are deflected with absorbed infrared temperature from objects, and move the gate plate. By changing air gap between gate and Si channel, the drain current of transistor will be changed. The geometrical parameters are obtained using analysis of the structure. A FEM simulation was performed using COMSOL Multiphysics software to verify the validity. This structure has many advantages; including compatibility with CMOS fabrication process, high sensitivity, low power consumption, no need signal amplification, ability to miniaturization of pixel size, much more than other techniques that used until now.

Corrosion of refractory alumina plates used in the sliding gate system of steelmaking ladle: Chemical experiment

The aim of this study is to investigate the corrosion process of the refractory Al2O3-ZrO2-C slide gate plate caused by chemical interactions with secondary refining slag. The plate is part of the steelmaking ladle slide gate system, therefore its lifespan extension and integrity are of concern. Post mortem plates with slag adhered on their channel surface were analysed and static cup corrosion test experiments were performed in a controlled atmosphere furnace for 1h at 1600°C. The corrosion product phases Gehlenite (Al2Ca2O7Si) and Spinel (MgAl2O4) identified by DRX were formed after the experiment, showing that the slag is able to chemically corrode the Al2O3-ZrO2-C plates. In addition, a comparison of the interface region between the slag and the post mortem plate and the interface region between the slag and the static cup corrosion test specimens showed that the corrosion products are swept away by the fluid flow. Even though chemical corrosion by slag has been identified as one of the causes of the plate channel degradation, the study suggests that it acts synergistically with other mechanisms of degradation.

Measurement of Temperature in GaN HEMTs by Gate End-to-End Resistance

We have used the gate end-to-end (GEE) resistance method to measure channel temperatures in GaN HEMTs. This method is appealing for its simplicity and sensitivity to temperature immediately adjacent to the base of the gate, where several important degradation mechanisms occur. This region is not normally accessible with optical measurement techniques, due to shadowing by the gate and field plate overhangs; yet, it is considerably hotter than the regions that can be reached with optics. We found agreement with a finite-difference model, with reasonable inputs for the thermal barrier resistance at the SiC–GaN interface and temperature coefficients. We repeated this successfully for a second GaN HEMT technology with a very different gate geometry. Finally, we conducted micro-Raman measurements on FETs from the first technology and found excellent agreement with the GEE measurement, once it had been adapted to the more-distant location of the micro-Raman laser spot, by means of our finite-difference model. We conclude that GEE is a valuable tool, complementary to micro-Raman, for calibrating thermal models.

Optical Properties of GaTe-ZnTe Nanolamellae Composite

A material composed of GaTe and ZnTe crystallites with average diameter of ∼ 37nm and 68nm respectively was obtained by heat treatment at the temperature of 1000K and 1073K of GaTe plates in Zn vapour for 24hours. The absorbance spectra of composite material obtained at 1073K and that calculated from diffuse reflection using the Kubelka-Munk formula contains the bands characteristic for light absorption in ZnTe and GaTe crystallites. The photoluminescence spectrum of composite material at the temperature of 80K is composed to the excitonic band in GaTe and impurity bands of ZnTe crystallites.

Improved Middle-Temperature Strength of Unfired Slide Gate Plate for Continuous Casting of Steel

Unfired Al2O3-C slide gate plate refractories bonded with novel silicon-modified phenolic resin (MPR) and additives of Al and Si were prepared. The MPR was synthesized by silica sol via in situ polymerization with lignin–phenolic resin. The results showed that the MPR with corundum owns a better wettability and higher char yield than commercial resin (CR). The middle-temperature mechanical properties such as cold modulus of rupture (CMOR), flexural modulus (E), and force–displacement of Al2O3-C refractory specimens bonded with MPR were improved especially ranging from 673 K to 1073 K (400 °C to 800 °C). The results showed that CMOR of the specimens bonded with MPR coked at 873 K (600 °C) had a considerable improvement with 7.04 MPa in sharp contrast to 3.31 MPa for CR-bonded specimens. It was suggested that the special organic–inorganic network structure of MPR and good wettability with corundum enhanced the bonding strength of Al2O3-C slide gate plate refractories.

Characterization of Cross-Sectioned Gallium Nitride High-Electron-Mobility Transistors with In Situ Biasing

AlGaN/GaN high-electron-mobility transistors (HEMTs) were characterized in cross-section by Kelvin probe force microscopy (KPFM) during in situ biasing. The HEMTs used in this study were specially designed to maintain full and representative transistor functionality after cross-sectioning perpendicular to the gate width dimension to expose the active channel from source to drain. A cross-sectioning procedure was established that produces samples with high-quality surfaces and minimal degradation in initial transistor performance. A detailed description of the cross-sectioning procedure is provided. Samples were characterized by KPFM, effectively mapping the surface potential of the device in two-dimensional cross-section, including under metallization layers (i.e., gate, field plates, and ohmic contacts). Under the gate and field plate layers are where electric field, temperature, and temperature gradients are all most commonly predicted to have peak values, and where degradation and failure are most likely, and so this is where direct measurements are most critical. In this work, the surface potential of the operating device was mapped in cross-section by KPFM. Charge redistribution was observed during and after biasing, and the surface potential was seen to decay with time back to the prebias condition. This work is a first step toward directly mapping and localizing the steady-state and transient charge distribution due to point defects (traps) before, during, and after device operation, including normally inaccessible regions such as under metallization layers. Such measurements have not previously been demonstrated for GaN HEMT technology.

Strengthening of Al2O3-C slide gate plate refractories with expanded graphite

Expanded graphite, fabricated by microwave irradiation of acidified flaky graphite, was used to partially replace graphite and carbon black in a commercial Al2O3-C refractory slide gate plate composition. The developed refractories exhibited enhanced cold and hot strength, as well as oxidation resistance. X-ray diffraction indicated the formation of SiC phase even at temperatures lower than the melting point of Si. Field emission scanning electron microscopy exhibited homogeneous formation of three dimensionally oriented nanostructured SiC whiskers in the samples fabricated with expanded graphite. The formation of the thicker primary whiskers and thinner secondary whiskers in the inter-aggregate space bridging two particles was observed frequently for the expanded graphite fortified samples. Whisker reinforcement of this nature has rarely been observed in refractory systems, which is credited for a considerable improvement in the hot modulus of rupture of the new compositions.

Slant Field Plate Model for Field-Effect Transistors

The simplified field plate model for field-effect transistors previously introduced is further developed to allow arbitrary transition angles between gate and field plate or adjacent field plates. The model shows that transition angles less than 30° (measured from the surface) can result in significant improvements in electric field management.

Electroluminescence Investigation of the Lateral Field Distribution in AlGaN/GaN HEMTs for Power Applications

The lifetime and stability of AlGaN/GaN heterostructure eld e ect transistors at high power levels can be enhanced by introducing eld plates to reduce electric eld peaks in the gate drain region. Simulations of the electric eld distribution along the channel using the 2D ATLAS software from Silvaco indicate that above a characteristic drain source voltage three spatially separated electric eld peaks appear, one located at the drain-side edge of the gate foot, one at the end of the drain-sided gate eld plate, and one at the end of the source shield eld plate. The close correlation between lateral electric eld and the electroluminescence due to hot electron related intra-band transitions can be very helpful when optimizing the electric eld distribution in high power devices. Electroluminescence microscopy images of devices with gate and source shield eld plate reveal the peaks located at the locations of enhanced electric eld. By studying the voltage dependence of the electroluminescence peaks the in uence of the eld plates on the electric eld distribution in source drain direction can be visualized.

PLACAS DE VÁLVULA GAVETA MAGNESIANAS PARA USO EM PANELAS NO LINGOTAMENTO DE AÇOS DE ALTA PUREZA

The production of cleaner steel has been demand for a growing market in Brazil and worldwide; and for such steels with low level of inclusions, refinement with addition of calcium has been widely used. That addition leaves a remainder of calcium in steel which may form phases of low melting point with silica and alumina present in the refractory during the casting. The slide gate plates, typically aluminous, not resist a single heat at certain levels of calcium and conditions of casting steel. The alternative here is the use of non-aluminous materials such as zirconia insert; however, it is a raw material of high cost, which requires a complex manufacturing process. The big challenge for the magnesia or basic material to be used in ladles, was its low thermal shock resistance, with intense crack formation due to high expansion of MgO. In this paper, it is presented the development and improvement of Magnesia Slide Gate Plates, Basic Plates for ladles, including high capacity ladles, their characteristics and properties. Extensive industrial tests were performed in Brazilian Steel Industry with satisfactory results. Magnesia Plates showed the same performance of plates with zirconia insert, and better cost-benefit