Alkaline pressure oxidative leaching of bismuth-rich and arsenic-rich lead anode slime

A new alkaline pressure oxidative leaching process(with NaNO3 as the oxidant and NaOH as the alkaline reagent)is proposed herein to remove arsenic,antimony,and lead from bismuth-rich and arsenic-rich lead anode slime for bismuth,gold,and silver enrichment.The effects of the temperature,liquid-to-solid ratio,leaching time,and reagent concentration on the leaching ratios of arsenic,antimony,and lead were investigated to identify the optimum leaching conditions.The experimental results under optimized conditions indicate that the average leaching ratios of arsenic,antimony and lead are 95.36%,79.98%,63.08%,respectively.X-ray diffraction analysis indicated that the leaching residue is composed of Bi,Bi2O3,Pb2Sb2O7,and trace amounts of NaSb(OH)6.Arsenic,antimony,and lead are thus separated from lead anode slime as Na3AsO4·10H2O and Pb2Sb2O7.Scanning electron microscopy and energy-dispersive spectrometry imaging revealed that the samples undergo appreciable changes in their surface morphology during leaching and that the majority of arsenic,lead,and antimony is removed.X-ray photoelectron spectroscopy was used to demonstrate the variation in the valence states of the arsenic,lead,and antimony.The Pb(IV)and Sb(V)content was found to increase substantially with the addition of NaNO3.

φ-pH diagram of As-N-Na-H_2O system for arsenic removal during alkaline pressure oxidation leaching of lead anode slime

In order to illustrate the thermodynamic characteristics of arsenic during alkaline pressure oxidation leaching process oflead anode slime(NaNO3as oxidant;NaOH as alkaline reagent),theφ-pH diagrams of As-Na-H2O,N-H2O,As-N-Na-H2Osystems at ionic mass concentration of0.1mol/kg and temperatures of298,373,423and473K were established according tothermodynamic calculation.The results show that the existence forms of arsenic are associated with pH value,which mainly exists inthe forms of H3AsO4,24H AsO-,24HAsO-,H2AsO2-and As2O3in lower pH region,while it mainly exists in the form of3AsO4-when pH>11.14.High alkali concentration and high temperature are advantageous to the arsenic leaching.The alkaline pressureoxidation leaching experiments display that the tendency of arsenic leaching rate confirms the thermodynamic analysis resultsobtained from theφ-pH diagrams of As-N-Na-H2O system,and the highest leaching rate of arsenic reaches95.85%at453K.

In-situ SiN combined with etch-stop barrier structure for high-frequency AlGaN/GaN HEMT

The etch-stop structure including the in-situ SiN and AlGaN/GaN barrier is proposed for high frequency applications.The etch-stop process is realized by placing an in-situ SiN layer on the top of the thin AlGaN barrier.F-based etching can be self-terminated after removing SiN,leaving the AlGaN barrier in the gate region.With this in-situ SiN and thin barrier etch-stop structure,the short channel effect can be suppressed,meanwhile achieving highly precisely controlled and low damage etching process.The device shows a maximum drain current of 1022 mA/mm,a peak transconductance of 459 mS/mm,and a maximum oscillation frequency(fmax)of 248 GHz.

Ferroelectric effect and equivalent polarization charge model of PbZr_(0.2)Ti_(0.8)O_(3)on AlGaN/GaN MIS-HEMT

PbZr_(0.2)Ti_(0.8)O_(3)(PZT)gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD)in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors(MIS-HEMTs).The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated.The polarization charge in PZT varies with different gate voltages.The equivalent polarization charge model(EPCM)is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas(2DEG).The threshold voltage(V_(th))and output current density(I_(DS))can also be obtained by the EPCM.The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT.The polarization charges of PZT can be modulated by different gate-voltage stresses and the V_(th)has a regulation range of 4.0 V.The polarization charge changes after the stress of gate voltage for several seconds.When the gate voltage is stable or changes at high frequency,the output characteristics and the current collapse of the device remain stable.

Effect of NaNO3 concentration on anodic electrochemical behavior on the Sb surface in NaOH solution

The effect of NaNO_3 concentration on the anodic electrochemical behavior of antimony in 4 M NaOH solution was investigated using cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) analyses. The mechanism of NO_3^-concentration effect on the anodic electrochemical behavior of antimony was proposed, and its availability was confirmed by experimental results. The effect of NaNO_3 on the anodic behavior of antimony in Na OH solution can be interpreted as a stepwise formation of different antimony compounds with different NaNO_3 concentrations. Metallic antimony is apt to be oxidized into Sb_2O_3 within the NaNO_3 concentration range of 0–0.48 M. NaSbO_3 can be found on the antimony surface when the NaNO_3 concentration increases gradually. Insoluable NaSbO_3 inhibits the anodic oxidation of antimony due to its shielding effect on the mass transport of the reactants and products. Surface morphology and composition were analyzed by X-ray photoelectron spectroscopy(XPS), scanning electronic microscopy(SEM), and electron dispersion spectroscopy(EDS) analyses. Results indicate that the anodic oxidation layer is composed of Sb_2O_3, NaSbO_3, and Sb. The atomic proportion of antimony in the form of NaSbO_3 increases with increasing NaNO_3 concentration due to the powerful oxidizing property of NaNO_3.

Comparative study on characteristics of Si-based AlGaN/GaN recessed MIS-HEMTs with HfO2 and Al2O3 gate insulators

Two types of enhancement-mode(E-mode)AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors(MIS-HEMTs)with different gate insulators are fabricated on Si substrates.The HfO2 gate insulator and the Al2O3 gate insulator each with a thickness of 30 nm are grown by the plasma-enhanced atomic layer deposition(PEALD).The energy band diagrams of two types of dielectric MIS-HEMTs are compared.The breakdown voltage(VBR)of HfO2 dielectric layer and Al2O3 dielectric layer are 9.4 V and 15.9 V,respectively.With the same barrier thickness,the transconductance of MIS-HEMT with HfO2 is larger.The threshold voltage(Vth)of the HfO2 and Al2O3 MIS-HEMT are 2.0 V and 2.4 V,respectively,when the barrier layer thickness is 0 nm.The C-V characteristics are in good agreement with the Vth's transfer characteristics.As the barrier layer becomes thinner,the drain current density decreases sharply.Due to the dielectric/AlGaN interface is very close to the channel,the scattering of interface states will lead the electron mobility to decrease.The current collapse and the Ron of Al2O3 MIS-HEMT are smaller at the maximum gate voltage.As Al2O3 has excellent thermal stability and chemical stability,the interface state density of Al2O3/AlGaN is less than that of HfO2/AlGaN.

Characteristics and threshold voltage model of GaN-based FinFET with recessed gate

In this work, AlGaN/GaN FinFETs with different fin widths have been successfully fabricated, and the recessed-gate FinFETs are fabricated for comparison. The recessed-gate FinFETs exhibit higher transconductance value and positive shift of threshold voltage. Moreover, with the fin width of the recessed-gate FinFETs increasing, the variations of both threshold voltage and the transconductance increase. Next, transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software. The relationship between the threshold voltage and the AlGaN layer thickness has been investigated. The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decreasing. Finally, a simplified threshold voltage model for recessed-gate FinFET is established,which agrees with both the experimental results and simulation results.

Simulation design of normally-off AlGaN/GaN high-electron-mobility transistors with p-GaN Schottky hybrid gate

A novel normally-off AlGaN/GaN high-electron-mobility transistor(HEMT)with a p-GaN Schottky hybrid gate(PSHG)is proposed,and compared with the conventional p-GaN normally-off AlGaN/GaN HEMTs.This structure can be realized by selective etching of p-GaN layer,which enables the Schottky junction and PN junction to control the channel charge at the same time.The direct current(DC)and switching characteristics of the PSHG HEMTs are simulated by Slivaco TCAD,and the p-GaN HEMTs and conventional normally-on HEMTs are also simulated for comparison.The simulation results show that the PSHG HEMTs have a higher current density and a lower on-resistance than p-GaN HEMTs,which is more obvious with the decrease of p-GaN ratios of the PSHG HEMTs.The breakdown voltage and threshold voltage of the PSHG HEMTs are very close to those of the p-GaN HEMTs.In addition,the PSHG HEMTs have a higher switching speed than the conventional normally-on HEMTs,and the p-GaN layer ratio has no obvious effect on the switching speed.

PEDOT:PSS薄膜的丝网印刷、后处理改性及在染料敏化太阳能电池中的应用

运用丝网印刷的方式在导电玻璃基底表面涂覆了聚(3,4-乙烯二氧噻吩)(PEDOT):聚苯乙烯磺酸盐混合物(PSS)薄膜,并采用稀H_2SO_4加甲醇混合溶液后处理的方式对其进行了改性.使用扫描电子显微镜(SEM)和原子力显微镜(AFM)观察处理前后薄膜的表面形貌及厚度的变化,对比了处理前后薄膜的电导率,并结合X射线衍射(XRD)和X射线光电子能谱(XPS)分析探讨了导致电导率变化的原因.最后,将PEDOT:PSS薄膜作为对电极组装了染料敏化太阳能电池(DSSC),运用电化学阻抗谱(EIS)研究了对电极的催化性能,并测试了DSSC的光伏性能.结果显示,经过后处理改性后,由于PSS被部分去除,PEDOT:PSS薄膜的表面形貌发生了显著改变,厚度变薄,粗糙度升高,电导率提升至原始的3倍以上,对I_3~–还原的催化活性升高,且组装的DSSC的性能也有了显著提高,光电转换效率由5.12%提升至6.64%.