A rapid method for determination of acid value in transformer oil by PPy modified electrode

A polypyrrole-modified glassy carbon electrode （PPy/GC electrode） was prepared and its electrocatalytic behavior towards naphthoquinone in the presence of acid was characterized by linear sweep voltammetry （LSV）. A well-defined new reduction peak appeared at a more positive potential than the original reduction peak. The new reduction peak current was linearly related to the acid value （AV） of oil. Based on it, a rapid electrochemical method for determining AV of transformer oil was developed using PPy/GC electrode. A working curve was obtained in the AV range of 0.01 to 0.40 mg（KOH）.g^-1, with a sensitivity of 39.42 μA0.5/（mg（KOH）.g-l） and the detection limit of 0.0014 mg（KOH）.g^-1 （signal-to-noise ratio is 3, standard deviation is 2.247%）. Moreover, the proposed method has been successfully applied to AV determination of several transformer oil samples with advantages of rapidness, high sensitivity and accuracy compared to the conventional method.     

4H-SiC monolithic Darlington transistors with slight current gain drop at high collector current density

Profit from high current gain features, 4 H-Si C power Darlington transistor has the capacity for handling high current transmission. In this paper, monolithic Darlington transistors were fabricated using a simultaneous formation process for both n-type(emitter) and p-type(base) ohmic contact. The isolated device shows current gain of 1061 and 823 with collector current density(JC) increasing from 200 to 800 A/cm2, exhibiting a slight current gain drop at high JC. By extracting the interface state density(Dit) between Si O2 and p-type 4 H-Si C, it is found that this advantage owes to the improvement of the shallow bulk minority carrier lifetime in base region. Furthermore, ISE-TCAD(technology computer aided design) simulation was carried out to study the relationship between base minority lifetime and the current gain, from which the total base minority lifetime is estimated to be 48 ns. The open base breakdown voltage(BVCEO) is 850 V at a leakage current of 2 μA due to the electric filed crowding at the isolation bottom between drive bipolar junction transistor(BJT) and output BJT. To solve this, non-isolated devices were also fabricated with improved BVCEOof 2370 V, indicating the superior potential of 4 H-Si C monolithic Darlington transistors for high power application, while the current gain is deceased to 420, which needs further improvement.     

Improved oxidation resistance of chemical vapor reaction SiC coating modified with silica for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a SiC coating modified with SiO2 was prepared by a complex technology. The inner SiC coating with thickness varying from 150 to 300 μm was initially coated by chemical vapor reaction (CVR): a simple and cheap technique to prepare the SiC coating via siliconizing the substrate that was exposed to the mixed vapor (Si and SiO2) at high temperatures (1 923?2 273 K). Then the as-prepared coating was processed by a dipping and drying procedure with tetraet...     

Synthesis of modified polyacrylamide with high content of hydroxamate groups and settling performance of red mud

Hydroxamated polyacrylamide(HPAM) was synthesized from polyacrylamide(PAM) with high relative molecular mass under the optimum reaction conditions(p H 12 and a molar ratio of hydroxylamine to amide groups of 1.5 at 50 °C for 12 h). The hydroxamate groups of HPAM were verified by Fourier transform infrared spectrum(FT-IR). 46%(molar fration) hydroxamate groups and 23%(molar fraction) carbonyl groups on HPAM were determined by conductometric titration combined with Kjeldahl's microanalysis method. The settling performance achieved at different flocculant dosages was investigated with high goethite-containing red mud slurry of simulated Bayer process synthesized in laboratory. It turns out that the settling performance of high goethite-containing red mud was better with HPAM. The average settling rate of red mud in the first 5 min and the turbidity of supernatant after settling for 30 min are 2.36 m/h and 507 NTU, respectively, at a flocculant dosage of 120 g/t, which is similar to that achieved with Hx-600.     

Fabrication of a monolithic 4H-SiC junction barrier schottky diode with the capability of high current

There is a great interest in monolithic 4H-Si C Junction Barrier Schottky(JBS) diodes with the capability of a high forward current for industrial power applications.In this paper,we report large-area monolithic 4H-Si C JBS diodes fabricated on a 10 μm 4H-Si C epitaxial layer doped to 6×1015 cm3.JBS diodes with an active area of 30 mm2 had a forward current of up to 330 A at a forward voltage of 5 V,which corresponds to a current density of 1100 A/cm2.A near ideal breakdown voltage of 1.6 k V was also achieved for a reverse current of up to 100 A through the use of an optimum multiple floating guard rings(MFGR) termination,which is about 87.2% of the theoretical value.The differential specific-on resistance(RSP-ON) was measured to be 3.3 m cm2,leading to a FOM(VB2/RSP-ON) value of 0.78 GW/cm2,which is very close to the theoretical limit of the tradeoff between the specific-on resistance and breakdown voltage for 4H-Si C unipolar devices.     

An improved sensitivity non-enzymatic ascorbic acid sensor based on a Ag2O nanowire modified Ag electrode

In this paper, the Ag2O nanowires had been prepared and applied for the fabrication of ascorbic acid sensors with high enhanced sensitivity by using self-assembly technology. The structures and morphologies of Ag2O nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The direct electrocatalytic oxidation of ascorbic acid in alkaline medium at Ag2O nanowires modified electrodes had been investigated in detail and the condition for determination of ascorbic acid was optimized, such as support-electrolyte, pH and scan speed. The oxidation peak current changed linearly with the concentration of ascorbic acid over the range from 2.0×10-8 mol/L to 1.0 mmol/L, and the detection limit can reach 1.0×10-8mol/L. Compared to a bare Ag electrode, a substantial decrease in the overvoltage of the ascorbic acid oxidation was observed at the Ag nanowires electrodes with oxidation starting at ca. 0.7V vs. Ag/AgCl (saturated KCl). The Ag2O nanowires modified electrode allows highly sensitive, low working potential, stable, and fast amperometric sensing of ascorbic acid, thus is promising for the future development of non-enzymatic ascorbic acid sensors.     

A betavoltaic microbattery based on PIN diodes

A betavoltaic Microbattery was studied.The diode was composed of a PIN structure with an active area of 10 mm×10 mm to collect the charge from a 10mCi Ni-63 source.An open circuit voltage of 0.16 V and a short circuit current density of 67.6 nA/cm2 were measured.An efficiency (η) of 1.44% was obtained.The performance of device was limited by high series resistance,edge recombination and attenuation of electron in PIN diodes.It is expected to be improved by optimizing the design and using more suitable radioisotope.     

Inducing effect of Pb(Zr_(0.4)Ti_(0.6))O_3 thin film derived by different processes in BiFeO_3/Pb(Zr_(0.4)Ti_(0.6))O_3 multilayer capacitor at room temperature

BiFeO3/PZT multilayer capacitor was prepared on Pt(100)/Ti/SiO2/Si(100) substrate. PZT buffer layer was derived by MOCVD method (label: PZT1) and sputtering method (label: PZT2) respectively. XRD analysis indicated that high (110) orientation of BFO in the BFO/PZT1 structure was achieved. SEM analysis indicated a better microstructure in the BFO/PZT1 structure compared with BFO/PZT2. The remnant polarization of the BFO/PZT1 was 82.5 μC/cm2 at an applied voltage of 8 V, compared with that of 25.2 μC/cm2 in the BFO/PZT2 structure. The BFO/PZT1 multilayer exhibited little polarization fatigue (<1.5%) upon 1×1010 switching cycles, at an applied voltage of 4 V. The leakage current density was about 2×10?7 A/cm2 at an applied voltage 4 V, in the BFO/PZT1 capacitor. All the results indicated that PZT can act as an inducing layer to the BFO and the MOCVD derived PZT has more inducing effect to the BFO thin film at room temperature.     

Dynamic Temperature Characteristics of Liquid Filled Photonic Crystal Fiber

The dynamic characteristics of high sensitivity temperature sensor are studied by using siphon method to fill the air hole near the core of the hollow photonic crystal fiber with Cargille matching liquid,and the two ends are fused with single-mode fiber in this work.We analyzed the working principle of filled photonic crystal fiber sensor by using the standard coupling mode theory of directional coupler.The coupling process was simulated by COMSOL software.When the photonic crystal fiber filled with 10 mm liquid was scanned by tunable laser,the temperature sensitivity was 7.50 nm /℃,the average temperature response time was 0.317 s,the average release time was 3.732 s,and the temperature variation linearity was 100%.The experimental results show that the liquid filled photonic crystal fiber has the advantages of high temperature sensitivity,fast response time and good linearity.     

Determination of residual monomers in polycarboxylate superplasticizer using high performance liquid chromatography

A procedure was developed for the determination of residual monomers in polycarboxylate superplasticizer (PCs) by reversed-phase high performance liquid chromatography (RP-HPLC).Four kinds of residual monomers were well separated and determined on a SinoChrom ODS-BP (C18) column with mobile phases composed of acetonitrile and phosphate buffer solution.The monomers were detected by UV detector at 205 nm and quantitatively analyzed with an external standard method.For those residual monomers,the linear response ranged from 4.0×10-6 mol·L-1 to 2.0×10-3 mol·L-1.The determination limit of acrylic acid,sodium methylallyl sulfonate and 2-Acrylamido-2-methylpropane sulfonic acid was 0.02×10-5 mol·L-1,while that of methoxy-polyethylene glycol monoacrylate was 0.1×10-5 mol·L-1.The relative standard deviation (RSD) of high concentration samples was less than 1%,while that of the low concentration samples was between 1%-4%.The standard (additional) recovery ratio was 97.4% -104.2%.     

Synthesis of refractory cordierite from calcined bauxite, talcum and quartz

A cordierite was synthesized from calcined bauxite, talcum, and quartz. The properties and microstructure of the cordierite sintered samples were characterized by Archimedes’ method, thermal dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and so on. The experimental results showed that calcined bauxite could broaden the range of synthesizing temperature from 1300 °C to 1420 °C and get pure cordierite. The bulk density and linear thermal expansion coeffi cient of the sample synthesized at 1420 °C for 2 h were 1.97 g·cm^?3 and 2.1×10^?6 °C^?1, respectively. The XRD analysis showed that the major crystalline phase was α-cordierite with almost no glassy matters, the SEM images illustrated a small vent hole and the size were 5–100 μm, the well-grown hexagonal and granular cordierite grains had the sizes distributed among 0.1–8 μm, and providing high mechanical strength and lower linear thermal expansion coeffi cient.     

Evolution and characterization of damage of concrete under freeze-thaw cycles

To study the internal damage of concrete under freeze-thaw cycles, concrete strains were measured using embedded strain gauges. Residual strain and coefficients of freezing expansion (CFE) derived from strain-temperature curves were used to quantify the damage degree. The experimental results show that irreversible residual strain increases with the number of freeze-thaw cycles. After 50 cycles, residual strains of C20 and C35 concretes are 320με and 100με in water, and 120 με and 60 με in saline solution, respectively. In lower temperature range (-10 ℃ to -25 ℃) CFE of C20 and C35 concretes decrease by 9.82×10-6/K and 8.44×10-6/K in water, and 9.38×10-6/K and 5.47×10-6/K in saline solution, respectively. Both residual strains and CFEs indicate that during the first 50 freeze-thaw cycles, the internal damage of concrete in saline solution is less than that of concrete in water. Thus residual strain and CFE can be used to measure the frost damage of concrete.     

Experimental studies of N~+ implantation into CVD diamond thin films

The effects of N+ implantation under various conditions on CVD diamond films were analyzed with Raman spectroscopy, four-point probe method, X-ray diffraction (XRD), Rutherford backseattering spectroscopy (RBS), ultraviolet photoluminescence spectroscopy (UV-PL), Fourier transformation infrared absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the N+ implantation doping without any graphitization has been successfully realized when 100 keV N+ ions at a dosage of 2 × 1016 cm-2 were implanted into diamond films at 550℃ . UV-PL spectra indicate that the implanted N+ ions formed an electrically inactive deep-level impurity in diamond films. So the sheet resistance of the sample after N+ implantation changed little. Carbon nitride containing C≡N covalent bond has been successfully synthesized by 100 keV, 1.2×1018 N/cm2 N+ implantation into diamond films. Most of the implanted N+ ions formed C≡N covalent bonds with C atoms. The others were free state nitroge     

The effect of the boron-ions implantation on the performance of RADFETs

In this work, we studied on the boron-ions implantation, including the implant dose and post-annealing temperature on the performance of PMOS radiation field-effect transistors(RADFETs) in experimental. The possible traps and defects induced by ions implantation in the gate-oxide and their further impacting on the sensitivity and dose range of RADFETs were analyzed qualitatively. Our devices had the dry/wet/dry sandwich gate-oxide of 420 nm thick. Different ion-implanting doses and post-annealing temperatures were carried out during the RADFETs fabrication. We built a real time auto-measurement system to realize the auto-state-switch between irradiation and read-out modes, and in-situ measurement of output voltage for ten devices in turn at once of radiation experiment. The threshold voltage, dose range and sensitivity of RADFETs were extracted and analyzed in detail. The results showed that the highest sensitivity of 229 mV/Gy achieved when the implant dose was2.2×1011 cm.2 and the post-annealing temperature was 1000°C, and the dose range of 34 Gy as well.     

Laser tuned field emission of the carbon nanotube arrays grown on an optical fiber

Laser was coupled into an optical fiber,on which covered a layer of well-aligned carbon nanotubes(CNTs)serving as cathode,to tune the field emission of the cathode.CNT arrays as field emission cathode were synthesized by chemical vapor deposition(CVD)on a naked fiber core.When the laser was coupled into the fiber,the turn-on voltage(Vto at a current density of 1 mA cm?2)decreased from 1.0 to 0.9 kV and the emission current density increased from 0.83 mA cm?2(at a 1 kV bias voltage)to3.04 mA cm?2 on 40μm diameter fiber.A photon absorption mechanism is attributed to the field emission improvement.The estimated effective work function of CNT arrays on the optical fiber decrease from 4.89 to 4.29 eV.The results show the possibility of constructing a waveguide type laser modulated field emission cathode.     

Construction of amperometric glucose biosensor based on <Emphasis Type="Italic">in-situ</Emphasis> fabricated hierarchical meso-macroporous SiO<Subscript>2</Subscript> modified Au film electrodes

Gold nanoparticles (GNPs) modified hierarchical meso-macroporous (HMMP) SiO₂ layer on the surface of Au film electrode was developed as a novel enzyme immobilization matrix for biosensors construction. HMMP SiO₂-Au bilayer film electrodes were in-situ fabricated with magnetron sputtering process and templating method. The as-prepared HMMP SiO₂ films were characterized by SEM, TEM, and cyclic voltammetry (CV). The modified layer of HMMP SiO₂ has interconnected pore channels, and the sizes of macropores and mesopores are about 330 nm and 9 nm, respectively. The HMMP SiO₂ modified gold film electrodes not only have no diffusion barrier for electrochemical probes, but also exhibit good electrochemical properties. In addition, the activity and stability of the immobilized enzyme can be commendably retained in HMMP SiO₂. The biosensor exhibits an excellent bioelectrocatalytic response to glucose with a linear range of 1.0×10^-4 M-1.0×10^-2 M, high sensitivity of 18.0 μA·mM^-1·cm^-2, as well as good reproducibility and stability.     

Sulfonic acid modified hollow silica spheres and its application in proton exchange membranes

In order to improve the proton conductivity of hollow silica spheres (HSS)/perfluorosulfonic acid ion-exchange (PFSA) composite membranes as proton exchange membrane, sulfonic acid groups were grafted onto the surfaces of HSS via post grafting methods. TEM images and FT-IR spectra of the obtained sulfonic acid groups modified hollow silica spheres (SAMHSS) illustrated that the sulfonic acid groups were successfully grafted onto the surfaces of HSS. Water uptake and swelling degree of SAMHSS/PFSA composite membranes were found much higher than those of HSS/PFSA membranes due to the introduction of hydrophilic sulfonic acid groups. In a range from 50 °C to 130 °C, the highest conductivity of composite membranes was obtained when 5 wt% SAMHSS was loaded. The maximum conductivity reached 7.5×10⁻² S·cm⁻¹ at 100 °C and 100% relative humidity, even the temperature increased to 130 °C, the conductivity of composite membranes with 5 wt% SAMHSS could reach 3.7×10⁻² S·cm⁻¹ at 100 % relative humidity, while the conductivity of the recast PFSA was only 2.2×10⁻³ S·cm⁻¹.     

The electromagnetic wave experiment for CSES mission: Search coil magnetometer

The seismic activities on the Earth can produce a disturbance of the electromagnetic field and particles in the ionosphere. The search coil magnetometer(SCM) mounted on China Seismo-Electromagnetic satellite(CSES) is designed to measure the magnetic field fluctuation of low frequency electromagnetic waves in the frequency range of 10 Hz–20 k Hz. The SCM comprises a three-axis search coil sensor mounted on a 4.5 m boom and an electronic box inside satellite module. The sampling rate of the SCM is 51.2 k Hz and the time resolution of the power spectrum density(PSD) is 2 s. The frequency resolution is 12.5 Hz.There are three operation modes: survey, detailed survey and calibration. In the survey mode, the SCM can provide a PSD in the whole frequency range of 10 Hz–20 k Hz and wave forms in the low frequency range below 2 k Hz while in the detailed survey mode the SCM can provide both PSD and wave forms in the whole frequency range of 10 Hz–20 k Hz. The sensitivity of the SCM instrument is 5.0×10~(-4) n T Hz~(-1/2) at 10 Hz, 5.0×10~(–5) n T Hz~(-1/2) at 200 Hz, 3.4×10~(-5) n T Hz~(-1/2) at 2 k Hz and 1.1×10~(-4) n T Hz~(-1/2) at 20 k Hz. The telemetry rate is ~0.85 Mbps in the survey mode and ~3.0 Mbps in the detailed survey mode. The phase difference between three axes can be made generally with a precision of less than 1.0°. The dynamic range of the SCM instrument is over 100 d B. The orthogonality of three mechanical axes of search coil senor is better than 0.13°. The performance of SCM can satisfy the requirement of scientific objectives of CSES mission.     

Bilayer carbon-based structure with the promotion of homogenous nucleation for lithium metal anodes

Lithium metal anodes (LMAs) are considered as the promising alternatives for next-generation high energy density batteries, but are still hampered by the severe growth of uncontrollable lithium dendrites. The growth of lithium dendrites induces poor cycling lifespan and serious safety concerns, dragging lithium metal batteries out of practical applications. We designed a bilayer carbon-based structure covered with Co/C nanosheets and vertical graphene sheets (VGS). The enormous specific surface area and uniformly distributed Co nanoparticles of the CC@Co/C-VGS host are derived from its unique design, which can reduce local current density and nucleation overpotential, resulting in a dendrite-free morphology and exceptional cycling stability. Symmetric cells exhibit over 400 cycles (800 h) at a high current density/capacity of 10 mA cm^?2/10 mA h cm^?2. Full cells using LiFePO₄ as the cathode have an enhanced rate capability and a prolonged lifespan, reaching 90 mA h g^?1 after 1000 cycles at 2 C with 73.5% capacity retention. This unique design sheds light on developing high-performance LMAs.

     

Nanometer structure and conductor mechanism of polymer modified by metal ion implantation

Polyethylene terephthalate (PET) has been modified by Ag, Ti, Cu and Si ion implantation with a dose ranging from 1 × 1016 to 2 × 1017 ions/cm2 using a metal vapor vacuum arc (MEVVA) source. The electrical properties of PET have been improved by metal ion implantation. The resistivity of implanted PET decreased obviously with an increase in ion dose. The results show that the conductive behavior of a metal ion implanted sample is different from Si-implantation samples. In order to un-derstant the mechanism of electrical conduction, the structures of implanted layer were observed in detail by XRD and TEM. The nano carbon particles were dispersed in implanted PET. The nano metallic particles were built up in metallic ion implanted layers with dose range from 1 × 1016 to 1 × 1017 ions/ cm2. The nanometer metal net structure was formed in implanted layer when a dose of 2 × 1017ions/ cm2 is reached. Anomalous fractal growths were observed. These surface structure changes revealed conducting mechanism evo