变流电路中电解电容的“硅解”研究

电解电容是现代电力电子系统中用量多 ,体积大 ,可靠性差 ,寿命短的最薄弱环节。提出用高频电流型有源滤波器取代电力电子变流器直流环的电解电容 ,实现电解电容的“硅解”。实验结果验证了“硅解”方案的可行性 。

Solubility of hemimorphite in ammonium sulfate solution at 25 °C

The solubility of natural hemimorphite in ammonium sulfate solution was measured by isothermal solution method at 25 °C and the dissolved residue of hemimorphite was investigated by X-ray powder diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy （FTIR） methods. The results show that zinc and silica in hemimorphite simultaneously dissolve in ammonium sulfate solution. The solubility of zinc in solution increases rapidly from 4.5381 mmol/kg in 0.5469 mol/kg ammonium sulfate solution to 11.5083 mmol/kg in 3.7038 mol/kg ammonium sulfate solution. The solubility of silica in solution increases slowly from 2.5509 mmol/kg in 0.5469 mol/kg ammonium sulfate solution to 7.2891 mmol/kg in 3.7038 mol/kg ammonium sulfate solution. The dissolved residue is the characteristic of hemimorphite Zn4Si2O7（OH）2·H2O based on the results of the XRD, SEM and FTIR. Thus, no phase transition occurs in the dissolution process of hemimorphite in ammonium sulfate solution.

Purification of metallurgical grade silicon by electrorefining in molten salts

Electrochemical studies on silicon deposition were performed in molten salt electrolytes. Purification of metallurgical grade silicon by electrorefining was carried out in molten Si-chloride salts at temperatures from 973 K to 1223 K. It was found that the use of a liquid alloy anode of silicon and copper was beneficial in molten CaCl2 with NaCl, CaO and dissolved Si. ICP-AES analysis results showed efficient removal of metal impurities, such as titanium, aluminum and iron, which are present in significant quantities in the feedstock. The contents of boron and phosphorus in the silicon after electrorefining were reduced from 36×10-6 and 25×10-6 to 4.6×10-6 and 2.8 ×10-6, respectively. The energy consumption of electrorefining was estimated to be about 9.3 kW?h/kg.

Direct Synthesis of High Purity Silicon Wires by Electrorefining in Molten KF-NaF Eutectic

The electrochemical synthesis silicon wires by electrorefining metallurgical grade silicon in thermally dried and pre-electrolyzed molten KF-NaF eutectic were studied at temperatures 800-900 ℃ using cyclic voltammetry and ac impedance. One oxidation peak at -0.14 V could be attributed to the reaction of Si to Si4＋. A cathodic peak occurred at -0.56 V in the cyclic voltammogram and one response semicircle in the ac impedance spectrum was observed, supporting a one-step electrochemical reduction process of Si4＋-→Si. The electrochemical reaction of silicon was controlled by the diffusion process. The purity of electrorefined silicon wires was up to 99.999% by ICP-MS analysis.

Influence of pyrolysis temperature on structure and dielectric properties of polycarbosilane derived silicon carbide ceramic

β-SiC ceramic powders were obtained by pyrolyzing polycarbosilane in vacuum at 800-1200 °C. The β-SiC ceramic powders were characterized by TGA/DSC, XRD and Raman spectroscopy. The dielectric properties of β-SiC ceramic powders were investigated by measuring their complex permittivity by rectangle wave guide method in the frequency range of 8.2-18 GHz. The results show that both real part ε′ and imaginary part ε″ of complex permittivity increase with increasing pyrolysis temperature. The mechanism was proposed that order carbon formed at high temperature resulted in electron relaxation polarization and conductance loss, which contributes to the increase in complex permittivity.

GaP/GaPN core/shell nanowire array on silicon for enhanced photoelectrochemical hydrogen production

Simultaneously improving the efficiency and stability on a large scale is significant for the development of photoelectrochemical(PEC)water splitting systems.Here,we demonstrated a novel design of GaP/GaPN core/shell nanowire(NW)decorated p-Si photocathode for improved PEC hydrogen production performance compared to that of bare p-Si photocathode.The formation of the p-n junction between p-Si and GaP NW promotes charge separation,and the lower conduction band position of GaPN relative to that of GaP further facilitates the transfer of photogenerated electrons to the electrode surface.In addition,the NW morphology both shortens the carrier collection distance and increases the specific surface area,which result in superior reaction kinetics.Moreover,introduction of N in GaP is beneficial for enhancing the light absorption as well as stability.Our efficient and facile strategy can be applied to other solar energy conversion systems as well.

An Analytical Model of Electron Mobility for Strained-Si Channel nMOSFETs

An analytical model of electron mobility for strained-silicon channel nMOSFETs is proposed in this paper. The model deals directly with the strain tensor,and thus is independent of the manufacturing process. It is suitable for （100〉/ 〈110） channel nMOSFETs under biaxial or （100〉/〈 110 ） uniaxial stress and can be implemented in conventional device simulation tools .

Feasibility of Using Trichloroacetic Acid Soluble Siliconas a Diagnostic Index of Silicon Deficiency in Rice

Pot experiments and field trials were conducted to investigate the changes in trichloroacetic acid (TCA) soluble silicon (Si) in the leaves of rice (Oryza sativa L.) and to examine the feasibility of using TCA-soluble Si content as an index for diagnosing Si deficiency. The TCA-soluble Si content was significantly higher in the leaves of both Si-treated and -untreated rice at the elongation stage compared with that at tillering stage. It was also higher in the Si-treated plants than in the controls throughout the whole growth period.However, whether dressed at elongation or booting stage, silicon fertilizer resulted in a significant increase in TCA-soluble Si one week to ten days after application. The same was true for the total Si accumulation in the plants. A close positive correlation was found between TCA-soluble Si and total it in plants grown on pot soils (r=0.669, P<0.01, n=26). The results obtained in the field trials revealed that the available Si extracted by sodium acetate (pH 4.0) could not predict the response of rice to added Si in the calcareous soils satisfactorily. No significant correlation was found between soil available Si content and rice yield, but TCA-soluble Si in the leaf blades of rice was significantly correlated both with rice yield (r=0.57, P<0.01,n=30) and with total plant Si (r=0.89, P<0.01, n=30). It is recommended that, with 95 per cent confidence,the critical value of TCA-soluble Si in the leaves of rice should be 52-57 mg Si kg-1, above which no positive response of rice to added Si would be expected.

Temperature-triggered Protein Adsorption and Desorption on Temperature-responsive PNIPAAm-grafted-silica:Molecular Dynamics Simulation and Experimental Validation

Poly(N-isopropylacrylamide)(PNIPAAm) grafted onto silica,which may be used for reverse phase chromatography(RPC),was simulated and synthesized for protein separation with temperature-triggered adsorption and desorption.Molecular dynamics simulation at an all-atom level was performed to illustrate the adsorption/desorption behavior of cytochrome c,the model protein,on PNIPAAm-grafted-silica,a temperature responsive adsorbent.At a temperature above the lower critical solution temperature(LCST),the PNIPAAm chains aggregate on the silica surface,forming a hydrophobic surface that is favorable for the hydrophobic adsorption of cytochrome c,which has a high exposure of hydrophobic patches.At temperatures below the LCST,the PNIPAAm chains stretch,forming hydrophilic surface due to hydrogen bonding between PNIPAAm and surrounding water.Desorption of cytochrome c on the PNIPAAm-grafted-silica surface occurs as a result of competition with water,which forms hydrogen bonds with the protein.The conformational transitions of both cytochrome c and PNIPAAm are monitored,providing molecular insight into this temperature-responsive RPC technique.PNIPAAm-grafted-silica beads were synthesized and used for the adsorption and desorption of cytochrome c at approximately 313 K and 290 K,respectively.The experimental results validate the molecular dynamics simulation.In comparison to conventional RPC,using temperature as a driving force for RPC reduces the risk of protein denaturation caused by exposure to chaotropic solvents.Moreover,it simplifies the separation process by avoiding the buffer exchange operations between the steps.

A dinoflagellate Cochlodinium geminatum bloom in the Zhujiang (Pearl) River estuary in autumn 2009

A severe Cochlodinium geminatum red tide (>300 km2) was observed in the Zhujiang (Pearl) River estuary, South China Sea in autumn 2009. We evaluated the environmental conditions and phytoplankton community structure during the outbreak. The red tide water mass had significantly higher dissolved inorganic phosphate (DIP), ammonia, and temperature, but significantly lower nitrite, nitrate, dissolved inorganic nitrogen (DIN), and DIN/DIP relative to the non-red-tide zones. The phytoplankton assemblage was dominated by dinoflagellates and diatoms during the red tide. C. geminatum was the most abundant species, with a peak density of 4.13×107 cell/L, accounting for >65% of the total phytoplankton density. The DIN/DIP ratio was the most important predictor of species, accounting for 12.45% of the total variation in the phytoplankton community. Heavy phosphorus loading, low precipitation, and severe saline intrusion were likely responsible for the bloom of C. geminatum.

Revisiting the dissolution of biogenic Si in marine sediments： a key term in the ocean Si budget

Of the ~240*10^(12)mol year^(-1)of biogenic silica(bSi)produced by diatoms and other silicifying organisms,only roughly 3%–4%escapes dissolution to be permanently buried.At the global scale,how,where and why b Si is preserved in sediment is not well understood.To help address this,I compile 6245 porewater dissolved Si concentrations from 453 sediment cores,to derive the concentration gradient at the sediment–water interface and thus diffusive fluxes out of the sediment.These range from\0.002 to 3.4 mol m^(-2)year^(-1),and are independent of temperature,depth and latitude.When classified by sediment lithology,predominantly siliceous sediments unsurprisingly have higher mean diffusive fluxes than predominantly calcareous or clay-rich sediment.Combined with the areal extent of these lithologies,the‘best-guess’global sedimentary b Si recycling flux is69 9 10^(12)mol year^(-1).

Preparation of MnO_2 and calcium silicate hydrate from electrolytic manganese residue and evaluation of adsorption properties

Electrolytic manganese residue(EMR), a high volume byproduct resulting from the electrolytic manganese industry, was used as a cheap and abundant chemical source for preparing MnO2 and EMR-made calcium silicate hydrate(EMR-CSH). The MnO2 is successfully synthesized from the metal cations extracted from EMR, which can effectively recycle the manganese in the EMR. By the combination of XRD, SEM and EDX analysis, the as-prepared MnO2 is found to exhibit a single-phase with the purity of 90.3%. Furthermore, EMR-CSH is synthesized from EMR via hydrothermal method. Based on the detailed analyses using XRD, FT-IR, FE-SEM, EDX and BET surface area measurement, the product synthesized under the optimum conditions(p H 12.0 and 100 °C) is identified to be a calcium silicate hydrate with a specific surface area of 205 m2/g incorporating the slag-derived metals(Al and Mg) in its structure. The as-synthesized material shows good adsorption properties for removal of Mn2+ and phosphate ions diluted in water, making it a promising candidate for efficient bulk wastewater treatment. This conversion process, which enables us to fabricate two different kinds of valuable materials from EMR at low cost and through convenient preparation steps, is surely beneficial from the viewpoint of the chemical and economical use of EMR.

An analytical model to explore open-circuit voltage of a-Si:H/c-Si heterojunction solar cells

The effect of the parameters on the open-circuit voltage, V_(OC) of a-Si:H/c-Si heterojunction solar cells was explored by an analytical model. The analytical results show that V_(OC) increases linearly with the logarithm of illumination intensity under usual illumination. There are two critical values of the interface state density(D_(it)) for the open-circuit voltage(V_(OC)), D_(it)^(crit,1) and D_(it)crit,2(a few 1010 cm^(-2)·e V^(-1)). V_(OC) decreases remarkably when D_(it) is higher than D_(it)^(crit,1). To achieve high V_(OC), the interface states should reduce down to a few 1010 cm^(-2)·e V^(-1). Due to the difference between the effective density of states in the conduction and valence band edges of c-Si, the open-circuit voltage of a-Si:H/c-Si heterojunction cells fabricated on n-type c-Si wafers is about 22 mV higher than that fabricated on p-type c-Si wafers at the same case. V_(OC) decreases with decreasing the a-Si:H doping concentration at low doping level since the electric field over the c-Si depletion region is reduced at low doping level. Therefore, the a-Si:H layer should be doped higher than a critical value of 5×10^(18) cm^(-3) to achieve high V_(OC).

Decomposition kinetics of zircon sand in NaOH sub-molten salt solution

Sub-molten salt was applied to the decomposition of zircon sand(ZrSiO4).The kinetics of the decomposition of zircon sand and the effects of reaction temperature,reaction time,NaOH content,agitation speed,and the NaOH/ore mass ratio on the decomposition rate of zircon sand in NaOH sub-molten salt were investigated.The results indicate that the decomposition rate of zircon sand increases with the increase in the reaction temperature,reaction time,and NaOH content.The shrinking-core model with surface chemical reaction-controlled process is the most applicable for the decomposition of zircon sand,with the apparent activation energy of 77.98 kJ/mol.The decomposition product is sodium zirconium silicate(Na2ZrSiO5),and the decomposition rate is higher than 99%under the optimal conditions.

Molten salt electrosynthesis of silicon carbide nanoparticles and their photoluminescence property

A one-step molten salt electrochemical strategy was proposed to synthesize SiC nanoparticles from ultra-fine silicon dioxide/carbon(SiO_(2)/C)mixtures.The electrosynthesis process and physicochemical properties of the synthesized products were systematically analyzed via X-ray diffraction,electron microscopy,Raman spectroscopy and photoluminescence spectroscopy,etc.A combined chemical/electrochemical reaction,electrochemical deoxidation,and in-situ carbonization reaction mechanism was proposed to reveal the electrochemical synthesis process of SiC nanoparticles from SiO_(2)/C in molten CaCl_(2).The as-prepared SiC with particle size ranging from 8 to 14 nm possesses a polycrystalline structure.In addition,the SiC nanoparticles demonstrate obvious photoluminescence property due to the synergetic size effect and microstructural characteristics.

Imaging the Dissociation Dynamics of Si2+ via Two-Photon Excitation at 193 nm

In the one-color experiment at 193nm, we studied the photodissociation of Si2+ ions prepared by two-photon ionization using the time-sliced ion velocity map imaging method. The Si+ imaging study shows that Si2+ dissociation results in two distinct channels: Si(3Pg)+Si+(2Pu) and Si(1D2)+Si+(2Pu). The main channel Si(3Pg)+Si+(2Pu)) is produced by the dissociation of the Si2+ ions in more than one energetically available excited electronic state, which are from the ionization of Si2(v=0-5). Particularly, the dissociation from the vibrationally excited Si2(v=1) shows the strongest signal. In contrast, the minor Si(1D2)+Si+(2Pu) channel is due to an avoided crossing between the two 22Πg states in the same symmetry. It has also been observed the one-photon dissociation of Si2+(X4Σg-) into Si(1D2)+Si+(2Pu) products with a large kinetic energy release.

Synthesis and Characterization of Modified Epoxy Resins by Silicic Acid Tetraethyl Ester and Nano-SiO_2

A kind of modified epoxy resins was obtained by condensation of epoxy resin with silicic acid tetraethyl ester（TEOS） and nano-SiO2. The reactions were performed with hydrochloric acid as a catalyst at 63 ℃. The structure, thermal stability and morphological characteristics of the modified epoxy resins were studied through infrared spectra（FT-IR） analysis, thermogravimetric（TG） analysis and scanning electron microscopy respectively. It has been found from the IR and TG study that modified epoxy resins have greater thermal stability than epoxy resins, and its thermal stability has been improved by the formation of inter-crosslinked network structure. The modified epoxy resins exhibit heterogeneous morphology and heterogeneity increases with more TEOS feeding, which in turn confirms the formation of inter-crosslinked network structure in modified epoxy resins.

Distributions of Inorganic Nutrients in the Bohai Sea of China

To study the contents and distribution of inorganic nutrients in the Bohai Sea of China, two cruise surveys were undertaken in August (summer) 2000 and January (winter) 2001, respectively. A total of 595 water samples were collected from 91 stations and five nutrients, i.e., nitrate, nitrite, ammonia, phosphate and silicate, were analyzed for each sample. The results show that the average concentration of dissolved inorganic nitrogen (DIN) in the Bohai Sea in winter (6.529 μmol L -1) is significantly higher than that in summer (3.717 μmol L -1). The phosphorus concentration in winter (0.660 μmol L -1) is also significantly higher than that in summer (0.329 μmol L -1). Mean silicate concentration in winter (7.858 μmol L -1) is, however, not significantly different from that in summer (7.200 μmol L -1). Nutrients also vary considerably in different areas in Bohai Sea. DIN concentration in the Laizhou Bay (4.444 μmol L -1), for example, is significantly higher than those in the Bohai Bay (2.270 μmol L -1) and Bohai Strait (2.431 μmol L -1), which is caused by the discharge of large amounts of nitrogen into Laizhou Bay via Yellow River. The nutrients show different vertical distribution patterns. In summer, nutrients in bottom layer are generally richer than those in surface and middle layers. In winter, however, nutrients are not significantly different in different layers. Compared with historic data, DIN contents have increased continually since the early 1980 s. Based on atomic ratios of different nutrients, nitrogen is still the limiting factor for algal growth in the Bohai Sea.

INVESTIGATION OF THE INTERACTIONS BETWEEN WATER AND MODIFIED SILICA GEL BY IGC AND TPD

In this work, the thermodynamic parameters for the adsorption of water vapor on untreated silica gel and silica gel treated with hygroscopic salts and silane coupling agent were determined by lnverse Gas Chromatography （IGC） in the infinite dilution region. The desorption activation energies of the water vapor on virgin and modified silica gels were estimated by using the Temperature Programmed Desorption （TPD） technique. The interactions between the water and the virgin and modified silica gels were discussed. Results showed that the thermodynamic parameters and desorption activation energy of water vapour on the silica gels increase with decreasing pore size and increasing the surface hydrophilic properties. The desorption activation energy of virgin and modified silica gels was found to increase with increasing the thermodynamic parameters. The larger the adsorption parameters and the desorption activation energy were, the interactions between water and virgin and modified silica gels were.

Froth flotation of scheelite – A review

Froth flotation of scheelite has regained new focus since the 2010s and research regarding floatability and reagents has made great progress over the years. The main objective was and remains the selective flotation of scheelite from other calcium-bearing minerals, in particular calcite, fluorite and apatite. Due to similar properties, most attempts have limited success or only specific application(linked to a type of ore or a location). This article aims at reviewing all general physical-chemical information on froth flotation of scheelite, including electrokinetic properties, influence of p H and already existing reagents as well as ones still under examination. It appears that chelating or mixed collectors and modified versions of sodium silicate and quebracho hold great promise for scheelite flotation, while the use of said depressants and/or promoters seems inevitable.