Silicon Mitigates Aluminum Toxicity of Tartary Buckwheat by Regulating Antioxidant Systems

Aluminum (Al) toxicity is a considerable factor limiting crop yield and biomass in acidic soil. Tartary buckwheatgrowing in acidic soil may suffer from Al poisoning. Here, we investigated the influence of Al stress on the growthof tartary buckwheat seedling roots, and the alleviation of Al stress by silicon (Si), as has been demonstrated inmany crops. Under Al stress, root growth (total root length, primary root length, root tips, root surface area, androot volume) was significantly inhibited, and Al and malondialdehyde (MDA) accumulated in the root tips. At thesame time, catalase (CAT) and ascorbate peroxidase activities, polyphenols, flavonoids, and 1,1-diphenyl-2-picrylhydrazyl(DPPH) and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) free-radical scavenging abilitywere significantly decreased. After the application of Si, root growth, Al accumulation, and oxidative damage wereimproved. Compared to Al-treated seedlings, the contents of ·O2− and MDA decreased by 29.39% and 25.22%,respectively. This was associated with Si-induced increases in peroxidase and CAT enzyme activity, flavonoidcompounds, and free-radical scavenging (DPPH and ABTS). The application of Si therefore has positive effectson Al toxicity in tartary buckwheat roots by reducing Al accumulation in the roots and maintaining oxidationhomeostasis.

Electromagnetic separation of primary iron-rich phases from aluminum-silicon melt

The difference of conductivity between primary iron-rich phases and aluminum melt has been used to separate them by electromagnetic force (EMF) which is induced by imposing a direct electric current and a steady magnetic field in molten Al-Si alloy. Theoretical analysis and experiments on self-designed electromagnetic separation indicates that primary needle-like β phases are difficult to separate; while primary α iron-rich phases can be separated by electromagnetic separation. Primary iron-rich phases have been removed from the melt successfully when the molten metal flows horizontally through separation channel. The iron content is reduced from 1.13% to 0.41%.

Effects of silicon content on microstructure and stress corrosion cracking resistance of 7050 aluminum alloy

Evolution of microstructure and stress corrosion cracking （SCC） susceptibility of 7050 aluminum alloy with 0.094%, 0.134% and 0.261% Si （mass fraction） in T7651 condition have been investigated. The results show that the area fraction of Mg2Si increases from 0.16% to 1,48% and the size becomes coarser, while the area fraction of the other coarse phases including Al2CuMg, Mg（Al,Cu,Zn）2 and A17Cu2Fe decreases from 2.42% to 0.78% with Si content increasing from 0.094% to 0.261%. The tensile strength and elongation of 7050-T7651 alloys is decreased with the increase of Si content by slow strain rate test （SSRT） in ambient air. However, electrical conductivity is improved and SCC susceptibility is reduced with the increase of Si content by SSRT in corrosion environment with 3.5% NaCl solution.

Microstructure and properties of high silicon aluminum alloy with 2% Fe prepared by rheo-casting

The morphology changes of both Fe-containing intermetallic compounds and the primary Si phase of Al-20Si-2Fe- 2Cu-0.4Mg-1.0Ni-0.5Mn （mass fraction, %） alloy produced by semi-solid rheo-diecasting were studied. The semi-solid slurry of high silicon aluminum alloy was prepared by direct ultrasonic vibration （DUV） which was imposed on the alloy near the liquidus temperature for about 2 rain. Then, standard test samples of 6.4 mm in diameter were formed by semi-solid rheo-diecasting. The results show that the DUV treatment suppresses the formation of needle-like ,β-Al5（Fe,Mn）Si phase, and the Fe-containing intermetallic compounds exist in the form of fine Al4（Fe, Mn）Si2 particles. Additionally, the primary Si grows up as fine and round particles with uniform distribution in α（Al） matrix of this alloy under DUV treatment. The tensile strengths of the samples at the room temperature and 573 K are 230 MPa and 145 MPa, respectively. The coefficient of thermal expansion （CTE） between 25 ℃ and 300 ℃ is 16.052 8×10^-6 ℃^-1, and the wear rate is 1.55%. The hardness of this alloy with 2% Fe reaches HB146.3. It is discovered that modified morphology and uniform distribution of the Fe-containing intermetallic compounds and the primary Si phase are the main reasons for reducing the CTE and increasing the wear resistance of this alloy.

Microstructural analyses of aluminum–magnesium–silicon alloys welded by pulsed Nd: YAG laser welding

Revealing grains and very fine dendrites in a solidified weld metal of aluminum–magnesium–silicon alloys is difficult and thus,there is no evidence to validate the micro-and meso-scale physical models for hot cracks. In this research, the effect of preheating on the microstructure and hot crack creation in the pulsed laser welding of AA 6061 was investigated by an optical microscope and field emission electron microscopy. Etching was carried out in the gas phase using fresh Keller’s reagent for 600 s. The results showed that the grain size of the weld metal was proportional to the grain size of the base metal and was independent of the preheating temperature. Hot cracks passed the grain boundaries of the weld and the base metal. Lower solidification rates in the preheated samples led to coarser arm spacing;therefore, a lower cooling rate. Despite the results predicted by the micro and meso-scale models, lower cooling rates resulted in increased hot cracks. The cracks could grow in the weld metal after solidification;therefore, hot cracks were larger than predicted by the hot crack prediction models.

Electrodeposition of Gold to Conformally Fill High-Aspect-Ratio Nanometric Silicon Grating Trenches: A Comparison of Pulsed and Direct Current Protocols

Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures.

Influence of hydrogen content on the behavior of grain reflnement in hypereutectic aluminum-silicon alloy

Dissolved hydrogen is harmful to mechanical properties of refinedhypereutectic aluminum-silicon alloys. In the present work, by using a stepped-form mold and thehydrogen-detecting instrument HYSCAN II, the relationship between the initial hydrogen content inthe melt and the refinement effect on the casting of hypereutectic aluminum-silicon alloy wasinvestigated. The experimental results show that the cooling rate, the hydrogen content and thegrain refinement effect are three interactive factors. When the hydrogen content is above 0.20mL/100 g and the cooling rate is lower than that in 50 mm-thick step, hydrogen dissolved in thealloy melt influences the grain refinement effect. With increasing the cooling rate, the criticalhydrogen content increases too. It is expected that much hydrogen in the melt make the netinterfacial energy larger than or equal to zero, resulting in the shielding of the particles AlPduring solidification and that the critical gas content is closely related to the critical radius ofembryo bubbles.

Numerical study of self-heating effects of small-size MOSFETs fabricated on silicon-on-aluminum nitride substrate

Compared with bulk-silicon technology, silicon-on-insulator (SOI) technology possesses many advan-tages but it is inevitable that the buried silicon dioxide layer also thermally insulates the metal – oxide – silicon field-effect transistors (MOSFETs) from the bulk due to the low thermal conductivity. One of the alternative insulator to replace the buried oxide layer is aluminum nitride (AlN), which has a thermal conductivity that is about 200 times higher than that of SiO2 (320 W·m ? 1·K? 1 versus 1.4 W·m? 1·K? 1). To investigate the self-heating effects of small-size MOSFETs fabricated on silicon-on-aluminum nitride (SOAN) substrate, a two-dimensional numerical analysis is performed by using a device simulator called MEDICI run on a Solaris workstation to simulate the electri-cal characteristics and temperature distribution by comparing with those of bulk and standard SOI MOSFETs. Our study suggests that AlN is a suitable alternative to silicon dioxide as a buried dielectric in SOI and expands the appli-cations of SOI to high temperature conditions.

Hydrogen Content and Porosity Behavior of Hypereutectic Aluminum-silicon Alloy with Phosphorus

By making castings that pick up gas from moisture in red sand molds,the porosity generated at different cooling rates was discussed during solidification of hypereutectic Al-25%Si alloy without and with phosphorus additions. The effect of phosphorus addition on hydrogen content in the melt was also studied. It was observed that the phosphorus addition made hydrogen content in alloy melts present a “see-saw' tendency.In addition to primary silicon refinement,the phosphorus promoted gas porosity formed not only in slowly cooled sections, but also in rapidly cooled sections. There was a small difference in density of full dense sample between P-refined and unrefined castings, with a larger density associated with phosphorous addition. The change of the surface tension seemed more reasonable to explain the mechanism of porosity behavior.

Machining studies of die cast aluminum alloy-silicon carbide composites

Metal matrix composites （MMCs） with high specific stiffness, high strength, improved wear resistance, and thermal properties are being increasingly used in advanced structural, aerospace, automotive, electronics, and wear applications. Aluminum alloy-silicon carbide composites were developed using a new combination of the vortex method and the pressure die-casting technique in the present work. Machining studies were conducted on the aluminum alloy-silicon carbide （SiC） composite work pieces using high speed steel （HSS） end-mill tools in a milling machine at different speeds and feeds. The quantitative studies on the machined work piece show that the surface finish is better for higher speeds and lower feeds. The surface roughness of the plain aluminum alloy is better than that of the aluminum alloy-silicon carbide composites. The studies on tool wear show that flank wear increases with speed and feed. The end-mill tool wear is higher on machining the aluminum alloy-silicon carbide composites than on machining the plain aluminum alloy.

THE CHARACTERISTICS OF MICROSTRUCTURES AND PROPERTIES FOR ADVANCED ALUMINUM/SILICON CONTAINED HOT-ROLLED TRIP STEELS

The microstructure characteristics with super fine ferrite grain size less than 5mm, appropriate retained austenite fraction around 5.0% and or removable abundant dislocations have been obtained by controlled rolling and cooling, which leads to well balance com- prehensive properties with high tensile strength of 510 and 615MPa, high elongation of 40% and 27%, low ratio of yield strength to tensile strength 0.83 and 0.80, as well as low ductile- brittle transition temperature less than -80 and -70℃ for advanced aluminum hot-rolled TRIP steel and silicon hot-rolled TRIP steel, respectively.

Dynamic investigation of the finite dissolution of silicon particles in aluminum melt with a lower dissolution limit

The finite dissolution model of silicon particles in the aluminum melt is built and calculated by the finite difference method, and the lower dissolution limit of silicon particles in the aluminum melt is proposed and verified by experiments, which could be the origin of microinhomogeneity in aluminum-silicon melts. When the effects of curvature and interface reaction on dissolution are not considered; the dissolution rate first decreases and later increases with time. When the effects of curvature and interface reaction on dissolution are considered, the dissolution rate first decreases and later increases when the interface reaction coefficient （k） is larger than 10 1, and the dissolution rate first decreases and later tends to be constant when k is smaller than 10-3. The dissolution is controlled by both diffusion and interface reaction when k is larger than 10-3, while the dissolution is controlled only by the interface reaction when k is smaller than 10-4.

A High-Fe Aluminum Matrix Welding Filler Metal for Hardfacing Aluminum-Silicon Alloys

A high Fe containing aluminum matrix filler metal for hardfacing aluminum silicon alloys has been developed by using iron,nickel,and silicon as the major strengthening elements,and by measuring mechanical properties,room temperature and high temperature wear tests,and microstructural analysis.The filler metal,which contains 3.0%-5.0% Fe and 11.0%-13.0% Si,exhibits an excellent weldability.The as cast and as welded microstructures for the filler metal are of uniformly distribution and its dispersed network of hard phase is enriched with Al Si Fe Ni.The filler metal shows high mechanical properties and wear resistance at both room temperature and high temperatures.The deposited metal has a better resistance to impact wear at 220℃ than that of substrate Al Si Mg Cu piston alloy;at room temperature,the deposited metal has an equivalent resistance to slide wear with lubrication as that of a hyper eutectic aluminum silicon alloy with 27% Si and 1% Ni.

Modification Effect of P+Sr+Ce Compound on Microstructure and Properties of Cast High Silicon Heat-Resist Aluminum Alloy

The P ＋ Sr ＋ Ce compound modification technologies of as-cast Al-21Si-1.5Cu-1.5Ni- 2.5Fe- 0.5Mg alloy were investigated by means of orthogonal test. Orthogonal test results show that 3% （CaH2PO4 ＋ 2CASO4）＋ 0.2%Sr ＋ 0.2%Ce is the optimum additive of modification treatment which can fine eutectic and primary silicon also can change the form of rich-iron phase at same time. The needle form of rich-iron phase is Al9FeSi3, which is prored by X-ray diffraction analysis and X-ray energy spectrum analysis. After compound modification treatment, the needle form of rich-iron phase disappeared and the fish bone form of rich-iron and rich-Ce phase that is AlsCeFe emerged. Both at room temperature and at 300℃, the tensile strength of the alloy after the modification treatment with the optimum additive is 30% lager than that of the alloy unmodified. Observed by SEM, the brittle intercrystalline tensile fracture changed into a blended one in which has many dimples.

Effect of Silicon Carbide and Titanium Hydride on the Foamability of Aluminum Alloy (6061)

Aluminum foam is a light weight material with good mechanical and energy absorption properties. In this study, aluminum foam composite was fabricated using aluminum powder 6061 and silicon carbide (SiC) powder. Titanium hydride (TiH2) was used as the foaming agent. Cold compact followed by hot pressing (sintering) was used to produce the composite precursor. Foaming was carried out, following the sintering process, by heating the aluminum composite precursor to a temperature above the melting point of aluminum (Al). The linear expansion of the foam and the percent porosity were found to increase as the SiC percentage decreased from 10 to 4%, whereas the density got lower. The percent porosity and linear expansion were both found to increase as the percentage of the foaming agent was increased from 0.5 to 1.5%. Compression stress was evaluated for two different porosity values (40% and 47%), and found to be higher for the samples with lower percent porosity at the same strain value. Effect of shape memory alloy fiber, made of nickel and titanium (NiTi), on the mechanical properties was also investigated. The compression stress was higher, in the densification region, for the samples in which NiTi was used.

Effects of ratio of hydrogen flow on microstructure of hydrogenated microcrystalline silicon films deposited by magnetron sputtering at 100 ℃

Hydrogenated microcrystalline silicon(μc-Si:H)films were prepared on glass and silicon substrates by radio frequency magnetron sputtering at 100°C using a mixture of argon(Ar)and hydrogen(H2)gasses as precursor gas.The effects of the ratio of hydrogen flow(H2/(Ar+H2)%)on the microstructure were evaluated.Results show that the microstructure,bonding structure,and surface morphology of theμc-Si:H films can be tailored based on the ratio of hydrogen flow.An amorphous to crystalline phase transition occurred when the ratio of hydrogen flow increased up to 50%.The crystallinity increased and tended to stabilize with the increase in ratio of hydrogen flow from 40%to 70%.The surface roughness of thin films increased,and total hydrogen content decreased as the ratio of hydrogen flow increased.Allμc-Si:H films have a preferred(111)orientation,independent of the ratio of hydrogen flow.And theμc-Si:H films had a dense structure,which shows their excellent resistance to post-oxidation.

Aluminum doping and dielectric properties of silicon carbide by CVD

Cubic β-SiC coating was grown onto the graphite substrate by the normal pressure chemical vapor deposition using CH3SiCl3(MTS) as a source precursor at 1 150 ℃. But the hexagonal Al4SiC4 phase was generated in the doped process with trimethylaluminium(TMA) as the dopant. Microstructure of the deposit coating as-prepared was characterized by scanning electron microscope(SEM),which consists of spherical particles with a very dense facet structure. The real component of permittivity ε′ and dielectric loss tanδ of the coatings undoped and doped by TMA were carried out by a vector network analyzer in the microwave frequency ranges from 8.2 GHz to 12.4 GHz. The results show that both of them have low values,and doped coating has lower ε′ and tan δ than undoped one due to the existence of Al4SiC4 impurity phase,which indicates that the desired Al/SiC solid solution at 1 150 ℃ in a normal argon atmosphere is not produced.

Electrical characteristics of SiGe-on-insulator nMOSFET and SiGe-silicon-on-aluminum nitride nMOSFET

This paper investigates the electrical characteristics and temperature distribution of strained Si/SiGe n-type metal oxide semiconductor field effect transistor （nMOSFET） fabricated on silicon-on-aluminum nitride （SOAN） substrate. This novel structure is named SGSOAN nMOSFET. A comparative study of self-heating effect of nMOSFET fabricated on SGOI and SGSOAN is presented. Numerical results show that this novel SGSOAN structure can greatly eliminate excessive self-heating in devices, which gives a more promising application for silicon on insulator to work at high temperatures.

Design and Analysis of MEMS Based Aluminum Nitride (AlN), Lithium Niobate (LiNbO₃) and Zinc Oxide (ZnO) Cantilever with Different Substrate Materials for Piezoelectric Vibration Energy Harvesters Using COMSOL Multiphysics Software

Interest in energy harvesters has grown rapidly over the last decade. The cantilever shaped piezoelectric energy harvesting beam is one of the most employed designs, due to its simplicity and flexibility for further performance enhancement. The research effort in the MEMS Piezoelectric vibration energy harvester designed using three types of cantilever materials, Lithium Niobate (LiNbO3), Aluminum Nitride (AlN) and Zinc Oxide (ZnO) with different substrate materials: aluminum, steel and silicon using COMSOL Multiphysics package were designed and analyzed. Voltage, mechanical power and electrical power versus frequency for different cantilever materials and substrates were modeled and simulated using Finite element method (FEM). The resonant frequencies of the LiNbO3/Al, AlN/Al and ZnO/Al systems were found to be 187.5 Hz, 279.5 Hz and 173.5 Hz, respectively. We found that ZnO/Al system yields optimum voltage and electrical power values of 8.2 V and 2.8 mW, respectively. For ZnO cantilever on aluminum, steel and silicon substrates, we found the resonant frequencies to be 173.5 Hz, 170 Hz and 175 Hz, respectively. Interestingly, ZnO/steel yields optimal voltage and electrical power values of 9.83 V and 4.02 mW, respectively. Furthermore, all systems were studied at different differentiate frequencies. We found that voltage and electrical power have increased as the acceleration has increased.

Effect of Annealing on Aluminum Oxide Passivation Layer for Crystalline Silicon Wafer

The surface of silicon was passivated by A1203 and acidify using nitric acid with SiOx as the bi-layer, it was expected that hydrogen bonding reduce interface states and negative field effect which yields maximum passivation. By optimizing the thickness of passivation layer and annealing condition, the minority carrier lifetime of p-type single crystalline Czochralski wafer could be improved from 10 μs to 190 μs. The formation and variation of hillock defect on passivation layer was founded to be affected by the thermal annealing temperature. For the purpose of obtaining high minority carrier lifetime and low hillock defect density simultaneously, using a lower heating and cooling speed in thermal annealing process is suggested.