Range Of Si Concentrations Research Articles

Sound velocities and density measurements of solid hcp-Fe and hcp-Fe–Si (9 wt.%) alloy at high pressure: Constraints on the Si abundance in the Earth's inner core

We carried out sound velocity and density measurements on solid hcp-Fe and an hcp-Fe–Si alloy with 9 wt.% Si at 300 K up to ∼170 and ∼140 GPa, respectively. The results allow us to assess the density (ρ) dependence of the compressional sound velocity (VP) and of the shear sound velocity (VS) for pure Fe and the Fe–Si alloy. The established VP–ρ and VS–ρ relations are used to address the effect of Si on the velocities in the Fe–FeSi system in the range of Si concentrations 0 to 9 wt.% applicable to the Earth's core. Assuming an ideal linear mixing model, velocities vary with respect to those of pure Fe by ∼+80 m/s for VP and ∼−80 m/s for VS for each wt.% of Si at the inner core density of 13 000 kg/m3. The possible presence of Si in the inner core and the quantification of its amount strongly depend on anharmonic effects at high temperature and on actual core temperature.

Silicon elicited varied physiological and biochemical responses in Indian mustard (Brassica juncea): a concentration dependent study

The present investigation was conducted to evaluate the silicon (Si) mediated responses in different cultivars of Indian mustard (Brassica juncea) and to evaluate if Si could be used as an essential, beneficial, or quasi-essential element for growth and development of these cultivars. Surface sterilized seeds were sown in pots and allowed to germinate under natural environmental conditions. At 10, 12, 14, 16, and 18 days after germination, a range of Si concentrations (0.0, 0.2, 0.4, 0.8 and 1.6 mM) was administered to the soil and at 30 days post germination the plants were sampled to assess growth and development, leaf gas exchange traits and plant biochemical parameters, including activities of carbonic anhydrase, catalase, peroxidase, superoxide dismutase, and protein and proline content. The results demonstrate a dual response to Si concentration: 0.8 mM of Si significantly increased plant growth and development (length of root and shoot, fresh and dry biomass, and leaf area) and photosynthetic efficiency, and enhanced the antioxidant response in T-59 over all the other cultivars tested, whereas, 1.6 mM of Si significantly reduced the above parameters. It is therefore concluded that low levels of Si could be used as a quasi-essential element for enhanced photosynthetic efficiency and antioxidant response ofBrassica junceaplants; however, the response is cultivar specific and concentration dependent.

Determination of Cell Potential for Silicon Electrodeposition

Electrowinning of Si from cryolite-based melts is a possible solution for mass production of high purity silicon. The required cell potential to deposit Si on a cathode of interest, copper, is fundamental information that needs to be measured for controlling the co-deposition of impurities. In this study, the potential was measured using cyclic voltammetry in a cryolite-6 pct SiO2 melt. The deposited Si on copper forms a Cu-Si alloy in which the activity of Si affects the decomposition potential. The measurements were carried out in a range of Si concentrations, allowing the prediction of potential change during the actual deposition process, where the Si content changes constantly. The results were compared with the values obtained from cyclic voltammetry on an inert electrode, graphite, to investigate if the formation of Cu-Si alloy is responsible for decreasing the potential.

Irradiation-induced precipitates in a neutron irradiated 304 stainless steel studied by three-dimensional atom probe

Irradiation-induced precipitates in a 304 stainless steel, neutron-irradiated to a dose of 24 dpa at 300 °C in the fuel wrapper plates of a commercial pressurized water reactor, were investigated by laser-assisted three-dimensional atom probe. A high number density of 4 × 10 23 m −3 of Ni–Si rich precipitates was observed, which is one order of magnitude higher than that of Frank loops. The average diameter was ∼10 nm and the average chemical composition was 40% Ni, 14% Si, 11% Cr and 32% Fe in atomic percent. Over a range of Si concentrations, the ratio of Ni to Si was ∼3, close to that of γ′ precipitate (Ni 3Si). In some precipitates, Mn enrichment inside the precipitate and P segregation at the interface were observed. Post-irradiation annealing was performed to discuss the contribution of the precipitates to irradiation-hardening.

Microstructure and mechanical properties of Mo–Si–C and Zr–Si–C thin films: Compositional routes for film densification and hardness enhancement

Transition metal carbides exhibit high hardness, thermal stability and excellent wear resistance making them attractive for applications such as tool and die coatings. However, when deposited in thin film form using physical vapor deposition methods the mechanical properties can degrade due to poor film density. In this study we examine the addition of SiC to two transition metal carbides, Mo2C and ZrC, as a possible route for film densification and hardness enhancement. Mo–Si–C and Zr–Si–C films were deposited with a range of Si concentrations using rf magnetron co-sputtering. Films were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, electron microscopy and nano-indentation and micro-indentation hardness testing. For Mo–Si–C the Si additions caused significant alterations to the microstructure, affecting the grain size, the amount of amorphous phases, and crystal structure. The hardness of the Mo2C films containing Si first increased slightly with Si content, and declined at higher Si concentrations, but was never above that expected for bulk Mo2C. For Zr–Si–C, two sets of experiments were conducted: one with a large substrate-to-source distance and low rate of deposition, giving compositionally uniform films, and the second with a very short distance giving a compositionally graded film. For the first set, ZrC films without Si exhibited high porosity and low hardness, but with 31.5% SiC, the films were at the bulk levels for ZrC and the porosity was significantly reduced. This hardness improvement was explained in terms of a continuous re-nucleation process and resultant nanocrystalline grain structure. For the second set of films a hardness enhancement above rule of mixtures was observed, with a maximum of 4500 HK10 for films containing 9.3% SiC. This was explained in terms of an implantation of Si atoms.

Effect of Silicon on the Kinetics of Nb(C, N) Precipitation during the Hot Working of Nb-bearing Steels.

The effect of Si on the rate of Nb(C, N) precipitation was investigated by using fractional softening measurements. Compression specimens, with diameters of 7.6 mm and lengths of 11.4 mm, were prepared from four Nb microalloyed steels containing a range of Si concentrations from 0.01 mass% to 0.41 mass%. Double-hit compression tests, with a strain of 0.3 for each pass and a strain rate of 0.1/sec., were employed. A solution heat treatment was applied immediately prior to each test. It was found that the rate of Nb(C,N) precipitation in hot deformed austenite increases with Si concentration. This phenomenon is attributed to the increases in the activities of C and N that result from Si addition.

Enhancement of Long-Wavelength Photoluminescence Due to Heat-Treatment in Si-Doped GaAs

ABSTRACTHighly officient radiative recombination even at room temperature was found at a wavelength of about 1.3 μm in heat-treated Si-doped GaAs. The range of Si concentrations and the condition of heat-treatment to yield this intense luminescence were determined. Excitation spectra of the PL lines suggest that such PL lines are related to pairs of Si-donor and Si- acceptor and such pairs combined with gallium vacancies.