Role Of Si Research Articles

EFFECTS OF SILICON ON THE ACTIVITIES OF DEFENSE-RELATED ENZYMES IN CUCUMBER INOCULATED WITH PSEUDOPERONOSPORA CUBENSIS

The relationship between silicon (Si) and plant disease has been investigated for many years, and there is an increasing interest in the use of Si for induction of defense mechanisms in response to fungal attacks. A confirmative role of Si in protecting plants against disease, however, has not yet been documented. The effects of silicon application on major defense-related enzymes activities were investigated in cucumber inoculated with downy mildew (Pseudoperonospora cubensis). The results showed that addition of Si to the nutrient solution significantly increased leaf Si content. Silicon supply to cucumber plants inoculated with P. cubensis significantly stimulated the activities of several defense-related enzymes. In particular, guaiacol peroxidase and polyphenol oxidase showed more intense and rapid activation. The optimum responses of enzyme activities were obtained at 3.6 mM Si. At this level of Si, the downy mildew disease index was reduced by more than 60% compared to control plants not receiving Si. It is concluded that the concentration of Si plays an important role in inhibiting P. cubensis via stimulating the activities of major defense-related enzymes.

The boson peak of silicate glasses: The role of Si–O, Al–O, and Si–N bonds

The role of Si-O, Al-O, and Si-N bonds on the boson peak of silicate glasses has been investigated from a study of amorphous Si, SiO(2), and two calcium aluminosilicates with 0 (Ca28-O) and 4.4 (Ca28-N) mol % Si(3)N(4). The low-frequency part of the vibrational density of states g(omega) has been calculated from inversion of literature data and new heat capacity measurements. As defined by g(omega)/omega(2), the boson peak correlates with the excess heat capacity observed with respect to Debye T(3) limiting law. That libration of SiO(4) tetrahedra represents the main source of low-frequency excitations in silica glass is illustrated by the strong difference between the anomalies of amorphous Si and SiO(2) glass and the marked decrease observed for SiO(2) phases of increasing density. When Al substitutes for Si, libration of AlO(4) tetrahedra appears hampered by the presence of a charge-compensating cation. Rigidification of the silicate network resulting from substitution of N for O causes the boson peak of Ca28-N to be smaller than that of Ca28-O and shifted toward higher frequencies as increased cross-linking hinders libration of SiO(4) or AlO(4) tetrahedra. In agreement with their universal phenomenology, the calorimetric boson anomalies of Ca28-O and Ca28-N plot on the master curve defined previously by SiO(2) and alkali silicate glasses.

Secondary phases and interfaces in a nitrogen-atmosphere sintered Al alloy: Transmission electron microscopy evidence for the formation of AlN during liquid phase sintering

A comprehensive transmission electron microscopy study has been made of the secondary phases and their interfaces with the matrix in an alloy of Al–2Mg–2Si–0.25Cu sintered in nitrogen. AlN was detected both at the Al–Mg2Si interface and inside Mg2Si grains as strings of nanocrystallites. Mg2Si did not exist at the sintering temperature; it was the solidified residue of the sintering liquid. The observation confirms the formation of AlN during liquid phase sintering of aluminium alloys in nitrogen. The likely pore filling processes are discussed in the light of the distribution of the AlN nanocrystallites. Two Al-, Si- and O-rich secondary phases were also identified, suggesting that, in addition to Mg, Si may have also played a role in disrupting the Al2O3 film that enveloped each Al powder particle. These findings improve the fundamental basis for understanding the sintering of aluminium alloys in nitrogen and the role of Si.

Silicon in Plant Tolerance Against Environmental Stressors: Towards Crop Improvement Using Omics Approaches

Silicon (Si) is a micronutrient. Its amount has been found to vary from plant to plant. Grasses contain much higher Si than Arabidopsis. Interestingly, Si in plants has been shown to enhance their tolerance against various abiotic and biotic stresses. Silicon induced resistance in rice against pathogenic fungi Magnaporthe grisea and Rhizoctonia solini have been well demonstrated. In addition, Si also plays an important role in providing tolerance to heavy metal toxicity and water stress. Systematic identification and characterization of Si-responsive genes responsive genes and proteins will help in better understanding the underlying mechanism of Si-induced tolerance in plants. High-throughput technologies, such as transcriptomics and proteomics, have tremendous potential in establishing the Si-responsive genes and proteins network in order to design next generation crop plants. Here, we will focus on the role of Si in conferring tolerance in plants against various environmental stressors. We highlight the importance of genomics and potential of proteomics and metabolomics in investigating Si responses in plants and discuss its suitability in crop improvement.

Effect of silicon on growth and salinity stress of soybean plant grown under hydroponic system

Silicon (Si) is abundant in the soil, yet its role in plant biology has been poorly understood. The role of Si in soybean growth and its effectiveness in salt stress alleviation was investigated. Sodium metasilicate (Na2SiO3) was given as Si source to hydroponically grown soybean (Glycine max (L.) Merr.). The plant growth attributes, i.e. plant height, plant fresh and dry biomass, chlorophyll contents and endogenous gibberellins (GAs) level improved with 2.5 mM Si, while endogenous abscisic acid (ABA) and free proline contents were not affected as compared to control. Sodium chloride (NaCl) significantly decreased growth attributes and endogenous gibberellins levels but markedly enhanced ABA and proline contents of soybean leaves. An addition of Si to salt stressed plants substantially alleviated the adverse effects of NaCl on growth, as it enhanced endogenous gibberellins, while reduced the levels of ABA and proline. GAs analysis of soybean leaves also showed that both early C13 hydroxylation and non C13 hydroxylation pathways of gibberellin biosynthesis were operating in soybean. The major GA biosynthesis pathway was identified as non C13 hydroxylation, which led to the formation of bioactive GA4. Current study suggests that Si application alleviates the detrimental effect of salinity stress on growth and development of soybean.

Enhancement of ferromagnetism in polycrystalline Si0.965Mn0.035:B films by boron plasma treatment

This paper reports that the polycrystalline Si0.965Mn0.035:B films have been prepared by cosputtering deposition followed by rapid thermal annealing for crystallization. The polycrystalline thin films consist of two ferromagnetic phases. The low temperature ferromagnetic phase with Curie temperature (Tc) of about 50 K is due to the Mn4Si7 phase in the films, while the high temperature one (Tc ∼250 K) is resulted from the incorporation of Mn into silicon. The films are treated by boron plasma excited with the approach of microwave plasma enhanced chemical vapor deposition for 40 minutes. After plasma treatment, it is observed that no extra magnetic phases or magnetic complexes exist in the films, while both the high temperature saturation magnetization and the hole concentration in the films increase. The obvious correlation between the magnetic properties and the electrical properties of the polycrystalline Si0.965Mn0.035:B films suggests that the hole carriers play an important role in Si:Mn diluted magnetic semiconductors.

Role of Si in improving the shape recovery of FeMnSiCrNi shape memory alloys

The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructure of these alloys remains single-phase austenite (γ) up to 6% Si addition and beyond that it becomes two-phase γ+δ-ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing into the microstructure after 7% Si and makes these alloys brittle. The amount of shape recovery increases monotonically till 6% Si addition and is proportional to the amount of stress induced ε martensite. Alloys containing >6% and <4% Si show poor recovery due to formation of δ-ferrite and stress induced α’ martensite respectively. Si addition decreases the stacking fault energy (SFE) of the γ phase and resulted in easier nucleation of stress induced ε martensite. The amount of athermal ε martensite decreases with increase in Si.

Role of Si and Ge as impurities in ZnO

The electronic and structural properties of Si in ZnO are studied using density functional calculations with both the generalized gradient approximation and a hybrid functional. Our calculations show substitutional Si on the Zn site SiZn to be significantly lower in energy than the Si interstitial Sii and Si on an O site SiO. SiZn is predicted to be a shallow donor in ZnO with a formation energy low enough to lead to significant incorporation of Si in the ZnO crystal. Interestingly, we find that SiZn has a lower formation energy and therefore higher solubility under Zn-rich conditions than under O-rich conditions. We also study the properties of Ge in ZnO for comparison, finding behavior similar to the Si impurity, but with an even lower formation energy. Our results suggest Si and Ge as suitable n-type dopants in ZnO.

Microstructural and Stress Corrosion Cracking Characteristics of Austenitic Stainless Steels Containing Silicon

Austenitic stainless steels (SSs) core internal components in nuclear light water reactors (LWRs) are susceptible to irradiation-assisted stress corrosion cracking (IASCC). One of the effects of irradiation is the hardening of the SS and a change in the dislocation distribution in the alloy. Irradiation may also alter the local chemistry of the austenitic alloys; for example, silicon may segregate and chromium may deplete at the grain boundaries. The segregation or depletion phenomena at near-grain boundaries may enhance the susceptibility of these alloys to environmentally assisted cracking (EAC). The objective of the present work was to perform laboratory tests in order to better understand the role of Si in the microstructure, properties, electrochemical behavior, and susceptibility to EAC of austenitic SSs. Type 304 SS can dissolve up to 2 pct Si in the bulk while maintaining a single austenite microstructure. Stainless steels containing 12 pct Cr can dissolve up to 5 pct bulk Si while maintaining an austenite structure. The crack growth rate (CGR) results are not conclusive about the effect of the bulk concentration of Si on the EAC behavior of SSs.

Ferromagnetism dependence on hole carriers in polycrystalline silicon films co-doped with Mn and B

Polycrystalline Si 0.96Mn 0.04:B films were prepared by cosputtering deposition followed by rapid thermal annealing for crystallization. The films are ferromagnetic with Curie temperatures of about 250 K. Through the approach of microwave plasma enhanced chemical vapor deposition, the films were treated by hydrogen plasma and boron plasma. After the plasma treatments, the structural properties of the films did not change, while both the saturation magnetization and hole concentration in the films changed. The correlation between the magnetic properties and the transport properties of the Si 0.96Mn 0.04:B films suggests that free hole carriers play an important role in Si:Mn diluted magnetic semiconductors.

Role of Si in the Luminescence of AlN:Eu,Si Phosphors

The luminescence properties of Si,Eu‐codoped AlN phosphors were investigated by means of cathodoluminescence. The concentration of Eu was kept constant, while that of Si was varied from 0 to 9.0 at.% using two different Si‐source starting powders, Si3N4 and SiC. The luminescence of Eu2+ in AlN is only observed for samples doped with Si. On the other hand, a concentration quenching is observed for samples doped with high amount of Si from Si3N4 while not for those doped from SiC. These results show the importance of Si in the luminescence properties of Eu2+‐doped AlN.

Sliding wear behaviour of T6 treated A356–TiB 2in-situ composites

Dry sliding wear behaviour of A356–TiB 2 composites in T6 condition was tested using a pin-on-disc wear testing machine. The composites were prepared by the reaction of a mixture of K 2TiF 6 and KBF 4 salts with molten alloy. The wear tests were conducted at normal loads of 19.6–78.4 N and a sliding speed of 1 ms −1. A detailed SEM study of wear surface and debris was carried out to substantiate the wear results. The results indicate that wear rate of the composites is a strong function of TiB 2 content rather than overall hardness of the composite. The role of Si and TiB 2 particles towards the overall mechanism has been discussed.

Alleviation of Copper Toxicity in Arabidopsis thaliana by Silicon Addition to Hydroponic Solutions

Copper (Cu) is an essential micronutrient for plants and is the a.i. in pesticides for some pathogens and algae. Elevated doses of Cu can cause toxicity in plants. While silicon (Si) is reported to alleviate the toxicity of some heavy metals, its role in reducing the symptoms induced by excess Cu is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in arabidopsis [Arabidopsis thaliana (L.) Heyn.]. Based on plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of phenylalanine ammonia lyase [PAL (EC 4.3.1.5), a stress-induced enzyme] activity in the shoot, Si was found to alleviate copper stress. Real-time reverse transcriptase-polymerase chain reaction analyses indicated that the RNA levels of two arabidopsis copper transporter genes, copper transporter 1 (COPT1) and heavy metal ATPase subunit 5 (HMA5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of arabidopsis to Cu stress, and this improvement operates on multiple levels, ranging from physiological changes to alterations of gene expression.

Production of an austenitic steel matrix composite reinforced by in-situ nodular eutectic: the role of Si

Production of an austenitic steel matrix composite reinforced by in-situ nodular eutectic: the role of Si

The molecular beam epitaxy growth, structure, and magnetism of Si1−xMnx films

The type-IV diluted magnetic semiconductor (DMS) [Si(20Å)∕Mn(x)]30 multilayers (MLs) with nominal thickness x=1, 1.5, and 2.0Å have been prepared by molecular beam epitaxy. The structure, magnetism, and electrical property of these MLs were investigated. Above room temperature ferromagnetism has been observed and structure probed by x-ray absorption spectroscopy. The Mn local structure is similar to Si simulation and the Mn chemical valences of the MLs are in the range from zero (Mn foil) to Mn+2. The relative carrier concentration is sensitive to the formation of room temperature ferromagnetism, suggesting that hole mediated mechanism play an important role in Si:Mn DMSs.

High-Temperature Oxidation of Cr-Mo Steels and Its Relevance to Accelerated Rupture Testing and Life Assessment of In-Service Components

Use of accelerated creep rupture testing to assess the remaining life of components operating at elevated temperatures, such as pipes and tubes, is a common practice. At high temperatures, oxide growth can affect the creep results by diameter reduction and thus can increase the stress. However, the nature of oxide layer and hence oxidation behavior can be affected by minor changes in alloying composition of steels. This article presents the study of oxide-scale growth and specimen diameter reduction kinetics during oxidation of two Cr-Mo steels used in the manufacture of boiler tubing. Oxidation tests were carried out on 1.25Cr-0.5Mo and 2.25Cr-1Mo steels at 600 °C and 700 °C for times up to 1000 hours, using cylindrical specimens (similar to those used for creep testing). At 600 °C, the oxidation resistance of 2.25Cr-1Mo steel was superior to 1.25Cr-0.5Mo steel. However, the oxidation resistance of the two steels at 700 °C was similar in spite of the difference in their Cr contents. Multilayer oxide scales of oxides with various compositions were observed to have formed over the two steels. The similarity in oxidation kinetics of the two steels at 700 °C (in spite of differences in Cr contents) is ascribed to their Si contents and the predominant role of Si in oxidation at this temperature. The article also discusses implications of the variation in the oxidation kinetics to the stress enhancement in creep specimens due to scaling losses, and possible inaccuracies in creep data, as a result of minor variations in alloying composition.

Role of Si on the Al behavior in the reaction layer of Al∕UMo diffusion couples

The basic experimental features characterizing the Al–Si∕U–Mo interface are identified in this atomistic modeling effort, such as the formation of interfacial compounds, Si depletion in the Al matrix near the interface, reduced Al diffusion in the UMo solid solution, and the interaction between Mo and Si which inhibits Al and Si diffusion to the UMo bulk.

The role of Si and Ca on new wrought Mg–Zn–Mn based alloy

The development of new wrought magnesium alloys for automotive industry has increased in recent years due to their high potential as structural materials for low density and high strength/weight ratio demands. However, the poor mechanical properties of the magnesium alloys have led to search a new kind of magnesium alloys for better strength and ductility. Magnesium alloys show strong susceptibility to localized corrosion in chlorides solutions due to their inhomogeneous microstructure. The existence of intermetallics in the microstructure of magnesium alloys might represent initiation sites for localized corrosion. This is due to the formation of galvanic couples between the intermetallics and the surrounding matrix. The main objective of this research is to investigate the corrosion behavior of new magnesium alloys; Mg–Zn–Mn–Si–Ca (ZSM X) alloys. The ZSM6 X1 + YCa alloys were prepared by using hot extrusion method. AC and DC polarization tests were carried out on the extruded rods, which contain different amounts of silicon or calcium. The potential difference in air between different phases and the matrix was examined using scanning Kelvin probe force microscopy (SKPFM). The phases present in the alloys have been identified by optical microscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy. Four different phases were found, i.e. intermetallics containing Si–Mn, Mg–Si, Mg–Zn and Mg–Si–Ca phase. All phases exhibited higher potential differences relative to magnesium matrix indicating a cathodic behavior. The potential difference revealed significant dependence on the chemical composition of the phases. Based on the results obtained from the scanning Kelvin probe force microscopy, the cathodic phases are effective sites for the initiation of localized corrosion in Mg–Zn–Mn–Si–Ca alloys.

Silicon–O–M–O–silicon superlattice

The success of heterojunction quantum wells and quantum dots in III–Vs has not been extended to silicon because the ideal barrier, SiO2, is amorphous, preventing the formation of quantum structures with silicon. The possibility of a few monolayers of oxide inserted between adjacent silicon layers was proposed and realized with a superlattice (SL) structure consisting of Si–Si–O–Si–Si–Si, having a monolayer of oxygen in each period introduced by adsorption onto the 2×1 reconstructed surface along the Si(100). Reduction of the period leads to a slight up-shift of the energy of the emitted light, indicating that the essential objective of boosting the optical transition by promoting direct transitions has not been realized. Annealing in H2+O2 results in significant improvement in PL and EL, showing that specific defects, e.g., Si–O complexes may be responsible for the observed light emission. The role of Si–O complex being the origin of emission is further supported by the observation that the emission of visible light from polycrystalline Si and SiO2 structure is similar to the epitaxial superlattice with oxygen. The computed strain in a new type of superlattices consisting of SiO2, and GeO2 is much lower than the Si–O SL. The EL in Si–O superlattice with the use of a Schottky barrier to provide electron–hole accumulation allows double injection into states higher in energy than the bandgap of Si, a prerequisite for injection laser without the need to use a wide-band pn-junction.

Effect of silicon on the formation of graphitic polyhedra and balloon-like particles

We conducted laser vaporization of graphite and graphite containing 1 at. % silicon in Ar gas atmosphere. Comparison of the products from the laser vaporization indicated that the coexistence of Si promoted graphitization in grown carbon particles of 90–1500 nm. Polyhedral graphite (PG) particles and balloon-like carbon (BC) particles with shells of graphitic layers were grown under control of Ar gas pressures of 0.1–0.7 MPa. We discuss possible roles of Si in graphitic structure growth and the formation mechanisms of the PG and BC particles.