Beneficial Effect Of Si Research Articles

SILICON ENHANCES THE SALT TOLERANCE OF TWO WHEAT CULTIVARS THROUGH DECREASING OXIDATIVE DAMAGE

Using two wheat (Triticum durum) cultivars (cvs. Vitron and Simeto) hydroponic solution experiments were conducted in order to study the genotypic variation in tolerance to NaCl toxicity and to investigate effect of silicon supplied to the nutrient solution on wheat plants grown at salt stress. The experiment was a 2×2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicon (Si) in nutrient solution, 1 and 2 mM, as Na 2 SiO 3 .9H 2 O. Silicon supplementation has an important role in alleviating salinity injury, however, the definite mechanisms stay scantily understood, and must be examined. The role of silicon application in improving growth, maintaining water status and alleviating oxidative injury of salt affected wheat plants were studied. Indeed, our results indicate salinity induced in wheat plants a notable increase in oxidative biomarkers, reduced plant growth and produced less dry matter content than those without NaCl. However, the reductions of seedling height, dry biomass, and soluble content were greatly alleviated due to Si addition to the culture solution. Thus, the beneficial effects of Si on oxidative biomarkers contents under NaCl stress were genotype-dependent. The beneficial effect of Si on alleviating oxidative stress was much more pronounced in Vitron (salt tolerant cultivar) than in Simeto (salt sensitive cultivar).

Improving oxidation resistance of γ-TiAl based alloy by depositing TiAlSiN coating: Effects of silicon

To improve oxidation resistance of γ-TiAl based alloys, Ti0.5Al0.4Si0.1N coating was deposited on Ti48Al2Cr2Nb alloy by arc ion plating system. Ti0.5Al0.5N coating was also deposited for comparison. TiAlSiN coating exhibited excellent cyclic oxidation resistance at 900 °C mainly due to Si promoted selective oxidation of Al and formation of a continuous Al2O3 top layer in oxide scale. Another beneficial effect of Si is promoting in situ formation of Ti5Si3 diffusion barrier layer at coating/substrate interface during thermal exposure, which inhibited interdiffusion between coating and alloy, especially nitrogen inward diffusion in alloy and helped the coating maintaining long term oxidation resistance.

Improvement of CoCr Alloy Characteristics by Ti-Based Carbonitride Coatings Used in Orthopedic Applications

The response of the human body to implanted biomaterials involves several complex reactions. The potential success of implantation depends on the knowledge of the interaction between the biomaterials and the corrosive environment prior to the implantation. Thus, in the present study, the in vitro corrosion behavior of biocompatible carbonitride-based coatings are discussed, based on microstructure, mechanical properties, roughness and morphology. TiCN and TiSiCN coatings were prepared by the cathodic arc deposition method and were analyzed as a possible solution for load bearing implants. It was found that both coatings have an almost stoichiometric structure, being solid solutions, which consist of a mixture of TiC and TiN, with a face-centered cubic (FCC) structure. The crystallite size decreased with the addition of Si into the TiCN matrix: the crystallite size of TiCN was 16.4 nm, while TiSiCN was 14.6 nm. The addition of Si into TiCN resulted in smaller Ra roughness values, indicating a beneficial effect of Si. All investigated surfaces have positive skewness, being adequate for the load bearing implants, which work in a corrosive environment. The hardness of the TiCN coating was 36.6 ± 2.9 GPa and was significantly increased to 47.4 ± 1 GPa when small amounts of Si were added into the TiCN layer structure. A sharp increase in resistance to plastic deformation (H3/E2 ratio) from 0.63 to 1.1 was found after the addition of Si into the TiCN matrix. The most electropositive value of corrosion potential was found for the TiSiCN coating (−14 mV), as well as the smallest value of corrosion current density (49.6 nA cm2), indicating good corrosion resistance in 90% DMEM + 10% FBS, at 37 ± 0.5 °C.

Mechanisms of Silicon-Mediated Amelioration of Salt Stress in Plants.

Silicon (Si), the second most predominant element in the earth crust consists of numerous benefits to plant. Beneficial effect of Si has been apparently visible under both abiotic and biotic stress conditions in plants. Supplementation of Si improved physiology and yield on several important agricultural and horticultural crops. Salinity is one of the major abiotic stresses that affect growth and yield. The presence of high concentration of salt in growing medium causes oxidative, osmotic, and ionic stresses to plants. In extreme conditions salinity affects soil, ground water, and limits agricultural production. Si ameliorates salt stress in several plants. The Si mediated stress mitigation involves various regulatory mechanisms such as photosynthesis, detoxification of harmful reactive oxygen species using antioxidant and non-antioxidants, and proper nutrient management. In the present review, Si mediated alleviation of salinity stress in plants through the regulation of photosynthesis, root developmental changes, redox homeostasis equilibrium, and regulation of nutrients have been dealt in detail.

Silicon alleviates arsenic-induced toxicity in wheat through vacuolar sequestration and ROS scavenging

ABSTRACTArsenic (As) is a phytotoxic element causing health hazards. This work investigates whether and how silicon (Si) alleviates As toxicity in wheat. The addition of Si under As-stress significantly improved morphophysiological characteristics, total protein, and membrane stability compared to As-stressed plants, suggesting that Si does have critical roles in As detoxification in wheat. Analysis of arsenate reductase activity and phytosiderophore (PS) release reveals their no involvement in the Si-mediated alleviation of As in wheat. Furthermore, Si supplementation in As-stressed plants showed a significant increase of As in roots but not in shoots compared with the plants grown under As stress. Further, gene expression analysis of two chelating molecules, TaPCS1 (phytochelatin synthase) and TaMT1 (metallothionein synthase) showed significant induction due to Si application under As stress compared with As-stressed plants. It is consistent with the physiological observations and suggests that alleviation of As toxicity in rice might be associated with As sequestration in roots leading to reduced As translocation in shoots. Furthermore, increased catalase, peroxidase, and glutathione reductase activities in roots imply the active involvement of reactive oxygen species scavenging for protecting wheat plants from As-induced oxidative injury. The study provides mechanistic evidence on the beneficial effect of Si on As toxicity in wheat plants.

Growth and N2fixation in Saline and/or Water Stressed Sesbania aculeata Plants in Response to Silicon Application

This study aimed at investigating the effects of silicon (Si) on dry matter yield (DM), N uptake and N2-fixation in Sesbania aculeata grown under water stress and/or salt stress using 15N. Irrigation regime had two levels, well watered (I1) and water stress (I2), and was made either with saline (Salt+) or with non saline water (Salt-). Silicon had positive impacts on DM of sesbania grown under water stress. Only root DM increased as a result of Si addition in well watered plants grown under salt stress or under both stress conditions. Moreover, root/shoot ratio was higher in Si-fed plants, under stresses, than those of non-fertilized plants. N yield significantly increased in salt stressed sesbania plant grown under well watering regime. However, the positive effect of Si in plants subjected to both stresses was only occurred in roots. In addition, Si application enhanced soil (Ndfs), fertilizer (Ndff) and N2-fixation (Ndfa) under salt and/or water stress conditions. The beneficial effect of Si on the amount of Ndfa was more pronounced under stress conditions. In the whole plant, significant effects of Si were obtained in water-stressed, salt-stressed and both water and salt-stressed treatments, where amounts of Ndfa increased by 8, 39 and 39%, respectively, as compared to their controls. Overall, response to Si was expressed more clearly when sesbania plants were subjected to stresses. Silicon may be considered as an important element for the symbiotic performance in legumes by mitigating the adverse effects of abiotic stresses.

Silicon improves growth and alleviates oxidative stress in rice seedlings (Oryza sativa L.) by strengthening antioxidant defense and enhancing protein metabolism under arsanilic acid exposure

Organoarsenic arsanilic acid (ASA) contamination of paddy soil is a serious but less concerned hazard to agriculture and health of people consuming rice as staple food, for rice is one major pathway of arsenic (As) exposure to human food. To date little research has studied the effect of ASA on biochemical process of rice. Silicon (Si) application is able to reduce the toxicities of heavy metals in numerous plants, but little information about ASA. This work investigated whether and how Si influenced alleviation of ASA toxicity in rice at biochemical level to have a better understanding of defense mechanism by Si against ASA stress. Results showed that ASA reduced rice growth, disturbed protein metabolism, increased lipid peroxidation but decreased the efficiencies of antioxidant activities compared to control plants, more severe in roots than in shoots. The addition of Si in ASA-stressed rice plants noticeably increased growth and development as well as soluble protein contents, but decreased malondialdehyde (MDA) contents in ASA-stressed rice plants, suggesting that Si did have critical roles in ASA detoxification in rice. Furthermore, increased superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities along with elevated glutathione (GSH) and ascorbic acid (AsA) contents implied the active involvement of ROS scavenging and played, at least in part, to Si-mediated alleviation of ASA toxicity in rice, and these changes were related to rice genotypes and tissues. The study provided physio-chemical mechanistic evidence on the beneficial effect of Si on organoarsenic ASA toxicity in rice seedlings.

Induction of Barley Silicon Transporter HvLsi1 and HvLsi2, increased silicon concentration in the shoot and regulated Starch and ABA Homeostasis under Osmotic stress and Concomitant Potassium Deficiency

Drought is one of the major stress factors reducing cereal production worldwide. There is ample evidence that the mineral nutrient status of plants plays a critical role in increasing plant tolerance to different biotic and abiotic stresses. In this regard, the important role of various nutrients e.g., potassium (K) or silicon (Si) in the mitigation of different stress factors, such as drought, heat or frost has been well documented. Si application has been reported to ameliorate plant nutrient deficiency. Here, we used K and Si either solely or in combination to investigate whether an additive positive effect on barley growth can be achieved under osmotic stress and which mechanisms contribute to a better tolerance to osmotic stress. To achieve this goal, barley plants were subjected to polyethylene glycol (PEG)-induced osmotic stress under low or high K supply and two Si regimes. The results showed that barley silicon transporters HvLsi1 and HvLsi2 regulate the accumulation of Si in the shoot only when plant suffered from K deficiency. Si, in turn, increased the starch level under both osmotic stress and K deficiency and modulated the glycolytic and TCA pathways. Hormone profiling revealed that the beneficial effect of Si is most likely mediated also by ABA homeostasis and active cytokinin isopentenyl adenine (iP). We conclude that Si may effectively improve stress tolerance under K deficient condition in particular when additional stress like osmotic stress interferes.

Remediation of cadmium toxicity in field peas (Pisum sativum L.) through exogenous silicon

Cadmium (Cd) is an important phytotoxic element causing health hazards. This work investigates whether and how silicon (Si) influences the alleviation of Cd toxicity in field peas at biochemical and molecular level. The addition of Si in Cd-stressed plants noticeably increased growth and development as well as total protein and membrane stability of Cd-stressed plants, suggesting that Si does have critical roles in Cd detoxification in peas. Furthermore, Si supplementation in Cd-stressed plants showed simultaneous significant increase and decrease of Cd and Fe in roots and shoots, respectively, compared with Cd-stressed plants. At molecular level, GSH1 (phytochelatin precursor) and MTA (metallothionein) transcripts predominantly expressed in roots and strongly induced due to Si supplementation in Cd-stressed plants compared with Cd-free conditions, suggesting that these chelating agents may bind to Cd leading to vacuolar sequestration in roots. Furthermore, pea Fe transporter (RIT1) showed downregulation in shoots when plants were treated with Si along with Cd compared with Cd-treated conditions. It is consistent with the physiological observations and supports the conclusion that alleviation of Cd toxicity in pea plants might be associated with Cd sequestration in roots and reduced Cd translocation in shoots through the regulation of Fe transport. Furthermore, increased CAT, POD, SOD and GR activity along with elevated S-metabolites (cysteine, methionine, glutathione) implies the active involvement of ROS scavenging and plays, at least in part, to the Si-mediated alleviation of Cd toxicity in pea. The study provides first mechanistic evidence on the beneficial effect of Si on Cd toxicity in pea plants.

Silicon-mediated changes in polyamines participate in silicon-induced salt tolerance in Sorghum bicolor L.

Silicon (Si) is generally considered a beneficial element for the growth of higher plants, especially under stress conditions, but the mechanisms remain unclear. Here, we tested the hypothesis that Si improves salt tolerance through mediating important metabolism processes rather than acting as a mere mechanical barrier. Seedlings of sorghum (Sorghum bicolor L.) growing in hydroponic culture were treated with NaCl (100 mm) combined with or without Si (0.83 mm). The result showed that supplemental Si enhanced sorghum salt tolerance by decreasing Na(+) accumulation. Simultaneously, polyamine (PA) levels were increased and ethylene precursor (1-aminocyclopropane-1-carboxylic acid: ACC) concentrations were decreased. Several key PA synthesis genes were up-regulated by Si under salt stress. To further confirm the role of PA in Si-mediated salt tolerance, seedlings were exposed to spermidine (Spd) or a PA synthesis inhibitor (dicyclohexylammonium sulphate, DCHA) combined with salt and Si. Exogenous Spd showed similar effects as Si under salt stress whereas exogenous DCHA eliminated Si-enhanced salt tolerance and the beneficial effect of Si in decreasing Na(+) accumulation. These results indicate that PAs and ACC are involved in Si-induced salt tolerance in sorghum and provide evidence that Si plays an active role in mediating salt tolerance.

Assessment of the role of silicon in the Cu-tolerance of the C4 grass Spartina densiflora

An experiment was designed to investigate the effect of silicon supply (0 and 500μM) on Spartina densiflora plants grown at two copper (Cu) concentrations: 0 and 15mM. Growth parameters together with total concentrations of calcium, Cu, potassium, magnesium, manganese, sodium and nitrogen were determined in roots and leaves. Photosynthetic traits were followed by measurement of leaf gas exchange, efficiency of PSII biochemistry, total content of photosynthetic pigments and concentration and carbamylation of Rubisco sites concentration ([Rubisco]). Respiration and oxygen isotope fractionation were measured in roots to study the in vivo activities of cytochrome oxidase (COX) and alternative oxidase (AOX) pathways, as well as AOX capacity. The results confirm that Si supply improves growth of S. densiflora under Cu stress. Improved growth was associated with higher net photosynthetic rate. Beneficial effect of Si on S. densiflora photosynthetic apparatus was associated with a reduction of the Cu impact on active Rubisco sites, as well as on the photochemical apparatus and chlorophyll concentration. Moreover, ameliorative effects of Si were associated with the avoidance of Cu translocation from roots to leaves. Finally in vivo activities of COX and AOX pathways were strongly inhibited in Cu-treated plants, and this reduction was not mitigated by Si-treatment.Therefore, Si appears to play an important role in Cu-tolerance of S. densiflora, not by avoiding its uptake by roots, but via some mechanism to avoid Cu translocation from roots to leaves, resulting in a general reduction of Cu-induced deleterious effects on the leaf photosynthetic apparatus.

EFFECT OF SILICON ON SOMATIC EMBRYOGENESIS AND SHOOT REGENERATION OF DRY DATE PALM (PHOENIX DACTYLIFERA L.) CV BARTAMUDA

Silicon (Si) has not been observed as an essential element for plant growth, however, the beneficial effect of Si has been recognized in many plant species. The use of Si is one of the important recent trends for improving embryogenesis, growth traits and morphological characters in the field of tissue culture, for using on a commercial scale. Therefore, in this study the effect of potassium silicate (K2SiO3) and sodium silicate (Na2SiO3) at different concentrations (0.0, 0.5, 1.0, 2.0, 4.0 and 8.0 mg/l) were examined on somatic embryogenesis and regeneration percentage of dry date palm cv Bartamuda In the light of the obtained results, treatment with Si had a positive effect. The highest percentage of somatic embryogenesis formation and callus degree was obtained on Murashige and Skoog (MS) medium supplemented with 4.0 mg /l K2SiO3 from embryogenic callus derived from shoot tip explants. Moreover, this medium gave the highest number of embryos/culture and the lowest degree of browning and hyperhydricity. However, the highest mean length of embryo was obtained on MS medium supplemented with 2.0 mg/l K2SiO3 compared with other treatments. Fresh and dry weight of embryo increased linearly with increasing concentration of Si treatments of both K2SiO3 and Na2SiO3. The highest germination percentage was obtained with embryos that matured on MS medium supplemented with 8.0 mg/l K2SiO3 or Na2SiO3. To our knowledge, this is the first study on the in vitro application of Si on dry date palm.

Raney Ni–Si Catalysts for Selective Hydrogenation of Highly Concentrated 2-Butyne-1,4-diol to 2-Butene-1,4-diol

Raney Ni–Si catalysts were synthesized by treating Raney Ni with silane in a fluidized bed reactor and tested in the selective hydrogenation of 2-butyne-1,4-diol (BYD) at high concentration. Structural characterizations including XRD patterns, TEM images, and X-ray photoelectron spectroscopy show that Raney Ni–Si catalysts are composed of a Ni core surrounded by nickel silicides. These species transform from Ni-rich silicide (Ni2Si) to Si-rich silicide (NiSi2) with increasing silicification temperature from 250 °C to 450 °C. The insertion of Si atoms into Raney Ni catalysts decreased the catalytic activity, but significantly improved the selectivity to 2-butene-1,4-diol (BED). The beneficial effect of Si on the selectivity hydrogenation of BYD may be caused by the presence of Si at Ni-defect sites, and the formation of the surface nickel silicide that suppress the further hydrogenation of BED. Compared with the traditional Lindlar-type catalysts, such Raney Ni–Si materials can be used extensively in organic synthesis for selective hydrogenation of alkynes, avoiding the associated hazards of toxic additives. Raney Ni–Si catalysts, synthesized by treating Raney Ni with silane, showed that the insertion of Si atoms into Raney Ni catalysts decreased the catalytic activity, but significantly improved the selectivity to 2-butene-1,4-diol.

Effect of silicon content on PVD film mechanical properties and cutting performance of coated cemented carbide inserts

The paper investigates the effect of Si content on TiAlSiN, TiSiN and TiAlN/TiSiN films mechanical strength, brittleness, fatigue and adhesion. The films used were deposited on cemented carbide inserts by employing cathodic arc evaporation. For determining coating strength properties, nanoindentations were carried out. Based on the data acquired and a FEM continuous simulation of nanoindentation, elasto-plastic laws for the films were determined. The adhesion of the coatings was evaluated by inclined impact tests and by Rockwell indentations. The fatigue of the examined coatings, at ambient and elevated temperatures, was characterized via perpendicular impact tests. Moreover, nano-impact tests were conducted for capturing the influence of Si-content on film brittleness. The cutting performance of the coated cemented carbide inserts was tested in milling stainless steel 304L at various cutting speeds. According to the obtained results, the beneficial effect of Si on the cutting performance of PVD coated tools was detected within an optimum cutting speed range. In addition, a superficial TiSiN layer on TiAlN coated cemented carbide tools leads to improved compound mechanical properties. These properties, as well as the cutting performance, depend on the TiSiN-film Si content and coating structure.

Alleviation of Chromium Toxicity by Silicon Addition in Rice Plants

The alleviatory effect of silicon (Si) on chromium (Cr) toxicity to rice plants was investigated using a hydroponic experiment with two Cr levels (0 and 100 μmol L −1), three Si levels (0, 1.25, and 2.5 mmol L −1) and two rice genotypes, differing in grain Cr accumulation (Dan K5, high accumulation and Xiushui 113, low accumulation). The results showed that 100 μmol L −1 Cr treatment caused a marked reduction of seedling height, dry biomass, soluble protein content, and root antioxidant enzyme activity, whereas significantly increased Cr concentration and TBARS (thiobarbituric acid reactive substances) content. However, the reductions of seedling height, dry biomass, and soluble content were greatly alleviated due to Si addition to the culture solution. Compared with the plants treated with Cr alone, Si addition markedly reduced Cr uptake and translocation in rice plants. No significant differences were observed between the two Si treatments (1.25 and 2.5 mmol L −1) in shoot Cr concentration and Cr translocation factor. Under the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si, higher root Cr concentration but lower shoot Cr concentration and Cr translocation factor were observed in Dan K5 than those in Xiushui 113, indicating that the beneficial effect of Si on inhibiting Cr translocation was more pronounced in Dan K5 than in Xiushui 113. Si addition also alleviated the reduction of antioxidative enzymes (superoxide dismutase (SOD) and ascorbate peroxidase (APX) in leaves; catalase (CAT) and APX in roots) and the increase of TBARS content in the Cr-stressed plants. Furthermore, the beneficial effects of Si on activities of antioxidative enzymes under Cr stress were genotype-dependent. The highest activities of SOD, POD (guaiacol peroxidase), CAT, and APX in leaves occurred in the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si for Xiushui 113 and in the treatment of 100 μmol L −1 Cr+1.25 mmol L −1 Si for Dan K5. The beneficial effect of Si on alleviating oxidative stress was much more pronounced in Dan K5 than in Xiushui 113. It may be concluded that Si alleviates Cr toxicity mainly through inhibiting the uptake and translocation of Cr and enhancing the capacity of defense against oxidative stress induced by Cr toxicity.

Effect of Silicon on Growth, Biochemical Constituents, and Mineral Nutrition of Cowpea

The effect of different concentrations (50, 100, 200, 400, and 800 mg kg−1) of silicon (Si) added to the soil was studied on growth performance, biochemical constituents, and nutritional status of cowpea [Vigna unguiculata (L.) Walp.]. Lower applications of Si resulted in an enhancement in relative yield, leaf area, chlorophyll, and iron (Fe) contents and a reduction in proline contents. A significant (P = 0.01) direct relationship between relative yield and lower applied Si concentrations was observed. A significant dependence of tissue Si concentration on soil Si concentration was observed. The results indicate a beneficial effect of Si on cowpea plants.

Ion-beam-induced crystallization of carbon-implanted silicon studied by auger electron spectroscopy

The influence of high-energy Si+ irradiation on carbon-implanted silicon at low temperature was studied. C+ Ions of kinetic energy 25 keV were implanted into Si(100) at room temperature with a dose density of 1×1017 ions cm−2 after amorphization of the surface region by Ge+ implantation at 200 keV. Subsequently, the amorphous and substoichiometric silicon–carbon matrix was subjected to a bombardment with 300 keV Si+ at 400°C to generate ion-beam-induced epitaxial crystallization. Rutherford backscattering spectroscopy combined with channelling disclosed the migration of the recrystallization front from the underlying amorphous silicon substrate up to the carbon-rich layer in dependence on the Si+ dose. Auger electron spectroscopy (AES) in combination with rotational sputter depth profiling provided detailed information about the depth-dependent composition, the different chemical states of the elements and the synthesized phases. The electron spectra reveal SiC phase formation with a corresponding electron density derived from plasmon energy losses. The plasmon-loss features in the Si LVV and KL23L23 spectra indicate the presence of fine-dispersed silicon carbide precipitates of average size ∽0.5–3 nm in a silicon–carbon matrix. Although a beneficial effect of Si+ irradiation on crystallization of the entire implantation zone could not be observed for dose densities ⩽1×1017 ions cm−2, this study demonstrates the successful application of AES for the characterization of heterogeneous materials with embedded nanoparticles in the matrix. © 1998 John Wiley & Sons, Ltd.

Effect of minor Si addition on the creep of a fully lamellar TiAl alloy

Considerable efforts have been made to improve the creep property of TiAl-based, two-phase alloys. While previous studies have demonstrated a beneficial effect of Si(0.25--1%) on the creep property of fully lamellar {gamma} alloys, the authors recently observed an opposite effect. That is, the addition of minor Si was found to be detrimental to the creep property of a fully lamellar TiAl in the present communication, the authors report this detrimental effect.

Effect of silicon on the growth and phosphorus uptake of rice

A pot experiment was conducted to measure the effect of silicon on phosphorus uptake and on the growth of rice at different P levels. Rice (Oryza sativa L. cv. Akebono) was cultured in Kimura B nutrient solution without and with silicon (1.66 mM Si) and with three phosphorus levels (0.014 mM P, low; 0.21 mM, medium; and 0.70 mM, high). Shoot dry weight with Si (+Si) in solution increased with increasing P level, while shoot weight without Si (−Si) was maximum at 0.21 mM P, suggesting that +Si raised the optimum P level for rice. +Si increased shoot weight more when P was low or high than when P was medium. The concentration and amount of inorganic P in shoots increased with increasing P level. +Si did not significantly decrease P uptake by rice at 0.014 mM P, however, uptake at 0.21 and 0.70 mM P was 27 and 30 percent less than uptake with −Si, respectively. In −Si with 0.21 and 0.70 mM P, inorganic P in shoots was more than double the concentration in shoots grown in +Si solutions. The Si concentration in shoots decreased slightly with increasing P level, although Si uptake was not significantly affected by P. +Si decreased the uptake of Fe and Mn by an average of 20 and 50 percent, respectively, thus P/Mn and P/Fe ratios increased in the shoot when P was low. From the results above, the beneficial effect of Si on the growth of rice was clearly shown when P was low or high. This effect may have resulted from decreased Mn and Fe uptake, and thus increased P availability within P deficient plants, or from reduced P uptake when P was high.

Healing layer formation in Fe–Cr–Si ferritic steels

The addition of small amounts of Si can dramatically improve the oxidation resistance of Fe and Fe–Cr steels. It is found that steels with Si contents above a certain critical value oxidise at a much slower rate and also become virtually immune to breakaway oxidation in high pressure CO2, The critical Si content for this behaviour is found to vary with the Cr content (wt-%) of the steel, from about 2·5% for mild steel to 0·7% for 9%Cr steel to 0·3% for 11%Cr steel in the temperature range 575–650°C. The lower Si content required for Cr steels than for mild steels is advantageous, because it is small enough not to degrade the other metallurgical properties such as creep strength. The beneficial effect of Si is thought to arise from the formation of a near continuous ‘healing’ layer of amorphous SiO2 at the oxide/metal interface which acts as a diffusion barrier to further transport of metal ions to the scale. The conditions required for the development of such layers are analysed using standard models of selective oxidation. The synergistic effect of Cr and Si is ascribed to the action of Cr as a secondary getter, in which it reduces the oxygen solubility in the metal and so reduces the Si content required to form a healing layer. Chromium also discourages the SiO2 from converting to fayalite (Fe2SiO4) which is a much poorer diffusion barrier. The conventional theory of selective oxidation and secondary gettering is found to describe reasonably well the compositional limits of healing layer behaviour in these ferritic steels. However, the silica also seems to encourage the formation of a chromia based layer at the base of the overlying oxide and the oxidation rate during healing seems to be limited eventually by this chromia layer rather than the silica layer, as would be expected in the conventional model.MST/1074