Increasing Si Content Research Articles

Structural heterogeneity, β relaxation and magnetic properties of Fe-Zr-B amorphous alloys with Si and Cu additions

Despite numerous studies on β relaxation of amorphous alloys, the relationship between structural heterogeneity and β relaxation and the effect on magnetic properties of Fe-based amorphous alloys is still unknow. In this work, the structure and magnetic properties of Fe84-xZr6B10Mx (M = Si, Cu; x = 0, 0.6, 1 at%) amorphous alloys were investigated. With the increase of Si content, the negative value of average chemical affinity (∆Hchem) of the alloys is increased, leading to the synergetic enhancement in structural heterogeneity and β relaxation. In addition to this, the increase of liquid-like regions (LLRs) reduces saturation magnetic flux density (Bs) and increases coercivity (Hc). However, the addition of Cu element decreases the negative value of ∆Hchem of the alloys, resulting in weakening of structural heterogeneity and β relaxation synergetically. The reduction of LLRs has resulted in increase in Bs. Moreover, Fe-Cu atom pairs with positive enthalpy of mixing increases the local density of quasi dislocation dipoles (QDDs), resulting in the increase of Hc.

Effects of Si on the stress rupture life and microstructure of a novel austenitic stainless steel

A novel Si-bearing austenitic stainless steel was designed as the cladding material for lead-cooled fast reactors with an operating temperature range of 450 °C–550 °C, and the effects of Si (1.0 wt% - 2.0 wt%) on the creep life and fractured microstructure of material were studied at 550 °C and 650 °C. Results show that the addition of Si increased the stress rupture life of steel at 550 °C whereas brought in an opposite effect at 650 °C, which was closely related to the precipitation behavior of σ phase at these two temperatures during creep. At 550 °C the precipitation of σ phase was quite slow, but it was substantially accelerated at 650 °C. Since the experimental materials used in this work were in a cold worked state, so deformation twins existed and they were discovered to be able to promote the nucleation and growth of σ phase on the grain boundaries. With the increase of Si content at 550 °C, σ phase became larger in quantity and denser in distribution on the grain boundary, which improved the anti-cracking ability of grain boundary and enhanced the creep life of material. However, at 650 °C, σ particles apparently coarsened and congregated on the grain boundary under thermal activation, leading to an evident drop in the stress rupture property of steel.

Influence of Si content on selective oxidation and oxide scale phase transition during hot-rolled coiling

The internal oxidation formed during the advanced high-strength steels hot-rolled coiling process can be inherited into the cold-rolled sheet and impact the final product quality. Herein, the influence of Si on the internal oxidation and oxide scale phase transition behavior of Fe–Mn–Si advanced high-strength steel after hot-rolled coiling are investigated. The results indicate that the internal oxidation depth increases with the increase of Si content and is accompanied by severe intragranular oxidation. Moreover, the interface between Mn–Si oxide and substrate provides a direct diffusion path, which accelerates the rate of internal oxidation. In addition, the displacement reaction of Si/Mn is the primary cause for the formation of continuous pure Fe at the interface of oxide scale/substrate.

The Effects of Foliar Supplementation of Silicon on Physiological and Biochemical Responses of Winter Wheat to Drought Stress during Different Growth Stages.

Drought is one of the major environmental stresses, resulting in serious yield reductions in wheat production. Silicon (Si) has been considered beneficial to enhancing wheat resistance to drought stress. However, few studies have explored the mediated effects of foliar supplementation of Si on drought stress imposed at different wheat growth stages. Therefore, a field experiment was carried out to investigate the effects of Si supplementation on the physiological and biochemical responses of wheat to drought stress imposed at the jointing (D-jointing), anthesis (D-anthesis) and filling (D-filling) stages. Our results showed that a moderate water deficit markedly decreased the dry matter accumulation, leaf relative water content (LRWC), photosynthetic rate (Pn), stomatal conductance (Sc), transpiration rate (Tr) and antioxidant activity [peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT)]. On the contrary, it remarkably increased the content of osmolytes (proline, soluble sugar, soluble protein) and lipid peroxidation. The grain yields of D-jointing, D-anthesis and D-filling treatments were 9.59%, 13.9% and 18.9% lower, respectively, compared to the control treatment (CK). However, foliar supplementation of Si at the anthesis and filling stages significantly improved plant growth under drought stress due to the increased Si content. Consequently, the improvement in antioxidant activity and soluble sugar, and the reduction in the content of ROS, increased the LRWC, chlorophyll content, Pn, Sc and Tr, and ultimately boosted wheat yield by 5.71% and 8.9%, respectively, in comparison with the non-Si-treated plants subjected to water stress at the anthesis and filling stages. However, the mitigating effect of Si application was not significant at the jointing stage. It was concluded that foliar supplementation of Si, especially at the reproductive stage, was effective in alleviating drought-induced yield reduction.

Effect of Si content on the oxidation behavior of CoCrWSi coatings at 900 °C

In this study, CoCrWSi coatings with different Si contents were prepared via high-velocity oxygen fuel spraying, and the effect of Si content on their high-temperature oxidation resistance in air was studied at 900 °C. The microstructures and chemical compositions of oxide scales were characterized through scanning electron microscopy, electron probe microanalysis, and X-ray diffraction. The results revealed that the oxidation resistance of the produced CoCrWSi coatings gradually increased with increasing Si content. Moreover, the beneficial effects of Si content on the oxidation resistance were discussed in terms of Si depletion. The addition of Si prevented the outward diffusion of Cr atoms, and inhibited internal oxidation, while the depth of internal oxidation varied significantly with the oxidation time.

Electrical properties of Al-Si surface composites through surface mechanical alloying on severe plastic deformed Al substrates

Surface mechanical alloying ‘SMA’ with Si powder on Al was used to achieve surface composite with improved dielectric properties compared with coarse-grained and annealed Al composites. Measured Dielectric constant ε', dielectric loss ε" and Capacitance CμF versus increasing frequencies (105-108 Hz) exhibit a frequency dependent behavior of composite containing Al-Si solid solution in a voltage range from 0.1 to 0.5 V at room temperature. Found that an increase of Si content in surface composite results in ε, tan δ & C increase due to formed solid solutions between Al & Si after SMA on pre-severe plastic deformed Al substrates. Concluding the important role played by the severe plastic deformed microstructure of Al electrode in controlling dielectric properties of Al surface containing Al-Si composite.

Microstructure and creep properties of cast hypereutectic Al-11Ce alloy with Si addition

This study systematically investigated the as-cast microstructure, heat and creep- resistance of Al-11Ce-xSi (x = 0, 0.9, 1.7 wt%) alloys. A tetragonal AlCeSi intermetallic compound was formed by adding Si. With the increase of Si content, the Chinese-script Al11Ce3/α-Al eutectics changed to rod-like structure and were gradually replaced by broad flaky AlCeSi/α-Al eutectics. The Al-11Ce alloy containing 0.9 wt% Si possessed the optimal tensile properties with an ultimate tensile strength of 129.2 MPa and an elongation of 4.3%, which were 8.4% and 65.4% higher than that of the based alloy, respectively. After aging at 400 ℃ for 1008 h, the microhardness of Si-containing alloys remained unchanged, indicating excellent coarsening resistance of the strengthening AlCeSi phases. Under tensile creep conditions at 300 ℃, the creep deformation of three alloys was the dislocation creep mechanism. Nevertheless, with the addition of 1.7 wt% Si, the steady-state strain rate of Al-11Ce alloy was decreased to 1/3 of its original value. The enhanced creep resistance was mainly attributed to the relatively high volume fraction of intermetallic phase, the reduced volume fraction of coarse primary phase, and the presence of AlCeSi precipitates that effectively hinder dislocations motion.

Onset Shift of Li Plating on Si/Graphite Anodes with Increasing Si Content

Mixing graphite with Si particles in anodes of Li-ion batteries provides increased specific energy. In addition, higher Si contents lead to thinner anode coatings at constant areal capacity. In the present study, we systematically investigated the influence of the Si content on the susceptibility of Li plating on Si/graphite anodes. Si/graphite anodes with Si contents from 0 to 20.8 wt% combined with NMC622 cathodes were manufactured on pilot-scale. After initial characterization in coin half cells and by SEM, pouch full cells with fixed N/P ratios were built. Rate capability at different temperatures, and Post-Mortem analysis were carried out. Results from voltage relaxation, Li stripping, SEM measurements, glow discharge optical emission spectroscopy (GD-OES) depth profiling, and optical microscopy were validated against each other. A decreasing susceptibility to Li plating with increasing Si content in the anodes could be clearly observed. A critical C-rate was defined, at which Li plating was detected for the first time. It was also found that at 0 °C the critical C-rate increases with increasing Si contents. At 23 °C the SOC at which Li dendrites were first observed on the anode also increased with higher Si content.

Effects of Si variation and Zr addition on the microstructure, oxidation resistance and mechanical property at 1523 K of Nb-Si-Ti/Zr/Hf-Cr/Al high-entropy superalloys

The present work investigated the influences of the variation of Si content and the minor amount of Zr addition on the microstructure, oxidation resistance and mechanical property at 1523 K of Nb-Si-Ti/Zr/Hf-Cr/Al high-entropy superalloys systematically. Alloy compositions with Nb-21.6(Ti/Zr)-3.1Hf-(9.4–15.6)Si-6.3Cr-3.1Al-1.0B (at. %) were designed using a cluster formula approach to realize the substitution of similar elements, in which these alloys were solid-solutionized at 1573 K for 24 h and then aged at 1273 K for 24 h. It was found that all these aged alloys are mainly composed of BCC-Nb solid solution (Nbss), Nb5Si3 and Cr2Nb phases, where the increase of Si content and the addition of Zr could significantly increase the volume fraction of Nb5Si3 in a form of coarse and primary particles. Consequently, high-Si alloys possess outstanding mechanical property at high temperature, as evidenced by the fact that the yield strength (σYS = 373 MPa) at 1523 K of high-Si/Zr alloy containing 15.6 at. % Si and 1.6 at. % Zr is much higher than that (σYS = 266 MPa) of the low-Si alloy with 9.4 at. % Si and 0 Zr. It is mainly ascribed to the existence of primary Nb5Si3 particles, besides the eutectic microstructure composed of Nbss and Nb5Si3, as well as fine Cr2Nb precipitates in Nbss. Moreover, a minor amount of Zr substitution for the Ti is conducive to the phase transition of α-Nb5Si3 to γ-Nb5Si3. Thus, this high-Si/Zr alloy exhibits an improved oxidation resistance after 50 h-exposure at 1523 K, due to the lowest mass gain of about 80.9 mg/cm2. The constitutions of oxide scales in these alloys were characterized and compared, from which it was found that the better oxidation resistance is closely related to the formation of dense oxide scales. This work will provide a new approach to obtain an optimum combination of mechanical property and oxidation resistance of superalloys through multi-component alloying.

Hot Corrosion Behavior of Co–Al–W Superalloys with Si Additions

The hot corrosion behavior of Co-9Al-9.5W-xSi (where x = 0%, 0.1%, 0.5%, at.%) alloys in a salt mixture at 900 °C was investigated. The effect of Si on hot corrosion resistance was examined using corrosion kinetics. The surface morphology of the corrosion products was explored via SEM with EDS and the phase constituents were examined using XRD. The results revealed that hot corrosion occurred as a combination of both sulfidation and oxidation behavior. With the increase in Si content, the hot corrosion resistance of the alloy was capable of remarkable advancement. Corrosion scales on the three Co-based alloys were mostly comprised of Co3O4, CoO, CoAl2O4, CoWO4, and Al2O3. The hot corrosion mechanism for the Co-based alloy in the presence of 75 wt.% Na2SO4 and 25 wt.% NaCl deposits were analyzed.

Unsupervised learning for identifying silicified and dolomitized zones in pre-salt using portable XRF data

The discovery of significant oil reserves in the pre-salt region along the eastern coast of Brazil marks a significant milestone in hydrocarbon exploration and production, triggering extensive discussions on the origin and composition of non-marine carbonate rocks. Dolomitization and silicification have been identified as major processes responsible for substantial syn/post-depositional alterations in pre-salt reservoir rocks. In this study, we assess the feasibility of employing machine learning techniques to identify highly dolomitized and/or silicified intervals. A 25-m-thick rock succession from a drill core in the Tupi oil field, Santos Basin, was selected for analysis. Chemical element measurements were collected at approximately 10 cm intervals using an Olympus Vanta M Series model portable XRF analyzer. Subsequently, the acquired dataset underwent preprocessing and processing steps, including: (i) standardization of the database, (ii) data cleaning and imputation, (iii) basic statistical analysis, (iv) data transformation, and (v) outlier removal. Due to the considerable number of variables, the dataset was reduced to three principal components (PCs) using principal component analysis (PCA). Unsupervised learning was performed using the k-Means clustering algorithm, which employs Euclidean distance to determine the similarity between objects. Pearson's correlation analysis was also conducted to support the chemical interpretation of the clusters by comparing them with macroscopic and microscopic geological information. To ensure the optimal representativeness of the data, five clusters (C1, C2, C3, C4, and C5) were defined. Clusters C1, C2, and C3 exhibited increasing values on PC1, while C4 and C5 were characterized by higher values on PC2 and PC3, respectively. Based on significant correlations identified by Pearson's analysis, we can conclude that there is a progressive increase in Si content represented by C1, C2, and C3, accompanied by a relative decrease in all other chemical elements measured by the portable XRF. C1 not only emerged as the most frequently occurring cluster but also displayed the most common chemical composition in the studied interval, with Ca > Si. C2 and C3 corresponded to more intensely silicified levels. C4 exhibited a stronger affinity to Ca and Mg, suggesting intensified dolomitization. C5 stood out due to its relationship with Ba, an element associated with barite, a mineral that may result from the percolation of hydrothermal fluids depending on the associated paragenesis.

Pre and postharvest characteristics of Dahlia pinnata var. pinnata, cav. As affected by SiO2 and CaCO3 nanoparticles under two different planting dates

Agriculture faces many challenges because of climate changes. The nutrients present in nano-sized form improve plant productivity, especially when used at the appropriate planting time. Field experiments were conducted as a factorial experiment for evaluating two planting dates (20th September and 20th October), foliar application with nanoparticles (NPs) including silica nanoparticles (SiO2-NPs) at 1.5 and 3 mM, calcium carbonate nanoparticles (CaCO3-NPs) at 5 and 10 mM and distilled water (control) on pre- and post-harvest characteristics of Dahlia pinnata var. pinnata Cav. The results indicate that the interactions during the late planting time (20th October) and exogenous applications of SiO2-NPs at 1.5 mM or CaCO3-NPs at 10 mM have improved plant growth including plant height, stem diameter, fresh and dry weights of plant, leaf area, inflorescence diameter, inflorescence stalk length, branches number, tuber numbers, inflorescences number on the plant, and the vase life. At the same time, insignificant differences appeared in the interaction during the planting dates and SiO2 or CaCO3 -NPs concentrations on inflorescence stalk diameter, total soluble solids, membrane stability index, maximum increase in fresh weight (FW), and Si and Ca contents. In addition, all exogenous applications of NPs at the late planting time promoted the plant growth characteristics like lignin %, cellulose %, inflorescence water content, change in FW, and total water uptake. Moreover, the controls through the two planting dates recorded the maximum change in water uptake and water loss values. In short, it can be recommended to use SiO2-NPs at 1.5 mM or CaCO3-NPs at 10 mM as a foliar application at the late planting time (20th October) for obtaining the optimum quantitative and qualitative parameters of D. pinnata.

Microstructure and mechanical properties of Si micro-alloyed (Ti28Zr40Al20Nb12)100-xSix (x=0, 0.1, 0.2, 0.5) high entropy alloys

The effect of Si micro-alloying on the microstructure and mechanical properties of (Ti28Zr40Al20Nb12)100-xSix (x = 0, 0.1, 0.2, 0.5) high entropy alloys are studied. Coarse grains mainly composed of two ordered B2 phases are obtained during solidification, while the hcp-Zr5Al3 type precipitate formed after annealing at 1200 °C for 24h. As the Si content increases, the phase morphology at the grain boundaries gradually changes from a completely continuous structure to a partially continuous structure, and finally transfers to a necklace-type structure. The phase morphology inside the grains simultaneously transforms into merely randomly distributed particles. The changes in phase morphology are attributed to the stronger chemical affinity between Zr and Si. Owing to the severe inhomogeneity caused by the Si addition, a dramatic decrease of the fracture strain is observed in compression tests for as-cast samples. For Si micro-alloyed alloys, the annealed samples show an improvement of both compression strength and fracture strain. The obtained results suggest that Si micro-alloying has less impact on phase composition, but significantly affects elemental segregation, phase morphology and thus the mechanical properties.

Effect of Mg and Si contents and TiC nanoparticles on the center segregation susceptibility of twin-roll cast Al–Mg–Si alloys

Center segregation during the twin-roll casting (TRC) has always been a barrier to the fabrication of high-performance Al–Mg–Si strips. In this work, Al–Mg–Si alloys with different Mg and Si contents were fabricated by vertical-type twin-roll caster to investigate the effect of Mg and Si contents on central segregation susceptibility. Alloys that undergo a eutectic reaction to form Si would lead to the enrichment of eutectic Si in the central region due to the low reaction temperature of eutectic Si, resulting the severe central segregation. For alloys with the same eutectic reaction during the solidification, the alloy with higher |ⅆT/ⅆ(fs1/2)| showed agglomeration of the eutectic phases due to its lower solidification rate. For the alloys with the same Mg/Si ratio, the width of central segregation increased with the increase in Mg and Si contents due to the increase in the proportion of near-equiaxed grains in the central region. The introduction of TiC nanoparticles could mitigate the central segregation band due to the control of solute diffusion by the fine near-equiaxed grain structure.

From promoting aggregation to enhancing obstruction: A negative feedback regulatory mechanism of alleviation of trivalent chromium toxicity by silicon in rice

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field.

Promoting methane combustion activity and stability by tuning multiple Ni–Si interactions in catalysts

Catalytic combustion holds great promise for eliminating unburned methane released by the natural gas industry, and the crucial factor is the development of cost-effective and efficient catalysts. Herein, the silicon component was introduced into nickel oxide by simultaneously regulating the precipitation of nickel precursors and the hydrolysis of silicon precursors. The generation of SiO4 groups in NiO inhibited the growth and sintering of NiO grains, meanwhile promoting the formation of active Ni2+ and adsorbed oxygen species for activation and oxidation of methane. With the increase of Si content, the existence of surface nickel silicate on NiO further improved the sinter resistance of NiO, but caused the diminish of Ni2+ and surface adsorbed oxygen species. The catalytic activity and stability were co-enhanced via facilely tuning the multiple Ni–Si interactions. The catalyst with abundant SiO4 groups and negligible nickel silicate exhibited considerably higher catalytic activity, sinter-resistance and water-resistance than NiO toward methane combustion.

Effect of Minor Fe, Si Contents on Microstructure and Property of 7085 Alloy during Fabrication Processes

Fe and Si elements can form non-dissolvable phases in Al-Zn-Mg-Cu alloys and furtherly affect the property of finished products while the influence of minor contents lacks sufficient investigations. In present work, 7085 alloy with different Fe and Si contents (named by LFS alloy, MFS alloy and HFS alloy as Fe and Si contents progressively enhanced) was investigated and corresponding microstructure and property during the whole fabrication were analyzed via OM, SEM and DSC observation and tensile property, fracture toughness and salty-spray corrosion property. The results showed that Fe-containing phase existed in as-cast microstructure of three alloys while part of Fe-containing phases of HFS alloy has Si element. After homogenization treatment, coarse eutectic phases had dissolved into the matrix while Fe-containing phase remained in the alloys. Similarly, Si element existed in some Fe-containing phases of HFS alloy. The order of area fraction of remaining Fe-containing phases for the three alloys was LFS alloy<MFS alloy<HFS alloy. After extrusion, Mg(Zn,Cu,Al)2 phase and Fe-containing phase possessed the majority, the former one was eliminated by solution treatment while the latter one had no obvious change. Under an unified aging treatment, the strength, elongation and fracture toughness were degraded with the increase of Fe and Si contents. Besides, the salt-spray corrosion property of HFS alloy was significantly inferior to LFS alloy and MFS alloy. This gave rise to a reference for controlling Fe and Si impurity of 7085 alloy for considering overall performance.

Composition-dependent structural characteristics and mechanical properties of amorphous SiBCN ceramics by ab-initio calculations

The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si-BN-C phase diagram are investigated employing <em>ab-initio</em> calculations. Both chemical bonds and local structures within the amorphous network, relate to the elemental composition. The distribution of nine types of chemical bonds is composition-dependent, where the B-C, Si-N, Si-C and B-N bonds hold a large proportion for all compositions. Si prefers to be tetrahedrally coordinated, while &nbsp;B and N prefer <em>sp²-like</em> trigonal coordination. In the case of C, the tetrahedral coordination is predominant at relatively low C content, while the trigonal coordination is found to be the main feature with increasing C content. Such local structural characteristics greatly influence the mechanical properties of SiBCN ceramics. Among the studied amorphous ceramics, SiB₂C₃N₂ and SiB₃C₂N₃ with low Si content and moderate C and/or BN content have high elastic moduli, high tensile/shear strengths and good debonding capability. The increment of Si, C, and BN content on this basis results in the decrease of mechanical properties. The increasing Si content leads to the increment of Si-contained bonds that reduce the bond strength of SiBCN ceramics, while the latter two cases are attributed to the raise of <em>sp</em>²-like trigonal configuration of C and BN. These discoveries are expected to guide the composition-tailored optimization of SiBCN ceramics.

X-ray Diffraction and Trace Element Analyses of K/Pg Boundary Samples Collected from Agost and Caravaca, Spain

The boundary between Cretaceous and Paleogene (K/Pg) plays an important role in deciphering the Earth’s history and biological evolution from Mesozoic to Cenozoic. As such, the delineation and characterization of the boundary layer has attracted significant attention. In this study, X-ray diffraction (XRD) and elemental analyses were conducted to characterize the samples of boundary layer and the layers around Agost and Caravaca, Spain. The XRD results showed that the layers immediately above and below the boundary layer are made of limestone, while in the boundary layer, a significant increase in the clay minerals smectite, kaolinite, and illite was observed. The major element analyses revealed an increase in Si and Al contents, confirming the presence of clay minerals. The trace element analyses showed elevated concentrations of V, Cr, Ni, Zn, Pb, and Th, but not for Rb, Cu, and U. The rare Earth element (REE) analyses showed elevated La, Ce, and Nd concentrations in the boundary layer. Correlation analyses between selected trace elements and REE showed good agreements, with R2 values of about 0.9. The results agreed well with the finding in the area, except the lower contents of Rb, Cu, and U; thus, they may promote further studies to make detailed comparisons.

Interactive effect of silicon and nitric oxide effectively contracts copper toxicity in Salvia officinalis L.

Excess copper (Cu) causes the toxic effects in plants and health hazards to humans. Therefore, in this study, the effect of sodium silicate (1 mM Si) and sodium nitroprusside (200 µM SNP as a releasing NO), was assessed on Cu tolerance in Salvia officinalis L. plants exposed to 400 µM CuSO4. Results revealed that the combined supplementation with Si and SNP rather than the single application of these chemicals lowered Cu concentrations and translocation factor and increased Mg, Zn, and Fe concentrations in roots and shoots. Furthermore, combined treatment more efficiently decreased electrolyte leakage enhanced the activities of POD and APX in the leaves and roots, and improved relative water content and the content of Chl. a and Chl. b in leaves and consequently further increased tolerance index. Silicon supply enhanced NO content and applying Si + SNP more than the treatment of Si alone increased Si concentrations in the roots and shoots under Cu stress. Therefore, the reciprocal interaction of Si and NO might enhance Cu tolerance in plants, and the combined application of Si and SNP might be a promising strategy to decrease heavy metal accumulation in medicinal plants grown in polluted lands.