Si Sn Research Articles

Analysis of the Microstructure, Phase Composition, and Oxidation Kinetics of Heat-Resistant Titanium Alloys with Gadolinium

The structure, phase composition, and local chemical composition of half-finished products (rods) made from Ti–Al–Mo–Zr–Si- and Ti–Al–Mo–Zr–Sn–Si-based alloys additionally microalloyed with 0.4 wt % gadolinium have been studied in this work. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Si composition was found to be characterized by the presence of Gd2O3 gadolinium oxide particles. The structure of the rod made from the Gd-alloyed Ti–Al–Mo–Zr–Sn–Si composition, which contains tin as a low-melting element, is characterized by the presence of Gd–Sn–O complex oxide particles, whose cores and shells are Gd5Sn3 intermetallics and Gd2O3 gadolinium oxide, respectively. The formation of such particles in both alloys occurs at the stage of ingot solidification, and the particles remain in the materials at all stages of their subsequent treatment. The oxidation kinetics of the alloys upon isothermal holding in a temperature range of 600–800°С is studied depending on the structure of half-finished products. The oxidation processes of the Ti–Al–Mo–Zr–Sn–Si alloy are less intensive than those of the Ti–Al–Mo–Zr–Si alloy. The alloying with gadolinium up to 0.4 wt % leads to the accelerated oxidation of the tin-free alloy, which is due to the presence of Gd2O3 particles precipitated at grain boundaries and interfaces. The alloying of the tin-containing composition with gadolinium almost does not affect the oxidation kinetics at 600–700°С and slightly decelerates the oxidation at 750–800°С; this is related to the presence of the Gd–Sn–O oxide particles in the structure, which are uniformly distributed over the grain body. The laws of oxidation of both the compositions free from gadolinium and alloyed with gadolinium were determined. It was shown that the oxide film formed upon the oxidation of both alloys is multilayer and consists of alternating layers of aluminum and titanium oxides. In this case, the progressive growth of oxide film layers alters the film exfoliation owing to the high brittleness of aluminum oxides. The presence of gadolinium oxide particles in both alloys leads to the porosity of diffusion zone of the base metal upon oxidation.

Fabrication of group IV semiconductor alloys on Si substrate applying Al paste with screen-printing

We investigated the influence of Sn and Ge ratio in Al paste to fabricate Si-based alloy semiconductor on large-area Si substrate using a conventional screen-printing process and high-temperature treatment steps. From the X-ray diffraction patterns, crystalline SiSn peaks with applying Al-Sn paste have been detected and Sn content in the SiSn layer was estimated around 0.35%, close to the level of solid solubility of Sn in Si. In addition, the Sn depth profile showed similar behavior with Al, which confirms the concept of a liquid epitaxial growth using Al. On the other hand, the SiGe peaks with applying Al–Sn–Ge paste were clearly observed and their main peaks were shifted to a higher angle linearly with decreasing the Ge ratio in the paste. It was suggested that Sn was segregated easily to the surface if in coexistence with Ge due to its lower solubility in SiGe systems.

Ultrasonic cavitation and acoustic streaming effects during liquid phase separation and dynamic solidification of ternary Al–Sn–Si immiscible alloy

Ultrasonic melt treatment is an environmentally friendly and no-polluting external field technology and has great application potential in materials fabrication. Power ultrasound with different intensities was introduced into the liquid phase separation and solidification process of ternary Al-45%Sn-5%Si immiscible alloy to explore the effects of ultrasound on the formation of macro- and microstructure. It was found that the previously apparent macrosegregation caused by the large density difference between immiscible liquid (Al) and (Sn) phases was gradually reduced and even suppressed with the increase of ultrasonic amplitude. Meanwhile, the ultrasonic waves also significantly modified monotectic structures, within which (Al) phase transformed from coarse dendrites to refined equiaxed grains, and (Si) phase evolved from long strips to small blocks. The introduction of ultrasound weakened the texture of solidified structure, whereas the growth orientation relationship between monotectic (Al) and (Si) phases remained unchanged. The theoretical analysis and calculation results indicated that ultrasonic cavitation and acoustic streaming were the dominant effects to modulate the macro- and microstructural evolution. This would improve the exploiting and utilization of immiscible alloys by ultrasonic processing technology.

Purification of metallurgical-grade silicon combining Sn–Si solvent refining with gas pressure filtration

In this study, the purification of metallurgical-grade silicon using a combination of solvent refining and gas pressure filtration was investigated in the Sn–Si alloy. After the solvent refining process, the silicon was separated from the solvent by gas pressure filtration. The effects of pressure differentials (p), separation temperatures (T), and silicon contents in the alloy (ω(a)) on the separation efficiency were evaluated. The filtration result was improved with a higher pressure differential. The separation temperature had little effect on the separation efficiency, whereas a higher silicon content in the alloy led to a decrease of the separation efficiency. The final purification result after separation was examined, and a better separation contributed to the removal of impurity. The optimal result for separation was obtained at p = 0.30 MPa, T = 250 °C, and ω(a) = 20 wt%, and 93.6% of tin was separated into the filtrate, while almost all the silicon was recovered and formed the separated silicon with a silicon content of 80.0 wt%. At the same time, most impurities were eliminated and 94.9% of B was removed after refining the sample twice.

Fast hydrothermal synthesis of hierarchical Sn-Beta zeolite with high Sn content in fluoride media

Abstract The incorporation of tetravalent Sn species into the framework of BEA zeolite possesses Lewis acidic property and thus exhibits prominent catalytic performances in several reactions. Unfortunately, the Sn-Beta zeolite obtained by hydrothermal synthesis method suffered from several drawbacks including long crystallization time, limited framework Sn content and large crystal size. To solve the problems, a hierarchical Sn-Beta zeolite was synthesized by an innovative hydrothermal method. A hollow mesoporous Sn–Si oxide produced by a simple aerosol process was used as the precursor. The crystallization was preformed in an extremely dense system for only 2–4 days. More Sn species from the precursor can be incorporated into the Beta zeolite as the framework Sn species, which benefits from the unique structure of the precursor. Moreover, the diffusion property is improved due to the formation of the mesopores. The obtained hierarchical Sn-Beta zeolite catalyst exhibits enhanced catalytic performance in the Baeyer–Villiger oxidation of bulky ketone.

Microstructures and mechanical properties of ternary Ti–Si–Sn alloys

Titanium based alloys are one of the important structural materials with applications ranging from aerospace to biomedical industries. Several ternary Ti–Si–Sn alloys were explored in this study to design the microstructure comprising of binary and ternary eutectics corresponding to Ti–Si, Ti–Sn and Ti–Si–Sn system. The microstructural evolution in these alloys was studied using a combination of characterization techniques and thermodynamic calculations. The predicted solidification path from thermodynamic calculations well supported the experimental microstructural data. In addition, mechanical property and microstructure relationship were determined by performing hardness measurements and evaluating stress-strain curves under compression.

(Invited) Development of Germanium-Tin-Related Semiconductor Heterostructures for Energy Band Design in Electronic and Optoelectronic Applications

Group-IV element semiconductor materials, germanium tin (GeSn) and germanium silicon tin (SiGeSn) have attracted much attention for electronic and optoelectronic applications because of those unique properties; direct transition with a high Sn content, higher carrier mobility than Si and Ge, low growth temperature, and low thermal conductivity [1-3]. GeSiSn realizes the control of energy band structure independently on the lattice constant of alloy. Also, GeSiSn/Ge(Sn) heterostructure provides a type-I energy band alignment with sufficiently large energy band offsets at both conduction and valence band edges simultaneously with the lattice constant matching. That promises an effective carrier confinement structure for quantum well laser and high electron mobility transistor. On the other hand, the development of crystal growth technology for GeSn-related materials is still a challenge, since the thermal equilibrium solid solubilities of Sn in Ge and Si are very low compared to a required substitutional Sn content higher than 10%. It is necessary to understand the behavior of Sn atoms in the epitaxial growth and post deposition process and to control the stability of Sn at substitutional site in GeSn-related epitaxial layers. In addition, the development of interface engineering technology is required for not only GeSn/GeSiSn heterostructure but also metal/GeSn and insulator/GeSn structures for nano-scale electronic devices. Recently, we examined the formation of double heterostructure with GeSiSn/GeSn/GeSiSn layers on Ge substrate using a molecular beam epitaxy (MBE) system [4]. The hard x-ray photoelectron spectroscopy measurement reveals that the sufficiently large energy band offset can be formed at the valence band edge of its GeSiSn/GeSn interface. We also demonstrated that the carrier confinement with this GeSiSn/GeSn/GeSiSn double heterostructure effectively improved the efficiency of photoluminescence (PL) [5]. However, we also found that the crystalline quality of the heteroepitaxial layers significantly influence on the PL intensity and it is necessary to understand the key factor of the crystallinity of heterostructures in order to reduce the dislocation and point defect in the epitaxial layers. For the low temperature growth of GeSn and GeSiSn hetero-epitaxial layers on Ge using MBE, a biaxial compressive strain is often induced into the epitaxial layers, as a GeSn or GeSiSn layer is often grown pseudomorphically on Ge substrate. The compressive strain of GeSn is a disadvantage for enhancing the luminescence efficiency because a higher Sn content is generally required to the indirect-to-direct crossover for a compressively strained GeSn compared to the unstrained case. In order to improve the efficiency of luminescence, it is important not only to enhance the Sn content but also to control the strain structure. We developed the strain relaxation technology of GeSn epitaxial layer on a substrate or buffer layer. We found that the ion implantation into Ge substrate effectively enhance the strain relaxation of GeSn layer. The degree of strain relaxation achieved over 90% for the GeSn layer grown on the Ge substrate after the boron ion implantation with 3x1014 cm-2, while the compressively strained GeSn layer was pseudomorphically grown on the Ge substrate without the ion implantation. This work was partly supported with a Grant-in-Aid for Scientific Research (S) (No. 26220605) and the Core-to-Core Program ICRC-ACP4ULSI from the JSPS.

Restoration and repair of equipment by supersonic cold gas-dynamic and micro-plasma spraying

The technological process of restoring and repairing of equipment and its components by supersonic cold gas-dynamic and micro-plasma spraying has been developed. For steel products Fe–Cr–Al-based composite powder has been used being surface reinforced with tungsten carbide particles. For nickel and titaniumproducts composite powder from an alloy of the Ni–Cr–Mn–Sn–Si–W–Re system (Ce, La, Y) has been applied being superficially reinforced by corundum nanopowder. During the work, a high hardness of the applied coating, corrosion resistance and wear resistance were achieved. Real examples of the successful restoration and repair by powder materials are given, and spraying technologies are proposed.

Tin addition for mechanical and electronic improvement of electrodeposited Si–O–C composite anode for lithium-ion battery

The silicon-based composite prepared by electrodeposition exhibits outstanding electrochemical performances for several thousand cycles because the co-deposited oxygen and carbon could act as buffer materials to reduce internal stress during charge-discharge cycling. However, it is not easy to increase the loading amount of active materials due to low structural stability at a high passing charge over 15 C cm−2 for electrodeposition, leading the low areal capacity of Si–O–C composite as an anode. In this study, we propose a new way to enhance the structural stability of silicon-based anode by an electrochemical co-deposition technique using tin as supporting material, namely Sn–Si–O–C composite. The co-deposited tin has a whisker-shaped structure, and it prevents the exfoliation of activated material during electrodeposition. Besides, tin whisker can act as an electron pathway, resulting in improved electrochemical performance including high rate performance. The enhanced electrical conductivity is investigated by electrochemical impedance analysis. The improved electrochemical performance of Sn–Si–O–C composite indicates the high potential as an electrode material for high-performance lithium-ion batteries.

Effect of Zr addition on B-removal behaviour during solidification purification of Si with Si–Sn solvent

This paper details a novel attempt for B removal from Si by adding Zr as the trapping agent in solidification refining with Si–Sn solvent. The premise of the study is as follows: (i) B becomes more thermodynamically unstable in Si–Sn melt and (ii) Zr has a strong affinity for B, which is expected to enhance the formation of the B–Zr intermetallic compound. The B-removal mechanism is discussed from the aspects of theoretical analysis and experimental design. The effects of different variables, such as the moving direction, moving rate, Zr addition content, and initial Sn content in Si–Sn alloys, on the B-removal fraction are observed. Furthermore, the solubility product of the B–Zr compound in the Si–Sn melt is measured using equilibrium technology, to be ≥ 9.62 × 10−10 (1605 K, Si-50 at.% Sn) and ≥3.32 × 10−10 (1575 K, Si-65 at.% Sn). Enriched B and Zr regions are found in the mushy zone, but separated from each other. The maximum removal fraction of B is 73.6%; further, the added Zr is almost completely eliminated and does not contaminate the refined Si. This study provides an alternative perspective for B removal via Si–Sn solvent refining to produce solar-grade Si.

Cu–Ni–Sn–Si alloys designed by cluster-plus-glue-atom model

Segregation in the solidification process and discontinuous precipitation during aging cause the service and processing performance of Cu–Ni–Sn alloys deteriorating severely. In this work, Si is added as a fourth element for the design of Cu80Ni15Sn5−xSix (x = 0, 0.625, 1.25, 1.875, 2.5) series alloys using cluster-plus-glue-atom model to solve these issues from the point of composition design. The results suggest that the introduction of Si leads to the disappearance of the lamellar structure formed in the as-cast alloys while also inhibiting discontinuous precipitation during aging. The solidus–liquidus temperature range is reduced with the addition of Si, and this strategy is most effective when the Si is in the solution state. With increasing Si content, the high-temperature conductive stability of the alloys is improved. Moreover, the hardness and conductivity of the Cu80Ni15Sn5 alloy designed by cluster-plus-glue-atom model are improved compared with those of C72900 (Cu78.96Ni16.65Sn4.39) commercial alloy, and the properties of Cu80Ni15Sn4.375Si0.625 alloy are basically equivalent to those of C72900 alloy. These findings indicate that alloys with excellent synthetic properties can be produced as long as the content and existential state of Si are reasonably controlled.

Experimental study on characteristics of laser metal deposited Al–Si–Sn–Cu/Ti–6Al–4V composite coatings

The development of laser based advanced coatings are continually implemented in order to meet the desired demands and performances of materials in industries. Many engineering materials used in industrial conditions are subjected to corrosion, wear and fatigue attack leading to rapid degradation of the material. This research is aimed at fabricating Al–Si–Sn–Cu quaternary coatings on Ti–6Al–4V alloy. A 3-kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the cladding process was used for the laser cladding process. The appropriate selection of laser processing parameter produced desirable result and properties. Enhanced surface hardness and tribological properties were achieved as a result of well optimized laser process parameters and appropriate selection of reinforced powders. The results of the micro-hardness revealed an improvement as the hardness measured for the cladded Al–Si–Sn–Cu layer was 602 HV0.1. While the micro-hardness of the Ti–6Al–4V substrate was 302 HV0.1. Also, the COF of Al–Si–Sn–Cu quaternary coatings are lower than that of the Ti–6Al–4V substrate, which was attributed to strengthening effect and higher load bearing aptitude of Ti3Al, CuTi2, AlSi3Ti2, SiTi, AlTi0.6V0.4, and Al0.25Sn0.75V3 hard phases present in the coatings. The protective intermetallic phases result to a reduction in coefficient of friction and therefore demonstrated superior wear resistance performance.

Single crystal growth and structure analysis of type-I (Na/Sr)-(Ga/Si) quaternary clathrates.

Single crystals of (Na/Sr)–(Ga/Si) quaternary type-I clathrates, Na8−ySryGaxSi46−x, were synthesized by evaporating Na from a mixture of Na–Sr–Ga–Si–Sn in a 6 : 0.5 : 1 : 2 : 1 molar ratio at 773 K for 12 h in an Ar atmosphere. Electron-probe microanalysis and single-crystal X-ray diffraction revealed that three crystals from the same product were Na8−ySryGaxSi46−x with x and y values of 7.6, 2.96; 8.4, 3.80; and 9.1, 4.08. It was also shown that increasing the Sr and Ga contents increased the electrical resistivity of the crystal from 0.34 to 1.05 mΩ cm at 300 K.

Boron separation from Si–Sn alloy by slag treatment

This study investigates a purification process for metallurgical-grade silicon (MG-Si) in which Si is alloyed with tin (Sn) and CaO–SiO2–CaCl2 slag is used to remove boron (B) impurity. Acid leaching was performed to remove the Sn phase after slag refining to recover high-purity Si from the Si–Sn alloy. The effect of refining time was investigated, and acceptable refining results were realized within 15 min. The effects of slag composition and Sn content on the removal of B were also studied. The results indicate that increasing Sn content favors B removal. With the increase of Sn to 50% of the alloy, the final B content decreased to 1.1 × 10−4wt%, 93.9% removal efficiency.

Optimised phase compositions and improved microwave dielectric properties based on calcium tin silicates

The Ca(1+2y)Sn(1-x)Si(1+y)O(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca(1+2y)Sn(1-x)Si(1+y)O(5-2x+4y) ceramics have been investigated. A single CaSnSiO5 phase with abnormally positive temperature coefficient of resonant frequency (τf = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τf compensator of CaSiO3 and Ca3SnSi2O9 phases with typically negative τf value. The CaSiO3 second phase was related to the Sn deficiency in the CaSn(1-x)SiO(5-2x) (0 <x < 1.0) composition, whereas the Ca3SnSi2O9 second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca(1+2y)SnSi(1+y)O(5+4y) (0 <y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (εr = 10.2, Q×f = 81,000 GHz and τf = −4.8 ppm/°C) was produced from the Ca(1+2y)SnSi(1+y)O(5+4y) (y = 0.4) ceramic.

Growth control and enrichment of Si crystals from Si-Sn melt by directional solidification

The growth control and enrichment of Si crystals using Si-50 at.% Sn melts via upwards and downwards directional solidification at various moving rates was investigated. As expected, a large area of quasi-bulk Si (98.6% enrichment percentage) was successfully obtained at the 0.01 mm/min upwards moving rate. Moreover, after HCl leaching, the residual at.% of Sn in the enriched Si area was easily reduced to the 0.00132–0.00163 range, which was almost the same as that for the solid solubility of Sn in Si. Furthermore, a model was established to explain the crystal growth process and enrichment mechanism during directional solidification. In conclusion, we chose the upwards moving direction for the follow-up experiments, which solved the most critical first step of using Si-based alloy solvent refining to produce solar grade Si.

Ti–Zr–Cu–Fe–Sn–Si–Ag–Ta bulk metallic glasses with good corrosion resistance as potential biomaterials

Ti47Cu38−xZr7.5Fe2.5Sn2Si1Ag2Tax (x = 1–4; at%, the same below) bulk metallic glasses (BMGs) with good bio-corrosion resistance and mechanical properties were fabricated by copper mold casting. Critical diameter of the Ti-based BMGs with 1 at%–4 at% Ta was 3 mm. The Ta-incorporated Ti-based BMGs exhibit higher open current potential and parallel passive current density in comparison with those of Ti–6Al–4V alloy in 0.9 wt% NaCl and Hank’s solution, implying their good corrosion resistance. The pitting corrosion potential of the Ti-based BMGs gradually increases up to about 1.25 V with Ta addition increasing up to 4 at% in 0.9 wt% NaCl solution. Among the present Ti-based BMGs, the alloy bearing 2 at% Ta exhibits the optimal integration of mechanical properties, including the compressive fracture strength exceeding 2000 MPa, relative low Young’s modulus of 98 GPa, plastic strain of 3.4% and high hardness of HV 599. The Ta-bearing Ti-based bulk metallic glasses with integration of relative high GFA, good mechanical properties and high bio-corrosion resistance are beneficial for biomedical applications.

The structural, elastic and thermodynamic properties of intermetallic phases in Mg–Sn–Si–Ca(Sr) alloys: A first-principles study

The structural, elastic and thermodynamic properties of Mg2Si, Mg2Sn, CaMgSi and MgSnSr phases in Mg–Sn–Si–Ca(Sr) alloys have been investigated by implementing first-principles calculations. Formation enthalpies and cohesive energies show that MgSnSr has the strongest alloying ability and CaMgSi has the highest structural stability. The bulk modulus B, shear modulus G, Young’s modulus E, G/B, Poisson ratio [Formula: see text], anisotropy index A[Formula: see text] are estimated after evaluating the elastic constants. The mechanical properties are further analyzed and discussed. Finally, the Gibbs free energy and Debye temperature of these phases are calculated by means of the quasi-harmonic Debye model in temperature ranging from 0 K to 1000 K.

Rational design of a Si–Sn–C ternary anode having exceptional rate performance

It is urgent to develop a new anode material that addresses the needs on high energy density as well as high power density of Li-ion batteries to meet the growing demands of high-performance mobile devices and electric vehicles. In this work, a new ternary composite (Si–Sn–C) anode material was designed to achieve exceptional rate performance by scavenging lost Si charge capacity at higher working potential of Sn (~ 0.9 V) under increased current densities. Si and Sn nanoparticles were separately compartmentalized in double-holed carbon nanofibers (Si–Sn–DHCNFs) to elucidate the working potential effect without a kinetic improvement by Sn. Si–Sn–DHCNFs showed high specific capacity (1000 mA h g−1 at 100 mA g−1) and exceptional rate performance (720 mA h g−1 at 10,000 mA g−1). Our work demonstrates that the design of new anode materials is a fruitful route to enhancing the power density of batteries.

Purification of metallurgical-grade silicon using Si–Sn alloy in presence of Hf, Zr, or Ti

Hf, Zr, or Ti was employed as additive to enhance removal of the main impurities from metallurgical-grade Si (MG–Si) during the Si–Sn alloy refining process. The microstructure of Si-Sn alloy without/with Zr, Hf, or Ti was observed and analyzed by electron probe microanalysis (EPMA) to investigate the distribution of impurities. Compositions of intermetallic phases precipitated in Sn or among the grain boundaries of Si were quantitatively analyzed using EPMA. The mechanisms of their formation and the removal of impurities are discussed. The results of Si refining showed that the addition of Hf or Zr slightly enhanced the removal of Al. The high refining temperature in the Si-Sn alloy refining process was responsible for the low extraction of B. Most of Zr, Hf, or Ti was removed simultaneously with other impurities during the Si–Sn alloy refining process.