Molecular dynamics study of correlations between IR peak position and bond parameters of silica and silicate glasses: Effects of temperature and stress

In the IR spectra of the silica and silicate glasses, the shifts of the maximum intensity position of the ν_{Si–O–Si,as} band upon heating or applying mechanical stress could be attributed to changes in the distribution of bond parameters such as bond length and bond angle. Upon heating, isotropic expansion occurs and the density changes; upon applying mechanical stress, anisotropic strain is induced and a significant change in the Si–O–Si bond angle is observed. From molecular dynamics simulations of a silica glass, we show that the peak position shift correlates better with the asymmetric change in the Si–O bond length distribution, rather than the Si–O–Si bridge angle, the O–Si–O tetrahedral angle, or the density change. This new finding provides an insight into how and why the ν_{Si–O–Si,as} IR peak of soda lime silica (SLS) glass shifts upon chemical strengthening via ion exchange and thermal tempering.     

Low-Temperature Purification of Silicon by Dissolution and Solution Growth in Sodium Solvent

Efficient low-cost processes for solar-grade Si production are needed to overcome the deficiency in the supply of Si. We have demonstrated a new method for the purification of Si crystal. Low-purity Si powder was dissolved in a Na melt (solvent), and Si grains were crystallized by Na evaporation from the Na-Si solution at 1173 K. Glow discharge mass spectrometry analysis revealed that the concentrations of impurity elements, except Na and B, were decreased in the crystallized Si grain. In particular, the concentration of Fe which was mainly included in the Si powder decreased from 3200 ppm by mass to 1.5 ppm by mass in a refined Si grain. Iron disilicide was crystallized from the solution before the crystallization of Si. It was suggested that impurities were reduced not only by crystallization from the Na-Si melt but also by the dissolution of Si into the melt. Na contaminating the refined Si grain was eliminated down to 0.055 mass ppm by heating at 1723 K under vacuum.     

The fast pyrotechnic reaction of silicon and red lead: heats of reaction and rates of burning

Heats of reaction were measured with a bomb calorimeter and linear rates of burning by an electronic timer. The former, reached a maximum at 10% Si for all sizes tested; the latter at 30% Si for coarse silicon and at 15% Si for fine silicon. An attempt was made to correlate both properties with rate of heat evolution. Reactions of mixtures containing <20% Si were violent owing to rapid rise of temperature to a high level, causing vaporization of products and rapid expansion of air above the delay element. Mixtures containing 20–50% Si were adaptable for practical use and reactions were mainly of the solid/solid type. The products are SiO₂, Pb, and unreacted Si.     

Optical absorption and emission of nitrogen-doped silicon nanocrystals

Silicon nanocrystals (Si NCs) may be both unintentionally and intentionally doped with nitrogen (N) during their synthesis and processing. Since the importance of Si NCs largely originates from their remarkable optical properties, it is critical to understand the effect of N doping on the optical behavior of Si NCs. On the basis of theoretical calculations, we show that the doping of Si NCs with N most likely leads to the formation of paired interstitial N at the NC surface, which causes both the optical absorption and emission of Si NCs to redshift. But these redshifts are smaller than those induced by doubly bonded O at the NC surface. It is found that high radiative recombination rates can be reliably obtained for Si NCs with paired interstitial N at the NC surface. The current results not only help to understand the optical behavior of Si NCs synthesized and processed in N-containing environments, but also inspire intentional N doping as an additional means to control the optical properties of Si NCs.     

PZTS系凝胶玻璃及玻璃陶瓷的结构研究

采用溶胶凝胶工艺在低温下合成均匀透明的ＰＺＴＳ新型多组元凝胶玻璃，并在凝胶玻璃中成功地析出ＰｂＴｉＯ３，Ｐｂ（Ｚｒ，Ｔｉ）Ｏ３纳米微晶。利用ＩＲ谱分析了凝胶玻璃中Ｓｉ－Ｏ－Ｓｉ，Ｓｉ－Ｏ－Ｔｉ等化学键在成胶过程中的形成以及在热处理过程中的变化，根据Ｋｉｓｓｉｎｇｅｒ原理估算了ＰＴＳ凝胶玻璃的析晶活化能。借助ＸＲＤ较系统地研究了凝胶玻璃在高温下的结晶结构。探讨了在ＰＺＳ、ＰＺＴＳ体系中ＺｒＯ２和Ｓｉ     

氮化硅晶须结构性能研究及其应用现状

在介绍晶须生长机制的基础上分析了氮化硅结构特点、物化性能,简单介绍了氮化硅的制备方法,较详细阐述了其作为复合材料的应用现状,最后对其今后的发展方向做了展望。     

Deposition and characteristics of iron–silicon thin film catalyst for CNT growth

Fe–Si catalyst thin films for the growth of carbon nanotubes were prepared using co-sputter deposition. As-deposited Fe–Si films consist of different amounts of α-Fe and amorphous Si. The amount depends on the Si concentration in the film. Hydrogen plasma etched Fe–Si films become particles having different sizes. The particle size is also dependent on the Si concentration. Correlation among the Si concentration, the particle size, and the growth rate of carbon nanotube was made. Optimal growth of carbon nanotubes at 370 °C was obtained at an average particle size of 45 nm or a Si concentration of 21%.     

氮化硅晶须结构的性能研究及其应用现状

本文在介绍晶须生长机制的基础上分析了氮化硅晶须的结构特点及物化性能,并简单介绍了氮化硅的制备方法,阐述了其作为复合材料的应用现状,并对其发展方向作了展望。     

Influence of the silicon and oxygen content on the properties of non-hydrogenated amorphous carbon coatings

This work reports the development of non-hydrogenated magnetron-sputtered silicon and silicon-oxygen containing amorphous carbon coatings with increasing silicon and oxygen contents respectively. The Si content of a-C:Si coatings increases linearly with the increase of the power applied to the Si target up to 24 at.%, while to the system a-C:Si:O the O content increases with the increase of the oxygen flow to a maximum of 27 at.%. The hardness of the a-C:Si coatings shows two distinct trends with the increase of the Si content, a decrease of hardness for Si contents lower than 10 at.% and an increment above this value are observed. The coatings of the system a-C:Si:O present a decrease of hardness and Young modulus with the increase of the O content. The tribological performance of the coatings is significantly improved by doping the amorphous carbon coatings with silicon and oxygen with a reduction of the friction from 0.17 for the undoped carbon coating to 0.034 for the coating of the system a-C:Si:O with the highest O content.     

Effects of zirconium addition on microstructure and ablation resistance of carbon fibre reinforced carbon and SiC ceramic matrix composite prepared by reactive melt infiltration

Abstract

Carbon fibre reinforced C and SiC binary ceramic matrix composites (C/C–SiC) were fabricated by a quick and low cost reactive melt infiltration (RMI) method with Si–Zr25 and Si melts. Effects of zirconium addition in infiltrated Si melt on microstructure and ablation resistance of the composite were investigated. The composite by Si–Zr25 melt infiltration was composed of SiC, ZrC, C and a little amount of ZrSi₂ without residual silicon, overcoming the problem of residual silicon in C/C–SiC composite by Si RMI. Compared with the composite by Si melt infiltration, the ablation resistance of the composite by Si–Zr25 was greatly improved by zirconium addition due to ZrO₂ and SiO₂ protecting layer formed during ablation.     

锂离子电池硅负极材料储锂前后的ESR研究

本文采用电子自旋共振(ESR)来研究硅材料作为锂离子电池负极材料的机理。组装了以硅为负极材料,金属锂为正极材料的模拟电池,充电至不同的储锂状态后,测试了负极的ESR谱,并和储锂之前的硅材料的ESR谱进行比较,有助于从能带理论的角度认识硅负极储锂的机理。     

Fabrication of Ni-silicide/Si heterostructured nanowire arrays by glancing angle deposition and solid state reaction

This work develops a method for growing Ni-silicide/Si heterostructured nanowire arrays by glancing angle Ni deposition and solid state reaction on ordered Si nanowire arrays. Samples of ordered Si nanowire arrays were fabricated by nanosphere lithography and metal-induced catalytic etching. Glancing angle Ni deposition deposited Ni only on the top of Si nanowires. When the annealing temperature was 500°C, a Ni₃Si₂ phase was formed at the apex of the nanowires. The phase of silicide at the Ni-silicide/Si interface depended on the diameter of the Si nanowires, such that epitaxial NiSi₂ with a {111} facet was formed at the Ni-silicide/Si interface in Si nanowires with large diameter, and NiSi was formed in Si nanowires with small diameter. A mechanism that is based on flux divergence and a nucleation-limited reaction is proposed to explain this phenomenon of size-dependent phase formation.     

不同Si/B比含银可溶性玻璃结构与抗菌性能

利用XRD测试分析手段对制备的Si-B-Zn-Ca-P-Ag-O系统分析,实验结果表明:随着体系中Si/B比的不同,抗菌材料结构发生从晶体到玻璃体的变化过程,并且在Si/B=3和5(molar ratio)时具有良好的抗菌效果,MIC(最小抑菌浓度)值分别为50mg/L和100mg/L.同时把生成的抗菌材料放在80℃的水中做耐久性实验,实验结果表明Ag离子是随着时间缓慢释放出来的,Si/B=3和5时的溶出量(3.00mg/L和2.35mg/L)明显高于Si/B=1和8.4时的溶出量(0.85 mg/L和0.53 mg/L).     

Structure,morphology, and photoluminescence of porous Si nanowires: effect of different chemical treatments

The structure and light-emitting properties of Si nanowires (SiNWs) fabricated by a single-step metal-assisted chemical etching (MACE) process on highly boron-doped Si were investigated after different chemical treatments. The Si nanowires that result from the etching of a highly doped p-type Si wafer by MACE are fully porous, and as a result, they show intense photoluminescence (PL) at room temperature, the characteristics of which depend on the surface passivation of the Si nanocrystals composing the nanowires. SiNWs with a hydrogen-terminated nanostructured surface resulting from a chemical treatment with a hydrofluoric acid (HF) solution show red PL, the maximum of which is blueshifted when the samples are further chemically oxidized in a piranha solution. This blueshift of PL is attributed to localized states at the Si/SiO₂ interface at the shell of Si nanocrystals composing the porous SiNWs, which induce an important pinning of the electronic bandgap of the Si material and are involved in the recombination mechanism. After a sequence of HF/piranha/HF treatment, the SiNWs are almost fully dissolved in the chemical solution, which is indicative of their fully porous structure, verified also by transmission electron microscopy investigations. It was also found that a continuous porous Si layer is formed underneath the SiNWs during the MACE process, the thickness of which increases with the increase of etching time. This supports the idea that porous Si formation precedes nanowire formation. The origin of this effect is the increased etching rate at sites with high dopant concentration in the highly doped Si material.     

共聚法制备聚硅硼酸铝铁絮凝剂及其絮凝性能研究

以硅酸钠为主要原料共聚法合成了絮凝剂聚硅硼酸铝铁,研究了絮凝剂的最佳制备条件及其对CODCr的去除效果。实验结果表明：絮凝剂中Al3＋/Si、Fe3＋/Si和B/Si物质的量比分别为1︰2、1︰1和1︰10时聚硅硼酸铝铁的絮凝效果最好。在最佳制备工艺下制备的絮凝剂的用量为130 mg/L,废水pH为6~8的条件下,对印染废水中CODCr的去除率高于60%。     

Study on Preparation and Properties of HVBR Reinforced with Si69-modified Carbon Nanotubes

Si69-modified CNTs/HVBR nanocomposites were prepared in dependence of different loadings of Si69-modified CNTs fabricated by mixing acid-treated CNTs with Si69 in toluene. FT-IR analysis illustrated the successful modification of CNTs. Experimental results showed that the Si69-modified CNTs could more significantly enhance the mechanical strength and thermal conductivity of the composites than the unmodified CNTs, indicating the Si69-modified CNTs could be more uniformly dispersed in the HVBR matrix, which was also verified form the SEM results. The DMA results indicated that the incorporation of Si69-modified CNTs could remarkably increase the glass transition temperature and decrease the height of the tanδ peak.     

Synthesis and NMR Characterization of Titanium and Zirconium Oxides Incorporated in SBA-15

Single oxides of Ti and Zr incorporated SBA-15 were prepared and characterized by N₂ adsorption, NMR, and XPS techniques. ²⁹Si MAS NMR results suggest the formation of Si–O–X linkages (X: Ti or Zr) by an increase in the ratio of Q ³/Q ⁴ in the presence of Ti or Zr. XPS analysis of Ti–SBA-15 catalysts indicate the presence of Ti–O–Si bonds in addition to Ti–O–Ti and Si–O–Si bonds, supporting the NMR evidence.     

硅烷偶联剂总硫含量与平均硫链长度的测试

研究固体和液体偶联剂Si69总硫含量与平均硫链长度的测试方法。采用元素分析仪,以管式炉燃烧-红外吸收法测试偶联剂Si69的总硫含量;用质量分数为0.04%的四丁基溴化铵/乙醇/甲醇溶液(体积比为18/45/137)作为流动相,C₁₈柱分离,等度洗脱的方式,采用高效液相色谱仪测试偶联剂Si69的平均硫链长度。结果显示:固体偶联剂Si69试样的总硫含量为11.512%,平均硫链长度为3.59;液体偶联剂Si69试样的总硫含量为21.924%,平均硫链长度为3.60;固体偶联剂Si69总硫含量的测试精密度比液体偶联剂Si69高。     

Effect of Si content on the microstructure and properties of Ti–Si–C composite coatings prepared by reactive plasma spraying

In this study, Ti–Si–C composite coatings were synthesized via plasma spraying of agglomerated powders prepared by a spray drying/precursor pyrolysis technology using Ti, Si, and sucrose powders. The influence of Si content, ranging from 0 wt% to 24 wt%, on the microstructure, mechanical properties, and oxidation resistance of the composite coatings was investigated. Results show that the phase composition of the Ti–Si–C composite coatings changes with the increasing Si content. The coatings without Si addition consist of TiC and Ti₃O; the coatings with 6–18 wt% Si are composed of TiC, Ti₅Si₃, and Ti₃O; the coatings with Si content of 24 wt% form only TiC and Ti₅Si₃ phases. As the Si content increases, the hardness of the Ti–Si–C composite coatings increases first and then decreases, depending on the intrinsic hardness of the ceramic phases, the brittleness of Ti₅Si₃, and the defects such as pores and cracks. The Ti–Si–C composite coatings have high wear resistance due to the in-situ synthesized high-hardness TiC and Ti₅Si₃. Owing to the high brittleness of Ti₅Si₃, the increasing Si content leads to higher wear volume loss at room temperature, which can be partially improved in high-temperature wear tests. The oxidation resistance of Ti–Si–C composite coatings increases with the increase of Si content, and the higher the oxidation temperature, the more obvious the influence of the Si addition on oxidation resistance.     

硅/石墨烯基自支撑薄膜的制备及电化学性能

采用简单的超声、抽滤和水合肼化学还原相结合的方法制备硅/石墨烯基自支撑薄膜,系统研究了硅含量对硅/石墨烯复合材料电化学性能的影响。结果表明：通过在石墨烯水凝胶的片层之间插入纳米硅颗粒,可以有效地控制硅体积变化,增加该复合膜的机械强度并提高其导电性。提高硅/石墨烯复合材料中硅含量的比例可以提升其可逆比容量和首次库仑效率,当硅质量分数为53%时,复合膜在0.1C倍率下的可逆比容量及首次库仑效率分别达到945.6mA·h/g和64.8%（纯硅的229倍和9倍）;继续提高硅含量的比例,可以提升其循环寿命（循环50次容量保持率60.9%、质量分数为67%的Si）,但材料比容量有所下降,说明石墨烯在稳定硅基复合材料电化学性能方面发挥着非常重要作用。