Influence of MnO_2 Mineralizer on the Crystal Structure,Properties of SiC Kiln Furniture Bonded with Fine Silicon Powder

The properties of SiC kiln furniture bonded with fine silicon powderare related to the bonder’s crystal structure. At high temperature, it will crystallize ina-cristobalite with great bulk effect. MnO2 mineralizer can make a-cristobalite convertto a-tridymite whose bulk effect is small. The crystal structure and its amount were investigated with XRD technique. The influence of different amounts of MnO2 on thecrystal structure and polycrystal transformation, and that of crystal structure on theproperties of kiln furniture were studied. The best proportion of MnO2 added was determined to be 2.0%.

Effect of Binder on the Structure and Properties of Silicon Powder-supported TiO_2 Photocatalysis Material

Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effects （including binder type and binder addition quantity） on the crystal structure and catalysis properties of photocatalyst. In this work, the catalysis activity was defined as the degradation rate of methyl orange solution upon ultraviolet lamp irradiation, and the specific areas were determined with nitrogen desorption method. TiO2 crystal form was measured with X-ray powder diffraction and their micro-morphology was observed with SEM. Experimental results indicate that these two binders do not affect the crystal form transformation of TiO2, but silica gol can increase the specific surface area of TiO2 photocatalyst obviously and the addition of sodium silicate can decrease it. In all, silica gol is a better candidate than sodium silicate for higher catalysis property. In conclusion, 6% silica gol is the optimal addition concentration. Under this condition, the ratio of anatase to rutile TiO2 is 64：36, the specific area is 29.67 m^2/g, and as expected, the degradation rate of methyl orange could be as high as 90% after irradiation for 5 days.

Influence and Characterization of Acidity on Fine Silicon Powder Immobilized Photocatalyst

TiO2 photocatalyst was supported with tetrabutyl titanate sol as precursor and fine silicon powder obtained from ferroalloys factory as carder to discuss the influence of pH value of gel precursor on microstructure and activity of photocatalyst in the process of synthesizing nano-TiO2 by using sol-gel method, the purpose of which is to provide fundamental data for the recycle of photocatalytic material. Under the irradiation of ultraviolet light, the photocatalytic degradation rate of methyl orange solution was used to characterize the photocatalytic activity of the sample. The specific surface area of the sample was tested by N2 desorption method, crystal form of TiO2 was analyzed by X-ray powder diffraction, and the microtopography of the sample was observed by scanning electron microscopy. The experimental results showed that the acidity of gel precursor could greatly affect the specific surface area and photocatalytic activity of the photocatalyst, and the optimum pH value of the precursor was determined as 2.0, and at this time the specific surface area of photocatalyst could reach 34.0 m^2/g. In the sample, the proporticn of anatase to rutile is 7：3, which makes l0 mg·L^-1 methyl orange solution fade after irradiation by 15W ultraviolet light for 24 h, and the degradation rate might be up to 98.1%.

Surface Passivation of Nanocrystalline Silicon Powder Derived from Cryomilling

The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.

Effects of Particle Size and Content of Silicon Powder on Strength and Microstructure of Coked Al_2O_3-ZrO_2-C Refractories

Effects of particle size （A：d50 = 336. 9 μm, B：d50 =123.5μm, C： d50=19.5 μm, D： dso=2.21μm） and content （1 wt% , 3 wt% , 5 wt% , 7 wt% ） of silicon powder on cold crushing strength （CCS） , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens＇ pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.

Effect of Pretreatment Temperature on Properties of Silicon Powder

In order to reduce the hydrolysis rate of Si powder and inhibit the swelling and cracking of cast samples,Si powder was treated at different temperatures for 5 h,and then slurries and SiC-Si3N4 materials were prepared.The effect of the preheating temperature on the composition of the Si powder,the hydrolysis rate as well as the nitridation of the SiC-Si3N4 materials was studied.The results show that with the increase of the pretreatment temperature of Si powder,the oxidation degree of Si powders increases,the viscosity of the slurry with PAAS dispersant decreases gradually,and the hydrolysis reaction of Si powder decreases gradually;the Si powder pretreated at 700℃ or lower has little effect on the nitriding process,while the Si powder pretreated at 800 t has a great effect on the nitriding process,which is not conducive to the nitriding sintering of the samples.Therefore,the Si powder pretreated at 700 t for 5 h has the best properties,which not only has lower hydrolysis rate and good slurry fluidity,but also has mild effect on the nitriding reaction.

Kinetic study on the direct nitridation of silicon powders diluted with α-Si_3N_4 at normal pressure

Silicon nitride （Si3N4） powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor （2.27 cm.s^-1） in the Arrhenius equation, activation energy （114 kJ·mol^-1）, and effective diffusion coefficient （6.2×10-s cm2.s^-1）. A formula was also derived to calculate the reaction rate constant.

Effect of Al Powder and Si Powder Additions on Structure and Properties of Unburned Magnesium Aluminate Spinel Refractories

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.

ELECTRORHEOLOGICAL PROPERTIES OF TALC POWDER/SILICONE OIL SUSPENSIONS UNDER DC FIELDS

In this study, the electrorheological （ER） behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil （SO） medium was investigated. Sedimentation stabilities of suspensions （c = 5 wt%） prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated.

PREPARATION OF NANOSIZED SILICON NITRIDE POWDERS BY AMMONO SOL-GEL PROCESSING

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Thermal expansion of lattice parameter of (powder) silicon up to 1473 K

The XRPD (X-ray powder diffxactometry) patterns of silicon powder with a unit cell structure of diamond were determined from 298 to 1473 K. Lattice parameters of Si linearly increase with temperature. The thermal shifts of the positions of all reflection peaks are linearly correlated with the temperature. The coefficients of the intrinsic linear thermal expansion and volumetric thermal expansion were determined as 3.87×10-6/K and 1.16×10-5/K respectively. It indicates that Si is still a suitable standard in the XRPD method at high temperatures.

硅酮粉改性超高分子量聚乙烯及其熔体纺丝加工性能

针对超高分子量聚乙烯(PE-UHMW)熔体加工性能差的问题,应用硅酮粉,采用熔融共混方法对PE-UHMW进行改性,以提高其熔体加工时的流动性。通过扫描电子显微镜与能量色散谱(EDS)表征了硅酮粉在PE-UHMW中的分布,并采用熔体速率测试、旋转流变测试,分析了硅酮粉含量对PE-UHMW熔体流动速率与流变性能的影响。对改性后的PE-UHMW采用熔体纺丝法制备了PE-UHMW单丝,并进行了拉伸强度测试。实验结果表明,随着硅酮粉的增加,其分散性逐渐变差,PE-UHMW熔体流动速率随硅酮粉含量先增加后降低,当硅酮粉质量分数达到4%,其熔体流动速率最高,复数黏度与储能模量最低,5%质量分数的硅酮粉在PE-UHMW基体中团聚较明显,改性后的PE-UHMW熔体流动性降低。熔体纺丝实验结果表明改性后的PE-UHMW可以通过普通单螺杆挤出机熔融挤出初生丝,经超倍热拉伸可以制备高强度单丝。当拉伸倍率为36时,质量分数3%的硅酮粉改性PE-UHMW单丝拉伸强度最高,可达1565MPa。因此综合考虑加工性能与单丝强度,采用质量分数3%的硅酮粉改性PE-UHMW较合适。

氮化硅粉改性及其陶瓷高温摩擦磨损性能研究

以商用氮化硅粉体为研究对象,重点考察了粉体种类、粒度、杂质离子含量、相组成对所制材料性能的作用规律。该研究探讨了不同粉体对氮化硅陶瓷密度、抗弯强度、导热系数、摩擦磨损性能和微观形貌的影响。结果表明:采用甲醇改性液处理20 min得到的氮化硅粉体,制备得到了热力学性能最佳的氮化硅陶瓷:密度为3.16 g·cm^(-3)、抗弯强度为(727±20) MPa、热导率为71.6 W·m^(-1)·K^(-1)、Si_(3)N_(4)陶瓷与C/SiC陶瓷在1200℃下摩擦系数低于0.7,高温下氮化硅陶瓷仍表现出优异的耐摩擦磨损性能。

晶硅太阳能电池制备过程中硅渣和金刚石线切割硅废料的回收利用研究进展

随着晶硅太阳能电池的快速发展,晶体硅片的需求大幅增加。晶体硅片在生产制备过程中,大量的硅以硅渣和金刚石线切割硅废料的形式流失。硅渣和金刚石线切割硅废料中硅的回收再循环利用对降低晶硅太阳能电池的成产成本、有效解决晶体硅片短缺以及环境污染等问题具有重要意义。本文通过对从硅渣和金刚石线切割硅废料中回收制备高纯硅的现有工艺和研究进展进行综述,对不同回收工艺的优势、缺陷以及改进措施进行分析,有助于研究人员选择合理的高纯硅回收策略,为晶硅太阳能电池产业的低成本、绿色可持续发展提供参考。

微硅粉制备充填胶凝材料研究现状

微硅粉是硅钢工业产生的废弃物之一,主要成分为二氧化硅,有较高的潜在胶凝活性。本文对微硅粉的理化性质、微硅粉改性、胶凝活性激发、工程应用等进行了综述。微硅粉作为添加剂广泛应用于混凝土工程中,其产生的C-S-H凝胶能显著改善混凝土的各项性能。使用微硅粉制备对重金属离子具有较强吸附能力的新型充填胶凝材料是微硅粉资源化利用的一条新途径。

硅泥在锂离子电池中的应用研究进展

光伏切割硅废料——硅泥,因其低成本、二维片状结构和高比容量(4200 mAh·g^(-1))的优势成为300 Wh·kg^(-1)以上高能量密度储能电池核心硅碳负极材料的理想原料之一。然而,硅泥存在成分复杂、粒径较大、导电性差、稳定性低和电化学性能差的问题,需要进行系统改性处理。本文综述了硅泥在锂离子电池中的应用研究进展。首先,分析了硅泥中金属杂质和非金属杂质对电池性能的重要影响。其中金属杂质可通过磁选和酸洗去除,非金属杂质可通过液-液萃取和热处理去除。其次,详细阐述了纯化后硅泥的原始性能和改性方法。通过硅泥纳米化可以抑制其膨胀,其中包括研磨、刻蚀、电热冲击和合金-脱合金等方式;通过直接元素掺杂硅和掺杂硅表面碳层来提高导电性;通过构建惰性层、导电层和一定作用的官能团等表面改性提高稳定性;还可以通过硅碳复合获得稳固的机械支撑和保护。最后,提出了基于硅泥为原料的硅基负极面临的挑战和研发方向,展望了未来发展前景,旨在为硅泥变废为宝提供参考,推动高能量密度锂离子电池快速发展。

镁含量对光伏废硅粉基硅化镁陶瓷的结构及其热电性能影响

硅化镁由于其组成元素丰度高以及优异的热电性能而被认为是最有前景的中温区热电材料之一.本项工作报道了直接利用光伏废硅粉作为硅源,采用高能球磨和放电等离子体烧结法制备了不同镁含量(镁硅摩尔比为1.9∶1、2∶1和2.1∶1)的硅化镁热电材料,并对材料进行了物相、结构和热电性能分析.研究结果表明:在300~780 K内,不同镁含量的硅化镁陶瓷材料电导率呈现先降低再升高的变化趋势,而Seebeck系数的变化较为平稳,镁硅摩尔比为2∶1的硅化镁陶瓷具有最高的功率因数,其值在800 K下可以达到82μW m^-(1)K^-(2).此外,不同Mg含量对硅化镁陶瓷的热导率的影响十分显著,随着Mg含量的增加,材料的热导率显著降低,在800 K下降低至1.01 W m^-(1)K^-(1).当镁硅摩尔比为2.1∶1时,硅化镁陶瓷在800 K下呈现出最高的ZT值~0.063.本工作表明过量的Mg有助于改善硅化镁的热电性能,同时以光伏废硅粉为原料制备硅化镁热电陶瓷是可行的,同时能够达到二次利用光伏废硅粉产生高附加价值的目的,对环境保护和资源再利用有一定重要意义.

印度高硅铁矿粉烧结性能试验研究

对印度高硅铁矿粉进行了理化性能的检测分析,根据鞍钢实际原料条件开展了印度高硅铁矿粉与鞍钢自产铁精矿的烧结杯配矿试验研究。实验结果表明,印度高硅铁矿粉矿配比对烧结矿转鼓强度和利用系数的影响较大,随着印度高硅铁矿粉矿配比的增加,烧结矿的成品率降低、燃耗增加,烧结矿[10,40)mm粒级占比降低、(0,5)mm粒级占比升高,烧结矿的低温还原粉化指标变差。综合考虑烧结生产各技术指标,印度高硅铁矿粉的的最佳配比为10%~20%。从提高低温还原粉化指标角度,印度高硅铁矿粉的的最佳配比10%左右为宜。

不同引发体系合成有机硅-聚苯乙烯核壳结构微球的研究

以羟基硅油、苯乙烯为主要原料,采用半连续乳液聚合方法制得具有核壳结构的有机硅-聚苯乙烯聚合物乳液,将其进行喷雾干燥制得聚合物粉末,考察了3种不同引发体系对聚合物乳液稳定性和单体转化率的影响,并对其进行了红外光谱、透射电子显微镜分析。结果表明,3种引发体系均成功合成了有机硅-聚苯乙烯共聚物,且制得的聚合物乳液有较明显的核壳结构和较好的稳定性;采用过硫酸铵、亚硫酸氢钠和过氧化二苯甲酰组成的复合引发体系(APS+NaHSO3+BPO)制备的聚合物乳液单体转化率最高,可达93.24%。对由APS+NaHSO3+BPO复合引发体系制备的聚合物粉末进行了扫描电镜和热失重表征,结果显示,在-50~180℃内有机硅-聚苯乙烯粉末没有明显的失重峰,在500~580℃区间内,粉末热失重达61.91%,表明该聚合物具有良好的耐高低温性能,可在较宽温度范围内使用并仍旧保持良好的性能。

矿物掺合料抗冲耐磨混凝土性能比对试验研究

为了研究矿物掺合料对混凝土性能的影响,对掺硅粉混凝土、掺HF外加剂混凝土、复掺硅粉和HF外加剂混凝土的拌合物性能、抗压强度、抗冲耐磨性能以及收缩性能进行比对试验,分析了几种不同组合下抗冲耐磨混凝土性能的差异。结果表明:混凝土中掺入硅粉或HF外加剂都能够提高混凝土的力学性能及抗冲磨性能,增长幅度随着硅粉和HF外加剂掺量的增加而增加;硅粉混凝土的早期收缩变形大,HF外加剂对混凝土的干缩变形性能没有明显影响;复掺HF外加剂和硅粉可以显著提高混凝土的力学性能及抗冲磨性能,发挥了硅粉和HF外加剂各自的优势,HF外加剂的加入可以改善硅粉对混凝土拌合物和易性的影响,但并未全面遏制硅粉混凝土收缩变形大的劣势,后期还应考虑通过其他手段来减小混凝土的收缩变形,提高混凝土的抗裂性能,以期获得更好的应用效果。研究成果可为硅粉混凝土、HF混凝土、复掺硅粉及HF外加剂在水利水电工程的抗冲耐磨混凝土中的应用提供参考。