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.

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%.

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。

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.

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。

Review on Enhancement of Nitridation of Si Powder

This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.

硅肥和磷矿粉复配对垃圾填埋场重金属污染土壤的修复

以四川省盐亭县云溪镇垃圾填埋场的紫色土为研究对象,将不同质量分数的硅肥(Si1:0.5%,Si2:1.0%)和磷矿粉(P1:0.2%,P2:0.4%,P3:1.0%)复配添加到土壤中培养90 d,研究钝化培养前后重金属Cd、Cu、Pb、Zn有效态含量的变化,并利用风险评价系数(risk assessment code,RAC)评价土壤修复效果。结果显示,高硅处理(Si2:1.0%)相比于低硅处理(Si1:0.5%)能显著降低重金属有效性,其中,Si2P3处理对Cd、Cu、Pb、Zn的钝化率最高,分别为30.79%、27.27%、27.13%、36.88%;Si2P1和Si2P2处理之间没有显著差异,而Si2P1处理可以显著降低重金属浸出毒性量和RAC。研究表明,复配钝化剂主要通过提高土壤pH和EC值,增强O-Si-O、Si-O-Si、H_(2)PO_(4)^(-)、PO4^(3-)等官能团的络合沉淀作用促使重金属由高活性的弱酸提取态、可还原态向低活性的可氧化态、残渣态转化。综合来看,Si2P1处理钝化剂施用量更低,更适合用于垃圾填埋场重金属污染土壤的修复。

低硅铁尾矿制备轻质泡沫混凝土试验研究

为解决低硅铁尾矿堆存量大、利用困难等问题,以杨家湾尾矿库内低硅铁尾矿为矿物掺和料,水泥为胶凝材料,Al粉为发泡剂,制备轻质泡沫混凝土,并考察了水泥掺量、水料比、发泡剂Al粉掺量、激发剂CaO掺量等因素对泡沫混凝土性能的影响。结果表明:在铁尾矿掺量55%、Al粉掺量0.14%、CaO掺量5%、聚丙烯纤维掺量0.3%、稳泡剂掺量0.25%、水料比0.55的条件下,经20±1℃恒温恒湿养护28d,可制备出抗压强度1.84MPa、干密度768.61kg/m^(3)、比强度2.394×10^(-3)Nm/kg的轻质泡沫混凝土,综合性能良好,符合JG/T266—2011《泡沫混凝土》之A08干密度等级、C1强度等级要求。机理分析表明:孔隙率的过度提高会破坏制品内部的孔隙结构,对制品强度造成负面影响;铁尾矿的添加有助于混匀料浆,促进Ca(OH)2的生成,为料浆进一步创造碱性环境,促进钙矾石、C—S—H凝胶等水化产物的生成,其与铁尾矿的交织分布会支撑起孔隙结构,改善力学结构,使泡沫混凝土即使在较低密度下仍表现出较好的力学性能。

基于炭/炭复合材料加工余料制备碳化硅粉末的组织及性能

以炭/炭复合材料加工余料为碳源,与硅粉充分混合,通过高温合成法制备单晶生长用碳化硅粉末,并对其显微组织和表面性能进行研究。结果表明:制备出的碳化硅粉末晶型为β-SiC,部分继承了炭/炭复合材料加工余料的管槽状、脊状结构。在拉曼光谱中,该粉末的折叠横光与折叠纵光的半峰全宽之比为0.709,其相对纯度高于以石墨粉为碳源同工艺制备的碳化硅粉末。该碳化硅粉末具有多孔特征,比表面积为25.7426 m^(2)/g,可用于物理气相传输单晶生长工艺,且已初步验证其可行性。

添加改性纳米碳和碳化硅颗粒对芒硝相变材料吸光、透光性能的影响

【目的】研究改性纳米碳颗粒和碳化硅颗粒对芒硝相变复合材料吸光性能和透光性能的影响。【方法】改性纳米碳粉和改性纳米碳化硅粉与芒硝相变材料结合,制备纳米颗粒芒硝复合相变材料,讨论不同波长对复合相变材料吸光、透光性和分散稳定性的影响;分散稳定性利用鞘流法图像仪对纳米颗粒进行分析,稳定性通过在50℃和室温下进行7 d静置后观察确定;采用积分反射仪分析相变材料吸光、透光性。【结果】鞘流法图像分析发现,改性纳米碳粉和改性纳米碳化硅粉形貌结构基本无变化且没有团聚现象,静置观察发现没有出现纳米颗粒分层和团聚现象;添加质量分数分别为0.1%、 0.5%、 1.0%的改性碳粉后,相变材料对紫外光的平均吸光度提高20%-35%,可见光的平均透过率下降26%-35%,红外光(波长为800-1 500 nm)的透光率下降10%-42%;分别添加相同质量分数的改性碳化硅后,相变材料对紫外光的平均吸光度提高22%-26.6%,可见光的平均透过率下降20%-29%,红外光(波长为1 500-2 700 nm)的透光率提高8%-29%。【结论】改性纳米颗粒在芒硝基相变材料中具有良好的分散性和稳定性;通过在传统芒硝基相变材料基础上添加不同含量的改性纳米颗粒,获得的纳米颗粒芒硝基相变材料对不同波长光的吸光率和透光率的基础性数据,为高性能纳米颗粒芒硝相变材料快速光热响应的研究打下基础。