Effects of Pore-forming Agents on Properties of Silicon Carbide Porous Ceramics Prepared from Crystalline Silicon Cutting Waste

SiC powder was rapidly synthesized in an induction furnace with crystalline silicon cutting waste and active carbon as raw materials,and then SiC porous ceramics were prepared at 1600 t for 4 h with carbon embedded using the powder as raw material,the starch and the graphite as pore-forming agents.Effects of additions of different pore-forming agents on the phase composition,microstructures,physical properties,and cold crushing strength of the porous ceramics were investigated.The results show that the main crystalline phases of the synthetic powder areα-S iC(6H-SiC)andβ-SiC(3C-SiC).The phase composition of the porous ceramics includesα-S iC(6H-SiC),β-SiC(3C-SiC),FeSi,quartz and Si2N20.The apparent porosity and closed porosity of the porous ceramics prepared by adding starch are higher,and the cold compressive strength of the porous ceramics added with graphite is higher.As increasing the additions of the starch,the apparent porosity,closed porosity and linear shrinkage ratio of the porous ceramics increase,and the bulk density decreases correspondingly.When 20 mass%starch is added,the apparent porosity,closed porosity,linear shrinkage ratio and cold compressive strength are 57.05%,2.03%,5.10%and 10.20 MPa,respectively.

Forms of phosphorus and silicon in the natural grain size surface sediments of the southern Bohai Sea

The forms of phosphorus and silicon in the natural grain sizes surface sediments of the southern Bohai Sea were studied. In sediments, the organic matter bound form of phosphorus was the main form of transferable phosphorus and ranged from 0.37 μmol/g to 1.57 μmol/g, accounting for 10.7% of the total phosphorus, others were the carbonate bound form, iron manganese oxide bound form and ion exchange able form; the transferable form of phosphorus accounted for 19.2% of the total phosphorus. Silicon’s carbonate bound form was predominant over others among its transferable forms, and content ranged from 1.55 μmol/g to 8.94 μmol/g, accounting for 0.05% of the total silicon; the total amount of transferable silicon forms accounted for only 0.12% of the total silicon. Therefore, 19.2% of the total phosphorus and 0.12% of the total silicon contained in the surface sediments of the southern Bohai Sea could participate in the biogeochemical cycling.

Deformation Behavior of Zr_(65)Cu_(17.5)Ni_(10)Al_(7.5)in Superplastic Forming with Silicon Mould: Simulation and Application

We investigated the deformation behaviors of Zr_65Cu_17.5Ni_10Al_7.5 in superplastic forming in silicon mould via numerical modeling and experiments. The data needed for the constitutive formulation were obtained from compressive tests to establish a material library for finite-element simulation using a DEFORM 3D software. A constant speed forming process of a micro gear was modeled where the loading force, feature size and amount of deformation in the micro gear in silicon mould were analyzed in detail for the optimal requirements of micro gear forming and the protection of silicon mould. Guided by the modeling parameters, an amorphous metal micro gear was successfully obtained by our home-made superplastic forming system with the optimized parameters （temperature of 683 K, top speed of 0.003 mm/s until the load force reaching limiting value at 1960 N, and a gradually decelerating process for holding the force to the end）. Our work gives a good example for optimization of superplastic forming and fabrication of BMGs in microparts.

Effects of light-mass structural forms on silicon carbide mirror

To reduce the mass of the mirror,silicon carbide was used as the material and four light-mass structures were designed. The properties of SiC mirror open back structure with triangular cell,open back structure with hexagonal cell,sandwich structure with triangular cell,sandwich structure with hexagonal cell,were analyzed by using finite element method. The results of the static,dynamic,and thermal properties of the four kinds of SiC mirror indicate that the surface figures of the SiC mirrors are all satisfactory with the design requirements. The properties of the mirrors with sandwich structure are better than those with open back structure,except the high cost. And the mirror with triangular cell has better combination properties than the mirror with hexagonal cell. Considering the overall performance and the cost,open back structure with triangular cell is the most suitable for the SiC mirror.

Geochemical Tracing of Ore-forming Material Sources of Carlin-type Gold Deposits in the Yunnan-Guizhou-Guangxi Triangle Area --A Case Study of the Application of the Combined Silicon Isotopes Geochemistry and Siliceous Cathodoluminescence Analysis

Abstract This paper deals with characteristics of silicon isotope compositions and siliceous cathodoluminescence of host rocks, ores and hydrothermal silicified quartz of the Carlin-type ore deposits in the Yunnan-Guizhou-Guangxi triangle area. The study shows that primary silicified quartz is nonluminescent but quartz in host rocks and secondary silicified quartz are luminescent by the action of cathode rays. Correspondingly, silicon isotope compositions of host rocks, ores and hydro6thermal quartz veins are clearly distinguished. In strata from the Middle Triassic to the “Dachang” host bed, δ30Si of the host rocks ranges from 0.0% ?0.3%, while that of primary ore-forming silicified fluids from ?0.1% to ?0.4%; in the Upper Permian and Lower Carboniferous strata and Indosinian diabase host beds, δ30Si of the host rocks is from ?0.1% to ?0.2% and that of the primary silicified quartz veins from 0.3 % ?0.5 %. This pattern demonstrates the following geochemical mineralization process, primary ore-forming siliceous fluids migrated upwards quickly along the main passages of deep-seated faults from mantle to crust and entered secondary faults where gold deposits were eventually formed as a result of permeation and replacement of the siliceous ore-forming fluids into different ore-bearing strata. This gives important evidence for the fact that ore-forming fluids of this type of gold deposits were mainly derived from upper mantle differentiation and shows good prospects for deep gold deposits and geochemical background for large and superlarge gold deposits.

酸化与富磷影响农田土壤硅的移动性

硅是水稻等禾本科作物生长发育不可或缺的营养元素,pH影响着土壤中硅的有效性和形态转化,而土壤磷与硅之间存在明显的竞争吸附效应。以常年水稻-瓜/菜轮作农田土壤为研究对象,进行等摩尔硅磷竞争吸附试验、土壤培养试验和硅分组试验,模拟探究土壤酸化和磷富集对土壤硅的有效性及移动性的影响,以期为农田硅、磷养分管理提供一定的理论依据。结果表明,在pH 3.5~6.4范围内,同时加入等摩尔浓度的硅和磷时,磷的存在会抑制土壤吸附硅,使土壤对硅的吸附量降低78%~350%。土壤对硅的吸附小于对磷的吸附,磷的添加导致了土壤中硅的解吸。土壤酸化和磷添加均降低了土壤对硅的吸附,且在pH较高时添加磷对降低土壤吸硅的效果更为显著。土壤酸化降低了可移动态硅、吸附态硅、有机结合态硅和铁铝锰(氢)氧化物结合态硅的含量,但增加无定形态硅含量。与pH 6.4相比,酸化使可移动态硅和吸附态硅含量分别降低了22.47%~54.32%、10.72%~33.40%;磷添加使可移动态硅含量增加了4.07%~9.40%,吸附态硅含量降低了1.19%~3.53%。pH可调控土壤硅的溶解与吸附-解吸过程,从而影响土壤硅的移动性;磷富集促进土壤吸附态硅的解吸,进而增强土壤硅的移动性。

改性木屑和稻壳生物炭对土壤镉形态和水稻镉吸收的影响

【目的】农田镉(Cd)污染对人类健康构成严重威胁,探究不同改性生物炭对我国南方Cd污染农田中Cd形态变化及其在水稻中的富集特征的影响,为南方红壤性水稻土的安全利用和农业发展提供科学依据。【方法】以木屑和稻壳制成木屑生物炭(WCBC)和稻壳生物炭(RHBC),并用KOH和K_(2)SiO_(3)进行改性,共得4种改性生物炭,KOH改性的木屑生物炭(WCBC-KOH)和稻壳生物炭(RHBC-KOH),K_(2)SiO_(3)改性的木屑生物炭(WCBCK_(2)SiO_(3))和稻壳生物炭(RHBC-K_(2)SiO_(3))。通过盆栽试验,研究不同生物炭和添加量(0.25%、0.5%、1%)对红壤性水稻土的影响,包括化学性质(pH和有效硅)、Cd形态、水稻生物量、各组织的Cd富集和硅含量的影响。【结果】6种生物炭均能提高水稻土pH和有效硅含量,且随添加量的增加而增加。添加生物炭减少了土壤中可交换态Cd含量,同时增加了土壤中残渣态Cd含量,导致土壤中Cd的生物有效性和流动性显著降低,进而减少水稻对Cd的吸收。此外,添加生物炭还可以提高水稻地上部干物质重和产量,同时还显著增加了水稻地上部各组织的硅含量。相关分析表明,土壤pH和有效硅含量与可交换态Cd和水稻各组织Cd含量极显著负相关,且土壤pH降镉作用大于土壤有效硅的作用。【结论】6种生物炭均可使土壤中Cd向植物难利用形态转化,同时促进水稻生长和提高水稻产量,添加KOH和K_(2)SiO_(3)改性生物炭的效果要优于未改性生物炭。

自成形硅表面微结构:表面特征及潜在应用

采用等离子体增强化学气相沉积法(Plasma Enhanced Chemical Vapor Deposition, PECVD)制备掺氢非晶硅膜,并对其表面结构学进行研究。该文发现在晶体硅衬底上沉积非晶硅薄膜时,会在表面形成非均匀分布的起泡缺陷。在已制备的非晶硅薄膜上进一步沉积了氮化硅/非晶硅的交替层,在起泡缺陷原位形成了一个完美的穹顶多壳的微结构,并且没有明显的结构坍塌。该文总结了自成形穹顶微结构的3个独特的结构特性,并进一步指出了该自成形穹顶微结构在纳米光学和微机电系统中的潜在应用。

大型无人机复合材料舵面整体制造技术

针对大型无人机复合材料舵面整体成型困难的问题,设计了一种金属组合阴模,以及硅橡胶+铝块可拆卸式芯模,采用手工铺贴方式和烘箱固化成型工艺,制备出内、外表观良好的舵面,且工艺稳定、制造简便、成本较低,结果验证了该方法的可行性和有效性。

瓷化粉形貌对陶瓷化硅橡胶性能的影响

为提升硅橡胶材料的本质安全,分别以硅灰石C-S6-A、C-S6-B和C-S6-C为瓷化粉,制备陶瓷化硅橡胶复合材料,研究瓷化粉形貌对陶瓷化硅橡胶复合材料性能的影响。实验结果表明:C-S6-B的粒径最大,为不规则的棒状,C-S6-A和C-S6-C的粒径相对较小,主要为不规则的片状;棒状形貌瓷化粉制备得到的陶瓷化硅橡胶复合材料的初始分解温度最高,达到488.9℃,极限氧指数值最高,为29.0%,拉伸强度最大,为7.30MPa,撕裂强度最大,为16.7kN/m,在高温下能形成更加紧实、致密的陶瓷体;与片状形貌的瓷化粉相比,使用棒状形貌瓷化粉制备得到的陶瓷化硅橡胶复合材料有着更佳的热稳定性、阻燃性能、力学性能和成瓷性能。

Semisolid forging electronic packaging shell with silicon carbon-reinforced copper composites

To fabricate electronic packaging shell of coppermatrix composite with characteristics of high ther mal conductivity and low thermal expansion coefficient, semisolid forming technology, and powder metallurgy was combined. Conventional mechanical mixing of Cu and SiC could have insufficient wettability, and a new method of semisolid processing was introduced for billets preparation. The SiC/Cu composites were first prepared by PM, and then, semisolid reheating was performed for the successive semisolid forging. Composite billets with SiC 35 % vol ume fraction were compacted and sintered pressurelessly, microstructure analysis showed that the composites pre pared by PM had high density, and the combination between SiC particles and Cualloy was good. Semisolid reheating was the crucial factor in determining the micro structure and thixotropic property of the billet. An opti mised reheating strategy was proposed： temperature 1,025 ℃and holding time 5 min.

Preparation and dielectric properties of porous silicon nitride ceramics

Porous silicon nitride ceramics with difference volume fractions of porosity from 34.1% to 59.2% were produced by adding different amount of the pore-forming agent into initial silicon nitride powder. The microwave dielectric property of these ceramics at a frequency of 9.36 GHz was studied. The crystalline phases of the samples were determined by X-ray diffraction analysis. The influence of porosity on the dielectric properties was evaluated. The results show thatα-Si3N4 crystalline phase exists in all the samples while the main crystalline phase of the samples isβ-Si3N4, indicating that theα/βtransformation happens during the preparation of samples and the transformation is incomplete. There is a dense matrix containing large pores and cavities with needle-shaped and flakyβ-Si3N4 grains distributing. The dielectric constant of the ceramics reduces with the increase of porosity.

Strength and elongation of spray formed Al–Si–Pb alloys

The strength and elongation to fracture of spray deposited Al-Si-Pb alloys were studied as a function of lead content, silicon content, and distance from the centre to periphery of the deposit. It is found that the ultimate tensile strength, proof stress and elongation to fracture decrease, linearly and exponentially, with the increase in lead content and porosity of the deposit, respectively. Both the strengths and elongation to fracture linearly increase with increasing distance from the centre to periphery of the deposit. The ultimate tensile strength and proof stress are higher at a higher silicon content and they have a linear relationship with the hardness of the deposit.

Microstructure and mechanical properties of A356 thixoformed alloys in comparison with gravity cast ones using new criterion

The effect of thixoforming process on morphologies of silicon particles that affect fracture mode of A356 alloy was investigated.Microstructure and fracture surfaces of thixoformed samples were investigated by image analyzing technique and scanning electron microscopy.A new combination parameter, called silicon density ratio (SDR) index, was introduced.SDR index approximates the collective effects of morphological characteristics of silicon particles on microstructure transparency of alloy in crossing the dislocation.It is suggested that samples with lower SDR index have superior mechanical properties, especially elongation, and consequently intergranular fracture mode.On the contrary, samples with higher SDR index have inferior mechanical properties and fracture path tends to propagate along the cell boundaries leading to transgranular fracture.

Preparation of SiC Porous Ceramics by Crystalline Silicon Cutting Waste

SiC porous ceramics were prepared at 1 400 ℃ for4 h with crystalline silicon cutting waste and activated carbon as main starting materials and NH4HCO3 as the pore-forming agent. Effects of NH4HCO3 additions( 0,20%,30%,40%,by mass) on the phase composition,microstructure,sintering properties,cold compressive strength and thermal shock resistance of as-prepared Si C porous ceramics were investigated. The results show that:( 1) addition of NH4HCO3 remarkably influences the apparent porosity and cold compressive strength of specimens. The apparent porosity achieves its maximum value( 63. 40%) when 40% NH4HCO3 is added,while the minimum cold compressive strength is 4. 77 MPa;( 2) the specimen with 40% NH4HCO3 has the best thermal shock resistance. The thermal cycling times between1 000 ℃ to room temperature reach 62;( 3) the addition of NH4HCO3 does not remarkably affect the phase composition of the specimens;( 4) the specimens include a large number of SiC particles and a small amount of SiC whiskers.

郭岩山不同海拔天然栲树林土壤硅形态特征

[目的]探究郭岩山不同海拔天然栲树林土壤硅形态的变化特征及其与土壤理化性质的相关关系,进一步揭示亚热带地区土壤硅形态含量对环境变化的响应机制。[方法 ]本研究以郭岩山自然保护区不同海拔天然栲树林土壤为研究对象,在郭岩山自然保护区海拔600、700、800、900 m分别设置标准地,采集不同海拔各土层(0~20、20~40、40~60 cm)的土样,测定土壤不同硅形态含量,分析环境变化对土壤中硅形态的影响。[结果 ](1)高海拔土壤有效硅(258.26 mg·kg^(-1))、水溶性硅(155.69 mg·kg^(-1))、活性硅(388.97mg·kg^(-1))及无定形硅(1 561.97 mg·kg^(-1))含量均显著高于低海拔土壤有效硅(93.16 mg·kg^(-1))、水溶性硅(78.38 mg·kg^(-1))、活性硅(231.84 mg·kg^(-1))及无定形硅(832.24 mg·kg^(-1))。深土层(40~60 cm)的土壤有效硅含量(227.53 mg·kg^(-1))显著高于0~20 cm(120.79 mg·kg^(-1))及20~40 cm(171.37 mg·kg^(-1))土层;(2)土壤有效硅含量与活性硅及水溶性硅含量呈极显著正相关,其中,活性硅是有效硅增加最重要的直接贡献形态,而水溶性硅是土壤硅转化过程中重要的过渡性形态;(3)土壤有机质和土壤pH值对各土壤硅形态含量的影响最显著,解释率分别达14.1%和9.2%,其中,土壤有机质与无定形硅及水溶性硅呈正相关,与土壤活性硅及有效硅呈负相关,而土壤pH值与有效硅、活性硅呈正相关,与无定形硅呈负相关。[结论 ]海拔引起的环境及土壤理化性质变化可改变土壤硅形态含量。研究结果为天然栲树林有效利用土壤硅及调控土壤硅形态提供了参考依据,对天然栲树林的保护具有重要的科学指导意义。

基于第一性原理的Si掺杂磁铁矿稳定性研究

磁铁矿中出现的杂质元素及其赋存形式具有很好的环境指示意义。Si是磁铁矿中常见的杂质之一,尽管Si与Fe在离子半径、化合价、置换能量效应等方面均存在较大差别,但无论磁铁矿的原位成分数据还是湿法化学分析数据均表明,磁铁矿中含有一定数量(热液环境中生成的磁铁矿晶体的SiO_(2)的质量分数可达6.19%)的Si。为探究Si在磁铁矿中是否能稳定存在及其具体存在位置,在VASP中建立Si在磁铁矿中不同位置的模型,然后利用密度泛函理论第一性原理计算Si在磁铁矿晶体中不同位置的形成能,以此判断Si在磁铁矿晶体中的稳定性。结果表明,Si替代磁铁矿八面体中心的Fe的掺杂形成能为-4.13 eV,替代四面体中心的Fe的掺杂形成能为-3.85 eV。值得注意的是,1个磁铁矿原胞内2个Fe^(3+)(四面体中心)全部被Si替代的形成能为-8.87 eV。从掺杂形成能的角度来看,Si在磁铁矿四面体及八面体的中心位置均可存在,但Si代替四面体中心位置的全部Fe^(3+)得到的结构最稳定。

炭黑和造孔剂对反应烧结碳化硅性能的影响

为提高反应烧结碳化硅的力学性能,以碳化硅微粉(55~44和5.0~3.5μm)和炭黑为原料,羧甲基纤维素纳(CMC)和羟丙基甲基纤维素(HPMC)为造孔剂,经1740℃保温1 h制备了反应烧结碳化硅陶瓷。研究了炭黑添加量(加入质量分数分别为5%、7.5%、10%、12.5%、15%)及不同质量比的造孔剂对反应烧结碳化硅物理性能的影响,并进行XRD和光学显微镜分析。结果表明:1)当炭黑添加量(w)从5%增加到15%时,材料弯曲强度从172 MPa升高到258 MPa,断裂韧性从3.31 MPa·m^(1/2)升高到3.77 MPa·m^(1/2);2)造孔剂能够优化游离Si的分布,当炭黑添加量为15%(w),造孔剂CMC与HPMC质量比为1.5∶4.5时,反应烧结碳化硅具有优异的力学性能,其弯曲强度为268 MPa,断裂韧性为4.42 MPa·m^(1/2)。

施用钢渣对水稻土硅素肥力的影响

施用钢渣种植水稻的盆栽试验结果表明,与对照相比,施用钢渣使土壤pH升高,土壤水溶态硅和无定形硅的含量下降,活性硅及有效硅含量上升,水稻植株含硅量增加。除水溶态硅外,上述影响均随钢渣用量增加或粒度变细而增强。

硫硅配施对土壤铜形态和水稻吸收铜的影响

铜是江西省农田中主要重金属污染物之一,为减轻和控制铜对水稻生长的危害,提高水稻产量和品质,通过盆栽试验,研究不同硫肥(0、30、60、90 kg·hm-2,以S计)与硅肥(0、0.5、1.0、1.5 g·kg-1,以Si计)配施对水稻吸收铜及土壤铜形态的影响。结果表明:(1)在铜污染的农田中施用硫、硅肥都能降低土壤中酸可提取态Cu含量,提高残渣态Cu的含量,但土壤铁锰氧化物结合态Cu和有机物/硫化物结合态Cu含量因硫、硅用量不同而存在差异;(2)硫、硅各处理可通过促进铜在水稻根部累积或减少土壤有效态Cu的含量,减少铜在茎、叶、糙米中的吸收累积。从对糙米中铜含量及产量的影响可知,硫用量30 kg·hm-2和硅用量1.0 g·kg-1互作效果最佳,在生产上具有应用前景。