碳电热还原法熔炼一次铝硅合金的反应过程

以Al2O3尾矿和烟煤为原料,在碳管炉内进行了一次铝硅合金熔炼,采用X射线衍射光谱对不同温度不同加碳量反应后的产物进行物相分析,探讨了由尾矿生产一次铝硅合金的反应过程并获得了合格的一次铝硅合金产品. 结果表明,尾矿加烟煤在碳管炉内还原时,在较低温度(<1600℃)下,尾矿中的SiO2与C反应生成SiC,当温度上升到1700~1800℃时,尾矿中的Al2O3开始与C反应生成铝氧碳化物,当温度继续升高到1800℃以上时,在较低温度生成的铝氧碳化物被SiC分解,生成铝和硅,成为一次铝硅合金,最终获得的一次铝硅合金含铝量达40%以上.     

多硅晶还原生产过程废料处理研究现状

介绍了改良西门子法的多晶硅还原生产工艺和硅晶生产过程中的废料的来源,阐述了近年来的多晶硅生产过程中废料的处理技术的研究现状,指出当前的回收处理方法多为酸碱法存在的缺点,安全、环保、经济、节能的回收处理方法应成为当前多晶硅还原生产过程废料处理研究关注的重点。     

高铝煤矸石铝硅分级提取实验研究

分级研究了热活化条件下高铝煤矸石在盐酸和氢氧化钠溶液中的铝硅溶出行为。采用X射线衍射仪（XRD）、扫描电镜（SEM）和比表面积测定仪（BET）对煤矸石试样做了表征分析。通过正交实验分析了反应温度、反应时间、初始酸碱浓度和固液比对热活化处理后高铝煤矸石中Al2O3和酸浸渣SiO2溶出率的影响。结果表明：酸浸溶出Al2O3反应过程中,固液质量比和酸浸时间对溶出率的影响最为显著,酸浸过程的最优工艺条件：初始盐酸质量分数为20%、酸浸温度为90 ℃、酸浸时间为2.5 h、固液质量比为1∶6,在此条件下,Al2O3的浸取率达82.95%;强碱溶解酸浸渣溶出SiO2反应过程最优工艺条件：碱溶温度为95 ℃、碱溶时间为2.0 h、NaOH质量分数为20%、固液质量比为1∶10,在此条件下SiO2溶出率为69.74%,碱溶温度和碱液浓度对溶出率的影响最为显著。     

原生多晶硅切割方硅芯技术研究

硅芯作为多晶硅生产过程中还原炉沉积生长所用的载体,目前主要有硅芯炉拉制圆硅芯和线切割方硅芯两种生产方式,通过对圆硅芯和方硅芯多方面进行对比分析,因为圆硅芯在硅芯基料熔化凝固的拉制过程中特别容易受到一些杂质污染,所以重点对原生多晶硅棒切割方硅芯进行研究,方硅芯是由原生多晶硅棒直接切割而成,减少了外界杂质的污染,有利于减少...     

碱激发剂中钠、硅对CFB飞灰合成地聚物的影响

以偏高岭土掺加石灰石和石膏模拟循环流化床(CFB)飞灰,研究了不同SiO2/Al2O3和Na2O/Al2O3对烧粘土材料合成地聚物过程中,凝结时间和抗压强度的变化规律;借助X射线衍射和拉曼图谱分析,证明了CFB合成地聚物过程中存在10种主要化学反应.同时发现:碱激发剂中钠含量变化主要影响活性硅、铝单体数量的多少,活性硅含量增加更有利于生成CSH和(Na,Ca)-PSS型地聚物;在SiO2-Al2O3-CaO-Na2O体系中,当Na2O/Al2O3≥1.1时,反应体系因生成水化石榴石而改变地聚反应历程,进而对样品抗压强度产生负效应;SiO2/Al2O3≥3.0时,样品凝结迅速,不利搅拌.     

埋炭气氛下碳热、铝热、硅热还原TiO2反应的热力学分析

通过热力学计算,探讨了埋炭气氛下碳热、铝热和硅热还原TiO2生成Ti(C,N)的可能性、生成途径、生成产物的相对稳定性以及对3种还原反应进行了对比.结果表明:埋炭气氛下,3种还原反应均可发生且生成的钛的非氧化物是以Ti(C,N)形式存在;在铝热和硅热反应中,不稳定的中间产物AlN和Al4C3会转为稳定的刚玉相,而Si3N4则转化为稳定的碳化硅或方石英;通过比较发现,碳热还原TiO2法是制备钛的非氧化物陶瓷最经济有效的方法.     

碳热还原镁橄榄石合成MgO-SiC复合粉体的热力学研究

本文对碳热还原镁橄榄石合成MgO-SiC复合粉体进行了热力学研究,结合实验,分析了反应的中间过程,对合成粉体具有重要的指导意义.热力学分析表明:当T=1923 K时,所形成的产物,从容易到困难排序依次为:MgO+SiC,MgO+Si,MgO+SiO,Mg+SiC,Mg+Si,Mg+SiO,Mg+SiO2;增大惰性气体流速,降低CO的分压,可以降低镁橄榄石解构温度.在不同氩气流量下的实验证明,增大氩气流量,促进了镁橄榄石的碳热还原反应,有益于MgO-SiC复合粉体的合成.以镁橄榄石与炭黑物质的量比为1∶5配料,混合均匀后,在氩气保护下,在气体流量分别为100 mL/min,300 mL/min,500 mL/min时,1650℃保温3h合成粉体.用X射线衍射仪(XRD)测试合成的物相,用扫描电子显微镜(SEM)观察各物相形貌.实验结果表明,合成的产物MgO为八面体,SiC为条形.过程分析表明,碳还原镁橄榄石生成MgO和SiO,是合成复合粉体的重要中间过程.     

煤矸石/粉煤灰对赤泥钠化还原焙烧反应的影响机制

煤矸石或粉煤灰与赤泥协同钠化还原焙烧均可实现其所含铁、铝、硅等元素的形态转化,使其易于分离回收;但对于它们分别与赤泥协同钠化还原焙烧反应差异性及机制的研究目前尚未见报道。采用X射线衍射分析方法,分别考察了煤矸石-赤泥、粉煤灰-赤泥体系钠化还原焙烧过程中,气氛类型、钠助剂添加量、焙烧温度、焙烧时间对还原焙烧产物物相组成的影响规律,并对两个反应体系中铁磁化效果及铝硅活化效果的差异性进行分析。结果表明：在钠化还原焙烧过程中,煤矸石-赤泥、粉煤灰-赤泥体系均可同步实现含铁物相的磁化和铝硅物相的活化,且随着钠助剂添加量、焙烧温度、焙烧时间的变化,含铁物相和铝硅物相呈现规律性变化;在相同铁磁化和铝硅活化效果前提下,煤矸石-赤泥体系所需钠助剂添加量、焙烧温度和焙烧时间均略低于粉煤灰-赤泥体系,这主要与煤矸石、粉煤灰中所含还原性物质和铝硅矿物的赋存形态、含量及微观结构有关。研究将为煤矸石、粉煤灰等煤基固废与赤泥协同钠化还原焙烧回收有价元素的原料筛选提供理论指导。     

掺铝钕高硅氧玻璃的制备及光谱性能研究

采用分相酸溶工艺制备了Na2O-B2O3-SiO2体系纳米多孔玻璃,并以此为基质进行了钕铝掺杂的实验,制备了掺钕铝高硅氧玻璃,光谱分析表明,所制得的玻璃在1064 nm附近有明显的发射峰.研究了掺杂浓度、烧结气氛对玻璃光谱性能的影响,分析了铝离子在共掺杂玻璃中的作用.结果表明在浓度为0.2 mol/L的Nd(NO3)3溶液中制备的掺杂高硅氧玻璃发光强度最强,还原气氛下烧结的掺杂高硅氧玻璃光谱强度高于在空气中烧结得到的高硅氧玻璃,同时在还原条件下铝离子能够明显的提高玻璃的发光强度.     

铝锌硅合金镀层的耐热性研究

为了解决铝锌硅合金镀层在不同环境中的极限使用温度，研究镀层的耐热性，在200～500℃保温不同时间后，观察表面外观形貌变化，采用SEM和EDS分析镀层截面组织演变和元素成分变化规律。研究表明：铝锌硅合金镀层板在不超过300℃环境中，可以长期使用，镀层组织无明显变化，可以保证镀层的耐腐蚀性能；使用环境温度超过300℃后，铝锌硅合金镀层中的Fe含量直线上升，形成Al-Zn-Fe金属化合物，镀层组织合金化，表面裂纹、鼓泡明显，导致镀层失效。     

封闭处理对镁合金磷酸钡转化膜的影响

在Na2SiO3和NaOH溶液中,研究了封闭处理对AZ91D镁合金磷酸钡转化膜的影响,采用扫描电镜(SEM)和X射线衍射谱(XRD)研究了封闭前后磷酸钡转化膜的表面形貌及其相组成,采用全浸蚀试验和电化学方法检测了膜层的抗腐蚀性能。结果表明,封闭后的磷酸盐转化膜更加平整、致密。与封闭前的转化膜相比,封闭后的转化膜新增了C、Si元素和一些晶态物质,如SiO2、BaSi4O9、Na2SiO3和MgF2。封闭处理可以明显提高镁合金磷酸钡转化膜的抗腐蚀性能。     

Experimental investigation on diamond wire sawing of Si3N4 ceramics considering the evolution of wire cutting performance

When diamond wire saw is used in machining silicon nitride ceramics (Si₃N₄ ceramics), the ultra-hardness of Si₃N₄ causes the saw wire to wear out, which leads to the saw wire cutting performance constantly changing during its life cycle, and thus the machined quality of Si₃N₄ ceramics is affected. Surface roughness and topography are important indicators of the quality of the machined surface. In this paper, the diamond wire saw cutting experiment of Si₃N₄ ceramics was carried out, the effect of the evolution of saw wire cutting performance on the surface roughness and topography of Si₃N₄ ceramics as-sawn slices was investigated based on the analysis of the changes of saw wire wear topography, breaking force, bow angle and kerf loss during the sawing process. The results show that the surface roughness along the saw wire motion direction and the workpiece feed direction tends to decrease and then increase with the evolution of the cutting performance of the saw wire, which accords well with the trend of the as-sawn slices surface morphology. The results of the study can provide experimental reference for the development of high precision diamond wire saw cutting technology for Si₃N₄ ceramics.     

Si_2ON_2-SiC复合材料制备研究

通过Ｓｉ粉、ＳｉＯ２微粉及ＳｉＣ,经氮化反应制备了Ｓｉ２ＯＮ２－ＳｉＣ复合材料,研究了烧结助剂、硅加入量、氮化制度对复合材料性能的影响,并对其进行强度、ＸＲＤ和ＳＥＭ分析后认为材料性能随烧结助剂、硅加入量变化而变化,氮化制度对材料的物相和显微结构有重要影响。     

Synthesis of alumina-bonded polycrystalline diamond by detonation

In this study, nanodiamond, aluminum isopropoxide, and hexogen (RDX) were used as starting materials to synthesize alumina-bonded polycrystalline diamond materials under high-temperature and high-pressure conditions generated by the detonation of the explosive. During detonation, the surface of the nanodiamond is coated with boron, silicon, and chromium through vacuum diffusion. Carbides of boron, silicon, and chromium referred as “bridges” are formed at the diamond/metal interface during the carbonization reaction. The "bridge" formed between diamond and nanoalumina considerably reduced the possibility of oxidation of nanodiamond as well as its graphitization during the detonation reaction. The phase, morphology, microstructure, and elemental composition of the detonation products were characterized by X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The results revealed that the explosion causes alumina and diamond to bond tightly to form alumina-bonded polycrystalline diamond composites. The thermal stabilities of the nanodiamond particles coated with boron, silicon, and chromium were found to be markedly higher, and the diamond phase remained intact even after heating at elevated temperatures. Thus, boron, silicon, and chromium reduced the wetting angle of diamond and alumina and improved the degree of bonding between them. Furthermore, boron facilitated the bonding between nanodiamond and alumina. In contrast, the bond was weaker in the case of silicon. Chromium also aided the bonding of the nanodiamond and alumina but introduced a large amount of oxygen into the composite.     

Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride. I: Effect of Si Powder Characteristics

This paper will present sintered reaction-bonded silicon nitride (SRBSN) material with a high thermal conductivity of 121 W·(m·K)⁻¹, which has been successfully prepared from a coarse Si powder with lower levels of oxygen and aluminum impurities, using a mixture of Y₂O₃ and MgSiN₂ as sintering additives, by nitriding at 1400°C for 8 h and subsequent post-sintering at 1900°C for 12 h at a nitrogen pressure of 1 MPa N₂. This thermal conductivity value is higher than that of the materials prepared from high-purity α-Si₃N₄ powder (UBE SN-E10) with the same additive composition under the same sintering conditions. In order to study the effects of Si powder characteristics on the processing, microstructure, and thermal conductivity of SRBSN, the other type of fine powder with higher native oxygen and metallic impurity (typically Al and Fe) contents was also used. The effects of Si particle size, native oxygen, and metallic impurities on the nitriding process, post-sintering process, and thermal conductivity of the resultant SRBSN materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of SRBSN could be achieved by using higher purity coarse Si powder with lower levels of oxygen and aluminum impurities. In addition, this work also shows that the nitriding temperature has no significant effect on the microstructure and thermal conductivity of SRBSN during post-sintering, although it does affect the characteristics of RBSN formed during nitridation.     

喷射成形硅铝合金镀覆工艺研究

研究了喷射成形硅铝合金(CE11)材料表面化学镀镍和镀金工艺,使用电子显微镜(SEM)及能谱分析仪(EDS)分析了沉积过程中CE11硅铝合金表面形貌和沉积层化学成分,采用热震、高温烘烤、焊接试验等方法检测了硅铝合金样件的镀层质量。结果发现,CE11硅铝合金经氟化氢铵和硝酸混合溶液粗化、超声波去膜、浸锌、预镀镍后化学镀镍,可以获得结合力良好的化学镀层,镀金后能耐400°C烘烤而仍然保持很好的结合力,能够满足金锗、金锡等合金的共晶焊接使用要求。     

Diamond nucleation suppression in chemical vapor deposition process

A systematic study of the effect of different pre-treatments of the Si substrate surface in suppressing diamond nucleation was performed to investigate the nature of the nucleation centers in chemical vapor deposition (CVD) of diamond. The Si substrates were initially scratched with diamond powder and then submitted to one of the following pre-treatments: thermal annealing in high vacuum and in air, deposition of an amorphous silicon film, and ⁸⁴Kr⁺ ion implantation. The pre-treated substrates were used in a hot filament CVD diamond process, and the diamond films obtained were analyzed by different techniques. The results suggest that the observed nucleation reduction under certain pre-treatment conditions is related to modifications induced on the original topographical features of the scratched substrate surface, which would be responsible for the CVD diamond nucleation. The dimensions of these surface features are estimated to be of the order of 5 nm.     

Thermal damage mechanisms of Si-coated diamond powder based polycrystalline diamond

The polycrystalline diamond (PCD) composites were synthesized from Si-coated diamond or diamond powder mixtures with Si. The characterizations of phase structures, morphologies and thermal stability of PCD were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The thermal damage mechanisms of PCD were studied under air condition up to 750 ℃ by thermal weight loss, XRD, SEM and wear tester. The results showed that the PCD was successfully synthesized by the Si-coated diamond with a homogeneous structure. The thermal stability and wear resistance of PCD with Si-coated diamond were better than those of PCD with uncoated diamond. It was determined that the chemical thermal damage mechanism with oxidation reaction dominated the damage of the PCD after high temperature annealing and the physical thermal damage mechanism also took effect on the exfoliation of binder and fine diamond grains from PCD.     

Preparation of Si–diamond–SiC composites by in-situ reactive sintering and their thermal properties

This article described a novel method of preparation of Si–diamond–SiC composites by in-situ reactive spark plasma sintering (SPS) process. The relative packing density of Si–diamond–SiC composite was 98.5% or higher in a volume fraction range of diamond between 20% and 60%. Si–diamond–SiC composites containing 60 vol% diamond particles yielded a thermal conductivity of 392 W/m K, higher than 95% the theoretical thermal conductivity calculated by Maxwell–Eucken's equation. Coefficients of thermal expansion (CTEs) of the composites are lower than the values of theoretical models, indicating strong bonding between the diamond particle and the Si matrix in the composite. The microstructures of these materials were studied by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). As a result of reaction between diamond and silicon, SiC phase formed.