激光闪射法测量耐火材料的热物理性能

介绍了应用激光闪射法测量耐火材料比热容、热扩散系数以及导热系数等热物理性能的原理,列举应用实例说明了测试方法,并且讨论了影响实验数据准确性的因素。     

微米级超薄石墨膜的导热性能测试

本文采用激光闪射法测量超薄石墨膜(几十微米厚度)的导热性能。由于石墨薄膜平面方向的热导率远高于厚度方向的热导率,通过特殊的In-Plane附件及相应的数学模型,可得到石墨薄膜平面方向的热导率。此方法改进了传统的闪射法,可应用于各种各向异性薄膜,以及高导热各向同性薄膜的导热测量。     

浅谈应用材料导热系数的测定方法

随着“双碳”目标的提出，应用材料的导热性能是评定该材料是否符合节能理念的重要指标之一。导热系数的测量则是对材料导热性能的重要衡定，如何选择合适的测量方法得到准确的导热系数非常关键。本文结合以往经验，对防护热板法、热流计法、圆管法、热脉冲法、热线法、激光闪射法以及瞬态平面热源法的测试原理、仪器设备、影响因素以及测试改进措施进行了综述，为应用材料的测定方法选择提供参考。对特定的材料在合理的适用范围内选择何种测试方法进行了展望。     

基于激光热成像技术的耐火材料导热系数测试新方法

为了满足耐火材料对导热系数测试快速、准确的需求,提出了基于激光加热耐火材料、结合红外热成像技术的材料导热系数测试新方法——激光热成像法,并与现有国家标准的闪光法测试导热系数常用的耐驰公司激光导热仪FLASHLINE-500进行数据对比,探讨了两种不同方法测试不同成分耐火材料导热系数的差异。结果表明:相比闪光法,采用激光热效应结合红外热成像技术的新测试方法能快速、准确地测量出不同耐火材料的导热系数;对材料的导热情况显示直观、明确,测试方法操作简单,抗干扰能力强,大大降低了测试的成本投入。     

混合硝酸熔盐的制备及其性能研究

采用静态法以硝酸钾、硝酸钠为二元基元和添加剂构成多元混合硝酸熔盐。通过DTA热分析、重量法、阿基米德法、激光闪射法等对熔盐的熔点、熔化热、密度、导热系数、热稳定性等性质进行了表征；同时研究了8种金属材料在熔盐中的耐蚀性。实验结果表明：加入添加剂能降低熔点、增加熔化热、提高热稳定性。当添加4% additive-X（无机硝酸盐系列加少量硅系列产品）时混合熔盐热稳定性与热物性最优，且熔盐对金属材料腐蚀性小，是一种未来太阳能热发电领域理想的传热蓄热介质。     

吸附制冷用混合吸附剂导热性能的研究

用水溶液挤压法制备了24个CaCl2/ENG成型混合吸附剂样品,利用目前闪光扩散法测量导热系数最先进的仪器——LFA447激光导热仪对样品进行了导热系数的测试。研究表明:挤压法制备的样品垂直于压力方向上的导热系数高于平行于压力方向上的,大约是其1.1~1.2倍,具有各向异性;在一定范围内,随着固化密度的增加导热系数不断增加,随着氯化钙和膨胀石墨质量比的减小导热系数也不断增大;在氯化钙和ENG的质量比为2∶1,固化密度从600kg/m3增加到700kg/m3的过程中导热系数增加得最为明显,固化密度和膨胀石墨的含量对成型吸附剂样品的导热系数的影响有耦合作用。     

低成本石墨烯基高导热厚膜的制备及其表征

石墨烯具有优异的导热性能,在半导体器件等领域具有广阔的应用前景。针对低成本高散热能力的应用需求,本文利用低成本的物理剥离法制备的石墨烯为主要原料,添加少量氧化石墨烯制备了具有良好导热性能的厚石墨烯膜。利用X射线衍射仪、扫描电子显微镜、拉曼光谱仪、X荧光发射光谱仪、激光闪射法等方式详细表征了所制备的石墨烯导热膜。结果表明:石墨化处理能够很好的提升导热膜中炭的有序程度,制备的导热膜具有良好的热导率,厚度为30μm与130μm的热导率分别为423Wm^(-1)K^(-1)和375Wm^(-1)K^(-1)。该方法制备的导热膜热导率随厚度的增加变化较小,具有良好的应用前景。     

高纯石墨标样热扩散系数测定及优化

为了选取合适的热扩散系数标测定标样,用热压烧结法制备了高纯石墨,利用激光闪射法测试了不同厚度石墨试样的热扩散系数,研究了石墨热扩散系数随厚度的变化规律,分析了产生这种变化的原因.结果表明:不同温度下的石墨热扩散系数均在试样厚度3㎜时最高。选用高纯石墨热做为热扩散系数标样时,试样的厚度应在3mm左右,这样才能使被测试样的测试结果更精确。     

激光热扩散法测定高炉炭砖导热性能的研究

着重介绍了用激光法测定炭砖的导热系数,结合实际应用,分析了影响炭砖导热系数测定结果的因素,并提出了相应的解决措施.     

短炭纤维 /沥青炭复合材料导热系数与石墨化度的关系

采用脉冲激光闪光法和XRD技术，分析了一种短炭纤维增强沥青炭复合材料的导热系数与石墨化度之间的关系，建立了两者之间的定量数学模型，并运用声子导热机制对其机理进行了分析。结果表明，随着石墨化度的升高，石墨微晶尺寸增大、结构渐趋完整，复合材料在平行于层面方向的室温导热系数逐渐升高，导热系数与石墨化度之间关系符合公式：λ=59.18 0．53exp(g／14.80)。     

四氯化硅和四氟化硅的研究比较

SiCl4主要是作为改良西门子法生产多晶硅的副产物得到,SiF4主要是作为磷肥工业的副产物氟硅酸分解得到,但是二者纯度都不能满足生产多晶硅的要求,需进行分离纯化得到高纯物质。本文针对SiCl4和SiF4的物化性质、合成工艺、精制方法、应用前景等方面做了探讨和比较,指出SiF4比SiCl4更具应用前景。     

Synthesis of colloidal solutions with silicon nanocrystals from porous silicon

In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm^-2, 1 A cm^-2, and 1.2 A cm^-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH₂, and SiH _x , as well as some kind of defects.

PACS

61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh     

Ordered arrays of nanoporous silicon nanopillars and silicon nanopillars with nanoporous shells

The fabrication of ordered arrays of nanoporous Si nanopillars with and without nanoporous base and ordered arrays of Si nanopillars with nanoporous shells are presented. The fabrication route is using a combination of substrate conformal imprint lithography and metal-assisted chemical etching. The metal-assisted chemical etching is performed in solutions with different [HF]/[H₂O₂ + HF] ratios. Both pore formation and polishing (marked by the vertical etching of the nanopillars) are observed in highly doped and lightly doped Si during metal-assisted chemical etching. Pore formation is more active in the highly doped Si, while the transition from polishing to pore formation is more obvious in the lightly doped Si. The etching rate is clearly higher in the highly doped Si. Oxidation occurs on the sidewalls of the pillars by etching in solutions with small [HF]/[H₂O₂ + HF] ratios, leading to thinning, bending, and bonding of pillars.     

Mechanism of structure formation of silicon nitride with combustion of silicon in nitrogen

Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 1, pp. 45–52, January–February, 1990.     

Composite silicon film with connected silicon nanowires for lithium ion batteries

Composite silicon film, which is composed of silicon nanowires, Si-Au eutectic and Si particles as the melding spots, was prepared as anode for lithium ion batteries by a special secondary deposition process with vapor-liquid-solid (VLS) mechanism. Au-Si eutectic particles act as the melding spots between silicon nanowires. An attractive electrochemical performance with 88% of the coulombic efficiency in the first cycle was obtained in the charge-discharge tests. The connection among silicon nanowires by dispersed Si-Au particles is the key factor for the enhancement of its electrochemical reversibility.     

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid-solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.     

Direct laser sintering of reaction bonded silicon carbide with low residual silicon content

Additive manufacturing (AM) techniques are promising manufacturing methods for the production of complex parts in small series. In this work, laser sintering (LS) was used to fabricate reaction bonded silicon carbide (RBSC) parts. First, silicon carbide (SiC) and silicon (Si) powders were mixed in order to obtain a homogeneous powder. This powder mixture was subsequently laser sintered, where the Si melts and re-solidifies to bind the primary SiC particles. Afterwards, these SiSiC preforms were impregnated with a phenolic resin. This phenolic resin was pyrolysed yielding porous carbon, which was transformed into secondary reaction formed SiC when the preforms were infiltrated with molten silicon in the final step. This resulted in fully dense RBSC parts with up to 84?vol% SiC. The optimized SiSiC combined a Vickers hardness of 2045?HV, an electrical conductivity of 5.3?×?10³?S/m, a Young's modulus of 285?GPa and a 4-point bending strength of 162?MPa.     

Evaporation-condensation derived silicon carbide membrane from silicon carbide particles with different sizes

Silicon carbide ceramic is a promising membrane material because of the high corrosive and high temperature resistance, and the excellent hydrophility. Here, a silicon carbide ceramic membrane with both substrate layer and separate layer composed of pure silicon carbide phase was successfully prepared. The effect of particle size on the microstructure and properties was investigated. The substrates were prepared from three silicon carbide particles at 2200 ℃. With the content increase of fine particle, the average pore size increased from 5.6 μm to 14.1 μm; meanwhile, the flexural strength of the substrate increased from 14.1 MPa to 24.6 MPa. The separation layers were made from particles of 3.0 μm and 0.5 μm. When sintered at 1900 ℃, the separation layer formed pore network with homogeneous structure. Such silicon ceramic membrane can be used in harsh conditions, including high temperature wastewater and strongly corrosive wastewater.     

利用稻壳合成SiC的研究

稻壳经细粉碎、酸处理、FeCl2·6H2O浸泡、过滤、干燥、高温分解与合成、HF溶液处理,即可得到SiC含量50％～70％的合成碳化硅。