含铍聚碳硅烷的制备及热解行为分析

为提高碳化硅陶瓷材料的耐高温性能,利用铍元素掺杂,对碳化硅陶瓷先驱体聚碳硅烷进行改性.文中以氧化铍、浓硫酸和乙酰丙酮为原料制备了乙酰丙酮铍(Be(acac)_2);将制备得到的乙酰丙酮铍与聚碳硅烷(Polycarbosilane,PCS)以不同比例反应,合成了一系列不同组成的含铍聚碳硅烷.利用热重分析仪(TGA)、真空管式炉、傅里叶变换红外光谱(FTIR)以及X射线衍射仪(XRD),研究了含铍聚碳硅烷的热解过程及热解产物的晶体结构.实验结果表明:含铍聚碳硅烷(PBeCS)样品从Be(acac)_2中将烯醇式结构及Be元素引入,且不同Be含量的PBeCS样品中C=C和C=O键的含量随着原料Be(acac)_2含量的增加而增加,后趋于稳定,最优的反应配比是Be(acac)_2质量分数为15%;PBeCS样品的热解过程主要经历三个阶段:200～400℃发生PBeCS自交联过程以及小分子量样品和气体的逸出;400～550℃,PBeCS的分子链的开始断裂;550～880℃,样品的进一步无机化,并且质量分数为15%的Be(acac)_2的PBeCS样品具有最高的陶瓷产率(75%).     

氧含量对碳化硅晶体的拉伸性能的影响

碳化硅具有良好的抗腐蚀和抗氧化性能,是先进核反应堆核燃料包壳的候选材料之一,但杂质元素会对碳化硅材料的机械性能产生重要影响。杂质元素对材料拉伸性能的影响可用第一性原理进行分析。首先构建一个2×2×2的3C-SiC超晶胞结构,使用VASP(Vienna Ab-initio Simulation Package)程序模拟SiC晶体的理想拉伸过程;在不同间隙位增加1个或2个氧原子,构建不同的碳化硅晶胞模型,并计算含氧SiC晶体拉伸强度;通过模拟计算了一个掺杂原子和两个掺杂原子在不同间隙位的拉伸强度,最后总结含氧量对SiC拉伸强度的影响。计算结果表明,掺氧后SiC材料更容易发生脆性断裂,同时氧原子增加后SiC的抗拉强度变小了,说明氧含量对SiC的拉伸性能有明显影响。     

新型牵引榴弹炮炮架结构分析计算

目的研究火炮总体设计和减轻火炮重量技术．方法针对近年来国外轻型牵引火炮炮架减重的综合技术,对总体设计和结构进行了分析,并建立了反应火炮总体性能和结构的多参数静力平衡方程,进行了相应的分析计算．结果用某牵引榴弹炮的性能指标和结构参数进行了方法推算,给出了可减轻火炮重量的轻型牵引火炮炮架的技术分析与计算方法．结论采用新型火炮减重综合技术,可以在保证火炮性能不变的前提下,大幅度地减轻火炮的重量     

新型牵引榴弹炮炮架结构分析计算

目的 研究火炮总体设计和减烃火炮重量技术。方法 针对近年来国外轻型牵引炎炮炮架减重的综合技术,对总体设计和结构进行了分析,并建立了反应火炮总体性能和结构的多参数静力平衡方程,进行了相应的分析计算。结果 用某牵引榴弹炮的性能指标和结构参数进行了方法推算,给出了可减轻火炮重量的轻型牵引火炮炮架的技术分析与计算方法。结论 采用新型火炮减重综合技术,可以在保证火炮性能不变的前提下,大幅度大地减轻火炮的重量     

非真空熔铸铍铜合金大规格铸锭的研究

在非真空熔铸铍铜合金大规格铸锭时,需要长时间的熔化和保温.由于铍在金属熔体中的氧化烧损量达到0.004 4%/min以上,熔体中的铍质量分数处于不断下降的状态,因而不同铸锭之间、同一铸锭头尾w（Be）偏差达到6%以上;铍及铍铜原料的大量烧损容易导致铸锭夹杂,进而影响铸锭的综合成品率;同时,由于铍具有强烈的脱氧作用,熔体极易吸气,铸锭内部容易出现气孔等铸造缺陷.通过上百炉次的试验,对熔铸工艺的每个细节深入研究和试验,确定了合理的熔铸工艺,在生产铍铜合金大规格铸锭时,铍及铍铜材料的烧损率分别降到6%及3%以下,铸锭化学成分偏差≤4%,铸锭综合成品率达到80%以上.     

轻质且环境耐用的推进部件

碳化硅基复合材料可在1500℃工作温度下,用来制造涡轮机械结构,此种材料结构比金属结构重量轻一半以上,可大幅改善火箭(或航天器)的系统性能。然而,碳化硅基     

材料科学与工程中分析-综合思维方法的探讨

材料宏观性能取决于其微观结构.采用不同的近似方法并选择合理的物理、力学模型,从宏观到微观对材料结构逐步进行分析,再经综合获得材料的宏观性能,这种分析-综合的思维方法有助于理解结构材料微观结构和力学性能以及功能材料微观结构与物理性能的关系,并可应用于机械设计等.结合数学中的分析-综合思维,即微积分,对物理、数学中分析和综...     

纤维增强复合材料在汽车覆盖件中的应用

采用碳纤维和玻璃纤维两种增强材料与环氧树脂基体材料,对汽车发动机罩进行了铺层结构设计、样件制造和性能对比分析。研究表明:纤维增强发动机罩在满足刚度、模态要求的同时能有效减轻质量,实现发动机罩减重51.2%。在不同工况下,将发动机罩自由模态、横向弯曲刚度、扭转刚度的仿真结果与试验结果和原钢制件发动机罩性能进行了对比,验证了设计的有效性。对复合材料发动机罩铺层优化设计进行了研究,通过优化发动机罩质量相对于初始设计减重9.7%,充分发挥了纤维复合材料在汽车轻量化方面的优势。     

碳粉注浆成型初探

通过对碳粉料浆性能与ｐＨ、分散剂加入量及Ｚｅｔａ电位关系的研究，确定了料浆制备的最佳工艺条件，获得了能满足用全碳质材料渗硅，制备反应烧结碳化硅的料浆，样品烧结密度和抗弯强度分别达２．９５ｇ／ｃｍ＾３和２２５ＭＰａ。     

碳粉注浆成型初探

通过对碳粉料浆性能与ｐＨ值、分散剂加入量及Ｚｅｔａ电位关系的研究，确定了料浆制备的最佳工艺条件，获得了能满足用全碳质材料渗硅，制备反应烧结碳化硅的料浆，样品烧结密度和抗弯强度分别达２．９５ｇ／ｃｍ３和２２５ＭＰａ。     

4m SiC主镜的轻量化及支撑技术

为设计出结构合理的4mSiC轻量化主镜,本文借助于有限元法完成了扇形轻量化主镜的参数设计,确定了90个支撑点的排布方式,并提出了将36组轴向和侧向力促动器共同设置在主镜背面的力分散器上的支撑方案。通过建立轻量化主镜的有限元模型,计算出不同的俯仰角下主镜的重力变形和不同温度载荷下主镜的热变形情况。重力变形分析结果表明主镜光轴水平时,镜面最大变形误差RMS仅为14．7nm,满足设计指标要求;热变形分析预算出1℃的轴向温差引起的镜面面形误差RMS值为278．0nm。若要保证4mSiC轻量化主镜的镜面面形,则必须设计出合理的热控装置,保证主镜的轴向温差不大于0．1℃。     

涂覆纳米TiO2薄膜的自洁玻璃研究

采用溶胶—凝胶法,并用浸渍提拉技术制备了涂覆纳米TiO2薄膜的自洁玻璃。通过热分析讨论了凝胶的转变过程。对比了自洁玻璃的亲水性,研究了该样品的光催化性能。研究表明,干凝胶的最佳热处理制度为升温速度为12℃／h．450℃时保温1h;镀膜6次的试样具有最好的光催化能力;样品在日光照射下也具有良好的亲水性和一定的自洁性能,但是,在可见光（不含紫外线）的照射下．没有体现出明显的亲水性和自洁性能。     

高温炉内黑体空腔精度研究

用热电偶保护管作为黑体空腔，使其成为辐射温度的测量目标。用辐射温度计代替铂铑热电偶从而节约贵金属，在几种不同情况下在高温炉内分别测量了ＳｉＣ管和高铝管的温度分布，对其精度等级进行了评价。结果表明，其精度主要取决于热电偶保护管的材料发射率，插入深度和波长。     

Radiative heat transfer and thermal characteristics of Fe-based oxides coated SiC and Alumina RPC structures as integrated solar thermochemical reactor

This paper investigated radiative heat transfer and thermal characteristics of Fe-based oxides coated SiC and Alumina reticulated porous ceramic structures as integrated solar thermochemical reactor. High-flux solar radiation absorption and axial temperature distribution in the ceramic foams reactor were analyzed by adopting surface-to-surface radiation model coupled to the P1 approximation for radiation heat transfer. The radiative heat transfer and thermal characteristics of different foam-type RPC structures, including SiC, CeO₂, FeAl₂O₄, NiFeAlO₄, Fe₃O₄/SiC, and NiFe₂O₄/SiC were evaluated. The mass flow rate and foam structural parameters, including the permeability, pore mean cell size, and extinction coefficients have significantly affected the axial temperature distribution, pressure drop, heat transfer, and fluid flow. Integrated porous structure to the solar receiver could maximize the incorporation of redox powder in the reacting medium, lower the pressure drop, and enhance the thermal performance of the thermochemical reacting system. SiC structure was the candidate materials in the case where more heat flux and high axial temperature distribution is needed. However, Fe-based oxide coated Al₂O₃ structure could be considered regarding the heat transfer enhancement along with the catalyst activity of oxygen carriers for solar thermochemical reacting system performance.     

Influence of the Source to Substrate Distance on the Growth,Tribological Properties and Optical Properties of Be Films

The Be films were prepared by thermal evaporation at different sources to substrate distances (SSD) on glass substrates. The decrease of SSD from 90 mm to 50 mm caused the increase of substrate temperature and the rising density of incident Be atoms, thus the properties of Be films greatly changed accordingly. The experimental results showed that the grain diameter in the Be films transited from below 100 nm to 300 nm, the film growth rate increased from 2.35 nm/min to 4.73 nm/min and the roughness increased from 7 nm to 49 nm. The performance study suggested that the friction coefficient of Be films increased from 0.13 to 0.27 and was related to the surface roughness and inner structure, the near-infrared reflectance of Be films increased from 40% to 85% with the increase of wavelength and concurrently decreased with the decrease of SSD, respectively. The performance study indicated that the Be film had the potential application in specific near-infrared reflectance optical system.     

Equation of state of Zr41 Ti14 Cu12.5 Ni10 Be22.5 bulk metallic glass

The knowledge of the equation of state （EOS） and the compressibility of a solid are of central importance for the understanding of the behavior and the application of a condensed matter. The compression behavior of Zr41Ti14Cu12.5Ni10Be22. 5 bulk metallic glass （BMG） is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with synchrotron radiation. A model of basic cell volume has been established and the equation of state of BMG is determined by the calculation of radial distribution function. The experimental results indicate that the BMG contains a large amount of vacancy-like free volume. Low pressure （ below 7 GPa） induces the collapse of the free volume to some extent and structure relaxation in the BMG.     

Fiber Optic Humidity Sensor Based on Self-Assembled Polyelectrolyte

Polyelectrolyte multilayers were self-assembled onto planar glasssubstrates and multimode optic fibers. The multilayer thin films deposited on glass substrates were characterized by using UV-vis spectroscopy and X-ray photoelectron spectroscopy. The multilayer thin films containing hydrophilic side-groups possessed are affinity for water molecules. The adsorption and desorption of free water vapor gave rise to the changes in the refractive index and in the reflectance of the thin films. A multilayer thin film based fiber optic humidity sensor with an LED light source of 0.85 μm was designed. Under certain conditions, the reflected light intensity of the thin film sensor was a function of the humidity of air. About 30 bilayers was optimal for the multilayer thin film sensor working at wavelength of 0.85 μm. This sensor can work over almost the whole relative humidity range with very good sensitivity.     

Preparation and mechanical properties of micro- and nano-sized SiC/fluoroelastomer composites

Micro- and nano-sized SiC/fluoroelastomer (FKM) composites were prepared by a mechanical mixing method. These composites were first characterized by a rotorless rheometer. Then the effects of micro- and nano-sized SiC on hardness, static and dynamic mechanical properties of the composites were investigated. The increasing amount of the SiC filler increased the curing efficiency of the biphenyl curing system, which was evident from the rheometric properties of the resulting composites. The tensile properties of composite increased with the increasing of micro- and nano-sized SiC content. When the micro- and nano-sized SiC content was higher than 20 phr, the composites showed almost unchanged tensile properties. The increasing of the tensile property was mainly attributed to the well dispersed micro- and nano-sized SiC particles characterized by SEM images. Compared to pure FKM, the composites exhibited a higher glass transition temperature and lower tan δ peak value.     

一种基于信号处理的光纤液体温度传感器

介绍了包层折射率随温度变化的光纤温度传感器的原理,并设计了一种利用液体作为包层的光纤液体温度传感器.该传感器采用了有效的硬件和软件补偿技术,硬件补偿就是利用差动放大器消除光源波动.软件补偿就是采集一些数据,利用数据融合的方法建立一个关于电压随温度变化的经验公式.这样就可以基本消除光源和探测器受温度因素的影响.     

原位碳化硅复合锆莫来石材料的制备及机理研究

通过反应烧结锆英石、氧化铝和碳黑的混合物制备了原位ＳｉＣ颗粒复合的锆莫来石材料并研究了烧结机理。结果表明：通过反应烧结可制得原位ＳｉＣ颗粒复合的锆莫来石材料;球状或椭球状的ＺｒＯ２晶粒以均匀分布和聚集体两种形式分布于ＳｉＣ、莫来石、氧化铝及玻璃相共同组成的基质中;反应烧结过程中,ＳｉＣ、莫来石的生成反应滞后于锆英石的分解反应;烧结前期以ＳｉＣ的生成反应为主,烧结后期以莫来石的形成及致密化进程为主。