Research on the structure and properties of SiC ceramic containing titanium and boron

碳化硅（SiC）陶瓷具有高强度、高硬度、耐高温、抗氧化、抗化学腐蚀、低热膨胀系数、高热传导率等众多特点，不仅被广泛应用在功能陶瓷、高级耐火材料、磨料及冶金原料等民用领域，还应用于航空航天领域，用作发动机的热端部件。为了提高先驱体转化法制备碳化硅陶瓷的耐高温性和吸波性能，本文将钛、硼元素引入陶瓷先驱体中，利用二者高温下生成的二硼化钛作为SiC陶瓷的烧结助剂，提高SiC陶瓷的耐高温性能，并利用钛元素提高陶瓷的吸波性能，系统研究了钛硼的引入，陶瓷结构与性能的演变规律。 首先，固定先驱体中硼元素的含量，研究钛元素含量（0、2.87、5.05和7.98%）和烧成方法对SiC陶瓷结构与性能的影响规律。研...Silicon carbide (SiC) ceramics have high strength, high hardness, high temperature resistance, oxidation resistance, chemical resistance, low thermal expansion coefficient, high thermal conductivity, and other characteristics. It is not only widely used in ceramics, advanced refractories, abrasives and metallurgical raw materials and other civilian areas, but also applied in the aerospace field an...学位：工学硕士院系专业：材料学院_工程硕士(材料工程)学号：2072013115009

Dynamic monitoring and analysis of land use based on RS and GIS in Zhifanggou watershed

以纸坊沟流域多年土地利用监测数据为基础 ,对其结果进行分析和讨论。结果表明 ,到 1 999年底 ,农业、林业、牧业用地面积比例分别为 1 6.9%、34.0 %、36.8%。人均基本农田由 1 975年 0 .0 5 4 7hm2 ,增到 1 999年的 0 .2 0 33hm2 ,坡耕地大幅度减少 ,粮食平均产量也由 1 975年的 5 61 kg/hm2 ,增到 1 999年的 2 31 9kg/hm2 ,流域林草有效覆盖率达到 5 7.4% ,植物种类和数量得到增加。走上了农林牧协调发展和生态环境良性循环的轨

农作物秸秆的厌氧消化试验研究

采用厌氧消化技术，研究了秸秆在中温、高温及环温条件下的生物气产量、发酵液乙酸浓度及甲烷含量的变化情况，比较了不同条件下TS和VS的去除率及产气率。结果显示，在试验的各个温度条件下，秸秆的厌氧消化都可以进行。在高温时干物质产气率可达到0．24m^3·kg^-1，比环温及中温时产气率分别提高42％和21％。但高温引起的酸化会使得系统的正常运行受到影响，中温和环温的甲烷含量在第8d都可以达到50％以上，系统启动快且在试验期间运行稳定，因此从能量投入产出、产气稳定性等因素综合考虑，中温厌氧消化是比较理想的农作物废弃物的处理方法

The surface properties of low oxygen high carbon type silicon carbide fiber

采用X射线光电子能谱(XPS)、X射线衍射(XRD)、SEM、拉曼光谱等分析方法对国产低氧高碳型碳化硅纤维表面进行了研究。结果表明,纤维表面光滑、致密,以SiC_xO_y组成为主、SiC次之、SiO_2最少,并有无定形碳存在。该纤维表面物理与化学特性有利于形成结合强度适中的复合材料界面,从而提高复合材料的强度和断裂韧性。In this paper,X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy and Raman spectroscopy were employed to study the surface physical and chemical properties of silicon carbide fibers with low oxygen and high carbon.Results show that fiber surface is smooth and compact,and disorderd free carbon exists in the surface of the fibers,which is in accordance with the chemical compositon of fibers.Also,the surface of fibers is mainly composed by SiO_xC_y,followed by SiC,and SiO_2.The fiber surface physical and chemical properties can help the combination of fibers and matrix with proper strength,which is beneficial to enhance the strength and improve the fracture toughness of the composite materials.国家自然科学基金面上资助项目(51002127);; 中央高校基本科研业务费资助项目(20720150082

Preparation of SiNO Ceramic by Pyrolysis Nitridation of Polycarbosilane

系统研究了热解和氧化条件对聚碳硅烷氮化热解法制备SInO陶瓷的影响.研究发现,氮化脱碳反应主要发生在800℃之前,且脱碳彻底,碳质量分数低于1%;在氮气气氛下继续烧成,最终生成陶瓷的氮质量分数可达35.65%.氮化前对聚碳硅烷进行氧化交联可提高陶瓷产率至61.84%,但是产物中氮质量分数显著降低到20%以下,产物为无定型态的SInO陶瓷.SiNO ceramic has very excellent comprehensive properties and is one of the best candidates for ceramic matrix composites.In this work,influences of pyrolysis and curing conditions on the SiNO ceramic prepared with pyrolysis nitridation are systematically studied.The results show that decarbonization is completed before 800 ℃ with carbon residue lower than 1%(by mass).After pyrolysis in N2,nitrogen content is as high as 35.65%(by mass).Oxidation curing before ammonolysis can improve ceramic yield.The ceramic yield is 61.84%(by mass)but the nitrogen content decreases significantly(below 20%)by mass,and the product is amorphous SiNO ceramic.Therefore,high-yield and low-carbon-content SiNO ceramic can be prepared with pyrolysis nitridation of polycarbosilane.国家自然科学基金(51002127

The influence of oxygen content on the structure and properties of Co-SiC fibers

系统研究了含钴聚碳硅烷交联丝的氧含量对所成含钴碳化硅(CO-SIC)纤维结构与性能的影响。研究结果显示,较之交联丝CO-PCS-AIr,CO-PCS-O2的氧含量较高,陶瓷产率较高,所成纤维的SICXOy相含量较高、β-SIC和COSI晶粒的增长速度较快,晶粒的尺寸较大,达到最大力学性能的烧结温度较低,电阻率也较低。该纤维电阻率在100~103Ω·CM之间可调,且具有一定的磁性,有望用作吸波纤维。In this work,it was systematically studied that how oxygen content of cured cobalt-containing polycarbosilance(PCS) fibers influences the structure and properties of cobalt-containing silicon carbide(Co-Si C) fibers.Compared to cured Co-PCS-air fibers,Co-PCS-O2 fibers have a higher oxygen content and higher ceramic yield.For Co-PCS-O2 fibers derived from cured Co-PCS-O2,lower pyrolysis temperature was required to reach maximum mechanical properties.And higher Si CxOycontent,higher growing speed and final sizes of β-Si C and Co Si grains and lower electrical conductivity were observed.Co-PCS-O2 fibers have a electrical conductivity controllable between 100-103Ω·cm and were magnetic to some degree,enabling this kind of fibers to have the potential to be used as wave-absorbing materials.国家自然科学基金面上资助项目(51002127;51072169

MIS3晚期查格勒布鲁剖面微量元素揭示的千年尺度气候变化

通过对巴丹吉林查格勒布鲁剖面时代上属MIS3晚期的地层层位(CGS3a层段)中14种微量元素的分析发现:除Co、Ba含量呈相反变化外,P、V、Cr、Mn、Ni、Zn、Pb、Y、Zr、Nb、Cu和As含量在风成沙丘砂中基本上表现为谷值,而在不同层位沙丘砂上覆的湖相中则相对为峰,构成与沉积旋回相应的元素变化旋回。元素在沙丘砂中呈现的谷值,主要揭示了干冷气候条件下东亚冬季风的侵蚀、搬运和堆积作用;在湖相中的相对富集,则与东亚夏季风盛行时暖湿气候背景下该地所处的特殊洼地地貌位置有关。元素旋回实际上代表的是东亚冬夏季风的气候变化旋回。分析结果显示:MIS3晚期剖面所在地至少经历了5次冬夏季风交替变化的气候旋回,反映了该时期我国沙漠地区的千年尺度气候变化。</p

氧碘化学激光器增益谱线的精细结构及腔内温度

采用可调谐二级管激光器做探测光源，测量了超音速氧碘化激光器增益谱线的精细结构，得到了各谱线相对强度的百分比。同时也推得了拉益线宽与腔内温度