Mechanism of Formation of Near-stoichiometric SiC Fibers

近化学计量比SiC是先驱体法制备超耐高温SiC纤维发展的主要方向。在先驱体中引入少量的烧结助剂，可生成近化学计量SiC纤维。本论文以纯PCS、含铝PCS、含铝和硼的PCS为原料，经熔融纺丝、氧化交联、热解后得Si-Al(B)-C-O纤维，然后通过化学组成、微观结构、物相和力学性能等分析，研究Si-Al(B)-C-O纤维在1300~1800℃烧成过程中发生的物理化学变化，研究氧含量、烧结助剂对近化学计量SiC纤维形成的影响和机理。研究发现，烧结助剂的存在和严格控制氧化交联过程中所引进氧的含量是制备高性能近化学计量SiC纤维的必要条件。当纤维中存在相对于化学计量SiC过剩碳时(C/Si>1)...Stoichiometric silicon carbide (SiC) is most promising to satisfy the requirements by high performance fiber-reinforced ceramic matrix composites. It has proved to be possible to produce stoichiometric SiC fiber through the addition of a small amount of additives in the polymer precursor. In this work, polycarbosilance (PCS), PCS containing aluminum, PCS containing aluminum and boron are used ...学位：工学硕士院系专业：化学化工学院材料科学与工程系_材料学学号：20033601

Deflection analysis of ligament between two fulcrums

分析了两种情况下的丝线的挠度 .一种是两个支点间丝线的直径是均匀的 ;另一种是丝线的直径是均匀变化的 .根据力学求解最大挠度的表达式 ,并讨论影响最大挠度的因素以及在实际 (特别是纤维的烧结和拉伸环节 )中的应用 .分析结果表明 :由于丝线长径比很大 ,丝线的最大挠度跟密度以及跨度的平方成正比 ,与所受的应力成反比 ,而同丝线的直径的具体数值和材料的刚度无关The deflection of filaments between two fulcrums was analyzed. Two kinds of filaments are (considered), one with uniform diameter and the other with a diameter gradient. The expressions of the (maximum) deflection were derived through mechanics analysis, and the parameters affecting the maximum (deflection) were discussed. The analysis indicates that the maximum deflection is directly proportional to density and the square of span, and inversely proportional to stress, but independent of diameter and elastic modulus

Effects of Sintering Conditions on the Liquid-phase Sintering of SiC-Y_2O_3-Al_2O_3 System

研究SiC-Al2O3-Y2O3体系在无压液相烧结过程中,不同的埋粉、烧结温度和保温时间对致密化过程的影响规律以及发生的主要物理化学变化.通过对烧结体失重率、线收缩率和密度的测量和断面形貌的观察发现,以BN为惰性埋粉时,烧结助剂挥发严重,密度低;以Y2O3为埋粉时,烧结过程中Y2O3从埋粉扩散进入坯体,造成烧结体质量增加,实际上未促进烧结;Al2O3和60%(-βSiC)-25%Al2O3-15%Y2O3埋粉有利于烧结,这是由于埋粉中Al2O3的含量较试样中的Al2O3含量高,具有较高的Al2O分压,能有效抑制烧结助剂的挥发.埋粉相同时,由于烧结和挥发的竞争,密度随烧结温度的升高或保温时间的增长先增加后降低.SiC ceramics were sintered using Al_2O_3 and Y_2O_3 as sintering additives.The effects of the powder bed,sintering temperature and sintering time on the densification and microstructure were investigated.The weight loss,linear shrinkage,relative densities and chemical compositions of the sintered samples were measured.And the crystal phase compositions was characterized by X-Ray Diffraction,and the microstructures was observed by SEM.It was found that the BN powder bed could not promote the densification effectively;With Y_2O_3 as the powder bed,large amount of Y_2O_3 diffused into the sample,but the materials did not densify;With Al_2O_3 or 60%(β-SiC)-25%Al_2O_3-15%Y_2O_3 as the beds,much improved densification was obtained,the density were up to 3.07 g/cm~3、3.08 g/cm~3 respectively,higher than with the BN powder bed,because the weight loss of the sintering aids was suppressed or the shrinkage was improved.And it was found that β-SiC could transform into α-SiC with the holding time.The final density increased initially with sintering temperature or holding time,but dropped then due to the evaporation of the additives.国家自然科学基金(50472056);; 福建省重大科技专项(200314007);; 国家“863”计划(2002AA305101)资

Effects of Sintering Additives on the Liquid-phase Sintering of SiC

研究了以Al2O3、Y2O3、Al2O3-Y2O3、SiO2-YAG为烧结助剂时,SiC液相烧结行为以及烧结过程中发生的主要物理化学变化.与传统固相烧结相比,液相烧结使SiC陶瓷性能显著提高.通过对烧结体失重率、线收缩率及密度的测量和断面形貌的观察发现:Al2O3对坯体致密化的促进效果较差;Y2O3为助剂烧结时,由于高温下剧烈挥发,不能有效促进致密化;不同配比的Al2O3-Y2O3助剂能有效促进坯体致密,当配比满足形成YAG的化学计量比要求时,最有利于SiC的烧结.同时对SiC的液相烧结机理也进行了探索.Silicon carbide ceramics have been widely used in petroleum chemical,automotive,mechanical and aerospace industries because of their excellent resistance to thermal shock,high temperatures,oxidation and chemical corrosion.In this paper liquid phase sintered silicon carbide ceramics were prepared with A_2O_3、Y_2O_3、A_2O_3-Y_2O_3 and SiO_2-YAG as sintering additives respectively.Compared with solid state sintered silicon carbide ceramics,the liquid phase sintered one exhibits superior performance.The effects of different additives on the densification and microstructure were also investigated by the measurement of weight loss,linear shrinkage and relative density as well as X-ray diffraction(XRD) and scanning electron microscopy(SEM) analysis.It is found that A_2O_3 was not effective sintering additive due to its high evaporation rate at the sintering temperature.With Y_2O_3 as the sintering additive,large amount of Y_2O_3 from the powder bed diffused into the sample,but the materials did not densify,so Y_2O_3 could not improved the densification of silicon carbide effectively.However,different ratios of A_2O_3-Y_2O_3 significantly promote the sintering,and much improved densification were obtained.With the best result for A_2O_3-Y_2O_3 ratio right for the formation of YAG,the final density was 3.03 g/cm~3,and SEM showed the densification of this sample was highest.The liquid-phase sintering mechanisms of SiC were also studied.国家自然科学基金(50472056);; 福建省重大科技专项(200314007);; 国家“863”计划(2002AA305101)资

Development of forcing culture and key postharvest technology for potential-exporting fruits in Taiwan

In Taiwan fruits, mango, papaya, waxapple, guava, litchi, atemoya, Indian jujube and table grape are becoming more important and potential items in exporting to foreign country, for example, Japan, Canada, mainland China and America. For some time past, the exporting value of those fruits was no growth or on the decrease because of the poor quality after transportation and unstable supply. In order to stabilize and prolong the supply period for exporting, improve quality during transportation and increase the shelf-life in market, we hope to improve and use forcing culture technology and to develop the key technique of postharvest handling. After evaluating the problem and probable technology, the following goals are very important, however: 1.To prolong the supply period of mango and atemoya for exporting. 2.To reduce the browning of table grape peel after cold treatment for quarantine. 3.To improve the techologies of quarantine and storage. 4.To develop the handling processes for long distance and time(by sea) transportation of waxapple, papaya, atemoya and Indian jujube. 5.To improve the quality of guava fruit during summer. The objectives of this study are to research and examine the problem or goals as above.芒果、木瓜、蓮霧、番石榴、荔枝、鳳梨釋迦、印度棗及葡萄為台灣水果中具有外銷潛力之水果；近年來，在開拓市場時，在出口值方面有呈負成長或停滯現象，其原因不外到貨品質不佳及供貨不穩，因此希望透過產期調節技術及關鍵貯運技術的開發，進而穩定及延長外銷水果供應期、提升水果到貨品質及延長櫥架壽命。而諸多問題及待開發技術中，以下列五項為首要工作： 一、以產期調節技術延長芒果及鳳梨釋迦外銷供應期。 二、改善葡萄冷藏後果梗褐變問題。 三、改善荔枝檢疫及貯運保鮮之技術。 四、蓮霧、木瓜、鳳梨釋迦及印度棗長期運輸技術之開發。 五、提升番石榴夏果品質。 本計畫即針對上述五項工作進行試驗及開發

JUNO Sensitivity on Proton Decay p→νˉK+p\to \bar\nu K^+ Searches

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this paper, the potential on searching for proton decay in $p\to \bar\nu K^+$ mode with JUNO is investigated.The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits to suppress the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar\nu K^+$ is 36.9% with a background level of 0.2 events after 10 years of data taking. The estimated sensitivity based on 200 kton-years exposure is $9.6 \times 10^{33}$ years, competitive with the current best limits on the proton lifetime in this channel

JUNO sensitivity on proton decay p → ν K + searches*

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this study, the potential of searching for proton decay in the $p\to \bar{\nu} K^+$ mode with JUNO is investigated. The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits suppression of the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar{\nu} K^+$ is 36.9% ± 4.9% with a background level of $0.2\pm 0.05({\rm syst})\pm$$0.2({\rm stat})$ events after 10 years of data collection. The estimated sensitivity based on 200 kton-years of exposure is $9.6 \times 10^{33}$ years, which is competitive with the current best limits on the proton lifetime in this channel and complements the use of different detection technologies