含乙烯基的聚硅氮烷先驱体纤维的制备

通过甲基乙烯基硅氮烷与聚硅氮烷共热聚反应,将乙烯基引入先驱体聚硅氦烷,分析了甲基乙烯基硅氦烷与降硅氮烷的结构。讨论了两者共热聚的反应过程,找到了适宜的制备方法。制得了几种不同乙烯基含量的聚硅氦烷,并经熔融纺丝制得的含乙烯基的聚硅氦烷纤维。     

不同分子量的陶瓷前驱体聚硅氮烷的结构与性能的研究

以甲基氢二氯硅烷、甲基乙烯基二氯硅烷为原料,采用氨解反应以及热聚合反应合成了一系列乙烯基氢基甲基聚硅氮烷(PSZ135-170),其数均分子量(Mn)在2.9×103~1.9×105之间,单位浓度聚合物的粘度(ηred)在0.06~0.49mL/g之间。通过FTIR和1H NMR对聚硅氮烷结构进行了表征,该系列聚硅氮烷具有无定型结构,可溶解于正己烷、甲苯、乙酸乙酯、二氯甲烷和N,N-二甲基甲酰胺等常用有机溶剂中,通过TGA分析了该系列聚硅氮烷的热性能,发现随着聚硅氮烷分子量的增加,在N2中25~700℃热解后剩余物的百分含量逐渐升高,最高可达72.58%。     

含活性基有机硅氮烷的合成及紫外光固化与热裂解研究

通过甲基乙烯基二氯硅烷及甲基氢二氯硅烷氨解并以NH4C l催化制备了四种含活性基团的有机硅氮烷。对其紫外光(UV)固化性能、机理及热裂解行为进行了研究。结果表明,紫外光可以有效地引发含活性基的有机硅氮烷固化,固化时主要发生N-H、-CH=CH2间的反应;增大低聚物中S i-H含量和硅氮烷的分子量,均可提高其裂解后的陶瓷产率。     

有机改性硅溶胶及疏水膜的制备

以硅酸钠为原料,经水解制得了硅酸低聚体(PS),再以六甲基二硅氮烷(HMDS)与PS反应引入硅三甲基,制得了有机改性硅溶胶(PSH),并采用浸提法在玻璃上涂胶制备了疏水膜.本文采用FT-IR、1H-NMR和TG-DTA对硅溶胶进行了分析表征.研究结果表明:聚硅酸中羟基被硅三甲基取代,制得的PSH热稳定性较好,涂膜玻璃具有疏水性且疏水性随着HMDS投料量的增加而增强.     

含Ti的SiC纤维的先驱体的合成

通过聚碳硅烷与钛酸丁酯的反应,合成了含钛聚碳硅烷 PTC-Ⅰ(Ti/Si 原子比=0.02—0.04)。PTC-Ⅰ的可纺性与熔点随 Ti 含量增加而有规律地变化。由二苯基硅二醇与钛酸丁酯的反应,可制得低聚体的聚钛硅氧烷,将其与聚碳硅烷反应,可以合成具有更高 Ti 含量的聚合物PTC-Ⅱ(Ti/Si 原子比=0.10)。PTC-Ⅰ与 PTC-Ⅱ都具有良好的可纺性,以它们作为先驱体制得了含 Ti 的 SiC 纤维。     

聚碳硅烷强化辐射交联的研究

合成了不同乙烯基含量的聚碳硅烷,研究了共Ｈｅ气氛条件下的电子束辐射交联不熔化处理,分析了含乙烯基聚碳硅烷纤维在辐照过程中的结构变化,结果表明,乙烯基起到强化聚碳硅烷辐射交联的作用,完成不熔体所需剂量显著降低。     

不同组成的陶瓷前驱体聚硅氮烷的结构与性能的研究

以不同比例的甲基氢二氯硅烷(0,20%,50%,80%和100%(摩尔分数))和甲基乙烯基二氯硅烷为原料,采用氨解反应以及热聚合反应合成了一系列不同组成的乙烯基氢基甲基聚硅氮烷(PVHMS),其重均分子量在8.61×104~4.0×105之间。通过FT-IR和1 H NMR对该系列聚硅氮烷的结构进行了表征,发现它们属于无定型结构;0%(摩尔分数)PVHMS为线型结构,呈粘流态,可溶解于常用有机溶剂中,在N2中1 000℃热解后剩余物百分含量为61.80%;20%(摩尔分数)PVHMS具有交联的支化结构,加热变硬,不溶于常用有机溶剂,热解后剩余物百分含量为57.41%;50%(摩尔分数)PVHMS为含有少量环状结构的线型聚合物,加热到91℃变软,可溶解于常用有机溶剂中,热解后剩余物百分含量为71.00%;80%(摩尔分数)PVHMS为含有少量环状结构的线型聚合物,加热到140℃左右变软,可溶解于常用有机溶剂中,热解后剩余物百分含量为80.81%;100%(摩尔分数)PVHMS具有流苏型支化结构,可溶于热的极性有机溶剂中,加热至300℃无明显的热塑性和热固性变化,热解后剩余物百分含量为85.30%。作为陶瓷前驱体该系列聚硅氮烷既具有易加工的性能,在陶瓷化过程中又具有较高的陶瓷化收率。     

以四烯丙基(二甲基)硅烷为核的超支化聚硅碳烷的合成与表征

以四烯丙基(二甲基)硅烷(B4)为核、甲基氢二烯丙基硅烷(AB2)为单体,通过硅氢加成反应,采用无核一步法、核一步法、核多步法合成了超支化聚有机硅碳烷。用FT-IR1、H-NMR、MALLS-GPC对该聚合物的结构进行了表征。研究了核多步法对超支化聚合物分子量及其分布的控制,结果表明,用核多步法合成超支化聚有机硅碳烷可有效地控制产物的分子量及其分布。     

国外有机硅材料研发动态

概述了国外有机硅材料最新研发动态.着重介绍了与电子工业、燃料电池有关的含硅材料和以含硅的聚酰亚胺、聚硅倍半氧烷为基础的材料,以及聚二茂铁硅烷和金刚烷为基础的有机硅氧烷等的性能和应用.     

聚碳硅烷,聚硅氮烷纤维电子束辐射交联的对比研究

研究了聚碳硅烷纤维和聚硅氮烷纤维电子束辐射交联的交联效果,分析了交联机理并提出了两种不同先驱体辐射交联的差异所在。结果表明,ＰＳＺ的不熔化剂量比ＰＣＳ低得多,但陶瓷产率不如ＰＣＳ提高得快;与ＰＣＳ相比,ＰＳＺ因含有大量活泼的Ｎ－Ｈ键,易于辐照交联不熔化,但也易于热分解,失重率较高。     

Effect of seeding on formation of silicon carbide nanostructures from mesoporous silica-carbon nanocomposites

Mesoporous silica-carbon nanocomposites (C-SiO(2)) were synthesized for the fabrication of highly crystalline silicon carbide (SiC) nanoparticles and nanofibers via carbothermal reduction. SiC nuclei were introduced into the mesopores as seeds by infiltration of preceramic precursor polycarbosilane (PCS) prior to the heat treatment of carbothermal reduction. When PCS with a mass percentage of 11-13% was infiltrated into the mesoporous C-SiO(2), SiC nanofibers and nanoparticles were produced at 1450?°C, even in the sample with low carbon content. The major morphology formed from the mesoporous C-SiO(2) nanocomposites without PCS infiltration was nanoparticles, while nanofibers dominated in the products of PCS-infiltrated compositions. The results indicate that the conversion of PCS into SiC nuclei in mesopores prior to carbothermal reduction has facilitated the formation of SiC nanofibers. Therefore infiltration of seeds into mesopores of C-SiO(2) precursors appears to be an effective means of accelerating the reaction and controlling SiC nanostructures.     

3D Cf/SiC抗高温氧化复合材料的制备及其构件的工程试验

采用低分子量聚碳硅烷(PCS)通过先驱体浸渍裂解(PIP)工艺、化学气相沉积(CVD)和粉末烧结技术相结合制备了3D C_f/SiC抗高温氧化复合材料。运用FTIR、¹H-NMR、凝胶渗透色谱法(GPC)、热失重-差热(TGA-DTA)、X射线衍射仪(XRD)和透射电子显微镜(TEM)等手段研究了低分子量PCS的结构及其无机化过程。结果表明: PCS的主要结构为[—Si(CH₃,H)—CH₂—]n,数均分子量为420,陶瓷化产率为70％左右,在1 200 ℃时基本转化为微晶态的β-SiC;3D C_f/SiC复合材料及其构件具有较好的耐高温氧化性能。     

低分子量聚碳硅烷制备3D-Cf/SiC复合材料

研究了低分子量聚碳硅烷 (PCS) 通过先驱体浸渍裂解 (PIP) 工艺制备C_f/SiC复合材料。分析表明:PCS的数均分子量为400,活性较强,陶瓷化产率为70％左右,在1200℃基本转化为微晶态的β-SiC。分别通过3种不同升温速率制备了3D-C_f/SiC复合材料试样,其弯曲强度分别为745.2MPa、686.7MPa和762.5MPa,明显高于文献报道3D-C_f/SiC复合材料弯曲强度300~500MPa的水平。试样断口的SEM照片均显示长的纤维拔出,有良好的增韧效果,低分子量PCS裂解得到的基体比较致密。实验结果说明,低分子量PCS适合于制备3D-C_f/SiC复合材料,并且提高升温裂解速率对材料性能影响很小。      

快速烧结法制备连续碳化硅纤维

通过熔融纺丝，不熔化处理制得连续聚碳硅烷（ＰＣＳ）不熔化纤维，采用快速烧结方法制备出性能较好的连续ＳｉＣ纤维。探讨了气封条件的选择，以及烧结速度对ＳｉＣ纤维的组成，结构及性能的影响。结果表明，快速烧结条件下，可以实现向纤维上施加张力以及纤维的无机化转变，烧结速度加快会降低纤维的Ｃ／Ｓｉ（原子比），同时有利于提高纤维的抗拉强度和热稳定性。     

Environmental impact of the use of contaminated sediments as partial replacement of the aggregate used in road construction

The Indiana Harbor Canal (IHC) is a waterway extensively polluted with heavy metals and petroleum. Since there are limited disposal options for the petroleum-contaminated sediments (PCSs) of the canal, the environmental impact of IHC dewatered sediment when used as partial replacement of the aggregate used in hot mix asphalt (HMA) for road construction was investigated. In order to assess the long term migration of the target contaminants into the environment, the TCLP, SPLP, and a Constant pH leaching test were applied to a HMA mixture containing 10% of dewatered PCS, a conventional HMA, and the dewatered PCS. None of the heavy metals significantly leached from any of the tested materials in any of the conducted tests. Despite the presence of PAHs in the PCS, these were not found in any of the leachate samples. Finally, among the measured VOCs, only acetone and 2-butanone were found to leach from the asphalt mixtures and the sediment in the Constant pH experiment. It was concluded that it may be environmentally safe to replace the aggregates of the HMA used in road construction in the studied proportions with dewatered PCS based upon leaching levels as compared to TCLP regulated levels. This could be a viable, beneficial use option for the PCS, and therefore, for the canal remediation.     

Effects of nano-SiC particles on the FSSW welded AZ31 magnesium alloy joints

The microstructure of nano-SiC enhancing friction stir spot welding (FSSW) joint with dwell time of 3?s was characterised by an onion ring structure which consisted of alternate SiC-free zones and SiC-rich zones where SiC particles refined the grains. However, onion ring structure disappeared and SiC particles dispersed homogeneously when dwell time was 5?s. The microhardness of stir zone (SZ) and tensile shear load of SiC enhancing FSSW joint were higher than those of conventional FSSW joints. After heat treatment at 200°C for an hour, grains of the SZ grew substantially and coursed reduction in mechanical properties of joints, while grain size of SZ and tensile shear load of SiC enhancing joint was invariant but the microhardness of SZ increased.     

苦参碱/羧甲基壳聚糖/磷酸化壳聚糖纳米粒子的制备及性能表征

为了克服壳聚糖只能溶于酸性水溶液的局限,对壳聚糖进行了化学修饰,通过引入磷酸基官能团,合成了可溶于中性水的磷酸化壳聚糖.以磷酸化壳聚糖和羧甲基壳聚糖为基材,采用聚电解质复合法制备了苦参碱/羧甲基壳聚糖/磷酸化壳聚糖纳米粒子水分散制剂.测试结果表明,纳米粒子的平均粒径为l00～200nm,纳米粒子对苦参碱的负载率最高可达66.2%.     

聚碳硅烷纤维氧化交联机理的研究

对聚碳硅烷(PCS)原丝在不同氧化交联温度区间生成的逸出产物进行红外、核磁和GC-MAS分析,并结合交联丝的红外分析,推测氧化交联的机理。结果表明,PCS的氧化交联主要是其Si—H氧化生成Si—OH,后者进而彼此缩合生成Si—O—Si交联结构;氧化交联温度高于150℃时,其部分Si—CH3也开始氧化生成Si—OH并进而交联;同时,在氧化交联过程还发生PCS侧链的热裂解,所形成小分子也通过Si—OH彼此结合,形成较大分子,且其分子量随交联温度的提高而提高。因此,要及时排除氧化交联过程废气,以免逸出产物黏附在纤维表面而导致粘结。     

SrTiO3-SrZrO3 solid solution: Phase formation kinetics and mechanism through solid-oxide reaction

The perovskite solid solution composition Sr(Ti_0.5Zr_0.5)O₃ (STZ (ss)) has been synthesized from the mixture of SrCO₃, TiO₂ and ZrO₂ powders through solid-state reaction. The phase formation mechanism and kinetics were investigated using TG/DSC, XRD. SrCO₃ in the precursor decomposes at relatively lower temperature than pure powder decomposition, due to the presence of acidic TiO₂. Upon calcinations of the precursor SrTiO₃ (ST) and SrZrO₃ (SZ) were formed separately in the system. Then ST defuses in to SZ to form STZ (ss). ST formation started at lower temperature (800 °C) with lower activation energy (47.274 kcal/mol) than SZ. SZ formation started at 1000 °C with high activation energy (65.78 kcal/mol). STZ (ss) formation started from 1500 °C with very high activation energy (297.52 kcal/mol). It is concluded that solid solution formed coherently with SZ lattice by the diffusion of Ti in to the SZ.     

Mechanism of cyclohexene vapor curing polycarbosilane fibers

Cyclohexene vapor, instead of air, is applied to cure polycarbosilane (PCS) fibers. The cured fibers are characterized by infrared (IR), electron spin resonance (ESR), elements analysis (EA) and simulated through the HyperChem^TM program for comparison. The curing process is investigated by thermoanalysis. The results indicate that the Si–H and Si–CH₃ bonds in PCS are induced by cyclohexene to cleavage and form Si-central radicals. A fully developed cross-linking fibers come into being through the combination of these radicals, and the byproducts, some cyclohexyls bonded onto PCS derived from cyclohexene, introduce the variations in IR spectra, weight gain and carbon contents increase of PCS. On the basis of investigation and simulation, a likely mechanism of curing reaction is presented.