聚丙烯腈纤维化学镀铅工艺条件的选择

为了探求以聚丙烯腈纤维为基体化学镀铅最佳工艺条件.以醋酸铅为主盐,三氯化钛为还原剂,EDTA和柠檬酸三钠为络合剂,通过化学镀的方法将金属铅镀覆于纤维表面.结果表明:镀液主要成分的浓度以及施镀的温度、镀液的pH值、施镀时间对金属铅镀覆于纤维表面效果有很大的影响.得出结论:醋酸铅、三氯化钛、EDTA、柠檬酸三钠的浓度范围分别为10.0～16.0g/L、20.0～30.0ml/L、50.0～70.0g/L、100.0～140.0g/L时,pH值为9.0～10.0,温度60℃水浴,施镀时间90min,聚丙烯腈纤维表面镀铅效果最好.     

石墨纤维在不同气氛下的高温热稳定性研究

将石墨纤维分别在氢气和氩气气氛下加热到900、1200、1500和1800℃保温4 h,测试石墨纤维在两种气氛下高温处理后的性能,用SEM和XRD观察和分析石墨纤维高温处理后的组织与形态。通过对比石墨纤维与钛锆钼(TZM)合金相应的性能,分析石墨纤维作为TZM合金增强体的可行性。结果表明,石墨纤维在氢气气氛下会被烧蚀而形成甲烷气体,在氩气气氛下则具有优良的热稳定性,即使长时间高温处理也不会使纤维微晶尺寸及组织发生较大变化,因此,石墨纤维可以用作TZM合金增强体。     

氧化结构对聚丙烯腈预氧纤维热稳定性的影响

将聚丙烯腈(PAN)原丝进行预氧化热处理,借助固体核磁(13C Solid-NMR)、热重红外联用分析仪(TG-IR)及力学性能测试等手段研究了PAN预氧纤维的结构及对热稳定性和力学性能的影响。结果表明:不同预氧化温度处理的预氧纤维热稳定性呈现先升高后降低趋势,是由形成的环化结构和氧化结构共同作用的结果:环化结构使热稳定性提高,而氧化结构达到一定含量后使热稳定性降低。在后续高温处理过程中预氧纤维中的氧元素与碳元素形成碳氧化合物,以CO和CO2的形式从纤维中脱除,形成结构型缺陷。经245℃处理形成适宜的预氧结构,碳元素脱除量最小,碳纤维的碳收率及拉伸强度最高。     

紫外光催化辅助SiC抛光过程中化学反应速率的影响

目的为了探究紫外光催化辅助抛光过程中,化学反应速率对SiC化学机械抛光的影响规律。方法通过无光照、光照抛光盘和光照抛光液3种光照方式,研究紫外光催化辅助作用对单晶SiC抛光过程中材料去除率的影响。测量不同条件下光催化反应过程中的氧化还原电位(ORP)值,来表征光催化反应速率,并进行了单晶SiC的紫外光催化辅助抛光实验,考察光催化反应速率对抛光效果的影响规律。结果实验表明,引入紫外光催化辅助作用后,材料去除率提高14%～20%,随着材料去除率的增加,光催化辅助作用对材料去除率的影响程度变小。光照射抛光液方式的材料去除率明显高于光照射抛光盘。不同条件下的抛光结果显示,化学反应速率越快,溶液的ORP值越高,材料去除率越大,表面粗糙度越低。在光照抛光液、H_2O_2体积分数4.5%、TiO_2质量浓度4 g/L、光照强度1500 mW/cm~2、pH=11的条件下,用W0.2的金刚石磨料对SiC抛光120 min后,能够获得表面粗糙度Ra=0.269 nm的光滑表面。结论在单晶SiC的紫外光催化辅助抛光过程中,光催化反应速率越快,溶液ORP值越高,抛光效率越高,表面质量越好。在H_2O_2浓度、TiO_2浓度、光照强度、pH等4个因素中,对抛光效果影响最大的是H_2O_2浓度,光照强度主要影响光催化反应达到稳定的时间。     

Ti2448合金在不同应变速率下的高温变形机制

通过对亚稳β-Ti2448合金进行Gleeble热模拟压缩实验,研究其在单相β区的高温变形机制。结果表明:Ti2448合金的高温变形机制与应变速率有关,在较低应变速率(10~(-3)～10~(-1)s~(-1))范围内,合金表现出初始应力峰值,随后逐渐软化直到达到稳态流变;其变形机制主要是形核和新晶粒长大的不连续动态再结晶(DDRX)。在较高的应变速率(1～63 s~(-1))范围内,合金首先表现出明显的硬化,随后略有软化,最后达到稳态;其变形机制主要是位错滑移主导的塑性变形,位错与晶界以及亚晶界之间的相互作用促使小角度晶界向高角度晶界的转变,表明变形机制为连续动态再结晶(CDRX)。     

黄铁矿机械化学的计算模拟(Ⅰ)——晶格畸变与化学反应活性的关系

采用基于密度泛函的规范保持赝势分子动力学方法 ,模拟了外应力对黄铁矿晶体结构的影响 ,计算了畸变晶格的能带结构和态密度。计算结果表明 :晶格畸变导致费米能级升高 ;过渡状态理论分析表明机械活化提高了化学反应速率常数 ,即交换电流密度 (J0FeS2 ,J0O2 )增大。根据半导体电化学能带模型和腐蚀电化学混合电位模型 ,晶格畸变导致晶体费米能级EF 升高和交换电流密度增大 ,从而使黄铁矿腐蚀电流增大 ,腐蚀速率提高。黄铁矿机械活化内在原因不仅是机械化学机制 ,更重要的是机械电化学机制     

不同有机官能团对室温下纳米银形貌控制合成的影响

选择10种含有不同官能团的有机物为表面修饰剂,如聚乙烯吡咯烷酮、吐温-80、十二烷基硫酸钠、聚丙烯酸钠、聚乙二醇、山梨醇、十二烷基磺酸钠、聚乙烯醇、十二烷基苯磺酸钠和十六烷基三甲基溴化铵等,在室温下进行了平均粒径在2～131nm范围内纳米银颗粒的控制合成研究.有机修饰剂中含有的不同官能团对制得的纳米银形貌的影响主要取决于有机修饰剂的官能团特性和还原剂的还原能力.在不同还原条件下,含多醚键的聚乙二醇、吐温-80皆易于合成出平均粒径为几纳米、粒径分布窄、分散性好的纳米银.在弱还原剂条件下,十六烷基三甲基溴化铵诱导生成了三角形片状纳米银,但是在强还原剂存在条件下生成了粒状纳米银.粒径大于10m的纳米银晶体的生长是通过小颗粒的聚集与熔合而成,而不是经过小颗粒的溶解-沉积过程形成.     

不同气氛下电火花沉积钛合金涂层的组织性能

分别在氮气、氩气和空气3种气氛下,在45钢上电火花沉积制备TC4钛合金涂层。利用OM、SEM、EDS、XRD、XPS等对钛合金沉积层的微观形貌、组织结构进行分析;利用纳米力学探针仪测试对比沉积层的力学性能;采用CETR摩擦磨损仪测试涂层的耐磨性。结果表明:氮气下电火花沉积生成含TiN及少量TiO和TiO2的陶瓷增强层。氮气中制取的涂层微裂纹较明显,但几无坑蚀和微孔,表面形貌优于氩气和空气下的沉积层。纳米硬度高达15.18GPa,无需增加沉积层厚度,即可获得较高硬度和抗变形能力。其摩擦因数为0.41,磨损量为2.2mg,均远低于45钢,也低于空气和氩气下制备的普通的钛合金涂层,并且改善了钛合金涂层的粘着磨损。     

铜在含硅气氛中表面改性的化学热处理研究

对铜在含硅气氛中低温沉积、随后进行扩散处理的表面化学热处理进行了研究。使用光学显微镜、Ｘ射线衍射（ＸＲＤ）仪、电子探针（ＥＰＭＡ）等对渗层进行了显微硬度、成分和结构分析，探讨了工艺参数对渗层的影响。研究结果表明，通过这种表面化学热处理可以在铜表面形成Ｃｕ５Ｓｉ和Ｃｕ１５Ｓｉ４，其硬度较基体有很大提高。     

提高中锰铸钢强韧性的新途径

分析了亚温处理工艺参数对中锰铸钢组织转变及强韧性的影响;测定并探讨了亚温处理后中锰铸钢的晶体学特性和物理特性;进行了磨损试验对比研究.     

聚丙烯腈原丝的热稳定化研究

采用FT-IR、XRD、DSC、元素分析仪、张力仪、密度测量等方法对聚丙烯腈原丝热稳定化过程中的纤维结构变化,加热历史对纤维热性能的影响,以及纤维张力的变化规律进行研究。结果表明,最终的热稳定化纤维中存在基团C=C—H和C—C—CN;前期热稳定化阶段施加牵伸能够增大结晶度和取向度,但对晶体面间距几乎没有影响;随热稳定化温度提高和加热时间延长,纤维DSC曲线的放热范围变宽,放热峰移向更高温度;预氧化纤维的张力大小受到牵伸率、热处理温度以及纤维原丝纤度的综合影响。     

Microstructure and performance of a cermet material heat-treated in nitrogen

A Ti(C,N)–TiN–WC–Co cermet material was subjected to a heat-treatment in nitrogen which substantially improved the plastic deformation resistance during cutting. The microstructure was characterised using analytical electron microscopy. It was found that a surface zone rich in titanium and nitrogen was induced by the heat-treatment. The high nitrogen activity in the surface region was the driving force for outward transport of titanium and inward transport of tungsten in the cobalt binder. An irregularly shaped nitrogen-rich titanium carbonitride reprecipitated from the binder phase during the heat-treatment, often as surrounding layers on already existing carbonitride grains. The morphological change of the hard phase might explain the dramatically improved plastic deformation resistance by obstructing grain boundary sliding. The experimental findings were in accordance with thermodynamic calculations performed using the Thermo-Calc software.     

Microstructure and cutting performance of Ti（C, N）-based cermets heat-treated in nitrogen

Ti（C, N）-based cermets were treated using hot isostatic pressing （HIP） at 1423 K in nitrogen. The microstructures compared with the as-sintered cermets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and electron microprobe analysis. It was found that high nitrogen activity in the surface zone resulted in the formation of gradient structure. Approximately 20-1am-deep, nitrogen-rich and titanium-rich hard surface zone was introduced by the heat treatment. The nitrogen activity was the driving force that caused the transportation of the atoms through the binder, titanium towards the surface, and tungsten and molybdenum inwards. In the surface zone, the particle size became fine, the inner rim disappeared, and the volume fraction of the outer rim and the binder phase considerably reduced. Small grains of TiN, WC, Mo2C, and nitrogen-rich carbonitlide phases formed in the surface zone during the heat treatment, improving the tlibological property of the heat-treated cermet.     

Chemical stability of chalcogenide infrared glass fibers

Infrared fibers from the chalcogenide family are becoming increasingly prevalent for applications in optical sensing and imaging. In this work, we study the chemical stability of these fibers during long-term storage in air and medium term immersion in water comparable to normal usage conditions during optical monitoring in aqueous environments. A detailed study of surface oxidation in Te-As-Se fibers shows that the oxidation is limited to a superficial layer and progress at a rate of about 20 Å per year. While the elemental glass is insoluble in water, the oxide layer solubilizes rapidly and can lead to surface pitting after oxide removal. The dissolution process is complete after about 2 h of immersion in water. The elemental glass on the other end is chemically stable in water and no significant oxidation process can be detected by cyclic voltammetry. Finally the useful optical properties of these fibers are essentially unchanged after extended storage or immersion in water despite surface oxide or surface pitting.     

Preparation of continuous Si-Fe-C-O functional ceramic fibers

A new polymer named polyferrocarbosilane（PFCS） was prepared from polydimethylsilane and ferrocene. The spinnability of this polymer can be tailored by controlling the content of ferrocene in the polymer. The prepared polymer was spun into a continuous polymer fiber that was subsequently cured in air and heat-treated finally in N2 up to 1 350 ℃ for conversion into Si-Fe-C-O fibers. The resulted Si-Fe-C-O fibers display low specific resistance and magnetic property due to the existence of Fe, which also reduces the specific resistance significantly to 10^-2Ω·cm at room temperature when the amount of ferrocene in feed is as low as 3.0% （mass fraction）. The resulted Si-Fe-C-O fibers, with C/Si molar ratio of about 1.3 and the maximum Fe content of about 2.0% （mole fraction）, are composed ofβ-SiC and small amount of Fe3Si-like crystalline and have an average tensile strength of about 2.0 GPa.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped conductive fibers based on polyaniline and polyacrylonitrile

Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirring with magnetic bar. This research was conducted to investigate conducting fibers of polyaniline:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with 5 mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electrical conductivity with different type doping agents (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

气压放大器的特性分析及设计方法

分析了原气压放大器结构所存在的缺点,设计了一种新结构,并对其进行了静、动态特性分析,从而确定了参数选择原则.结果证明,新结构较原结构具有输入与输出比线性化、放大倍数精度高、抗干扰性强、结构简单等特点.并改善了其制造工艺性,具有实际应用的意义.     

Chemical stability of layered lithium cobalt nitrides in air

The chemical stability in air of a layered lithium nitridocobaltate Li_2.13Co_0.43N has been investigated using in situ XRD diffraction as a function of time. A high reactivity of the nitride with air moisture is found with the rapid emergence of lithium hydroxide. The ageing process finally leads to the decomposition of the nitride into lithium carbonate (Li₂CO₃), cobalt hydroxide (Co(OH)₂) and the release of gaseous NH₃. The effect of the ageing process on the electrochemical properties of this promising anode material for Li-ion batteries is reported. The discharge–charge properties of the compound slightly deteriorate after few hours while they are dramatically affected after 15 h. The present results suggest handling of these anodic materials in dry air would be possible with satisfactory electrochemical properties.     

Chemical processes during the heat treatment of basalt fibers

It has been established that, during the heat treatment of an unsubmixed (unsub-blended) glass (with the contents of Ca and Mg, corresponding to the natural basalt) at the first stage of the oxidation process, magnetic nanoparticles (>20 nm according to the transmission electron microscopy data) of (Mg, Fe)₃O₄ are formed in a nonmagnetic glassy matrix (that is, the oxidation proceeds as internal reaction), followed by the crystallization of alumosilicate phases. In the glasses enriched in CaO, such a crystallization occurs simultaneously with the evolution of the spinel phase. An analysis of the distribution of cations over the fiber cross section has demonstrated that annealing under oxidative conditions is conductive to an increase at the surface of fibers in the concentration of Ca in the case of utilizing an unsubmixed material and that of Na in the case of the glass with a higher content of CaO. The long-term annealing of the nanocomposite at the temperatures of its production results (according to the measurement data of magnetic properties) in the interaction of a part of the formed (Mg, Fe)₃O₄ with the alumosilicate matrix. Original Russian Text ? A.V. Knot’ko, A.V. Garshev, I.V. Davydova, V.I. Putlyaev, V.K. Ivanov, Yu.D. Tret’yakov, 2007, published in Korroziya: Materialy, Zashchita, 2007, No. 3, pp. 37–42.