固态缩聚碳纤维/尼龙1010复合物的熔化行为

本工作借助示差扫描量热法(DSC)和X-射线衍射分析(WAXD)首次研究了通过固态缩聚反应得到的初生态纤维/尼龙1010复合物的结晶特征和熔化行为。实验结果表明:在固态缩聚反应条件下,反应温度、反应时间、碳纤维含量以及产物分子量对初生态复合物的熔化行为有着明显的影响,但其晶系结构和晶胞参数不改变。碳纤维的存在对尼龙1010大分子起着加速晶体形态,限制大分子结晶正常生长的界面效应,碳纤维表面固有的特性致使初生态碳纤维/尼龙1010复合物在DSC扫描过程中呈现出放热峰特征。     

超声粉末模压成型超高分子量聚乙烯微塑件的相结构演变规律

以带有微孔阵列(直径为150μm)的印制电路板(PCB)为微型腔镶块,将此微镶块应用于超声粉末模压成型工艺(micro-UPM),按照设定的成型工艺参数成型出超高分子量聚乙烯(UHMWPE)微圆柱阵列塑件。差示扫描量热分析和纳米压痕实验数据表明,UHMWPE粉末未预热时所成型出的微圆柱阵列塑件整体上由初生态和熔化再结晶两相结构组成,当UHMWPE粉末预热温度由室温28℃逐渐升高到85℃时,所成型出的微圆柱阵列塑件整体上由初生态和熔化再结晶两相结构变成为单相熔化再结晶结构。X射线衍射实验数据表明,micro-UPM微塑件基体部分的结晶度大于微圆柱部分的结晶度,且(110)晶面的晶粒尺寸大于(200)晶面的晶粒尺寸。     

注塑成型二亚苄基山梨糖醇/茂金属等规聚丙烯的结晶结构及力学性能

利用普通注塑(CIM)和振动剪切注塑(OSIM)方法制备了二亚苄基山梨糖醇(DBS)不同质量含量的茂金属等规聚丙烯(m-iPP)试样,并研究了制品的结晶结构和性能。对试样的X射线衍射和差示扫描量热分析表明,DBS的加入使γ晶相对含量(fγ)减少,这是由于DBS生成网络结构增强了成型过程中α和γ晶的取向生成,进而抑制了试样中的γ晶含量。对试样的力学性能研究发现,添加0.5%DBS且经过OSIM成型的m-iPP试样具有最高的拉伸强度为45.2 MPa。     

形态控制技术获取自增强制件研究

在成型过程中向成型设备或模具分别输入具有不同振频和振幅的振动场、不同拉伸比的拉伸应力场、不同剪切速率的剪应力场、以及先剪切后拉伸的复合应力场等,成功地改变了聚合物凝聚态结构;改变了结晶聚合物的结晶度、取向度、晶粒尺寸、晶胞参数;生成了不同的串晶结构、串晶互锁结构。分别得到了具有突出高强度、高模量的试样,自增强同时又自增韧的试样,在单方向应力场中获得双向自增强结构的试样,以及在极少量高分子组分诱导下性能大幅度提高的试样。     

气体辅助注射成型高密度聚乙烯的结晶形态

通过扫描电镜(SEM)观察了气体辅助注射成型(GAIM)和常规注射成型(CIM)高密度聚乙烯(HDPE)的结晶形态,发现CIM试样为区分不明显的皮芯结构,而GAIM试样形成了包括球晶、串晶和取向片晶的多层结构.且GAIM试样球晶尺寸显著小于CIM制品.在结晶形态分析的基础上,初步探讨了气体辅助注射成型制品结晶形态的形成机理.     

聚碳酸酯球晶的形态结构研究

利用偏光显微镜和透射电子显微镜观察了聚碳酸酯(PC)溶液结晶的形态结构,PC在苯酚-四氯乙烷溶液中根据结晶温度的不同可生成带状球晶、延伸球晶、负球晶和层状球晶结构。     

热工艺对激光选区熔化Hastelloy X合金组织及拉伸性能的影响

采用激光选区熔化技术制备Hastelloy X试样,研究热等静压和固溶处理对Hastelloy X试样显微组织及拉伸性能的影响。结果表明:沉积态组织中可观察到熔池形貌、柱状晶及晶内的胞晶结构,无析出物,其拉伸性能表现出高强度低塑性特点,高温拉伸断口沿激光扫描熔化道断裂。经热等静压后,组织演变为等轴晶,晶界及晶内存在较多的析出物,裂纹愈合,试样拉伸强度降低,塑性提升,尤其是高温屈服强度降低了约48%,高温伸长率提升了约59%。经热等静压+固溶处理后,晶粒尺寸及形貌与热等静压态相比近乎无差异,但晶内析出物明显减少,该状态下的综合拉伸性能最优。     

聚丙烯熔体结晶过程中声发射源的实验研究

用光学显微镜观察了六种聚丙烯试样熔体在非等温结晶过程中形态织构的变化。并且与在同样条件下试样结晶过程中观察到的声发射现象进行对照。证实聚丙烯熔体结晶过程中产生声发射讯号主要是在结晶后期,特別是球晶生长结束并形成边界后,在球晶边界和球晶内部形成微缺陷的过程所导致的。它与球晶形成时体积收缩、内应力的产生和增加直接有关。     

气体辅助注射成型聚丙烯的多层次结构

用扫描电镜(SEM)观察了气体辅助注射成型(GAIM)和常规注射成型(CIM)等规聚丙烯(iPP)在不同部位的结晶形态。发现CIM试样的"皮-芯"结构不明显,而GAIM试样在不同部位则形成了包括球晶、串晶和取向片晶,进而表现出明显的多层次结构。在结晶形态分析的基础上,初步探讨了GAIM制品多层次结构的形成机理。     

尼龙69等温结晶球晶形态与生成条件研究

利用偏光显微镜研究了等温结晶时尼龙69的球晶形态与生成条件，发现样品在原始熔点以下至200℃的温度结晶，主要生成正光性和负光性的放射状球晶；在248℃结晶可生成层状放射状球晶；在212℃-177℃结晶，生成三种环状负球晶；在174℃结晶，生成双四瓣环状负球晶。     

聚乳酸/蒙脱土纳米复合材料的冷结晶及熔融行为

采用熔融插层法制备了插层型的聚乳酸/蒙脱土纳米复合材料(PLA/MMTs)。利用差示扫描量热仪(DSC)和X射线衍射(XRD)对该纳米复合材料的结晶及熔融行为进行了研究。结果表明,PLA/MMTs复合体系不能从熔体冷却结晶,但可在较慢的升温过程中固态下冷结晶;蒙脱土不会改变PLA基体结晶的α晶型,但具有异相成核作用,促进了PLA基体的冷结晶在更低的温度下进行;复合体系在较慢升温速率下的双重熔融现象源于原始晶粒熔融重结晶行为。     

影响湿纺PAN初生纤维取向和性能因素的探讨

采用声速法、X射线衍射、沸水收缩率、密度分析等分析检测手段,研究了湿纺凝固浴浓度和温度对初生纤维聚集态取向和性能的影响.研究表明:凝固浴浓度为70%,凝固浴温度为50℃,初生纤维的总体取向、晶区和非晶区取向较大,并且具有圆形的截面、较大的体密度.     

X-ray analysis of the structure of a thermotropic main-chain liquid-crystalline copolyester

The structure and phase behaviour of the thermotropic main-chain liquid-crystalline copolyester poly[(phenyl-p-phenylene)-co-(terephthalate)-co-(p-hydroxybenzoate)] (PES) prepared from terephthalic acid, phenylhydroquinon andp-hydrobenzoic acid (molar ration 45/45/10) is determined by X-ray diffraction and differential scanning calorimetry. This random copolyester shows up to 340°C periodicc-axis order in its X-ray diffraction pattern as well as sharp and diffuse reflections at the equator and other crystallographic directions, indicating well ordered three-dimensional crystalline structure. Two crystalline modifications are observed for quenched and annealed fibres, which are both orthorhombic with slightly different unit cell sizes. Indications of other phases at still higher temperatures are reported. They are believed to be a novel mesophase followed by a nematic liquid-crystalline phase and the isotropic melt.     

Structure, mechanical properties and electrical resistivity of rapidly solidified Pb-Sn-Cd and Pb-Bi-Sn-Cd alloys

A series of Pb-Sn-Cd alloys containing up to 60 wt % Bi were quenched from the melt to room temperature by melt spinning. The structure of rapidly solidified (melt spun), Pb-30 wt % Sn-10 wt % Cd, Pb-30 wt % Bi-20 wt % Sn-10 wt % Cd, and Pb-60 wt % Bi-10 wt % Sn-10 wt % Cd have been investigated by means of an X-ray diffraction technique. From X-ray analysis a crystalline metastable phase, designated (Pb-Bi) is detected. The formation of a metastable crystalline phase in the range of composition investigated causes a pronounced increase in the electrical resistivity. Desirable values of hardness and elastic constants are critically evaluated. It is also observed that the values of the Fermi energy are a few electron volts. Calculated values for the concentration of the conduction electrons, N, m_-3 of Pb -60 wt % Bi-10 wt % Sn-10 wt % Cd rapidly solidified is found to be 0.985×10₂₈ m_-3.     

Correlation of microhardness and morphology of poly(ether-ether-ketone) films

We have applied microindentation to a series poly(ether-ether-ketone) films crystallized at different temperatures from the melt and from the glass to measure their microhardness. The morphology of the samples was characterized by X-ray diffraction, density measurements and differential scanning calorimetry. The results show that a relationship between microhardness, density and degree of crystallinity can be established for samples crystallized at various temperatures from both the glass and the melt. The values of the microhardness of the crystalline component of the samples can be correlated with the lamellar thickness of the polymer crystals.     

TITANIUM-NICKEL SHAPE MEMORY ALLOY PROCESSED BY RAPID SOLIDIFICATION

A rapidly solidified equiatomic titanium-nickel alloy for shape memory applications has been produced by melt spinning under an argon atmosphere. The effect of rapid solidification processing and subsequent annealing treatment on the structure and transformation characteristics of the melt spun ribbons have been investigated. Most of the fine grained ribbons have been ground to powder in a vibratory mill and consolidated by a powder metallurgy method to produce bulk shape specimens. In addition, titanium-nickel powder compacts containing varying amount of nickel from 49 to 55 atomic per cent have been examined. The thermoelastic martensitic reaction characteristics are discussed in relation to the refined grain structure and the state of order of the spun products. The quench hardening capability of nickel-rich alloys (≥ 51 at %Ni) is described and related to the supersaturated structure produced by quenching.     

X-ray and thermal studies on the crystalline phases of normal alkanethiols n-C_{n}H2 _{n} +1SH (n = 18, 19, 22, 23, 24)

Crystal structures, polymorphism, and phase transitions of five n-aklanethiols (n-C _n H_{2 n +1}SH: CnSH), C18SH, C19SH, C22SH, C23SH, and C24HSH have been investigated by means of differential scanning calorimetry and X-ray diffraction. Normal alkanethiols with odd carbon number have only one crystalline form, the E2 form. While, n-alkanethiols with even carbon number have two low-temperature crystalline forms, the most stable E1 form and the meta-stable E1′ form. When even n-alkanethiols are crystallized from the solution (solution growth crystal: SGC), they crystallize into the E1 form. When they are cooled from the melt (melt growth crystal: MGC), on the other hand, the E1′ form appears. In all crystalline phases, two n-alkanethiol molecules are connected at SH end mutually by hydrogen bond resulting in forming a dimer in both forms. The SH groups and the CH₃ groups are arranged on the respectively different layer surfaces resulting in the bilayer structure in the E1 form. In the E1′ form, on the other hand, although the molecules form dimers locally, the SH and methyl groups do not form the one layer surface, respectively, but are arranged disorderly. At temperature just below the melting point, characteristic high-temperature phase, the rotator phase, is observed in even n-alkanethiols as well as in n-alkane system.     

The influence of microstructure on fatigue crack propagation in polyoxymethylene

An analysis of the influence of crystalline microstructure on fatigue crack propagation in poly-oxymethylene is presented. A series of test specimens containing a variety of diverse micro-structures was prepared through controlled thermal treatments of plaques from four different lots of polyoxymethylene. Extensive characterization of the crystalline microstructure was carried out in order to permit a direct comparison between the fatigue behaviour and crystalline microstructure. The degree of crystallinity and tie molecule density were both found to have a significant affect on fatigue crack propagation rate while average spherulite size did not appear to influence fatigue behaviour. Additionally, the fatigue fracture surfaces of many of the test specimens were examined. Three distinct surface topographies were observed and found to correlate with different stages of crack growth. In the region near the end of fatigue crack propagation, closely spaced surface markings that resemble fatigue striations were observed.     

Electron microscopic observation of rapidly cooled ZrO2-3 mol% Sm2O3 from the melt

Electron microscopic observation was made on ZrO₂-3 mol % Sm₂O₃ specimens prepared from the melt using two different cooling rates, namely rapid quenching using a hammer-anvil apparatus and free cooling on a water-cooled copper hearth. The observed microscopic features, such as fully tetragonal grains with parallel twins or herringbone structure, anti-phase boundary contrast in a dark-field image, tweed structure, etc., were found to be quite similar to those observed in similarly prepared ZrO₂-3 mol % Y₂O₃ specimens. It was specifically noted that the tweed structure, which requires atomic diffusion, was not suppressed by the rapid quenching, indicating a very fast growth rate. Trace analysis was also conducted on the tweed structure observed in freely cooled specimens.     

Differential melting in compacted high-modulus melt-spun polyethylene fibres

The compaction of high-modulus melt-spun polyethylene fibres has been investigated for compaction temperatures above the optimum. After such treatment the specimens are liable to be non-uniform because of differential melting. Individual compacted fibres are observed to melt not only from the outside inwards, but also in certain internal regions, depending upon the availability of local free volume. The regions of different stability have been identified and inferences drawn concerning the structure of the initial fibres. It is suggested in particular that the longitudinal regions of deficit density (which exhibit cratering in transverse sections and melt before their surroundings) are a result of initial crystallization occurring within a rigid framework inside the fibre, possibly nucleated on a strained molecular network. The presence of banded recrystallization around residual fibres demonstrates that this phenomenon develops via interaction of neighbouring lamellae as they grow.