常用醇类低温保护剂水溶液的DSC研究

利用差示扫描量热仪(Pyris-Diamond DSC),研究了乙二醇、丙三醇、1,3丙二醇、1,3丁二醇和2,3丁二醇水溶液的过冷行为、水合性质以及玻璃化转变温度,得出了这些性质与溶液浓度的关系.过冷度和未冻水含量在低浓度时没有明显的规律性;而在中高浓度则具有相同的变化规律:随着溶液浓度的增大而增大.各低温保护剂在水合性质上所表现出的差异性,体现了保护剂的官能团(羟基、甲基)所起到的重要作用.保护剂在玻璃化转变温度的明显差异,则反映它们在玻璃化能力方面的强与弱.     

纳米低温保护剂玻璃化过程中热学性质的研究

本文利用差示扫描量热仪(DSC)对含有羟基磷灰石(HA)纳米颗粒的丙三醇溶液玻璃化过程中的主要热学性质进行了测定。其中包括玻璃化与反玻璃化温度的测定,玻璃化过程中比热的测定。结果表明加入HA纳米颗粒后的丙三醇溶液的反玻璃化温度(Td)表现出明显的上升趋势,当溶液浓度高于50%时玻璃化温度(Tg)也稍有升高;加入纳米颗粒后溶液在整个玻璃化过程中比热明显减小,并且减小程度与HA颗粒浓度及粒径大小均表现出一定的非线性关系。     

ZnO-MgO-P2O5磷酸盐玻璃酸溶机理研究

采用表面失重法分析40ZnO-10MgO-50P2O5玻璃在酸性溶液中的溶解过程.实验结果表明:含二价金属阳离子的磷酸盐玻璃在水中溶解速度缓慢,但在酸性溶液中,因R2 和H 离子交换加速,破坏了结构的稳定性,磷氧基团很容易发生水解,在pH＜3时,玻璃的溶解速率会急剧增大.溶解速率随温度升高呈现指数增加的趋势,溶解活化能随pH值的升高而降低;在高浓度盐酸溶液中,溶解速率随浓度变化出现极值,这一切均应归于H 和H2O活度的双重作用;通过对失重曲线变化的研究发现:玻璃的溶解过程分为两个阶段,第一阶段失重量与时间平方根成正比,第二阶段失重量与时间成正比,说明玻璃表面的水化层经历了形成、发展和稳定的过程.     

电沉积溶液浓度及温度对修复混凝土裂缝的影响

研究了电沉积法修复混凝土裂缝中溶液浓度及温度的影响,测定了电沉积过程中的试件质量增加率、表面覆盖率、裂缝愈合率及裂缝填充深度.结果表明,表面覆盖率、裂缝愈合率随电沉积溶液浓度的增加而降低,而裂缝填充深度随浓度的增加而增大,质量增加率随浓度的变化无明显规律;表面覆盖率随电沉积溶液温度的升高而减小,裂缝愈合率随温度的升高而增大,质量增加率随温度变化的规律不明显,温度对裂缝填充深度的影响较小.     

热处理条件对玻璃转变温度的影响

一、前言玻璃的转变温度,是指在加热或冷却过程中,玻璃的物理性质发生剧烈变化的温度。由于它反映了玻璃态物质的结构特征,并对决定生产工艺参数有密切关系,而成为人们注意研究的重要玻璃特征性质之一.测定转变温度最常用的方法是膨胀计法,此外,还可以根据粘度、密度及电导率等性质随温度变化的规律     

热塑性聚酰亚胺热转变行为研究

采用凝胶渗透色谱(GPC)测定一种热塑性聚酰亚胺(TPI)的分子量及其分布;利用差示扫描量热仪(DSC)测定TPI的玻璃化转变温度(Tg);考察了分子量大小、热处理温度和热处理时间对玻璃化转变温度的影响.结果表明:Tg随数均分子量的增大而增加,采用Kanig-Ueberreiter方程关联Tg与数均分子量,其线性拟合度最高;由于聚酰亚胺的结构特点--存在自由端基,在高温可发生固相热环化反应,相应其分子量随处理温度的升高和处理时间的延长而增大,表现为聚合物的Tg有所升高.     

车用ABS温相关本构模型及材料参数的确定

通过不同温度下（243 K、263 K、296 K、333 K、353 K和383 K）的单向拉伸试验,研究了温度对玻璃态和玻璃化转变区的丙烯腈-丁二烯-苯乙烯三元共聚物（ABS）力学性能的影响。结果表明：在低于玻璃化转变温度（383 K）的范围内,屈服强度和极限拉伸强度随温度的升高呈线性下降;杨氏模量随温度的上升呈非线性下降。本文结合双层黏塑性本构模型,利用sim-flow优化工具获取本构模型在不同温度下的材料参数,建立了温相关双层黏塑性本构模型,该本构模型可以很好地预测ABS在243~383 K范围内的应力-应变曲线。     

壳聚糖涂膜材料的传热特性研究

采用XRD,TG,DSC表征了壳聚糖的分子结构(包括脱乙酰度、结晶度、玻璃化温度),测定了壳聚糖涂膜液的特性粘度,研究了壳聚糖的结构和使用条件(时间、温度)对壳聚糖涂膜传热特性的影响规律.结果表明:壳聚糖的玻璃化转变温度随其结晶度的增大而升高;脱乙酰度越大、特性粘度越小、玻璃化温度越低,涂膜的热传递速率越快;壳聚糖涂膜的贮藏时间越长,其热传递速率越慢.     

聚丙烯腈/二甲基亚砜溶液的流变学性质

用HAAKE公司RSl50L型流变仪研究了PAN／DMSO溶液的流变学性质．讨论了温度、溶液浓度及PAN的分子量对流动曲线的影响。结果表明,在较低的剪切速率下,随温度的升高、浓度的降低及分子量的减小,流动曲线下移,并且开始向非牛顿区转变的临界切变速率增大．在较高剪切速率下,初始粘度低的溶液的粘度最高．在一定的浓度和剪切速率下溶液的粘度随温度的变化符合Arrhenius方程式．溶液在非牛顿区存在粘度突变现象．     

支链数目和支链长度对梳形支化聚苯乙烯动态粘弹行为的影响

以主链长度相当、支链数目和支链长度依次变化的梳形支化聚苯乙烯为对象,使用平板式旋转流变仪测定其动态粘弹参数的温度谱和频率谱,研究了支链数目和支链长度对梳形支化聚苯乙烯动态粘弹行为的影响。结果表明,梳形支化聚苯乙烯的玻璃化转变温度高于相同相对分子质量范围的线型聚苯乙烯,而且随支链数目增加其玻璃化转变温度持续增大;梳形支化聚苯乙烯的粘流转变温度低于相同相对分子质量范围的线型聚苯乙烯,随支链长度增加,粘流转变温度和橡胶弹性平台区储能模量明显增大。与主链运动相对应的松弛过程发生在低频区,其特征松弛时间随支链数目增加明显延长,在更高频率下会出现与梳形支化聚苯乙烯的支链解缠结相关的支链松弛,随支链长度增加,支链特征松弛时间延长。     

Electrical conductivity,crystallinity and glass transition in vulcanised rubber

Temperature variation of electrical conductivity has been measured for rubber vulcanised with different concentrations of sulphur. Change of amorphous character with sulphur concentration has also been measured from the amorphous halo of the Debye-Scherrer x-ray photographs of the samples. The conductivity of vulcanised rubber in glassy state shows a slow and gradual increase; but during glass transition it increases suddenly to a high value which again exhibits gradual increase in high elastic state. X-ray studies show that with increase of sulphur, the amorphous region decreases due to formation of cross-links by the chain units. The decrease of conductivity with increase of sulphur is then due to decrease of amorphous region. The fast decrease of conductivity with sulphur at low concentration in the high elastic state indicates high rate of formation of cross-links at such concentration.     

Ultrastable nanostructured polymer glasses

Owing to the kinetic nature of the glass transition, the ability to significantly alter the properties of amorphous solids by the typical routes to the vitreous state is restricted. For instance, an order of magnitude change in the cooling rate merely modifies the value of the glass transition temperature (T(g)) by a few degrees. Here we show that matrix-assisted pulsed laser evaporation (MAPLE) can be used to form ultrastable and nanostructured glassy polymer films which, relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, are 40% less dense, have a 40 K higher T(g), and exhibit a two orders of magnitude enhancement in kinetic stability at high temperatures. The unique set of properties of MAPLE-deposited glasses may make them attractive in technologies where weight and stability are central design issues.     

The equilibrium and non-equilibrium thermal behaviour of aqueous ternary solutions based on complex physiological support media,containing NaCl,and dimethyl sulphoxide or glycerol

The effects of substituting a physiological support medium for water on phase diagram relationships in ternary systems composed of an aqueous component base (water or Eagle's minimum essential medium), NaCl, and a cryoprotective agent (glycerol or dimethyl sulphoxide) have been studied by differential thermal analysis. Primary solidification and eutectic transformations were observed, and both the transition temperatures and devitrification behaviour of non-equilibrium glassy phases were recorded. For most solutions it was found that substitution of the complex support medium for water had very little effect on equilibrium phase relationships. However, the aqueous component substitution resulted in small but measurable changes in the thermal behaviour of non-equilibrium glassy phases. In general, glass stability is enhanced. It is believed that the formation of stable glass phases plays a significant role in cryoprotection.     

宽过冷液相区铁基非晶合金的形成和磁性

用熔体急冷法制备出具有明显的玻璃转变和较宽的过冷液相区的Fe-Co-(Nb)-Zr-B非晶合金,研究了热稳定性和软磁性能。结果表明,在Fe-Co-Zr-B四元合金中添加适量的Nb可以显著扩大过冷液相区,提高合金的热稳定性。当冷却速率降低时,急冷合金具有非晶和纳米晶的复相结构。非晶合金的饱和磁化强度随Nb含量的增加而减小。不同Nb含量的非晶合金的饱和磁致伸缩系数均较低。在低于晶化温度的温度下退火可以有效地降低矫顽力,改善软磁性能。晶化导致软磁性能降低。     

Micromechanical modelling of the viscoelastic behaviour of an amorphous poly(ethylene)terephthalate (PET) reinforced by spherical glass beads

Homogenization micromechanical models are applied to predict the linear viscoelastic properties of an amorphous poly(ethylene)terephthalate (PET) composite in the range of glass transition by using the elastic-viscoelastic superposition principle defined by Hashin [1]. An amorphous PET is reinforced by glass beads and is submitted to dynamic mechanical tests at temperatures surrounding its quasi-static glass transition temperature. The viscoelastic properties of the matrix and the elastic properties of the beads are measured experimentally. The micromechanical models predictions of the linear viscoelastic behaviour in the glassy state are acceptable. In the rubbery state, the beads seem to reduce the molecular mobility of the matrix driving to a large change in the viscoelastic properties of the materials. Thus, this paper aims to emphasize that classical homogenization micromechanical models, which depend only on the constituent behaviour, shape and distribution, cannot predict this change in the linear viscoelastic behaviour of the beads/PET composites.     

Crystallization of amorphous Fe73.5Si13.5B9Nb3Cu1

A study is reported on the devitrification behaviour of the amorphous alloy Fe73.5Si13.5B9Nb3Cu1. Samples of the studied glass underwent isothermal and non-isothermal heat treatments in a thermal analysis apparatus. In addition some samples were very rapidly heated to very high temperatures by means of a laser beam. In this way a large temperature range was explored and information was obtained on the overall thermal evolution of the studied amorphous alloy. The experimental results suggest that, as recently proposed in the literature, nanocrystallization can be linked to a rate limiting Nb diffusion stage in the crystal growth process. However topological short range ordering (TSRO) and chemical short range ordering (CSRO) also affect the devitrification behaviour. In the case of the studied alloy, three temperature ranges can be defined. At low temperature only TSRO occurs. Above a temperature that lies approximately in the range 450–500°C, glass in glass phase separation occurs up to a temperature that lies approximately in the range 700–750°C, above which it appears to be very limited. The occurrence of glass in glass phase separation appears to be necessary to obtain a fine microstructure, because Nb concentrates in the boron depleted, iron rich glassy phase. The occurrence of TSRO prior to demixing should be avoided if nanocrystallization is desired. All this appears to be satisfied by isothermally treating the sample at a temperature of 555°C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties of blends of poly(methyl methacrylate) and poly(vinylidene fluoride)

The mechanical properties of blends of the crystallizable polymer poly(vinylidene fluoride) and the amorphous material poly(methyl methacrylate) have been investigated as a function of composition both for glassy amorphous materials and for partially crystalline materials. The data obtained were interpreted in terms of the molecular and super-molecular structure of the blends and in terms of their dynamic properties.The main conclusions were that the mechanical properties are not strongly dependent on details of the distribution of the two components in the material nor on the crystal modifications present. The mechanical properties were found to depend primarily on the location of the glass transition temperature relative to the elongation temperature and on the presence or absence of crystalline regions. The degree of crystallinity was found to play an important role in determining the properties only at lower values of this quantity. The advantage of these blends is that the important parameters, namely, the degree of crystallinity and the location of the glass transition temperature, can be adjusted at will by varying the composition appropriately. This allows well-defined variations of the mechanical properties to be achieved.     

Deformation and fracture behaviour of wheat starch plasticized with glucose and water

The mechanical properties of wheat starch and the effects of plasticizers upon them are studied in flexure at 293 K. For compositions low in water and glucose the material is glassy, with a flexural modulus between 0.7 and 5.0 GPa. The addition of water and glucose to wheat starch plasticizes the material through its glass transition into a rubbery state. The flexural moduli of the rubbery samples are in the range 50 to 200 MPa, which is indicative of a partially crystalline polymer. For starch-water mixtures the glass transition occur in the water content range 18 to 20%. The addition of glucose progressively shifts the glass transition to lower water contents. At strains below 0.04 brittle failure is only observed in the glassy samples. The surface morphology of the fractured samples shows features typical of pure synthetic glassy polymers.     

Microstructure of amorphous 304 stainless steel-carbon alloys synthesized by magnetron sputter deposition

The results of a study of the effect of increasing carbon concentration on the crystalline-to-amorphous transition in high rate sputter-deposited 304 SS-carbon alloys are reported. Characterization using X-ray diffraction, transmission electron microscopy, electron microprobe analysis and differential thermal analysis showed that the amorphous state was formed at carbon concentrations greater than 5 at.%. Stabilization of the amorphous state at this low carbon concentration indicates that the rapid deposition process is a powerful technique for the synthesis of amorphous alloys.