Ce_(1-x)Ca_xO_(2-x)的溶胶-凝胶法的合成及其性质

用溶胶 -凝胶法合成了 Ce1-x Cax O2 -x(x=0～ 0 .3 5 )系列固体电解质 ,系统地研究了其晶体结构随Ca O含量的变化关系 .XRD测试表明 ,该体系于 1 60℃即形成萤石结构纯相 .高温 XRD表明 ,从室温至80 0℃ ,Ce1-x Cax O2 -x(x=0～ 0 .3 5 )未出现结构相变 .此法合成温度远低于传统的高温固相合成法和水热合成法的温度 .合成物的颗粒小 ,粒度均匀 .在 1 3 0 0℃即可烧结成高致密度样品 .XPS测试表明 ,掺杂 Ca O后吸附氧浓度明显增大 ,氧空位增多 ,电导率和氧离子迁移数增大 ,改善了 Ce O2 基固体电解质的性能 .     

“半稀溶液”中超高分子量聚乙烯链缠绕结构的演变行为北大核心CSCD

通过熔融共混法制备超高分子量聚乙烯/线性低密度聚乙烯(UHMWPE/LLDPE)和超高分子量聚乙烯/聚乙烯蜡(UHMWPE/PE-wax)共混物,以振荡剪切流变测试和脆断截面SEM研究不同浓度UHMWPE对共混物流变行为和材料微观形貌变化的影响,尤其是UHMWPE在共混物中达到一定浓度开始形成缠结结构时的行为变化。UHMWPE/LLDPE共混物在流变测试中相容性良好,当UHMWPE浓度大于0.84%(wt),即临界交叠浓度(孤立高分子线团逐渐靠近开始成为线团密堆积时的浓度)的4倍,频率扫描曲线在低频区显示为与频率无关的类固态凝胶行为,网络结构开始形成;时间扫描曲线表明UHMWPE的浓度在大于0.84%(wt)时储能模量逐渐增大,UHMWPE的缠结有所体现。采用分子量低于缠结分子量Me的聚乙烯蜡为基体,UHMWPE/PE-wax共混物的时间扫描在浓度0.84%(wt)(临界交叠浓度的4倍)时储能模量增加明显。通过SEM观察UHMWPE/PE-wax共混物脆断面,发现该浓度下开始出现丝状物结构,表明了缠结和网络结构的形成。     

“半稀溶液”中超高分子量聚乙烯链缠绕结构的演变行为

通过熔融共混法制备超高分子量聚乙烯/线性低密度聚乙烯(UHMWPE/LLDPE)和超高分子量聚乙烯/聚乙烯蜡(UHMWPE/PE-wax)共混物,以振荡剪切流变测试和脆断截面SEM研究不同浓度UHMWPE对共混物流变行为和材料微观形貌变化的影响,尤其是UHMWPE在共混物中达到一定浓度开始形成缠结结构时的行为变化。UHMWPE/LLDPE共混物在流变测试中相容性良好,当UHMWPE浓度大于0.84%(wt),即临界交叠浓度(孤立高分子线团逐渐靠近开始成为线团密堆积时的浓度)的4倍,频率扫描曲线在低频区显示为与频率无关的类固态凝胶行为,网络结构开始形成;时间扫描曲线表明UHMWPE的浓度在大于0.84%(wt)时储能模量逐渐增大,UHMWPE的缠结有所体现。采用分子量低于缠结分子量Me的聚乙烯蜡为基体,UHMWPE/PE-wax共混物的时间扫描在浓度0.84%(wt)(临界交叠浓度的4倍)时储能模量增加明显。通过SEM观察UHMWPE/PE-wax共混物脆断面,发现该浓度下开始出现丝状物结构,表明了缠结和网络结构的形成。     

新型电解质材料CaZr_(0.1)Ti_(0.9)O_3的制备与电性能

采用溶胶-燃烧法合成了可用于固体氧化物燃料电池(SOFC)的新型固体电解质材料CaZr_(0.1)Ti_(0.9)O_3.通过XRD、交流复阻抗等电化学方法对样品的结构、电导性能进行了表征,并考察了材料的烧结性能. 结果表明,溶胶-燃烧法可以成功制备出具有良好烧结性能的CaZr_(0.1)Ti_(0.9)O_3电解质粉末,1 400 ℃下得到的烧结体的相对密度可达到95%. 电性能测试表明,CaZr_(0.1)Ti_(0.9)O_3烧结体在中温范围内具有较高的氧离子电导率(σ_(800 ℃)＝2.24×10~(-3)S/cm)、低的电导活化能(0.89 eV).     

粉体特性对Sm(Co,Fe,Cu,Zr)_(6.9)高温永磁合金磁性能的影响

分别采用球磨和气流磨工艺制备了Sm(Co,Fe,Cu,Zr)6.9合金粉体。研究了粉体的形状和粒径对烧结磁体磁性能的影响规律。与球磨工艺相比,气流磨制备的粉体颗粒外形更规则。在平均粒径相同的情况下,采用气流磨粉体烧结时效后的永磁合金样品取向度更高,室温剩余磁化强度Mr、最大磁能积(BH)max和500℃条件下的Mr,iHc,(BH)max均优于采用球磨粉体经相同工艺制得的样品。外形规则的气流磨粉体制得的合金样品在室温和500℃条件下的磁性能均随粉体粒径减小呈先升高后降低的趋势,室温下6.8μm气流磨粉体烧结时效样品的磁性能达到最优,为Mr=8092 Gs,iHc=18.3 kOe,(BH)max=123 kJ.m-3;该样品在500℃条件下的磁性能仍达到Mr=5177 Gs,iHc=9.0 kOe,(BH)max=39 kJ.m-3。     

Ba0.4Sr0.6Ci1-xFexO3-δ系阴极材料的制备和表征

采用甘氨酸.硝酸盐(GNP)法合成了中温固体氧化物燃料电池阴极材料Ba0.4Sr0.6Co1-xFexO3-δ=0.0～0.8)系列粉体.利用XRD和SEM对材料的结构和微观形貌进行分析,用直流四端子法测量了烧结陶瓷体在中温(450～800℃)范围内的电导率.结果表明.制备的样品为单一钙钛矿相,随着Fe含量增加,XRD衍射峰值向高角度方向稍有偏移.电导率随着温度及Fe含量的变化出现极大值,在x<0.2时,Ba0.4Sr0.6Co1-xFexO3-δ系列烧结体在 (450～800℃)XE的电导率,随Fe掺入量的增大而增大,x=0.2样品的电导率最高,800℃时达244.7 S·cm-1,远超过文献报道值,进一步增大Fe含量导电性能变差.     

YxTi2On(1.7≤x≤2.1)系固态电解质的共沉淀法合成及电导率研究

以TiCl3、YCl3溶液和氧化钛、氧化钇为原料,通过共沉淀法和固相法制备了YxTi2On(1.7≤x≤2.1,x=1.7,1.8,1.9,2.0,2.1)系烧绿石型固态电解质样品。粉体经700℃处理后在透射电镜下可见其粒径小于100 nm的晶粒。用共沉淀法制得的样品通过1500℃/5 h烧结后的相对密度近94%,且比用固相法经1550℃/5 h烧结所获相同组成样品的相对密度明显要高。X衍射表明样品A(x=1.7)的主晶相为烧绿石和二氧化钛,而样品D(x=2.0)和E(x=2.1)都为烧绿石。从扫描电镜照片可见,样品E的晶界随着烧结温度的提高变得更清晰,晶体生长也更充分。随着Y2O3含量的增加,YxTi2On(1.7≤x≤2.1)系电解质的电导率随之增加。用共沉淀法所得样品的电导率明显高于相应固相法所得样品。随烧结温度和测量温度的提高,样品E的电导率增加。     

提高超高分子量聚乙烯的耐磨性：交联与结晶

耐磨性能是超高分子量聚乙烯(UHMWPE)制品的重要评价指标,其增强机理为在摩擦表面阻止分子链滑移和脱落.改善耐磨性在本质上是形成有效的分子链整体网络.对于人工关节用交联UHMWPE模塑料,辐照改性会残存有自由基,容易造成氧化降解,破坏长期耐久稳定性.发展能够替代辐照交联的新方法,具有重要的现实意义.在本文中,我们选用不同分子量(M_w)的原料树脂,通过改变结晶热历史实现结晶度(X_c)大范围调节,以及改变γ辐照剂量调整交联密度(V_d).测定了各种样品的体积磨损率,建立X_c、V_d、M_w与磨损率的关系.研究发现,随着X_c、V_d、M_w增加,磨损率线性降低;更为重要的是,对于所有分子量的UHMWPE,通过增加结晶度能够使磨损率降至比传统辐照交联方法更低的水平.利用高结晶度改善耐磨性,由于不会引起活性自由基,从根本上消除了氧化风险,具有明显的优势.研究结果为发展新型的高耐磨人工关节用UHMWPE模塑料提...     

固体电解质Ce_(0.9)Er_(0.1-x)Pr_xO_(1.95+δ)的微观结构及电性能

采用柠檬酸溶胶-凝胶法制备了固体电解质Ce0.9Er0.1-xPrxO1.95+δ(x=0.02~0.08),利用X射线粉末衍射(XRD)、原子力显微镜(AFM)、拉曼光谱(Raman)、X射线光电子能谱(XPS)和交流阻抗谱研究了样品的微观结构和电性能.XRD结果表明,800℃煅烧的所有样品均形成了单相立方萤石结构;Raman光谱结果表明,Ce0.9Er0.05Pr0.05O1.95+δ具有氧缺位的立方萤石结构;XPS分析表明,Ce0.9Er0.05Pr0.05O1.95+δ存在氧缺位,Pr3+离子和Pr4+离子共存;AFM观测结果表明,1300℃下烧结的样品比1400℃下烧结的样品致密;交流阻抗谱结果表明,Pr掺杂量x=0.05时,Ce0.9Er0.05Pr0.05O1.95+δ的电导率最高(σ600℃=1.34×10-2S/cm,Ea=0.90 e V),比未掺杂Pr的Ce0.9Er0.1O1.95(σ600℃=8.81×10-3S/cm,Ea=0.92 e V)提高了52%,说明在Ce0.9Er0.1O1.95中适量掺杂Pr可提高材料的电导率,降低活化能.     

超高分子量聚乙烯模塑板材的抗冲击机制

超高分子量聚乙烯(UHMWPE)是一种具有突出抗冲击特性的高性能工程塑料,有关其合成、加工和应用的研究是现今高分子科学的研究热点之一,但是UHMWPE抗冲击的内在机制仍未明确.本文选取黏均分子量约为5×106,悬臂梁双缺口冲击强度分别为54.7, 93.4, 105和152 kJ/m2的4种UHMWPE为研究对象,通过分子结构和凝聚态结构表征,探究了UHMWPE的抗冲击机理.研究发现, 4种UHMWPE具有相同的晶型、接近的结晶度和片晶厚度; UHMWPE在微观上表现出重复性的“延展-断裂”式的抗冲击过程,“延展-断裂”条带的数量和宽度与冲击强度正相关;非晶区的缠结密度与冲击强度呈线性负相关关系,相关性指数高达0.9,即在UHMWPE的合成和加工过程中,控制非晶区的缠结密度对最终制品的抗冲击强度至关重要.     

STUDIES ON THE NATURE OF THE MACROMOLECULAR CONDENSED STATE OF "NASCENT" ULTRA HIGH MOLAR MASS POLYETHYLENE*

 Ultra high molar mass polyethylene (UITPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC,effect ofannealing the recrystallized specimen at 120～I30℃, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220℃, possibly higher than 300℃, the exact temperature is however not sure because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120～130℃.     

DSC ofγ-irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight

The melting and the crystallization of-irradiated (doses: 0–6Mrad) ultra-high molecular weight nascent polyethylene (UHMWPE) and high density nascent polyethylene with normal molecular weight (NMWPE) were investigated by DSC. The heat of melting of the nascent UHMWPE (DSC degree of crystallinity, respectively) increases up to a dose of 3 Mrad, after which it slightly decreases. The heat of the second melting of UHMWPE and of the first and second melting of NMWPE increases slightly up to a dose of 3 Mrad, after which it does not change. The X-ray degree of crystallinity of the nascent non-irradiated and irradiated polymers was 0.62±0.02. The calorimetric crystallinity was compared to the X-ray one. The results show that radiation does not affect the polymer crystallinity, but influences the thermodynamic heat of melting. The increase ofH _m vs. dose in UHMWPE is explained in terms of processes of tie molecule scission within the amorphous regions and on the surface of the crystals, which predominate over crosslinking up to a dose of 3 Mrad. That leads to an increase in the conformational mobility of the molecules and to an increase in the enthalpy, according to Peterlin's formula. The scission of the chains at the points of entangling of the tie molecules leads to a decrease in the temperature and to an increase in the enthalpy of crystallization of UHMWPE vs. dose. In NMWPE these effects are considerably weaker.     

Mechanical properties and enzymatic degradation of poly[(R)-3-hydroxybutyrate] fibers stretched after isothermal crystallization near Tg

Poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers with high tensile strength were prepared by stretching the fibers after isothermal crystallization near the glass transition temperature. Two samples with different molecular weights (M_w = 0.7 × 10⁶ and 4.3 × 10⁶) were used to investigate the effect on tensile strength. Increasing the time for isothermal crystallization of P(3HB) fibers resulted in a decrease in the maximum draw ratio. But, the tensile strength of P(3HB) fibers increased remarkably when the isothermal crystallization time was prolonged to more than 24 h. The tensile strength of low-molecular-weight drawn fibers was higher than that of high-molecular-weight fibers. Therefore, it can be concluded that this procedure does not increase the tensile strength of the high-molecular-weight drawn fibers. This is because, in this drawing method, small crystal nuclei grow initially during the isothermal crystallization process. Then, the molecular chains between the small crystal nuclei that acted as the entanglement points are oriented by stretching. In the case of the high-molecular-weight fibers, because the molecular length between the entanglement points of the small crystal nuclei is too long, the molecular chains are not sufficiently oriented by the stretching process. However, in the case of the low-molecular-weight fibers, the molecular length is suitable for generating the extended chains. Based on the result of X-ray analysis of P(3HB) fibers stretched after isothermal crystallization, fibers have the oriented α-form crystal with 2₁ helix conformation and β-form with planar zigzag conformation. The enzymatic degradation of the stretched P(3HB) fibers was performed by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The enzymatic erosion rate of β-form was faster than that of α-form in the P(3HB) fibers stretched after isothermal crystallization.     

高取向聚对苯二甲酸乙二酯纤维的热收缩应力

为得到具有更高拉伸强度和模量的半晶聚合物纤维,需要使分子链充分结晶和取向,然而这种高度取向样品受热时,随着温度的升高,取向的非晶态分子链熵力增大,解取向可以自发进行.在外加张力较小时,纤维产生热收缩;在定长状态下,表现为外加张力增大,此过程被视为取向材料中＂冻结＂内应力的释放,通常将这种内应力称为热收缩应力。     

An investigation of post treatment on properties and structure of ultrahigh molecular weight polyethylene parts prepared by selective laser sintering for biomedical application

Combined with customization advantage of selective laser sintering (SLS) and excellent performance of ultrahigh molecular weight polyethylene (UHMWPE), it is possible to meet the requirements of artificial joints for biomedical application. However, high viscosity of UHMWPE melt limits the strength of UHMWPE sintered parts. Inspired from metal and ceramic materials, this work aims to improve the performance of UHMWPE parts prepared by SLS using post treatment methods, including heat treatment and hot isostatic pressure (HIP) treatment. Consequently, HIP treatment shows superiority on promoting the performance of UHMWPE sintered parts compared with heat treatment. With the condition of temperature and isostatic pressure, a novel definition of “bonding neck” is given to explain the enhancement of cohesion between each UHMWPE particle in different post treatment. Without any fortifier, the biological safety of artificial joints manufactured by SLS is further guaranteed. Under the isostatic pressure of 12 MPa and temperature of 185°C in HIP treatment, the mechanical strength, tribological performance and other properties are improved dramatically. The tensile strength of the specimen is up to 8.0 MPa, the elongation at break is 99.3%, the impact strength is 8.8 MPa, the friction coefficient is 0.11, the wear rate is 9.3 × 10^?4 mm³/Nm and samples do not show cytotoxicity at the same time.     

THE RHEO-OPTICAL FTIR STUDY OF POLYESTERPOLYETHER SEGMENTED COPOLYMER

The polyester-polyetber segmented copolymer has been investigated by rheo-optical FTIR during stretehing for the informastion on strain induced crystallizatinn of soft segment chains, hard and soft chain orientation.At room temperature 15℃, the soft segment chains of polyester-polyether being to crystallize at 220% strain and the degree of crystallixation increa(?)e with draw ratio, but there will not be any soft segment chains crystallization above 21℃even at bigber strain. The average orientation of hard segment chains are higher than that of the soft chain at high strain level, both are positive oriented into the stretching direction at allover strain level. This indicates that the b(?)d (?)ent ch(?)ins are dispersed into the elastomeric phase and without forming spherulite.     

基于同步辐射超小角X射线散射的高密度聚乙烯空洞化行为研究

以一系列高温结晶后自然冷却的高密度聚乙烯(HDPE)为研究对象,利用同步辐射超小角X射线散射(USAXS)和示差扫描量热技术(DSC)对样品的微观结构进行了分析,并在线研究了单轴拉伸过程中的空洞化行为.结果表明,结晶温度高于110℃后自然冷却到室温的样品中存在热稳定性不同的两组片晶,等温过程形成结构完善的厚片晶,而在冷却过程会形成有缺陷的薄片晶,两组片晶的熔点分别在133和110℃附近.在30℃拉伸时,所有样品都可观察到空洞化并伴随发白现象.并且,等温结晶中形成片晶厚度越大的样品,相应的空洞化现象越明显.在拉伸过程中,空洞出现在屈服点附近,其法向方向平行于拉伸方向,后随应变的增加发生转向,法向方向与拉伸方向垂直.样品中空穴的长度为900~1200 nm.另一方面,随着冷却过程生成薄片晶比例的增加,空洞化趋势下降.此外,提高拉伸温度,样品更倾向发生塑性形变,空洞化程度减弱.     

茂金属聚乙烯的非等温结晶行为及其动力学研究

为探索分子量和支链含量对聚乙烯非等温结晶过程的影响,选用3组样品:(1)不同分子量的无支链线形聚乙烯;(2)低分子量的支链含量不同的试样;(3)高分子量的支链含量不同的试样.用DSC研究了这3组样品的非等温结晶动力学.结果表明:(1)与支链含量相比,分子量大小对结晶的影响是次要的,但高分子量样品的结晶度比低分子量样品低;(2)支链对聚乙烯的非等温结晶有重要影响,在支化聚乙烯中起决定作用;(3)无论是高分子量试样还是低分子量试样,支化含量增加,聚乙烯的结晶温度、结晶度、结晶动力学以及晶体的熔点等显著降低.     

一锅法合成含磺酸基超支化聚氨酯

N-三羟甲基甲基氨基乙磺酸(TES)的胺基与异佛尔酮二异氰酸酯(IPDI)环上活性较高的NCO在低温15℃下发生选择性反应,生成AB3型单体.随后提高反应温度(70～90℃),使AB3型单体原位聚合,一锅法合成出含磺酸基超支化聚氨酯.随着聚合温度的提高,超支化聚氨酯的支化度、分子量及分子量分布系数变大.90℃时,聚合产物的Mn为22410,支化度达到0.87.以此含磺酸基超支化聚氨酯为基础制得的聚合物电解质膜具有良好的耐热性、机械强度,其锂盐室温(约25℃)的离子电导率为3.1×10-5S/cm,100℃达到1.4×10-3 S/cm.     

Nascent particle sizes and degrees of entanglement are responsible for the significant differences in impact strength of ultrahigh molecular weight polyethylene

The physical properties of ultrahigh molecular weight polyethylene (UHMWPE) are generally highly dependent on its molecular weight. However, in our study, it was found that two UHMWPE samples of similar molecular weight, SLL‐5 and GUR 4150, have significantly different impact strengths, with the Charpy impact strength of GUR 4150 being almost 3.4 times that of SLL‐5. To reveal the reasons, the structure–property relations of these UHMWPE materials were investigated. Morphologies of the nascent particles and impact fracture surfaces, the melting behavior, rheological behavior, and three‐phase (crystalline, amorphous, and interphase) contents were characterized by scanning electron microscopy, differential scanning calorimetry, advanced rotary rheometer, and Raman spectroscopy, respectively. It was observed that no significant differences in the crystal structures of SLL‐5 and GUR 4150, but GUR 4150 had smaller nascent particles sizes and a lower degree of entanglement when compared with those of SLL‐5. Accordingly, a mechanism to clarify the significant difference in the impact strengths of GUR 4150 and SLL‐5 was developed. More importantly, this work may be useful for improving the preparation technologies and industrial applications of UHMWPE. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 632–641