尿嘧啶和5-溴尿嘧啶的低温热容

采用综合物性测量系统(PPMS)的热容测量模块在1.9-300 K温度区间内对两种药物中间体(尿嘧啶和5-溴尿嘧啶)的低温热容进行了测量与研究. 结果表明, 在测量温区内两种化合物的低温热容随温度的上升而逐步增加, 无任何热异常现象产生; 在相同温度下, 5-溴尿嘧啶的热容数值始终高于尿嘧啶. 利用低温热容理论模型对热容数据进行了拟合, 并计算得到了0-300 K温区的摩尔熵变、焓变等热力学函数. 此外, 通过热容拟合数据计算得到的尿嘧啶和5-溴尿嘧啶在298.15 K的标准摩尔规定熵分别为(132.48±1.32)和(165.39±1.65) J·K^-1·mol^-1.     

四方晶体稀土-铁-硼系金属间化合物的结构和磁性

用磁测量和X射线衍射方法研究了R_(15)B_7Fe_(78)(R=MM,Pr,Nd,Sm,Gd,Y)和Nd_(15)B7(Fe_(1-x)M_x)_(78)(M=Co,Mn,Cr)的结构和内禀磁性。X射线衍射实验表明,这些化合物皆属四方结构。R_(15)B_7Fe_(28)的晶格常数随稀土原子序数的增加而减小,反映了镧系收缩的特点。居里温度随稀土金属原子序数的增加而增高,反映了稀土-铁原子间的间接交换作用的影响,Gd_(15)B_7Fe_(78)具有最高的居里温度。在Nd_(15)B_7(Fe_(1-x)M_z)_(78)中,以Co代Fe时,晶格常数随x的增加而减小;居里温度随x的增加而单调显著上升。以Mn代Fe时,晶格常数随x的增加而增大;居里温度则随x的增加而急剧下降。居里温度的变化,说明R_(15)B_7Fe_(78)的居里温度主要由3d过渡族原子间的直接交换作用所决定的。以Co代Fe,当x=0.2时,Nd_(15)B_7(Fe_(1-x)Co_x)_(78)的饱和磁化强度出现极值。     

分解水制氢的硝酸钾-碘混合循环初探

本文提出了一个分解水制氢的新混合循环——硝酸钾-碘混合循环首先对该循环进行了热力学分析。(3)式的热分解反应的标准吉氏自由能变化随温度的上升而减小。△G°=0时的温度约为943K,1273K时的△G°约为—120kJ/mol-H_2,故作为热化学循环制氢的高温吸热反应是合适的;(4)式所示的电解反应,其标准理论分解电压为0.54 V。实验结果表明,热分解反应在1073K时的转化率达85％,接近平衡转化率。电解反应的过电压较低。在实验条件下,测得分解电压加过电压在50,100,200mA/cm2的电流密度下分别为0.61,O.66和0.71V。     

微生物燃料电池影响因素及作用机理探讨

以生活污水为初始接种体, 以醋酸钠水溶液为原料, 构建了一个无媒介体、无膜的单室微生物燃料电池, 考察了溶液的浓度、外电阻、温度和氧气的加入等因素对电池性能的影响, 监测了电池外电压和两极电极电势的变化过程, 分析了微生物燃料电池的运行机理. 研究结果表明: (1) 阳极吸附的微生物的活性是影响电池输出电压(输出功率)的关键因素. 营养液初始浓度越高, 微生物活性越高, 输出最大电压越高, 输出电压与浓度之间的关系符合MONOD方程; 溶液中溶氧的存在使微生物活性明显降低, 但溶氧浓度降低到一定程度后, 活性逐步恢复; 随着电池温度的升高, 微生物活性快速上升, 但温度突变到50 ℃后, 微生物活性明显降低; (2) 电池换水后, 由微生物活性所决定的阳极电势迅速达到平衡, 而阴极电势需要较长的时间才能达到极大值; (3) 随电流密度的变化, 两极电极电势相应发生变化, 其变化趋势符合原电池的基本规律; (4) 随外电阻的变化, 电池输出功率出现极大值, 即当外电阻为200 Ω时, 电池输出功率达到346 mW/m2.     

278.15-313.15 K下糖-水二元体系的介电常数

测定了D-(-)-果糖、D-(+)-葡萄糖、D-(+)-半乳糖、D-(+)-木糖和D-(-)-核糖五种糖的水溶液在不同质量摩尔浓度和不同温度下的介电常数(D). 结果表明, 在一定温度下, 这些糖的水溶液介电常数对数值都随糖浓度的增大而减小; 在一定糖浓度时, 介电常数值随温度升高而减小. 果糖、葡萄糖、半乳糖和木糖水溶液的介电常数(D)随温度的变化均满足关系式: lgD=A1-B1(T-298.15), 而核糖水溶液则符合: lgD=A2-B2(T-298.15)+C2(T-298.15)2. 此外, 这五种糖的水溶液的介电常数与摩尔分数(x)满足关系式: lg(D/D0)=-B3x. 在相同温度和浓度时, 介电常数的大小顺序通常为: 水>半乳糖-水>果糖-水>葡萄糖-水≥木糖-水(而核糖较特殊).     

Ba0.95Ce0.9Y0.1O3-α固体氧化物燃料电池性能

以Ba0.95Ce0.9Y0.1O3-α为固体电解质,Pt为电极,组成氢-空气燃料电池,测定了该电池600～1000℃下电流-电压特性、电极极化特性和电解质中各电荷载流子(质子、氧离子、电子空穴)迁移数及其电导率。实验表明,该电池放电性能良好,能稳定地输出电能,1000℃时的最大输出电流密度为680mA.cm^-^2。正、负Pt电极极化特性很小,放电时的电压耗损主要由电解质电阻产生。在氢-空气燃料电池条件下,Ba0.95Ce0.9Y0.1O3-α显示混合离子(质子+氧离子)导电性。随着温度升高,质子迁移数减小而氧离子迁移数增大,当温度为780℃时,质子和氧离子迁移数相同(0.46),在低于780℃时,质子电导占优势,而在高于780℃时,氧离子电导占优势。     

Ba0.95Ce0.9Y03-α固体氧化物燃料电池性能

以Ba0.95Ce0.9Y0.1O3-α为固体电解质,Pt为电极,组成氢-空气燃料电池,测定了该电池600～1000℃下电流-电压特性、电极极化特性和电解质中各电荷载流子(质子、氧离子、电子空穴)迁移数及其电导率.实验表明,该电池放电性能良好,能稳定地输出电能,1000℃时的最大输出电流密度为680 mA@cm-2.正、负Pt电极极化特性很小,放电时的电压耗损主要由电解质电阻产生.在氢-空气燃料电池条件下,Ba0.95Ce0.9Y0.1O3-α显示混合离子(质子+氧离子)导电性.随着温度升高,质子迁移数减小而氧离子迁移数增大,当温度为780℃时,质子和氧离子迁移数相同(0.46),在低于780℃时,质子电导占优势,而在高于780℃时,氧离子电导占优势.     

低场下钕-铁-硼永磁体居里温度的测量

本文报道了一种测量高矫顽力钕-铁-硼永磁体居里温度的新方法和一些实验结果。新方法的原理是在弱交流场下,测量磁性材料的磁化率κ随温度的变化,从而确定它的居里点。由于测量时所加交流磁场低达2.5Oe,材料近似地处于自发磁化状态,因而消除了外磁场的影响。     

镉-氧化汞电池低温放电电压滞后现象的研究

镉-氧化汞扣式碱性电池在低温(如-40℃)放电时有较严重的电压滞后现象.此种滞后现象是由氧化汞电极所产生的.本工作应用恒电流和动态恒电位等极化方法研究氧化汞电极的电极反应.氧化汞电极的滞后电压随温度升高而减小,随放电率的增高而增大,且能达最大值.此最大滞后电压几与温度无关,但与电极中所含导电材料的性质有关.例如,使用银粉作为导电材料时所测得的最大滞后电压约为40毫伏,而镍粉则约为140毫伏.电池中的电毛细活性杂质会加重电压滞后现象.例如,若在电池中使用化学稳定性较差的隔膜,则其电压滞后现象会因电池搁置时间的增长而更为严重.上述电压滞后现象是由于氧化汞电极在阴极还原时的新相形成超电努所造成的,最大滞后电压即相当于形成最小生长核心时的新相形成超电势.     

聚(2,5-苯并噁唑)的流变性能

用自制的3-氨基-4-羟基苯甲酸盐酸盐(ABBAH)在多聚磷酸(PPA)中合成聚(2,5-苯并噁唑)(ABPBO),利用衰减全反射红外光谱(ATR-IR)表征了其化学结构.分别用平板流变仪和毛细管流变仪对合成的ABPBO-PPA溶液进行动态和稳态流变测试.结果表明:ABPBO-PPA溶液的储能模量(G ')和损耗模量(G')均随频率升高而增大,且储能模量比损耗模量上升得更快;ABPBO-PPA溶液随温度升高趋于牛顿流体,随浓度升高非牛顿性更显著,ABPBO-PPA溶液表现出强烈的假塑性,并且不同温度下溶液的剪切黏度差值随剪切应力增大而减小.     

Influence of γ-ray Irradiation on the PTC Effect of EPDM/Carbon Black Composite

Introduction The positive temperature coefficient(PTC) effect is characterized by an increase of resistivity with an elevated temperature.The PTC effect of carbon black(CB) filled polymers is useful for self-regulation heaters,over-current protectors,sensors,etc.Much work has been done on the PTC effect of the carbon black filled crystalline polymer composite[1-4],whereas carbon black filled amorphous polymers have not drawn researchers much attention because the PTC effect in these composites is small or cannot be detected[5-7].In this work,the influence of γ-ray irradiation on the PTC effect of CB filled amorphous ethylene-propylene-diene terpolymer(EPDM) composites was studied.     

YBa2Cu3O7-x/Thermoplastic polymer composite thermistors

Conducting YBa₂Cu₃O_7-x was incorporated in to polyethylene matrices to produce composite materials with low room temperature resistivity and sizable positive temperature coefficient (PTC) resistance effects. The intensity of the PTC effect for these composites was found to be as large as 10 orders of magnitude. The location of the PTC phenomenon is determined by the choice of polymer matrix. The mechanism for the PTC effect in crystalline polymer composites is related to the percolation behaviour of the composites and the thermal expansion of the polymer matrix.     

Effects of thermal volume expansion on positive temperature coefficient effect for carbon black filled polymer composites

Polymeric positive temperature coefficient (PTC) materials have been prepared by incorporating carbon black (CB) into two different polymer matrices, crystalline high density polyethylene (HDPE) and amorphous polystyrene (PS). The effects of thermal volume expansion on the electrical properties of conductive polymer composites were studied. The volume fraction of conductive particles behaves like a switch from insulator to conductor in the polymeric PTC composite. Our mathematical model and experimental model have proved that the abrupt resistivity increase at PTC transition range and at the percolation curve close to the critical volume fraction for both polymeric PTC composites have the same conductive mechanism. The thermal expansion is one of the key factors responsible for the PTC effect and can be seen by comparing the PTC transition curves from model predictions and experiment. Furthermore, the model predicts PTC curves of CB/PS composite more successfully than it does for the CB/HDPE composite, and the reasons for this are also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3078–3083, 2007     

Roles of work of adhesion between carbon blacks and thermoplastic polymers on electrical properties of composites

The effect of the work of adhesion between carbon blacks and different thermoplastic polymers on the positive temperature coefficient (PTC) of composites was investigated. Thermoplastic polymers, such as EVA, LDPE, LLDPE, HDPE, and PP, were used with the addition of 30 wt% of carbon blacks. The work of adhesion based on the surface free energy of a composite was studied in the context of two-liquid contact angle measurements using deionized water and diiodomethane. It was observed that the resistivity on PTC behavior was greatly increased near the crystalline melting temperature, due to the thermal expansion of polymeric matrix. It was shown that the PTC intensity defined as the ratio of the maximum resistivity (rho(max)) to the resistivity at room temperature (rho(RT)) had the largest value on CB/HDPE composites. From the experimental results, the decrease in the work of adhesion induced by interactions between carbon black surfaces and polymer chains is an important factor in the fabrication of a PTC composite.     

Influences of Plasma Treatment and 60Co γ-Ray Radiation on the Over-Voltage Positive Temperature Coefficient of High Density Polyethylene/Carbon Black Nano Composites

Argon plasma-pretreated high-density polyethylene (PHDPE) was blended with the conductive nano carbon black (CB) and inorganic flame retardant (magnesium hydroxide, Mg(OH)₂) was added. Influences of the CB content, plasma treatment time, plasma treatment power, and dosage of ⁶⁰Co γ-ray radiation on positive temperature coefficient (PTC) behaviors of composite were studied. In addition, the over-voltage resistance behavior of the composites was also investigated. The free radical of PHDPE was measured by 1,1-diphenyl-2-picryhydrazyl (DPPH) method. The gel contents of composite were measured by solvent extraction method. The results showed that the room-temperature volume resistivity and PTC effect of composite were improved significantly with plasma treatment. The PHDPE composite with ⁶⁰Co γ-ray radiation eliminated the negative temperature coefficient (NTC) effect in the composites effectively, and the PTC intensity of composite was increased. With increasing of radiation dosage from 20 Mrads to 80 Mrads, the gel content of composites increased up to 83.84% and the response temperature of composites shifted to low temperature (127.5 °C to 114.8 °C). In this work, the composites also successfully passed the over-voltage resistance test, and possessed good reproducibility.     

炭黑填充聚甲基乙烯基硅氧烷硫化胶的阻温特性与电阻弛豫

研究了炭黑填充硅橡胶硫化胶的热循环以及热处理过程中的导电行为,发现在热循环中阻温关系曲线逐渐向低电阻方向移动,而在恒温下发生电阻弛豫现象;分析了硫化胶的导电机制,讨论了阻温关系发生移动的原因.     

不同粒径炭黑混合对复合型导电材料PTC性能的影响

研究了炭黑分散效果对具有PTC效应的高密度聚乙烯／炭黑导电复合材料性能的影响。实验结果表明，由不同粒度和比表面积的两种炭黑混合后填充的复合材料同由导电性能较好的乙炔炭黑填充复合材料比较，前者具有较低的渗滤阀值、较高的临界温度、优良的PTC特性以及电阻稳定性好的特点．     

Enhanced Reproducibility of Positive Temperature Coefficient Effect of CB/HDPE/PVDF Composites with the Addition of Ionic Liquid

Developing an effective method for improving the reproducibility of positive temperature coefficient(PTC) effect is of great significance for large-scale application of polymer based PTC composites, owing to its contribution to the security and reliability. Herein, we developed a carbon black(CB)/high density polyethylene(HDPE)/poly(vinylidene fluoride)(PVDF) composite with outstanding PTC reproducibility, by incorporating 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([OMIm][NTf_2]) into the composite. After multiple repeated temperature cycles, the PTC performance of as-prepared material keeps almost unchanged and the varition of resistance at room temperature is less than 7%. Our studies revealed that [OMIm][NTf2] contributes to the improvement of PTC reproducibility in two ways:(i)it acts as an efficient plasticizer for refining the co-continuous phase morphology of HDPE/PVDE blends;(ii) it inhibits the crystallization of PVDF through the dilution effect, leading to more overlaps of the volume shrinkage process of HDPE and PVDF melt which results in the decrease of interface gap between HDPE and PVDF. This study demonstrated that ionic liquids as the multifunctional agents have great potential for improving the reproducibility in the application of the binary polymer based PTC composites.     

Carbon black‐filled polyolefins as positive temperature coefficient materials: The effect of in situ grafting during melt compounding

For the production of polymer‐based conducting composites serving as positive temperature coefficient (PTC) materials with lower room‐temperature resistivity and sufficiently high PTC intensity, carbon black has been pretreated with acrylic acid and some initiator and then melt‐mixed with low‐density polyethylene. Because of the in situ formation of covalent bonding at the filler/matrix interface, the distribution status and thermally induced displacement habit of the conductive fillers have changed accordingly. As a result, the electrical performance of the composites can be tailored as desired. The amount of acrylic acid and the treatment sequence of carbon black exert an important influence on the effectiveness of the modification. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 127–134, 2003     

Effect of Initiator on the Over-Voltage Positive Temperature Coefficient of Linear Low Density Polyethylene/Carbon Black Nano Composites

The composite of linear low density polyethylene (LLDPE) with carbon black (CB) and inorganic flame retardant (aluminum hydroxide, Al(OH)₃) was prepared by melt-blending method. The effect of cross-linking on the stability of positive temperature coefficient (PTC) of composite and the elimination of negative temperature coefficient (NTC) of composite were investigated. LLDPE was chemically cross-linking with different contents of initiator (dicumyl peroxide, DCP). The cross-linking effects of composite were analyzed by gel content analysis, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). By the effect of DCP, not only the composite appeared a high PTC intensity, but also the NTC effect of composite was eliminated. In this investigation, the optimum PTC intensity of composite reached 5.87 orders of magnitude for the composition of LLD0.l0C33.7A28, and the PTC transitional temperature of composite decreased with increasing of DCP content. In addition, the good reproducibility of composites was proved by thermal cycling, and successfully passed the test of over-voltage resistance.