电场对溶液相变过程影响的热刺激去极化电流分析

为了研究电场对冰晶形成及冰晶结构影响的内部机理,采用热刺激去极化电流(TSDC)测量方法对生物溶液进行了热刺激去极化电流特性的研究,从而根据热刺激去极化电流峰值位置与大小判断电场在溶液相变过程中的作用。以去离子水和氯化钠NaCl生理盐水(其中NaCl质量分数为0.9%)为试样,对比测量了对试样加电场和不加电场条件下的热刺激去极化电流特性。结果表明,在生物溶液低温冷冻过程中施加电场会影响冰晶的结构组成并宏观表现为微小热刺激去极化电流。去离子水冰的热刺激去极化电流曲线上分别在125 K和213 K温度附近出现2个明显的电荷释放峰,其中低温峰是由于玻璃态下水分子偶极转向极化而产生的,高温峰则源于陷阱中空间电荷的释放。而对于生理盐水,只能观察到在138 K温度附近有1个峰,然后随着温度的升高而呈不断增大趋势,可能是由于生理盐水冰中Na+、Cl-热离子极化电导所致。研究表明热刺激去极化电流测量方法可以作为一个分析外加电场对生物溶液低温保存影响机理的有效手段。     

论聚合物热刺激电流谱中的空间电荷峰

一、前言热刺激电流技术能灵敏地反映聚合物的分子运动,以及电荷在聚合物中的贮存、转移过程,是一门较好的热分析技术在国内也已得到愈来愈广泛的应用。聚合物试样的极化方式不同,其热刺激电流谱也不同。本文讨论采用常规试验方法所得到的热刺激电流谱。常规方法试验程序是:试样升温至一定的极化温度,施加直流电场并使试样充分极化,然后使试样在存在电场的情况下冷却至低温,再除去电场,使试样线性升温,测得其热刺激去极化电流与温度的关系──热刺激电流谱。试验是在自     

热刺激电流技术在电缆上的应用

<正> 热刺激电流(TSO)即为去极化电流或电荷释放电流。将绝缘或半导体材料加热至一定温度,施以一定对间的直流电压,以达充分极化,随之降温至低温,使各类极化电荷冻结,而后以等速升温,测出试样经检流计短接的热刺激电流随温度的变化关系,即为热刺激电流谱。在某些温度下,出现电流峰值,这代表材料中某种微观结构的去极化。热刺激电流属介电谱中的一种,是研究高分子材料结构与性能间关系的有效工具。通过它可以求得材料中自由电子迁移率、势井电荷量及     

合成绝缘子材料的TSC试验研究

通过采用热刺激电流法对合成绝缘子材料进行热刺激电流(TSC)的探索性对比测试,力图探索热刺激电流法在评价合成绝缘子特性中的应用可能性.文中对比了同一厂家的两批合成绝缘子试样的TSC特性,初步的试验发现,新旧合成绝缘子之间的TSC测试结果是明显不同的,结合试样的憎水性试验以及微观结构的分析,表明TSC测试结果在一定程度上能够与合成绝缘子材料的老化联系起来.通过深入系统的研究合成绝缘子的TSC特性和合成绝缘子材料的老化特性之间的关系,将能够为合成绝缘子老化特性及老化程度的评价提供新的方法.     

多壁碳纳米管/交联聚乙烯的空间电荷特性研究

为研究多壁碳纳米管(MWNTs)对多壁碳纳米管/交联聚乙烯复合绝缘材料空间电荷特性的影响,采用电声脉冲法对熔融密炼制作的MWNTs/XLPE纳米复合材料试样进行空间电荷分布测试。同时利用极化-去极化电流法测试试样的去极化电流,并用标准油杯电极测试试样的直流击穿场强。结果表明:在不同电场强度下,MWNTs质量分数为0.2%的复合材料试样的空间电荷注入量和累积量都明显小于纯XLPE,具有较强的空间电荷抑制能力;在室温条件下,MWNTs质量分数为0.2%的复合材料的直流击穿场强小于纯XLPE,但稳定性好。     

电晕老化对硅橡胶材料热刺激电流和表面情况影响研究

文中使用了电晕老化测试平台,对硅橡胶进行了初步的电晕老化试验,然后对电晕老化后的试样进行了热刺激电流和扫描电镜测试,并对测试结果进行了初步分析。试验结果表明电晕老化造成了硅橡胶绝缘材料热刺激电流增大、表面裂解的现象,从而造成了绝缘材料的劣化。     

温度对PDC法测试冲击电容器结果的影响研究

为了研究不同测试温度对冲击电容器极化去极化电流法(PDC)测试结果的影响,对未老化和热老化10天的冲击电容器分别进行了20℃、40℃、60℃、80℃下的PDC测试。通过分析不同测试温度下的极化去极化电流,得到了冲击电容器不同测试温度下的直流电导率、0.1 Hz下的介质损耗因数值(tanδ)和时间常数不对称系数(τ_as)。结果表明,随着测试温度的上升,冲击电容器热老化前后极化电流、直流电导率及0.1 Hz下的介质损耗因数值均随着测试温度的升高先增大后适当减小。而时间常数不对称系数虽然随着温度变化有一定的波动,但变化并不明显,因此,在对冲击电容器进行PDC测试时可选择时间常数不对称系数作为判断冲击电容器绝缘状态的依据。     

有机酸对变压器油纸绝缘进一步热老化的催化作用试验研究

为研究有机酸对电力变压器油纸绝缘进一步热老化的催化作用,制作了初始水分质量分数均为0.4%的绝缘纸试样和不同类型的酸性绝缘油溶液,在室温(25℃)和90℃下,研究了酸在油纸绝缘系统中的溶解分布特性。接着在90℃下对油纸绝缘试样进行加速热老化,测试了不同老化阶段试样的绝缘纸聚合度以及油纸绝缘试样的极化去极化电流。结果表明:甲酸主要分布在绝缘纸中,并会导致纸中水分向油中扩散,硬脂酸主要分布在绝缘油中;相比于硬脂酸,甲酸极大地加速了绝缘纸的降解速率,使极化去极化电流曲线的上移幅度也更大;甲酸酸值达到0.1×10-3、硬脂酸酸值达到0.3×10-3时会对油纸绝缘进一步热老化起到明显的催化作用;在分析实际运行中影响变压器油纸绝缘热老化的因素时,需特别考虑甲酸等低分子强极性酸对油纸绝缘进一步热老化的催化作用。     

TSC测试中寄生电流的特性研究

热刺激电流测试(TSC)中寄生电流的存在对测试结果会产生一定的影响.通过对TSC电极系统的热电效应测试和聚酰亚胺的寄生电流、TSC测试,分析了寄生电流产生的机理及特性,探讨了寄生电流对TSC测试的影响.研究表明寄生电流主要由聚酰亚胺中的恒偶极子松弛产生,热电效应和聚酰亚胺内部陷阱电荷释放并非主导因素.当聚酰亚胺内部结构发生变化时,寄生电流将改变.寄生电流叠加于TSC电流中,严重影响了TSC测试精度,为消除其影响可扣除TSC电流中的寄生电流.     

臭氧浓度对HTV硅橡胶材料的老化作用

为了研究电晕放电过程中所产生的臭氧对高温硫化(HTV)硅橡胶老化作用的影响,利用研制的臭氧老化试验装置,考虑臭氧浓度及作用时间等因素,对HTV硅橡胶复合绝缘子试样进行了系统的臭氧老化试验,并且对老化后的试样进行了扫描电镜(SEM)、傅里叶红外光谱(FTIR)分析、憎水性和热刺激电流(TSC)测试。试验结果表明,臭氧能够导致硅橡胶材料表面缺陷增多,憎水性丧失,而且浓度越高,老化会越严重。进一步分析得出,硅橡胶材料在臭氧环境作用下,材料表面平滑、致密的物理结构被破坏,产生了孔洞等缺陷,并且当臭氧环境作用强度达到一定程度后,材料的物理结构的破坏将更为严重;同时,化学基团含量发生变化,试样中Si-O-Si结构减少,羟基和Si-O键增多,试样主链和侧链断裂。     

Dielectric properties of poly(phenylene sulfide) as a function of temperature and frequency

Dielectric properties of poly(phenylene sulfide) (PPS), a kind of super engineering plastic, were investigated over a wide temperature range by measuring its frequency spectra of complex permittivity and thermally stimulated polarization and depolarization currents (TSPC and TSDC). Experimental results indicate that its permittivity and dielectric loss factor remain stable and maintain low values up to around 140 °C, despite the fact that its glass transition appears at a much lower temperature of 88 °C. As for TSPC and TSDC, a very small peak associated with the glass transition appears at about 110 °C. Furthermore, a much clearer TSPC peak due to orientation of dipole moments associated with the ether linkage induced by the cross‐linking reaction appears at about 150–170 °C. The corresponding TSDC peak due to randomization of these dipoles is very small compared to the TSPC peak, since PPS was cross‐linked during the high‐temperature process in the TSPC measurement, which made rotation of the dipoles difficult. At temperatures higher than 150 °C, both the real and imaginary parts of the complex permittivity show significant increases with increase in temperature and decrease in frequency. This is attributable to the transport of the charge carriers. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

TSDC in epoxy networks of well-controlled architecture:Experimental evidence for local and non-local relaxation process

Local and non-local relaxation processes were distinguished by investigating the heating rate dependence of the thermally stimulated discharge current (TSDC) line-shape in the case of three epoxy networks of well-controlled architecture. These networks were chosen because their chain dynamics differ by the relative extent of their local and short-scale cooperative molecular motions, as a consequence of marked differences in crosslink density. As far as local motions are concerned, the TSDC evolution measured at low temperature can be accounted for by using a model based on a distribution of activation energies. On the other hand, the higher temperature part of the spectrum of the densely crosslinked network, which mainly results from cooperative motions, shows a much different behavior which cannot be fitted by such a distribution model     

The influence of ions on the thermally stimulated discharge currentspectra of water-treed additive-free low-density polyethylene

The effects of water treeing on steady state dc currents and thermally stimulated discharge current spectra (TSDC) of additive-free low density polyethylene (LDPE) were studied using heavily water-treed material in solutions of LiCl, LiCl plus HCl, MnCl₂ and FeCl ₃. Significant changes in the dc conductivity of treed samples are attributed to the effects of ions. For such samples, graphs of the logarithm of current versus inverse temperature show three distinct linear regions. The transition temperatures demarcating these regions appear to correlate with those reported for thermal relaxations. TSDC spectra of water-treed samples show a dependence on both the ionic solutions used and on the poling conditions. For LiCl treed samples, twin peaks in the TSDC spectra were produced only under specific poling conditions. These peaks may be correlated with thermal relaxations observed using differential scanning calorimetry (DSC). The melting point temperature and the melting peak area derived from DSC spectra were reduced by treeing     

Electrical conduction and dielectric relaxation in polyethylene terephthalate succinate

Electrical conduction and complex permittivity are examined in polyethylene terephthalate succinate, focusing on their relations to dielectric relaxation processes. Both the real and imaginary parts of the complex permittivity, namely, the dielectric constant ε′_r and the dielectric loss factor ε′′_r, increase with a decrease in frequency, especially at high temperatures. They are both ascribed to the transport of ionic mobile carriers. Namely, the carrier transport forms a conduction current that should contribute to ε′′_r. On this occasion, if charge exchange does not occur at the two electrodes, heterocharge layers should be formed before the electrodes. This should increase the charge density on the electrodes, thus contributing to ε′_r. In addition to the increase in ε′_r and ε′′_r due to mobile ions, two relaxation processes, one due to micro‐Brownian motion of dipoles and the other due to orientation and magnitude change of the dipole moment induced by two end groups in the polymer main chain, are observed. Corresponding to these two relaxation processes, two thermally stimulated discharge current (TSDC) peaks appear. The two TSDC peaks as well as the increments in ε′_r and ε′′_r become larger when the crystallinity of the sample decreases. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 1–8, 2010; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20956     

Space- and surface-charge analysis of plasma-preprocessed PTFE thinfilms

The space- and surface-charge behavior of corona-charged polytetrafluoroethylene thin films after plasma processing were studied experimentally by space-charge density distribution measurement and thermally stimulated discharge current (TSDC) measurement. The effect of the antistatic process using low-pressure discharge plasma and charge elimination process dipping in tap water was examined. The surface composition of the samples which were plasma- processed was analyzed with X-ray photoelectron spectroscopy (XPS) to study the mechanisms of antistatic process. It was found that charge elimination of plasma-processed samples was enhanced, independently of the kind of processing gas during the plasma processing. Oxygen and nitrogen atoms were observed from the XPS measurement of plasma-processed samples. In particular, a large amount of nitrogen atoms was found on the surface of the samples plasma processed in pure nitrogen gas. The samples plasma processed in pure nitrogen gas showed a large hetero TSDC peak at room temperature before the charge-elimination process. This might be due to nitrogen atoms on the sample surface that were generated during plasma processing     

The hydration structure studied by TSDC. Myoglobin and haemoglobin

The coordination scheme of water in myoglobin and haemoglobin, the two oxygen carrier proteins in vertebrates, is still far from being fully understood. The TSDC (thermally stimulated depolarization currents) technique is a sensitive tool to study water molecules bound to biological macromolecules and characterized by mobility and order degree, quite different from those of bulk water. TSDC spectra for both proteins were recorded in the temperature range 100 to 300 K, at very low hydration levels (h=0.01 to 0.62) obtained with different procedures. Different classes of water molecules were found: the preferred hydration sites and the water dipole activation energies are discussed. In particular, the existence of a critical hydration level which induces a partially irreversible structural transition was monitored in myoglobin. The technique allowed estimation of the average number of hydrogen bonds established by the water molecules in the inner cages of haemoglobin at different hydration levels     

Thermal step and TSDC measurement in PVC

The space charge behavior of some polyvinylchloride (PVC) samples with different molecular microstructures, obtained through chemical modification of PVC has been analyzed by means of the thermal step (TS) and the thermally stimulated discharge current (TSDC) techniques. The magnitude of the space charge distribution has been shown to be lower as the degree of chemical modification increases. Combining the TS and the TSDC methods allowed us to study minority carriers, which could not be observed by a single TS measurement     

Effects of Mn-doping on TSDC and degradation of BaTiO3

The effects of Mn-doping on TSDC (Thermally Stimulated Depolarization Current) and electrical degradation of BaTiO₃ have been investigated. TSDCs of un-doped BaTiO₃ and Ba(Ti_1−x Mn_x)O_3−δ exhibited the three sharp TSDC peaks around phase transition temperatures. TSDC of Ba(Ti_0.995Mg_0.005)O_2.995 increased gradually from 50^∘C and this anomalous depolarization current kept going up well above the Curie temperature (∼130^∘C). TSDCs of un-doped BaTiO₃ and Ba(Ti_0.995Mn_0.005)O_3−δ decreased in the temperature range above the Curie point, whereas a slight increase in TSDC was confirmed at the specimen of Ba(Ti_0.99Mn_0.01)O_3−δ. TSDCs of Ba(Ti_0.995−y Mg_0.005Mn_y)O_3−δ (y = 0.005, 0.01) were lower than that of Ba(Ti_0.995Mg_0.005)O_2.995.     

熔融碳酸盐燃料电池烧结电极制备方法

该文探讨一种环保的、可连续生产的适合熔融碳酸盐燃料电池(molten carbonate fuel cell,MCFC)使用要求的烧结电极制备方法,以泡沫镍和冲孔镀镍钢带为支撑体,聚乙烯醇与羧甲基纤维素钠的混合溶液作为黏结剂,T255羰基镍粉为导电活性材料,运用拉浆法在不同的烧结温度下制备MCFC电极。在此基础上,采用煤油浸入法测量了制备电极的孔隙率,利用扫描电镜分析电极的微观形貌,通过热重分析仪测试镍浆的失重和热流变化,并对组装后MCFC中电极的电化学性能进行测试。测试结果表明,以镀镍钢带为支撑体的电极较泡沫镍电极具有更好的强度和电化学性能,在一定的烧结条件下,采用拉浆工艺能够制备满足MCFC要求的电极。     

Space charge behavior in low-density polyethylene

The space charge distribution in low-density polyethylene (LDPE) was measured with the pulsed electroacoustic (PEA) method. We used three types of LDPE: LDPE-L and LDPE-H were prepared by the high pressure process, and m-LDPE was polymerized with a metallocene catalyst. Space charge in LDPE strongly depended upon the electrode material. Semiconductive electrodes enhanced carrier injection into LDPE and, as a result, space charge. The density, polymerization process, applied field, temperature and so on also affected the space charge behavior. This space charge behavior was compared with the results of dc current measurements