礦物及固體絕緣材料電阻率測量的小型電極【中文6350字】【PDF+中文WORD】

礦物及固體絕緣材料電阻率測量的小型電極【中文6350字】【PDF+中文WORD】,中文6350字,PDF+中文WORD,礦物,固體,絕緣材料,電阻率,測量,小型,電極,中文,6350,PDF,WORD SCIENCE CHINA Technological Sciences Science China Press and Springer-Verlag Berlin Heidelberg 2011 *Corresponding author(email:)RESEARCH PAPER April 2011 Vol.54 No.4:819825 doi:10.1007/s11431-011-4302-7 Design and application of a small electrode experimental installation for resistivity measurement of mineral and solid insulating material WANG Ling1,2*,LUO Ke1,LI ZiQiang1,GUAN SongYun1,GE Wei1&ZHANG JunYuan1 1 College of Materials and Chemical&Chemistry Engineering,Chengdu University of Technology,Chengdu 610059,China;2 Key Laboratory of Diamond Film,Chengdu University of Technology,Chengdu 610059,China Received October 20,2010;accepted January 7,2011;published online February 3,2011 There has not been an effective method to measure the resistivity of small-size sample of mineral and solid insulating material until now.According to the Chinese National Standard(GB/T1410-2006)and features of digital high resistance meter,a small electrode experimental installation was developed;it can work with current high resistance meter;the sample decreases to 18 mm from standard size 100 mm in diameter and reduces by 30.86 times in area.A three-electrode system is supported and pre-cisely positioned by two insulating bases whose diameter is 60 mm and height is 20 mm,which ensures accuracy of device structure and reliability of measuring results.The key technological parameters are as follows:diameter of high voltage elec-trode is 18mm;diameter of measuring electrode is 14.6 mm;internal diameter and external diameter of guard electrode are 16 and 18 mm,respectively;the gap between guard electrode and measuring electrode is set at 0.6 mm.These parameters are ad-equate for the measurement of flat specimen of mineral and solid insulating material whose diameter is 18 mm.According to the confirmatory experiment on the volume resistivity and surface resistivity,the measuring results are almost the same,using a small electrode experimental installation and a standard electrode.resistivity,insulating property,insulating material,mineral physics,material physics Citation:Wang L,Luo K,Li Z Q,et al.Design and application of a small electrode experimental installation for resistivity measurement of mineral and solid insulating material.Sci China Tech Sci,2011,54:819825,doi:10.1007/s11431-011-4302-7 1 Introduction The resistivity of materials is an important parameter to char-acterize its electrical properties 1,2,and the common meas-urement methods are four-point probe method and three-electrode method 3.The four-point probe method is mainly used in measuring the resistivity of semiconductor and con-ductive materials.For example,Wang et al.4 used this method to develop an accurate four-line AC electrical resis-tance measurement(ERM)apparatus which can monitor in situ the crystallization kinetics of amorphous alloys-Ni80P20,FeZr2 and Fe86B14.Li et al.5 fabricated a series of Co/Cu/Co sandwiches with a semiconductor Si buffer layer using high vacuum electron-beam evaporation method;they studied the dependence of GMR effect and magnetic anisotropy of the sandwiches on the Si buffer layer.Zhou et al.6 studied the change law between temperature and electrical conductivity of Sn(Pb)Te-Bi2Te3 compounds;they concluded that as the temperature goes up,the con-ductivity of the samples decreases rapidly,and its conduc-tivity reaches the max under usual temperature.Ozols et al.7 studied electrical resistivity of SMC with different polymer contents and the SMC with permalloy powders uncoated or coated.Tang et al.8 investigated the tem-perature dependence on resistivity of La1xSrxMnO3 com-820 Wang L,et al.Sci China Tech Sci April(2011)Vol.54 No.4 pounds.The three-electrode method is mainly used for re-sistivity of insulating material.Vila et al.9 researched influence of electron-beam irradiation on the volume resis-tivity of polyethylene and kapton by using this method.Gonon et al.10 studied variation tendency between water content and resistivity of epoxy composites.Insulating material,or dielectric,is a material in which a voltage applied across two points on or within the material produces a small and sometimes negligible current 11.Now,the American National Standard D 257-1999 12 and Chinese National Standard GB/T1410-2006 13 have set rules on the measuring methods(three-electrode method)for resistivity of insulating material.The method is to proc-ess the sample into standard-size wafer(=100 mm,h=13 mm),then measure it with a high resistance meter.Non-metallic minerals play an irreplaceable role in the in-sulating material because of their excellent insulating prop-erty.But there is no effective measurement method for measuring the resistivity of mineral due to difficulties in sample processing or other reasons at present.As a result,it is difficult to study the insulating property of non-metallic mineral.The primary cause is the sample is easy to crack during processing because there may be cleavage,crack or defect in minerals.So it is very difficult to obtain such a large-size standard sample.In addition,for other solid insu-lating material,it is not convenient to process or obtain standard samples in some cases.In recent years,non-metallic mineral is increasingly used in insulating material because of its excellent electrical property and low price.For example,in China the amount of this material used as filler in plastics and rubber reached 375 104 and 120 104 t,respectively in 2005,which indi-cated that it has become a very important part of mineral materials 14.Therefore,to research and develop a kind of experimental installation for measuring resistivity of small-size samples of minerals and solid insulating materi-als can not only study mineral insulating property but also make it possible to measure resistivity of mineral powder and other powder materials1)because the sample size is re-duced largely;thus it is of great significance to exploit min-eral resources and to research and produce new type of mineral materials and insulating materials.In this study,according to the Chinese National Standard(GB/T1410-2006)and the features of high resistance meter,a small electrode experimental installation was developed,which can work with high resistance meter and measure the resistivity of small-size sample(diameter=18 mm)of mineral and solid insulating material.This intallation can measure the volume resistivity and surface resistivity of some non-metallic mineral and solid insulating material sys-temically,and the results of measurement are consistent with their known data and the data measured by the stan-dard electrode(sample diameter=100 mm).2 Resistivity measurement principles of solid insulating material According to the Chinese National Standard GB/T1410-2006,volume resistivity and surface resistivity of the solid insulating material are measured by high resistance meter.The high resistance meter consists of measurement system,three-electrode system and metal shielded box.The diameter of a sample depends on the size of measur-ing electrode,guard electrode and high voltage electrode.Figure 1 is a schematic diagram of a three-electrode sys-tem which is fit for measuring solid insulating material whose diameter is 100 mm.In order to avoid electromag-netic interference,the three-electrode system should be put in the metal shielded box.The measurement principle is as follows.When the volume resistivity of sample is measured(Figure 1(a),the measuring electrode(1-1#)is linked with the measuring junction by the wire(1-2#),high voltage Figure 1 Schematic diagram of the three-electrode method for measuring resistivity of solid insulating material(diameter=100 mm).0#,Sample;1-1#,Measuring electrode;2-1#,Guard electrode;3-1#,High voltage electrode;1-2#,2-2#,3-2#,Wires.(a)Measurement principle of volume resistivity;(b)measurement principle of surface resistivity.1)Wang L,Li Z Q,Luo K,et al.Study on the measurement method for resistivity of mineral powderTaking micro-crystal muscovite for example.Powder Technol,2011(to appear).Wang L,et al.Sci China Tech Sci April(2011)Vol.54 No.4 821 electrode(3-1#)with high voltage terminal by the wire(3-2#)and guard electrode(2-1#)with the grounded junc-tion by the wire(2-2#).The electric current goes through the sample just in the direction of arrowhead(Figure 1(a).Then the volume resistance(Rv)of sample 0#is measured directly by the high resistance meter.According to the Chinese National Standard GB/T1410-2006,the volume resistivity(v)can be calculated by .vVAeRh(1)In the formula,v is the volume resistivity(cm);h,the thickness of the sample(cm);Rv,the volume resistance(),which is measured directly by the high resistance meter;Ae,the effective area of the guard electrode,which is deter-mined by the size of electrode and calculated by the for-mula:21().4dgAe(2)In the formula,d1 is the diameter(cm)of the measuring electrode(Figure 1,1-1#);g,the gap between the measuring electrode and guard electrode(cm);=3.1416.For the standard measuring electrode with diameter=100 mm,Ae=21.237 cm2,and for the self-made small measuring electrode with diameter=18 mm,Ae=1.863 cm2.When the surface resistivity of the sample is measured(Figure 1(b),measuring electrode(1-1#)is linked with the measuring junction by the wire(1-2#),guard electrode(2-1#)with high voltage terminal by the wire(2-2#)and high voltage electrode(3-1#)with the grounded junction by the wire(3-2#).The electric current goes through the sam-ple just in the arrowhead direction(Figure 1(b).The sur-face resistivity(S)of sample 0#can be calculated auto-matically by eq.(3)using the surface resistance(Rs)meas-ured from high resistance meter 15.212.lnsSRdd(3)In the formula,s is surface resistivity();Rs,the surface resistance();d1,the diameter(cm)of the measuring elec-trode;d2,the internal diameter(cm)of the guard electrode.3 Development of the small electrode exper-imental installation Figure 2 is a structural diagram about the small electrode experimental installation used to measure resistivity of mineral and solid insulting material.The measurement prin-ciple is the same as that of the standard electrode system(Figure 1).Because the size of three-electrode of the ex-perimental installation is small,it is important to confirm the size and exact position of the three-electrode and other key technical parameters in this study.3.1 Key technical parameters of the small measuring electrode system The core of whole device is the three-electrode system(Figure 2).And the key technology is to confirm the inter-nal diameter and external diameter of the guard electrode,the diameter of measuring electrode,the gap between guard electrode and measuring electrode,etc.(i)Internal diameter and external diameter of guard elec-trode.The size of the three-electrode is directly determined by the diameter of the sample.If the sample size is under-size,the size of three-electrode will be reduced accordingly.At last,the gap between guard electrode and measuring electrode will become undersized,which will affect the safety in utilization;on the contrary,if the sample diameter were oversized,the installation would not be designed to be a small one.After several experiments,the optimum di-ameter of sample is=18 mm,and its area is 254.34 mm2.Compared with the standard sample(=100 mm,area is 7850 mm2),the area is reduced by 30.86 times,so it is possible to measure the resistivity of small-size sample of minerals and solid insulating materials.In the process of insulation resistance measurement,in order to offset error caused by surface and volume effects,the external diameter d3 of guard electrode(2-1#)and di-ameter d4 of high voltage electrode(3-1#)should be the same as the diameter d0 of sample 0#,d3=d4=d0=18 mm.In addition,due to the small size of the electrode,if guard electrode(2-1#)was too thick,it would lead to decrease in the gap between 1-1#and 2-1#,which might reduce the system security and increase the difficulty in processing.Considering all the factors,the minimum thickness of the guard electrode(2-1#)is 1mm,and the internal diameter of guard electrode(2-1#)is d2=16 mm.(ii)The diameter of the measuring electrode.According to eq.(3),d2/d1 is a fixed value,which is related to surface resistivity,and has nothing to do with the size of the sample.Hence,the value can be obtained by high resistance meter directly.The value of the standard electrode,d2/d1=54 cm/50 cm=1.08,is constant which also applies to the small electrode.Therefore,the diameter of the measuring electrode can be calculated as d1=16 mm/1.08=14.8 mm when the internal diameter of guard electrode(2-1#)is d2=16 mm.(iii)The gap between the guard electrode and the measuring electrode.As the internal diameter of guard electrode is d2=16 mm,the diameter of measuring elec-trode is d1=14.8 mm and the gap is 21/2,gdd the gap is(16 mm 14.8 mm)/20.6 mm.g 822 Wang L,et al.Sci China Tech Sci April(2011)Vol.54 No.4 Figure 2 Structural drawing of small electrode resistivity measurement installation on the resistivity measurements of mineral and solid insulating material(diameter=18 mm).0#,d0,Sample and its diameter;1-1#,d1,Measuring electrode and its diameter;2-1#,d2,d3,Guard electrode,its internal diameter and external diameter;3-1#,d4,High voltage electrode and its diameter;2-2#,3-2#,Rotatable conductive screw;5-1#,up-insulating base;5-2#,down-insulating base;6-1#,Stainless steel mounting bolts;M4,M6,diameter of thread;The remaining number is the size of relevant parts(unit:mm).Attention should be paid to that the maximum working voltage of the high resistance meter is 1 kV,and DC break-down strength is 33 kv/mm in air.Under that circumstance,the critical breakdown gap is g=1 kV/33 kV/mm0.03 mm.That is to say,it usually will not be breakdown as long as g0.03 mm.However,the impurities on the sample surface and suspended particles in the air might fall into the gap when the installation is used;if g is undersize,the gap would be breakdown easily.In our installation,g is 0.6 mm which is 20 times larger than the critical breakdown gap,which can ensure the system security.3.2 Accurate location of small measuring electrode system As shown in Figure 2,the installation includes two bases,the up-insulating base and down-insulating base both with diameter 60 mm and height 20 mm.They can support and locate precisely the three-electrode system to ensure accu-racy of the device structure and reliability of the measure-ment results.Because the gap between the guard electrode(2-1#)and the measuring electrode(1-1#)is only 0.6 mm,if a three-electrode system could not be accurately positioned,it would be difficult to get secure reliable measurement data and be prone to a short circuit and damage the device.In order to facilitate measurement,the guard electrode(2-1#)and the high voltage electrode(3-1#)connect with the measurement system of the high resistance meter by the conductive screws(2-2#,3-2#),respectively.Measuring electrode(1-1#),after an appropriate extension(1-2#),can be connected to the measurement system of the high resis-tance meter.Meanwhile,in order to place sample accurately and conveniently in a fixed position,both the guard electrode(2-1#)and the measuring electrode(1-1#)should outstretch 1 mm more than the insulating base(5-1#),and the high voltage electrode(3-1#)hollow 1mm more than the insu-lating base(5-2#),then a groove(=18.5 mm1 mm)is formed for the sample.In addition,in order to match the high voltage electrode(3-1#)with the measuring electrode(1-1#),stainless steel mounting bolts(6-1#)are used to fix and position the insu-Wang L,et al.Sci China Tech Sci April(2011)Vol.54 No.4 823 lating base(5-1#,5-2#)precisely;in order to facilitate an easy placement and removal of sample,the insulating base(5-1#),relative to the insulating base(5-2#),can rotate at 360 degrees in XY plane and along Z-axis.3.3 Materials selection of small electrode experimental installation As shown in Figure 2,materials of small electrode experi-mental installation mainly include the electrode materials and insulating base materials.(i)Electrode materials.The electrodes for insulating ma-terials should be of a material that is readily applied,allows intimate contact with the specimen surface,and introduces no appreciable error because of electrode resistance or con-tamination of the specimen.Commonly used electrode ma-terials are annealed aluminum foil,spraying metal layer,conductive powder,burned silver,conductive rubber,brass and mercury electrodes,etc 15.The structure characteris-tics of the small electrode experimental installation require the electrodes and conductive screws not only to have good conductivity but also to have sufficient mechanical strength for actual processing and matching with the fixed base.Moreover,in relation to the price,application and reusabil-ity,the final option for the electrode material is solid con-ductive metals,including red copper,silver-copper alloys,stainless steel and so on.In this study,the electrode and conductor screw are made of red copper which has good conductivity(when the temper-ature is 20C,the resistance rate is only 1.69102 mm2/m),a certain mechanical strength plus good corrosion resistance,and is easy for welding and processing 16.(ii)Insulating base materials:Because insulation resis-tance measured by the PC68 digital high resistance meter is very high,reaching as high as 11017,according to eqs.(1)and(2),the relevant volume resistivity of insulating mate-rial(h=3 mm)could reach as high as 7.081018 cm and surface resistivity 11017.If insulation resistivity of the fixed base is relatively low,the measuring results will have a greater error.Therefore,it is required that the fixed base should possess extremely high insulation resistivity(v1017 cm)to avoid a greater impact on the measuring results;simultaneously,the insulating base materials should have strong mechanical strength to conduct support and fixment.Accordingly,the selections for materials are PTFE(F-4),tetrafluoroethylene-ethylene copolymer(F-40),PCTFE(F-3),etc.In this study,PTFE(F-4)is used as the insulating base material;its molecular formula 17 is(CF2CF2)n;it has a good chemical stability and excellent electrical properties(volume resistivity v1017 cm);its long-term working temperature is 250C,decomposition temperature is 415C;its relative dielectric constant(r=2.0)and dielectric loss angle tangent(tg1012 Shus PVC electrical tape 1.261014 2.041014 Table 2 The measuring data of surface resistivity()of small-size sample and standard sample Sample Standard sample (=100 mm)Small-size sample (=18 mm)Standard value of insulation Micro-crystal muscovite 4.391010 2.161010 Isinglass(Perpendicular to the 001)18 4.331011 2.741011 10111012 800-mesh micro-crystal muscovite insulating pouring sealant 19 1.421014 3.741014 10131014 Epoxy phenolic glass cloth rigid laminated sheet(3240)16 2.371014 4.351014 10131014 Silastic 1.191014 1.081014 Soft phlogopite plates 16 5.521010 6.031010 10101011 Alkyd soft mica plate(5131B)6.321013 5.891013 Shus PVC electrical tape 4.131013 3.881013 Wang L,et al.Sci China Tech Sci April(2011)Vol.54 No.4 825 This work was supported by the National Natural Science Foundation of China(Grant No.50974025),the National Key Technologies R&D Pro-gram of China(Grant No.2004BA810B02),the Applied Foundation of Basic Research in Sichuan Province(Grant No.07JY029-029),the Spe-cialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20095122110015)and the Scientific Research Founda-tion of the Education Ministry for Returned Chinese Scholars,China(Grant No.2010-32).1 Liu Q C.Electrical Insulation Design Principles-book2-insulation structure pandect(in Chinese).Beijing:Machinery Industry Press,1988.137 2 Qiu C J,Wang Y H,Wang Y J.Physical Properties of Materials(in Chinese).Harbin:Harbin Institute of Technology press,2003.47-116 3 Guan Z D,Zhang T Z,Jiao J S.Physical Properties of Inorganic Ma-terials(in Chinese).Beijing:Tsingh