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 中國科學(xué): 技術(shù)科學(xué) 2011 年第 41 卷第 7 期: 890 -895 【中文6350字】 礦物及固體絕緣材料電阻率測量的小型電極實驗裝置與應(yīng)用 汪靈①②*, 羅柯①, 李自強①, 關(guān)淞云①, 葛偉①, 張浚源① 成都理工大學(xué)材料與化學(xué)化工學(xué)院, 成都 610059，中國; 成都理工大學(xué)金剛石薄膜實驗室, 成都 610059，中國 收稿日期: 2010-10-20； 接受日期: 2011-01-07；在線發(fā)布日期：2011-02-03 目前還沒有一種礦物及固體絕緣材料小塊樣品電阻率測量的有效方法。為此，根據(jù)國家標(biāo)準(zhǔn)GB/T1410-2006 和數(shù)字高阻計特點,研制了一種與通用高阻計配套使用的小型電極實驗裝置, 將試樣直徑由標(biāo)準(zhǔn)電極的100 mm 減小到18 mm,試樣面積減少了30.86 倍；該裝置采用2個直徑60 mm×高20 mm的絕緣基座對三電極系統(tǒng)進(jìn)行支撐和精確定位,以實現(xiàn)裝置結(jié)構(gòu)的精準(zhǔn)性和測量結(jié)果的可靠性,其關(guān)鍵技術(shù)參數(shù)是高壓電極和測量電極的直徑分別為18 和14.6 mm,保護(hù)電極內(nèi)徑和外徑分別為16和18 mm,保護(hù)電極與測量電極間隙尺寸為0.6 mm,適用于直徑φ=18 mm的礦物及固體絕緣材料平板試樣電阻率測量；體積電阻率和表面電阻率驗證實驗結(jié)果表明,采用小型電極實驗裝置與標(biāo)準(zhǔn)電極測量結(jié)果一致。 1、 前言 電阻率是表征材料電學(xué)性能的重要參數(shù)[1, 2],其常用測量方法是四探針法和三電極法[3]四探針法主要用于半導(dǎo)體和導(dǎo)體材料電阻率的測量,例如:王亞平等人[4]以四探針法為基礎(chǔ),發(fā)展了一種高精度四線交流電阻測試設(shè)備,能夠原位監(jiān)測Ni80P20, FeZr2 和Fe86B14 非晶合金的晶化動力學(xué)過程。李冠雄等人[5]采用高真空電子束蒸發(fā)方法制備半導(dǎo)體材料Si為過渡層的Co/Cu/Co 三明治膜過程中,利用四探針法研究了三明治膜的巨磁電阻效應(yīng)及磁各向異性與Si過渡層的關(guān)系。周西松等人[6]利用四探針法研究了Sn(Pb)Te-Bi2Te3系熱電材料的電導(dǎo)率隨溫度的變化規(guī)律,結(jié)果表明常溫下樣品的電導(dǎo)率最大, 之后隨溫度升高明顯降低。Ozols等人[7]使用四探針法研究了在不同聚合物含量和有無鐵鎳合金粉末涂層的條件下軟磁化合物的電阻率。Tang 等人[8]利用四探針法研究了La1?xSrxMnO3 系列混合物在不同溫度下的電阻曲線。而三電極法則主要用于絕緣材料電阻率的測量, 例如: Vila 等人[9]采用三電極法研究了電子照射對聚乙烯與聚酰亞胺膠帶體積電阻的影響。Gonon等人[10]使用三電極系統(tǒng)研究了環(huán)氧復(fù)合材料電阻率隨含水量的變化趨勢。絕緣材料是指當(dāng)電壓施加在材料兩點之間或其內(nèi)部時, 只產(chǎn)生極小甚至可以忽略不計的微弱電流[11]。 目前,絕緣材料電阻率測量方法(三電極法)已有相應(yīng)的美國標(biāo)準(zhǔn)ASTM D 257-1999[12]和國家標(biāo)準(zhǔn)GB/T1410-2006(與國標(biāo)IEC60093-1980 等效)[13]。其方法是：將樣品加工成直徑為=100 mm 左右、厚h=1~3 mm的標(biāo)準(zhǔn)尺寸，然后利用高阻計進(jìn)行測量。非金屬礦物通常具有優(yōu)良的絕緣性能,但是，由于樣品加工困難等原因，目前還沒有一種測量礦物電阻率的有效方法,難以對非金屬礦物絕緣性能進(jìn)行表征和研究。其主要原因是:許多礦物的解理發(fā)育,或本身存在裂紋與缺陷,在加工過程中容易開裂,難以獲得如此大的標(biāo)準(zhǔn)尺寸樣品。另外,對于其他固體絕緣材料,在一些情況下要加工或獲取標(biāo)準(zhǔn)尺寸的樣品也是非常困難的。 近年來，非金屬礦物因其優(yōu)良的電氣性能和低廉的價格被越來越多的應(yīng)用于絕緣材料中，例如：2005年我國的礦物填料在塑料和橡膠中的用量已分別達(dá)到375×104 和120×104 t，成為我國礦物材料產(chǎn)業(yè)的重要組成部分[14]。因此，研究一種適用于礦物及固體絕緣材料小塊樣品電阻率測量的實驗裝置和方法，不僅對礦物絕緣性能的表征和研究具有不可替代的作用，而且由于實驗樣品尺寸的大幅減少，將使礦物粉體及其他粉體材料電阻率測量成為可能，這對于礦物資源開發(fā)利用以及新型絕緣材料研究與應(yīng)用都具有十分重要的意義。 本工作根據(jù)中國的標(biāo)準(zhǔn)GB/T1410-2006 和數(shù)字高阻計特點，研制出一種適用于礦物及固體絕緣材料小塊樣品(直徑φ=18 mm)電阻率測量的小型電極實驗裝置，并與通用高阻計配套使用，對一些非金屬礦物及固體絕緣材料的體積電阻率和表面電阻率進(jìn)行較系統(tǒng)測量， 通過與標(biāo)準(zhǔn)電極(樣品直徑φ=100 mm)測試結(jié)果以及這些材料已知數(shù)據(jù)進(jìn)行比較分析，獲得了一致的結(jié)果。 2、 固體絕緣材料電阻率測量原理 根據(jù)國家標(biāo)準(zhǔn)GB/T1410-2006, 固體絕緣材料體積電阻和表面電阻率采用高阻儀表進(jìn)行測量。高阻儀表由數(shù)據(jù)測量系統(tǒng)、三電極系統(tǒng)和金屬屏蔽箱組成。試樣直徑大小由測量電極、保護(hù)電極和高壓電極所組成的三電極系統(tǒng)尺寸大小共同決定。圖1是適用于直徑φ=100 mm 固體絕緣材料電阻率測量的三電極系統(tǒng)工作原理示意圖，為了消除外來電磁干擾所產(chǎn)生的影響，三電極系統(tǒng)應(yīng)放置于金屬屏蔽箱中, 其測量原理如下。 測量體積電阻時(圖1(a))， 測量電極1-1#通過導(dǎo)線1-2#與高阻儀表的測量端相連，高壓電極3-1#通過導(dǎo)線3-2#與高阻儀表的高壓端相連，保護(hù)電極2-1#則通過導(dǎo)線2-2#與高阻儀表的接地端相連，電流按圖1(a)箭頭所示方向穿過測試樣品，被測樣品0#的體積電阻(Rv)由高阻儀表可直接讀取。 圖1 適用于直徑=100 mm 固體絕緣材料電阻率測量的三電極系統(tǒng)工作原理示意圖 0#－試樣; 1-1#－測量電極; 2-1#－保護(hù)電極; 3-1#－高壓電極; 1-2#, 2-2#, 3-2#－導(dǎo)線(a) 體積電阻測量原理; (b) 表面電阻測量原理 根據(jù)體積電阻(Rv)測試結(jié)果和國家標(biāo)準(zhǔn)GB/T1410-2006 計算公式如下, 可得到被測樣品的體積電阻率（ρv） ρv= RvAeh (1) 式中，v 為體積電阻率(Ω·cm)；h為樣品厚度(cm) ；Rv為體積電阻(Ω), 由高阻計直接測試得到；Ae為被保護(hù)電極的有效面積，由電極尺寸決定，其計算公式為： Ae=ππd1+g24 （2） 式中， d1 為測量電極(圖1,1-1#)直徑(cm)，g為測量電極與保護(hù)電極的間隙(cm), πp=3.1416。對于直徑φ=100 mm 的標(biāo)準(zhǔn)電極, Ae=21.237 cm2；對于直徑φ=18mm 自制小型電極, Ae=1.863 cm2。 測量表面電阻率時(圖1(b)),測量電極1-1#通過導(dǎo)線1-2#與高阻儀表的測量端相連，保護(hù)電極 2-1#通過導(dǎo)線2-2#與高阻儀表的高壓端相連,高壓電極 3-1#則通過導(dǎo)線3-2#與高阻儀表的接地端相連， 電流按圖1(b)箭頭所示方向從測試樣品表面通過, 被測樣品0#的表面電阻率(ρs)由高阻儀表根據(jù)表面電阻(Rs)測量數(shù)據(jù),經(jīng)如下公式自動換算得到[15]。 ρs=Rs2πl(wèi)nd2d1 （3） 式中,ρs 為表面電阻率; Rs 為表面電阻(Ω)；d1 為測量電極直徑(cm)；d2 為保護(hù)電極(圖1, 2-1#)內(nèi)徑(cm)。 3 、 小型電極實驗裝置的研制 圖2是一種適用于直徑φ=18 mm 礦物及固體絕緣材料電阻率測量的小型電極實驗裝置結(jié)構(gòu)圖，其測量原理與標(biāo)準(zhǔn)電極系統(tǒng)(圖1) 完全相同。由于該裝置的三電極尺寸較小，其研制的關(guān)鍵是三電極尺寸大小等重要技術(shù)參數(shù)確定及其精確定位。 3.1 小型電極系統(tǒng)的關(guān)鍵技術(shù)參數(shù) 三電極系統(tǒng)是整個裝置的核心，如圖2 所示,其技術(shù)關(guān)鍵是保護(hù)電極的內(nèi)外徑、測量電極的直徑以及保護(hù)電極與測量電極之間的間隙尺寸大小等關(guān)鍵技術(shù)參數(shù)的確定。 （i）保護(hù)電極的內(nèi)外徑尺寸。樣品直徑的大小直接決定三電極的尺寸大小。樣品直徑過小, 三電極尺寸將相應(yīng)減小, 并導(dǎo)致保護(hù)電極與測量電極之間的間隙尺寸g 過小,從而影響整個裝置的使用安全性;相反, 若樣品尺寸過大,又使得實驗裝置失去其小型化意義。經(jīng)過多次試驗,最終確定樣品直徑φ=18 mm,其面積為254.34 mm2。而φ=100 mm 的標(biāo)準(zhǔn)樣品, 其面積為7850 mm2,與之相比,小型電極樣品面積減少了30.86 倍,使礦物及固體絕緣材料小塊樣品電阻率測量成為可能。 在絕緣電阻測量時,為了抵消表面或體積效應(yīng)引起的誤差, 保護(hù)電極2-1#外徑d3和高壓電極3-1#直徑d4應(yīng)與樣品0#直徑d0相同, 即d3=d4= d0=18 mm。另外,由于電極尺寸較小,如果保護(hù)電極2-1#厚度過大, 將導(dǎo)致與高壓電極3-1#之間隙尺寸過小而降低系統(tǒng)的安全性,并將大大增大加工難度。因此,綜合各方面因素，保護(hù)電極2-1#的最小厚度為1 mm,則保護(hù)電極2-1#內(nèi)徑d2=16 mm。 （ii） 測量電極直徑尺寸。由公式(3)可知, d2/d1 為定值, 表面電阻率與d2/d1 比值有關(guān), 而與試樣大小無關(guān), 因此,可由高阻計直接讀取. 由于標(biāo)準(zhǔn)電極d2/d1=54 cm/50 cm=1.08, 此常數(shù)不可更改, 那么小型電極d2/d1 也應(yīng)等于1.08。由于小型電極的保護(hù)電極2-1#內(nèi)徑d2=16 mm,那么可確定測量電極1-1#直徑d1 = 16 mm/1.08=14.8 mm。 （iii） 保護(hù)電極與測量電極之間的間隙尺寸。由于保護(hù)電極2-1#內(nèi)徑d2=16 mm,測量電極1-1#直徑d1=14.8 mm,并由于二者之間的間隙距離g= d2-d1/2,那么,可確定間隙尺寸 g=(16 mm-14.8 mm) / 2 =0.6 mm 需要說明的是,由于高阻計最高工作電壓通常為1 kV,而空氣的直流擊穿強度為33 kV/mm[16],在最高工作電壓下,臨界擊穿間歇g=1 kV/(33 kV/mm)≈0.03 mm。也就是說,一般情況下,只要間歇尺寸g> 0.03 mm, 就能保證不被擊穿。但是,在使用過程中,由于樣品表面雜質(zhì)和空氣中懸浮顆?？赡苈淙腴g隙中,如果g 過小,就容易被擊穿, 難以保證設(shè)備安全. 由于該裝置g=0.6 mm,大于臨界擊穿間歇近20 倍, 能夠保證電極系統(tǒng)的安全使用。 圖2 適用于直徑=18 mm 礦物及固體絕緣材料電阻率測量的小型電極實驗裝置結(jié)構(gòu)圖 0#, d0－測試樣品及其直徑; 1-1#, d1－測量電極及其直徑; 2-1#, d2 , d3－保護(hù)電極及其內(nèi)外徑; 3-1#, d4－高壓電極及其直徑;2-2#, 3-2#－可調(diào)導(dǎo)體螺桿; 5-1#－上絕緣基座; 5-2#－下絕緣基座; 6-1#－不銹鋼固定螺栓; M4, M6－螺桿螺紋直徑; 其余數(shù)字為相關(guān)零件的尺寸大小(單位: mm) 3.2 小型電極系統(tǒng)的精確定位 如圖2 所示,該裝置采用直徑60 mm×高20 mm的上絕緣基座5-1#和下絕緣基座5-2#對三電極系統(tǒng)進(jìn)行支撐和精確定位, 以實現(xiàn)裝置結(jié)構(gòu)的精準(zhǔn)性和測量結(jié)果的可靠性。因為, 保護(hù)電極2-1#與測量電極1-1#的間隙距離只有0.6 mm, 如果三電極系統(tǒng)不能精確定位, 將難以獲得可靠測量數(shù)據(jù), 并容易出現(xiàn)短路, 使儀器遭到破壞. 為了便于測量, 保護(hù)電極2-1#和高壓電極3-1#分別通過導(dǎo)體螺桿2-2#和3-2#與高阻計測量系統(tǒng)實現(xiàn)聯(lián)接, 而測量電極1-1#則通過適當(dāng)加長與測量端口相連。 同時,為了便于樣品精確放置在固定位置, 保護(hù)電極2-1#和測量電極1-1#相對基座5-1#向下伸出1mm,而高壓電極3-1#相對基座5-2#向內(nèi)凹陷1 mm,從而形成φ=18.5 mm×1 mm樣品放置凹槽。 另外, 為了使高壓電極3-1#與測量電極1-1#吻合,采用不銹鋼固定螺栓6-1#將基座5-1#和5-2#進(jìn)行固定和精確定位；為了便于樣品安放和取出方便,使基座5-1#能夠相對于基座5-2#沿Z 軸和XY 平面內(nèi)360°活動和轉(zhuǎn)動。 3.3 小型電極實驗裝置的材料選擇 如圖2 所示，小型電極實驗裝置材料主要包括電極材料和絕緣基座材料。 (i) 電極材料。電極材料應(yīng)選取能與試樣緊密接觸的材料,而且不會因施加外電極引進(jìn)雜質(zhì)而造成測量誤差,還要保證測量使用的方便、安全等。常用的電極材料有退火鋁箔、噴鍍金屬層、導(dǎo)電粉末、燒銀、導(dǎo)電橡膠、黃銅和水銀電極等[15]。而從小型電極實驗裝置的結(jié)構(gòu)特點來看不僅要求電極和導(dǎo)體螺桿有較高的導(dǎo)電性能,而且要有足夠的機械強度以便于實際加工和與固定基座相配合, 另外考慮價格、使用難易程度、重復(fù)使用性后決定選用固體導(dǎo)電金屬作為電極材料, 可選用的材料有: 紫銅、銀銅、不銹鋼等。 本實例選用紫銅作為電極和導(dǎo)體螺桿材料,因為紫銅具有良好的導(dǎo)電性能(20℃時,電阻率僅為1.69×10-2Ω.mm2m),并具有一定的機械強度和良好的耐腐蝕性, 易于焊接、加工等優(yōu)點[16]。 (ii) 絕緣基座材料: 由于PC68高阻計所測的絕緣電阻極高, 最高可達(dá)1×1017Ω, 根據(jù)公式(1)和(2)換算成h=3 mm 的絕緣材料的體積電阻率最高可達(dá)7.08×1018Ω.cm, 和表面電阻率最高可達(dá)1×1017。如果固定基座絕緣電阻率相對較小會對測試結(jié)果產(chǎn)生較大的誤差. 因此,固定基座首先要求有極高的電阻率(ρv >1017Ω.cm),以避免對測試結(jié)果產(chǎn)生較大的影響；同時,要求材料有較強的機械強度,以起支撐固定作用。據(jù)此,可選用的材料有聚四氟乙烯(F-4)、四氟乙烯和乙烯共聚物(F-40)、聚三氟氯乙烯(F-3)等。 本實例選用聚四氟乙烯(F-4)作為絕緣基座,其分子式為[17] —( CF2-CF2)— n, 化學(xué)穩(wěn)定性較好,長期工作溫度 250℃,分解溫度為 415℃,電氣性能優(yōu)良(體積電阻率ρv >1017Ω.cm), 相對介電常數(shù)(εγ=2.0)和介質(zhì)損耗角正切(tgσ<2×10-4)在已知固體絕緣材料中是最低的, 機械強度也較高(抗張強度s =1370~3000 N/cm2)[16]。 4 驗證實驗 4.1實驗樣品與加工 實驗樣品有兩類，一類是固體非金屬礦物，主要有： 微晶白云母，四川鑫炬礦業(yè)資源開發(fā)股份有限公司生產(chǎn)；白云母片,四川丹巴云母廠提供。另一類是固體絕緣材料,主要有: 800目微晶白云母絕緣灌注膠片,本課題組研制；環(huán)氧酚醛玻璃布板(3240)，四川東方絕緣材料股份有限公司生產(chǎn)；硅橡膠，四川東方絕緣材料股份有限公司生產(chǎn)；金云母軟板,成都興東方電工材料研究有限公司生產(chǎn)，醇酸柔軟云母板(5131B)，成都興東方電工材料研究有限公司生產(chǎn)；舒氏PVC 電氣膠帶, 舒氏集團生產(chǎn)。 將同一樣品分別加工成直徑φ=100 mm和φ=18mm,厚度h=0.3~3 mm 的圓片。但舒氏PVC 電氣膠帶除外,其制備方法是: 將膠帶剪成數(shù)條使其呈米字型層層緊密平鋪, 直至平鋪成邊長 a>100 mm, 厚h=3 mm 的正方板, 然后分別剪成直徑φ=100 mm和φ=18 mm 圓片。另外,由于體積電阻和表面電阻對材料表面污穢和水膜等比較敏感, 需進(jìn)行清潔與烘干處理,其方法是:用沾有無水乙醇的脫脂棉擦拭每個樣品表面,然后用蒸餾水沖洗,再將清洗后的樣品放入電熱恒溫鼓風(fēng)干燥箱中,在控溫110℃的條件下烘干24 h,取出后分別裝入密封袋中待測。 4.2電阻率的測試方法 采用上海精密科學(xué)儀器有限公司生產(chǎn)的PC68 型數(shù)字高阻計(工作電壓220 V,電壓誤差±3%,測量范圍1×103~1×1017 ), 并分別使用標(biāo)準(zhǔn)電極和小型電極對標(biāo)準(zhǔn)樣品和小塊樣品的體積電阻和表面電阻率進(jìn)行測試分析。測試條件: 溫度 t=15℃,對濕度 RH=62%, 施加電壓U=500 V。所有測量均重復(fù)三次,分別取其平均值作為最終結(jié)果。 4.3測量結(jié)果與分析 表1和2是礦物及固體絕緣材料標(biāo)準(zhǔn)樣品與小塊樣品體積電阻率(Ω.cm)和表面電阻率(Ω)測量結(jié)果?？梢钥闯?采用標(biāo)準(zhǔn)電極對φ=100 mm 標(biāo)準(zhǔn)樣品測試結(jié)果與同一樣品的已知的標(biāo)準(zhǔn)值基本相同, 說明該儀器的測試結(jié)果符合測量要求；同時，與采用小型電極對φ=18 mm 的小塊樣品的測量結(jié)果也基本相同,說明小型電極也能夠比較準(zhǔn)確地測量礦物及其他固體絕緣材料小塊樣品的電阻率。需要說明的是,表1和2中測試結(jié)果并不是絕對相同,其原因是電阻率測試結(jié)果還與測試溫度、濕度、樣品烘干時間等因素有關(guān),而且儀器誤差和各個材料的不均勻性等對測試結(jié)果也有一定的影響?？偟膩砜? 其測試數(shù)據(jù)變化在儀器的正常誤差范圍之內(nèi)。以上結(jié)果說明,采用小型電極實驗裝置測量電阻率是有效的,適用于直徑φ=18 mm 礦物及固體絕緣材料小塊樣品體積電阻率和表面電阻率的測量。 5 結(jié)論 (ⅰ) 研制了一種能夠與通用高阻計配套使用, 適用于礦物及固體絕緣材料小塊樣品電阻率測量的小型電極實驗裝置,將試樣直徑由標(biāo)準(zhǔn)電極的100 mm 減小到18 mm,樣品面積減少了30.86 倍。 (ⅱ) 該裝置采用2個直徑60 mm×高20 mm 的絕緣基座對對測量電極、保護(hù)電極、高壓電極所組成的三電極系統(tǒng)進(jìn)行支撐和精確定位, 以實現(xiàn)裝置結(jié)構(gòu)的精準(zhǔn)性和測量結(jié)果的可靠性,其關(guān)鍵技術(shù)參數(shù)是高壓電極和測量電極直徑分別為18 和14.6 mm,保護(hù)電極內(nèi)徑和外徑分別為16 和18 mm,保護(hù)電極與測量電極間隙尺寸為0.6 mm。 (ⅲ) 驗證實驗結(jié)果表明,小型電極實驗裝置與通用高阻計配套使用, 能夠?qū)χ睆溅?18 mm礦物及固體絕緣材料平板試樣的體積電阻率和表面電阻率進(jìn)行測量, 其結(jié)果與采用標(biāo)準(zhǔn)電極測量結(jié)果一致。 表1 礦物及固體絕緣材料標(biāo)準(zhǔn)樣品與小塊樣品體積電阻率(Ω.cm)測量結(jié)果 表2 礦物及固體絕緣材料標(biāo)準(zhǔn)樣品與小塊樣品的表面電阻率(Ω.cm)測量結(jié)果 參考文獻(xiàn) 1 劉其昶. 電氣絕緣結(jié)構(gòu)設(shè)計原理-中冊-絕緣結(jié)構(gòu)總論. 北京: 機械工業(yè)出版社, 1988. 137 2 邱成軍, 王元化, 王義杰. 材料物理性能. 哈爾濱: 哈爾濱工業(yè)大學(xué)出版社, 2003. 47–116 3 關(guān)振鐸, 張?zhí)? 焦金生. 無機材料物理性能. 北京: 清華大學(xué)出版社, 1992. 207–212 4 王亞平, 盧柯. 非晶態(tài)合金晶化過程的高精度電阻監(jiān)測研究. 中國科學(xué)E 輯: 技術(shù)科學(xué), 2000, 20: 193–199 5 李冠雄, 沈鴻烈, 沈勤我, 等. Si 過渡層對Co/Cu/Co 三明治膜巨磁電阻效應(yīng)的影響. 中國科學(xué)E 輯: 技術(shù)科學(xué), 2000, 30: 15–21 6 周西松, 鄧元, 韋國丹, 等. 溶劑熱法合成系熱電材料Sn(Pb)Te-Bi2Te3系熱電材料及其性能研究. 中國科學(xué)E輯: 技術(shù)科學(xué), 2003, 33: 217–221 7 Ozols A, Pagnola M, García D I, et al. Electroless coating of Permalloy powder and DC-resistivity of alloy composites. Surf Coat Tech,2006, 200: 6821–6825 8 Tang G C, Yu Y, Chen W, et al. The electrical resistivity and thermal infrared properties of La1?xSrxMnO3 compounds. J Alloy Compd, 2008,461: 486–489 9 Vila F, Sessler G M, Sykj H. The influence of electron-beam irradiation on the volume resistivity of polyethylene and kapton. J Electrostat,2005, 63: 749–754 10 Gonon P, Hong T P, Lesaint O, et al. Influence of high levels of water absorption on the resistivity and dielectric permittivity of epoxy composites. Polym Test, 2005, 24: 799–804 11 ASTM D 1711-2002. Standard Terminology Relating to Electrical Insulation. American Society for Testing and Materials, Philadelphia,2002 12 ASTM D 257-1999. Standard Test Methods for DC Resistance or Conductance of Insulating Materials. American Society for Testing andMaterials, Philadelphia, 1999 13 GB/T 1410-2006, 固體絕緣材料體積電阻率和表面電阻率試驗方法. 中國國家標(biāo)準(zhǔn)化管理委員會, 北京, 2006 14 袁繼祖. 非金屬礦物填料與加工技術(shù). 北京: 化學(xué)工業(yè)出版社, 2006. 8 15 伍洪標(biāo). 無機非金屬材料實驗. 北京: 化學(xué)工業(yè)出版社, 2002. 341–343 16 李正吾. 新電工手冊. 合肥: 安徽科技出版社, 2000. 1794–1885 17 廣州電器研究所上海試驗站譯. 電工材料手冊. 北京: 中國工業(yè)出版社, 1963. 76 18 礦產(chǎn)資源綜合利用編委會. 礦產(chǎn)資源綜合利用手冊. 北京: 科學(xué)出版社, 2000. 599 19 趙燕玲. 微晶白云母在絕緣灌注膠功能復(fù)合材料中的應(yīng)用基礎(chǔ)研究. 碩士學(xué)位論文. 成都: 成都理工大學(xué), 2007. 37 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