ASTM_C_657_-_93_2013.pdf

Designation:C65793(Reapproved 2013)Standard Test Method forD-C Volume Resistivity of Glass1This standard is issued under the fixed designation C657;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the dcvolume resistivity of a smooth,preferably polished,glass bymeasuring the resistance to passage of a small amount of directcurrent through the glass at a voltage high enough to assureadequate sensitivity.This current must be measured understeady-state conditions that is neither a charging current nor aspace-charge,buildup polarization current.1.2 This test method is intended for the determination ofresistivities less than 1016cm in the temperature range from25C to the annealing point of the glass.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For specific hazardstatements,see Section 5.2.Referenced Documents2.1 ASTM Standards:2D257 Test Methods for DC Resistance or Conductance ofInsulating MaterialsD374 Test Methods for Thickness of Solid Electrical Insu-lation(Withdrawn 2013)3D1711 Terminology Relating to Electrical InsulationD1829 Test Method for Electrical Resistance of CeramicMaterials at Elevated Temperatures(Withdrawn 2001)33.Summary of Test Method3.1 The dc volume resistance is measured in accordancewith Test Methods D257,with the specimen located in aheating chamber with adequate temperature control,electricalshielding and insulation of the sample leads as described inTest Method D1829.4.Significance and Use4.1 This experimental procedure yields meaningful data forthe dc volume resistivity of glass.It is designed to minimizespace charge,buildup polarization effects,and surface conduc-tances.The temperature range is limited to room temperatureto the annealing point of the specimen glass.5.Cautions5.1 Thermal emfs should be avoided.Connections involv-ing dissimilar metals can cause measurement difficulties.Evencopper-copper oxide junctions can produce high thermal emfs.Clean,similar metals should be used for electrical junctions.Platinum is recommended.Welded or crimped connectionsrather than soldered joints avoid difficulties.Specimen elec-trodes shall have sufficient cross section for adequate electricalconductance.6.Apparatus6.1 Resistance-Measuring Devices,and the possible prob-lems associated with them are discussed thoroughly in Section9 and Appendixes A1 and A3 of Test Methods D257.Furtherdiscussion of electrometer circuitry is covered in Annex A1 tothis test method.6.2 Heating Chamber(Fig.1)For heating the specimen,asuitable electric furnace shall be used.The construction of thefurnace shall be such that the specimen is subjected to auniform heat application with a minimum of temperaturefluctuation.An adequate muffle should be provided to shieldthe specimen from direct radiation by the heating elements.This may be made of a ceramic such as aluminum oxide orequivalent.A grounded metallic shield shall also be providedwithin the furnace,preferably of silver,stainless steel,orequivalent,to isolate electrically the specimen test circuit fromthe heating element.Furnaces for more than one specimen canbe constructed.The control thermocouple may be located inthe heating chamber outside the metallic shield,as shown inFig.1,or inside the metallic shield.6.3 Two Flat Contacting Electrodes,smaller in diameterthan the specimen electrodes(see 7.6),shall be used to1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Oct.1,2013.Published October 2013.Originallyapproved in 1970.Last previous edition approved in 2008 as C657 93(2008).DOI:10.1520/C0657-93R13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 sandwich the specimen.Sufficient thickness should be used tomaintain an adequate pressure and to provide heat equalizationbetween the specimen and the contacting electrodes.6.3.1 Fig.2 shows the specimen setup in the heatingchamber.The bottom electrode shall be placed at the end of ametal rod and shall support the specimen in the center of thefurnace.The unguard