ISO INTERNATIONAL STANDARD 7991 First edition 1987-12-15 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEKAYHAPOAHAAOPTAHM3ALMANOCTAHAAPTW3ALWM Glass - Determination of coefficient of mean linear thermal expansion Referencenumber ISO 7991 : 1987 (E) for Standardization No reproduction or networking permitted without license from IHS Not for Resale Foreword Iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through Iso technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in iaison with Iso, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the Iso Councit. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISo 7991 was prepared by Technical Committee ISO/TC 48, Laboratory glassware and related apparatus. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. ? International Organization for Standardization, 1987 Printed in Switzerland Copyright International Organizationfor Standardization No reproduction or networking permitted without license from IHS Not for Resale INTERNATIONAL STANDARD ISO7991:1987 (E) Glass - Determination of coefficient of mean linear thermal expansion Scope and field of application For the purposes of this International Standard, the nominal reference temperature, to, is 20 C; therefore the coefficient of This International Standard specifies a method for determining mean linear thermal expansion is denoted by α(20 oC; t). the coefficient of mean linear thermal expansion of glass in the elastic solid-like state,wellbelowthetransformation tempera- ture (seeISO 7884-8). 4 Apparatus This International Standard applies to all glasses of normal bulk-production compositions. it does not apply to fused silica, 4.1 Device for measuring the specimen length, to an ac- glass ceramics or other glasses of similarly low linear thermal curacy of 0,1%. expansion coefficients. 4.2 Push-rod dilatometer, capable of determining changes 2 References in length of the specimen of 2 × 10-5 l。 (i.e. 2 μm per 100 mm). ISo7884-8,Glass-Viscosityandviscometric fixedpoints Part 8: Determination of (dilatometric) transformation tem- Thecontactforceoftheextensometershouldnotexceed1N. That force shall act through contacts of planes with spherical perature. facesthe radiiof curvature of whichshall be not lessthanthe IEcPublication 584-1,Thermocouples ---Part1:Reference rod diameter of the specimen. In some special assemblies (see tables. figure 1)parallel planes areneeded. The specimen-holding assembly shall ensure that the specimen is held firmly in position and shall prevent even small changes in Definition itsalignmentwithrespecttothepush-rodaxisthroughoutthe For the purposes of this International Standard, the following test (see examples given in the annex). definition applies. If the specimen-holding assembly is made of vitreous silica, see coefficient of mean linear thermal expansion, α(to; t) : The the precautions given in 7.2. ratio of the change in length of a specimen within a From time to time, a performance test shall be carried out using temperature interval to that temperature interval, related to the a reference material (see clause 8). initial specimen length. Itisgivenbythefollowingequation: 4.3 Furnace,compatiblewiththedilatometerassembly.for temperatures up to 50 oC