1、DEUTSCHE NORM February 1998 Glass (IS0 7991 : 1987) Determination of coefficient of mean linear thermal expansion DIN IS0 7991 - ICs 81.040.1 O Descriptors: Glass, thermal expansion, testing. Supersedes DIN 52328, March 1985 edition. Glas - Bestimmung des mittleren thermischen Lngen- ausdehnungskoef
2、fizienten (IS0 7991 : 1987) This standard incorporates International Standard IS0 7991 Glass - Determination of coefficient of mean linear thermal expansion. A comma is used as the decimal marker. National foreword This standard has been prepared by ISO/TC 48. The responsible German body involved in
3、 its preparation was the Normenausschu Materialprfung (Mate- rials Testing Standards Committee), Technical Committee Physikalische Prfverfahren fr Glas. DIN IS0 7884-8 and DIN IEC 584-1 are the standards corresponding to International Standard IS0 7884-8 and IEC Publication 584-1, respectively, refe
4、rred to in clause 2 of the IS0 Standard. Amendments DIN 52328, March 1985 edition, has been superseded by the specifications of DIN IS0 7991. Previous editions DIN 52328: 1961 -01, 1967-04, 1985-03. National Annex NA Standard referred to (and not included in References) DIN IS0 7884-8 Glass - Viscos
5、ity and viscometric fixed points - Part 8: Determination of (dilatometric) transformation temperature (IS0 7884-8 : 1987) IS0 Standard comprises 7 pages. No pari of this standard may be reproduced without the prior permission of Ref. No. DIN IS0 7991 : 1998-02 IN Deutsches Institut fr Normung e. V.,
6、 Berlin. leuth Verlag GmbH, D-i0772 Berlin, has the exclusive right of sale for German Standards (DIN-Normen). English price group 07 Sales No. 0407 02.99 Page 1 IS0 7991 : 1987 Glass Determination of coefficient of mean linear thermal expansion Foreword IS0 (the International Organization for Stand
7、ardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right
8、to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison 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 Intern
9、ational Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 7991 was prepared by Technical Committee ISO/TC 48, Laboratory glassware and related apparatus. Users should note that al
10、l 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. Page 2 IS0 7991 : 1987 1 Scope and field of application This International Standard specifies a method for determin
11、ing the coefficient of mean linear thermal expansion of glass in the elastic solid-like state, well below the transformation tempera- ture (see IS0 7884-8). This International Standard applies to all glasses of normal bulk-production compositions. It does not apply to fused silica, glass ceramics or
12、 other glasses of similarly low linear thermal expansion coefficients. 2 References IS0 7884-8, Glass - Viscositv and viscometric fixed points - Part 8: Determination perature. IEC Publication 584-1, tables. of dilatometric transformation tem- Thermocouples - Part I: Reference 3 Definition For the p
13、urposes of this International Standard, the following definition applies. coefficient of mean linear thermal expansion, dto; t) : The ratio of the change in length of a specimen within a temperature interval to that temperature interval, related to the initial specimen length. It is given by the fol
14、lowing equation: 1 1-1, a(to; I) = - x - lo t - to . (1) where to is the initial or reference temperature; t is the actual (constant or variable) specimen tem- perature; lo is the length at temperature to of the specimen of glass under test (usually a rod made from the glass); I is the specimen leng
15、th at temperature t. For the purposes of this International Standard, the nominal reference temperature, to, is 20 OC; therefore the coefficient of mean linear thermal expansion is denoted by a(20 OC; t). 4 Apparatus 4.1 curacy of 0,l %. Device for measuring the specimen length, to an ac- 4.2 in len
16、gth of the specimen of 2 x 100 mm). Push-rod dilatometer, capable of determining changes Io (i.e. 2 pm per The contact force of the extensometer should not exceed 1 N. That force shall act through contacts of planes with spherical faces the radii of curvature of which shall be not less than the rod
17、diameter of the specimen. In some special assemblies (see figure 1 parallel planes are needed. The specimen-holding assembly shall ensure that the specimen is held firmly in position and shall prevent even small changes in its alignment with respect to the push-rod axis throughout the test (seo exam
18、ples given in the annex). If the specimen-holding assembly is made of vitreous silica, see the precautions given in 7.2. From time to time, a performance test shall be carried out using a reference material (see clause 8). 4.3 Furnace, compatible with the dilatometer assembly, for temperatures up to
19、 50 OC above the expected transformation temperature. The working position of the furnace relative to the dilatometer assembly shall be defined with a repeatability of 0,5 mm in both the axial and the radial directions. Within the range of testing temperatures (i.e. up to tempera- tures about 150 OC
20、 below the highest expected transformation temperature, rg, and at least up to 300 OC), the furnace shall be capable of maintaining a constant temperature to f 2 OC over the whole specimen length. 4.4 Furnace control device, suitable for the desired rate of increase in temperature up to (5 f 1) OC/m
21、in within the test range (see 6.1) and for a cooling rate of (2 k 0.2) OC/min for the annealing procedure according to 5.2. Page 3 IS0 7991 : 1987 4.5 Temperature-measuring device (e.g. a thermocouple of type E, J or K in accordance with IEC 584-1), capable of determining the temperature of the spec
22、imen to f 2 OC in the temperature range between to and i. 5 Test specimen 5.1 Shape and size The test specimen is usually in the form of a rod. Its shape depends on the type of dilatometer used. The length Io shall be at least 5 x IO4 times the resolution of the dilatometers measuring device for the
23、 change in length. NOTE - The specimen may be, for example, a rod either with a cir- cular cross-section having a diameter of 5 mm or with a square cross- section 5 mm x 5 mm, and between 25 and 100 mm in length. In cer- tain cases, a cross-section of at least 100 mm2 is more convenient see the anne
24、x). 5.2 Preparation The test specimen shall be annealed before the test by heating it to about 30 OC above the transformation temperature and then cooling it to about 150 OC below the transformation temperature at a rate of (2 k 0.2) OC/min, followed by further cooling to room temperature in draught
25、-free air. 5.3 Number The test shall be carried out with two test specimens (see also 7.4). 6 Procedure 6.1 Choice of the test range In accordance with clause 3, the nominal reference temperature is 20 OC. For practical reasons, however, the measurement may be started between 18 and 28 OC. The prefe
26、rred final actual temperature is 290 OC 10 x 10-6 K-1. If the results for the two test specimens differ by not more than 0,2 x K-, take the arithmetic mean. If the difference is larger, repeat the test with two other test specimens. 8 Performance test In order to check that the whole test device is
27、functioning cor- rectly, the test procedure and calculation laid down in clauses 6 and 7 shall be carried out on a specimen of a reference material, the value of the coefficient of mean linear thermal expansion of which is certified. Recommended reference materials are as follows : - vitreous silica
28、 annealed according to 7.2; - sapphire single crystal; - chemically pure platinum. NOTE - Sintered alumina A1203i as a reference material is very insen- sitive to the thermal treatment applied in the test procedure laid down in this International Standard. However, the values of the mean linear ther
29、mal expansion coefficient differ from one rod to another. The shape and dimensions of the reference specimen shall be similar to those of the specimens usually tested in the test device. Care shall be taken to ensure that the thermal expansion behaviour of the reference material is not altered by th
30、e test. If the reference material is a glass, it shall be annealed (or re- annealed) in accordance with 5.2, unless other procedures are specified by the certifier. li Standardization (ISO), 1, rue de Varemb, Case postale 56, CH-121 1 Geneva 20, Switzerland. Enquiries about sources of certified refe
31、rence materials (CRMsi may be addressed to the Secretariat of REMCO, International Organization for Page 5 IS0 7991 : 1987 9 Test report e) type of test run (constant or increasing temperature, rate of increase); The test report shall include the following information : a) reference to this Internat
32、ional Standard; b specification, type and state of delivery of the glass fi expressed in IO-6K-1 - K-1; coefficient of mean linear thermal expansion a(20 OC; t) to two significant figures, if a(20 OC; t) 10 x 10-6 K -1. d) type of push-rod dilatometer used; For the temperatures to and t, use the nom
33、inal values (see 7.4). Devices for self-adjusting alignment of specimen and push-rod axis (This annex forms an integral part of the standard.) Ideally the axes of the test specimen and push-rod coincide, and the length lo should lie in the same axis. In practice, small deviations between the axes of
34、 the test specimen and push-rod may occur. Such deviations are negligible only when that misalignment remains constant throughout the test. Similar considerations hold true for the push-rod direction and the working direction of the extensometer. Changes in alignment (e.g. caused by vibration of the
35、 apparatus) shall be avoided by appropriate devices as shown in the examples (figures 1 and 2). An example for minimizing changes in alignment in a dilatometer assembly working almost vertically is illustrated in figure 1. The guiding devices made from platinum wire prevent further lateral changes i
36、n the position of specimen and push- rod once the stable position is achieved by slight shaking. The axial movements caused by thermal expansion, however, are not hindered. Exactly vertically mounted dilatometer assemblies have been found to be the most sensitive with respect to changes in alignment
37、 during the test. Page 6 IS0 7991 : 1987 1 Specimen-holding tube with dilatometer base and sealed end plug ground flat perpendicular to tube axis, made from fused silica 2 Push-rod made from fused silica 3 Guiding device for the push-rod, made from platinum wire, 0.5 to 1 mm in diameter 4 Guiding de
38、vice for the specimen, made from platinum wire, 0,5 to 1 mm in diameter NOTE - Between the base and the push-rod, half the tube is cut away so that the test specimen can be easily changed. Figure 1 - Example of a specimen-holding and push-rod assembly of a dilatometer working almost vertically Page
39、7 IS0 7991 : 1987 An example for minimizing changes in alignment in a distance holders. The push-rod is also supported by two dilatometer working horizontally is illustrated in figure 2. The spheres of suitable diameter guided on the same guide-rod. support for the specimen consists of four spheres
40、(e.g. made After the apparatus has been shaken gently the test specimen from ruby or fused silica), a cylindrical guide-rod, and suitable and push-rod achieve a stable position. A 12 Dilatometer base 7 Test ,men (, / A-A specimen 3 3 1 Specimen-holding tube with dilatometer base made from fused sili
41、ca 2 Push-rod made from fused silica 3 Distance holders made from fused silica 4 Supporting spheres made from fused silica or ruby 5 Guide-rod made from fused silica NOTE - Between the base and the push-rod, half the tube is cut away so that the test specimen can be easily changed. J Figure 2 - Example of a specimen-holding and push-rod assembly of a dilatometer working horizontally
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