1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPrAHM3AMR I-IO CTAHAAPTHSAMM Pi , y-q - 3; ” yj; : ;k.f ; .t .I,;, y! ,$ ?yj.$, .$.A.,i ,l Glass - Viscosity and viscometric fixed points - Part 8 : Determination of (dil
2、atometric) transformation temperature IS0 7884-8 First edition 1987-12-15 Reference number IS0 7884-8 : 1987 (E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards
3、 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 to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take
4、 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 IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the mem
5、ber bodies voting. International Standard IS0 7884-8 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
6、 implies its latest edition, unless otherwise stated. 0 International Organization for Standardization, 1997 l Printed in Switzerland INTERNATIONAL STANDARD IS0 7884-8 : 1987 (E) Glass - Viscosity and viscometric fixed points - Part 8 : Determination of (dilatometric) transformation temperature 0 In
7、troduction International Standard IS0 7884, Glass - Viscosity and viscometric fixed points, consists of the following separate parts : Part 7 : Principles for determining viscosity and viscometric fixed points. Part 2 : Determination of viscosity by rotation viscometers. Part 3 : Determination of vi
8、scosity by fibre elongation viscometer. Part 4 : Determination of viscosity by beam bending. Part 5: Determination of working point by sinking bar viscometer. Part 6 : Determination of softening point. Part 7 : Determination of annealing point and strain point by beam bending. Part 8 : Determination
9、 of (dilatometricl transformation temperature. 1 Scope This part of IS0 7884 specifies a method of determining the (dilatometric) transformation temperature tg of a glass by means of the thermal expansion method. This temperature character- izes a certain glass transition range from the elastic brit
10、tle (low temperature) state to the viscous (high temperature) state of glass. The transformation temperature has been found useful for specifying cooling programmes and estimating the upper temperature limit of applicability of the respective glassware. NOTE - The more direct viscometric method of a
11、nnealing point and strain point determination (see IS0 7884-7) serves similar purposes. The determination of the transformation temperature fg might be con- venient if a suitable device for determining the coeffrctent of thermal expansion is available in the laboratory. dN.s * 1 dPa.s = 1 x = 1 P (P
12、 is the symbol for poise) 2 Field of application This method is applicable to all glasses of normal bulk- production compositions. Generally, the transformation temperature ts falls in the range from 350 to 800 “C, depending on the type of glass. 3 References ISO 7991, Glass - Determination of coeff
13、icient of mean linear thermal expansion. IEC Publication 5841, Thermocouples - Part 7 : Reference tables. 4 Definition For the purposes of this part of IS0 7884, the following defini- tion applies. transformation temperature ts of glass : The temperature corresponding to the point of intersection of
14、 two tangents, drawn from the low-temperature branch and the high- temperature branch of the dilatometer curve (see clause 5 and figure I). NOTE - The transformation temperature lg corresponds to a dynamic viscosity of the order of 1013.3 dPa.s*. No exact relation exists be- tween to and the fixed p
15、oints L9f3 and L9f4 according to IS0 7884-7. For usual silicate glasses, r9f3 is 5 to 10 X higher than tg. For some special cases (e.g. borosilicate glasses with high SiO2 content) rPf3 is up to 30 “C higher than tg. However, rYf3 can be up to 20 OC lower than tg (e.g. in the case of crown glasses h
16、aving an La203 content). In these extreme cases the annealing point L9f3 is the more appropriate informa- tion about cooling programmes required and the temperature limit of applicability of the respective glassware. 1 IS0 7884-8 : 1987 (E) 5 Principle 7.2 Pretreatment The transformation temperature
17、 is determined by measuring the change in length, related to the length at initial temperature, of a rod made from the glass under test with temperature. The relative change in length is plotted against the temperature fdilatometer curve). The dilatometer curve is determined for a defined rate of te
18、mperature increase. From this dilatometer curve the transfor- mation temperature is determined by a graphical procedure as shown in figure 1. 6 Apparatus 6.1 Dilatometer, capable of the determination of changes in length of the specimen to 2 x 10-s x I0 (i.e. 2 pm per 100 mm). NOTE - Differential di
19、latometers may also be used. The reference curves may be evaluated directly, taking the first minimum as tg, or they may be redrawn as shown in figure 1 and evaluated as described in clause 5. The contact force shall not exceed 1 N. This force shall not act via conical tips or conical end faces of t
20、he test specimen, but only via contacts of planes with spherical faces whose radii of curvature shall be not less than the rod diameter of the test specimen. 6.2 Furnace, compatible with the dilatometer assembly, for temperatures up to 50 OC above the expected transformation temperature. 6.3 Furnace
21、 control device for the desired rate of temperature increase of (5 + 1) Wmin in the range above 200 OC. The temperature distribution within the furnace during the increase shall be smoothed to such an extent that devi- ations over the whole length of the test specimen remain less than 5 OC. 6.4 Temp
22、erature measuring device (e.g. thermocouple type E, J or K according to IEC 584-l 1, capable of determining the mean temperature of the specimen to f 2 OC. 6.5 Recording device for the change in length and for the temperature. 7 Test specimen 7.1 Shape The shape of the test specimen depends on the f
23、orm of the specimen holder of the dilatometer assembly. The test specimen length shall be at least 5 x 104 times the resolution of the extensometer . The test specimen shall be a rod with a cross-section of about IO to 25 mm2, and in any case of such a value that the stress arising from the contact
24、force of the dilatometer remains less than 0,l N/mm? This is to avoid viscous or elastic deforma- tions of the rod during the test. The test specimen shall be annealed before the test by heating it to about 30 OC above the estimated transformation temperature and then cooling it to about 150 OC belo
25、w the estimated transformation temperature at a cooling rate of (2 + 0,2) Wmin, followed by further cooling in draught-free air to room temperature. In figure 2 an example of a dilatometer curve is shown for an in- sufficiently annealed specimen. Such a curve, however, can be used for preliminary es
26、timation of the value of the transforma- tion temperature prior to a repeated annealing procedure as specified in the preceding paragraph. 8 Procedure The whole of the following procedure shall be performed twice. If no deformation takes place in a test specimen, it may be re- tested after re-anneal
27、ing (see 7.2). Insert the test specimen at room temperature into the dilatometer and set the extensometer. Heat the test specimen from 200 “C at a constant rate of temperature increase of (5 f 1) Wmin and record the temperature t and the related change in length. Correct for a possible temperature d
28、ifference between the specimen and the hot junction of the thermocouple as caused by the temperature increase. NOTE - The amount of the correction may be found empirically from appropriate runs of the dilatometer in accordance with IS0 7991, working on a glass with a sufficiently higher transformati
29、on temperature lg. 9 Expression of results 9.1 Evaluation of transformation temperature If not recorded directly, plot the relative change in length against the temperature as shown in figure 1. Draw the tangent to the low-temperature branch of the dilatometer curve at a point about 150 OC below the
30、 estimated transformation temperature. NOTE - A slight deviation from that temperature results generally in changes of less than 1,5 OC in transformation temperature. Draw the tangent to the high-temperature branch of the dilatometer curve at the point of inflection (see figure 1). Read from the gra
31、ph the temperature that corresponds to the point of intersection of the two tangents. If the values of this temperature found in both runs of the test differ by not more than 5 X, then take the arithmetic mean and round it to the nearest entire degree Celsius. This is the transformation temperature.
32、 If the difference between the results of both runs is greater than 5 “C, then repeat the whole test on a new sample. 2 IS0 7884-8 : 1987 (E) 9.2 Precision Repeatability : 3 OC Reproducibility : 6 “(2 IO Test report The test report shall include : a) reference to this part of IS0 7884; b) descriptio
33、n of the sample; c) method of sampling; d) number of test specimens; e) method of preparation and form of the test specimens; f) type of apparatus used; g) corrections applied; h) multiple use of test specimens; i) transformation temperature, tg, in degrees Celsius; j) any changes observed in the gl
34、ass during and/or after measurement. 3 ISO7884-8:1987(E) E $ s : Q 5 k & .G & $5 4 -5 z i= 2 $3 2 2 i+ . d / 0 z / + I 4 I 1 l521C I I I 0 450 500 550 Temperature t, C Figure 1 - Example of a dilatometer curve and the evaluation of transformation temperature (521 “C in this case) of a glass Temperature t, OC / /- quenched Figure 2 - Example of the dilatometer curve of a glass in the annealed and in a quenched state 4 IS0 7884-8 : 1987 (E) UDC 666.11.01 : 532.13 Descriptors : glass, tests, determination, thermodynamic properties, dilatometry. Price based on 4 pages
