1、BRITISH STANDARD BS EN 821-2:1997 Advanced technical ceramics Monolithic ceramics Thermo-physical properties Part 2: Determination of thermal diffusivity by the laser flash (or heat pulse) method The European Standard EN821-2:1997 has the status of a British Standard ICS 81.060.99BSEN821-2:1997 This
2、 British Standard, having been prepared under the directionof the Sector Board for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 November1997 BSI 04-2000 ISBN 0 580 28389 5 National foreword This British Standard is the English language
3、 version of EN821-2:1997. It supersedes BS7134-4.2:1990. The UK participation in its preparation was entrusted to Technical Committee RPI/13, Advanced technical ceramics, which has the responsibility to: aid enquirers to understand the text; present to the responsible European committee any enquirie
4、s on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British
5、 Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British S
6、tandard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cov
7、er, an inside front cover, pages i and ii, theEN title page, pages2 to15 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. N
8、o. Date CommentsBSEN821-2:1997 BSI 04-2000 i Contents Page National foreword Inside front cover Foreword 2 Text of EN 821-2 3ii blankEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN821-2 June 1997 ICS 81.060.99 Descriptors: Ceramics, powdery materials, thermodynamic properties, tests, determinat
9、ion, diffusion, thermal conductivity English version Advanced technical ceramics Monolithic ceramics Thermo-physical properties Part2: Determination of thermal diffusivity by the laser flash (or heat pulse) method Cramiques techniques avances Cramiques monolithiques Proprits thermo-physiques Partie2
10、: Dtermination de la diffusivit thermique par la mthode Flash laser (ou impulsion de chaleur) Hochleistungskeramik Monolithischer Keramik Thermophysikalische Eigenschaften Teil2: Messung der Temperaturleitfhigkeit mit dem Laserflash- (oder Wrmeimpuls-) Verfahren This European Standard was approved b
11、y CEN on1997-05-24. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards
12、may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the C
13、entral Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingd
14、om. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1997 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN821-2:1997 EE
15、N821-2:1997 2 BSI 04-2000 Foreword This European Standard has been prepared by Technical Committee CEN/TC184, Advanced technical ceramics, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or b
16、y endorsement, at the latest by December1997, and conflicting national standards shall be withdrawn at the latest by December1997. EN821 consists of three Parts: Part1: Determination of thermal expansion; Part2: Determination of thermal diffusivit; Part3: Determination of specific heat capacity (ENV
17、). According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, P
18、ortugal, Spain, Sweden, Switzerland and the UnitedKingdom. Contents Page Foreword 2 1 Scope 3 2 Normative references 3 3 Definitions 3 4 Principle 3 5 Apparatus 6 6 Test pieces 8 7 Calibration 9 8 Test procedure 9 9 Results 10 10 Test report 11 Annex A (informative) Fundamental equations for calcula
19、tion 12 Annex B (informative) Deviations from ideal behaviour 12 Annex C (informative) Bibliography 14 Figure 1 Schematic representation of transient at rear face of test piece 4 Figure 2 Schematic diagram of thermal diffusivity apparatus 5 Figure 3 Schematic diagram of a typical ambient and low tem
20、perature test piece holder 7 Figure 4 Heat loss correction curves 11 Table 1 Values of constant W xfor a range of transient times 10 Table B.1 Coefficients for the decay time heat loss correction 13 Table B.2 Finite pulse time correction constants 14EN821-2:1997 BSI 04-2000 3 1 Scope This Part of EN
21、821 specifies a method for the determination of thermal diffusivity of advanced monolithic technical ceramics, to an accuracy of approximately5%. It is suitable for the measurement of thermal diffusivity values in the range0,1mm 2 /s to1000mm 2 /s at temperatures greater than180 C. Annex A gives the
22、 mathematical derivation of the calculations, and Annex B contains instruction on actions necessary when the calculations cannot be made in the usual way. NOTE 1It is not advisable to exceed the temperature at which the test piece was manufactured. NOTE 2This method involves the use of a high powere
23、d pulsed laser system or high energy photoflash equipment as well as high vacuum and high temperature furnace capability. Such equipment therefore should be operated within established safety procedures. (See EN60825). 2 Normative references This European Standard incorporates, by dated or undated r
24、eference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incor
25、porated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN45001, General criteria for the operation of testing laboratories. EN60584-1, Thermocouples Part1: Reference tables. EN60584-2, Thermocouples Part2: Tolerances. 3 Definitions F
26、or the purposes of this Part of EN821, the following definitions apply. 3.1 thermal diffusivity thermal conductivity divided by heat capacity per unit volume 3.2 thermal conductivity density of heat flow rate divided by temperature gradient under steady state conditions 3.3 specific heat the heat ca
27、pacity per unit mass 3.4 transient half time the time required for the temperature to rise to half of its peak or maximum 4 Principle Thermal diffusivity is a measure of the heat flow in a material under non-steady state conditions. It can also be related to thermal conductivity via the specific hea
28、t of the material using the relationship: where Thermal diffusivity is measured by applying a high intensity short duration heat pulse to one face of a parallel sided homogeneous test piece, monitoring the temperature rise at the opposite face as a function of time, and determining the transient hal
29、f time (t 0,5 ). The transient temperature rise (seeAnnex A) is shown schematically in Figure 1. The signal from the temperature detector is recorded with an appropriate data acquisition system. The experimental data are subject to both systematic and random errors e.g.those associated with a) test
30、piece thickness determination; b) time measurement on transient curve; c) response time of detectors; d) response time of recording and analysis equipment; e) trigger delays; f) non-uniform heating of the test piece. NOTEImprovement in the accuracy can be obtained by increasing the sophistication of
31、 the data collection and analysis systems. (1) a is the thermal diffusivity in m 2 /s is the thermal conductivity in Wm 1 K 1 is the density in kg/m 3 c p is the specific heat in J/(kgK)EN 821-2:1997 4 BSI 04-2000 Figure 1 Schematic representation of transient at rear face of test pieceEN 821-2:1997
32、 BSI 04-2000 5 Figure 2 Schematic diagram of thermal diffusivity apparatusEN821-2:1997 6 BSI 04-2000 5 Apparatus NOTE 1The essential features of the apparatus are shown inFigure 2. 5.1 Heat pulse source The heat pulse source may be a pulsed laser, a flash tube or an electron beam. The pulse energy s
33、hall be uniform over the face of the test piece. NOTE 2This is reasonably simple to achieve in the case of the flash lamp, which should be housed in a totally reflecting box with a hole, and a light guide of approximately25mm diameter abutting the sample. NOTE 3Significant errors in derived data can
34、 arise if the temperature rise exceeds5K, especially in materials where the thermal diffusivity is strongly temperature dependent. The pulse source shall produce a rise in temperature not exceeding10K (preferably not exceeding5K) on the rear face of the test piece. For measurement at high temperatur
35、e, the use of a laser is recommended; flash tubes are usually restricted to a maximum of400 C. NOTE 4Where a laser is used, it is recommended that a neodymium-glass laser system is utilized because of its excellent beam uniformity over the whole diameter. “Footprint” paper or photographic film can b
36、e used to monitor this uniformity and also to align the beam centrally on the sample front face. 5.2 Environmental control chamber 5.2.1 General The environmental control chamber shall be either a furnace (see5.2.2), a cryostat (see5.2.3), or a draught-proof enclosure (for ambient temperature measur
37、ements). 5.2.2 Furnace, capable of operation within the temperature range required, and of sufficient size to contain the specimen holder (see5.6). The heating elements for the furnace may be constructed from either: a) nickel-chrome alloy, for temperatures up to1000 C; or b) platinum or silicon car
38、bide, for temperatures up to1500 C; or c) graphite, tantalum or tungsten, for temperatures above1500 C. In steady state conditions the drift in temperature shall be less than0,01K/s. The temperature of the test piece shall be monitored either by a thermocouple in accordance with EN60584-1 or by an o
39、ptical pyrometer (preferably two-colour). An appropriate inert atmosphere or vacuum shall be used when necessary to protect furnace parts and test piece holder (see5.6) from oxidation, and to protect the test piece and its coating (see6.3) from structure/phase changes, stoichiometric changes and com
40、patibility problems. NOTE 1Care should be taken to avoid decomposition of materials at high temperatures and under reducing conditions. At high temperatures some types of ceramics may vaporize (e.g.nitrides and silicates) or otherwise react with the environment or the applied coating. The furnace sh
41、all either be fitted with a window, transparent to the incident heat pulse radiation, or else the heat pulse source may be placed inside the furnace, for example at temperatures where a flash lamp may be employed. The furnace shall also be fitted with a window, transparent to the emitted thermal rad
42、iation opposite the rear face of the test piece, for measurement of temperature using a pyrometer and for transmission of the transient pulse to a remote detector. 5.2.3 Cryostat, capable of temperature control to0,01K NOTE 2Various liquids can be used (in a vacuum flask) to provide the low temperat
43、ure environment e.g.liquid nitrogen, liquid oxygen, solid carbon dioxide-acetone mixture, iced water etc., or a slow flow of boiled and pre-heated liquid nitrogen. 5.3 Transient detector 5.3.1 General The transient detector shall be either an infra-red detector (see5.3.2) or a thermocouple (see5.3.3
44、). It shall be capable of detecting changes of1% of the total rear face temperature rise of the test piece with a rapid linear time response, which shall discriminate to1% of the half rise time of the transient (t 0,5 ). 5.3.2 Infra-red detector, of type appropriate to the minimum test piece tempera
45、ture required e.g.a liquid nitrogen cooled indium antimonide (InSb) cell (for test piece temperatures down to40 C) or a lead sulphide (PbS) cell (for test piece temperatures down to250 C). The detector shall be kept at some distance from the test piece (remote from the high temperature environment)
46、and hence a lens shall be used to focus the radiation from the centre of the rear face on to the detector. Therefore all viewing windows and lenses shall transmit radiation in the appropriate wavelength band. The sensor shall always be protected against damage or saturation from the direct laser bea
47、m energy. 5.3.3 Thermocouple, of appropriate type for the required temperature range, manufactured in accordance with the tolerances given in EN60584-2, allowing use of the reference tables given in EN60584-1. The wire diameter shall be0,15mm. NOTE 1The thermocouple may serve a secondary purpose of
48、monitoring the test piece temperature by switching into a digital thermometer.EN821-2:1997 BSI 04-2000 7 The wire ends of the thermocouple shall be prepared to minimize heat losses from the test piece into the wires, and are pressed against the test piece by using fine(1mm to2mm diameter) twin bore
49、alumina tube and springs. NOTE 2Figure 3 shows an example of a test piece and thermocouple holder suitable for use at ambient temperature and below. Non-conducting test pieces shall be coated on the rear face (see6.3) in order to effect the thermocouple junction, where the wires are open ended and separated by approximately1mm. The extra thickness of the high conductivity coating shall not increase the transient at t 0,5by more than1% and this shall be checked by calculation. NOTE 3The use of
