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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 EN 82
2、1-2:1997 has the status of a
British Standard
ICS 81.060.99
BS EN 821-2:1997
National foreword
This British Standard is the English language version of EN 821-2:1997. It supersedes BS 7134-4.2:1990.
The UK participation in its preparation was entrusted to T
3、echnical Committee
RPI/13, Advanced technical ceramics, which has the responsibility to:
— aid enquirers to understand the text;
— present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;
— monitor related i
4、nternational 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 Standards which implement international or European publications referred to in this document ma
5、y 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 Standard does not purport to include all the necessary provisions of a contract. Users of Briti
6、sh 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 cover, an inside front cover, pages i and ii, the EN title pa
7、ge, pages 2 to 15 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.
Amd. No.
Date
Comments
This British Standard, having b
8、een prepared under the direction of the Sector Board for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on
15 November 1997
? BSI 04-2000
ISBN 0 580 28389 5
Amendments issued since publication
BS EN 821-2:1997
Contents
9、
Page National foreword Inside front cover Foreword 2
Text of EN 821-2 3
? BSI 04-2000 i
10、
ii blank
EUROPEAN STANDARD NORME EUROPéENNE
EUROP?ISCHE NORM
EN 821-2
June 1997
ICS 81.060.99
Descriptors: Ceramics, powdery materials, thermodynamic properties, tests, determination, diffusion, t
11、hermal conductivity
English version
Advanced technical ceramics — Monolithic ceramics — Thermo-physical properties
Part 2: Determination of thermal diffusivity by the laser
flash (or heat pulse) method
Céramiques techniques avancées — Céramiques monolithiques — Propriétés thermo
12、-physiques —
Partie 2: Détermination de la diffusivité thermique par la méthode Flash laser
(ou impulsion de chaleur)
Hochleistungskeramik — Monolithischer Keramik — Thermophysikalische Eigenschaften —
Teil 2: Messung der Temperaturleitf?higkeit mit dem Laserflash- (oder W?rmeimpuls-)
Verfahr
13、en
This European Standard was approved by CEN on 1997-05-24. 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 bibliograph
14、ical references concerning such national standards 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 responsibilit
15、y of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxemb
16、ourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
CEN
European Committee for Standardization Comité Européen de Normalisation Europ?isches Komitee für Normung
Central Secretariat: rue de Stassart 36, B-1050 Brussels
? 1997 CEN — All righ
17、ts of exploitation in any form and by any means reserved worldwide for CEN
national Members. Ref. No. EN 821-2:1997 E
EN 821-2:1997
Foreword
This European Standard has been prepared by
Contents
Page
Technical Committee CEN/TC 184, Advanced technical ceramics,
18、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 by endorsement, at the latest by December 1997, and conflicting national standards shall be withdrawn at the latest by December 1997.
19、
EN 821 consists of three Parts:
— Part 1: Determination of thermal expansion;
— Part 2: Determination of thermal diffusivit;
— Part 3: Determination of specific heat capacity
(ENV).
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following coun
20、tries are bound to implement this European Standard: Austria, Belgium,
Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the
United Kingdom.
Foreword 2
1 Scope 3
2 Normative references
21、 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 calculation 12
Annex B (informative) Deviations from
ideal behaviour 12
Annex C (informative) Bibliography
22、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 temperature test piece
holder 7
Figure 4 — Heat loss correction curves 11
Table 1 — Val
23、ues of constant Wx for 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 14
2 ? BSI 04-2000
1 Scope
This Part of EN 82
24、1 specifies a method for the determination of thermal diffusivity of advanced monolithic technical ceramics, to an accuracy of approximately ? 5 %. It is suitable for the measurement of thermal diffusivity values in the range 0,1 mm2/s to 1 000 mm2/s at temperatures greater than – 180 ?C.
Annex A
25、 gives the mathematical derivation of the calculations, and Annex B contains instruction on actions necessary when the calculations cannot be made in the usual way.
NOTE 1 It is not advisable to exceed the temperature at which the test piece was manufactured.
NOTE 2 This method involves the
26、use of a high powered 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 EN 60825).
2 Normative references
This European Standard incorporat
27、es, by dated or undated reference, 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 Europea
28、n Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies.
EN 45001, General criteria for the operation of testing laboratories.
EN 60584-1, Thermocouples — Part 1: Reference tables.
EN 60584-2, Thermocouples
29、 — Part 2: Tolerances.
3 Definitions
For the purposes of this Part of EN 821, 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 st
30、eady state conditions
3.3
specific heat
the heat capacity 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 ca
31、n also be related to thermal conductivity via the specific heat of the material using the relationship:
(1)
where
a is the thermal diffusivity in m2/s
? is the thermal conductivity in Wm–1K–1
? is the density in kg/m
32、3
cp is the specific heat in J/(kg·K)
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 transie
33、nt half time (t0,5). The transient temperature rise
(see Annex 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
34、with
a) test 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.
NOTE Improvement in the accuracy can be obtained by increas
35、ing the sophistication of the data collection and analysis systems.
? BSI 04-2000 3
4
? BSI 04-2000
EN 821-2:1997
Figure 1 — Schematic representation of transient at rear face of test p
36、iece
? BSI 04-2000
5
EN 821-2:1997
Figure 2 — Schematic diagram of thermal diffusivity apparatus
EN 821-2:1997
15
? BSI 04-2000
5 Apparatus
NOTE 1 The essential features
37、 of the apparatus are shown in Figure 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 shall be uniform over the face of the test piece.
NOTE 2 This is reasonably simple to achieve in the case of the flash lamp, which shou
38、ld be housed in a totally reflecting box with a hole, and a light guide of approximately 25 mm diameter abutting the sample.
NOTE 3 Significant errors in derived data can arise if the temperature rise exceeds5 K, especially in materials where the thermal diffusivity is strongly temperature depen
39、dent.
The pulse source shall produce a rise in temperature not exceeding 10 K (preferably not exceeding 5 K) on the rear face of the test piece.
For measurement at high temperature, the use of a laser is recommended; flash tubes are usually restricted to a maximum of 400 ?C.
NOTE 4 Where a la
40、ser 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 be used to monitor this uniformity and also to align the beam centrally on the sample front face.
5.2 Environ
41、mental control chamber
5.2.1 General
The environmental control chamber shall be either a furnace (see 5.2.2), a cryostat (see 5.2.3), or a draught-proof enclosure (for ambient temperature measurements).
5.2.2 Furnace, capable of operation within the temperature range required, and of sufficien
42、t size to contain the specimen holder (see 5.6).
The heating elements for the furnace may be constructed from either:
a) nickel-chrome alloy, for temperatures up to 1 000 ?C; or
b) platinum or silicon carbide, for temperatures up to 1 500 ?C; or
c) graphite, tantalum or tungsten, for temperatur
43、es above 1 500 ?C.
In steady state conditions the drift in temperature shall be less than 0,01 K/s. The temperature of the test piece shall be monitored either by a thermocouple in accordance with EN 60584-1 or by an optical pyrometer (preferably two-colour).
An appropriate inert atmosphere or v
44、acuum shall be used when necessary to protect furnace parts and test piece holder (see 5.6) from oxidation, and to protect the test piece and its coating (see 6.3) from structure/phase changes, stoichiometric changes and compatibility problems.
NOTE 1 Care should be taken to avoid decomposition
45、 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 shall either be fitted with a window, transparent to the incident h
46、eat 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 radiation opposite the rear face of the test piece, for measureme
47、nt of temperature using a pyrometer and for transmission of the transient pulse to a remote detector.
5.2.3 Cryostat, capable of temperature control to 0,01 K
NOTE 2 Various liquids can be used (in a vacuum flask) to provide the low temperature environment e.g. liquid nitrogen, liquid oxygen,
48、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 (see 5.3.2) or a thermocouple (see 5.3.3). It shall be capable of detecting changes o
49、f < 1 % of the total rear face temperature rise of the test piece with a rapid linear time response, which shall discriminate to 1 % of the half rise time of the transient (t0,5).
5.3.2 Infra-red detector, of type appropriate to the minimum test piece temperature required
e.g. a liquid nitrogen c
50、ooled indium antimonide
(InSb) cell (for test piece temperatures down
to 40 ?C) or a lead sulphide (PbS) cell (for test piece temperatures down to 250 ?C).
The detector shall be kept at some distance from the test piece (remote from the high temperature environment) and hence a lens shall be us
51、ed 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 beam energy.
5.3.3 Thermocou
52、ple, of appropriate type for the required temperature range, manufactured in accordance with the tolerances given in
EN 60584-2, allowing use of the reference tables given in EN 60584-1. The wire diameter shall
be 0,15 mm.
NOTE 1 The thermocouple may serve a secondary purpose of monitoring the
53、 test piece temperature by switching into a digital thermometer.
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 (1 mm to 2 mm diameter) twin bore alumina tube a
54、nd springs.
NOTE 2 Figure 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 (see 6.3) in order to effect the thermocouple junction, where the wires are open ended and separate
55、d by approximately 1 mm. The extra thickness of the high conductivity coating shall not increase the transient at t0,5 by more
than 1 % and this shall be checked by calculation.
NOTE 3 The use of a number of thermocouple junctions in differential mode may be used to increase the sensitivity
56、 of measurement of the transient.
5.4 Signal amplifiers
Signal amplifiers, including spike protections, analogue-digital converters, high temperature bias circuitry. They shall have low noise and fast response so as not to introduce errors into the transient measurements. None of the electronic
57、 components shall become saturated or the signals distorted. The integration time shall be less
than 0,3 ms.
1 Brass screw
2 Thermocouple wires
3 Spring
4 Pin-vice chuck
5 Insulating plastic
6 Alumina twin bore
58、tube
7 Polished nickel reflector
8 Transparent plastic
9 Test piece
Figure 3 — Schematic diagram of a typical ambient and low temperature test piece holder
5.5 Data acquisition system
The system for acquiring and storing data may be either a computer data processor (preferr
59、ed) or a storage oscilloscope. The system shall be equipped with an accurate means of recording the energy pulse to initiate the recording system, for example a triggering photocell.
NOTE The computer data processor is able to analyse several thousands of data points from the transient, and can
60、be programmed to drive the laser and trigger systems, collect data, analyse for heat losses etc., print out results and produce plots of thermal diffusivity against temperature. The oscilloscope is not very accurate and does require a means to photograph the trace for manual analysis.
It is import
61、ant in both cases to verify the accuracy of time bases and response times.
5.6 Test piece holder
For tests at near ambient temperature or below, the test piece holder may be constructed from a material of poor thermal conductivity (e.g. a plastics material). An example is shown in Figure 3. At hi
62、gher temperatures, where plastics materials become unsuitable, the test piece holder shall be constructed of suitably refractory materials (metals, graphite, etc.) in such a manner as to minimize heat transfer between it and the test piece, e.g. by allowing the test piece to be clamped at only thre
63、e points on or near its periphery. For use at temperatures below room temperature, the test piece holder shall be constructed in such a way that it can be inserted into an evacuated stainless steel vessel which can be placed inside the cryostat
(see 5.2.3).
When a thermocouple is employed as t
64、he transient detector, the test piece holder shall incorporate a device which pushes the two thermocouple leads into contact with the conducting rear surface of the test piece using a spring arrangement (e.g. as shown in Figure 3).
The test piece holder shall also be of such design as to mini
65、mize the amount of incident energy arriving on the sides of the test piece, either directly or scattered to the transient detector, especially when an infra-red detector is employed. When using a laser energy source, the specimen holder shall be equipped with apertures to the front and rear of the t
66、est piece, the diameters of which are not more than 0,5 mm and not less than 0,2 mm smaller than the diameter of the test pieces, such that only the
front face of the test piece receives the energy pulse.
When using a flash-lamp energy source and a thermocouple as a transient detector, the use of apertures is advisable to avoid spurious detector level changes immediately after the heat pulse has been fired (see clause 8).
6 Test pieces
6.1 Sampling
Test pieces or components should be sam
【BS英國標(biāo)準(zhǔn)】BS EN 82121997 Advanced technical ceramics — Monolithic ceramics — Thermophysical properties
