1、Nuclear fuel technology Guidelines on the measurement of the specific surface area of uranium oxide powders by the BET methodBS ISO 12800:2017BSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06 ISO 2017Nuclear fuel technology Guidelines on the measurement of the specifi
2、c surface area of uranium oxide powders by the BET methodTechnologie du combustible nuclaire Lignes directrices pour le mesurage de laire massique (surface spcifique) des poudres doxyde duranium par la mthode BETINTERNATIONAL STANDARDISO12800Second edition2017-06Reference numberISO 12800:2017(E)Nati
3、onal forewordThis British Standard is the UK implementation of ISO 12800:2017.The UK participation in its preparation was entrusted to Technical Committee NCE/9, Nuclear fuel cycle technology.A list of organizations represented on this committee can be obtained on request to its secretary.This publi
4、cation does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2017 Published by BSI Standards Limited 2017ISBN 978 0 580 87784 1ICS 27.120.30Compliance with a British Standard cannot confer immunity
5、 from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2017.Amendments/corrigenda issued since publicationDate Text affectedBRITISH STANDARDBS ISO 12800:2017 ISO 2017Nuclear fuel technology Guidelines on the measureme
6、nt of the specific surface area of uranium oxide powders by the BET methodTechnologie du combustible nuclaire Lignes directrices pour le mesurage de laire massique (surface spcifique) des poudres doxyde duranium par la mthode BETINTERNATIONAL STANDARDISO12800Second edition2017-06Reference numberISO
7、12800:2017(E)BS ISO 12800:2017ISO 12800:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or
8、 mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva
9、, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 12800:2017ISO 12800:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reprodu
10、ced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.I
11、SO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgISO 12800:2017(E)Foreword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 14.1 Summary of the BET method . 14.2 Isothermal
12、adsorption curves 14.3 Conditions and assumptions . 25 Procedure. 35.1 Sample preparation 35.2 Volumetric measurement 35.3 Gravimetric measurement 35.4 Original and single-point methods 35.5 Dynamic method (carrier gas method) . 45.6 Alternative methods . 46 Expression of results 46.1 Methods of cal
13、culation . 46.1.1 Multipoint determination 46.1.2 Single-point determination 76.2 Precision and accuracy. 77 Test report . 7Bibliography 8 ISO 2017 All rights reserved iiiContents PageBS ISO 12800:2017ISO 12800:2017(E)ForewordISO (the International Organization for Standardization) is a worldwide fe
14、deration 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 com
15、mittee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document a
16、nd those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Pa
17、rt 2 (see www .iso .org/ directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development o
18、f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents).Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the voluntary nature of s
19、tandards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www .iso .org/ iso/ foreword .html.This document
20、was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection, Subcommittee SC 5, Nuclear installations, processes and technologies.This second edition cancels and replaces the first edition (ISO 12800:2003), which has been technically revised.iv IS
21、O 2017 All rights reservedBS ISO 12800:2017ISO 12800:2017(E)ForewordISO (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 committ
22、ees. 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, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Int
23、ernational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the di
24、fferent types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO
25、 shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents).Any trade name used in this doc
26、ument is information given for the convenience of users and does not constitute an endorsement.For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade O
27、rganization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www .iso .org/ iso/ foreword .html.This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection, Subcommittee SC 5, Nuclear installations, pr
28、ocesses and technologies.This second edition cancels and replaces the first edition (ISO 12800:2003), which has been technically revised.iv ISO 2017 All rights reserved INTERNATIONAL STANDARD ISO 12800:2017(E)Nuclear fuel technology Guidelines on the measurement of the specific surface area of urani
29、um oxide powders by the BET method1 ScopeThis document gives guidelines on the determination of the specific surface area of as-fabricated uranium dioxide powder by volumetric or gravimetric determination of the amount of nitrogen adsorbed on the powder, and can be applied to other similar materials
30、, e.g. U3O8, UO2-PuO2powders, and other bodies with similar surface areas, e.g. powder granules or green pellets, provided that the conditions described are fulfilled. Modifications using other adsorbing gases are included.The method is relevant as long as the expected value is in the range between
31、1 m2/g and 10 m2/g.2 Normative referencesThere are no normative references in this document.3 Terms and definitionsNo terms and definitions are listed in this document.ISO and IEC maintain terminological databases for use in standardization at the following addresses: ISO Online browsing platform: a
32、vailable at h t t p :/ www .iso .org/ obp IEC Electropedia: available at h t t p :/ www .electropedia .org/ 4 Principle4.1 Summary of the BET methodThe BET method is based on the determination of the amount of gas necessary to cover the surface by a monomolecular layer. This amount is determined fro
33、m the isothermal adsorption curve of nitrogen (N2) at the temperature of liquid nitrogen (77,4 K) according to Reference 2. The amount of N2adsorbed at a given pressure is determined by volumetric or gravimetric measurement6. In order to remove surface contamination of the adsorbent, the sample has
34、to be evacuated and heated under appropriate conditions before the measurement is performed.4.2 Isothermal adsorption curvesThe isothermal adsorption curve describes the relationship between the mass of the adsorbate, mA(N2), adsorbed per gram of adsorbent (e.g. UO2powder) at an equilibrium pressure
35、 of p at constant temperature T, as shown in Formula (1):mA= null(p,T) (1)Generally, the relative pressure p/p0is introduced instead of the absolute pressure p, where p0is the saturation vapour pressure which is 1,013 105Pa for nitrogen at 77,4 K. ISO 2017 All rights reserved 1BS ISO 12800:2017ISO 1
36、2800:2017(E)Most isothermal adsorption curves can be classified according to Reference 3 to be one of the five common types (see Figure 1).Materials with pure micropores (2 nm diameter) result in a type 1 adsorption curve. Most frequently, types 2 and 4 adsorption curves are observed where the adsor
37、ption energy of the first layer, E1, is much higher than that of subsequent layers, En. When E1 En, type 3 or type 5 adsorption curves result. The BET method can be applied to type 2 and type 4 curves only. The practice shows that the UO2,U3O8and PuO2powders meet this condition.KeyX relative pressur
38、eY specific amount adsorbedType 1 Langmuir typeType 2 adsorption followed by condensationType 3 condensation typeType 4 two-fold adsorptionType 5 condensation followed by adsorptionFigure 1 Classification of adsorption isotherms4.3 Conditions and assumptionsThe method can only be applied to material
39、s wherea) nitrogen is not absorbed by the material,b) nitrogen does not react chemically with the adsorbent,c) all pores can be reached by the nitrogen molecule, and2 ISO 2017 All rights reservedBS ISO 12800:2017ISO 12800:2017(E)Most isothermal adsorption curves can be classified according to Refere
40、nce 3 to be one of the five common types (see Figure 1).Materials with pure micropores (2 nm diameter) result in a type 1 adsorption curve. Most frequently, types 2 and 4 adsorption curves are observed where the adsorption energy of the first layer, E1, is much higher than that of subsequent layers,
41、 En. When E1 En, type 3 or type 5 adsorption curves result. The BET method can be applied to type 2 and type 4 curves only. The practice shows that the UO2,U3O8and PuO2powders meet this condition.KeyX relative pressureY specific amount adsorbedType 1 Langmuir typeType 2 adsorption followed by conden
42、sationType 3 condensation typeType 4 two-fold adsorptionType 5 condensation followed by adsorptionFigure 1 Classification of adsorption isotherms4.3 Conditions and assumptionsThe method can only be applied to materials wherea) nitrogen is not absorbed by the material,b) nitrogen does not react chemi
43、cally with the adsorbent,c) all pores can be reached by the nitrogen molecule, and2 ISO 2017 All rights reserved ISO 12800:2017(E)d) a type 2 or type 4 adsorption curve is observed.The BET theory includes the following assumptions. The adsorption energy of the first layer is independent of the degre
44、e of occupation. The adsorption energy as well as the kinetic parameters and condensation/evaporation equilibrium conditions for the second and higher layers are equal. The probability of adsorption at a vacant site is independent of the occupation of the neighbouring sites. Horizontal interactions
45、between the adsorbed N2molecules can be neglected. The heterogeneity of the adsorbent surface can be neglected.5 Procedure5.1 Sample preparationImpurities on the sample surface, especially water vapour, shall be removed before the adsorption measurement. Conditions for removing impurities (vacuum, t
46、emperature, time) have to be found which are compatible with the powder type. Chemical reactions (decomposition), sintering, change of crystal structure and other processes on the surface shall be avoided. Long evacuation periods are needed for highly porous powders. In order to shorten the heating
47、time, the optimum temperature should be determined. In most cases, the measured specific surface area first increases with an increase in the heating temperature and then decreases, e.g. by sintering of the powder.The optimum pre-treatment of hyperstoichiometric UO2powder depends on its specific sur
48、face area, intra-particle open pore size, and stoichiometry. For powders with a specific surface area between 2 m2/g and 8 m2/g, evacuation down to 2 mPa to 10 mPa (105Torr to 104Torr) followed by heating for 2,5 h at (150 C 10 C) is sufficient. Equivalent conditions, like 1,5 h at (180 C 10 C) or o
49、thers, can be utilized as well. To prevent sintering, heating temperatures higher than 350 C should be avoided if the O to U ratio exceeds 2,10. Shorter heating times to 20 min are possible. Instead of evacuation, the powder can be purged with purified inert gas at the temperatures and for the times mentioned above after having verified that there is no deleterious effect on characteristics of powders.Mass of sample required depends upon material density and expected specific surface area.
