Bsi bs en 13925 1 2003 (2008)

BRITISH STANDARD BS EN 13925 1 2003 Non destructive testing — X ray diffraction from polycrystalline and amorphous materials — Part 1 General principles The European Standard EN 13925 1 2003 has the s[.]

Non-destructive

testing — X-ray

diffraction from

polycrystalline and

amorphous materials —

Part 1: General principles

The European Standard EN 13925-1:2003 has the status of a

British Standard

ICS 19.100

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Confirmed December 2008

This British Standard was

published under the authority

of the Standards Policy and

Strategy Committee on

20 March 2003

© BSI 20 March 2003

ISBN 0 580 41463 9

National foreword

This British Standard is the official English language version of

EN 13925-1:2003

The UK participation in its preparation was entrusted to Technical Committee WEE/46, Non-destructive testing, which has the responsibility to:

A list of organizations represented on this committee can be obtained on request to its secretary

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Summary of pages

This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 13 and a back cover

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Amendments issued since publication

EUROPÄISCHE NORM March 2003

ICS 19.100

English version

Non-destructive testing - X-ray diffraction from polycrystalline

and amorphous material - Part 1: General principles

Essais non destructifs - Diffraction des rayons X appliquée

aux matériaux polycristallins et amorphes - Partie 1:

Principes généraux

Zerstörungsfreie Prüfung - Röntgendiffraktometrie von polykristallinen und amorphen Materialien - Teil 1:

Allgemeine Grundlagen

This European Standard was approved by CEN on 14 November 2002.

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 may be obtained on application to the Management Centre 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 Management Centre 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, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2003 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members.

Ref No EN 13925-1:2003 E

Contents

page

Foreword 3

Introduction 4

1 Scope 5

2 Normative references 5

3 Terms and definitions 5

4 General principles of X-ray powder diffraction (XRPD) 6

5 Meaning of the word “powder” in terms of X-ray diffraction 7

6 Characteristics of powder diffraction line profiles 7

7 Types of analysis 8

7.1 General 8

7.2 Phase identification (also referred to as “Qualitative phase analysis”) 8

7.3 Quantitative phase analysis 8

7.4 Estimation of the crystalline and amorphous fractions 9

7.5 Determination of lattice parameters 9

7.6 Determination of crystal structures 9

7.7 Refinement of crystal structures 9

7.8 Characterisation of crystallographic texture 9

7.9 Macrostress determination 10

7.10 Analysis of crystallite size and microstrain 10

7.10.1 General 10

7.10.2 Determination of crystallite size (size of coherently scattering domains) 11

7.10.3 Determination of microstrains 11

7.11 Electron radial distribution function (RDF) 11

8 Special experimental conditions 11

Annex A (informative) Relationships between the XRPD standards 12

Bibliography 13

Foreword

This document (EN 13925-1:2003) has been prepared by Technical Committee CEN/TC 138 "Non-destructive testing", the secretariat of which is held by AFNOR

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 September 2003, and conflicting national standards shall be withdrawn at the latest by September 2003

This European Standard about “Non-destructive testing - X-ray diffraction from polycrystalline and amorphous

material” is composed of:

- EN 13925-1 Part 1: General Principles;

- EN 13925-2 Part 2: Procedures;

- prEN 13925-3 Part 3: Instruments;

- prEN 13925-4 Part 4: Reference Materials

In order to explain the relationship between the topics described in the different Standards, a diagram illustrating typical operation involved in XRPD is given in annex A

Annex A is informative

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom

Introduction

X-ray powder diffraction (XRPD) is a powerful Non Destructive Testing (NDT) method for determining a range of physical and chemical characteristics of materials These include the type and quantities of phases present, the crystallographic unit cell and structure, crystallographic texture, macrostress, crystallite size and micro-strain, and the electron radial distribution function

This standard aims to describe the general aspects of the XRPD technique and its applications but not to define a specific or detailed standard for each field of application or type of analysis

The main purposes of the standard are therefore:

- to provide practical guidance, unified concepts and terminology for use of the XRPD technique in the area of Non Destructive Testing with general information about its capabilities and limitations of relevance to laboratories working at different levels of sophistication, from routine testing to research;

- to provide a basis for quality assurance in XRPD laboratories allowing performance testing and monitoring of instruments and the comparison of results from different instruments;

- to provide a general basis (without imposing specifications) for further specific NDT product standards and related Quality Assurance applications, with aspects common to most fields of application

In order to make the standard immediately usable in a wide range of laboratories and applications, diffractometers with Bragg-Brentano geometry are considered in most detail

Radiation Protection. Exposure of any part of the human body to X-rays can be injurious to health It is therefore essential that whenever X-ray equipment is used, adequate precautions should be taken to protect the operator and any other person in the vicinity Recommended practice for radiation protection as well as limits for the levels

of X-radiation exposure are those established by national legislation in each country If there are no official regulations or recommendations in a country, the latest recommendations of the International Commission on Radiological Protection should be applied

1 Scope

This European Standard specifies the general principles of X-ray diffraction from polycrystalline and amorphous materials This materials testing method has traditionally been referred to as “X-ray Powder Diffraction (XRPD)”, and is now applied to powders, bulk materials, thin film, and others As the method can be used for various types of materials and to obtain a large variety of information, this standard reviews a large number of types of analysis but remains non-exhaustive

2 Normative references

This European Standard incorporates 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 European Standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies (including amendments)

EN 13925-2:2003, Non-destructive testing - X-ray diffraction from polycrystalline and amorphous material - Part 2: Procedures

3 Terms and definitions

For the purposes of this European Standard, the general terms and definitions concerning X-ray powder diffraction1)and the following apply

3.1

powder

large number of crystallites and/or particles (i.e grains, agglomerates or aggregates; crystalline or non-crystalline) irrespective of any adhesion between them

3.2

block

self-adhering single piece of interconnected particles or crystallites

3.3

specimen

portion of the sample in the specific form used in the diffraction instrument for a given data collection process

3.4

phase

portion of a physical system sharing a common molecular and inter-molecular structure irrespective of any subdivision by size distribution or shape

NOTE The term 'phase' is used as a short form for a 'crystallographic phase' or a 'thermodynamic phase' throughout this standard, unless explicitly stated otherwise

3.5

diffraction line

region of the diffraction pattern containing an intensity maximum and corresponding to diffraction from a set of lattice planes

NOTE Often interchangeably referred to as a ‘peak’, ‘reflection’ or ‘Bragg reflection'

1) a draft of European Standard (WI 00138078 "Non-destructive testing - Terminology - X-ray powder diffraction") is in preparation

4 General principles of X-ray powder diffraction (XRPD)

X-ray diffraction results from the interaction between X-rays and electrons of atoms Usually, i.e in the so called kinematic description of diffraction, atoms are conceived as point scatterers Depending on the atomic arrangement, interferences result between the scattered rays Interferences are constructive when the path difference between two diffracted rays differ by an integral number of wavelengths This selective condition is described by the Bragg equation, also called Bragg's law:

where

hkl is a set of lattice planes identified by the Miller indices h,k,l,

dhkl is the distance between successive crystal lattice planes (also called the "d-spacing")

λ is the wavelength of the X-rays used and is of the order of magnitude of the d-spacing θhkl is the angle between the incident beam and the hkl lattice planes and half of the so called "diffraction angle", i.e the angle between the directions of the incident beam and the diffracted beam (see Figure 1)

n is the diffraction order (see hereafter):

1) the equation (1) (Bragg equation), is satisfied if the path difference (AB+BC) between the rays scattered from successive lattice planes of the same set is an exact multiple of λ (see Figure 1)

Key

d Separation between two successive lattice planes

θ Angle between the incident beam and the lattice planes separated by a distance of d

A and C Points on the incident beam (So) and the diffracted beam (S)

B and D represent two of the point scatterers, one in each lattice plane

Figure 1 — Diffraction of X-rays from two successive lattice planes

2) the diffraction of nth order from lattice plane hkl is equivalent to a diffraction of first order from the set of lattice planes nh, nk, nl For most purposes in XRPD, n is taken as unity and equation (1) is more commonly used in the form:

where the symbols are as in equation (1)

In XRPD the specimen is ideally polycrystalline with crystallites in all orientations, enabling diffraction to be

observed according to equation (1) The positions of the diffraction lines are characteristic of the crystal lattice, their intensities depend on the crystallographic unit cell content, and the line profiles on the perfection and extent of the crystal lattice

Under these conditions the diffraction line has a finite distribution of intensity arising from atomic arrangement, thermal motion and structural imperfections as well as from instrument characteristics This intensity distribution is described as the convolution of a function combining the contributions of the various instrument characteristics with

a function describing the intrinsic specimen contributions to broadening

To determine the diffraction pattern of a specimen, two experimental methods can be used alternatively:

 the “angular dispersive technique” where the X-rays are monochromatic and the measurement is made by scanning the diffraction angle,

 the “energy dispersive technique“ where the rays are polychromatic and the energy or wavelength of the X-rays photons is measured at a fixed diffraction angle

A series of references of general values to X-ray diffraction and Crystallography are used in this standard (see Bibliography [1, 2, 3, 4, 5, 6, 7])

5 Meaning of the word “powder” in terms of X-ray diffraction

The term “powder”, as used in XRPD, does not strictly correspond to the usual sense of the word in common language In X-ray powder diffraction the specimen can be a ”solid substance divided into very small particles”, but

it can also be a solid block for example of metal, ceramic, polymer, glass or a thin film or even a liquid The reason for this is that the important parameters for defining the concept of a powder for a diffraction experiment are the number and size of the individual crystallites that form the specimen and not their degree of accretion

An ‘ideal’ powder for a diffraction experiment consists of a large number of small, randomly oriented crystallites (coherently diffracting crystalline domains) If this number is sufficiently large, there are always enough crystallites

in any diffracting orientation to give reproducible diffraction patterns To obtain a reproducible measurement of the intensity of diffracted X-rays, the crystallite size has to be sufficiently small This size depends on the volume of the specimen from which diffracted X-rays are detected and hence on the X-ray absorption, specimen shape and diffraction geometry (see EN 13925-2:2003, 4.3.2) [4 (p.365ff)]

6 Characteristics of powder diffraction line profiles

The main characteristics of diffraction line profiles are position, maximum intensity, area and shape (characterised

e.g by width, asymmetry or by analytical function, empirical representation) Diffraction patterns are often interpreted quantitatively to various levels of approximation using:

a) line position: often taken as the 2θ location of the maximum of the diffraction line, but can be defined by various statistical and convenience criteria;

b) range of line profile: 2θ region where the intensity is assumed to pertain to the diffraction effect;

c) peak height: intensity above the background at the 2θ position of the maximum line intensity (Imax);

d) integrated intensity: area of the diffraction line profile above the background (Iint);

e) line width: typically Full Width at Half Maximum (FWHM, the line breadth at half of the peak height) or integral breadth (the width of the rectangle having the same area and height as the observed line profile, β = Iint/Imax), but can be defined by various statistical and convenience criteria;

f) profile descriptions using shape parameters: analytical functions (Gaussian, Lorentzian, pseudo-Voigt, Pearson VII, Voigt; split versions of these functions are used for asymmetric line profiles) or fundamental parameters methods (see EN 13925-2:2003, annex D);

g) asymmetry parameters: asymmetric diffraction intensity distributions can be defined by separate breadth and shape parameters on each side of the maximum of the diffraction line or in terms of the ratio of parameters between the sides

7 Types of analysis

7.1 General

Some of the most common types of analysis using XRPD are briefly described below These analyses specifically relate to particular material characteristics When these characteristics occur simultaneously, they often complicate the individual analyses (e.g the presence of preferred crystallographic orientation complicates quantitative phase analysis and the presence of microstrains complicates the measurement of crystallite size.)

7.2 Phase identification (also referred to as “Qualitative phase analysis”)

The identification of the phase composition of an unknown sample by XRPD is usually based on the visual or computer assisted comparison of a portion of its X-ray powder pattern to the experimental or calculated pattern of a reference material Ideally, these reference patterns should be as accurate as those from well-characterised single-phase specimens In most cases this approach makes it possible to identify a crystalline compound by its

d-spacings (mainly determined by the periodic distances between atoms) and by its relative intensities (related to the kinds of atoms and their geometric arrangement within the unit cell) It is unimportant whether the compound appears in a single-phase sample or in a mixture together with other crystalline or amorphous phases

This comparison of the diffraction pattern of the unknown sample with the standard data can be based either on a suitably chosen range of the diffraction pattern or on a set of reduced data such as a list of d-spacings and normalised intensities “Imax“, a so-called (d Imax)-list This information (whole diffraction pattern or (d,)-list which is the crystallographic fingerprint of the material), can be compared to (d Imax)-lists of single-phase samples compiled

in a database containing the experimental or calculated characteristics of identified crystalline substances The most commonly used database is the Powder Diffraction File (PDF) [8], updated annually (It is often important to specify the database and version used)

7.3 Quantitative phase analysis

If the sample under investigation is a mixture of two or more known phases (e.g as a result of a phase identification), at least one of which is crystalline, then in many cases the percentage by volume or by mass of each crystalline species and any amorphous material can be determined Quantitative phase analysis is based on the integrated intensities of one or more individual diffraction lines although peak heights are sometimes used as an approximation to integrated intensities These intensities may be compared to the corresponding values from calibration samples Where used a calibration sample shall be a single phase or a mixture of known phase composition Alternatively, standard-free methods (e.g the Rietveld method) can be used to quantify the components if their structures are known

The methods most commonly used for quantitative phase analysis are:

 the ”external standard method“;

 the ”internal standard method“(addition of a known amount of a crystalline phase not present in the original sample);

 the ”spiking method“ also called the "standard addition method" (addition of a known amount of a crystalline phase that is present in the original sample)

The latter two methods are not applicable to polycrystalline blocks but only to loose powders as they are based on adding known quantities of a crystalline phase to the sample being studied