CR 10316:2001
(Main)Optical emission analysis of low alloy steels (routine method) - Guidelines for the preparation of standard routine method for optical emission spectrometry
Optical emission analysis of low alloy steels (routine method) - Guidelines for the preparation of standard routine method for optical emission spectrometry
The purpose of this document is to describe concepts and procedures for calibration and analysis of the equipment based on spark source optical emission spectrometry. Optical emission spectrometers are equipments that provide a quality and quantity characterization of electromagnetic radiation which is emitted by a test sample when excited by a suitable source.
Analyse des aciers faiblement alliés par spectrométrie d'émission optique (méthode de routine) - Lignes directrices relatives à la préparation d'une méthode normalisée de routine pour la spectrométrie d'émission optique
L'objectif du présent document est de décrire des concepts et des procédures relatifs à l'étalonnage et à l'évaluation du matériel utilisé en spectrométrie d'émission optique avec excitation par étincelle. Les spectromètres à émission optique permettent une caractérisation quantitative et qualitative des rayonnements électromagnétiques émis par un échantillon d'essai lorsqu'il est excité par une source appropriée.
Analiza z optično emisijsko spektrometrijo malolegiranega jekla (rutinska metoda) - Vodilo za pripravo standarda za rutinsko metodo z optično emisijsko spektrometrijo
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Standards Content (Sample)
SLOVENSKI STANDARD
01-april-2003
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Optical emission analysis of low alloy steels (routine method) - Guidelines for the
preparation of standard routine method for optical emission spectrometry
Analyse des aciers faiblement alliés par spectrométrie d'émission optique (méthode de
routine) - Lignes directrices relatives a la préparation d'une méthode normalisée de
routine pour la spectrométrie d'émission optique
Ta slovenski standard je istoveten z: CR 10316:2001
ICS:
77.040.30 Kemijska analiza kovin Chemical analysis of metals
77.080.20 Jekla Steels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN REPORT
CR 10316
RAPPORT CEN
CEN BERICHT
December 2001
ICS
English version
Optical emission analysis of low alloy steels (routine method) -
Guidelines for the preparation of standard routine method for
optical emission spectrometry
Analyse des aciers faiblement alliés par spectrométrie
d'émission optique (méthode de routine) - Lignes
directrices relatives à la préparation d'une méthode
normalisée de routine pour la spectrométrie d'émission
optique
This CEN Report was approved by CEN on 21 January 2001. It has been drawn up by the Technical Committee ECISS/TC 20.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. CR 10316:2001 E
worldwide for CEN national Members.
Contents
Foreword.3
1 Scope and field of application.3
2 Terms and definitions .3
3 Basic principles of optical emission spectrometry .5
4 Apparatus.5
5 Interferences .8
6 Performance criteria.9
7 Optimization of instrument parameters .10
8 Test sample preparation.11
9 Calibration.11
10 Analysis .12
11 Safety .12
Bibliography .13
Foreword
This CEN Report has been prepared by Technical Committee ECISS/TC 20 "Methods of chemical analysis of
ferrous products", the secretariat of which is held by SIS.
1 Scope and field of application
The purpose of this document is to describe concepts and procedures for calibration and analysis of the equipment
based on spark source optical emission spectrometry. Optical emission spectrometers are equipments that provide
a quality and quantity characterization of electromagnetic radiation which is emitted by a test sample when excited
by a suitable source.
2 Terms and definitions
For the purposes of this CEN Report, the following definitions apply:
2.1
absolute error
the difference between the measured and the true value
2.2
accuracy
the closeness of agreement between an observed value and an accepted true value
2.3
analyte line
the spectral line of an element which is used to establish the element concentration
2.4
background equivalent concentration
the quantity of analyte which, when subjected to excitation, provides a net intensity equal to the spectral
background
2.5
calibration
the series of operations which, under specified conditions, establishes the relationship between the instrument
output and the known values of the element being determined
2.6
calibration curve
the mathematical or graphical relationship between instrument output and known values of an element, under given
conditions
2.7
certified reference material
a reference material whose properties are certified by a technically valuable procedure and which is provided with a
certificate, either attached or referenced, issued by a certification body
2.8
drift
a slow change over time in instrument response
2.9
instrumental drift correction
the correction of instrumental drift with time, in order to keep calibration constant
2.10
limit of detection
the minimum concentration at which the signal generated by a given element can be positively recognised above
any background signals with a specified degree of certainty
2.11
matrix
the sum of the principal elements in a sample
2.12
matrix effect
the effect of the main constituents of a spectrographic sample on the intensity of the analyte line of the element
being measured
2.13
nominal value
the value used to indicate a characteristic of a reference material
2.14
primary standard
a standard showing the best metrological properties in a specified field
2.15
random error
the component of an error of measurement which, during several measurements of the same measurand, changes
with an unknown pattern
2.16
reference material
a material or substance which has sufficiently defined properties to be used for the following purposes: calibrate an
instrument, evaluate a measuring system or assign values to other materials
2.17
reference standard
a standard, generally with the best metrologic properties available at a certain location, which is used for the
metrological measurements performed at that location
2.18
relative error
the absolute error divided by the true value
2.19
repeatability
the value within which the absolute difference between two single test results obtained with the same method in the
shortest possible time by the same operator, using the same apparatus, at the same calibration values and under
the same drift conditions may be expected to lie within a specified probability (95 % if not indicated)
2.20
reproducibility
the value below which the difference between two single test results obtained with the same method on the same
material by different operators using different instruments at different laboratories and at different times may be
expected to lie within a specified probability (95 % if not indicated)
2.21
secondary standard
a standard whose value is established by comparison with a primary standard
2.22
span
the magnitude of the difference between two limits in the nominal range of an instrument
2.23
specified working range
range of values of an element for which instrumental errors are within acceptable limits
2.24
spectral line
the characteristic line emitted by an element during the electronic transition from the excited state to the ground
state
2.25
systematic error
the component of an error of measurement which, during several measurements of the same measurand, remains
constant or changes with a known pattern
2.26
true value
the value which characterizes a perfectly defined quantity in the conditions which exist at the moment when the
quantity is observed
2.27
uncertainty of measurement
an evaluation of the range of values within which the true value lies
3 Basic principles of optical emission spectrometry
If a sufficient amount of energy is applied to an atomized gas, the gas atoms "are excited", i.e. they emit a radiation
with a characteristic wavelength. It is thus possible to obtain an emission spectrum where each line corresponds to
a quantum jump or a transition from a given energy level to a lower one, whose value is known. Each atom is
characterized by a series of possible energy levels. Therefore, if suitably excited, an atom produces a typical
emission spectrum. The intensity of spectral lines depends both on how likely transition is and the number of atoms
involved. Since the portion of excited atoms relates to the total number of atoms of the same element which are
present in the test sample, it is possible to establish, within certain limits, a relationship between the intensity of the
electromagnetic radiation emitted and the quantity of atoms present. By a suitable adjustment it is also possible to
correlate intensity to quantity and execute quantitative measurements.
Usually a single equipment is used to atomize, or better vaporize in atomized form, the substance under test and to
excite the atomic gas thus obtained. The simplest way to excite the gas is heating a substance by direct contact
with a flame. The first excitation source used for spectrometry has been flame, since this is particularly suitable to
excite alkaline substances, for which purpose it is still used. Electric arc and spark are used to achieve higher
temperatures and excite a larger number of elements. Optical emission spectrometers, either simultaneous or
sequential, encompass all these features. They are used on a large scale in the steelmaking industry and more
generally in the metallurgical industry for production control.
4 Apparatus
An optical emission spectrometer is composed of:
a) a source for excitation;
b) an optical system;
c) a detector;
d) one or more reading instruments;
e) hardware and software management system.
A source is the system which provides the necessary excitation energy to be applied to the test sample. The source
referred to in this standard is a thermal excitation source. This type of source excites the sample by raising its
temperature, so that the shock among high-kinetics atoms produces an electronic jump from the ground state to the
excited one. The most common source is an electronic arc. The test sample, that acts as a cathode, excites and
produces plasma which emits raditations over a wide range of wavelengths (from distant IR to vicinal UV). A
suitable multi-channel spectrometer resolves radiations into their respective wavelengths. Among these, analyte
lines (1 to 3 in number) are selected for each element to reach the multi-channel spectrometer either
simultaneously or one by one. Each electromagnetic radiation is then processed by the detection system, a
photomultiplier, and transformed into a measurable electronic signal.
Plasma electromagnetic radiations are emitted by both gas atoms and test sample atoms.
The task of the hardware is to check instrument parameters while the software processes data (for example, entry
and control of the electronic signal coming from photomultipliers, selection of suitable signal amplification scales,
etc.).
4.1 Source
The source provides the energy necessary to release solid-state atoms and gives them the speed required to get
sufficient energy for transition at the subsequent emission of characteristic radiations.
In a spark, the discharge between two electrodes is not continuous, rather it is composed of a series of very short
damped oscillatory discharges at a constant frequency (50 Hz single-frequency) or high (50 Hz to 1 KHz multi-
frequency) and very high peak voltages (> 15 kV). These ohmic drops generate almost instantaneous (some
hundredths of a second) voltaic arcs that make the test sample sublimate with consequent generation of a thick
plasma and emission of electromagnetic radiations.
4.1.1 Technical features
The atomization and spark-excitation system is composed of a generator that operates at low or high voltage
according to test material conductivity. The generator includes a transformer, a condenser, an inductance and a
synchronous initiator. Operating conditions depend on the type of source and material conductivity. In general, the
parameters that determine the analytical conditions of a discharge are as follows:
a) voltage;
b) inductance;
c) resistance;
d) capacitance;
e) frequency;
f) flow rate;
g) pre-discharge rate;
h) integration rate.
The sample discharge strikes in an argon atmosphere at a flow rate that is a function of both test sample and
source conditions. It is necessary that the analysis is carried out in the absolute absence of oxygen. The position
and cleanliness of the electrode are also important factors for a good discharge. The frequency of electrode
cleaning and repositioning depends on test conditions and type of test sample.
4.2 Optical system
In emission spectrometry two types of optical systems are mainly used:
1) optical system with monochromator;
2) optical system with polychromator.
The former is used for sequential analysis, the latter to measure several spectral lines simultaneously. Optical
system can operate under vacuum (10-5 m barr), with inert flow or in pressure. Inert gas does not absorb the
radiations that correspond to the analyte lines provided on the instruments, particularly when the spectral band
used is below the wavelength (190 nm) of oxyge
...
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