ČSN EN ISO 5842 - Prášková metalurgie - Izostatické lisování zatepla - Detekce argonu technikami plynové chromatografie a hmotnostní spektrometrie

3.11 solvent cleaner

liquid cleaning substance that is either ethanol, CH3CH2OH, acetone, (CH3)2CO or iso-propanol, CH(CH3)2OH

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Equipment for argon detection

Gas chromatography

Principle

Gas chromatography (GC) is a separation technique where the mobile phase is gaseous. When GC is used as analytical technique, a known amount of sample is evaporated and dissolved into the mobile phase, also called the carrier gas. The sample compounds are carried by this mobile phase through a chromatographic column and further through detectors. Due to different specific interactions between the sample compounds and stationary phase (stationary phase is usually a chemical that can selectively attract components in a sample mixture), the sample compounds are retained individually and “travel” through the column with different velocities. This leads to a separation of individual components in time. The so-called retention time is the amount of time that elapsed from injection of the sample to the recording of the peak maximum of the component band (peak). When using non-specific detectors, the retention time is the only indication in chromatography for the correct identification of an individual sample component.

Apparatus and reagents

The carrier gas for argon detection shall be helium with purity ≥ 99,9999 % by volume. Measurement starts with fusion of a test portion in a graphite crucible under helium gas at a temperature of about 2 200 °C. The instrument samples a known volume of gas which subsequently enters the column(s) where the gases are separated. The apparatus shall, by an integrated function, correctly identify the signal which belongs to the separated argon. As an example, in Figure 1, a time relayed valve ejects all other gases to leave-out argon as the only analyte producing a signal. However, the chromatograph column may not be able to separate argon from all gases that may originate from the test sample. In that case, it can be necessary to integrate into the apparatus a separation and/or chemical conversion step prior to the gas stream entering the chromatograph column. The argon is ionized by an ionization source in a chamber followed by detection and quantification by the detector. An illustration of an apparatus is shown in Figure 1.

Key

1

furnace

7

gas chromatograph column

2

particle filter

8

relayed valve

3

gas chromatograph

9

ion source

4

helium carrier gas

10

ionized argon

5

test sample

11

detector

6

sampling valve (gas sample)

 

 

Figure 1 — Example illustration of a gas chromatography apparatus

Equipment detection limit

The detection limit of the equipment shall at most correspond to a content of 0,02 μg/g argon in a test sample prepared according to Clause 6.

NOTE 1 The detection limit does not correspond to the lowest level that can be quantified with statistical certainty.

NOTE 2 0,02 μg/g is sometimes referred to as 0,02 mg/kg, 0,02 ppm by mass or 20 ppb by mass.

Mass spectrometry

Principle

Mass spectrometry (MS) is an instrumental method to identify and quantify chemical compounds or elements. It involves a sample that is being dissolved in a carrier gas. The carrier gas carries the compounds through the instrument to the detector. After ionization, the instrument detects extracted argon based on the mass/charge ratio.

Apparatus and reagents

The carrier gas for argon detection shall be helium with purity ≥ 99,9999 % by volume. Measurement starts with fusion of a test portion in a graphite crucible under helium gas at a temperature of about 2 200 °C. The gases are ionized by an ionization source in a chamber. Subsequent detection and quantification of the extracted argon (mass/charge ratio of 40) is made by a mass spectrometer. However, a chemical compound or element that originates from the test sample may give rise to an overlapping signal with the extracted argon. In that case, it can be necessary to integrate into the apparatus a separation and/or chemical conversion step prior to the ionization. An illustration of an apparatus is shown in Figure 2.

Key

1

furnace

6

aliquot (gas sample)

2

particle filter

7

ion source

3

mass spectrometer

8

mass selector

4

helium carrier gas

9

ionized argon

5

test sample

10

detector

Figure 2 — Example illustration of a mass spectrometry apparatus

Equipment detection limit

The detection limit of the equipment shall at most correspond to a content of 0,02 μg/g argon in a test sample prepared according to Clause 6.

NOTE 1 The detection limit does not correspond to the lowest level that can be quantified with statistical certainty.

NOTE 2 0,02 μg/g is sometimes referred to as 0,02 mg/kg, 0,02 ppm by mass or 20 ppb by mass.

Calibration and functionality test

General

Calibrate the detector according to the recommendations of the equipment supplier and at each of the following occasions:

a) after it is installed and commissioned;

b) after replacement of critical parts or components of the equipment;

c) whenever the equipment functionality test significant deviates from expected values.

Functionality test of the apparatus shall be carried out at each of the following occasions:

1) daily, before detection;

2) after calibration;

3) after replacement of the carrier gas container;

4) whenever inaccuracy of the instrument is suspected.

Gas chromatograph

Calibration

Calibration consists of dosing through the apparatus, a gas mixture with a known pressure and a known level of argon (which is detectable but not high). Apart from argon, the gas mixture shall consist of helium with a low level of impurities. The gas mixture (helium + argon) shall be of purity ≥ 99,9995 % by volume.

The integrated detector response signal of the instrument shall be correlated to the known level of argon in the calibration gas mixture.

Functionality test

Functionality of the apparatus shall be ensured prior to detection. The functionality test shall be performed through measurement of at least one blank sample and at least one reference sample. If the measured values from the blank sample and/or reference sample deviates from the expected values, the source of the error shall be investigated and eliminated.

Single reference samples shall have a detectable argon content and a mass of 0,7 g ± 0,2 g with a non-slender geometry (square, round, or equivalent form).

If the measured result of the blank sample and the reference sample are satisfactory, the test procedure may commence.

NOTE The measurement of a blank sample is sometimes referred to as a blank test. The blank test can either be performed using no sample or using a sample without presence of argon.

Mass spectrometer

Calibration

Calibration consists of dosing through the apparatus, a gas mixture with a known pressure and a known level of argon (which is detectable but not high). Apart from argon, the gas mixture shall consist of helium with a low level of impurities. The gas mixture (helium + argon) shall be of purity ≥ 99,9995 % by volume.

The integrated detector response signal of the instrument shall be correlated to the known level of argon in the calibration gas mixture.

Functionality test

Functionality of the apparatus shall be ensured prior to detection. The functionality test shall be performed through measurement of at least one blank sample and at least one reference sample. If the measured values from the blank sample and/or reference sample deviates from the expected values, the source of the error shall be investigated and eliminated.

Single reference samples shall have a detectable argon content and a mass of 0,7 g ± 0,2 g with a non-slender geometry (square, round, or equivalent form).

If the measured result of the blank sample and the reference sample are satisfactory, the test procedure may commence.

NOTE The measurement of a blank sample is sometimes referred to as a blank test. The blank test can either be performed using no sample or using a sample without presence of argon.

Sample preparation for argon detection

A test piece shall be removed from the PM HIP component. The test piece shall be extracted from the parent PM HIP material or from a sacrificial part integrated to the PM HIP can.

Single test samples with a mass of 0,7 g ± 0,2 g with a non-slender geometry (square, round, or equivalent form) shall be produced from the test piece. The samples shall be free from can material.

The technique to extract the test piece and to section the test sample is at the discretion of the provider of the PM HIP service.

Test procedure for argon detection

General

The samples shall be immersed or rinsed in a solvent cleaner (with adequate grade of purity for the purpose) to remove surface contaminations.

The dry mass of each individual test sample shall be determined and recorded using a precision scale with an accuracy of at least 0,001 g.

Test procedure using gas chromatography

The following procedure shall be followed:

— place a single use graphite crucible in the furnace using a crucible tong;

— degas while heating above 2 200 °C;

— cool the crucible for at least five seconds;

— manually place a single test sample prepared according to Clause 6 in the crucible; or in the test sample loading sluice, if such a utility is integrated into the apparatus;

— start the test;

— after the fusion and measuring cycle, remove the crucible and record the displayed value;

— prior to discarding spent crucible, the operator shall inspect the inside to ensure the sample is present and melted.

Test procedure using mass spectrometry

The following procedure shall be followed:

— place a single use graphite crucible in the furnace using a crucible tong;

— degas while heating above 2 200 °C;

— cool the crucible for at least five seconds;

— manually place a single test sample prepared according to Clause 6 in the crucible; or in the test sample loading sluice, if such a utility is integrated into the apparatus;

— start the test;

— after the fusion and measuring cycle, remove the crucible and record the displayed value;

— prior to discarding spent crucible, the operator shall inspect the inside to ensure the sample is present and melted.

Test report

When the purchaser has specified an argon detection test according to this document the provider of the PM HIP service shall provide a test report to the purchaser.

The test report shall, as a minimum, include the following information:

a) a reference to this document, i.e. ISO 5842:2022;

b) all details necessary for the identification of the parent PM HIP component;

c) expression of result as:

— approved (≤ agreed argon limit)

or

— not approved (> agreed argon limit)

d) date of test and authorized signature;

e) test equipment and laboratory identification.

(informative) Precision

Precision

An interlaboratory study of test samples was performed in 2019 and 2020, using the procedures described in ISO 5725-1 and ISO 5725-2. Each of the 12 laboratories made 14 tests of industry-made PM HIP material (non-cobalt tool steel grade). Of the 14 tests, each laboratory made 7 tests on material with a low-level content and 7 tests on material having a high-level content.

The labs used 2 types of equipment to perform the tests, gas chromatography technique and mass spectrometer technique, and the precision is presented for both tests together and separate.

There is no estimate of bias because there is no accepted reference material.

In Table A.1, the repeatability is presented as one standard deviation and the repeatability limit (r). The difference between two test results exceeds the repeatability limit (r) on average not more than once in 20 tests on identical test material, in the normal and correct operation of the method by one operator using the same apparatus within the shortest feasible time interval between the tests.

Table A.1 — Repeatability as standard deviations and limit for all laboratories, and separately for laboratories using either gas chromatograph (GC) or mass spectrometer (MS)

Tested samples

Number of laboratories

Mean argon content

µg/g

Repeatability standard deviation sr

Repeatability limit r

Low level

- only GC

- only MS

12

5

7

0,047

0,045

0,048

0,010 µg/g

0,009 µg/g

0,011 µg/g

0,028 µg/g

0,025 µg/g

0,031 µg/g

High level

- only GC

- only MS

12

5

7

0,217

0,182

0,241

0,035 µg/g

0,036 µg/g

0,035 µg/g

0,098 µg/g

0,101 µg/g

0,098 µg/g

In Table A.2 the reproducibility is presented as one standard deviation and the reproducibility limit (R). The difference between test results reported by two laboratories exceeds the reproducibility limit (R) on average not more than once in 20 reports on identical test material, in the normal and correct operation of the method.

Table A.2 —Reproducibility as standard deviations and limit for all laboratories, and separately for laboratories using either gas chromatograph (GS) or mass spectrometer (MS)

Tested samples

Number of laboratories

Mean argon content

µg/g

Reproducibility standard deviation sR

Reproducibility limit R

Low level

- only GC

- only MS

12

5

7

0,047

0,045

0,048

0,019 µg/g

0,015 µg/g

0,022 µg/g

0,053 µg/g

0,042 µg/g

0,062 µg/g

High level

- only GC

- only MS

12

5

7

0,217

0,182

0,241

0,067 µg/g

0,071 µg/g

0,052 µg/g

0,188 µg/g

0,199 µg/g

0,146 µg/g

Bibliography

[1] ISO/IEC Guide 99:2007, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)

[2] ISO 3529‑3:2014, Vacuum technology — Vocabulary — Part 3: Total and partial pressure vacuum gauges

[3] ISO 5725‑1:2003, Accuracy (trueness and precision) of measurement methods and results – Part 1: General principles and definitions

[4] ISO 5725‑2:2003, Accuracy (trueness and precision) of measurement methods and results – Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method

[5] ISO 11323:2010, Iron ore and direct reduced iron — Vocabulary

[6] ISO 14532:2014, Natural gas — Vocabulary

[7] ISO/TS 14907‑1:2015, Electronic fee collection - Test procedures for user and fixed equipment - Part 1: Description of test procedures

[8] ISO 18115‑1:2013, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in spectroscopy

[9] ISO 20553:2006, Radiation protection — Monitoring of workers occupationally exposed to a risk of internal contamination with radioactive material

[10] ASTM A988/A988M – 15A Standard Specification for Hot Isostatically-Pressed Stainless Steel Flanges, Fittings, Valves, and Parts for High Temperature Service

[11] P Mellin, M Östlund, W Fredriksson, C Pellegrini, H Blom, O Björnberg, A Strondl. Detecting Argon Trapped in Reference Samples Made by Hot Isostatic Pressing. In proceedings of World PM2016, Hamburg, 2016

[12] P Mellin, O Björnberg, I Bengtsson, D Gonzalez, M Östlund, H Blom, J Karlsson, S Kiamehr. A proposed Swedish national standard and best practice for detection of Ar in PM HIP material. In proceedings of Euro PM2018, Bilbao, 2018