Hitachi OE700 Series, Руководство по эксплуатации

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Hitachi High-Tech Analytical Science
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55
10 Faults
10.3 Information regarding nitrogen analysis
Nitrogen (N) analysis, particularly in steel, does not fundamentally differ from analysis
of other non-metals such as phosphorus or sulphur. The challenge consists in the
presence of N
2
in the atmosphere. Even the smallest leak in the area of the valves and
fittings, the argon supply or the spark stand immediately leads to fluctuating and/or
incorrect analysis values, although the burn spot – as the general evaluation criterion for
"good sparking" – is still in order. The same applies for a too high N
2
content in the used
argon. Careful work and repeated checks of the instrument condition are prerequisites
for precise and correct N analysis.
Argon quality
Since nitrogen can also be present as contamination in the used argon, argon must be
very pure. The N
2
content should be below 1 ppm. That is only ensured from a purity of
at least 99.9999 %, corresponding to quality
1
6.0 (also referred to as 6N0). However,
that quality is relatively expensive.
A less expensive solution is so-called spectrometer argon (argon for spectrometry). It
has at least 99.999 % (Ar 5.0) and can therefore contain a maximum of 10 ppm of
contaminations. From experience we can assume that with respect to the N
2
content the
qualities 6.0 and 5.0 barely differ in Europe and the States so that usually spectrometer
argon can be used for analysing nitrogen. However, there is no guarantee as to the high
degree of purity. The difference in price results from the guarantee and the special
bottling procedure.
Spectrometers of Hitachi High-Tech Analytical Science allow to easily check the used
argon by means of a pure aluminium sample.
As far as the Al matrix is part of the spectrometer analysis programs, recalibration
sample RA10 is used. A pure aluminium sample is also included in the scope of delivery
of instruments without Al matrix. A small bottle of Ar 6.0, however, is useful for cases of
doubt.
1. The quality indicates the minimum percentage of gas in abbreviated form. The number of nines in the
percentage is indicated in front of the dot. The digit following the dot is equal to the first of nine devi-
ating digits in the percentage. Ar 4.6, for example, indicates an Ar degree of purity of at least
99.996 %. Ar 5.0 accordingly contains at least 99.999 % of argon.