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H-500
Hydrogen
Determinator |
 Oxygen/Hydrogen
model
OH-900
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| Overview |
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The H-500 analyzer incorporates the latest technology.
It is designed for the rapid and accurate determination
of hydrogen in steel and steel-alloys.
The hydrogen is detected by means of a dual range thermal
conductivity cell with auto zero control. The H-500
features a microcontroller, PC software for statistical
and scientific data processing, a high resolution interfaced
balance and a stand alone printer.
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| Operating
technique |
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The furnace temperature is set between 900° C and
1000° C. Samples are accurately weighed on the electronic
balance. By pushing a button, the sample weight is transferred
into the memory. Alternatively, weights can also be
entered manually, if required. The sample is placed
into the horizontally positioned furnace (A);
the start button is pressed 10 to 15 seconds later;
the furnace is then rotated upwards (B), for
the sample to fall into the hot zone and then moved
back to the horizontal position. The analysis then runs
automatically, its progress can be followed on the on
the PC screen. At the end of the analysis the furnace
is rotated downwards, (C) for the sample to fall
into a heat resistant bin. |
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| Gas dose calibration |
The H-500 can be calibrated with standards or by gas dosing.
When calibrating by gas dosing a known volume of helium is
injected into the nitrogen carrier gas. The volume of the
gas dose capillary is known so it is possible to calculate
the relationship between the fixed volume of helium at a sample
weight of 5g. The difference between the thermal conductivity
of helium (33) and hydrogen (39) is taken into consideration
by the calibration calculation. For safety reasons it is preferable
to use helium rather than hydrogen for gas dosing. |
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| PC
control with Windows 2000/XP software |
Comprehensive
analyser control and easy operation are provided by
the software running on PC, connected to the analyser.
Click software
from the main menu for more information about software.
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| Thermal
conductivity cell |
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Hydrogen concentrations are determined by a thermal
conductivity detector. This detector was especially
developed by ELTRA in order to guarantee low drift,
high resolution and wide measuring ranges. |
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| Sampling the molten metal |
An
evacuated pin sampler is a convenient method of taking
a sample. This sampler is a quartz tube with an ID of
6 or 8mm. A small thin membrane (B) of quartz is produced
during the sealing of the evacuated tube, when the sampler
is immersed in the molten metal the membrane ruptures
and the vacuum sucks the metal into the tube. In order
to minimise the loss of hydrogen from the hot sample
it is necessary to immerse the sample in water. The
quartz is broken off the sample. During this critical
cooling phase it is necessary to agitate the sample
to prevent bubbles adhering to the surface which would
increase the cooling time. The sample is then placed
in liquid nitrogen or dry ice to ensure there is no
further loss of hydrogen.
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| Sample preparation |
Sections
of the sample are cut using an abrasive wheel cut off machine,
coolant should be used to prevent the sample heating up. Any
surface oxidation should be removed by abrasion. Finally the
sample is washed in acetone and then rinsed in ether. It is
advisable to ensure all the solvents have been removed by
drying in hot air or placing it in a vacuum chamber for 30
seconds. The vacuum method is the most efficient, particularly
if there is any micro porosity in the sample. |
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| Electronic flow controller |
An essential part of the gas flow system is the the electronic
flow controller. This provides a stable gas flow, thus eliminating
the known disadvantages of mechanical flow controllers. The
instrument operates at atmospheric pressure thus reducing
the problems of leakes associated with pressurized systems. |
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Next:
H-500 Specifications |
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