Indicator of nitrogen-free diamond
1. Designation
The indicator of nitrogen-free diamonds is the compact
autonomous device intended for the selection of
Type IIa diamonds from the natural rough material or the brilliants, in
particular, the brown diamonds suitable for the high-temperature working at a
high pressure for the purpose of their discoloration. Into the group of
selection enter the crystals of diamond with the brown nuances of the colors
such as Type IIb and Type IaB1 which are also suitable for the thermo
baric working but being encountered it is extremely rare.
2. Operating principle
The operating principle of the device consists in the
registration of the intensity of the passing through the tested crystal ray of
short-wave ultraviolet radiation and is based on the essential difference in the
absorption of this emission by nitric and nitrogen-free diamonds. Crystals of
Type IIa (with the small content of nitrogen) and Type IIb (with the admixture
of boron) are practically transparent for the ultraviolet wavelengths up to the
boundary of their own optical absorption near 225 nm. But in
In the device as the source of the narrowly-directed
ultraviolet radiation is used light-emitting diode with the wavelength 265 ± of
10 nm. The emission of this range is absorbed in the indicated nitric natural
crystals of diamond and is not experienced essential absorption in the
nitrogen-free diamonds and in Type IaB1 crystals.
The registration of the passing through the crystal ray
is realized by photodiode with the increased spectral sensitivity in the
short-wave region of ultraviolet.
3. The design features
The common form of the device is represented in
photograph of one of the versions of its design performance, Fig. 1.
Fig. 1.
General view of the device with the gauge of output voltage.
On the cover plate of the housing of the device is
located the working table in center of which there is a small opening for the
directed ultraviolet radiation. The tested crystal of diamond must be placed to
the table completely overlapping the opening indicated. The receiving light ray
photodiode is fixed in the head of special holder. Electrical signal from the
photodiode will be given to the converting amplifier located in the housing of
the device. On the cover plate of the device there are terminals of the analog
output of the amplifier to which for measuring the DC voltage in the range to
two volts it is possible to connect the usual multimeter in preference with the
function of memorization of the maximum value of voltage during the time of
measurement.
The special feature of the device is the presence of
light indicator - the red color LED, light from which appears in the special
opening at the cover of the device if the tested crystal belongs to the
necessary to us type. (In this case the signal from the photodiode at the output
of amplifier must exceed 50 mV - adjustable point of operation of Schmitt
trigger. This point is established during the preliminary calibration of the
device.)
Two switches are located on the front panel of the
housing. One of them is intended for turn-on of the ultraviolet emitting diode
and another is used in the electric supply circuit of the converting amplifier
of photodiode. The 9 V galvanic small batteries are used in both cases. The
estimated time of a constant work of the batteries before their replacement is
about 500 hours.
4. Example of advantageous use of the device
The indicator of nitrogen-free diamonds can be used for
the prediction of the results of applying the HPHT technology - processing of
the brown crystals of diamond at a high pressure and high temperature. Below in
photographs, Fig. 2 and Fig. 3, the thoroughly tested groups of the nitric and
nitrogen-free crystals before and after of this working are represented.
Fig. 2. Result of the thermo baric processing of the nitric
crystals of diamond.
Fig. 3. Result of the thermo baric processing of the
nitrogen-free crystals of diamond.
The groups of the brown crystals of diamond represented
on the photographs are outwardly similar but easily and rapidly they are
distinguished with the aid of our movable compact device.
5.
Safety engineering
Instrument does not require the application of special
safety engineering. The ultraviolet diodes of a series 265 nm adapt for cleaning
of water, air and surfaces, do not generate ozone and vapors of mercury, they
are used for phototherapy. It is forbidden to look into the opening of radiation
source on the table of the device without glasses. Protect the device from the
dust.
Contact person: Dr. Valentin Ryzhov ( ryzhov@hppi.troitsk.ru )
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