Copper of the high purity
V. Zadov1, A. Dementyev2, V. Medvedev3, Е. Kholodovych4
1
Siberian Technology University, Krasnoyarsk, Russia
Company "Vedanta", Krasnoyarsk, Russia
3
Company "Technostandart", Krasnoyarsk, Russia
4 Company "Nanotech", Kiev, Ukraine
2
ABSTRACT
Work examines some aspects of the technology of obtaining separately pure
metals on an example of obtaining powder copper by the cleanliness of more than
99,999% and one of the promising trends of further studies - creation “of nano-inks”.
INTRODUCTION
The high purity of metal makes it possible to obtain a maximally possible
electrical conductivity of copper conductor. This is especially important with the
production of microcircuits and printed-circuit boards. In this case it is necessary to
determine the admixtures, which most adversely affect the conductivity and exerts the
harmful alloying influence on the silicon base of microcircuits. Such limiting
admixtures are the criterion of the purity of the metal, used for the specific goals.
The promising trend of the use of copper of high cleanliness is the creation “of
nano-inks”. They make it possible to bring the electrically conducting figure with a
minimum width of line on the order 100 nanometers and less. The temperature of
welding the particles of the metal after solvent elimination occurs 100 - 200 degrees
with the complete absence of the oxidized layers.
Cleaning copper with its production begins from the fire refining. This makes
it possible to obtain metal with the maximum cleanliness of order 99.9%. Further
follows the electrolytic refining, conducted if necessary into two stages and making it
possible to obtain metal with the cleanliness of order 99.995%. The subsequent
refining makes it possible to obtain product with cleanliness 99.999% and more. By
the main disadvantage with the electrolytic method of cleaning is the presence in
cathode sediment the micro of quantities of electrolyte and colloidal particles of
arsenates, hydroxysulfates of antimony and other similar connections, which
positively and electrophoresis are transferred to the cathode.
For eliminating this transfer can be used the polymer membranes with the
openings, obtained as a result of the bombardment of the basis of the membrane with
alpha particles, or the cation-exchange membranes, completely not penetrated for the
colloidal particles. It is obvious that any membranes increase the resistance of
electrolyte and the corresponding power expenditures.
EXPERIMENT
To a certain extent indicated problems are solved with obtaining of the metal
in the form of powder, since the crystallites of copper practically do not contain
foreign inclusions. Obtaining powder copper of high cleanliness by known chemical
methods requires the high cleanliness of the reagents used and solvents. Copper is in
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air practically instantly covered with the thin layer of oxides; therefore the highly
dispersed powders, whose sizes are compared with the thickness of the oxidized layer,
they are easily oxidized by oxygen. And their obtaining it is carried out in a
atmosphere of inert gas. Conditionally it is possible to consider that the powder with
the size of the particles not more than 1 micrometers is in air unstable.
Obtaining the powders of copper with the sizes of the spherical particles of
less than one micrometer is accomplished by evaporation of the metal, heated to the
temperature, close to the boiling point and with the subsequent condensation on inert
gas. From the point of view of the decrease of power expenditures, is more expedient
the method of the explosive evaporation of thin wire during the supplying to it
discharge from the powerful capacitor. A drawback in this method is complexity
obtaining the wire of high cleanliness in view of its inevitable pollution with the
production. But this deficiency can be removed.
Obtaining clean substances with the content of base material 99.9999% is
carried out by physical methods - zone melting or single-crystal growth according to
«Czochralski». Taking into account the high thermal conductivity of copper and the
large unstable width of the molten zone, it is expedient to clean that not containing the
limiting admixtures by zone melting of copper salt and then to obtain metal.
CONCLUSIONS
Generalizing that presented above, we can assert that the developed by us
little expensive and effective technologies make it possible to today obtain in the
industrial volumes powder copper of in effect any cleanliness of base material.
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