Abstract. The investigation of
structure properties of natural graphene-containing material shungite is
performed. The specimens for investigation were found from deposits from
Karelia and Onega-region in Russia (Shunga, Zazjogino, Maksovo, Chebolaksha).
The central object of investigations was the volume concentration of conducting
carbon which is separated by nonconducting quarts seams. In the most important
method of carbon concentration determination it was choose the nondestructive
electric-force spectroscopy method. As a control it was choose the express-analysis
method which is consist in chemical analysis of weight concentration of carbon
in the gases which are received by shungite burning in tube stove. In the
reason of physical sense the result of express-analysis is the weight carbon
concentration in burned specimen. But the electro-force spectroscopy method is
able to found only surface properties of material. With the purpose of
possibility to comparison of results founded by both methods it was proposed
the method of recalculation of weight concentration to volume concentration. In
the basis of recalculation it was made the supposition about volume equality of
volume carbon atom and volume quarts components – atoms of silicon and oxygen.
It is discussed the correctness of this supposition. It is noted that its
acceptance bring to perfectly plausible results which are harmony with
experiments. The investigated specimens were made by the mechanical cutting of
plates from volume shungite pieces having length to several centimeters which
are found from different deposits with following grinding and polishing of made
flat surface. It was investigated in all 32 specimens having weight carbon concentration
(determined by express-analysis method) from 3 to 96 per cent. The analysis of
specimen properties was made by atom-force microscope. The electric properties
of specimen were found by measuring of spreading of electric current between
the cantilever point edge and specimen surface. The typical dimension of
investigated regions of specimen was 20 to 20 micrometers. On the some
specimens the measuring were made in smaller ground right until 3 to 3
micrometers. The space precision of microscope was 0,03 micrometers. The
results of measuring were two-color conductivity maps which was the near to
chaotic alternation of white and black regions. In this case the white regions
corresponds to conducting carbon and black regions corresponds to nonconducting
quarts. For the describe of founded conductivity maps it was discussed two
before proposed models of shungite structure – “cubes with percolation” and
“sand with liquid”. It is discussed the peculiarities of both models which
found its points in conductivity maps. For more detailed investigation of carbon
space structure distribution the maps were subjected to binomial processing.
For this case on the map was putted the square net consist of square cells
having dimension 20 to 20 cells. After this procedure the so cells which black
region was more the half of cell area were painted to black color and cells
which black region was less the half of cell area were painted to white color.
The received by the same manner binomial maps having 400 cells were subjected
to statistic processing. For this case the total area occupied by cells of
white or black color is calculated. The results of this calculation is the
space characteristic of carbon distribution over the specimen area. It was
found that these calculated values of white and black areas have large scattering
which value is so large as some times. For the founding of total statistic law
it was proposed two system of specimen grouping – by the value of whole white
or black cells areas on the conductivity maps and by the value of volume carbon
concentration which was received by express-analysis method. It was shown that
the first method can give some unity of samples by the regions of conductivity
maps but the concentration scattering is not removed. The second method gives
some increasing of scattering by the size of regions on conductivity maps but
good co-ordinate specimens by carbon concentration. By this reason in the
general investigation method was choose the second method which make possibility
of breaking whole specimens quantity to nine groups divided by carbon
concentration more or less steady in the interval from 5 to 97 per-cents. For
the founding of correction of binomial statistical analysis there was made the
investigation of net steps influence to distribution of cells so and other
colors. It was shown that the net steps influence is in large degree for this
phase which concentration is less then other phase concentration. In the other
cases it may be think that the results of conductivity maps breaking from the
net steps are depended not more then some per-cents. In the these work frame it
was recognized the optimal net consist of 20 to 20 cells on so and other
coordinates. In the result the whole net contains 400 cells. It was measured
the parameters of received field which is the quantity of white and black cells
over the each individual specimen. In agreement with established specimens
grouping it was made the statistical processing of received results with
calculation of arithmetical average and quadratic deviation. It was shown that
when the carbon concentration is increased the quantity of white cells is
increased and black decreased. This tendency describes the relative area of
appropriate phases. So it is shown that also by equal carbon concentration the
structure parameters of conductivity maps has large difference which is reaches
several times but this difference is decreased when the concentration is
increased. In the possible reason of this large difference is established the
nearly to chaotic character of space distribution of carbon and quarts parts of
shungite which is determined by its natural origin. It was investigated the
quantity of white cells in bicolor conductivity maps fields over the groups
from the volume carbon concentration. By way of approach to received results it
was proposed the empiric formula as a quadratic polynomial which was calculated
by the least quadratic method. With the data of concentration and fields areas
it was constructed the equation system which was resolved with the help of
office program «Excel» through the construction of reverse matrix. This system
solution took place the numerical coefficients of unknown quadratic polynomial.
By the graphic construction of this polynomial it was shown that its is very
nearly to straight line which describes the linear connection between the
carbon concentration and white cells quantity. It is found that this
approximate dependence is slightly exceed abovementioned straight line and
convexity in top to the side of more concentration. In the possible reason of
this difference it is made the proposition about not whole confidence of
correction degree of recount of weight concentration to volume also by the
reason exceeding of silicon atoms volume above carbon and oxygen atoms volume.
The graphic construction of this dependence for black cells made the same curve
but have convexity to bottom in the comparison of straight line which is
correspond to linear connection between carbon concentration and cells quantity.
It was shown that the summa both these curves is equal to whole quantity of
cells in field which is equal to 400 units. For the purpose of surface
distribution comparison between white and black cells over the field area it
was made the recalculation of surface concentration into volume. In suppose of
structure unification in the surface and volume of specimen it was shown that
for recalculation of surface carbon concentration into volume carbon
concentration the surface concentration value must be raised to the power of
3/2. It was made the comparison of carbon concentrations which was received by
two methods: by the conductivity maps and by express-analysis method. It was
shown that electro-force spectroscopy method in comparison with express-analysis
method gives the values of concentration which are enough near but slightly decreased
about the value of 11%. On the basis of graphic interpretation by the least
quadratic method it is found the empirical dependence of distinction between
the results which were received both methods from volume carbon concentration.
It is shown that the approximate function is near to straight line which is
arranged slightly lower then zero level which is correspond to equality both
concentrations. By the volume concentration increases the distinction between
both values received by both methods is decreased. It is shown that when the
concentrations are near zero the methods distinction is about 12% and when the
concentration appropriate to 100% the distinction decreases to 2-3%. It is
shown that the high proximity of both method results allows to regard
electro-force spectroscopy method as the suitable instrument for carbon
concentration determination in shungite without the destruction of specimen. It
was proposed the analytical dependence which made be able to calculate carbon
concentration from electro-force spectroscopy method. It is proposed some
practical recommendations about using of this method. As a significant demand
for the works development it is established the necessity of further
investigations of shungite deposits in expedition conditions.
Key words: carbon, shungite, electro-conductivity.
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