УДК 666.233
INFLUENCE OF DETONATION NANODIAMOND CONSENTRASION ON THEIR
HYDROSOLS’ STRUCTURE FORMATION
E.U. Gosudareva
Scientific supervisor Ph.D. G.A. Chiganova
Language advisor V.G. Anduseva
Siberian Federal University
Sols of detonation nanodiamonds (DND) are widely applied in different areas. They
are the basis of diamond coatings, DND insertion improves lubricant compositions and
polishing pastes, DND have been used in electrochemical coating for decades. Dimensional
and surface DND characteristics make their application in biology and medicine varied and
possible.
For effective use of DND it’s necessary to study the laws of their sediment stability.
To scrutinize DND hydrosols sedimentation the volumetric method (a classic method
of interface and colloid science) was used in this work. The method consists of measuring a
̅̅̅̅̅
volume of seceding dispersed phase precipitate (𝑉
𝑟𝑒𝑙. ).
0,1-1,5 mass % nanodiamond aqueous suspensions were used for the study. They
were obtained by three-minute ultrasonication at 22 kHz. Produced on the CSC SB RAS and
SFU joint section the nanodiamonds cleaned from non-diamond carbon by heat treatment in
the air in the presence of boron trioxide B2O3 were studied. Such sols were shown to be
sedimentation stable in the absence of electrolytes for a long time. The average size of
particles or of their solid aggregates in the aqueous medium is 13 nm. The size of most
particles ranges from 10 to 100 nm (disk centrifuge CPS 24000).
The DND hydrosols were observed in the presence of 0,2 M potassium chloride KCl
solutions. According to calculations of particles interaction energy, based on the DerjaguinLandau-Verwey-Overbeek’s theory (DLVO), the potential barrier, which prevents particles
aggregation, is completely suppressed at this electrolyte concentration.
The volumetry results are shown on Fig. 1. Fig. 1 plots that the velocity of DND
particle sedimentation decreases with the rise of dispersed phase concentration. Besides in the
initial period of time the qualitative difference of graphs is seen between low-concentrated
hydrosols (0,1 and 0,2 mass %) and systems with higher DND content (0,3-1,5 mass %). In
case of low DND concentration sharp decline of sedimenting precipitate volume is observed
whereas in other cases sedimentation appears to be gradual. It can be interpreted as follows: at
low DND concentration aggregates settle structureless. But at с ≥ 0,3 mass % continuous
coagulation structure forms almost immediately. For such structure fast definition of precise
frontier between settling dispersion and continuous medium is typical.
To understand the correlation of DND concentration and structure formation (Fig. 2)
the solid phase volume fraction 𝜑(𝑡) in precipitate was calculated using experimental data
and such initiate parameters of the system as continuous medium density (distilled water; 1
g/sm3) and solid phase density – DND pycnometric density (3 g/sm3):
𝜑(𝑡) =
𝑉𝑠.𝑝.
𝑚𝑠.𝑝.
𝑚𝑠.𝑝.
𝜌0 𝑐
=
=
=
,
𝑉(𝑡) 𝑉(𝑡) ∙ 𝜌𝑠.𝑝. 𝜌𝑠.𝑝. 𝑉0 ̅̅̅̅̅
𝑉𝑟𝑒𝑙. (𝑡) 𝜌𝑠.𝑝. ̅̅̅̅̅
𝑉𝑟𝑒𝑙. (𝑡)
where 𝑉𝑠.𝑝. , 𝑚𝑠.𝑝. , 𝜌𝑠.𝑝. – volume, mass and density of solid phase in hydrosol,
𝑉0, 𝜌0 – continuous medium characteristics,
𝑉(𝑡) – precipitate volume,
𝑐 – hydrosol’s mass concentration.
Fig. 1 – Volumetry of DND hydrosols of various concentrations
Data from Fig. 2 graphs also confirm the formation of dense aggregates at early
concentrations (to 0, 2 mass %), which sediment in precipitate actively. Increasing dispersed
phase concentration leads to precipitation of loose aggregates due to formation of coagulation
structure, where growing aggregates settle gradually from sol above the precipitate. The gain
of sedimentation volume density at further increase of concentration is determined by growth
in the number of particles in the volume of the continuous medium and corresponding rise of
interparticle contacts. Coagulation decelerates due to the upgrowing hardness of the lattice.
Fig. 2 – The dependence of solid phase volume fraction in sedimentation precipitate on
original solid phase volume fraction in the system at different settling time (T = 299 K)
The experiment similar to this but without electrolyte was conducted in [1] – Fig. 3.
The comparison of two experiments shows that the insertion of electrolyte in the
system reduces solid phase volume fraction by several times and changes the dynamics.
Without the electrolyte at the set time (24 hours) and DND concentration higher than 0,15 %
the equilibrium shifts towards the formation of big loose aggregates, which consolidate
gradually loosing the volume. Whilst in electrolyte presence coagulation structure forms and
has been constructed from sedimenting aggregates.
Fig. 3 – The dependence of solid phase volume fraction in sedimentation precipitate on
original solid phase volume fraction in systems with and without electrolyte (T = 299 K)
Obtained results on the issue of aggregative and sediment DND hydrosols’ stability
can be used for optimization of polishing pastes and DND-based suspensions consistent [2, 3].
Thus, in [3] it was reported, that essential condition of polishing pastes’ high performance
properties is aggregative instability leading to the formation of sedimentary stable coagulation
structure. However, increasing dispersed phase concentration leads to the creation of
mechanical defects on the polished surfaces in the form of diamond scurf. Thereby it looks
quite promising to consider the application of relatively low amounts of DND with
simultaneous injection of electrolyte, which would ensure coagulation structure formation.
List of references:
1 Chiganova, G. A. Particle aggregation in ultradispersed diamond hydrosols / G. A.
Chiganova // Colloid Journal. – 2000. – V. 62, № 2. - P. 274.
2 Semenova, O. V. Substrate surface precision treatment by ultradispersed diamond
powders for microelectronics: abs. dis. … cand. tech. sciences: 05.03.01 / Semenova Olga
Vasilyevna. – Krasnoyarsk, 2000. – 23 p.
3 Yuzova, V. A. Polishing compositions based on new ultradispersed abrasive
powders for processing elements of radio-electronic means: abs. dis. … cand. tech. sciences:
05.16.06 / Yuzova Vera Alexandrovna. – Krasnoyarsk, 1998. – 23 p.