The effect of modification diamond nanopowders detonation synthesis to change their electrokinetic and electrophysical characteristics

Development of methods for controlling the change in the functional cover and the energy composition of the surface of detonation synthesis diamond nanopowders is necessary to create stable suspensions and materials from them. The aim of this work is to study changes in the electrokinetic and electrophysical characteristics of the powder as a result of the modification of detonation synthesis diamond nanopowders using a liquid-phase thermochemical treatment. Diamond nanopowders of grades ASUD-75 - ASUD-99 with different sp2-hybridization carbon content, manufactured at the V.I. Bakul National Academy of Sciences of Ukraine from the product of detonation synthesis of diamond from the company "ALIT" (Zhytomyr) investigated. Diamond nanopowders of ASUD-90 grade after their modification by means of liquid-phase thermochemical treatment using: a melt of alkalis, a mixture of nitric and sulfuric acids, a mixture of chromic and sulfuric acids were investigated by electrophoresis using a device "Dzeta-potential-analizer" company "Mikromeritiks". Electrokinetic characteristics of diamond nanopowders: the magnitude and sign of the electrokinetic potential, electrophoretic mobility are determined. The methods were used to study the physicochemical characteristics of nanopowders: electrical resistivity, carbon content of sp2-hybridization, mass fraction of impurities in the form of an incombustible residue, and specific surface area. In this work, it was established by electrophoresis that the value of the electrokinetic potential and electrophoretic mobility of the powder decrease by 2-10 times with a decrease in the mass fraction of sp2-hybridization carbon from 23.6 to 0 wt%. Using the ASUD-90 nanopowder as an example, it is shown that the modification of the nanopowder by the liquid-phase method using thermochemical treatment with mixtures of oxidants leads to a decrease in the values ​​of electrophoretic mobility by 1.1-7.5 times and electrokinetic potential by 1.1-7.3 times. It was found by dielectric measurement that the tangent of the dielectric loss angle of diamond nanopowders of grades ASUD-90 - ASUD-99 is in the range 0.3046 - 0.3146. Modification of the ASUD-90 grade nanopowder using a liquid-phase thermochemical treatment leads to a change in the interval of the dielectric loss tangent, namely 0.2450-0.3249. According to the degree of increase in the ratio of the dielectric loss tangent from 0% humidity to 100% humidity, the methods for modifying nanopowders can be arranged as follows: modifying using a melt of alkalis (ASUD-90-1 sample, S = 12.8%) <mixture of chromic and sulfuric acids (sample ASUD-90-3, S = 13.8%) <mixture of nitric and sulfuric acids (sample ASUD-90-2, S = 20.8 %).

Features of the physicochemical properties of narrow fractions of aggregates of diamond nanopowders modified with iron ions

The paper presents the results of a study of the physical and chemical properties of narrow fractions of diamond nanopowders with a low content of non-diamond carbon grade ASUD-99. Six fractions with different average diameters of diamond particle aggregates from 28.785 to 3.891 μm were obtained by separating a 0.2 % aqueous suspension of the initial powders by the sedimentation method. It has been found that the smallest aggregates consist of larger particles with a smaller specific surface area and a lower interaction energy between them. This conclusion is confirmed by a decrease in the porosity of the obtained aggregates. So, if the pore volume in the largest aggregates of diamond particles is 0.859 ml/g, then in the smallest 0.550 ml/g, while the pore radius of diamond aggregates in different fractions changes insignificantly. Separation in a magnetic field at different currents of diamond nanopowders with a specific magnetic susceptibility of 0.52×10-8 m3 kg, treated with a solution of 5 % iron chloride, made it possible to obtain five fractions that differ from each other in specific magnetic susceptibility (c) – from magnetic fractions with c = 4.30×10-8 m3/kg to diamagnetic – with c = –0.11×10-8 m3/kg. It is shown that the modification of diamond nanopowders with iron ions increases the separation selectivity and makes it possible to isolate diamagnetic powders.

Thermal and Physical Characterization of PEG Phase Change Materials Enhanced by Carbon-Based Nanoparticles

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g·mol−1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3–3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64–0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du Noüy ring tensiometer and a drop-shape analyzer.

Purification and Functionalization of Diamond Nanopowders

Purification of diamond nanopowder (DNP) was conducted in a less-destructive mild polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5). The wide-angle X-ray diffraction (XRD) showed that the intensity of the characteristic diamond d-spacing (111) at 2.07 Å from purified DNP (PDNP) was fairly increased compared to pristine DNP, indicating that significant amount of carbonaceous impurities were removed. Chemical modification of pristine DNP and PDNP with 4-ethylbenzoic acid was carried out to afford 4-ethylbenzoyl-functionalized DNP (EBA-g-DNP) and PDNP (EBA-g-PDNP). The morphologies of EBA-g-DNP and EBA-g-PDNP from scanning electron microscopy (SEM) were further affirmed the feasibility of chemical modification. The results suggested that the reaction condition was indeed viable for the one-pot purification and functionalization of DNP. The resultant functionalized DNP could be useful for nanoscale additives. Hence, EBA-g-DNP and EBA-g-PDNP was brominated by using N-bromosuccinimide (NBS). The resultant N-brominated DNP and PDNP could be used as initiator for the atom transfer radical polymerization (ATRP) to introduce many polymers onto the surface of functionalized DNP and PDNP.