We reported on the synthesis of nanosized hydroxyapatite particles by wet chemical precipitation method and the consolidation of the nanoparticles by spark plasma sintering. We studied the effect of the synthesis temperature on the particle size and phase composition of the obtained HAp. During synthesis beyond HAp, another phase supposedly nonstoichiometric HAp was also formed as a by-product that can be detected by thermal analysis combined with XRD. Its amount gradually decreased with the increase in synthesis temperature and practically disappeared at 80°C. Using this nanopowder for sintering, the spark plasma-sintered ceramics retained their nanostructure comprising only HAp phase in contrast to the powders synthesized at lower temperature when transformed products of the nonstoichiometric HAp could also be detected.

Hydroxyapatite / graphene (HAP/GNPs) composites were prepared by spark plasma sintering (SPS).Sintering was carried out at various temperatures (700°C and 900°C) and holding times (5 and 10 min). Mechanical and structural properties were studied. The highest relative density ~ 96% was

Decomposition of poly(vinyl chloride) (PVC) was studied in inductively coupled radiofrequency thermal plasma in neutral, oxidative and reductive conditions. The exhaust gases were analysed by Fourier transform infrared spectroscopy (FT-IR), and their main components were identified as CO, CO 2 , C 2 H 2 , H 2 O and HCl. The weaker bands in the infrared spectra were assigned by density function theory calculations and P-R separation method. The extent of PVC decomposition was calculated from the amount of solid soot, which was also studied by transmission electron microscopy (TEM) for morphology and composition. Organic compounds adsorbed on the surface of the soot were extracted by toluene and analysed by gas chromatography mass spectrometry (GC/MS). The extracts *Marked-up Revised Manuscript Click here to view linked References

Herein we present a continuous and catalyst free method for the synthesis of graphene sheets from aliphatic alcohols in a radiofrequency thermal plasma jet. Nine aliphatic linear alcohols (ethanol-decanol) were tested as possible precursors for the massive production of graphene sheets. Moreover, additional tests were also carried out with the inclusion of gaseous oxygen in order to promote the formation of graphene and to eliminate the unwanted carbon byproducts. The obtained materials were investigated by electron microscopy, Raman and infrared spectroscopy. The thermal stability of products was also evaluated using thermogravimetry. The surface chemistry features were analyzed using acid-base titration and X-ray photoelectron and IR spectroscopy. Finally, the adsorption performance of graphene sheets was tested in the removal of 4-chlorophenol from aqueous solutions. The highest content of graphene sheets was found in the product obtained from ethanol with the production rate of ca. 1.5 g/h. The plasma processing of higher alcohols yielded a mixture of graphene sheets and spherical carbon nanoparticles.

Decomposition of chlorobenzene as a model molecule of aromatic chlorinated compounds was studied in radiofrequency (RF) thermal plasma both in neutral and oxidative conditions. Optical emission spectroscopy (OES) was applied for the evaluation of the plasma excitation and molecular rotational-vibrational temperature. Atomic (C, H, O) and molecular (CH, OH, C 2 ) radicals were identified, while the morphology of the formed soot was characterized by electron microscopy. Organic compounds adsorbed on the surface of the soot after plasma processing were comprised of various polycyclic aromatic hydrocarbons (PAH) and chlorinated PAH molecules. Their amount was greatly affected by experimental conditions, especially the oxygen content and plate power. The higher input power reduced the ring number of the PAH molecules. Addition of oxygen significantly reduced the amount of both PAHs chlorinated PAH molecules but enhanced the formation of polychlorinated benzene compounds.

Synthesis of zirconium carbide (ZrC) powder was investigated applying a non-conventional atmospheric radiofrequency (RF) thermal plasma process. In one case, zirconium dioxide (ZrO2) was reacted with solid carbon or with methane with varying molar ratio. In the other, zirconium-propoxide (NZP), containing both constituents, was thermally decomposed in the Ar plasma. Temperature-dependent thermodynamic analysis was performed in the 500-5500 K temperature range to estimate the formation of possible equilibrium products for each reaction stoichiometry. Broad temperature range exists for the stability of solid ZrC for each explored reaction system. In accordance with this prediction, X-ray diffraction studies detected the ZrC as the major phase in all the prepared powders. The yield of particular runs ranged from 39 % to 98 %. Practically, full conversion was typical for the case of NZP precursor, however only partial conversion could be detected in ZrO2 reactions. The average particle size of the powders falls between 10 nm and 100 nm depending on the type of the reaction systems (either calculated from the specific surface area or derived from broadening the XRD reflections). The transmission electron micrographs indicated mostly globular shape of the nanosize particles. Quantitative analysis of the surface of the powders by X-ray photoelectron spectroscopy revealed the presence of oxygen and carbon. Evaluating the spectra of the powders prepared from NZP, and taking in the account its spherical shape, a ZrC core covered by a very thin (≈1.0 nm) ZrO2 layer may be accounted for the measured oxygen and a thicker carbonaceous layer.

Mulitlayer graphene reinforced silicon nitride composites were prepared by spark plasma sintering to investigate the effect of the graphene addition on mechanical properties. The composites contained multilayer graphene (MLG) in various (0, 1, 3 and 5 wt%) content. Significantly higher fracture toughness of 8.0 MPa m 1/2 was obtained at 1% MLG content, however, on further increasing the graphene content the toughness did not increase, but dropped to the value of the monolithic silicon nitride. The maximum hardness of 18.8 MPa was also obtained at 1% MLG, while at higher MLG contents it gradually decreased.

Silicon carbide (SiC) ceramics have superior properties in terms of wear, corrosion, oxidation, thermal shock resistance and high temperature mechanical behavior, as well. However, they can be sintered with difficulties and have poor fracture toughness, which hinder their widespread industrial applications. In this work, SiC-based ceramics mixed with 1 wt% and 3 wt% multilayer graphene (MLG), respectively, were fabricated by solid-state spark plasma sintering (SPS) at different temperatures. We report the processing of MLG/SiC composites, study their microstructure and mechanical properties and demonstrate the influence of MLG loading on the microstructure of sintered bodies. It was found that MLG improved the mechanical properties of SiC-based composites due to formation of special microstructure. Some toughening mechanism due to MLG pull-out and crack bridging of particles was also observed. Addition of 3 wt% MLG to SiC matrix increased the Vickers hardness and Young's modulus of composite, even at a sintering temperature of 1700°C. Furthermore, the fracture toughness increased by 20% for the 1 wt% MLG-containing composite as compared to the monolithic SiC selected for reference material. We demonstrated that the evolved 4H-SiC grains, as well as the strong interactions among the grains in the porous free matrices played an important role in the mechanical properties of sintered composite ceramics.