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Diamond-SiC composites are attractive for improving the catastrophic fracture behaviour of SiC. However, fundamental knowledge is missing about the structure of this system and the mechanism of diamond graphitization. We used spark plasma sintering to study the diamond-Si-SiC system between 1600 and 2000°C in the function of nanocrystalline (ND) and microcrystalline (MD) diamond addition as well as the quantity of Sibonding phase. Increasing sintering temperature induces intense graphitization and formation of nano-onions, few-layered graphene and well-ordered graphite in the prepared composites at elevated temperature. High resolution transmission electron microscopy study demonstrates the occurrence of the previously erroneously identified 5H-SiC polytype in the samples prepared at 2000°C. Regardless of Si and diamond contents, SiC formation is not confirmed even at high temperature.

Levocetirizine dihydrochloride is an effective antiallergenic drug applied mostly orally; however, developing a topical formulation for localized treatment could be beneficial. To achieve this, a modified formulation technique is necessary to enhance bioavailability efficiency and minimize possible side effects. Therefore, levocetirizine particles were prepared by immobilization on mesoporous silica material. Both the dihydrochloride form and its free base of levocetirizine were fixed on a silica-type Syloid support. Immobilization of the active ingredient levocetirizine in a free base form on a Syloid support by mixing in a dichloromethane solution provides better surface coverage (65.5%) than immobilization in the dihydrochloride form in water or methanol (24.5% for both). The successful binding of levocetirizine was confirmed by X-ray photoelectron spectroscopy and infrared measurements. The active ingredient in the form of hydrochloride is more likely to be in the pores, while the free base is bound to the surface in larger quantities. The time-dependent levocetirizine release showed that the liberation of the active ingredient from the Syloid is slower than the dissolution of the starting active ingredient itself, so it may be suitable for exerting a more reliable and prolonged local effect. A gel containing a Syloid-fixed levocetirizine free base was tested in vivo in a croton oil-induced ear edema mouse model. When compared to a reference gel, the half-dose formulation containing levocetirizine free base demonstrated a similar efficacy to Fenistil gel, indicating that the new formulation may offer superior effectiveness at lower doses. [ABSTRACT FROM AUTHOR]

A simple synthetic method was developed to prepare 4[Agpy2ClO4]·[Agpy4]ClO4 in a low-temperature decomposition process of [Agpy4]ClO4. A detailed IR, Raman and far-IR study including factor group analysis has been performed, and the assignation of bands is given. The compound decomposes quickly with a multistep ligand loss process with the formation of [Agpy2]ClO4 and AgClO4 intermediates and AgCl as an end product around ~ 85, ~ 350 and 450 °C, respectively. During the first decomposition step, a small fraction of the ligands is lost in a redox reaction: perchlorate oxidizes the pyridine, forming carbon, carbon dioxide, water and NO, while it itself is reduced into AgCl. In the next step, when AgClO4 forms after complete ligand loss and reacts with the carbon formed in the degradation of pyridine at lower temperatures and produces NO, CO2 and H2O. This reaction becomes possible because the AgCl formed in the redox reactions makes a eutectic melt with AgClO4 in situ, which is a favorable medium for the carbon oxidation reaction. AgCl is known to reduce the temperature of decomposition of AgClO4, in which process forms AgCl as well as O2 and so is an autocatalytic process. The loss and degradation of pyridine ligand are endothermic; the redox reactions including carbon oxidation and AgClO4 decomposition into AgCl and O2 are exothermic. The amount of absorbed/evolved heats corresponding to these processes was determined by DSC both under N2 and O2 atmospheres. [ABSTRACT FROM AUTHOR]

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 m1/2 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. [ABSTRACT FROM AUTHOR]

Decomposition of poly(vinyl chloride) (PVC) was investigated in radiofrequency thermal plasma in neutral, oxidative and reductive conditions. Optical emission spectroscopy (OES) was applied for the characterization of the plasma column. OES was used to identify active plasma components such as excited atoms, ions, radicals and molecules. The spectra were dominated by molecular C2, CN, OH, and CH bands, and atomic H, Ar, C, Cl and O lines. Emission intensities of main species were monitored versus various experimental parameters. The rotational-vibrational temperatures determined from different bimolecular species were considered in the range of 2000-6400 K. Solid soot samples were collected and purified to investigate the possibility of graphene formation as a by-product of the decomposition process. [ABSTRACT FROM AUTHOR]

We studied the fabrication of functionally graded Al2O3–CeO2-stabilized-ZrO2 (CTZ) ceramics by spark plasma sintering. The ceramic composite exhibits a gradual change in terms of composition and porosity in the axial direction. The composition gradient was created by layering starting powders with different Al2O3 to CTZ ratios, whereas the porosity gradient was established with a large temperature difference, which was induced by an asymmetric graphite tool configuration during sintering. SEM investigations confirmed the development of a porosity gradient from the top toward the bottom side of the Al2O3–CTZ ceramic and the relative pore volume distributed in a wide range from 0.02 to 100 µm for the samples sintered in asymmetric configuration (ASY), while for the reference samples (STD), the size of pores was limited in the nanometer scale. The microhardness test exhibited a gradual change along the axis of the ASY samples, reaching 10 GPa difference between the two opposite sides of the Al2O3–CTZ ceramics without any sign of delamination or cracks between the layers. The flexural strength of the samples for both series showed an increasing tendency with higher sintering temperatures. However, the ASY samples achieved higher strength due to their lower total porosity and the newly formed elongated CeAl11O18 particles. [ABSTRACT FROM AUTHOR]

Abstract: Continuous synthesis of TiB x (x≈0.5–2) nanoparticles from various low cost solid precursors such as titanium and titanium dioxide admixed with boron and/or carbon in radiofrequency thermal plasma was studied. Feasibility of TiB2 formation was predicted by thermodynamic equilibrium calculations in the 500–5000K temperature range. In all the investigated system high temperature reactions resulted in nanometer-sized TiB x powders with a mean size varying between 13 and 83nm. The yield of particular runs ranged from 38% to 97%. Among the synthesized products in addition to TiB x , oxidized precursor residues were also found in smaller quantities. Although addition of carbon to the precursors could not completely prevent surface oxidation of boride particles, it contributed to the reduction of the mean particle size of the formed TiB2. [Copyright &y& Elsevier]