On the Effect of the Distances between Coal and Wood Particles during Their Joint Pyrolysis on Sulfur Oxides Formation

The simultaneous pyrolysis of coal with wood was experimentally found to allow reducing concentrations of sulfur-containing substances in gases released. The objective of experimental studies is comparison of the sulphate of calcium and aluminum in the ash of coal-wood mixtures after pyrolysis of the latter in a dense “packing” of aggregate particles of these two fuels and at a few millimeters distance between particles. The 3B-grade lignite, T-grade bituminous coal and pinewood sawmill waste were chosen as feedstocks for pyrolysis experiments because they are widespread in Russia as well as many other countries. The elemental composition of all raw materials and pyrolysis residues was determined. The inorganic composition of obtained pyrolysis product in the solid phase was characterized by X-ray analysis. The content of aluminum and calcium sulfate in residue in case of simultaneous processing of coal with wood was found to be higher, compared to the processing of coal only (within the random errors of the experiment), than those established for such mixtures under conditions of dense “packing” of large masses (up to 15 g).

Direction-Dependent Properties in Inverted Carbon Nitride Colloidal Glasses with Gradient Porosity

It is well known that the step from a dense packing of colloidal beads to the inverted systems was important for the optimization of photonic crystal properties. Inverted opals made of high-refractive index semiconductors have attracted great attention due to their supreme optical features such as the occurrence of a photonic band-gap and because of an astonishing behavior in photocatalysis or for photovoltaics caused by so-called slow photons. It is much less known that photonic glasses, despite being disordered, exhibit unique optical properties too like random lasing or high-contrast structural colors. In analogy to opals and inverted opals, one can expect that inverted colloidal glasses may lead to an amplification of photonic properties as well or even to the emergence of unexpected features. An inverted photonic glass is characterized by a dense packing of monodisperse voids with colloidal dimensions without any long-range order. The preparation of inverse photonic glasses has rarely been reported by now and cases for materials composed of a semiconductor as a pore-wall material are unknown. The synthesis of porous carbon nitride (C₃N₄) with inverted colloidal glass structure is demonstrated here using a template approach. The formation of the template with glass-like order is achieved by analytical ultracentrifugation (AUZ) of size-selected silica colloids, followed by infiltration of a precursor sol, transformation to carbon nitride and the final removal of the template. The use of AUZ is particularly important because it even allows to use a mixture of differently sized template particles, which are gradually fractionated. Monoliths with optimized morphological features exhibiting a gradient porosity and highly accessible pores are obtained. The result are materials with a graded structure. What makes such functional gradient material interesting is, a dependence of the optical features on the position can be expected. In addition, the method presented here allows to synthesize materials with adjustable composition ranging from carbon over nitrogen-doped carbon to C₃N₄ with either graphitic or polymeric structure. Therefore, the optical band gap is highly adjustable and tunable with regards to the photonic properties, as confirmed by optical absorption and photoluminescence measurements.

Direction-Dependent Properties in Inverted Carbon Nitride Colloidal Glasses with Gradient Porosity

It is well known that the step from a dense packing of colloidal beads to the inverted systems was important for the optimization of photonic crystal properties. Inverted opals made of high-refractive index semiconductors have attracted great attention due to their supreme optical features such as the occurrence of a photonic band-gap and because of an astonishing behavior in photocatalysis or for photovoltaics caused by so-called slow photons. It is much less known that photonic glasses, despite being disordered, exhibit unique optical properties too like random lasing or high-contrast structural colors. In analogy to opals and inverted opals, one can expect that inverted colloidal glasses may lead to an amplification of photonic properties as well or even to the emergence of unexpected features. An inverted photonic glass is characterized by a dense packing of monodisperse voids with colloidal dimensions without any long-range order. The preparation of inverse photonic glasses has rarely been reported by now and cases for materials composed of a semiconductor as a pore-wall material are unknown. The synthesis of porous carbon nitride (C₃N₄) with inverted colloidal glass structure is demonstrated here using a template approach. The formation of the template with glass-like order is achieved by analytical ultracentrifugation (AUZ) of size-selected silica colloids, followed by infiltration of a precursor sol, transformation to carbon nitride and the final removal of the template. The use of AUZ is particularly important because it even allows to use a mixture of differently sized template particles, which are gradually fractionated. Monoliths with optimized morphological features exhibiting a gradient porosity and highly accessible pores are obtained. The result are materials with a graded structure. What makes such functional gradient material interesting is, a dependence of the optical features on the position can be expected. In addition, the method presented here allows to synthesize materials with adjustable composition ranging from carbon over nitrogen-doped carbon to C₃N₄ with either graphitic or polymeric structure. Therefore, the optical band gap is highly adjustable and tunable with regards to the photonic properties, as confirmed by optical absorption and photoluminescence measurements.

Superoscillations in Finite-Energy Airy Beams

Superoscillations naturally arise in optical fields with dense packing of nodal points of amplitude. Airy wave packets are highly oscillatory and rich of phase singularities. We study to the best of our knowledge, for the first time, the superoscillatory behavior in a band-limited Airy beam whose spectrum is sharply truncated. Our results show that not as expected, the superoscillations occur outside of the Airy-like region, but in regions above a defining line where the beam stops being Airy-like. The degree of superoscillation can be very high there.

Structure directing effect of aqueous alkali metal ion (Li+, Na+ and K+) clusters on polyoxoanion configuration in vanadium-molybdenum polyoxometalate solid solutions

In structural chemistry context, the dense packing and the structural directing agent (SDA) often play crucial role in the formation of desired crystal structure. Herein, we present two isomorphous decavanadate-type...