Evolution of physico-chemical properties of Dicranopteris linearis-derived activated carbon under various physical activation atmospheres

This work emphasizes the effect of the physical activation using CO2 and steam agents on the physicochemical properties of activated carbon produced from Dicranopteris linearis (D. linearis), a fern species widely distributed across tropic and subtropic ecoregions. The D. linearis-derived chars produced under pyrolysis at 400 °C for 1 h were activated in various CO2-steam proportions. As revealed by the IR and Raman spectra, the structure of the activated chars was heavily dependent on the relative proportion of CO2 and steam. The total specific surface area (SSA) of the activated chars proportionally increased with the increase in steam proportion and was comparable to the values of commercial activated char products. Specifically, the activation under CO2− and steam-saturated conditions has correspondingly resulted in SSA increasing from 89 to 653 m2g−1 and from 89 to 1015 m2g−1. Steam also enhanced the development of mesoporous structures of the D. linearis-derived char products, thereby extending their potential applications, particularly for industries that require high rigidity in the product such as pharmaceutical and cosmetic sectors.

Мineral Powders Dispersion Degree Effect on the Properties of the Cementing Alkaline System

This paper presents the results of studies on mineral powders dispersion degree effect on the properties of alkaline cement-water paste where powders are of natural and technogenic origin. The change dependences between the total specific surface area and the duration of grinding have been studied, and the optimal grinding time for raw materials has been revealed. The developed formulations of cementing alkaline binders, with the use of mineral powders and wastes from the cement industry, are distinguished by short setting times and high consumption of alkaline grout to obtain a cement paste of normal density, which requires further research. And the obtained influence patterns of the degree of dispersion on the properties of the "mineral powder - Na2SiO3" binder will make it possible to create strong and durable artificial building composites competing with concretes based on Portland cement. The results presented in this article were obtained within the framework of studies on the implementation of scientific project No. 05. 607.21.0320. "Development of technology for new building composites based on clinkerless cement of alkaline activation using substandard natural and secondary raw materials" supported by the Federal Target Program "Research and Development in Priority Areas of Development of the Scientific and Technological Complex of Russia for 2014-2020". The unique identifier for the agreement is RFMTFI60719X0320.

The pure yttrium oxide microspheres for nuclear medicine

Cancers of liver are a problem of modern medicine. A common method of treatment is surgery. In patients who do not need surgery, various methods of local exposure can be prescribed (radiofrequency ablation, chemoembolization, brachytherapy, etc.). In the last decade, a method of treating cancer of liver — radioembolization of the liver-has been introduced into practice. The method is based on selective intra-arterial injection of glass or rubber microspheres containing yttrium radionuclide, resulting in local radiation exposure to tumor tissue. Recently, there has been increasing interest in the production of ceramic microspheres of the yttrium-90 (90Y) isotope. Narrow-fraction microspheres of pure yttrium oxide were obtained as a result of processing yttrium oxide powder in an air RF plasma. The resulting microspheres were subjected to ultrasonic treatment in deionized water, as a result of which the total specific surface area of the particles decreased by 10 %. Yttrium oxide microspheres were etched in a solution of sodium chloride for 11 days, after which the surface of the particles did not undergo significant changes. As a result, microspheres were obtained that have potential applications in nuclear medicine.

The Thermal Parameters of Mortars Based on Different Cement Type and W/C Ratios

This study examines the thermal parameters of mortars based on different cement type and water-cement W/C ratios. The presented relationships are important from the point of view of thermal insulation of the entire building component, of which the mortar is a part. The thermal properties of the mortar, and in particular its dependence on the degree of moisture, is important information from the point of view of hygrothermal simulations of building components. The moisture effect on the thermal properties was tested using nine mortar types. The study consisted of producing nine types of mortar on the basis of three cements (CEM I 42.5R, CEM II A-S 52.5N, CEM III A 42.5N). For each cement type, three variants of specimens were prepared which differed according to their water/cement ratio (0.50, 0.55 and 0.60). The main research of thermal parameters was carried out using a non-stationary method based on the analysis of changing heat flux readings. The thermal conductivity, volume-specific heat and thermal diffusivity values were analyzed. The tests performed allowed for determination of the density of specimens, water absorbability and thermal parameters in three water saturation states: dry, natural and wet. Additional microstructural tests were performed using mercury intrusion porosimetry. The obtained parameters were used to determine the relationship between the measured properties. An adverse effect of dampness on the thermal insulation of the studied materials was confirmed. In extreme cases, the increase in thermal conductivity due to material high moisture was 93%. The cement used affects the relationship between the total specific surface area and the W/C ratio. As expected, the total porosity of specimens was higher for mortars with higher W/C ratios. A strong correlation has been demonstrated between the total surface area and thermal conductivity. The opposite results were obtained when assessing the relationship between the total specific surface area and water absorbability. In case of specimens CEM II A-S 52.5N, the relation was the proportional, and in specimens CEM III A 42.5N, the relationship was inversely proportional to the W/C ratio.

Egg Albumin-Assisted Hydrothermal Synthesis of Co3O4 Quasi-Cubes as Superior Electrode Material for Supercapacitors with Excellent Performances

Novel Co3O4 quasi-cubes with layered structure were obtained via two-step synthetic procedures. The precursors were initially prepared via hydrothermal reaction in the presence of egg albumin, and then the precursors were directly annealed at 300 °C in air to be converted into pure Co3O4 powders. It was found that the size and morphology of final Co3O4 products were greatly influenced by the amount of egg albumin and hydrothermal durations, respectively. Such layered Co3O4 cubes possessed a mesoporous nature with a mean pore size of 5.58 nm and total specific surface area of 80.3 m2/g. A three-electrode system and 2 M of KOH aqueous electrolyte were employed to evaluate the electrochemical properties of these Co3O4 cubes. The results indicated that a specific capacitance of 754 F g−1 at 1 A g−1 was achieved. In addition, the Co3O4 cubes-modified electrode exhibited an excellent rate performance of 77% at 10 A g−1 and superior cycling durability with 86.7% capacitance retention during 4000 repeated charge-discharge process at 5 A g−1. Such high electrochemical performances suggest that these mesoporous Co3O4 quasi-cubes can serve as an important electrode material for the next-generation advanced supercapacitors in the future.

Mineralogical and physico–chemical properties of bentonites from the Jastrabá Formation (Kremnické vrchy Mts., Western Carpathians)

In the past years an increasing demand for bentonites resulted in the opening of new bentonite deposits in the Jastrabá Formation. The shortage of information, in particular analytical data, on the bentonites from the newly opened Jastrabá Fm. deposits was the motivation for the current study. Smectite is the predominant mineral in all bulk bentonites from the new deposits. Its amount varied between 43 and 90 wt. %. The bulk bentonites also contain variable amounts (10–57 wt. %) of mineral admixtures such as feldspars, mica, opal-CT, kaolinite, quartz and sometimes goethite. The smectite mineral comprising the studied bentonites was montmorillonite. The octahedral Al in the structure of montmorillonite was partially substituted by Mg, and to a lesser extent by Fe. The interlayer space of montmorillonite is occupied predominantly by divalent exchangeable cations (Ca2+ and Mg2+). The dehydroxylation temperature of smectites (>600 °C) determined on the DTG curves indicates the presence of the cis-vacant variety of montmorillonites. The mean crystallite thicknesses of smectites (TMEAN) calculated by BWA analyses ranges from 7.2 to 11.5 nm. The shape of the crystallite thickness distributions (CTDs) for smectites is lognormal in all cases. Cation exchange capacity (CEC) and total specific surface area (TSSA) increases with increasing amount of smectite. The CEC of 101 meq/100g and TSSA of 616 m2/g correspond to bulk bentonite from the Stará Kremnička III deposit containing 89 wt. % of smectite.

Methods of analysing morphology of kaolinites: relations between crystallographic and morphological properties

A study was made of the extent to which the lateral surfaces contribute to the surface area of five kaolinites of different crystallinities. Methods used included the low-temperature adsorption of N2and Ar as measured by a volumetric technique coupled with microcalorimetry, the interpretation of the adsorption isotherms of alkyldodecylammonium ions, particle-size distribution curves, and shadowed transmission electron microscopy. With the exception of surfactant adsorption and adsorption calorimetry using Ar, these methods gave different and debatable results. For instance, specific lateral surface area values expressed as a percentage of total specific surface area varied from 17·0 to 40·4% for the most crystalline sample and from 12·0 to 54·3% for the least crystalline. It is shown that the decrease in crystallinity of samples is accompanied by a reduction in crystallite size from 0·8 to 0·08 µm and a decrease in lateral surface area from 34·0 to 12·0%.