The impact of Na2O on the synthesis of α-C2SH with different mineral composition and the stability of intermediate and final products

In this work the effect of Na₂O on the synthesis of α-C₂S hydrate (2CaO·SiO₂·H₂O), named as α-C₂SH, with different mineral composition and the stability of intermediate and final products were investigated. It is worth noting that new results was discovered by evaluating the mineral composition of hydrothermally synthesized α-C₂SH samples (200?°C; 2–72?h). It was found that Na₂O additive significantly influenced the formation and stability of intermediate and final products: within 12?h of hydrothermal treatment together with α-C₂SH a new calcium silicate hydrate phase, killalaite, was obtained in the products. Besides, the mineral composition of formed compounds slightly varied by prolonging the duration of synthesis to 24?h. For the first time it was proved that Na⁺ ions are not incorporated into the crystal structure of the main synthesis product, α-C₂SH. On the contrary, the mentioned ions are intercalated into the crystal structure of other calcium silicate hydrates. Moreover, the investigated alkaline additive reduced the recrystallization temperature of the synthesis products to wollastonite by 50?°C and significantly decreased the values of both specific area and total pore volume of α-C₂SH till 8.496?m²/g and 0.05084?cm³/g, respectively. The synthetic products were characterized by XRD, DSC, SEM/EDX and N₂ adsorption analysis.     

Phase composition of the products of nitriding ferrosilicon with zircon concentrate additives

The process of nitride formation during combustion of iron silicon with the addition of zircon concentrate in nitrogen gas is investigated. It is determined that in the presence of zircon (5–70%) ferrosilicon burns in a surface regime, and the products of combustion are multiphase. For the optimal parameters of synthesis (nitrogen pressure 4–7 MPa and sample diameter 35–40 mm) the products of combustion are a composition consisting of a ceramic constituent (Si₃N₄-ZrO₂-Si₂N₂O) and iron (α-Fe). The method of acidic enrichment is used to obtain a composite ceramic powder with iron mass content 0.5%     

Surface properties of carbons obtained from hexachlorobenzene and hexachloroethane by combustion synthesis

The paper describes the combustion synthesis of carbon materials from hexachloroethane (C₂Cl₆), hexachlorobenzene (C₆Cl₆), and a mixture of these compounds. The chemical composition (elemental analysis), structural composition (XRD, Raman spectroscopy), microstructure (SEM), surface physicochemical properties (low-temperature nitrogen adsorption, XPS, FTIR) and electrochemical behavior (cyclic voltammetry) of the solid reaction products were investigated. Their unique structural and surface properties depend on the chemical composition of the starting compounds. The properties of the carbon samples tested are much like those of carbon black, but the material from hexachloroethane exhibits the most distinctly amorphous features. In contrast, the adsorptive properties (porous structure) of the sample obtained from hexachlorobenzene tend to resemble those of activated carbon.     

Structure and properties of a composite material obtained by thermal explosion in a mixture of Ni + Al + Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

The synthesis of a composite material by thermal explosion in a reaction mixture of Ni + Al + Cr₂O₃ was studied. The thermodynamic parameters of combustion of the systems studied were estimated to predict the composition of the inorganic products (condensed or gaseous) of self-propagating high-temperature synthesis and calculate the adiabatic combustion temperature. It is shown that the synthesis process involves competing reactions in the sample volume which are responsible for the formation of a multiphase product. The influence of the content of Cr₂O₃ in the reaction system on the strength characteristics of the product synthesis was studied. The microstructure of the synthesized samples was examined, and their micro-hardness, toughness and residual porosity were determined. The possibility of obtaining a homogeneous material based on NiAl intermetallic compound containing dissolved chromium and chromium oxide nanoparticles is shown.     

Characteristics of phase formation during combustion of the MgO-Al2O3-Mg(NO3)2·6H2O-Al-B system

The research revealed the carbon micro traces in the synthesis products of magnesium aluminate spinel produced by the method of self-propagating high-temperature synthesis (SHS) in the MgO-Al₂O₃-Mg(NO₃)₂·6H₂O-Al system with boron additives. The phase composition, structure, and morphological features of the surface of the samples were examined. The gases evolving during combustion were analyzed. IR spectroscopic analysis showed that carbon has a diamond-like lattice similar to the lattice of detonation nanodiamonds. It was shown that low-energy nuclear reactions (boron-proton reaction) proceed in the combustion wave during high-speed SHS processes under certain conditions. Based on the experimental data, the most probable mechanisms of carbon formation in the synthesized products were formulated and proposed.     

Developing Ways of Obtaining Quality Hydrolyzates Based on Integrating Catalytic Peroxide Delignification and the Acid Hydrolysis of Birch Wood

Traditional processes of acid-catalyzed hydrolysis of wood are ineffective due to the low quality of formed glucose solutions contaminated with impurities that inhibit fermentation of glucose to ethanol. This problem grows during the hydrolysis of birch wood containing large amounts of hemicellulose. This work proposes producing quality glucose solutions using sulfuric acid (H₂SO₄, 80%) catalyzed hydrolysis at 25°C the cellulosic products formed during the catalytic peroxide delignification of birch wood. It is established that the composition of cellulosic products strongly affects the contents of glucose, xylose, and impurities inhibiting the enzymatic synthesis of bioethanol: furfural, 5-hydroxymethyl furfural, and levulinic acid. High yields (80.4–83.5 wt %) of glucose are achieved using cellulosic products produced by integrating the processes of sulfuric acid hydrolysis of hemicelluloses from birch wood and peroxide delignification of prehydrolyzed wood in the presence of catalysts: 2% H₂SO₄ and 1% TiO₂. Concentration of inhibitors of enzymatic processes in these hydrolyzates is below the allowable limits. Hydrolyzates with maximum glucose content (86.4–88.5 wt %) and minimum concentration of inhibiting impurities produced by acid hydrolysis of cellulosic products treated with an 18% solution of NaOH. Gas chromatography, HPLC, and chromato-mass spectrometry are used to analyze the composition of hydrolyzates. Cellulosic products are examined by SEM, XRD, and chemical analysis.     

The use of plastic waste as carbon raw materials to obtain TiC-based powders

Plastic pollution is one of the most pressing environmental problems, and a huge amount of effort and money is directed towards solving it. The existing processing methods are ineffective. The main component of all plastic materials (C_xH_y) is carbon. High-purity fine titanium carbide was obtained using plastic waste (polyethylene terephthalate – C₁₀H₈O₄) as a carbon raw material. Combustion processes, phase composition and structure of the obtained materials were studied. A probable mechanism for the formation of titanium carbide during the combustion of the (Ti + C₁₀H₈O₄) mixture was proposed. During the synthesis, polyethylene terephthalate decomposes into carbon, hydrogen and oxygen. Carbon and oxygen react with titanium and form titanium oxycarbide. Titanium oxycarbide is saturated with carbon to form titanium carbide and carbon dioxide. The remaining hydrogen and carbon dioxide are released from the synthesis products, which leads to self-purification of the synthesis products. The obtained results will create the basis for the development of a fundamentally new, cost-effective technology for recycling plastic waste into carbides and carbide-containing materials.     

Effects of reactants proportions on features of in-situ magnesiothermic self-propagating high temperature synthesized boron carbide powder

The effects of reactant proportions were investigated on features (phase composition, micromorphology and crystal development) of B₄C (boron carbide) powder synthesized by in-situ magnesiothermic SHS (self-propagating high temperature synthesis) method, which was based on the perspective of thermodynamic design. The results showed that the reactant proportions were the fundamental reasons affecting the phase composition of the products during the reaction process. Mg addition could decrease the Mg₃B₂O₆/MgO mass ratio of the SHS products. Moreover, C addition would increase the C/B mass ratio of the leached products. When the C molar ratio was 0.2, free boron appeared in the leached products, and the composition of boron carbide was B₁₃C₂. When the C molar ratio ≥0.6, the composition of boron carbide changed into B₄C, while free carbon began to appear. The lattice parameters a and c of boron carbide crystal dropped with the increase of the C/B mass ratio from 0.1 to 0.3. Meanwhile, carbon atoms gradually entered the boron carbide unit cell. When the C/B mass ratio exceeds 0.3, the lattice parameters tended to be constants of a = 5.608 Å, c = 12.039 Å, while free carbon began to appear in the leached products.     

Solution combustion synthesis of nanostructured iron oxides with controllable morphology,composition and electrochemical performance

Nanostructured iron oxides have emerged as promising materials for electrochemical energy storage and conversion devices due to their high theoretical capacity, eco-friendliness and earth abundance. Particularly, the morphology- and composition-controllable synthesis of nanostructured iron oxides is extremely important to optimize their electrochemical performance. However, the development of facile and effective synthetic method is still a great challenge. In this paper, we demonstrated a one-pot solution combustion synthesis (SCS) approach for the time- and energy-effective preparation of nanostructured iron oxides with controllable morphology and composition just by tuning the molar ratio (φ) of fuel (glycine) to oxidizer (ferric nitrate). Innovatively, the effects of φ value on the control of combustion reaction mechanism, morphology and composition of SCS products, and the electrochemical properties in relation to the morphology and composition have been systematically investigated. The results revealed that with the increase of φ value, the reaction mechanism varied from pyrolysis to combustion and the combustion phenomenon changed from volumetric mode to self-propagating mode. Correspondingly, the morphology of products evolved from uniform nanoneedles to porous nanosheets, and finally into aggregated nanoparticles. Meanwhile, the phase composition of these products changed from amorphous α-Fe₂O₃ to crystalline α-Fe₂O₃, and eventually into α-Fe₂O₃/Fe₃O₄ composites. When evaluated as lithium ion battery anode, the as-prepared α-Fe₂O₃/Fe₃O₄ porous nanosheets (φ = 1.0 product) exhibited the best electrochemical properties (a high reversible capacity of ~ 1200 mA h g^?1 and an excellent rate capability) among all the SCS products, which may be attributed to its mesoporous structure (supply favorable accessibility for electrons), nanosheet morphology (shorten the transport length of Li⁺) and appropriate proportion of Fe₃O₄ phase (enhance the electronic conductivity). Consequently, the facile SCS method demonstrated here might provide a new methodology for the morphology and composition-controllable synthesis of nanomaterials, for which a number of prospective applications in electrochemical fields can be envisioned.     

Direct synthesis of iso-paraffins from syngas with slurry phase reaction

The direct synthesis of gasoline-range iso-paraffins from synthesis gas (CO + H₂, syngas) via modified Fischer–Tropsch (FT) reaction was investigated in the slurry phase reaction system, the contact state of hybrid catalyst components and the composition of hybrid catalyst were optimized in this reaction system. The results show that the FT reaction and the in situ hydroconversion of its products occurred over hybrid catalysts containing Co/SiO₂, very high selectivity of gasoline-range iso-paraffins could be achieved.     

A thermodynamic study of the Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>-CO system

The equilibrium composition of the Fe₂O₃-H₂-CO system depending on temperature and pressure was calculated by the methods of chemical thermodynamics at different molar ratios between the system components. It was found that the equilibrium composition of the mixtures formed in this system mainly depends on ratios between the system components. The effect of the partial pressures of H2 and CO on the equilibrium composition of products in the Fischer-Tropsch synthesis was determined.     

Synthesis of aluminium titanate by means of isostructural heterogeneous nucleation

The synthesis of tialite was carried out by means of the solid state reaction technique using heterogeneous nucleation. The influence of the temperature of synthesis and simultaneous sintering (1250–1350 °C) on the yield of reaction and densification of the systems was investigated. Reference samples, consisting of stoichiometric mixture of titanium and aluminium oxides as well as the samples containing such additives as MgO, SiO₂ and MgTi₂O₅ were prepared. Applying the DSC analysis the synthesis temperatures of systems differing in the substrate composition were determined. The phase composition of synthesis products was determined by means of XRD analysis combined with Rietveld's method. The density of the obtained materials was determined by the Archimedes method. SEM observations enabled microstructures and homogeneity of sinters to be compared.On the basis of the conducted research it was found that using oxide additives containing magnesium cations allows the synthesis efficiency exceeding 95% as early as at the temperature of characterized by a homogeneous microstructure with a lower number and a smaller size of microcracks.     

Influence of forced cycling on the fischer-tropsch synthesis. Part I. Response to feed concentration step-changes

The response of the Fisher-Tropsch synthesis to composition step-change was studied as part of a larger study on the influence of forced feed composition cycling on the product distribution from this synthesis reaction. Using a promoted iron catalyst, studies were conducted at 384 kPa total pressure in a fixed-bed differential reactor held at 246°C by means of an oil bath. It was determined that the reaction rate was not influenced by mass or heat transfer effects. The maxima in the curves of steady state rate versus feed composition for various products occurred considerably above the stoichiometric ratio for each product olefin. This fact suggested that the rate was probably controlled by hydrogen adsorption in the initiation sequence. Support for this interpretation was also found from the response of the rates of production of light hydrocarbons (C₂ to C₅) to the step-changes in feed concentration.     

Thermodynamic analysis of the gasification of coal from the Daurskoe deposit

The equilibrium composition of the products of the fluidized-bed pressure gasification of brown coal from the Daurskoe deposit in Transbaikalia krai for the production of process gas (in particular, synthesis gas) was calculated with the use of a method of chemical thermodynamics. The gasification was performed at P = 0.1 MPa and the blast coefficient α₁ = 0.3–0.35 in the presence of 36 wt % of water vapor in a temperature range of 100–1500°C. It was found that, at a Cl₀ pressure of 0.1 MPa, a temperature of 850°C, and the air-steam blast composition of α₁ = 0.3 and α₀ + 36 wt % H₂O, the gasification products of the organic matter of coal (OMC) mainly consisted of CO and H₂.     

Synthesis of Alkali Aluminosilicates — Materials for Alkali Contaminated Environments at High Temperatures

Alkali corrosion has become a problem in industrial furnaces especially because of the increasing use of secondary fuels. In the corroded lining material alkali aluminosilicates such as kalsilite, leucite or nepheline could be identified. According to ternary phase diagrams these substances have very high melting points which would make them suitable for high temperature applications in alkali corrosive environments. This study presents systematic synthesis experiments to produce alkali aluminosilicates by thermal (800°C, 1000°C, 1200°C) and hydrothermal (200°C) treatment starting from the nominal compositions of KAlSi₂O₆, KAlSiO₄, and NaAlSiO₄., KOH NaOH, quartz powder, and Al(OH)₃ were used as raw materials. The phase composition was analyzed by using X‐ray diffraction (XRD). The alkali corrosion was tested using alkali salts as corrosive substances. The synthesis experiments resulted in multiphase reaction products. The hydrothermal method yielded only for the initial composition according to the stoichiometry of KAlSiO₄ crystalline phases of the same composition. The thermal method produced for all sets of synthesizing parameters mixtures of stoichiometric and nonstoichiometric alkali aluminosilicates. In the corrosion test, material of the nominal composition of KAlSiO₄ showed the best results. The material was corrosion resistant independently from the initially applied synthesizing parameters.     

On-line GC and GC–MS analyses of the Fischer–Tropsch products synthesized using ferrihydrite catalyst

Fischer–Tropsch (FT) synthesis reaction was performed using ferrihydrite catalyst. During 100 h of FT synthesis reaction, composition changes of the reaction product were studied according to the reaction time using an on-line GC, and the final FT products collected in traps were analyzed by GC–MS. Also, an effect of gas feed ratio of H₂/CO on the selectivity of the synthetic products was studied. As a H₂/CO feed ratio increased, not only CO conversion and activity of catalyst improved two times, but also CO₂ conversion was reduced by approximately 40% thereby improving the efficiency of catalyst significantly.     

Peculiarities of the composition of solid phases formed in aqueous calcium–silicate systems with a medium of variable acidity

The effect of a medium’s acidity on the composition of the solid phase formed in aqueous calcium-silicate systems is investigated. Solutions of Са(NO₃)₂ and Na₂SiO₃ are used for the synthesis; the pH values were varied in the range 7.00–12.00. Freshly precipitated solid phases and products of their annealing at 1000°C were studied by the methods of Fourier IR spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM).     

Syngas Stoichiometric Adjustment for Methanol Production and Co-Capture of Carbon Dioxide by Pressure Swing Adsorption

Methanol is an important raw material in industry and is commonly produced from syngas. The stoichiometric ratio (H₂–CO₂)/(CO + CO₂) of the methanol synthesis reactor feed stream must be adjusted to approximately 2.1. In this study, the replacement of the solvent unit within a coal to methanol process by a pressure swing adsorption (PSA) unit is proposed. The PSA produces a hydrogen enriched stream, to adjust the stoichiometric ratio of the methanol feed stream, and simultaneously captures the carbon dioxide for future sequestration. The feed flow rate is sub divided into eight 4-bed PSA units, operated with a defined phase lag between them in order to flatten the products (composition and flow rate) oscillations. The results show that the stoichiometric adjustment is possible and that oscillations on the products flow rate and composition are reduced to less than 3%. A carbon dioxide stream of 95.15% is obtained with a recovery of 94.2% and a productivity of 82.7 mol CO₂/kg/day. The power consumption of the global process is 119.7 MW, which includes the requirements for the rinse stream (64.4 MW) and the compression of the CO₂ product to 110 bar for sequestration (55.3 MW).     

Thermal destruction of gel compositions based on ethyl silicate and boric acid

The physicochemical processes taking place in heat treatment of gel compositions with an additive of H₃BO₃ are considered. The phase composition of the heat treatment products is studied. The synthesis of oxygen-free SiC and B₄C compounds in heat treatment of sol-gel compositions in a reducing medium is identified. Translated from Steklo i Keramika, No. 1, pp. 23 – 26, January, 1999.     

Solution combustion synthesis and sintering behavior of CaAl2O4

The influence of the quantity of urea on the synthesis of calcium aluminate by solution combustion method was studied. It was shown that the amount of urea has a big influence on morphological characteristic and phase composition of the combustion products.The sintering behavior of the combustion products, before and after milling, was studied by rate controlled sintering method, based on which a thermal schedule was designed improving the sintering of CaAl₂O₄.