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The structural changes occurring in tialite due to the formation of magnesium-titanate–aluminum-titanate solid solutions were determined. For this purpose, a DFT simulation of the structural changes was performed. The simulation proposed a number of possible atomic substitutions occurring in the elementary cells of the tialite, along with calculations of the lattice parameter changes in this material. Next, the actual changes occurring in the structure of the tialite due to the formation of solid solutions, obtained in different ways, were investigated. After comparing the obtained results, it was possible to confirm the mechanism of the formation of tialite solid solutions, through which one magnesium atom and one titanium atom substituted two aluminum atoms simultaneously. The results of this experimental work were confirmed by theoretical calculations (the differences in the values of the lattice parameters, measured in the experiment and calculated in the simulation, were less than 0.5%), through which changes in the lattice parameters with Mg and Ti substitution were observed.

Aluminium titanate - tialite belongs to the compounds with pseudobrookite structure. The polycrystals made of tialite show valuable useful thermal properties: low thermal expansion, very low thermal conductivity and high resistance to thermal shock. These properties result from the cracks present in the microstructure, resulting from significant differences in the lattice coefficients of aluminium titanate. The basic disadvantage of tialite consist in a thermal decomposition occurring at the temperatures of about 750–1280 °C. This decomposition can be limited by structural and microstructural stabilization. The addition of cations, e.g. magnesium or iron, leads to the formation of stable solid solutions, while the addition of SiO2 or ZrO2 leads to the formation of secondary phases - diffusion barriers occurring at intergranular boundaries. Most often these additives are introduced simultaneously and at the reaction sintering stage. Stable solid solutions are usually produced by a classical solid phase reaction between the initial oxides: Al2O3, TiO2 and MgO. In this work, an innovative synthesis was applied to produce solid solutions, involving a heterogeneous isostructural nucleation with magnesium titanate. The polycrystals obtained in this way, at a much lower temperature, with a high content of solid solutions (95–96 %), high density, homogeneous microstructure with necessary microcracks were obtained. As a result, the obtained polycrystals exhibit the typical pseudobrookite structure behaviour as a function of temperature.

The study aimed at evaluation of the rheological properties of aqueous suspensions of SiC stabilized with either TMAH (tetramethyloammonium hydroxide) or NaOH in the amount of a given dispersant in the range of 0–1.0 wt% as calculated on the dry mass of SiC powder. The optimal amount of the dispersants was finally evaluated at 0.4–0.6 wt %, based on the results of rheological studies (flow curves and viscosity curves) and the sedimentation rate, which corresponded to the pH of the suspension within the range of 9.5–10.5. The amount of the dispersant here did not depend on the solid volume fraction in the suspension, but rather, according to the zeta potential measurement results, the pH range guaranteed the formation of a stable suspension. This effect allowed to propose a dispersant mechanism for stabilizing the suspension. The maximum amount of silicate anions formed, accordingly, in the pH range of 9.5–10.5 on the surface of SiC particles, which in turn could be able to adsorb Na+ or TMA+ cations and thus increase the thickness of the Stern layer, increasing electrostatic repulsion between the SiC particles and improving the stabilization of suspensions and their rheological properties. However, the increase in suspension pH deteriorated their stabilization – most likely due to the occurrence of polymerization of amorphous silica and the presence of additional cations in water increasing its ionic strength. These suggestions were confirmed by the results of XPS analysis of the chemical state of SiC particle surfaces.

The paper presents a simple approach to obtain boron carbide powder by direct synthesis from elements. For the first time expanded graphite (EG) powder, which is a reactive form of carbon with a unique structure and microstructure, was used as a carbon source for the synthesis of this carbide. As a boron source, fine-grained amorphous boron powder was used. The synthesis was carried out in excess of boron, i.e.; the B to C ratio was 10:1 in mass. The simplicity of the synthesis was based on the fact, that the substrates did not require homogenization because a layer of boron powder was placed over a layer of expanded graphite in a closed graphite crucible. The reaction chamber was heated at temperatures from 1550 to 1650 °C for 2 h in argon. As a result, a fine-grained boron carbide powder (crystallite size of 20–40 nm) which did not require further chemical and mechanical treatment (aggregate size about 1 μm) was prepared. The plausible mechanism of the boron carbide synthesis was the transport of carbon towards boron via carbon monoxide (vapour phase) and its subsequent reaction leading to carbide formation.

The article aims to verify the possibility of obtaining an organic–inorganic material acting as both a binder and a lustrous carbon carrier in bentonite-bonded molding sands. Due to the wide industrial application, organoclays can be considered as innovative materials supporting the foundry technology in meeting environmental requirements. In this study, the organic modification of montmorillonite in calcium bentonite (SN) was performed by poly(acrylic acid) (PAA) and its sodium salt (PAA/Na). Additionally, for the purpose of comparison, the sodium-activated bentonite/poly(acrylic acid) (SN-Na/PAA) composites were also prepared. The collective analysis of the research results used in the assessment of the mineral/polymer interaction mechanism indicates surface adsorption combined with the intercalation of PAA monolayer into the mineral interlayer spaces. Materials were characterized by the combination of Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) methods. Based on the XRD analysis, the influence of PAA/Na on the aluminosilicate layered structure was found to be destructive, which may adversely affect the binding properties of SN/PAA/Na composites considered as a potential group of new foundry binders. The SN/PAA and SN-Na/PPA composites (with appropriate polymer content) can act as a binding agent in the synthetic molding sand technology, despite coating the bentonite particles with polymer molecules. The risk of losing the mineral′s binding capacity is reduced by the good binding properties of pol(acrylic acid) itself. The article is the first stage (preceding the thermal analysis and the strength tests of molding sands with the prepared organobentonites) in determining the possibility of obtaining a new full-value foundry binder in molding sands with bentonite.

This paper presents novel results of research focused on reaction sintering of a mixture of expanded graphite and amorphous boron. It has been shown that as a result of combining the synthesis from the elements with sintering under pressure, dense boron carbide polycrystals (95% TD) can be obtained in which stable structures dominate, i.e., boron carbides of stoichiometry B13C2 and B4C. Sintering was carried out on boron excess systems, and reaction mixtures with the following mass ratios (B:C = 5:1; 10:1; and 15:1) were used. Boron excess systems were used due to the presence of additional carbon during sintering since the matrix, reactor lining, and heating elements were made of graphite. 1850 °C was considered to be the optimum reaction sintering temperature for all of the systems tested. This shows that a reduction in the sintering temperature of 200–300 °C was observed with respect to traditional sintering techniques. Micro-cracks are present in the sinters, the presence of which is most likely due to the difficulty in removing the gaseous products which accompany the boron carbide synthesis reaction. The elimination of these defects of sintering requires further research.

The aim of this study was to produce dense, single phase polycrystals. The research was carried out on the submicron tungsten carbide powder without additives, with either a carbon or tungsten additive and on the powder with both additives. The primary task of carbon was to reduce surface oxide impurities which passivate WC grains; tungsten in turn bounds free carbon in the WC. The authors manufactured fine-grained, dense (96–98% T.D.) and single-phase WC polycrystals, using the technique of pressureless sintering at the temperature not exceeding 2000 °C. A positive effect of carbon addition on tungsten carbide sinterability was observed, whereby a dense, fine-grained polycrystals can be obtained at 1900 °C. It was also observed that a significant excess of temperature of sintering process resulted in a strong abnormal grain growth of WC grains.

SiC-TiC composites, with 0, 5, 10 and 20 vol.% of TiC, were sintered by the hot-pressing technique at temperature of 2000?C under argon atmosphere. SiC sintering process was activated by liquid phase created by the reaction between Al2O3 and Y2O3, in which it is possible to dissolve passivating oxide layers (SiO2 and TiO2) and partially SiC and TiC carbides. Microstructure observation and density measurements confirmed that the composites were dense with uniformly distributed components. Differences in thermal expansion coefficients between SiC and TiC led to complex stress state occurrence. These stresses combined with the liquid-derived separate phase between grains boundaries increased fracture toughness of the composites, which ranged from 5.8 to 6.3MPa?m0.5. Opposite to the bending strength, fracture toughness increased with the TiC volume fraction. By means of simulation of residual thermal stresses in the composites, it was found that with the increasing volume fraction of TiC, tensile stress in TiC grains is reduced simultaneously with strong rise of compressive stresses in the matrix.

Previous studies concerning pure tungsten carbide polycrystalline materials revealed that nanolayers of graphite located between WC grains improve its thermal properties. What is more, pressure-induced orientation of graphene nano platelets (GNP) in hot pressed silicon nitride-graphene composites results in anisotropy of thermal conductivity. Aim of this study was to investigate if addition of GNP to WC will improve its thermal properties. For this purpose, tungsten carbide with 0.5–6 wt.% of GNP(12)-additive underwent hot pressing. The microstructure observations performed by SEM microscopy. The anisotropy was determined via ultrasonic measurements. The following mechanical properties were evaluated: Vickers hardness, bending strength, fracture toughness KIc. The influence of GNP(12) addition on oxidation resistance and thermal conductivity was examined. It was possible to manufacture hot-pressed WC-graphene composites with oriented GNP(12) particles, however, the addition of graphene decreased both thermal and mechanical properties of the material.

The paper presents results of research designed to obtain a dense silicon carbide materials shaped by slip casting of aqueous suspensions. Aluminum oxide and yttrium oxide were used as sintering additives in a weight ratio of 3:2 in an amount of 10% by mass relative to the dry weight. The slip was electrostatically stabilized by adjusting pH. Measurement of the zeta potential as a function of pH and viscosity tests as a function of pH and volume fraction of the solid phase allowed for making selection of the suspension parameters, such as the solid volume loading (30%) and pH of ~ 8.5. Results of these investigations confirmed that it is possible to produce pseudoplastic slips suitable for slip casting. The increase in the strength of green bodies, allowing for their green processing, was obtained by addition of a commercial acrylic binder. SiC casts were sintered at 2050°C, which led to materials with high density and fine, homogeneous microstructure. The fracture toughness test revealed a positive effect of the sintering additives on KIc of the material, increasing its value to approximately 5 MPa·m1/2.

This study presents the results of investigations concerning hot-pressing of submicron WC powders without sintering additives and with the addition of carbon or tungsten or both elements simultaneously. Dense polycrystals of diverse microstructures and phase compositions were obtained. Attempts were made to correlate a microstructure and phase composition of sinters with their thermal and mechanical properties. It was found that the presence of graphite nanolayers on grain boundaries in WC sinters with the addition of carbon favourably influences their thermal conductivity. All produced polycrystals are characterised by a high fracture toughness. The smallest scatter of KIc results is observed for compositions activated by a carbon addition. The presence of the graphite nanolayers as well as grain size in WC sinters with carbon additions reduce the polycrystal hardness. All WC polycrystals, regardless of introduced additives, are characterised by high bending strength and by high values of the Young and Kirchoff moduli. The tested polycrystals are not suitable for machining carbon steel of C45 grade.

Silicon carbide and silicon nitride are recognized as phases with very good mechanical properties. Many parts of machines and mechanical devices are made of these materials. Particulate composites basing on both mentioned phases have significant potential of properties improvement. The aim of presented work was to check the difference in wear behavior when materials surfaces were attacked by hard, loose particles in wet environment (pulp). Investigations were performed on silicon carbide, silicon nitride and two composites on their matrices. The basic performed test was the Miller Test according to ASTM Standard. The detail microstructural and mechanical characterization of investigated materials was done. Residual stress state caused by coefficients of thermal expansion mismatch was calculated using FEM approach. The second phases for composites were selected to introduce the compressive stress state into the matrix phase. Comparative studies of abrasive wear of “pure” phases and composites performed showed differences between dominating wear mechanisms. Tests results proved that the influence of the second phase presence in the materials was significant for the wear rate.

Metals belonging to groups 4-6 of periodic table of elements form with carbon compounds named metal-like carbides (WC, TiC1-x, NbC, TaC, CryCz). It was established that is possible to achieve dense sintered bodies of this carbides at temperatures near 2000oC using only carbon powder as an additive. Its role consists in reduction of oxide impurities. Presented paper summarized investigations on sintering of metal-like carbides with carbon. Dense WC, TiC1-x, NbC, TaC and CryCz bodies were characterized by KIc factor value. A special care was taken on microstructure and the way of fracture description in relation to the critical stress intensity factor (KIc). It was established that the way of fracture and the finally fracture toughness depend on type of microstructure and degree of nonstoichiometry.

It is known that SiC powders can be densified at relatively low temperatures (1850-2000 °C) with some oxide additions. In this work the densification behavior, microstructure and mechanical properties (bending strength, fracture toughness, hardness) of SiC ceramics pressureless sintered with different additions chosen from oxide groups: Al 2 O 3 + Y 2 O 3 , Al 2 O 3 + Y 2 O 3 + MgO, were investigated. It was found that oxide additives facilitate densification of sinters and significantly improve mechanical properties of SiC ceramics. The best activating oxide additions have been identified.

The results of investigations on the role of carbon in SiC sintering, presented in the first part of this paper, indicate that this additive prevents the mass transport mechanisms ineffective in densification. Thereby they suggest that porosity is eliminated due to boron. In order to verify such a hypothesis we measured the kinetics of SiC sintering at constant temperature of 2150 °C. The samples used in this study, contained carbon at a constant concentration of 3 wt.% and boron up to 4 wt.%. It was found that at the carbon concentration of 3 wt.% the optimum addition of boron was 0.2–0.5 wt.%. Although the results of kinetic measurements did not allow for a unanimous identification of the mass transport mechanism, they revealed an unexpectedly high rate of densification. Within 60 s the system reached 0.9 theoretical density. Microstructural observations combined with the results of kinetic measurements suggest that boron activates the sintering process by promoting the formation of a liquid phase, Si–B–C.

The commonly accepted hypothesis says that the role of sintering activators such as carbon and boron consists in modifying the relation between the energy of surface and that of grain boundaries in SiC. This means that dihedral angles in samples containing one of the activators, both of them or none should be different. To verify this hypothesis we measured dihedral angles in all the mentioned cases. The observed values of dihedral angles were always much bigger than the limiting one of 60°. Moreover, they did not differ significantly and, according to the statistical analysis could be treated as constant. As a consequence our results contradict the opinion saying that the activators modify the energy of surface and grain boundaries.

The role of carbon in activating the process of SiC sintering is not fully understood. In the present work we examined the weight and microstructure changes of samples sintered with different additions of carbon (up to 16 wt.%). The measurements were carried out in the temperature range 1000–2200 °C. In comparative studies we examined the variations of oxygen content with the sintering temperature. The obtained results indicate that carbon blocks the mass transport processes which are ineffective in densification and enables maintaining proper dispersion of SiC grains up to the temperatures where, due to boron, pore elimination begins. On the basis of microstructural observations of SiC sintered with different amounts of carbon it has been stated also that this additive prevents grain growth of SiC on sintering.

This work presents measurements concerning sintering description according to two the: Kuczynski and Frenkel models. Investigation covered selected metal–like carbides: TiC0,8, NbC and WC. Kinetic equations were also developed, according to Kuczynski model to describe sintering of each carbide and it was attempted to determine mechanisms of mass transport mechanism dominating at each sintering stage. Parameters describing sintering process of each of investigated carbides: α and β constants, the initial shrinkage rate α-1, the limit of shrinkage at infinite time β-1 and initial apparent viscosity of system were in turn determined using Frenkel model. Such data allowed to achieve full characterization of carbide sintering.

The activation of silicon carbide by boron and carbon is required to obtain dense monophase sintered body from SiC powder. The presence of carbon renders casting from aqueous suspension impossible. The SiC powders with boron and extra carbon were prepared by combustion method (SHS), where carbon was bound to SiC particles in a stable way. The experiments showed that this powder could be used for processing by casting of aqueous suspension. Finally nearly dense polycrystals were obtained by pressureless sintering.

The results of preliminary investigation on preparation of perovskite pigments by solid state reaction are presented. The effects of different raw materials used as component carriers on formation of colored pigments were examined. Pigment composition, optimum chromophore addition, type of mineralizer and the conditions of synthesis were determined experimentally as well as the resulting color, phase composition and morphology of powders. The wet method of preparation of starting mixtures was also analyzed.

The paper presents the results of investigation the novel and simple method of synthesis of silicon carbide. As raw material for synthesis was used shungite, natural mineral rich in carbon and silica. The synthesis of SiC is possible in relatively low temperature in range 1500–1600 °C. It is worth emphasising that compared to the most popular method of SiC synthesis (Acheson method where the temperature of synthesis is about 2500 °C) the proposed method is much more effective. The basic properties of products obtained from different form of shungite and in wide range of synthesis temperature were investigated. The process of silicon carbide formation was proposed and discussed. In the case of synthesis SiC from powder of raw materials the product is also in powder form and not requires any additional process (crushing, milling, etc.). Obtained products are pure and after grain classification may be used as abrasive and polishing powders.