Phase Formation Temperature Research Articles

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.

Enhancing strength and ductility of CuCrZr high-conductivity alloy via lamellar heterostructures on grain boundaries

Heterogeneous lamellar structure materials have attracted extensive attention due to their exceptional strength and ductility. In this study, Y element was introduced into CuCrZr alloys to adjust the liquid phase formation temperature of the CuZrY phase during the solution annealing process. By employing cold rolling deformation prior to annealing to elongate the grains, the liquid phase was promoted to wet the elongated grain boundaries during the annealing process, ultimately forming lamellar CuZrY heterostructures distributed along the grain boundaries. The heterogeneous lamellar structure, the grain boundary distribution characteristics, and the effect of Y on stacking fault energy enhanced the hetero-deformation induced working hardening, thereby improving both the strength and ductility of the CuCrZrY alloy. Besides, the investigated CuCrZrY alloy achieved an excellent combination of tensile strength, uniform elongation, electrical conductivity and thermal conductivity, with values of 527 MPa, 10.66%, 83% IACS and 335.5 W/(m·K), respectively. Therefore, the method of controlling liquid phase temperature through composition adjustment and liquid phase infiltration path through grain deformation offers new possibilities for the design of heterogeneous lamellar structure materials.

3D morphological evolution of the Fe-Rich phase and mechanical properties of the recyclable A356 alloy

Efficient utilisation of recycled aluminium promotes low-carbon and green manufacturing in the aluminium industry. However, the low tolerance of Al for Fe content limits its application. The morphological evolution of the Fe-rich phase and the mechanical properties of recycled A356 alloys with varying Fe contents were investigated using optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), synchrotron radiation X-ray computed tomography (SRXCT), and Thermo-Calc thermodynamic calculations. The results show that with increasing Fe content, the morphology of the Fe-rich phase transformed from fine-granular and short rod-like structures into coarse needle-like and Chinese-script. In three dimensions (3D), the larger Fe-rich phases displayed a multibranched structure composed of rod-like and plate-like phases rather than a single morphology. Notably, at an Fe content of 0.4 %, the Fe-rich phases presented Chinese-script and short rod-like shapes in sections but did not significantly change the 3D morphology or type of the Fe-rich phase. However, the Fe-rich phases in the 0.4 %Fe alloy exhibited higher thickness and sphericity, which improved the ductility of the alloy. Thermodynamic calculations indicate that the initial formation temperature of the Fe-rich phase in the 0.4 % Fe alloy overlaps with that of the Al-Si eutectic reaction, which is referred to as the critical Fe content. At the critical Fe content, the ternary eutectic reaction of Al-Si-(AlFeSi) suppressed the rapid growth of the Fe-rich phase and mitigated their negative impact on ductility.

Exploring the effect of exchange coupling in (SrFe9.8Al2La0.2O19)1-x/(Co0.7Zn0.3Fe2O4)x nanocomposites synthesised by sol–gel auto combustion method

Extensive research has been conducted over the last decade to develop permanent magnets utilizing less rare earth materials. Exchange-coupled nanocomposite magnets are a fascinating development in the field of permanent magnets. They involve the combination of hard and soft ferrites, resulting in a unique and evolving magnet. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol−gel approach. The combination of high coercivity of a hard phase SrFe9.8Al2La0.2O19 (SFALO) and high saturation magnetization of a soft phase, Co0.7Zn0.3Fe2O4 (CZFO), allowed us to develop exchange-coupled bi-magnetic nanocomposites by varying the mass percentage (x = 0, 0.1, 0.2, 0.3, 0.4, 1). Thermogravimetric analysis (TGA) up to 1200 °C was used to investigate the material’s thermal properties with the phase formation temperature. Detailed atomic/nano-scale structural characterizations of these nanocomposites were performed by X-ray diffraction and Transmission Electron Microscopy. The average particle size was calculated from the SEM analysis and it was observed that most of the composites with ratio x = 0.1, 0.3 & 0.4 was 145 nm and x = 0.2 was 165 nm. The Switching Field Distribution (SFD) curve revealed the exchange coupling between soft and hard magnetic particles. The findings indicate that the inclusion of a soft magnetic phase has a considerable impact on the exchange coupling between the hard and soft ferrite phases. As the spinel concentration increased, in the composite the saturation magnetization increased from 18 emu/g to 48 emu/g. From the stroner-wholfrathmodel, the decrease in the remanence ratio below 0.5 concludes the crystallites are randomly oriented. The nanocomposite with the ratio x = 0.1 was observed with the high magneto crystalline anisotropy of 2183.23 × 102 (J/m3) and a high energy product (BH)max of 5.5 kJ/m3. The aforementioned features of nanocomposites demonstrate their potential for use in permanent magnet applications.

Immobilization of heavy metals with chlorine and liquid phase formation during thermal treatment of MSWI fly ash

Due to effective detoxification, thermal treatment is a preferred treatment technology of municipal solid waste incineration (MSWI) fly ash. However, immobilization behavior of heavy metals during thermal treatment is unclear. In this work, a circulated fluidized bed fly ash with SiO2 addition and a grate furnace fly ash with high silica-aluminum coal ash addition were used to investigate combined effect of active chlorine content, liquid polymerization degree, temperature of initial liquid phase formation and liquid phase formation rate on the immobilization ratios of Zn, Pb and Cd by principle component analysis (PCA). The results show that the decrease in active chlorine content favors the immobilization of Zn, Pb and Cd because chlorination volatilization is reduced. Both the increase in liquid polymerization degree and the formation of initial liquid phase at low temperature promote the immobilization of Zn, Pb and Cd for physical encapsulation. However, a rapid formation of liquid phase is not favorable for the immobilization of Zn, Pb and Cd, because transfer of heavy metals between crystals and liquid phase is impeded by high viscosity of liquid phase during fusion. The results can provide a reference for how to achieve the immobilization of heavy metals by adjusting the chemical composition of MSWI fly ash during thermal treatment.

The room temperature signature of micro to nanocrystalline calcium copper titanate (CCTO) thin film by a modified sol-gel technique and tailoring its material property

This study aims to identify an alternative route for the low-temperature synthesis of calcium copper titanate (CCTO) thin films and to explore a new understanding of precursor composition strategy and its relationship to thin-film combustion synthesis using a modified sol-gel technique. Micro-sized to nano-sized CCTO thin films were effectively deposited onto various substrates using a rapid and modified sol-gel process at remarkably low temperatures (∼100 °C), with room temperature phase formation of CCTO observed via FTIR and Raman spectroscopy. Calcium nitrate, copper nitrate, and titanium (IV) butoxide served as precursor materials to create the sol for spin coating. The resulting CCTO thin films were polycrystalline, uniform, and compact. The surface morphology and optical properties of these films were analyzed using Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (FESEM-EDAX), X-Ray Diffraction (XRD), and UV–VIS spectrophotometry. XRD confirmed various phases of CCTO on different substrates, with significant intensity variations in the peaks at different annealing temperatures. The XRD patterns on three different substrates-glass, SnO2 coated glass, and SiO2 coated Si—revealed different CCTO phases such as CCTO (301), CCTO (220), CCTO (400), and CCTO (422). EDAX analysis confirmed the presence of Ca, Cu, Ti, and O. The band gap varied from 2.5 to 3.8 eV depending on the annealing temperature. Capacitive vs. frequency response, dielectric loss, and I-V characteristics of the films were measured using MIM (Metal-Insulator-Metal) or SIM (Semiconductor-Insulator-Metal) structures.

Experimental investigation and thermodynamic modelling of WC-Fe-Ni-Co-Cr cemented carbides

This work investigates the effect of Cr addition into the FeCoNi binder phase of the cemented carbides (WC-FeCoNi) using experimental and computational techniques. Liquid phase formation temperatures and C contents of WC-Fe-Ni-Co-Cr alloys were used as experimental results. Based on this, a thermodynamic modelling was conducted on the W-C-Fe-Ni-Co-Cr system using the CALPHAD (CALculation of PHAse Diagrams) approach. Taking into account the experimental and theoretical results, it was shown that the error in the solidus and liquidus temperatures were lower in the database generated in this work in comparison to the commercial thermodynamic databases for steels and cemented carbides. Using the database developed in the present work, the experimental data can be well reproduced.In addition, the maximum solubility of Cr to avoid the formation of Cr-rich carbides was also deduced from this study.

Li2O addition as a means of achieving low-temperature densification of SiC ceramic

In order to achieve low-temperature densification of SiC ceramic, β-SiC nanopowder was doped with Li2O together with Y2O3–Al2O3–MgO as sintering aids, and then spark plasma sintered at temperatures ranging from 1450 °C to 1600 °C for 30 min under 30 MPa pressure in argon. The densities, microstructures and mechanical properties of SiC ceramics were systematically investigated, in comparison to the counterparts sintered with Y2O3–Al2O3–MgO additives. Since Li2O has a low melting point, Li2O addition effectively decreased the formation temperature of liquid secondary phase, enabling SiC ceramics to obtain higher density and lower porosity after low-temperature sintering (T ≤ 1550 °C). Besides, Li2O addition was found to decrease the viscosity of liquid phase and enhance grain growth of SiC through dissolution-reprecipitation process. When sintered at 1550 °C, Li2O addition led to a remarkable increase of density from 3.03 g/cm3 to 3.21 g/cm3 for SiC ceramic. Meanwhile, the SiC ceramic with Li2O addition exhibited a high Vickers hardness of 22.75 ± 0.35 GPa and a good fracture toughness of 3.83 ± 0.27 MPa m1/2. The research results are expected to benefit the low-cost fabrication of SiC ceramics based on pressure-assisted sintering and alleviate the thermal damage of SiC fiber in hot-pressed SiCf/SiC composites.

Ca substitution effects on structure transformation and physical properties of (Eu,Ca)FeAs2 co-doped with La and Co

In this study, Ca substitution and carrier doping effect on phase formation temperature and physical/superconducting properties of (Eu0.9-xCaxLa0.1)(Fe0.97Co0.03)As2 ((Eu,Ca)112, x = 0–0.4) compounds were investigated. The best synthesis condition for obtaining pure phases vary (850–900 °C) depending on the Ca substitution amount. Ca substitution in the EuFeAs2 structure induced a structural transformation from orthorhombic I2mm to monoclinic P21/m symmetry. Single crystals of EuFeAs2 and (Eu0.9La0.1)FeAs2 were grown and their crystal structures were determined. Density functional theory calculations confirmed the transformation and stability of the La-doped Eu112 crystal structure with Ca substitution. Compared with the parent compound EuFeAs2, the effective substitution of Ca reduced the lattice constants. The magnetic and transport properties of (Eu0.9-xCaxLa0.1)(Fe0.97Co0.03)As2 compounds were studied using the temperature and field dependence of the magnetization and electrical resistivity measurements. Ca substitution suppressed the magnetic ordering of Eu and gradually reduced the Néel temperature TNEu. As determined by the magnetization and electrical resistivity data, the onset of critical temperature (Tc) values increased with Ca substitution increment from 26 K to 32.2 K and 31 K–34.8 K, respectively. Ca substitution slightly increased the upper critical field values, while the coherence length ξ values were slightly decreased. The Ca substitution and sintering temperature dependence of superconductivity, upper critical fields, lower critical fields, and Eu-related magnetic transitions were extracted. The new series of Eu-containing iron-based superconductors with high Tc provides an interesting playground in this field.

A novel method to enhance the superconducting properties of Bi2Sr2CaCu2O8+δ superconducting thin films by self-assembly NiO nanorods

The utilization of Bi-based superconductors in magnetic field environments is limited due to their anisotropic structure and lack of efficient magnetic flux pinning sites. Therefore, to enhance the performance of Bi-based superconductors in a magnetic field, this study presents the preparation of Bi2212 high-temperature superconducting thin films with varying NiO doping levels on SrTiO3 (STO) single crystal substrates with different concentrations of NiO seed layers via the self-assembly method. Additionally, phase purity, crystal structure, surface morphology, and transport properties were thoroughly analyzed. According to the results, the NiO seed layers prepared on the STO substrates presented epitaxial growth characteristics, with the NiO second phase in the Bi2212 matrix growing epitaxially along the seed layers. As NiO doping slightly broadens the phase formation temperature range of Bi2212 superconducting thin films, the self-assembly method can be utilized to prepare NiO nanorods with epitaxial growth in Bi2212 thin films. Notably, the self-assembled NiO-doped Bi2212 thin film demonstrated higher critical current carrying capacity, with its Jc reaching 6.28 × 104 A/cm2 at 10 K in self-field. This provides a technical reference for improving the performance of high-temperature superconducting thin films under a high magnetic field.

Manganese-substituted strontium ferrite catalyst on honeycomb structured cordierite support for oxidation of diesel particulate matter

Perovskite-based catalysts have been explored as low-cost substitutes for platinum (Pt)- based catalysts for diesel particulate matter (DPM) oxidation. In this work, manganese (Mn)-substituted strontium ferrite (SrFeMnO3-δ) (SFM) as a catalyst was coated on the honeycomb structure of cordierite support and tested for its catalytic performance for DPM oxidation using a real-world engine. The characteristic diffraction peaks due to the presence of the perovskite structure of SFM were observed for the cordierite-supported SFM. Mn was substituted in the lattice of un-substituted strontium ferrite and no other impurities were formed upon the Mn-substitution. Highly agglomerated SFM particles were formed solely due to the perovskite phase formation temperature (900 °C). The SFM catalyst enhanced catalytic Printex-V oxidation performance compared to its oxidation without the catalyst, where Printex V was used as the model DPM. The SFM catalyst showed high CO2 selectivity upon the oxidation of DPM. These results infer that the SFM catalyst possesses promise as an alternative to commercially available DOC catalysts based on PGM for DPM oxidation. SFM-coated cordierite support performed much better in terms of particle number, mass and surface area than commercial diesel oxidation catalyst (DOC) or without DOC at no engine load. The performance is substantially higher even at moderate engine loads of up to 40% and comparable at very high engine loads of 100%. Detailed investigations on a real engine exhaust and measurement of crucial parameters like particle number, mass and surface area suggest convincing and relatively rare evidence for its potential as a catalyst for diesel exhaust emission control catalyst.

The Success of Fabrication of Pure SmFe2 Phase Film with Outstanding Perpendicular Magnetic Anisotropy.

This study used DC magnetron sputtering technology to fabricate Sm-Fe films and systematically investigated the phase transition behavior of Sm-Fe films with different Fe ratios. It was found that at higher Fe content, the films consisted of Sm2Fe17 or SmFe7 phases; as Fe content decreased, the films were mainly composed of SmFe3 or SmFe2 phases; at higher Sm content, the films primarily consisted of Sm phase. Sm is prone to volatilization at high temperatures, so Ta was used as a capping layer to effectively suppress Sm volatilization, successfully synthesizing pure SmFe2 phase films at a nearly 1:2 ratio. The magnetic properties and magnetostrictive behavior of the SmFe2 films were investigated, revealing that pure-phase SmFe2 films exhibit good perpendicular magnetic anisotropy and magnetostriction properties. The larger stress along the perpendicular-to-film direction, resulting from the absence of substrate-induced constraints, contributes to the excellent perpendicular magnetic anisotropy of the films. This study successfully synthesized pure-phase SmFe2 films and discovered a new method for fabricating perpendicularly anisotropic films. The research findings are of great significance for the efficient synthesis of desired films with high phase formation temperatures containing volatile elements.

Solidification behavior of the FeOt-SiO2-CaO-Al2O3-(ZnO) slag system

Slag solidification behavior significantly influences the tapping of the Zn fuming process and slag valorization. In this work, the effect of ZnO and CaO concentration on slag solidification was investigated under a pO2 of approximately 10−10 atm using confocal laser scanning microscopy (CLSM) at various cooling rates. It was concluded that in the low CaO slag, the ZnO increased the onset formation temperature of the fayalite phase. An increase in CaO concentration facilitated wustite precipitation and prevented spinel formation in the slag at cooling rates exceeding 1 °C/s, while it enhanced melilite generation and inhibited fayalite precipitation in the slag at cooling rates below 1 °C/s. Furthermore, the slag mineralogy was studied as a function of equilibration temperature and CaO concentration of the slag through water quenching experiments under the Ar atmosphere. When slags with a CaO concentration of 3–20 wt% were quenched from 1050 to 1200 °C, the amorphous and spinel phases were observed in all quenched slags, whereas the wustite phase was only identified in slags with a CaO concentration above 10 wt%. Additionally, the fayalite phase was detected in slags containing 3–5 wt% CaO, quenched at temperatures of 1150–1050 °C. Notably, as the quenching temperature decreases and the CaO concentration increases, the observed phases in the quenched slag become more complex, and the solid particles grow coarser. The FeOt-SiO2-(4.7–5.7 wt%)ZnO-(8.3–10.1 wt%)Al2O3–CaO-1.3 wt%MgO-1.1 wt%Cr2O3 (FeO/SiO2 = 1.44) slags with a CaO concentration of below 20 wt% is suggested to be quenched from 1150 °C or 1200 °C to prevent the precipitation of a SiO2-containing phase and coarse wustite.

Controlling the Fe-intermetallic phases and mechanical properties of secondary Al-9Si-1Fe alloy with Cr and Mn additions

In secondary Al-Si based alloys, microalloying with Mn and Cr can modify harmful platelet-type AlxFeySiz intermetallic phases to less detrimental α-Alx(Fe, Mn, Cr)ySiz phase (script or polygonal morphologies). However, the α-Alx(Fe, Mn, Cr)ySiz phase morphology, phase composition and the addition of Fe-correcting elements can be influenced by solidification conditions. Therefore, this research is aimed to highlight the morphological evolution and mechanisms of α-Alx(Fe, Mn, Cr)ySiz phase in a Cr added Al-9 %Si-1 %Fe-0.2 %Cr (all weight percentage thereafter, unless otherwise stated) alloy with varying Mn concentrations (0.25 %, 0.5 %, and 0.8 %). Microstructure evolution of Fe intermetallic phases is investigated under different casting conditions using a wedge-shaped die, Cu-chill block and melt quenching experiments. Thermodynamic simulations have been performed using CALculation of PHAse Diagrams (CALPHAD) method and compared with the experimental results for phase composition and formation temperatures of α-Alx(Fe, Mn, Cr)ySiz phase. The results indicated that for 0.25Mn-0.2Cr addition to Al-9Si-1Fe alloy, compact morphology containing polygonal phases are formed in Cu-chill casting, while the wedge castings predominantly show a mixed structure with platelets and script type morphologies. Tensile tests revealed a higher elongation value of 6.6 % for mixed structure with platelet and script phases, which is decreased to 4.2 % for polygonal phases in Al-9Si-1Fe-0.2Cr-0.25Mn alloy. This study highlights the importance of solidification conditions on morphologies of Fe-intermetallic phases and the mechanical properties by comparing selected literature relevant to high pressure die-casting process.

Contrasting effects of waste glass and scheelite tailings additions upon the properties of tailings-based foam ceramics and its mechanisms

Although solid waste is a good raw material for preparing foam ceramics, the mechanisms of the discrepancies in different solid wastes affecting the properties of foam ceramics remain unelucidated. In this study, the properties of tin tailings-based foam ceramics with different proportions of waste glass (WG) or scheelite tailings (ST) were measured. Significant discrepancies in the influence effects were observed, with higher closed porosity for added WG and higher apparent porosity for added ST. To interpret this phenomenon, the effects of the main fluxing agents of the ST and WG were investigated, and the results indicated that their influence effects were controlled by the type and content of the fluxing agent. Furthermore, the structure and crystalline phase of foam ceramics demonstrated that their compressive strength was jointly driven by their microstructure and crystal phases, but other properties depended only on the microstructure. The pore size and type were significantly affected by the change in liquid phase characteristics and aluminosilicate, with the addition of WG dramatically decreasing the number of pore windows and the addition of ST increasing the content of anorthite. Further sintering process analysis results revealed that the chemical reactions in materials change with chemical compositions, which resulted in significant differences in the crystalline compositions of the foam ceramics for WG and ST additions, and the presence of WG obviously reduced the formation temperature of the liquid phase. Overall, our research provides a theoretical basis for better utilizing different solid wastes to prepare foam ceramics.

Phase Formation during the Synthesis of the MAB Phase from Mo-Al-B Mixtures in the Thermal Explosion Mode.

This work focused on the production of the MoAlB MAB phase through self-propagating, high-temperature synthesis in the thermal explosion mode. The influence of the method of a Mo-Al-B-powder reaction mixture preparation on the combustion temperature, mechanism, and stages of the MAB phase formation in the combustion process was investigated. The combustion temperatures of the mixtures obtained in the rotary ball mill and high-speed planetary ball mill were 1234 and 992 °C, respectively. The formation of intermediate compounds Mo3Al8 and α-MoB in the combustion front, along with MoAlB, was established using the time-resolved X-ray diffraction method. In the case of the mixture prepared in a ball mill, the primary interaction in the combustion front occurred through the Al melt, and in the case of using a planetary mill, solid-phase reactions played an important role. The mechanical activation of the mixture in a planetary mill also accelerated the processes of phase formation. The method of a reaction mixture preparation has virtually no effect on the MoAlB MAB phase content in combustion products (92-94%), but it does affect their structure. The synthesis products have a lamellar structure composed of MAB grains with a thickness of ~0.4 μm and a length of ~2-10 μm.

Correlation study on firing temperature and color of plain pottery excavated from the Tang Dynasty tomb of Liu Jing in Shaanxi, China

Plain pottery excavated from the Tang Dynasty tomb of Liu Jing was taken as the research object. The color, chemical composition, microstructure, and phase were tested to investigate the influencing factors of color for plain pottery fragments. The results indicated that the contents of Fe2O3 and TiO2 in all fragments varied little, and the influence of humic acids in clay as well as the firing atmosphere on the appearance color of plain pottery was excluded. Therefore, the main factor affecting color saturation (C*) was identified as the firing temperature (T). More importantly, the correlation between C* and firing temperature was established by replicas fired at different temperatures. Before the appearance of the glass phase, iron-containing minerals played a major role in coloring, and after that, iron ions in the glass phase and iron crystallization rose the important function of coloring. Consequently, with the increase of firing temperature, C* value increased firstly and then decreased. The inflection point of the fitted C* − T curve corresponded to the glass phase formation temperature. By comparing the estimated firing temperatures obtained by the fitted C* − T correlation curve with the known firing temperature of replicas, it was demonstrated that the color measurement is an ideal method for deducing the firing temperatures of ancient plain pottery.

Formation of a ceramic structure of promoted iron oxide catalyst

The paper concerns with the mechanism of the promoters influence on the ceramic structure of the iron oxide catalyst for the dehydrogenation of olefin and alkylaromatic hydrocarbons. The research shows the dynamics of changes in the porous structure of alloyed and unalloyed catalysts as a result of heat treatment in air at several temperatures significantly exceeding the operating temperature. Moreover, the paper presents data on the mechanical strength of alloyed and unalloyed model catalysts. Indeed, the particles are sintered to each other at the contact points of the globules forming a mechanically strong and thermally stable framework. However, the particles are sintered to each other at the contact points of the globules forming. Supposedly, potassium performs the function of a kind of flux. It lowers the temperature of the melting phase formation, which ensures a strong sintering of the ceramic material (catalyst) particles to each other. Hereby, there is a formation of a stable framework without a noticeable reduction of the catalyst working surface. The addition of zirconium oxide as an alloying agent provides an increase in the depth and degree of annealing of imperfections during the restructuring of the catalyst structure. Additionally, it provides the redistribution of the released energy. This assumption is confirmed by increasing of the alloyed catalyst granules mechanical strength. The results of research can be used for development and modification of iron-oxide catalysts for dehydrogenation of olefinic and alkylaromatic hydrocarbons.

Synthesis of spherical Si3N4 powders by liquid‐phase modified carbothermal reduction and nitridation

Abstractβ‐Si3N4 powder with well‐dispersed spherical particles was synthesized by liquid‐phase modified carbothermal reduction and nitridation. The influence of the type and content of additives on the particle morphology was investigated. The liquid phase formed at the reaction temperature modifies the morphology of the Si3N4 powder. The Si3N4 products precipitated along the liquid‐solid interface, thus forming a spherical morphology and promoting the transformation from α‐Si3N4 to β‐Si3N4. The type of additives has a strong influence on the formation temperature and viscosity of the liquid phase and hence affects the product morphology. In the samples with CaF2 and CaO additives, sufficient liquid phase occurred and spherical particles were obtained. In the sample with Y2O3, however, the liquid phase was insufficient due to the higher formation temperature, thus resulting in an irregular particle morphology.

The foaming mechanism and properties of SiO2–Al2O3–CaO-based foamed ceramics with varied foaming agents

To select suitable high-temperature foaming agents, SiO2–Al2O3–CaO-based foam ceramics (SACFC) were successfully prepared with different foaming agents based on phosphorus tailings and coal gangue. The effects of high-temperature foaming agents (CaCO3, carbon black, MnO2 and Fe2O3) on the microstructure and compressive strength of the SACFC were investigated, and the corresponding foaming mechanism was revealed. The results indicated that CaCO3 could increase the porosity of SACFC due to high-temperature decomposition. However, the precipitation of needle-like anorthite reduced the mechanical properties. Because the high-temperature oxidation temperature of carbon black was lower than the molten phase formation temperature, bubbles floated up and gathered on the surface of SACFC, leading to a decrease in strength. The continuous release of O2 from MnO2 during the sintering process promoted the growth and aggregation of large pores, which was detrimental to the strength. The CO2 generated by the redox of Fe2O3 by CO/C was the main factor for the foaming of SACFC. During the high-temperature foaming, the synergy effect of Fe2+ and Fe3+ promoted the formation of a uniformly distributed pore structure. When 2 wt.% Fe2O3 was added, SACFC obtained the optimal comprehensive performance with bulk density and compressive strength of 0.78 g/cm3 and 3.50 MPa.