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In order to improve the thermal shock resistance of MgO-based ceramics, aluminum titanate (Al2TiO5)-toughened MgO-based ceramics were successfully prepared by solid state sintering at 1450 °C and 1550 °C for 3 h starting from MgO and as-synthesized Al2TiO5 powders. The effects of various contents of Al2TiO5 second phase on the sintering behavior and thermal shock resistance of MgO-based ceramics were investigated. The sintering behavior of sintered samples was evaluated by comparing the relative density, apparent porosity, bending strength, phase composition as well as microstructure. The thermal shock resistance of sintered samples was characterized by using the residual bending strength after three thermal cycles and thermal expansion coefficient. The obtained samples with 10 wt% Al2TiO5, which were sintered at 1550 °C for 3 h, showed the highest relative density, lowest apparent porosity as well as optimum bending strength. In addition, the samples added 15 wt% Al2TiO5 at 1550 °C with a dwell time of 3 h were the highest residual bending strength and lowest thermal expansion coefficient. It revealed that the enhancement in thermal shock resistance was ascribed to the reduction of thermal expansion coefficient.

Precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI) were used to fabricate SiC/SiC composites on a four-step 3D SiC fibre preform deposited with a pyrolytic carbon interface. The effects of fabrication processes on the microstructure and mechanical properties of the SiC/SiC composites were studied. Results showed the presence of irregular cracks in the matrix of the SiC/SiC composites prepared through PIP, and the crystal structure was amorphous. The room temperature flexural strength and modulus were 873.62 MPa and 98.16 GPa, respectively. The matrix of the SiC/SiC composites prepared through CVI was tightly bonded without cracks, the crystal structure had high crystallinity, and the room temperature bending strength and modulus were 790.79 MPa and 150.32 GPa, respectively. After heat treatment at 1300 °C for 50 h, the flexural strength and modulus retention rate of the SiC/SiC composites prepared through PIP were 50.01% and 61.87%, and those of the composites prepared through CVI were 99.24% and 96.18%, respectively. The mechanism of the evolution of the mechanical properties after heat treatment was examined, and the analysis revealed that it was caused by the different fabrication processes of the SiC matrix. After heat treatment, the SiC crystallites prepared through PIP greatly increased, and the SiOxCy in the matrix decomposed to produce volatile gases SiO and/or CO, ultimately leading to an increase in the number of cracks and porosity in the material and a decrease in the material load-bearing capacity. However, the size of the SiC crystallites prepared through CVI hardly changed, the SiC matrix was tightly bonded without cracks, and the load-bearing capacity only slightly changed.

The CaCO3 coated corundum aggregates were prepared by impregnating tabular corundum aggregates with sizes of 1–5 mm in calcium hydrogen citrate solution and heat treatment at 430 °C, which were also used in Al2O3–MgO castables. The effects of Ca2+/Cit3− mole ratio in precursor solution on coating characteristics of CaCO3 coated corundum aggregates as well as the effects of CaCO3 coatings on properties and microstructure of castables were investigated. It is found that the thickness and continuity of CaCO3 coating is increased and the size of CaCO3 particles in coatings decreases first and then increases as Ca2+/Cit3− mole ratio is decreased. High-temperature properties of castables are improved by in-situ formation of calcium hexaaluminate (CA6) layer at aggregate/matrix interface after sintering at 1600 °C. The Al2O3–MgO castables exhibit the best thermal shock resistance when Ca2+/Cit3− mole ratio is 1/3. It is contributed by deflections of cracks and consumptions of fracture energy in a continuous platelet CA6 layer with thickness of 10 μm, which is in-situ formed through reaction between Al2O3 and CaO derived from CaCO3 coatings. The present investigation provides a novel approach to enhance thermal shock resistance of the Al2O3–MgO castables.

In this study, composite ceramic slurries based on submicron-micron-sized cordierite-zirconia were prepared with varied zirconia content. Standard bending strength and fracture toughness testing samples were directly designed and fabricated using stereolithography 3D printing followed by different sintering schemes to study the mechanical reinforcement effect. The physical compositions and microstructures of the samples were characterized. The additively manufactured cordierite-zirconia composites exhibit excellent mechanical properties. Maximum measured bending strength (136 MPa) and fracture toughness (1.8 MPa m1/2) were reached by adding 2 wt% and 6 wt% zirconia, namely an increase of 44% and 66% relative to pure cordierite, respectively. The strengthening and toughening mechanisms of the composites were further explained mainly by microstructural analysis. This study provides an alternative and direct design and manufacturing method for the mechanical measurement and reinforcement of ceramic composite parts based on the use of 3D printing technology.

In order to improve the surface properties of Al alloy, TiAlN ceramic coatings composed of alternating TiAl layer and TiAlN layer were prepared by FCVA technology. The influence of N2 flow rate on the microstructure, mechanical and tribological performance of multilayer TiAlN coatings was systematically studied. The results showed that the coating exhibited a multi-phase structure with mainly fcc TiAlN phase and a small amount of TiN and AlN phases. As the N2 flow rate increased from 50 to 80 sccm, the preferred orientation varied from TiAlN (220) plane to (111) plane due to lattice distortion. The hardness and elastic modulus of multilayer TiAlN coatings first increased and then decreased with the increase of N2 flow rate. However, the average friction coefficient and wear rate of multilayer TiAlN coatings exhibited an opposite trend to the hardness, H/E and H3/E2 values. The adhesion gradually decreased from 27.3 to 14.9 N due to the continuous increase of the compressive stress in the coating with the increase of N2 flow rate. When the N2 flow rate was 70 sccm, the coating showed the lowest average friction coefficient and wear rate, which was attributed to the highest hardness and the best resistance to cracking and plastic deformation.

In this study, Fe2+:ZnSe transparent ceramics with different doping concentrations were prepared from annealed FeSe and ZnSe powders by hot pressing. The as-prepared ceramics consisted of a cubic ZnSe phase and compact microstructures. Doping concentrations of Fe2+ ions in the range 0.66–3.05 at.% were accurately realised, which could influence the absorption intensity of Fe2+:ZnSe transparent ceramics. An absorption peak was observed at ∼3 μm, and its intensity could be controlled by the concentration of Fe2+ ions. FexZn1-xSe (0.0066 ≤ x ≤ 0.0305) ceramics with Fe2+ ions concentrations in the range 0.66–3.05 at.% exhibited significant absorption cross sections from 0.6676 × 10−19 to 0.1075 × 10−18 cm2. The specimen doped with 1.55 at.% Fe2+ ions displayed the highest transmittance of 67% at a wavelength of 14 μm and a carbonate absorption peak at 9 μm. The proposed transparent ceramic technique appears promising for preparing Fe2+:ZnSe laser gain media because of its advantage of allowing control over Fe2+ concentration.

The unfired Al2O3–C slide plates have the advantages of energy saving, environment friendly, efficiency and relatively low-cost. However, the decomposition and oxidation of the phenol-formaldehyde (PF) resin at elevated temperatures deteriorate the properties and decrease service life of the unfired slide plates. In order to improve the property of resin, the doped PF resin is prepared by incorporating Al(H2PO4)3, Zn and B4C powders. The effects of the doped resin on medium-high temperature properties and microstructure of the unfired slide plate materials have been investigated. The results show that Zn and B4C doped resin contributes to notable increasing the density and strength properties at medium temperature, because Zn and B4C easily oxide and thus protect resin from oxidation, leading to form a dense structure. Zn and B4C doped resin can significantly improve hot modulus of rupture of the materials at 1400 °C, which is due to Zn and B4C react with oxidative gases leading to increase in concentration of C(g), CO and N2, Al and Si would react with C(g), CO(g) and N2(g) to form AlN and SiC whiskers creating strengthening effect. Specimens with Zn and B4C doped resin addition have good oxidation resistance at 1500 °C, because Zn and B4C in the surface of the material react with O2 to form ZnAl2O4 or mullite containing dense glass film, which would retard O2 diffusion into the inner of the specimens.

In this article, a unique high infrared emissivity porous ceramic coating was prepared by slurry spraying method. In the first step, flower-like CeO2 powder particles were synthesized by precursor pyrolysis method using Ce2(CO3)3·8H2O as the transition phase. Subsequently, flower-like CeO2 ceramic particles (filler) and silicate (binder) were deposited by air spraying. The microstructure and phase composition of the prepared particles and the ceramic coating were examined using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). High temperature performance of the coating was assessed by conducting prolong isothermal oxidation and thermal shock tests. Infrared emissivity of the coating was tested at 750 °C by employing infrared radiation instrument. The prepared coating exhibited excellent high temperature resistance and high infrared emissivity (e3-5μm = 0.887, e8-14μm = 0.889 and e2.5-19μm = 0.893) at 750 °C. This was attributed to the presence of a large number of pores (within and among CeO2 particles) in the coating. In the end, possible mechanisms related with high infrared emissivity of the coating were discussed in detail.

In this work, the Al2O3-reinforced high Nb–TiAl laminated composite is successfully fabricated by an innovative way of direct-current magnetron sputtering combined with the foil-foil metallurgy, with assistance of vacuum hot-pressed sintering. Here, the Nb-coated aluminum foil and titanium foil, microstructure evolution, the lamellar plane distribution and the mechanical performances are carefully studied. Specifically, the composite is composed of the α2-Ti3Al, γ-TiAl and α-Al2O3 phase, in which the high Nb–TiAl matrix has a fully lamellar microstructure and a high content (∼6.5%) of Nb. Taken the textured titanium foil as raw material, the multi-stage annealing process is proved to be an effective way to control the lamellar plane distribution in the high Nb–TiAl matrix, showing that 82.3% of the lamellar planes forms an angle less than 30° from the RD-ND plane of the composite. Moreover, the bending strength and fracture toughness of the composite reach 817 MPa and 12.41 MPa m1/2, respectively. Further, the toughening and strengthening mechanisms are also detailly discussed. We believe that the major findings in this work can provide a new idea to design the high strength-toughness intermetallic-ceramic composites.

In this study, a new type of highly porous ceramic was successfully fabricated from α-Al2O3 whiskers and nano-sized Al2O3 particle slurry by vacuum infiltration with the subsequent annealing in air. It was found that with an increase in the alumina slurry amount or sintering temperature, the porosity of the foam ceramic decreased while its compressive strength increased. The optimal alumina slurry content and sintering temperature were equal to 4 g, and 1350 °C, respectively. The as-synthesised porous foam ceramic exhibited a low density of 0.65 g/cm3, high porosity of 83.51%, high compressive strength of 3.84 MPa, and low thermal conductivity of 1.37 W/m⋅K at room temperature, suggesting its potential applications in high-temperature gas filtration and thermal insulation materials.

In the present work, non-stoichiometric 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics with nero-zero τf were prepared by using the conventional solid-phase reaction method. The effects of additional magnesium contents on the sintering behavior, phase evolution, microstructure, and microwave dielectric properties of the ceramics were investigated. Based on the XRD analysis, the relationship between phase composition and microwave dielectric properties was investigated. The τf value was closely related to secondary phase, such as MgSiO3 and Mg2TiO4. The Q × f and er depended on the grain size distribution and porosity. Optimally, samples with a x value of 0.075 and sintering at 1425 °C for 3 h showed microwave dielectric characteristics of er = 9.78, high Q × f = 68,048 GHz and near-zero τf = + 4.57 ppm/°C. As a result, the 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics are regarded a potential candidate for microwave dielectric applications.

The plasma electrolytic fluorination (PEF) process was conducted on 6061 Al alloy in the NH4F-EG non-aqueous electrolyte at room temperature. The microstructure and composition of the resultant coating were characterized by SEM, EDS, XRD and XPS. Also the coating growth and plasma discharge behavior were investigated by means of a well-designed jig, digital camera and OES, in order to understand the process characteristics. Results showed that the coating was dominantly composed of AlF3, and characterized by a flake-like microstructure accompanying with some micro-pores and numerous micro-cracks. The internal of the coating was porous with a compact barrier layer near the substrate/coating interface. The fluorination of the substrate contributed the inward growth of the coating. PEF discharge sparks were characterized by tiny size and weak intensity during the whole process, of which the plasma electron temperature was about (3510 ± 110) K. Also, the discharge behavior and coating growth mechanism of the PEF process on Al alloy were discussed.

Our previous investigations indicate that the thermal shock resistance (TSR) of hydratable magnesium carboxylate (HMC) bonded Al2O3–MgO castables is superior to castables bonded with calcium aluminate cement as a result of the in-situ formation of micro-sized spinel (MgAl2O4). In the present study, to further enhance the TSR of HMC bonded castables, the submicron alumina powders were added into the castables to decrease the size of the spinel particle through a reaction of submicron alumina with nano magnesia pyrolyzed from HMC. The effects of submicron alumina powders on the TSR, slag corrosion resistance, and microstructure of HMC bonded castables were investigated. The results show that the size of the in-situ spinel particle decreases from approximately 2 μm to approximately 0.8 μm and the spinel gradually transforms into the aluminum-rich spinel after adding submicron alumina powders. The residual strength retention ratio of the samples raises from 37.5% to 50.0%, and the thermal stress damage resistance index (R՛՛՛՛) of the samples increases from 3.1 m to 7.2 m with the increase in the amount of submicron alumina to 2.0 wt% after thermal shock. The microcracks in the castables matrix of sample 2A are more and shorter than those of sample 0A after thermal shock. This is attributed to the fact that the resistance of microcracks propagation in the castables is enhanced via smaller spinel with uniform distribution. Besides, the penetration index of the castables decreases from 20.8% to 9.8% with the increase of submicron alumina content powders to 2.0 wt%. This is because the submicron alumina powders decrease the porosity of the castables, and the smaller size of the aluminum-rich spinel has a stronger adsorption capacity for Fe2+ ions.

The luminescence modulation based on photochromic reaction is universally applied in anti-counterfeiting applications. In this investigation, the Yb3+ and Ho3+ co-doped Sr2SnO4 ceramics were prepared by a conventional high temperature solid-state reaction. The basic microstructure and optical properties of the ceramics are analyzed. It is found the 280 nm irradiation can induce a photochromic reaction in the Sr2SnO4:xYb3+/Ho3+ ceramics, and the 480 nm irradiation can partially decolor the colored ceramics. Based on the photochromic reaction, the luminescence intensity modulation using the UC and DC modes has been investigated. The luminescence modulation ratio based on DC mode is much higher than that based on UC mode, which is ascribed to the larger absorption of the sample at 435 nm relative to the UC excitation wavelength. The present study results reveal the mechanism of the modulation difference of the UC and DC mode.

Sintering performance at high temperatures is a serious issue for tetravalent metal pyrophosphate MP2O7 ceramics (M = Ti, Zr, Hf, Ge, Sn, etc.). Herein, we investigated the influence of high synthesis temperatures and amounts of ZrP2O7 precursors on the properties of ZrP2O7 ceramics. A ZrP2O7 powder was first synthesised via a solid-state reaction; this powder was used in the fabrication of the ZrP2O7 ceramic using a combination of two-step sintering and in situ bonding using MgO as the sintering aid. The phase composition and microstructure of the ZrP2O7 powder as well as the ZrP2O7 ceramic were studied by X-ray diffraction and scanning electron microscopy. The physical properties and room-temperature thermal conductivity of the ZrP2O7 ceramic were investigated. The ceramic exhibited high thermal stability at 1350 °C. This study indicates that the mechanical properties of the ZrP2O7 ceramic can be enhanced while maintaining their low thermal conductivity by sintering it at 1300 °C with the addition of an appropriate amount of the ZrP2O7 precursors to the ZrP2O7 powder.

In this study, TiB2–B4C composite ceramics were prepared using Y2O3 and Al2O3 as the sintering aids. Different contents of B4C were added to seek promoted comprehensive mechanical properties of the composites. The mixed powders were sintered at 1850 °C under a uniaxial loading of 30 MPa for 2 h via hot-pressing. Through the measurement of XRD, SEM and related mechanical properties, the influence of B4C content on the microstructure and mechanical properties of TiB2–B4C composites ceramics was discussed. The experimental results show that TiB2–B4C composite ceramics exhibit excellent mechanical properties, which can be attributed to the dense microstructure and fine grain size. In addition, TiB2–B4C composite ceramic shows a relatively high comprehensive properties when the addition amount of B4C is 20 wt%. The relative density, Vickers hardness, fracture toughness and flexural strength are measured to be 99.61%, 27.63 ± 1.73 GPa, 4.77 ± 0.06 MPa m1/2, 612.5 ± 28.78 MPa, respectively.

The garnet structure is a promising solid material for nuclear waste because it can contain all kinds of actinides. Yttrium iron garnet Y3Fe5O12 (YIG) is the model component of this kind of substitute. In this study, Nd-doped YIG ceramic samples were prepared by microwave sintering at different sintering temperatures (1100 °C, 1200 °C, and 1300 °C) for different sintering time (0.5 h, 2 h, 4 h, and 6 h). The effects of synthesis temperature and sintering time on the solubility and microstructure of Y3-xNdxFe5O12 (0 ≤ x ≤ 3.0) were evaluated. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and backscattering scanning electron microscopy (EBSD) results show that single phase garnet structure can be synthesized and enhanced solubility of Nd in YIG was found at higher temperatures. The solubility of Nd in garnet is 50 mol% (x = 1.5) and 60 mol% (x = 1.8) at 1200 °C and 1300 °C, respectively. There is no significant dependence of the solubility on sintering time. The SEM analysis and Archimedes drainage test show that the relative density of Y1.2Nd1.8Fe5O12 ceramics is 88.15% and 99.94% at 0.5 h and 6 h, respectively, indicating dense YIG could be obtained with a relatively long sintering time. The results show that microwave sintering can rapidly and efficiently synthesize the YIG ceramic samples.

There is an urgent demand for advanced neutron-shielding materials that can be particularly used at extremely high temperatures in nuclear energy system. In this study, GdBO3–Al18B4O33 composite ceramics (GACCs) were successfully fabricated by the pressureless sintering of Al4B2O9 and Al2O3 using different firing temperatures and varying quantities of Gd2O3 used as the neutron-shielding agent. The properties of the obtained samples, including the crystalline phases, microstructure, thermophysical properties, and neutron-shielding capacity, were studied systematically. The structural stability determined by thermal cycle tests is reassessed based on the thermal stress caused by the mismatch between the thermal expansion coefficients of multiple phases in the material system, and it is further verified via numerical simulations performed using the finite element method. Moreover, the influence of the sample thickness and dispersion density of Gd on the shielding capacity of the material were also investigated and parameterised to guide the design of borate-based shielding materials. The results suggest that GACCs are promising candidates for high-temperature structural materials and excellent neutron-shielding materials in novel nuclear systems.

A novel electromagnetic wave (EMW) absorber was prepared by combustion synthesis. Boron carbide (B4C) powders with different grain sizes using a molten-salt-assisted combustion technique with B2O3, CB (carbon black), and Mg powders as starting materials, and NaCl as an additives. The effects of the NaCl content on the phase compositions and the microstructure of the products were characterized. A combustion front quenching method was used to elucidate the mechanism for the B4C powders synthesis. The dielectric, and EMW absorbing properties in the X-band were also investigated. The results showed that the addition of NaCl significantly reduced the grain size of B4C powders. Nanoscale B4C powders with cubic polyhedral structures were synthesized using 6 wt% NaCl (labeled as N-6). According to the quenching test results can be obtained that the first step in the combustion synthesis was melting B2O3 into a glassy substance. At the same time, Mg melted and formed a liquid pool into which the NaCl dissolved, followed reduction of the B2O3 to B. The formed B eventually reacted with CB to form B4C, and the B4C particles precipitated from the matrices. The N-6 sample exhibits optimal dielectric and EMW absorbing properties, because of a high specific surface area that enhances interfacial and space charge polarization.

In this study, titanium matrix composites (TMCs) were prepared by plasma activated sintering. The microstructure and mechanical properties of the composites were studied, and the strengthening mechanism was determined. The results showed that the main phases of Ti-rich samples are TiB, α-Ti and β-Ti, while the primary phases of TiB2-rich samples are TiB2 and TiB. The composites containing 70 wt%TC4-30 wt%TiB2 demonstrated the best performance which achieved a balance of high strength and ductility, with a yield strength of 1800 ± 28 MPa and compressive strength of 2215 ± 39 MPa. The key reinforcing and toughening mechanisms were due to the dislocation defects and stacking faults in the samples, which consume more fracture energy during crack propagation and comprehensively improve the strength and toughness of the composites. Furthermore, crack deflection and whisker pull-out caused by TiB can toughen the composites.

The efficient optimisation of radiation shielding materials (RSMs), which protect people from potential radiant threats, is highly desirable; however, it remains challenging. This study addresses the low-cost fabrication of the ceramic-based RSMs, aluminium borate-based ceramics using Bi2O3 as a novel simultaneous shielding agent and sintering promoter. The phase compositions, microstructures, sintering kinetics, and performances of the as-prepared Bi2O3 doped aluminium borate ceramics (BDABCs) are systematically researched. Finally, co-shielding tests for neutron and gamma radiation are performed. The results demonstrate that Bi2O3 can positively influence the sintering densification process of BDABCs via the evident reduction in the sintering activation energy. The migration of the Bi2O3–B2O3 liquid phase affects the pore structure, crystal morphology, and thermal conductivity of the samples. The obtained BDABCs exhibited highly reliable mechanical properties with a maximum elastic modulus and modulus of rupture of 124.3 GPa and 54.9 MPa, respectively; controllable thermal conductivity from 1.32 to 6.16 W m−1 K−1; and 12 wt% Bi2O3-doped sample (1400 °C × 3 h, 1.5 cm) shows the best radiation shielding performance, including 58.6% neutron and 26.6% γ rays. The obtained results manifest the enormous potential of BDABCs as structural materials and functional RSMs.

Al2O3–SiC–C (ASC) castables were performed using brown fused alumina as aggregates, silicon carbide, white fused alumina, ultrafine α-Al2O3, microsilica, calcium aluminate cement, silicon powder and ball pitch as matrixes. Microstructural observations and analysis of the effects of firing atmosphere and Si powder addition were investigated in this paper. The results show that the strength and strain tolerance of ASC castables with Si powder addition were significantly improved, but their thermal shock resistance was slightly degraded. Compared with the samples after firing in air atmosphere, cold strength and thermal shock resistance of samples after firing in reducing atmosphere were improved, and hot strength of samples tested in reducing atmosphere was little affected by the pretreatment conditions. The difference in properties was closely related to the phase composition and microstructure of ASC castables fired in air atmosphere and reducing atmosphere. The growth process of SiC whiskers was also discussed in detail.

Quartz and clay are substituted gradually by fly ash using a triaxial ceramic formulation under simulated industrial conditions and the effects of fly ash substitution on the macroscopic properties and microstructures of the sintered ceramics are evaluated systematically. With the substitution of 35 wt% (1250 °C), the ceramic sample exhibited optimal properties, including linear shrinkage of 15.61%, bulk density of 2.39 g cm-3, water absorption of 0.62% and flexural strength of 41.70 MPa, due to the accelerated densification and fly ash-spurred needle-shaped mullite. The microstructure analysis shows that the sintered matrix consists of three types of particles, quartz-, clay- and feldspar-like particles showing sintering behavior with respect to filling the glassy matrix with preserved morphology, precipitating mullite crystals, and fusing with the surrounding glassy matrix, respectively. The strength of the fly ash - containing ceramics is analyzed by the dispersion-strengthening mechanism and porosity and the results indicate that the fly ash particles affect the mechanical strength due to Griffith flaws when the total porosity is less than 25% and pores at higher total porosity. This study provides a viable strategy to recycle industrial fly ash in the production of architectural ceramics.

C/MgO composite powders were prepared by combustion synthesis using magnesium oxalate and magnesium powders as raw materials. The phase composition and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy/energy dispersive spectroscopy (FESEM/EDS), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The synthetic mechanism was explored through TG-FTIR and combustion front quenching techniques. It was found that the C/MgO composite powders contained a large quantity of MgO nanofibers. When the molar ratio of magnesium oxalate and magnesium was 1:4, the carbon content of the product reached a maximum of 9.45 wt %. In the composite powders, cubic MgO particles were encapsulated by a thin carbon layer, and there was a tiny gap between MgO and the carbon layer; a large number of MgO nanofibers with aspect ratios of 80–100 were found. The cubic MgO particles of the products are the direct decomposition of MgC2O4, and the MgO nanofibers are the reaction product of gaseous Mg and CO2/CO at high temperature. Meanwhile, the carbon deposited on the MgO particles can inhibit the grain growth of MgO particles and result in the refinement of MgO particles. The uniform dispersion of carbon and the weak C/MgO interface combine, making the composite powders a potential additive for low-carbon MgO–C refractories with excellent thermal shock resistance.

Lead-free (1-x)BaTiO3-xSr(Zn1/3Nb2/3)O3 (abbreviated as BT-xSZN, x = 0–0.08) relaxor ferroelectric ceramics were prepared using the traditional solid phase technology, and the effects of SZN modification on their phase structures, microstructures, dielectric performance, ferroelectricity and energy storage performance were studied in detail. A pure perovskite phase was observed in the BT-xSZN ceramics. The BT-based ceramics modified by SZN exhibited refined grain size. As the SZN content was increased, the breakdown strength initially increased and then decreased, and the ferroelectric loops gradually became ‘slim’. The BT-xSZN (x = 0.07) ceramics demonstrated a favourable energy storage performance with high recoverable energy density (Wrec = ~1.45 J/cm3) and energy storage efficiency (η = ~83.12%) at 260 kV/cm. Results indicate that the energy storage performance of BaTiO3 ceramics modified by SZN can be remarkably improved, widening their applications in energy storage at low temperatures.

Silicon-based materials with designed morphology and composite structure have received increasing interest in recent years due to the potential wide application for energy storage devices. However, these Si-based nanocomposites were usually synthesized and functionalized with other materials at a high temperature. Herein, one flocculent carbon network-twined C/Si/SiC nanocomposites were synthesized by a novel in-situ laser irradiation method using SiC targets as both a template and the source of C and Si. The fragmentation, decomposition and reshaping processes of bulk SiC to flocculent C/Si/SiC are simultaneously accomplished in one step, which can provide a more stable structure between epitaxial Si layer and C layer. What is more, due to the distinct laser-induced loose microstructure and flocculated carbon nanosheets, such nanocomposites exhibit a high specific surface area and hierarchically porous structure.

To elevate the mechanical and anti-ablation properties of Hf1-xZrxC coating on C/C composites, HfC/PyC core-shell structure nanowires (HfCnw/PyC) with different PyC layer thickness were synthesized by two steps of CVD. Influences of HfCnw/PyC on the microstructure and mechanical properties of Hf1-xZrxC coating were researched. Toughening mechanism of HfCnw/PyC was also investigated. PyC layer exhibited a lamellar structure and combined well with HfCnw. After incorporating HfCnw/PyC, Hf1-xZrxC coating structure converted from columnar crystal to isometric crystal. HfCnw improved H, E, Kc and bonding strength of Hf1-xZrxC coating, which is ascribed to the nanowire pullout, debonding, bridging and crack deflection mechanism. With the PyC layer thickness increasing, H and E of the coating reduced, Kc and bonding strength of the coating increased. Because of the moderate bonding strength between HfCnw/PyC and coating matrix, lamellar structure of PyC layer and higher Kc of PyC, toughening effectiveness of the core-shell structures gradually enhanced with the PyC layer thickness increasing.

The isothermal oxidation behavior of WC-based cemented carbides with AlxCoCrCuFeNi (x = 0, 0.5, 1.0, 1.5) high-entropy alloy (HEA) binders at 600–800 °C in air was studied by a thermogravimetric method, as well as WC-Co for comparison. The oxidation of the WC-HEA cemented carbides accompanies swelling and follows a linear law that is controlled by reaction at the oxide layer/matrix interface. The WC-HEA cemented carbides show better oxidation resistance than WC-Co, even though WC-Co has a denser microstructure and coarser WC grain size. With increase of Al content in the HEA binder, the oxidation rate of WC-HEA decreases, and the specific mass gains of the samples with HEA binder containing Al are at least 20% smaller than that of WC-Co after isothermal oxidation at 800 °C for 2 h. Moreover, as the HEA content increases from 5 to 20 wt%, the specific mass gain reduces from 61.89 to 24.55 mg/cm2. Selective oxidation of the HEA binder occurs, and the excellent anti-oxidation property of the HEA binder impedes inward diffusion of oxygen to the oxide layer/matrix interface, which suppresses oxidation of the matrix and enhances oxidation resistance of the WC-HEA. The results also indicate that the improved oxidation resistance of the WC-HEA system should not be attributed mainly to the formation of a dense oxide layer with high tungstate content during oxidation.

Hydratable alumina (HA) is a superior Ca-free refractory binder, but the quick hydration rate restricts the working time of castables bonded with HA. In this work, HA was grounded for 1 h and 6 h by a rotational ball mill to study the effect of grinding on the hydration of HA and properties of HA-bonded castables. HA samples with and without grinding were cured at 30 °C and then terminated by freeze-vacuum drying. The phase composition and microstructure of the dried HA samples were then examined. Moreover, flow ability and mechanical strength of castables containing ungrounded and grounded HA were also investigated. The results indicate that the specific area of HA particles were decreased by grinding as the micro-pores and micro-cracks on the surface of HA particles were blocked by smaller HA particles, thereby decreasing the hydration rate of HA and increasing the flow ability of castables.

High toughness and high hardness Si3N4 ceramics with fine and bimodal microstructure was prepared by combination of HfB2 additive and spark plasma sintering (SPS). HfB2-free SPSed Si3N4 ceramics at 1600 °C exhibited major α-Si3N4 phase, a fine and equiaxed grain microstructure, high Vickers hardness (21.3 ± 0.2 GPa), and low fracture toughness (3.7 ± 0.3 MPa m1/2). The introduction of 2.5 vol% HfB2 into Si3N4 ceramics at 1600 °C promoted α-to β-Si3N4 phase transformation, produced a fine and bimodal microstructure, significantly improved the toughness (7.7 ± 0.6 MPa m1/2) but slightly decreased the hardness (20.4 ± 0.6 GPa) which was higher than that of traditionally hot-pressed or pressurless sintered Si3N4 ceramics (~14–18 GPa).

The rich mineral resources of magnesite have been decreasing rapidly, while the low-grade magnesite is abandoned, and the requirement on utilization of low-grade magnesite is causing much attention. La2O3 has been introduced as an additive in this study, considering its positive role in the modification of the magnesia matrix. Low-grade magnesite containing 0–3 wt% La2O3 was fired at 1550 °C for 3 h. The effect of La2O3 on the microstructural evolution and thermomechanical property of sintered low-grade magnesite was investigated. The results showed that La2O3 markedly improve the microstructure of sintered low-grade magnesite. The distribution state of the low melting monticellite phases among the periclase grains evolved from distribute continuously to concentrate in isolation at the triple-point junction of the periclase grains, and the generated CaO·3SiO2·2La2O3 based dendrites phases interlaced in the magnesia matrix. The hot modulus of rupture (HMOR) was significantly enhanced with increasing addition of La2O3 due to the low-melting monticellite phases were transformed to CaO·3SiO2·2La2O3 phases based dendrites with large aspect ratio, effectively reducing the availability of monticellite. Besides, the bridging phenomenon resulting due to the dendritic phase exhibited an optimal toughening effect, attributing to the increase in crack deflection and resistance to crack propagation.

Semiconducting β-SiC nanofibers coated carbon fibers were introduced to reinforce Si3N4 ceramics, giving rise to forming hierarchical microstructure and excellent microwave absorbing performance. Dielectric properties of Cf-SiCNFs/Si3N4 ceramic composite (denoted as S-CS) has been investigated in the X-band (8.2–12.4 GHz) at elevated temperatures (from room temperature to 800 °C). The temperature-dependent dielectric of S-CS exhibits a multi-relaxation characteristic, which is related to the hierarchical structure, complex component, and electromagnetic frequency. The thermal dielectric behavior is discussed by Debye theory, and the relaxation factor κ is first introduced to predict the temperature-dependent multi-relaxation behavior intuitively. Combining the impedance matching theory, the relaxation factor κ can perfectly predict the best electromagnetic wave absorbing performance of S-CS (– 20.37 dB) both consideration of thickness and frequency at 800 °C, which is an effective way to characterize the electromagnetic absorbing performance at high temperature.

This study explored the effect of diamond content (0, 0.3, 0.6, and 0.9 wt%) onTi(C0.5,N0.5)-based cermets prepared via vacuum sintering with respect to their final mechanical properties and microstructures, characterized using X-ray diffractionand scanning electron microscopy. After liquid phase sintering, all cermets exhibited a ‘black core/grey rim'and partial ‘white core/grey rim'structure. The cermet with 0.6 wt% diamond exhibited optimal mechanical properties with a Vickers hardness of 1795 ± 32 H V, transverse rupture strength of 2026 ± 45 MPa, and plane strain fracture toughness of 12.95 ± 0.3 MPa m1/2. This is due to grain refinement and the uniformly distributed ‘white core/grey rim'grains. During the incipient liquid formation stage,a higher carbon activity arising due to diamond graphitization may shift the equilibrium towards the product, thereby yielding additional white cores due to the consumption of heavy elements in the binder. Excessive diamond introduction inhibited the dissolution of Ti(C0.5,N0.5) into the binder, resulting in fewer white cores.

The unfired Al2O3–Al–C slide plates were prepared using tabular alumina aggregates and fines, Al powder and graphite powder as starting materials, and phenol formaldehyde resin as binder. The effects of trace Zn on properties and microstructure of samples at elevated temperatures were investigated. Post mortem investigations on the newly developed Al2O3–Al–C slide plates with trace Zn were carried out. The results showed that the properties of the unfired slide plate materials at low temperature (500–700 °C) were remarkably enhanced in presence of trace Zn, and the high temperature properties above 1000 °C of the slide plates with Zn were also greatly improved in comparison to the conventional ones. After used in 90 t ladles for 2 consecutive heats, the bore enlargement of the newly developed slide plates was less than 2 mm/heat, and roughening on the sliding surface was slight, showing good high temperature service performance. The improved properties were attributed to the high reactive Zn reacting with O2 or CO to form ZnO ceramic phase and protected phenolic resin from oxidation at low temperature, and the vaporized Zn could promote non-oxide Al4C3 and AlN formation and growth at high temperature, creating strengthening and toughening effects.

The corrosion behavior of WC-MgO composite in H2SO4 and NaOH solution has been studied with electrochemistry and microstructure analysis method. The aim of this work is to explore the corrosion behavior and mechanism of WC-MgO whisker composite in acid and alkali solution. The result suggests that WC-MgO composite possesses higher corrosion resistance in H2SO4 solution than in NaOH solution. The key reason for better corrosion resistance in H2SO4 solution is the stable WO3 passive film. The oxidation of WC leads to corrosion induced crack along with grain boundaries. It can be attributed to the preferential corrosion of grain boundary and volume expansion caused by WC phase oxidation. The corrosion induced crack on the surface may decrease mechanical properties of WC-MgO composite. In NaOH solution, the main corrosion mechanism is the dissolution of WC phase but MgO is relatively stable.

Cubic silicon carbide (3C–SiC) is an excellent protective film on graphite and has been fabricated via laser chemical vapor deposition (LCVD) with an extremely high deposition rate by our research group. To understand comprehensively its growth behavior, the polycrystalline 3C–SiC thick films with the preferred orientation of and were characterized by diverse measurements, especially electron back-scatter diffraction (EBSD). Along the growth direction of the -oriented 3C–SiC, the microstructure changed from equiaxed grains to elongated grains with orientation, and eventually the -oriented columnar grains. The stacking faults in the -oriented 3C–SiC could be marked as -oriented 6H–SiC. On the other hand, in the -oriented 3C–SiC films, the microstructure changed from mainly equiaxed grains to large columnar grains. The high-density stacking faults in -oriented 3C–SiC films may lead to the identification of the nominal 2H, 4H and 6H polytypes by Raman spectra and EBSD. The (0001) planes of 2H-, 4H–SiC are perpendicular to the growth direction, while that of 6H–SiC are parallel.

Binderless carbides (WC-(0–10)wt.%TaC) were prepared via pressureless sintering at a relatively low temperature of 1850 °C using micro-scaled initial powders. The phase evolution, microstructures, physical and mechanical properties, and densification behaviors of these materials were investigated. The results showed that the binderless carbides had a single WC phase regardless of TaC addition. TaC dissolved into WC, resulting in the lattice expansion of the latter. With the increase in TaC addition up to 10 wt%, the lattice parameters, a and c, of hexagonal WC, as calculated using the Nelson–Riley extrapolation method, increased from 0.290963 nm to 0.284075 nm–0.291838 nm and 0.284929 nm, respectively. The proper addition of 2.5 wt% of TaC inhibited the coalescence of the WC particles and resulted in a homogeneous grain size. Furthermore, the dissolution of TaC improved the sinterability and facilitated densification, resulting in a low porosity of A02B02C00. The increase in TaC addition mitigated the mechanical properties owing to the decrease in sinterability, increase in porosity, and abnormal grain growth. Hence, almost full densification of binderless carbide was successfully consolidated at 1850 °C. The Vickers hardness of 26.51 GPa and fracture toughness of 9.95 MPa m1/2 achieved approached the corresponding levels of binderless carbides prepared via pressure-assisted sintering.

The Ni60-based self-lubricating composite coatings on the surface of Ti6Al4V alloys were successfully fabricated by laser cladding using different Ti3SiC2 ceramic additions. The microstructure, phase compositions and microhardness of the ceramic coatings were analyzed, the dry-sliding tribological properties and corresponding wear mechanisms of Ti6Al4V alloy and these ceramic coatings at different temperatures (RT, 300, and 600 °C) were also investigated systematically. The results show that the coatings are mainly comprised of γ-Ni solid solution, intermetallic compound TixNiy, hard phase TiC, TiB and Ti3SiC2 ceramic phase, the microhardness of the coatings was significantly improved compared with that of the substrate. Due to the synergetic action of the Ti3SiC2 lubricant and hard phase, the composite coatings possess better friction reduction and wear resistance performance than the Ti6Al4V alloys at all test temperatures. The lowest coefficient of friction (COF) (0.30 at 600 °C) was obtained when the composition was Ni60-5% Ti3SiC2(wt%), and the most excellent wear resistance (0.63 × 10−5mm3/Nm at 600 °C) was observed in the coating with composition of Ni60-15% Ti3SiC2(wt%). The abrasive wear, adhesive wear as well as oxidation wear are the main wear mechanisms of the Ti6Al4V alloy at 600 °C, while the coatings (composition: Ni60-10% Ti3SiC2 and Ni60-15% Ti3SiC2) are predominated by hard phase peeling off, three-body abrasive wear and oxidation wear at 600 °C.

Via a traditional sintering process, (1-x) [0.85BaTiO3-0.15Bi(Mg2/3Nb1/3)O3] - x Na0.5Bi0.5TiO3 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) (BT-BMN-NBT) ceramics were synthesized. The sintering temperature and density of the BT-BMN-NBT ceramics decreased with the increasing NBT content. All samples exhibited a pseudocubic phase and formed stable solid solutions with dense microstructures. The crystal structure of the BT-BMN-NBT ceramics gradually transformed from BT to NBT with increasing NBT content. The introduction of NBT with a high maximum polarization (Pmax) could not only enhance the relaxor ferroelectric (RFE) characteristics of the BT-based RFE, but also compensate for the reduction in Pmax of BT-based RFE that is due to the enhanced RFE characteristics. The temperature that corresponds to the maximum dielectric constant increases monotonously with the NBT content. Pmax of the BT-BMN-NBT ceramics increases significantly as the NBT content increases. The best energy storage (ES) performances (x = 0.3) of a releasable energy density (Wrec) of 2.91 J/cm3 and 85.55% efficiency were realized at 200 kV/cm. Compared with the unmodified BT-BMN ceramics (1.67 J/cm3), Wrec was improved by 1.48 times, which originated from the NBT modification induced increase in Pmax (39.5 μC/cm2) to 2.34 times the nominal BT-BMN value (16.9 μC/cm2). The results prove that the addition of NBT could improve the ES performances of BT-based relaxor ferroelectrics at low-field by increasing the polarization.

In this paper, a series of TaCN composite films with different carbon content were deposited by the magnetron sputtering system and the microstructure, mechanical and tribological properties were investigated. The results showed that the deposited TaCN films exhibited a three-phase of face-centered cubic (fcc) Ta(C,N), hexagonal closed-packed (hcp) Ta(C,N) and amorphous CNx. With the increase of carbon content, the hardness of the TaCN films first increased and then decreased, after reaching a maximum of 33.1 GPa; the adhesion strength increased gradually; the coefficient of friction decreased monotonically and the wear property initially improved and then weakened at room temperature. The coefficient of friction of the TaCN film at 28.21 at.% carbon decreased first, then increased and then decreased again and its high-temperature wear rate first decreased slightly and then increased, as the temperature increased from room temperature (RT) to 600 °C. The TaCN film at 28.21 at.% carbon exhibited excellent an elevated-temperature tribological properties.

The objective of this study was to develop chemically bonded phosphate ceramic (CBPC) coatings with relatively low curing temperature, properly prolonged curing time, and enhanced oxidation resistance. The coating was synthesised using aluminium phosphate as binder, surface modified MgOw/MgO as curing agent, and spherical microscaled Al particle as filler. The MgOw/MgO curing agent was surface coated by an Al2O3 layer via sol-gel routes. The Al2O3-coated MgOw/MgO agent facilitated a controllable curing process owing to the sustained-release effect of the surrounding microstructure. The weight loss profiles of all CBPCs with a surface modified curing agent exhibited a quasi-parabolic trend. The curing time decreased with the addition of the curing agent, and the Al2O3-coated MgOw curing agent was more effective owing to the good dispersion and larger particle number/volume percentage. The thermogravimetric and differential scanning calorimetry curves proved that the Al element exhibited similar effect as Mg2+, which could also enhance the curing process via substitution reaction between the basic metal ions with hydrogen in phosphate. Therefore, the addition of Al filler resulted in further curing and densification, exhibiting a decrease in the curing time (30–50 min) and increase in the weight loss (~40%). Proper binder-to-curing agent-to-filler mass (B:C:F) ratio was very important, and the CBPCs with improved surface roughness, hardness, and free of cracks were synthesised at a B:C:F ratio of 10:1:0.05. During oxidation at 800 °C, the Al filler in the CBPCs transformed into a continuous Al2O3 layer, which protected the Ti6Al4V alloy from further oxidation.

Three kinds of four-step three-dimensional braided silicon carbide fiber-reinforced silicon carbide matrix composites with pyrocarbon interface were prepared through precursor infiltration and pyrolysis under 1100 °C, 1300 °C, or 1500 °C, and they were oxidized at 1300 °C with simulated air. The effects of pyrolysis temperature on the microstructure and oxidation behavior of the composites were investigated. Results indicated that the SiC crystallite size and crystallinity of the as-fabricated composites increased with increasing pyrolysis temperature. During oxidation, the three composites initially underwent similar near-linear mass-loss stages associated with the consumption of carbon component. Subsequently, they exhibited different mass-gain stages associated with the oxidation of SiC component. The composites prepared at 1100 °C followed a linear mass-gain rule, whereas the composites prepared at 1300 °C and 1500 °C followed a two-step parabolic mass-gain rule. The mechanism of mass-gain behavior change was proposed, which might be associated with the pyrolysis-temperature-dependent precursor-derived ceramic SiC microstructure and its evolution during oxidation.

The sintering temperatures were set according to the TG/DSC analysis. The solid-phase sintering method was used to prepare the NASICON-type solid electrolyte in ATi2(PO4)3 (A = Li/Na/K) system. FT-IR spectroscopy conforms to the different chemical bond strengths of Li+, Na+, and K+ in phosphate compositions. The main crystal phases retrieved from the three compositions are NASICON-type ATi2(PO4)3 (A = Li/Na/K) in rhombohedral structure with the R 3 ‾ c space group. The presence of heterogeneous LiTiPO5 phases can reduce the grain boundary resistance and increase the density of LiTi2(PO4)3 electrolyte. However, heterogeneous TiP2O7 in NTP and KTP compositions does not contribute to the ionic conductivity. SEM results reveal that the crystal grains of LTP composition are denser than that of NTP and KTP, which is more beneficial to improve ionic conductivity. The LTP electrolyte sintered at 800 °C for 10 h shows the highest ionic conductivity of 3.1 × 10−5 S cm−1 at 25 °C.