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Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was −35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached −29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.

Polymer-derived SiBCN ceramics (PDCs-SiBCN) are promising ultrahigh-temperature ceramics owing to their excellent high-temperature oxidation resistance and electromagnetic wave (EMW)-absorbing capa...

In order to reduce the sintering temperature and improve the mechanical properties of B4C ceramics, ZrB2 was formed in situ using the SPS sintering method with ZrO2 and B4C as raw materials. Thermodynamic calculations revealed that CO pressure affected the formation of ZrB2 at temperatures from 814 °C to 1100 °C. The experimental results showed that the ZrB2 grain size was

In order to reduce the sintering temperature and improve the mechanical properties of B

In order to improve the mechanical properties of B4C ceramics, B4C@TiB2 composite powders with core-shell structure are prepared by molten salt method using B4C and Ti powders as raw materials. And B4C ceramics were prepared from B4C@TiB2 composite powders by spark plasma sintering (SPS). The results show that the B4C@TiB2 composite powders exhibit intact core-shell structure. The B4C@TiB2 composite powders improves the mass transfer during spark plasma sintering. When the molar ratio of B4C/Ti is 2/1, the relative density, Vickers hardness, fracture toughness and flexural strength of the BT1/2 sample are 94.2%, 26.9 GPa, 5.34 MPa·m1/2 and 570 MPa, respectively, which is best comprehensive properties.

The effect of B4C addition (0, 3 wt%, 6 wt%, 9 wt%) on the mechanical properties and oxidation resistance of Al2O3-C refractory ceramics was studies in the paper. The results indicated that the addition of B4C could reduce the apparent porosity, increase the mechanical strengths and improve the oxidation resistance. After fired at 1100 °C, the specimen with 6 wt% B4C achieved lowest porosity and permanent linear change. The cold crushing strength was improved from 14.65 MPa to 47.18 MPa. The cold modulus of rupture was significantly improved from 12.1 MPa to 36.29 MPa. When the fired temperature rose to 1450 °C, the lowest porosity and permanent linear change were obtained when B4C additive was 3 wt%. CCS was significantly improved from 12.40 MPa to 57.32 MPa. CMOR was also increased from 7.16 MPa to 28.71 MPa correspondingly. Meanwhile, the oxidation index could be also reduced from 47.6% to 3.9% when B4C content was 6 wt%. These improved properties were due to the formation of liquid phase B2O3 by the reaction between B4C and O2/CO. The compact structure was constructed by volumetric expansion of B2O3.

In this study, a novel phosphate-based adhesive was prepared by using homemade aluminum phosphate as a matrix and by adding different fillers simultaneously. The effects of calcination temperature and filler composition on the bonding mechanism and high-temperature bonding strength of the adhesive for high-temperature alloys were studied. The results indicated that the crystalline transformation of AlPO4 occurred at 500 °C. AlPO4 has two crystalline forms at 500 °C: orthorhombic and hexagonal. The addition of CuO to the fillers resulted in the exchange of Fe and Cu at the substrate interface and enhanced the high-temperature bonding strength of the specimens. The maximum tensile strength of the specimens reached 3.9 MPa at 500 °C. These composites have potential applications in aviation, aerospace, and other fields.

The effect of nano-zirconia addition on the microstructure and properties of corundum castables was studied using corundum, kyanite, alumina powder, gel powder, and nano-ZrO2 as raw materials. The results showed that adding 1.2(wt)% nano-ZrO2 could reduce the median pore diameter of the castables from 480 to 200 nm at 110 °C. After the castables were heated at 1100 °C, the cold modulus of rupture increased by 29.95%, to 24.71 MPa, and the cold compressive strength increased by 50.32%, to 116.37 MPa. The hot modulus of rupture increased by 114.95%, to 3.59 MPa after being treatment at 1500 °C, the high surface energy of nano-ZrO2 can increase the interface energy and bonding strength between adjacent particles.

The work was to develop novel high temperature microwave absorbing material based MgZr4(PO4)6 (MZP) ceramic. The results show that thermal expansion process at higher temperature expand along c-axis while shrink along the a-axis. The conductivity of MZP ceramic was increased by 1000 orders due to the increase in magnesium ion mobility. In addition, the results indicates that the dielectric properties were dependent on temperature at all measured frequencies. The real and imaginary parts of dielectric constant increased from 4.0–5.2 and 0.024 to 0.4, respectively. The reflection loss varied with the change in thickness and the minimum reflection loss value was -26.66 dB at 800℃, suggesting that MZP ceramic was a promising novel high temperature microwave absorbing material.

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al2O3 by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process.

The effect of the particle size (50–325 mesh) and content (0–0.1 wt%) of metallic aluminum powder on the explosive spalling resistance of corundum-based refractory castables were investigated in this study based on air permeability, pore size distribution, heat release, fracture energy and microstructural analyses. The experimental results show that the addition of Al powder significantly improves their explosive spalling resistance. As observed, the explosive spalling resistance of the castables was mainly influenced by the permeability mechanism and the fracture energy. Permeable paths were generated in the microstructure of the sample during the overlapping period between the curing process and the H2 gas forming one, derived from the Al–H2O reaction. The highest permeability level was obtained when 0.075 wt % of Al powder with size of 100 mesh was incorporated into the corundum-based refractory castables. At the same time, the fracture energy of the castable samples was increased accordingly.

In this work, β-Sialon of different morphologies was generated using in situ morphological regulation and simulation. Their effects on the thermo-mechanical properties of Al2O3-C refractories were then investigated. The results indicate that columnar, plate-like, and hexagonal prism β-Sialon were formed from specimens without additives, with Fe2O3 as a catalyst, and with Ni as a catalyst, respectively. Transmission electron microscope (TEM) analysis results confirmed that the three morphologies of β-Sialon grow along with (110), (101), and (100), respectively. Density functional theory (DFT) results show that the addition of catalyst atoms could reduce the adsorption energy of gaseous Al2O on different crystal planes, which promotes the formation of β-Sialon. The formation of three different shapes of β-Sialon gave rise to materials with good mechanical strength. The cold modulus of rupture (CMOR) and cold crushing strength (CCS) of the specimen containing plate-like structure was slightly higher than those with a columnar and hexagonal prism, with maximum CMOR and CCS values of 27.2 MPa and 105.2 MPa, respectively. In addition, good thermal shock resistance was obtained due to the formation of β-Sialon; the residual strength ratio of the specimen with columnar β-Sialon was 78% after five thermal shock cycles, and those with plate-like and hexagonal prism reached 93% and 86%, respectively.

Iron-containing siliconboron carbonitride (SiBCN) ceramics with multiple heterogeneous interfaces were fabricated using the microstructural design and polymer-derived ceramics (PDC) approach. The characterization results revealed the in-situ generation of nanocrystals, including graphite, belt-like silicon nitride (Si3N4), and silicon carbide (SiC) whiskers, in amorphous SiBCN matrix after annealing. At the same time, these dielectric lossy phases successfully constructed multiple heterogeneous interfaces and three-dimensional network structures. Consequently, the conductivity of the ceramics increased from 4.49 × 10−9 (annealed at 800 °C) to 0.67 × 10−4 S cm−1 (annealed at 1600 °C). The real part of permittivity improved from 4.57–3.36 (annealed at 800 °C) to 10.90–8.38 (annealed at 1600 °C) in the frequency range of 2–18 GHz. The formation of multiple heterogeneous interfaces caused interfacial polarization and increased the multiple relaxations, which ultimately led to a superior microwave absorption property with a minimum reflection loss (RLmin) of −34.28 dB and an effective absorption bandwidth (EAB) of 3.76 GHz (8.64–12.4 GHz).

β-Sialon with whisker-like, columnar, and plate-shaped structures was successfully synthesized with Al2O3–C refractory compositions. In the presence of a catalyst, the preferential growth face of columnar β-Sialon was (100), whereas plate-like β-Sialon preferred (101) and (111). DFT calculations demonstrated that the SiO adsorption energy on the (100), (101), and (111) faces of β-Sialon crystal were –34.95, –52.88, and –45.08 eV, respectively. Therefore, the (101) and (111) faces were more stable in Al-rich β-Sialon. With the increase in catalyst content, the Si-rich Si–Al–O–N liquid phases, which contributed to the generation of columnar β-Sialon, were converted into the Al-rich Al–Si–O–N system that was conducive to the formation of plate-like β-Sialon. Compared to the sample without the catalyst, the CMOR and HMOR of the specimen were increased by 45.07% and 60.47%, respectively, with the addition of Fe2O3. This was attributed to the formation of β-Sialon with a one- or two- dimensional shape.

The exploration of new strategies to fabricate phosphors with tunable luminescence and enhanced thermal stability has been pursued since a long time. In this study, we propose and demonstrate a novel methodology of coating g-C3N4 on phosphors by a vapor deposition method to synthesize core–shell phosphors with tunable luminescence and improved thermal stability. By this method, flaky g-C3N4 can be evenly coated on the surface of the precursors Y2O3:Eu3+,Tb3+ and Y2O3:Eu3+,Tb3+@SiO2 with a thickness of 8 nm. Under the excitation at 368 nm, the CIE coordinates can be adjusted from blue region (0.1713, 0.1887) to white (0.3074, 0.3232) and yellow (0.4565, 0.4703) regions by controlling the amount of g-C3N4. Moreover, the thermal stability of phosphors can be improved by the g-C3N4 coating shell at elevated temperatures due to the isolation of luminescence centers, modification of surface defects, and efficient energy transfer from g-C3N4; the emission intensity of Eu3+ at 398 K improved by 13% after coating with g-C3N4. The above-mentioned effects of g-C3N4 were also proved to work well on the Ca9.5Na2(PO4)7:Eu2+ yellow-green emitting phosphor, indicating that this methodology has general applicability for improving luminescent properties of phosphors.

Polymer-derived SiBCN ceramics (PDCs-SiBCN) are promising ultrahigh-temperature ceramics owing to their excellent high-temperature oxidation resistance and electromagnetic wave (EMW)-absorbing capability. In this paper, the microstructure evolutions, the dielectric properties, and EMW absorption properties of Y

In this paper, the effects of the matrix pore structure on the strength and corrosion resistance of corundum castables are reported. Pore diameters of castables fired at 110 °C could be decreased from 550 nm to 72 nm when 4% Al2O3-SiO2 gel powder was added. The pore diameter of the castables decreased from 850 nm to 500 nm after firing at 1100 °C, but increased from approximately 2 μm–8 μm after firing at 1500 °C. The strength of castables fired at 1500 °C increased remarkably with the addition of Al2O3-SiO2 gel powder. A maximum cold modulus of rupture (CMOR) of 62.34 MPa was obtained when 4% Al2O3-SiO2 gel powder was added. After slag corrosion, the penetration index fell from 16.6% to 4%, suggesting that a homogeneous pore size distribution and a smaller pore size played an important role in improving the penetration resistance.

β-Sialon bonded Al2O3–C refractories possess high strength and superior thermal shock performance. In this study, the growth of preferred β-Sialon (Si3Al3O3N5) and its effects on thermo-mechanical properties of Al2O3–C refractories were investigated via simulations and experiments. The results indicate that the additive Fe2O3 contributed to the formation of β-Sialon and helped its column structure become plate-like. Transmission electron microscopy confirmed that the (101) crystal plane was a growth plane of plate-like β-Sialon. The growth mechanism of β-Sialon was suggested by density functional theory; calculation results revealed that the key step for the formation and growth of β-Sialon was the adsorption of the gaseous molecule Al2O on the Si3N4 (101) crystal plane. It was found that the existence of Fe atoms could significantly reduce the adsorption energy. Additionally, Al2O3–C refractories containing plate-like β-Sialon possessed a high cold modulus of rupture and crushing strength, which increased by 40% and 15%, respectively, compared with the specimens containing column β-Sialon. It was also found that the formation of plate-like β-Sialon resulted in significantly better thermal shock resistance for the Al2O3–C refractory specimens, and the residual strength loss ratio of the sintered specimens was only 4% after five thermal shock cycles.

One-dimensional La3+-doped mullite of diameter 20–30 nm and length 2–3 μm was prepared by a molten salt method. The electrical properties of La(x)Al(6-x)Si2O13 (x = 0, 0.5%, 1.0%, 2.0%) can be effectively adjusted by the La3+ doping content. The electrical conductivity increased from 1.18 × 10−8 (x = 0) to 2.09 × 10−6 S cm−1 (x = 2.0%). The real part of permittivity was improved from 2.5 (x = 0) to 3.2 (x = 2.0%) in the frequency range 2–18 GHz. The presence of La3+ increased the dielectric loss types and improved the characteristic impedance matching, leading to excellent electromagnetic wave absorption with a minimum reflection loss of −18 dB. First-principles calculations revealed that La doping can decrease the band gap of mullite from 3.677 to 3.541 eV and induce the formation of local dipole moments, which can ultimately improve both the electrical conductivity and the dielectric polarization.

Several phosphate-bonded castables were prepared using corundum as a raw material and 48 wt.% phosphoric acid as a binder. The phase composition, microstructural evolution, and properties of the castables samples were analyzed, and a relationship between the microstructures and properties of the castables was established. The results revealed that the cold modulus of rupture of the specimens increased by 19 % to 33.02 MPa after firing at 1 100 °C when the alumina micropowder content increased from 10 % to 15 %. X-ray diffraction analysis revealed that corundum and AlPO4 were present in the castables fired at both 1 100 °C and 1 500 °C. The intensities of the AlPO4 diffraction peaks increased as the alumina micropowder content and sintering temperature increased. Scanning electron microscopy revealed that AlPO4 was tightly arranged and packed with particles.

Columnar β-Sialon bonding phases were in situ synthesised in Al2O3-C refractory composites and their growth mechanism was simulated based on first-principles calculations. The experimental results indicated that the addition of Fe2O3 as a catalyst accelerated the transformation of Si3N4 to β-Sialon, resulting in a well-developed columnar structure. The (100) facet was the primary surface for crystal growth during the transformation process of Si3N4 into β-Sialon. According to first-principles calculations, the surface energy of the (100) facet decreased greatly due to the substitution of (Si, N) pairs with (Al, O). The catalyst could promote the adsorption of gaseous phases on the (100) facet of Si3N4 and decreased the gas adsorption energy of both SiO and Al2O. Owing to the presence of in situ synthesised columnar β-Sialon bonding phases, the residual crushing strength of Al2O3-C refractory composites after 5 thermal shock cycles increased by 25.1%.

Fe-Mo catalyst with different molar ratios (1:0, 1:0.5, 1:1, 1:2, 1:3) were prepared by chemical co-precipitation method, and they were added to phenolic resin as catalysts. The microstructure and physicochemical properties of catalyst and crystalline carbon after phenolic resin pyrolysis were characterized by XRD, SEM, FT-IR, XPS and TEM. The results showed that the Fe/Mo molar ratio played a significant role in the graphitization of phenolic resin and the morphology of carbon nanotubes. The graphitization of the phenolic resin first increased and then decreased with the addition of Mo. When the Fe/Mo molar ratio was 1:2, the phenolic resin achieved the highest graphitization, and the formed carbon nanotubes had the highest crystallinity. The Fe atoms were in an electron-deficient state due to the electrons transferring from Fe to Mo, which enhanced the hydrocarbon compounds absorption on the surface of catalyst. And Mo was carbonized by carbon atoms to form α-MoC1-x, and then decomposed into β-Mo2C and graphite carbon, obtaining carbon atoms orderly arrangement and carbon nanotubes. Therefore, both the grain size and electron structure of catalyst significantly affect the catalytic properties of Fe-based catalyst.

A study of non-oxide bonding phases formed in situ by adding La2O3 to Al2O3-C refractories, and their influence on the thermo-mechanical properties, is presented. Calculations of the thermodynamics of the Al-Si-O-C-N system were thoroughly explored. Phase assemblage and microstructure were analyzed by means of X-ray diffraction and scanning electron microscopy. The results were that β-Sialon (Si3Al3O3N5) and 15R-Sialon (SiAl4O2N4) formed during sintering at 1400 °C. In addition, the presence of the rare earth oxide, La2O3, promotes columnar β-Sialon formation in a plate-like grain morphology, and this can improve the in situ synthesis of 15R-Sialon. The non-oxide bonding phases give rise to specimens with excellent strength and toughness. Increasing the La2O3 content from 0 wt% to 0.6 wt% enhanced the cold modulus of rupture and the cold crushing strength of the specimens fired from 31.1 MPa to 34.6 MPa, and from 101.3 MPa to 113.8 MPa, respectively. Meanwhile, the displacement was increased by 68% to 0.32 mm. The generation of plate-like β-Sialon and 15R-Sialon also had a positive effect on the hot strength and thermal-shock resistance. The hot modulus of rupture of the specimens fired improved by 21% compared to specimens without La2O3. After three thermal-shock cycles, the residual strength ratios of the specimens fired were above 88%.

The microstructural evolution and comprehensive properties of alumina refractory bonded with calcium aluminate cement and silica sol have been studied. Results have been correlated with the microstructural and phase evolutions using X-ray diffraction and scanning electron microscopy, as function of the pre-formed spinel powders. Matrix samples were obtained for phase and microstructural characterization in details, and the results were compared with those corresponding to the refractory castables. The room temperature and high temperature properties, including permanent of linear change, mechanical properties, hot modulus of rupture (HMOR) and slag resistance were measured. The castables exhibited a microstructural optimization and properties enhancement due to the addition of pre-formed spinel. A lot of secondary spinel and CA6 (CaO·6Al2O3) with small size were produced in the castables, and the contents of micro pores were greatly increased. As a result, the permanent of linear change of castables was decreased by 61%, while cold modulus of rupture (CMOR) and HMOR were increased more than 45% and 100%, respectively. The penetration indexes in the static slag resistance were decreased from 28.8% to 12.2%.

In this paper, the morphology of CA6 was adjusted by changing the particle sizes of alumina powders (D50 = 7.26, 5.33 and 2.37 µm), and the effect of this on the thermo-mechanical properties of corundum based high temperature composites was investigated. The results indicated that when the alumina particle size was decreased from 7.26 to 2.37 µm, the morphology of calcium hexaluminate (CA6) transformed from equiaxial to platy shape. The microstructure changes of CA6 may be due to differences in CA6 nuclei numbers and the contact area between alumina and calcium dialuminate. This transformation process can proceed without liquid. Because of the transformation of the CA6 morphology, the hot modulus of rupture and residual cold modulus of rupture of corundum composites fired at 1600°C increased by 143 and 192%, respectively. The loop areas of in-situ elastic modulus also increased by 20%. The fracture ways of composites were transformed from intergranular to transgranular. Therefore, corundum-based composites with excellent properties including room temperature and high temperature properties can be obtained by adjusting the microstructure of CA6.

A graphite/SiC composite was synthesized at different calcination temperatures using microsilica and carboxymethylated cellulose. The oxidation resistance and wettability (with water) of graphite/SiC were investigated. The results showed that carboxymethylated cellulose could react with microsilica to form a coating of SiC on the surface of graphite at elevated temperatures. Consequently, SiO₂ phase was converted into SiC phase above 1 600 °C. The microstructure of the SiC coating on graphite became denser with the increase in temperature. Thermogravimetric curves revealed that the weight loss of graphite was approximately 97.3 wt.% whereas the value decreased to 29.78 wt.% when SiC was formed. Differential scanning calorimetry analysis showed that the SiC coating decreased the enthalpy of the carbon oxidation reaction from 12.02 kJ g⁻¹ to 1.14 kJ g⁻¹, confirming excellent oxidation resistance. Furthermore, the water contact angle of graphite was approximately 78.5° whereas that of the graphite/SiC composite was reduced to 43°. The study of the formation of graphite/SiC composite showed that SiO₂ could be reduced using carboxymethylated cellulose to SiO (g), which was deposited on the graphite to form SiC coating.

In this paper, submicron spinel-containing calcium aluminate (SP-CA) cements were prepared at temperatures of 1200 °C (RA12), 1300 °C (RA13), and 1450 °C (RA14) using reactive alumina, magnesium hydroxide, and calcium carbonate as raw materials. The microstructural characteristics and high temperature properties of refractory castables bonded by SP-CA cement were investigated. The results indicated that the mineralogical compositions of SP-CA were spinel (MgAl 2 O 4 , MA) and CaAl 2 O 4 (CA). The spinel phases presented no definite borders or shapes, with average size ranging from 0.1 μm to 1.2 µm at different sintering temperatures. After heating alumina-spinel castables, the submicron spinel particles bonded with corundum and hibonite (CA 6 ) grains could strengthen the castable body. However, the large sized ( '''' of castable RA12 was 39.7 m, which is significantly higher than that of castable AS (19.8 m). The corrosion rate of castable RA12 was 5 mm 2 /min, which is significantly lower than that of castable AS (7.4 mm 2 /min). Small pore size and submicron spinel played relevant roles in corrosion behavior.

The microstructure evolution and properties of Al 2 O 3 –SiC–C refractories with different Fe 2 O 3 content (0, 0.5, 1.0 wt%) heat-treated at 1400 °C were investigated. Also, the in-situ growth mechanism of diamond-shaped mullite platelets was discussed. The experimental results indicate that there were only mullite and SiC whiskers formed in the absence of the additive. However, both whisker-shaped and diamond-shaped mullite phases could be generated aside from SiC whiskers, which were satisfactorily correlated with Fe 2 O 3 addition. Interestingly, the introduction of Fe 2 O 3 changed the morphology of mullite whiskers from the curved structure (without additive) to the straight and elongated shape (with additive). Furthermore, these two-dimensional mullite platelets were better developed resulting in the larger size and higher yield with 1.0 wt% Fe 2 O 3 . XRD, SEM, TEM and HRTEM analyses reveal that with the addition of Fe 2 O 3 , mullite phases in refractory samples grew preferentially toward the crystal facets along (130) and (4 2 − 0) directions of mullite nanocrystals, thus, a diamond-shaped structure was generated. As the well-developed mullite platelets were formed, the cold modulus of rupture (CMOR) and the cold crushing strength (CCS) increased from 6.5 MPa to 10.3 MPa and from 38.7 MPa to 55.7 MPa, respectively. Meanwhile, after three thermal shock cycles, the CCS of samples containing 1.0 wt% Fe 2 O 3 only decreased by 2.6 MPa, and the residual strength ratio of CCS (CCSst) reached the maximum value of 95.3%. These results suggest that the in situ synthesized platelet-shaped mullite phase observably improved the thermal shock resistance of Al 2 O 3 –SiC–C refractories.

In this paper, using industrial alumina, calcined magnesite, ground calcium carbonate as raw materials, spinel-containing calcium aluminate cements (CMA) were prepared at 1500 °C with different calcine holding times (3 h and 6 h). The mineral composition and microstructural characteristics of prepared cement samples were studied using X-ray diffraction and scanning electron microscopy, and their hydration and rheological behavior were also investigated. The results indicated that increasing holding time can promote growth of CaAl2O4 grains and reduce setting time. The hydration mechanism of CMA follows the nucleation and crystal growth–diffusion (NG–D) process, and the hydration rate of CMA–3 h in the acceleratory period is higher than that of CMA–6 h, but there is no significant distinction in deceleration and stabilization periods. The slowdown of hydration rate directly affects the rheological behavior of CMA slurry, leading to decrease in yield stress, and thixotropic character. Also, the storage modulus (G') growth rate of CMA–3 h slurry is significantly higher than for CMA–6 h slurry, indicating the CMA synthesized at 1500 °C for 6 h possesses lower hydration activity.

The Al 2 O 3 –SiC–C refractory samples were prepared from raw materials of calcined bauxite, brown fused alumina, tabular alumina, flake graphite, silicon carbide and metallic Si powders. The Fe 2 O 3 powders were used as additive and the phenolic resin was applied as binder. The effects of calcination temperature on microstructural evolution and thermo-mechanical properties of the samples had been studied. Thermodynamic calculation of Al–Si–O–C systems shows that both mullite and SiC were as equilibrium phases after coking at elevated temperatures. The experimental results indicate that the mullite whiskers with large aspect ratio were formed after fired at 1000 °C in a coke bed. When the temperature was raised to 1400 °C, a new phase of SiC whiskers was formed in addition to the mullite whiskers. Morever, a large number of the mullite platelets with diamond shape were generated. The property tests show that as the firing temperature rose from 1000 °C to 1400 °C, the value of cold modulus of rupture (CMOR) was increased by 57.1% to 8.2 MPa, and the cold crushing strength (CCS) was raised from 47.5 MPa to 54.8 MPa; also, the flexural modulus (FM) and load displacement were almost 30% and 20% increased respectively. It is also found that the hot modulus of rupture (HMOR) measured at 1400 °C reached the maximum value of 8.1 MPa after firing at 1000 °C. Furthermore, after three thermal shock cycles, the residual strength ratio of samples after cured at 200 °C was only 47.5% while the value rose to 96.4% after fired at 1400 °C. It is believed that the substantial enhancement in the thermo-mechanical properties of Al 2 O 3 –SiC–C refractory samples under room and elevated temperatures could be attributed to the synergistic effect of in-situ formed SiC whiskers, mullite whiskers and diamond-shaped mullite with plane structure.

In this paper, the alumina-based refractory castables were prepared using calcium aluminate cement (CAC) as binder. The phase composition and microstructural evolution of the castable samples during the heating process were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), and thermal expansion analysis. The relationship between the microstructural characteristics of castables and the properties of elastic modulus was investigated. The results showed that, after the castables were cured at room temperature for 24 h and dried at 110 °C for 24 h, the main phases present after hydration were Al 2 O 3 , C 3 AH 6 , and AH 3 . C 3 AH 6 and AH 3 would be transformed into C 12 A 7 and AlO(OH) or Al 2 O 3 , as temperature increased from 110 °C to 800 °C, the microcrack caused by decomposition of the hydrates will led to the lower values of both the elastic modulus and strength of the castable samples. From 900 °C to 1000 °C, CA was recrystallized through the reaction between C 12 A 7 and A, resulting in an increase in elastic modulus and strength. Between 1100 °C and 1200 °C, CA 2 would be formed, which resulted in a volume expansion of the material and a slight increase in elastic modulus. Finally, the CA 6 phase was formed as the temperature increased to 1400 °C. The enhancement of the strength and elastic modulus of the castable samples could be attributed to their strong interlocking bonds between platelet CA 6 and matrix particles at high temperature.

The influence of the addition of Ni(NO3)2 · 6H2O on the microstructure and mechanical properties of low-carbon MgO–C refractory composites was investigated. The results indicated that MgO whiskers and carbon nanotubes could be generated in low-carbon MgO–C refractory composites with Ni(NO3)2 · 6H2O in a reducing atmosphere at 1 200 °C. The magnitudes of the cold crushing strength, the cold modulus of rupture, the fracture displacement, and the residual cold crushing strength are increased by 47 %, 66 %, 8 % and 26 %, respectively. The MgO–C refractory composites with the addition of 0.6 wt.% Ni(NO3)2 · 6H2O result in better overall properties. The MgO whiskers were generated via a dissolution–diffusion–precipitation mechanism, and their growth is in accordance with the vapour–liquid–solid model.

A series of high alumina refractory castables were prepared via casting with tabular alumina aggregates (0.088 – 5 mm), fine powders, and calcium aluminate cement as starting materials. The effect of the median diameter of alumina (D50 = 7.26 μm, 5.33 μm, 2.37 μm) on the thermo-mechanical properties of the refractory castables was investigated. The results indicate that the decrease in the alumina particle size from 7.26 μm to 2.37 μm has little influence on both the apparent porosity and bulk density of castables. However, the median pore size of castables fired after 1 600 °C decreased drastically from 4.7 μm to 2.4 μm correspondingly, which led to significant growth in the strength and thermal shock resistance of castables. The cold modulus of rupture and crushing strength were increased by 201 % and 120 %, respectively. At the same time, the hot modulus of rupture and elastic modulus were also increased by 143 % and 127 %, respectively. The residual elastic modulus was enhanced twice after three thermal cycles.

The effects of interfacial bond and homogeneous microstructure on the physical properties of Cu–W composites have been investigated. To acquire strong interfacial bond and homogeneous microstructure, different modified W powders have been designed, which W powders were coated with different Cu contents using electroless plating method. The results showed that by increasing the Cu content of the coating, the microstructure of Cu–W composites becomes homogeneous, and the physical properties, including thermal, electrical and mechanical properties, improved greatly. When 20Cu@W composite powders were used to fabricate Cu–W composites, the physical properties reached the optimal values: The thermal conductivity was 239 W/(m·K) which was close to the theoretical vaule of 240 W/(m·K), the electrical conductivity was 50.6%IACS, coefficient of thermal expansion was the minimum value of 7.3 × 10 − 6 /K, the bending strength and Vickers hardness were 976.7 MPa and 224.8 HV, respectively. These optimal values were much higher than those of mixed Cu–W composites. The properties enhancement of Cu–W composites is attributed to the strong interfacial bond between Cu and W and homogeneous microstructure. This enhancement effect was strengthened by increasing the coating's Cu content, resulting in the continuous improvement of the physical properties.

This research studied the effects of several dispersants on the morphologies of cement hydrates and properties of refractory castables. The results showed that the cement hydrate morphologies were closely related to the types of dispersants used. With naphthalene sulfonate formaldehyde condensate (FDN) and sodium tripolyphosphate (STPP) as dispersants, the cement hydrate of C 3 AH 6 obtained anomalistic shapes, and the AH 3 particles showed a diameter of not more than 1 μm. When propionic acid (PA) was added, C 3 AH 6 formed inerratic cubical grains, whereas AH 3 changed from particles to long column agglomerates; the ratio of the long radius increased with increasing PA concentrations. The addition of PA as dispersant generated CaCH 3 CH 2 CO 2 + , which resulted in a decrease in Ca 2+ concentration. Also, the relatively higher apparent porosity satisfied the space requirement for the growth of C 3 AH 6 , eventually resulting in larger inerratic cubical grains. The H + hydrolyzed from PA accelerated the growth on the (100) and (110) crystal planes of AH 3 ; thus, gibbsite stretched along the c -axis. The maximum values of CCS and CMOR for refractory castables prepared with PA as dispersant were 5.6 MPa and 46.6 MPa, respectively, which were higher than those for refractory castables with FDN and STPP. The observed excellent performance in strength might be related to the bridging effect resulting from the long-column AH 3 .

MgZr4(PO4)6 (MZP) with Ce-doped content of 0%, 1%, 3% and 5% was synthesized by solid state reaction. The results showed that the oxygen octahedron would contract along the a-axis and expand along the b-axis and c-axis with Ce doping content increase. The electrical conductivity of MZP measured by impedance spectroscopy showed that Ce doping could enhance ionic conductivity of MZP from σ = 1.063 × 10−8 to 1.16 × 10−7 S/cm due to the bottleneck phenomenon in the magnesium ion migration channel. Moreover, the complex dielectric constant of MZP was measured by network analyzer, and the results showed that the real part of the permittivity increased from 3.2 to 4.1 in a frequency range of 2.0–18.0 GHz. The lowest reflection loss was −8 dB at 15.4 GHz when the doping content reaches 5%, which indicated that MZP was promising as a novel microwave absorbing material.

The effect of colloidal silica (CS) on the hydrate phases and microstructure evolution of calcium aluminate cement (CAC) was investigated. Samples hydrated with CS were obtained and characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared spectroscopy (FT-IR), hydration heat measurement and Nuclear Magnetic Resonance (NMR). The results revealed that SiO2 nanoparticles may affect the hydrates crystallization process. There was a compact structure in the CAC paste with CS, while petal-shaped hydrates with a porous structure were formed in the pure CAC paste. The maximum value of electrical conductivity for CAC paste with CS suggested that the early stage of hydration for CAC was accelerated. However, the hydration heat curves revealed that the late stage of the CAC hydration process was inhibited, and the hydration degree was reduced, this result was in accordance with Thermogravimetry-Differential scanning calorimetry(TG-DSC) curves. The fitting results of hydration heat curves further showed that the hydration degree at NG (nucleation and crystal growth) process stage was promoted, while it was limited at the phase boundaries stage, and the diffusion stage in the hydration reaction was brought forward due to the addition of CS. According to these results and analyses, the differences in the hydration process for CAC with and without CS can be attributed to the distribution and nucleation effect of SiO2 nanoparticles.

Selective catalytic reduction of NOx with NH3 is one of the most widely used technologies in denitration. Vanadium-based catalysts have been extensively studied for the deNOx process. V2O5/WO3(MoO3)TiO2 as a commercial catalyst has excellent catalytic activity in the medium temperature range. However, it has usually faced several problems in practical industrial applications, including narrow windows of operation temperatures, and the deactivation of catalysts. The modification of vanadium-based catalysts will be the focus in future research. In this paper, the chemical composition of vanadium-based catalysts, catalytic mechanism, the broadening of the temperature range, and the improvement of erosion resistance are reviewed. Furthermore, the effects of four major systems of copper, iron, cerium and manganese on the modification of vanadium-based catalysts are introduced and analyzed. It is worth noting that the addition of modified elements as promoters has greatly improved the catalytic performance. They can enhance the surface acidity, which leads to the increasing adsorption capacity of NH3. Surface defects and oxygen vacancies have also been increased, resulting in more active sites. Finally, the future development of vanadium-based catalysts for denitration is prospected. It is indicated that the main purpose for the research of vanadium-based modification will help to obtain safe, environmentally friendly, efficient, and economical catalysts.

This study investigated the effect of the sintering temperature on the microstructural evolution and properties of Al2O3–C refractory samples, which were prepared using corundum, flake graphite, reactive alumina, Al and Si powders. The phenolic resin and nanometallic Ni were respectively applied as the binder and catalyst. The results indicate that hexagonal AlN particles, generated from the reaction of Al–N2 in Al2O3 refractories at 1000 °C, could transform into whiskers at 1200 °C. By increasing the sintering temperature to 1400 °C, a large number of plate-shaped β-Sialon could be generated. Under the action of Ni catalyst, the β-Sialon phases in refractories grew preferentially toward the crystalline facets (210) and (011) of AlN crystal and formed the plate-shape structure. When plate-shaped β-Sialon formed, the cold crushing strength (CCS) and cold modulus of rupture (CMOR) increased from 90.57 MPa to 148.67 MPa and from 22.83 MPa to 33.02 MPa, respectively. After two thermal shock cycles, the CCS of the refractories containing the plate-shaped β-Sialon had only decreased by 4.5 MPa. Thus, the in situ formation of plate-shaped β-Sialon could significantly improve the thermal shock resistance of Al2O3–C refractories.

Al2O3-C refractory samples were prepared using corundum, flake graphite, Al and Si powders and phenolic resin as raw materials. The in-situ synthesis mechanism of Al5O6N in Al2O3-C refractories was studied and the effect of adding nano metallic Fe on the formation and microstructure of Al5O6N phase was also investigated. Thermodynamic calculations show that Al5O6N can potentially be synthesized in a reducing atmosphere at 1600°C over a narrow range of N2 and CO pressures. Experimental results proved that Al5O6N phase was synthesized after 1600°C heat treatment when nano Fe was added to Al2O3-C refractories. As the content of nano Fe increases, Al5O6N particles show disappearance of oriented growth, with octahedron shapes turning into spherical agglomerations.

Calcium aluminate cement with micro MgAl2O4 spinels (CMA) was prepared using a solid-state reaction. The results indicated that three mineral phases of CaAl2O4, CaAl4O7 and MgAl2O4 could be formed when the calcined temperature reaches 1300 °C. The submicron MgAl2O4 particles are homogeneously distributed among the phases of CaAl2O4 and CaAl4O7. Based on the Krstulovic–Dabic model, the hydration mechanism and kinetic parameters of calcium aluminate cement (CAC) and CMA were respectively studied by isothermal calorimetry. It was determined that the total hydration heats of CAC and CMA are, respectively, 309.756 J/g ± 15.5 and 275.496 J/g ± 13.8. The results showed that these two types of cement have the same hydration process. The nucleation and crystal growth process is the main reaction at the initial stage and then transforms into a diffusion controlled process.

In this study, La–Zn-substituted SrFe12O19 ferrites were synthesized using the traditional ceramic process. The by-products of iron oxide scales from a steel plant were used as the main raw materials. The influence of the La–Zn substituent and the calcination temperature on the microstructure and magnetic properties of Sr1 − x La x Fe12 − x Zn x O19 ferrites was investigated. The results showed that with the increase in the x value, the crystalline lattice constant of the a- and c-axes and the cell volume decreased. There was no α-Fe2O3 phase in the ferrites when the value of x was 0.3. The corresponding saturation magnetization (M s) and remnant magnetization (M r) values were, respectively, about 65 emu g− 1 and 39.5 emu g− 1. Both values of M s and M r rise to the maximum value. When the calcination temperature was reduced from 1200°C to 1150°C, the average particle size decreased from 0.9 μm to 0.7 μm and M s remained at 65 emu g− 1. However, the coercivity increased from 2690 Oe to 3100 Oe.

The effect of adding Fe nanosheets on the microstructure of phenol resin and low-carbon MgO–C refractories was investigated. The results indicate that well-crystallised carbon nanotubes (CNTs) of 50–100 nm in diameter and of micrometre scale in length could be generated at 1000 °C. The yield of CNTs decreases and the diameter of CNTs increases significantly as the coking temperature increases. The growth mechanism of vapour–solid (V–S) is transformed into the vapour–liquid–solid (V–L–S) mechanism at 1200 °C for CNTs in low-carbon MgO–C refractories. The mechanical properties and thermal shock resistance at 1000–1400 °C of the specimens with 0.5 wt% Fe nanosheets are greatly improved compared with specimens without Fe nanosheets. The largest magnitudes in the cold crushing strength (CCS), the cold modulus of rupture (CMOR), the hot modulus of rupture (HMOR), and the residual cold modulus of rupture (CMOR st ) are 25%, 44%, 24%, and 30%, respectively. The results are attributed to in situ formation of CNTs and the subsequent generation of bridging and crack deflection mechanisms in the matrix. However, as the coking temperature increases, the yield of the CNTs becomes lower and their diameter becomes larger. Thus, the favourable contribution on the thermal shock resistance decreases gradually.

The spalling and corrosion during the thermal cycles are the main causes of the damages observed in Al 2 O 3 SiC C castable composites that are used in molten-iron system. Using the catalyst of nano Ni and ball pitch in the matrix, Al 2 O 3 SiC C castable composites were prepared with the anti-oxidant addition of silicon. The results indicate that the high temperature of the Al 2 O 3 SiC C castable composites can be increased by above 42%, and the thermal shock resistance can be enhanced by above 20% because the ball pitch is carbonized and releases C x H y vapor, which can be pyrolized to carbon atoms and subsequently deposited into carbon fibers under the catalyst action. The starting temperature of carbon fiber growth is approximately 900 °C, and their diameter and aspect ratio can increase with the rising temperature. The in-situ generation of carbon fibers in Al 2 O 3 SiC C castable composites can significantly improve the fibers’ thermo-mechanical properties.

This study simulated the bulk structure and surface energy of Al2O3 based on the density of states (DOS) and studied the synthesis and microstructure of one-dimensional Al2O3 whiskers. The simulation results indicate that the (001) surface has a higher surface energy than the others. The growth mechanism of Al2O3 whiskers follows vapor–solid (VS) growth. For the (001) surface with the higher surface energy, the driving force of crystal growth would be more intense in the (001) plane, and the alumina crystal would tend to grow preferentially along the direction of the (001) plane from the tip of the crystal. The Al2O3 grows to the shape of whisker with [001] orientation, which is proved both through modeling and experimentation.