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Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material, phenolic resin as the binder, aluminum powder (2%, 4%, and 6% by mass) and silicon powder (when Al powder addition is 4%, Si powder addition varies: 1% and 2%, by mass) as additives. The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures (1 000, 1 400, and 1 600 ℃ for 3 h) were studied. The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1 000 or 1 400 ℃, and meanwhile AlN reinforcement phase forms in the matrix, which greatly improves the hot modulus of rupture of the samples at 1 400 ℃; however, the heat treatment at 1 600 ℃ has little influence on the strength; the addition of Al powder and Si powder results in the formation of low melting point phases, greatly reducing the hot modulus of rupture. However, the low melting point phases promote sintering, which enhances the density and the cold modulus of rupture, and decreases the volume change during heating. The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only. [ABSTRACT FROM AUTHOR]

To extend the service life of the upper checker bricks in the regenerator of glass furnaces with petroleum coke as fuel, the corrosion resistance of magnesia-chrome and alumina-chrome bricks with the similar apparent porosity was systematically researched. The results show that the Cr2O3 content and the microstructure present significant effects on the corrosion resistance. The molten corrosion reagent forms silicate and vanadate phases with low melting points between MgO crystals in magnesia-chrome bricks, and the volume strain generated by the melting and solidification process leads to the cracking and spalling of refractories, which intensifies the corrosion process. The encapsulation of alumina particles by alumina-chrome solid solutions in alumina-chrome bricks avoids contact with the low melting point liquid phases and improves the corrosion resistance of refractories. [ABSTRACT FROM AUTHOR]

A novel strategy was exploited for the fabrication of AlN–AlON refractories via nitrogen gas pressure sintering of Al4O4C. The phase transformation and microstructure evolution during the reaction at 1600–1800°C were thoroughly investigated. The results indicated that the high N2 pressure was essential for the effective nitridation. The in situ generated AlN–AlON refractories had a homogeneous local chemical composition, and the (101) plane of AlN and the (222) lattice plane of Al5O6N were bonded at their grain boundary with no amorphous phase. The as‐fabricated AlN–AlON refractories treated at 1700°C by a 20 atm nitrogen pressure exhibited an optimum bending strength of 111.10 MPa, combining an apparent porosity of 20% with a low bulk density of 1.97 g/cm3. The diffusion of the generated oxygen led to an increase in the apparent porosity and decrease in the bulk density at 1800°C. Furthermore, the fabrication mechanism of AlN–AlON refractories under the nitrogen gas‐pressure was discussed. [ABSTRACT FROM AUTHOR]

The fracture toughness and thermal insulation capacity of foam glass are of critical importance for its application as insulation lining of industrial flue, pipeline, and buildings. However, the nonuniform pore size distribution, significant brittleness, and low ability to hinder infrared radiation transfer lowered its mechanical properties and thermal insulation capacity. Therefore, the present work introduced a small amount of K2Ti6O13 whiskers (PTW) into foam glass to overcome these problems. The microstructure, mechanical properties, and thermal insulation ability of PTW containing foam glass were investigated. The results show that the introduced PTW improved the pore size distribution uniformity during the foaming process. The controlled structure and inhibited crack propagation by PTW contributed to the significantly enhanced mechanical strength and fracture toughness. Porosity was the key factor affecting the thermal insulation ability of samples at low temperatures, while the thermal conductivity of samples at above 400 ℃ was greatly decreased owing to the high infrared radiation reflectance of the introduced PTW. Compared with foam glass without PTW addition, both the maximum cold modulus of rupture (5.1 MPa) and optimized thermal conductivity (0.044–0.061 W/m·K at 25–800 ℃) were obtained in the sample added with 5 wt.% PTW foamed at 820 ℃. The researched high mechanical strength, fracture toughness, and thermal insulation foam glass exhibit huge prospects as insulation lining in the practical engineering fields. [ABSTRACT FROM AUTHOR]

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material, phenolic resin as the binder, aluminum powder (2%, 4%, and 6%, by mass) and silicon powder (when Al powder addition is 4%, Si powder addition varies:1% and 2%, by mass) as additives. The effects of the aluminum powder and silicon powder addition on the properties and the microstructure of the refractories heat treated at different temperatures (1 000,1 400,and 1 600 °C for 3 h) were studied. The results show that the Al powder addiiion can greatly enhance the cold modulus of rupture of the samples fired at 1 000 or 1 400 °C,and meanwhile AlN reinforcement phase forms in the matrix, which greatly improves the hot modulus of rupture of the samples at 1 400 °C; however, the heat treatment at 1 600 °C has liitle influence on the strength; the addition of aluminum powder and silicon powder result in the formation of low melting point phases, greatly reducing the hot modulus of rupture. However, the low melting point phases promote sintering, which enhances the density and the cold modulus of rupture, and decreases the volume change during heating. The specimens added with aluminum and silicon all have higher cold modulus of rupture than those added with Al powder only. [ABSTRACT FROM AUTHOR]

Yttrium ferrite (YFeO3) is highly attractive as a promising multiferroic material and also has been proven to have potential in the field of near-infrared reflective cold pigments. In this work, YFeO3 powders were fabricated via metal citrate xerogel mediated molten salt procedure at different temperatures. The complexation process of the metal citrate xerogel as a precursor was promoted by the salt medium, and the molten salt medium reduces the reaction temperature to obtain morphologically distinctive YFeO3 without impurity. The orange YFeO3 powders possessed outstanding near-infrared reflection characteristics and high solar reflectance. The relationship of particle size, particle shape, charge state distribution, magnetic performance and near-infrared reflection performance of YFeO3 was investigated. Specifically, with the increase of calcining temperature, particle size increases, thereby increasing the infrared reflectivity. The rising in the amount of Fe2+–Fe3+ ion pairs increased the absorption of free carriers, thereby reducing the infrared reflectivity. The two factors contributed together to the near-infrared reflectivity, which first increased and then decreased with the increase of calcining temperature. In addition, the increase in the ratio of Fe2+ also hindered the super-exchange and Dzyaloshinskii–Moriya interaction of Fe–O–Fe, thereby improving of the weak-ferromagnetic behavior of YFeO3. [ABSTRACT FROM AUTHOR]

Corundum porous materials with different contents of calcium hexaluminate formed in situ were prepared using pure calcium aluminate cement as the calcium source. The surface fractal dimensions of the porous materials were calculated based on the experimental data of mercury intrusion. Correlations between pore structural parameters and the permeability coefficients k1 and k2 of the porous materials were then studied based on the grey system theory. The results showed that pores in the corundum porous materials have great fractal characteristics. The surface fractal dimension was a significant pore structural parameter that reflected the complexity of pore shape, pore surface, and pore‐size distribution, which had the maximum correlation coefficient with the permeability of this type of porous materials. The apparent porosity and pore‐size distribution had relatively high correlation coefficients to the permeability as well. Increasing the apparent porosity and the volume percentage of larger pores, and decreasing the volume percentage of smaller pores all benefited the permeability of the porous materials. In addition, the mean pore size and median pore size showed lower correlation coefficients to the permeability—especially for porous materials with a wide pore‐size distribution. [ABSTRACT FROM AUTHOR]

The structure, magnetic properties and charge state of Al/Bi-substituted YMn0.8Fe0.2O3 were investigated. The Y(Mn0.8Fe0.2)0.95Al0.05O3 and Y0.95Bi0.05Mn0.8Fe0.2O3 solid solutions all exhibited the hexagonal P63cm space group, similar to YMnO3. The magnetic structures of Al-substituted YMn0.8Fe0.2O3 were not uniform, and were predominantly antiferromagnetic with weak ferromagnetic properties at low temperatures. The ratios Mn2+:Mn3+ and Fe2+:Fe3+ noticeably decreased upon Al substitution in YMn0.8Fe0.2O3, and the magnetic transition temperature was reduced dramatically. The cluster glass state behavior observed in Y(Mn0.8Fe0.2)0.95Al0.05O3 was absent in the case of Y0.95Bi0.05Mn0.8Fe0.2O3, which indicated weakened ferromagnetic interactions in the latter. This may be related to the decreased oxygen content in Y0.95Bi0.05Mn0.8Fe0.2O3. Bismuth substitution can strengthen the antiferromagnetic interactions in YMn0.8Fe0.2O3. [ABSTRACT FROM AUTHOR]

Dielectric and magnetic properties of Zr substituted YMnFeO ceramics were investigated in this work. Single phase in space group of P6cm and homogeneous microstructure were identified in the YZrMnFeO ceramics, while small amount of secondary phase located at the grain boundary was detected in the YZrMnFeO ceramics. Compared with YMnFeO, the significantly reduced room-temperature dielectric loss was obtained in the YZrMnFeO ceramics, and this improvement has great scientific significance for the potential applications of multiferroic materials. The XPS analysis results confirmed that Fe ions disappeared and the Mn content was obviously decreased, when 5 at.% Zr was introduced to the Y sites of YMnFeO. The reduced Mn and Fe ions contents led to the obviously reduced dielectric loss of YZrMnFeO ceramics. The existence of enhanced weak ferromagnetic properties and cluster glass state behavior at low temperature was detected in Zr substituted YMnFeO ceramics. The present work suggests a promising YMnO based multiferroic ceramics with reduced room-temperature dielectric loss. [ABSTRACT FROM AUTHOR]

The crystal structure, valence state of magnetic ions and magnetic properties of Y0.98Sr0.02Mn0.8Fe0.2O3ceramics were investigated. The results showed that the same ferroelectric hexagonal structure as YMnO3was maintained in the present Y0.98Sr0.02Mn0.8Fe0.2O3ceramics. Compared with YMnO3, the magnetic transition temperature of Y0.98Sr0.02Mn0.8Fe0.2O3was enhanced and the valence state of Mn ions was increased. In Y0.98Sr0.02Mn0.8Fe0.2O3ceramics, Fe ions presented the valence state of +2 and +3. The enhanced magnetic properties should be related to the ferromagnetic double-exchanges between Mn4+and Mn3+ions. [ABSTRACT FROM AUTHOR]

YCeMnFeO (x = 0, 0.05 and 0.1) solid solution ceramics were prepared and the magnetic, dielectric and electrical properties were investigated. The structures of the present ceramics were maintained in hexagonal P6cm space group as the ferroelectric YMnO. The magnetic structures of the solid solution ceramics were not uniform, and all the compositions were predominantly antiferromagnetic with weak ferromagnetic properties at low temperature. The antiferromagnetic transition temperatures of the present ceramics were decreased upon Ce substitution, originating in the weakened antiferromagnetic exchange interactions of Mn ions. Varied valence distributions of Fe and Mn ions led to the effective paramagnetic moment decreasing with Ce introduction. Compared with YMnFeO, the dielectric loss of YCeMnFeO ceramics was reduced and the resistivity was enhanced, which should be related to the decreased Mn content in the mixed structure of Mn ions. Whereas, the presence of Mn-Mn ions pair led to the increased conductivity and dielectric loss in the YCeMnFeO ceramics. [ABSTRACT FROM AUTHOR]

The effects of the oxidation treatment (in air atmosphere at 400,600 and 800 °C for 3 h) of Si3N4 powder synthesized by self-propagating combustion and the types of dispersants (sodium polyacrylate, sodium hexametaphosphate, trimerization sodium phosphate, and calcium lignosulfonate) on the anti-settling, the zeta potential and the viscosity of the Si3N4 slurries were investigated. The results show that:(1)after the oxidation treatment in air atmosphere at 800 °C for 3 h, the Si2N2O content in the obtained powder increases;the corresponding slurry has the best stability, large zeta potential absolute value and the smallest viscosity;(2)the Si3N4 slurry prepared with sodium hexametaphosphate as dispersant has good stability, the highest zeta potential absolute value and the lowest viscosity;(3)the Si3N4 slurry prepared with 0.021% sodium hexametaphosphate has the highest zeta potential absolute value and low viscosity. [ABSTRACT FROM AUTHOR]