Liugang Chen

Effect of B2O3 on Volume Stability and Strength of Corundum-based Castables

Abstract Calcium aluminate cements (CAC) with 0.21 wt% B2O3 and without B2O3 were used as binders of corundum-based castables. The properties of the castables with and without B2O3 after heat treatment at 110 °C, 1,100 °C and 1,450 °C were investigated, with emphasis on studying the effect of B2O3 in CAC on the volume stability and high temperature strength of the castables. It is found that a very small amount (about 0.01 wt%) of B2O3 introduced by the cement alleviates the expansion of the castables after firing at 1,450 °C and decreases the high-temperature strength of castables as the presence of B2O3 should generate liquid phase.

Al-O-Si Bond Formation in Boehmite-Fumed Silica Mixtures during Mechanochemical Activation

Al-O-Si bond formation in boehmite-fumed silica mixtures during mechanochemical activation was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), magic angle spinning nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). The intrinsic structure deformation of the boehmite was examined with XRD. Formation of new Al-O-Si bonds was illustrated by the incorporation of Al3+ in Si-O-Si linkages, the change in the Al coordination number of boehmite, and the appearance of new resonance in the 29Si NMR spectrum of the ground mixture. The presence of Al-O units in silica frameworks was verified by the increase of Al 2p binding energy and the decrease of Si 2p binding energy.

Influence of high-energy ball milling and additives on the formation of sphere-like α-Al2O3 powder by high-temperature calcination

Abstract In comparison with the typically worm-like α-Al2O3 powders formed from an unground Al(OH)3 precursor calcined at 1450°C, spherical α-Al2O3 powders with ~1 μm in size were prepared by the calcination of a ground Al(OH)3 precursor with 5 wt.% [NH4]+BF4− under the same calcination conditions. The influence of a high-energy ball milling pretreatment as well as of the additives on the morphological evolution of α-Al2O3 powders was studied using the commercial precursor Al(OH)3 as raw material. The results indicate that the morphology of α-Al2O3 powders is closely related to the morphology of the Al(OH)3 precursor and to the introduction of different additives. The refinement of the Al(OH)3 precursor in aggregate size and of the primary crystal size by high-energy ball milling has effectively suppressed the neck growth of α-Al2O3 grains. In contrast to the findings made previously with the introduction of 5 wt.% [NH4]+Cl−, the morphology of the α-Al2O3 particles could be significantly improved from a ground Al(OH)3 precursor with the addition of 5 wt.% [NH4]+BF4−, which resulted in the formation of spherical α-Al2O3 powders with 1 μm size at 1450°C.

Theoretical Prediction and Synthesis of (Cr2/3Zr1/3)2AlC i-MAX Phase

Guided by predictive theory, a new compound with chemical composition (Cr2/3Zr1/3)2AlC was synthesized by hot pressing of Cr, ZrH2, Al, and C mixtures at 1300 °C. The crystal structure is monoclinic of space group C2/ c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr2/3Zr1/3)2AlC stoichiometry, with secondary Cr2AlC, AlZrC2, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (Cr2/3Zr1/3)2AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr2/3Hf1/3)2AlC, of the same structure, was predicted to be stable.

Influences of NH4F additive and calcination time on the morphological evolution of α-Al2O3 from a milled γ-Al2O3 precursor

Abstract The influences of an NH4F additive content and calcination time on the morphological evolution of α-Al2O3 were investigated by using commercial γ-Al2O3 precursor as raw material. The results showed that the morphological evolution of α-Al2O3 was highly related to the addition of NH4F, the additive content, and the calcination time. Square-like α-Al2O3 powders with a primary crystal size of ~200 nm were formed from the milled γ-Al2O3 precursor with 1 wt.% NH4F at 1300°C for 2 h, whereas round cake-like, hexagonal platelets, slender-like, and other irregularly shaped α-Al2O3 pieces in the size range of 0.2–2 μm were synthesized from the milled γ-Al2O3 precursor with 20 wt.% NH4F addition under the same calcination. Both morphological regularity and particle size distribution of α-Al2O3 were greatly facilitated by increasing the calcination time from 2 to 5 h. The addition of NH4F may lead to an alteration of the α-Al2O3 growth process by a change in the scale of the developing microstructure.

Composition Modification of ZnO Containing Fayalite Slag from Secondary Source Copper Smelting

Fayalite based slag is formed during the smelting process of secondary copper resources. It was found that with the presence of high ZnO, the slag became viscous, causing a slag tapping problem. In the present paper, the phase relations of the slag system ZnO-“FeO”-SiO2-Al2O3-CaO (ZnO = 0–12 wt%, Al2O3% = 0–15 wt%, CaO = 0–1.5 wt%, with iron saturation) at 1150 °C is studied by using quenching technique followed by phase identification and compositional analysis of equilibrated samples. The dependence of FeO and Al2O3 solubility in the liquid slag on the chemical composition of slag is characterized. Based on the experimental data, the solid fraction of the slag, which may considerably, influences the slag viscosity, at the tapping temperature can be reasonably estimated and, therefore an appropriate modification of the slag composition can be made.

Freeze‐Lining Formation from Fayalite‐Based Slags

Formation of freeze-linings from aggressive process slags is used in industrial pyrometallurgical processes to protect the furnace wall. In this laboratory study, the formation of freeze-linings from fayalite-based (FeO-SiO2-Al2O3-CaO) slags was investigated. This was performed with a gas-cooled probe at 1200 °C under protective atmosphere. The microstructure of the freeze-linings formed on the samples was characterized using scanning electron microscopy (SEM). The influence of cooling rate, slag agitation and slag composition on the freeze-lining formation was studied by varying the gas-flow rate, rotating the crucible and changing the CaO and Al2O3 contents in the fayalite-based slag, respectively. The results indicate that fayalite (Fe2SiO4) precipitated from the slag and grew into large columnar crystals along the heat gradient from the cooled probe to the bath slag. The thickness of the freeze-lining increased with increasing cooling rate, while an increase in the slag agitation and the CaO and Al2O3 contents in the slag decreased the thickness of the freeze-lining. These macroscopical observations are discussed with respect to the microstructural evolution in the formed freeze-lining samples.

Rheological behavior of fayalite based secondary copper smelter slag in iron saturation

A fayalite based slag is formed during the smelting process of secondary copper containing resources. Of particular importance is the slag viscosity which quantifies the flow properties of the slag and affects the reaction kinetics, the refractory corrosion in the smelter and operational practice. In the present work, a high temperature rheometer system has been employed to study the rheological behavior of the industrial slag system FeO-ZnO-SiO2-Al2O3-CaO (FeO/SiO2 = 1–1.5, ZnO = 6–8 wt %, CaO = 1.5 wt % and Al2O3= 4.5 wt %) at 1150 °C with iron saturation. The slag behaves as a shear thinning fluid. The degree of shear thinning was quantified by fitting the flow curve with the Oswald-De Waele power law model. The relation between the slag composition and the flow behavior index has been discussed.

Mg-O-Si chemical bond formation in light burned magnesia and fumed silica mixture during mechanical activation

Mg-O-Si chemical bond formation in a light burned magnesia (MgO) and fumed silica (SiO2) mixture during mechanical activation was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), magic angle spinning nuclear magnetic resonance (MAS-NMR), and X-ray photoelectron spectroscopy (XPS). Crystallinity and intrinsic structure changes of the starting mixture during high-energy milling were examined by XRD. The formation of new Mg-O-Si chemical bonds of the ground mixture was illustrated by the incorporation of Mg2+ in Si-O-Si linkages, the appearance of new resonance in the 29Si NMR spectrum and the decrease of the Si 2p binding energy. The formation of Mg-O-Si chemical bonds created during grinding partly contributed to the lowered temperature of complete forsterite formation from 1400 to 1100°C.