Guibo Qiu

Synthesis and characterization of glass-ceramics prepared from high-carbon ferrochromium slag

Glass-ceramics have been successfully prepared from high-carbon ferrochromium slag (HCFS) and waste glass (WG), and the microstructural characterization and mechanical properties of the glass-ceramics were subsequently investigated. The development of HCFS-based glass-ceramics involves the nucleation and crystallization stages from the parent glass. With the increase in mass ratio of HCFS and WG (R(H/W)) from 0.60 to 1.67, the number of bridging oxygens of Si in the parent glass is reduced, as shown via Raman spectroscopy. Thus, their degree of polymerization decreases with it, and the temperature of nucleation and crystallization increase, which is consistent with the DSC results. The SEM images and EDS results indicate that the increasing value of R(H/W) decreases the crystal grain size and consequently increases the microhardness of the glass-ceramics. But the porosity simultaneously increases, which makes the bending strength increase at first and subsequently decrease. And the optimum properties of HCFS-based glass-ceramic samples in the present work are obtained when R(H/W) reaches 1.29, that is, a bending strength of 104 MPa and a microhardness of 9860 MPa.

Preparation and characterization of regenerated MgO-CaO refractory bricks sintered under different atmospheres

Regenerated MgO-CaO brick samples containing 80wt%, 70wt%, and 60wt% MgO were prepared using spent MgO-CaO bricks and fused magnesia as raw materials and paraffin as a binder. The bricks were sintered at 1873 K for 2 h under an air atmosphere and under an isolating system. The microstructure, mechanical properties at room temperature, and hydration resistance of the regenerated samples were measured and compared. The results indicated that the isolating sintering generated a strongly reducing atmosphere as a result of the incomplete combustion of paraffin, and the partial oxygen pressure was approximately 6.68 × 10−7 Pa. The properties of the regenerated bricks sintered under air conditions were all higher than those of the bricks sintered under a reducing atmosphere. The deterioration of the bricks was a result of MgO reduction and a decrease in the amount of liquid phase formed during sintering under a reducing atmosphere.

Dispersion Characterization of Short Slag Fiber in Aqueous Solution

Slag fiber with desirable properties is a promising candidate for applications as fillers or reinforced materials. Its poor dispersion in bulk materials, however, becomes the major challenge. Some aspects of its physicochemical properties were focused upon in the present article. The effect of three kinds of dispersants, viz., sodium carboxymethyl cellulose (CMC), anionic polyacrylamide (APAM), and cationic polyacrylamide (CPAM), as well as their combinations on the dispersion of slag fiber in aqueous solution was investigated. The viscosities of fiber suspensions were measured and the results were correlated with the dispersion of suspensions. It was shown that the slag fiber appeared amorphous, smooth surface with high length/diameter (L/d) ratio and negatively charged in water. The dispersion of slag fiber in aqueous solution directly depended on the dispersants. The optimal uniform and stable fiber suspension could be achieved under the dispersant concentration of the combination of 2 wt% CMC and 0.25 wt% APAM. In this case, the fiber concentration was as large as 25 g/L. In addition, the plausible dispersion mechanism of slag fiber in aqueous solutions was elucidated based on the electrostatic steric stabilization. GRAPHICAL ABSTRACT

High mercury leachate containing HgS 2 2− complex ion: Detoxifying solidification and high efficiency Hg extraction

Clean and efficient treatment of high-mercury leachate produced from remediation of mercury-polluted soil has become a huge challenge for environmental scientists. In this work, cement solidification was firstly adopted to treat the high-concentration mercury leachate, which had high alkalinity. Different mercury concentrations, namely 3.120mg/L Hg mercury leachate and 9.243mg/L Hg mercury concentrated leachate, were separately solidified by Portland cement. The results indicated that simply using the cement can properly solidify both the leachates to meet the waste landfill standard, with liquid (mL)/solid (g) ratio (L/S ratio) of 4:10-6:10. In order to make full use of mercury in the leachates, a Hg extraction method was subsequently carried out under different experimental parameters, such as temperature and pH value. It was shown that the Hg extraction ratio could reach as high as 99.84% and almost all the mercury in the leachate could be transformed to HgS precipitate; moreover, the Hg concentration in the treated leachate was reduced from 3.120 to 0.005mg/L at pH2.98 and 30°C, which was much less than the limit of the national standard, indicating that the leachate had been completely cleaned and could be discharged freely. Hence, simple cement solidification renders high-mercury leachate nontoxic, and the Hg extraction method can successfully recover the Hg and enable the residual leachate to be discharged safely.

Properties of regenerated MgO–CaO refractory bricks: Impurity of silicon dioxide

Abstract Regenerated MgO–CaO refractory brick samples with 0, 1·5, 3·0 wt-% SiO2 addition were prepared by using spent MgO–CaO bricks and fused magnesia as raw materials. Their phases, microstructures and flexural strength at room and 1573 K were investigated, respectively, and the maximum content of SiO2 impurity in regenerated samples had been subsequently achieved. The results showed that main phases of regenerated samples were all MgO, free CaO (f-CaO), Ca3SiO5 (C3S) and Ca2FeAlO5. Because some Al3+, Fe3+ had dissolved in the crystal lattice of C3S, it resulted in the decreasing of content of f-CaO and low melting point phase of C4AF along with the increasing of SiO2 addition, moreover, the flexural strength of regenerated samples at room temperature reduced while flexural strength at 1573 K enhanced. The maximum content of SiO2 impurity was about 4·11 wt-% in regenerated samples considering their properties for cement kiln.

Low-temperature-controlled synthesis and growth mechanism of AlN whiskers

Abstract Aluminium nitride whiskers were successfully synthesised by direct nitridation of Al and Al2O3 in graphite crucible under nitrogen atmospheres. The influence of reaction conditions such as molar ratio of Al:Al2O3 and reaction temperature on the formation of the AlN whiskers have been investigated in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction and energy-dispersive X-ray spectroscopy. Through characterising the microstructure and phase constitution of the as-prepared samples, the optimum synthesis conditions of the AlN whiskers were obtained. Moreover, the growth mechanism of AlN whiskers was discussed combining thermodynamic analysis indicating that the AlN whiskers could be grown via vapour–liquid–solid mechanism.