Preparation of glass-ceramics with low density and high strength using blast furnace slag,glass fiber and water glass

To reduce the production costs of glass-ceramics and broaden the application field of solid waste in steel industry, low-density and high-strength glass-ceramics were produced by using blast furnace slag as the basic material, choosing glass fiber and water glass as the strengthening agents. The effects of glass fiber and water glass on the phase composition, microstructure, apparent density, water absorption and compressive strength of glass–ceramics were investigated. The results show that the rod structure of glass fiber can be retained in the sintered samples and high content of diopside and augite significantly improve the compressive strength of glass-ceramics. Tiny spherical crystalline phases can be obtained for the glass-ceramics soaked in the moderate concentration of water glass. The BGW-2 samples fabricated with 70% blast furnace slag, 30% glass fiber and 4% water glass, exhibit excellent comprehensive properties. The bulk density, water absorption and compressive strength of BGW-2 are 1.76 g/cm³, 2.26% and 68 MPa, respectively. Consequently, using blast furnace slag to prepare glass-ceramics can be another applicable way to utilize blast furnace slag efficiently.     

The direct experimental observation and solidification mechanism of heavy metals in blast furnace slag glass-ceramics

Glass-ceramics with high performance and high crystallinity was produced using rare earth blast furnace slag (REBFS) as the primary raw material, along with composite nucleating agents Fe₂O₃ and Cr₂O₃. The migration pattern, distribution characteristics, and solidification properties of heavy metals in glass-ceramics were investigated by the controlled heat treatment. The findings indicated that the heat treatment temperature has a significant effect on the distribution and color of heavy metals in glass-ceramic. In the crystallized glass-ceramic, spinel acts as the crystal core for heavy metal solidification, Cr, Cu, and Mn can exist stably in the spinel by the solid solution. The glass-ceramic was expected to be used as a decorative building material.     

Bulk nucleated fine grained mono-mineral glass-ceramics from low-silica fly ash

Cr₂O₃-nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-silica fly ash and additives of SiO₂, Al₂O₃ and MgCO₃, via two steps of heat treatment for nucleation and crystal growth. The starting glass approached the composition of CaMg_0.75Al_0.4Fe_0.1Si_1.75O₆, derived from CaMg_0.75Al_0.5Si_1.75O₆, which belongs to diopside – Ca-Tschermak solid solutions. The influence of Cr₂O₃ (up to 0.75 wt.%) on the development of crystalline phases, the properties and the microstructure of the resultant glass-ceramics crystallized at different temperatures was investigated.     

Dissolution behavior of a novel Al2O3-SiC-SiO2-C composite refractory in blast furnace slag

Al₂O₃-SiC-SiO₂-C composite refractories are interesting potential blast furnace hearth lining materials that feature several advantageous properties. In this study, the corrosion resistance of a novel Al₂O₃-SiC-SiO₂-C composite refractory to blast furnace slag was investigated by adopting a rotating immersion method (25 r/min) at 1450–1550 °C and comparing it against a conventional corundum-based refractory at 1550 °C as a benchmark. The results showed that the apparent activation energy of Al₂O₃-SiC-SiO₂-C composite refractory over the dissolution process in the slag is 150.4 kJ/mol. Dissolution of the Al₂O₃ and 3Al₂O₃·2SiO₂ phases appeared to be the main cause of Al₂O₃-SiC-SiO₂-C composite refractory corrosion. High-melting-point compounds in the slag layer formed a protective layer which mitigated the corrosion. The novel Al₂O₃-SiC-SiO₂-C composite refractory is better suited to blast furnace hearth lining than the conventional corundum-based refractory, because the carbon phase and SiC phase in the material are not readily wetted by the blast furnace slag and therefore are more resistant to slag penetration. Higher melting point phases also may crystallize on the hot face of the hearth lining due to the high thermal conductivity of the Al₂O₃-SiC-SiO₂-C composite refractory, promoting a more stable protective layer.     

Dehydration of 2,3-butanediol into 3-buten-2-ol catalyzed by ZrO2

Vapor-phase catalytic dehydration of 2,3-butanediol was investigated over metal oxides such as CeO₂, La₂O₃, Yb₂O₃, ZrO₂, Al₂O₃, TiO₂, ZnO, Fe₂O₃, NiO, and Cr₂O₃. In the dehydration of 2,3-butanediol, 3-buten-2-ol was preferentially produced over monoclinic ZrO₂ along with major by-products such as butanone and 3-hydroxy-2-butanone. Over ZrO₂ calcined at 900 °C, 3-buten-2-ol was produced with a maximum selectivity of 59.0% at 300 °C without producing 1,3-butadiene.     

Photooxidation of iodide ion on some semiconductor and non-semiconductor surfaces

In 80% aqueous ethanol, TiO₂ (anatase), ZrO₂, ZnO, V₂O₅, Fe₂O₃ and Al₂O₃ photocatalyze the oxidation of iodide ion but CdO and CdS do not; the wavelength of illumination is 365 nm. However, Fe₂O₃ fails to bring in a sustainable photocatalysis in 60% aqueous ethanol. The photooxidation of iodide ion on TiO₂, ZrO₂, ZnO, V₂O₅ and Al₂O₃ in 60% aqueous ethanol was studied as a function of [I⁻], amount of catalyst suspended, airflow rate, light intensity and solvent composition. The metal oxides examined show sustainable photocatalytic activity. Iodine formation is larger with illumination at 254 nm than at 365 nm. The mechanisms of photocatalysis on semiconductor and non-semiconductor surfaces have been discussed. Photocatalytic generation of iodine has been analyzed using a kinetic model. The photocatalytic efficiencies are of the order V₂O₅ > TiO₂ > ZrO₂ > ZnO > Al₂O₃ and V₂O₅ > TiO₂ > ZrO₂ > ZnO=Fe₂O₃ > Al₂O₃ in 60% and 80% aqueous ethanol.     

Indirect mineral carbonation of titanium-bearing blast furnace slag coupled with recovery of TiO2 and Al2O3

Large quantities of CO_2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO_2 emission reduction and comprehensive utilization of the solid waste.This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace(TBBF) slag,in which the TBBF slag is roasted with recyclable(NH_4)_2SO_4(AS) at low temperatures and converted into the sulphates of various valuable metals, including calcium, magnesium, aluminium and titanium. High value added Ti-and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH_3 produced during the roasting is used to capture CO_2 from flue gases. The NH_4HCO_3 and(NH_4)_2CO_3 thus obtained are used to carbonate the CaSO_4-containing leaching residue and MgSO_4-rich leaching solution, respectively. In this study, the process parameters and efficiency for the roasting, carbonation and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium,magnesium, titanium and aluminium reached 92.6%, 87% and 84.4%, respectively, after roasting at an AS-to-TBBF slag mass ratio of 2:1 and 350 °C for 2 h. The leaching solution was subjected to hydrolysis at 102 °C for 4 h with a Ti hydrolysis ratio of 95.7% and the purity of TiO_2 in the calcined hydrolysate reached 98 wt%.99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH_3. The carbonation products of Ca and Mg were CaCO_3 and(NH_4)_2 Mg(CO_3)_2·4H_2O, respectively. The latter can be decomposed into MgCO_3 at 100–200 °C with simultaneous recovery of the NH_3 for reuse. In this process, approximately 82.1% of Ca and 84.2%of Mg in the TBBF slag were transformed into stable carbonates and the total CO_2 sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO_2 obtained can be used directly as an end product, while the Al-rich precipitate and the two carbonation products can act, respectively, as raw materials for electrolytic aluminium,cement and light magnesium carbonate production for the replacement of natural resources.     

Development of a new glass–ceramic by means of controlled vitrification and crystallisation of inorganic wastes from urban incineration

This paper reports the results of a study of the feasibility of recycling the solid residues from domiciliary waste incineration by producing a glass-ceramic. The major components of the raw material (TIRME F+L), which was from a Spanish domiciliary incinerator, were CaO, SiO₂ and Al₂O₃ but nucleating agents, such as TiO₂, P₂O₅, and Fe₂O₃ were also present in reasonable amounts. It was found that a relatively stable glass with suitable viscosity could be obtained by mixing 65 wt% TIRME F+L with 35 wt% glass cullet. The heat treatment required to crystallise the glass produced from this mixture, designated TIR65, was nucleation at 560°C for 35 min followed by crystal growth at 100°C for 120 min. The resulting glass-ceramic contained a number of crystalline phases, the most stable being clinoenstatite (MgSiO₃), or perhaps a pyroxenic phase which incorporates Ca, Mg and Al in its composition, and åkermanite (Ca₂MgSi₂O₇). The microstructure contained both fibre-like and dendritic crystals. The mechanical properties were acceptable for applications such as tiles for the building industry. ©     

Sinter-crystallisation in the diopside–albite system: Part I. Formation of induced crystallisation porosity

The sinter-crystallisation was investigated in three model glasses (G1, G2 and G3) belonging to the diopside–albite system and forming between 30 and 60% diopside, respectively. The effect of bulk crystallisation on the sintering was studied by the addition of 0.7 wt.% Cr₂O₃ as nucleating agent to the G2 glass.The degree of sintering was evaluated by the variation of the apparent density while the crystallisation, by the increasing of the absolute density. The structure and morphology of the sintered glass-ceramics was observed by SEM-BSE.The results highlighted that the densification is not influenced by the variation of the composition among the three glasses but is inhibited by the diopide formation in G2-Cr where bulk nucleation takes place. It was shown that, due to the volume variation related to the diopside crystallisation, a spherical intragranular pores were formed in the glass-ceramics. The amounts of this porosity, named induced crystallisation porosity, increased as function of the crystallisation trend.     

Effect of annealing on the structure and magnetic properties of mechanically milled TiO2–Fe2O3 mixture

A mixture of Fe₂O₃ and TiO₂ oxides has been mechanically milled to form TiFe₂O₄ spinel phase. X-ray diffraction (XRD) pattern of the as-milled mixture shows the presence of both Fe₂O₃ and TiO₂ phases. The diffraction peaks become broader and their relative intensity drastically decreases due to the particle size reduction and accumulation of strains. The milled powder was then subjected to annealing at different temperatures (600, 750, 900, 1200 °C). Annealing at 600 °C and 750 °C does not show any significant change in the phase formation. Nonetheless, XRD patterns show a narrowing and an increase in the intensity of Fe₂O₃ peaks with respect to TiO₂, which was reflected by an evolution in particle nano-structure following SEM analysis. An increase in the intensity ratio of the major peaks belonging to Fe₂O₃ relative to the as-milled mixture, which was associated with a reduction of the amount of TiO₂, suggested a possible insertion of Ti into the Fe₂O₃ crystal lattice. However, in VSM measurements, annealing at 600 °C and 750 °C does not change the ferromagnetic phase but the effect of annealing was a notable reduction in the values of both Ms and Mr (saturation magnetization and remanence magnetization respectively) Ultimately, as the powder was heated to 900 °C a new phase seemed to have emerged, this phase was confirmed by SEM, XRD, and magnetic measurements (VSM) where it change phase from ferromagnetic to paramagnetic phase.     

Cr2 O3、TiO2对高炉渣制备微晶玻璃晶化方式的影响

以包钢高炉渣为主要原料,采用熔融法制备CaO-SiO2-MgO-Al2O3系微晶玻璃,主要通过差热分析方法,并借助于Augis-Bennett方程和Ozawa方程研究了分别添加2%Cr2O3和8%TiO2作晶核剂时基础玻璃的晶化方式.研究结果表明:添加2%Cr2O3作晶核剂时,晶体生长指数均可实现大于3,晶化方式为整体晶化;而添加8%TiO2作晶核剂时,晶体生长指数均不可能大于3,晶化方式为表面晶化.因此,Cr2O3是高炉渣制备透辉石类微晶玻璃适宜的晶核剂成分,可单独用作晶核剂,而TiO2无法使基础玻璃整体晶化,不能单独用作晶核剂.研究结果为利用高炉渣成功研制开发透辉石类微晶玻璃在晶核剂种类选择确定方面提供了理论指导.     

The effect of Cr2O3 as a nucleating agent in iron-rich glass-ceramics

In this work, the effect of Cr₂O₃ as a nucleating agent, in iron rich glasses has been investigated by means of DTA, XRD and density measurements. By Cr₂O₃ addition, from 0·4 to 1·0 wt%, a lowering of the crystallisation peak temperature resulted in the DTA trace, the maximum effect corresponding to 0·7 wt%. By evaluating the degree of crystallisation of the glass at 0·7 wt% Cr₂O₃, the highest efficiency in the nucleation process also corresponds. The optimum values for the nucleation and crystallisation time and temperature, determined for 0·7 wt% Cr₂O₃ addition, have been 70 min at 630°C and 30  min at 800°C. The crystalline phases formed at different thermal treatment temperatures of the parent glass have been investigated by XRD; the spinel is the only phase after the nucleation; pyroxene is the major phase after the crystallisation. The results of this study have highlighted that a small percentage of Cr₂O₃ strongly affects the spinel formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallisation of high iron content glasses. ©     

Synthesis of magnetically recoverable ferrite (MFe2O4, M Co,Ni and Fe)-supported TiO2 photocatalysts for decolorization of methylene blue

Effects of ferrite materials as supports (CoFe₂O₄, NiFe₂O₄, and Fe₃O₄) on nano-TiO₂ were elucidated by their use in the oxidation of methylene blue. These photocatalysts, which were synthesized by co-precipitation, were characterized by XRD, SEM, EDS and VSM. The crystalline phase of TiO₂ onto magnetic MFe₂O₄ was formed by anatase and rutile. TiO₂/CoFe₂O₄ exhibited the strongest magnetic property of the prepared catalysts, and the photocatalytic efficiencies followed the order TiO₂/CoFe₂O₄ > TiO₂/NiFe₂O₄ > TiO₂/Fe₃O₄. MB decolorization was enhanced with the amount of TiO₂ on the photocatalyst, and was moderately affected by the extent of structural distortion of ferrite supports.     

Separation and characterisation of fused alumina obtained from aluminium-chromium slag

Aluminium-chromium slag is a by-product of the thermal reduction of aluminium during chromium smelting, which is generally considered solid waste with a low utilisation rate. In this work, a fused carbonisation reduction method has been proposed to separate the Al₂O₃ and Cr₂O₃ from the slag and produce fused alumina and chromium carbide materials for refractory applications. The thermodynamic parameters of this process were determined using a standard thermal analysis method. In the molten slag, Cr₂O₃ reacts with C to produce high-density chromium carbide, which effectively precipitates at the bottom of the reaction vessel, while Al₂O₃ is converted into the corundum phase during cooling. The results of chemical analysis showed that the Al₂O₃ content in fused alumina was greater than 95 wt%, while its main crystalline phase was the corundum with a bulk density of 3.57 g cm^?3, thermal conductivity of 6.4–7.4 W m^?1 K^?1 (at temperatures above 600 °C), and average thermal expansion coefficient of about 7.5–8.2 × 10^?6/°C (in the temperature range of 800–1300 °C).     

Promoting role of transition metal oxide on ZnTiO3–TiO2 nanocomposites for the photocatalytic activity under solar light irradiation

Transition metal oxide (Fe₂O₃, Co₃O₄ and CuO) loaded ZnTiO₃–TiO₂ nanocomposites were successfully prepared by solid state dispersion method. The structural, morphological and optical properties of samples were characterized by TGA/DTA, XRD, BET, FT-IR, DRS, PL, XPS and SEM techniques. The photocatalytic activity of samples was investigated by degradation of 4-chlorophenol in water under sunlight. The Fe₂O₃ loaded sample was found to exhibit much higher photocatalytic activity than the other composite powders. 7Fe₂O₃/ZnTi sample has the highest percentage of 4-chlorophenol degradation (100%) and highest reaction rate (1.27 mg L⁻¹ min⁻¹) was obtained in 45 min. The enhancement of photocatalytic activity for ZnTiO₃–TiO₂ sample with Fe₂O₃ addition may be attributed to its small particle size, the presence of more surface OH groups, lower band gap energy than other samples in this paper and the presence of more hexagonal ZnTiO₃ phase in the morphology.     

Synthesis of a Ti–Cr–V alloy by pulsed current assisted reaction

Preparations of a Ti–Cr–V alloy were tried by applying pulsed electric current through compacted mixtures of TiO₂, V₂O₅, Cr₂O₃ and C, and of TiH₂, Cr and V after ball-milling into fine powder. TGA and DTA curves for a mixture of TiO₂, V₂O₅, Cr₂O₃ and C showed that weight decreased up to about 1423 K. The Ti–Cr–V alloy could not be prepared from a mixture of TiO₂, V₂O₅, Cr₂O₃ and C. However, from a mixture of TiH₂, Cr and V, the Ti–Cr–V alloy formed together with phases of Cr_1.93Ti_1.07, Ti or C.     

The effect of synthesis conditions on the phase composition and structure of thorium bearing murataite ceramics

Samples of thorium-bearing ceramic with a target composition (wt%) 5 Al₂O₃, 10 CaO, 55 TiO₂, 10 MnO, 5 Fe₂O₃, 5 ZrO₂, 10 ThO₂ were produced by melting in glassy carbon crucibles in a resistive furnace and by cold crucible inductive melting (CCIM) at a vibration power of 10 kW and operation frequency of 5.28 MHz. All the samples contained 85–95 vol% murataite polytypes with 5- (5C), 8- (8C), and 3-fold (3C) elementary fluorite unit cell composing core, intermediate zone and rim of the grains, respectively, and minor crichtonite, perovskite, pyrochlore, rutile, etc. A feature of the ceramics obtained by melting in glassy carbon crucibles is formation of Fe (II) titanate whereas the inductive-melted ceramics contained traces of vitreous phase due to melt contamination with a cold crucible putty material. Melting rate in the cold crucible of up to 350 kg/(m² × h) has been achieved. The ceramics obtained have excellent chemical durability.     

The optimization of the microstructure and phase assemblage of high chromia refractories

The effect of Al₂O₃ and ZrO₂ addition in chromia-based refractories was investigated. The strength of ZrO₂-bearing chromia refractories was greatly enhanced by 4–8 wt% Al₂O₃ additive. In the range of 0–12 wt% ZrO₂ addition, 6 wt% ZrO₂ was most beneficial to the improvement in thermal shock resistance. Corrosion resistance was compared by exposing to three kinds of coal slag with various CaO contents. As the substitution of ZrO₂ for Cr₂O₃ increased, slag penetration increased, particularly in the case of the slag containing ∼16 wt% CaO. Considering the trade-offs between corrosion resistance, thermal shock resistance and mechanical properties, the optimum phase assemblage of high chromia refractories consists of the large granular Cr₂O₃ grains bonded by annular (Cr, Al)₂O₃ grains and well-distributed fine ZrO₂ grains.     

Enhanced H2S sensing performance of TiO2-decorated α-Fe2O3 nanorod sensors

Pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were synthesized via thermal oxidation of Fe thin foils, followed by the solvothermal treatment with titanium tetra isopropoxide (TTIP) and NaOH for TiO₂ nanoparticle-decoration. Subsequently, gas sensors were fabricated by connecting the nanorods with metal conductors. The structure and morphology of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were examined via X-ray diffraction and scanning electron microscopy, respectively. The gas sensing properties of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors with regard to H₂S gas were examined. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor showed a stronger response to H₂S than the pristine Fe₂O₃ nanorod sensor. The responses of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors were 2.6 and 7.4, respectively, when tested with 200 ppm of H₂S at 300 °C. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor also showed a faster response and recovery than the sensor made from pristine Fe₂O₃ nanorods. Both sensors showed selectivity for H₂S over NO₂, SO₂, NH₃, and CO. The enhanced sensing performance of the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor compared to that of the pristine Fe₂O₃ nanorod sensor might be due to enhanced modulation of the conduction channel width, the decorated nanorods’ increased surface-to-volume ratios and the creation of preferential adsorption sites via TiO₂ nanoparticle decoration. The dominant sensing mechanism in the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor is discussed in detail.     

Interaction of Al2O3-rich slag with MgO–C refractories during VOD refining—MgO and spinel layer formation at the slag/refractory interface

The interaction mechanisms between a pitch-bonded MgO–C refractory and an Al₂O₃ rich (～15 wt%) stainless steelmaking slag were investigated by rotating finger tests in a vacuum induction furnace. A porous MgO layer (instead of a dense MgO layer) was observed at the hot face of the MgO–C bricks. This implies that under the present low oxygen pressure conditions, the oxygen supply from the slag is insufficient to meet the demand of reoxidising the entire amount of Mg vapor generated from the MgO–C reaction to form a fully dense MgO layer. A Mg(Al,Cr)₂O₄ spinel layer with zoning was found at the slag/brick interface in the top slag zone specimen of Test 3 (CHS3). Based on the thermodynamic analyses with and experimental data, a mechanism of Mg(Al,Cr)₂O₄ spinel formation is proposed. Initially, hot face periclase grains take up Cr₂O₃, and to a much lesser extent, Al₂O₃ from the slag. The further diffusion of Cr₂O₃ and Al₂O₃ from the slag establishes a spinel layer of three distinct compositions of the type MgAl_2(1?x)Cr_2xO₄, with x decreasing when moving from the interior to the exterior spinel layer. Due to the low oxygen pressures, the thermodynamically less stable, dissolved Cr₂O₃ in the hot face periclase decomposes and forms chromium-rich metal droplets.