Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of ceramics from steel slag

Ferric oxide is one of the key factors affecting both the microstructure and the properties of CaO-MgO-SiO₂-based ceramics. Research on this effect is significant in the utilization of iron-rich solid wastes in ceramics. Ceramic samples with various Fe₂O₃ contents (0wt%, 5wt%, and 10wt%) were prepared and the corresponding physical properties and microstructure were studied. The results indicated that Fe₂O₃ not only played a fluxing role, but also promoted the formation of crystals. Ceramics with 5wt% of Fe₂O₃ addition attained the best mechanical properties with a flexural strength of 132.9 MPa. Iron ions were dissolved into diopside, consequently causing phase transformation from diopside and protoenstatite to augite, thereby contributing to the enhancement of its properties. An excess amount of Fe₂O₃ addition (10wt% or more) resulted in deteriorated properties due to the generation of an excess volume of liquid and the formation of high-porosity structures within ceramics.     

铬铁矿球团焙烧固结特性

本文系统研究铬铁矿球团的焙烧固结特性.结果表明：预热时间对于预热球强度影响不大,在预热时间为10 min时,随着预热温度的提高,预热球强度和氧化率呈直线型增加,适宜温度为1050益,此时预热球强度可达每个400 N以上;与传统铁矿球团相比,铬铁矿球团焙烧所需的温度高,焙烧时间为10 min时,焙烧温度从1250益提高到1350益,球团强度从每个1078 N提高到1973 N.在铬铁矿球团预热和焙烧过程中,铬尖晶石( Fe,Mg)( Cr,Fe,Al)2 O4氧化生成富镁的( Fe,Mg)( Cr, Fe,Al)2O4和铬铁铝复合氧化物(Cr,Fe,Al)2O3,当温度高于1000益时,(Cr,Fe,Al)2O3新相生成,其主要以环状分布在颗粒外层,颗粒内部为针状与(Fe,Mg)(Cr,Fe,Al)2O4形成交织结构,降低Cr/Fe比或升高焙烧温度均有助于(Cr,Fe,Al)2O3向颗粒外层富集和再结晶长大,有利于球团的固结,提高球团强度.     

Synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> magnetic composite nanoparticles by a one-pot process

Fe₃O₄@SiO₂ core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe₃O₄@SiO₂ core–shell structures from prepared Fe₃O₄ nanoparticles. The properties of the Fe₃O₄ and Fe₃O₄@SiO₂ composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe₃O₄ particles were approximately 12 nm in size, and the thickness of the SiO₂ coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe₃O₄@SiO₂ powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe₃O₄ powder (79.55 A·m2·kg–1), which demonstrates that Fe₃O₄ was successfully wrapped by SiO₂. The Fe₃O₄@SiO₂ composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.     

Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Using coal fly ash slurry samples supplemented with different amounts of Al₂O₃, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al₂O₃. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al₂O₃ content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.     

Influence of CeO<Subscript>2</Subscript> addition on the preparation of foamed glass-ceramics from high-titanium blast furnace slag

Foamed glass-ceramics doped with cerium oxide (CeO₂) were successfully prepared from high-titanium blast furnace slag by one-step sintering. The influence of CeO₂ addition (1.5wt%–3.5wt%) on the crystalline phases, microstructure, and properties of foamed glass-ceramics was studied. Results show that CeO₂ improves the stability of the glass phase and changes the two-dimensional crystallization mechanism into three-dimensional one. XRD analysis indicates the presence of Ca(Mg, Fe)Si₂O₆ and Ca(Ti, Mg, Al)(Si, Al)₂O₆ in all sintered samples. Added with CeO₂, TiCeO₄ precipitates, and crystallinity increases, leading to increased thickness of pore walls and uniform pores. The comprehensive properties of foamed glass-ceramics are better than that of samples without CeO₂. In particular, the sample added with a suitable amount of CeO₂ (2.5wt%) exhibits bulk density that is similar to and compressive strength (14.9 MPa) that is more than twice of foamed glass-ceramics without CeO₂.     

Microstructures and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dispersion-strengthened copper alloys prepared through different methods

Al₂O₃ dispersion copper alloy powder was prepared by internal oxidation, and three consolidation methods—high-velocity compaction (HVC), hot pressing (HP), and hot extrusion (HE)—were used to prepare Al₂O₃ dispersion-strengthened copper (Cu–Al₂O₃) alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density (98.3% vs. 99.5% for HP and 100% for HE), which resulted in the lowest electrical conductivity (81% IACS vs. 86% IACS for HP and 87% IACS for HE). However, this alloy also exhibited the highest hardness (77 HRB vs. 69 HRB for HP and 70 HRB for HE), the highest compressive strength (443 MPa vs. 386 MPa for HP and 378 MPa for HE), and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3sf</Subscript> addition on the friction and wear properties of (SiC<Subscript>p</Subscript>+Al<Subscript>2</Subscript>O<Subscript>3sf</Subscript>)/Al2024 composites fabricated by pressure infiltration

Aluminum (Al) 2024 matrix composites reinforced with alumina short fibers (Al₂O_3sf) and silicon carbide particles (SiC_p) as wear-resistant materials were prepared by pressure infiltration in this study. Further, the effect of Al₂O_3sf on the friction and wear properties of the as-synthesized composites was systematically investigated, and the relationship between volume fraction and wear mechanism was discussed. The results showed that the addition of Al₂O_3sf, characterized by the ratio of Al₂O_3sf to SiC_p, significantly affected the properties of the composites and resulted in changes in wear mechanisms. When the volume ratio of Al₂O_3sf to SiC_p was increased from 0 to 1, the rate of wear mass loss (K_m) and coefficients of friction (COFs) of the composites decreased, and the wear mechanisms were abrasive wear and furrow wear. When the volume ratio was increased from 1 to 3, the COF decreased continuously; however, the K_m increased rapidly and the wear mechanism became adhesive wear.     

优化配矿强化西澳超细粒磁铁精矿球团焙烧研究

进行了西澳超细粒磁铁精矿分别配加国产磁铁精矿和巴西赤铁精矿制备氧化球团矿的实验研究.结果表明,以100%西澳超细磁铁精矿为原料制备氧化球团矿时,球团预热及焙烧性能较差,在预热温度为1050℃、预热时间20 min及焙烧温度1300℃、焙烧时间40 min的条件下,预热球团和焙烧球团矿抗压强度分别为每个502和2313 N.西澳超细粒磁铁精矿配加40%国产磁铁精矿或20%巴西赤铁精矿时,球团适宜预热温度由1050℃分别降低到950和975℃,适宜的焙烧温度由1300℃分别降低到1250和1280℃;而且焙烧球团矿的抗压强度分别提高到每个2746 N和每个2630 N.焙烧球团矿的微观结构研究表明:配加国产磁铁精矿后,焙烧球团矿中Fe2 O3晶粒发育优良,晶粒间互联程度提高,晶粒粗大,孔隙率低,固结更加紧密.配加20%巴西赤铁精矿时,焙烧球团矿中Fe2 O3晶粒基本连接成片,Fe2 O3晶体发育良好.优化配矿是改善西澳超细粒磁铁精矿球团矿预热及焙烧性能的有效途径.     

Adsorption and catalytic combustion of ARB on CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

CuO-Fe2O3 composite material with strong magnetism and a large surface area is prepared by the co-precipitate method. Its adsorption properties towards Acid Red B (ARB) and the regeneration by catalytic combastion of organic compounds have been studied. The results show that the prepared CuO-Fe2O3 composite is an excellent adsorbent for ARB adsorption at acid condition. The presence of Cl^- has no effect on ARB adsorption. But the SO4^2- can inhibit ARB adsorption. After being recovered by the magnetic separation method, the adsorbent can be regenerated by catalytic oxidation of absorbate at 300℃ in air atmosphere. The combustion reactions of ARB in the presence or absence of CuO-Fe2O3 are studied by in situ diffuse refieclion FTIR. The results indicate that, in the presence of CuO-Fe2O3, the degradation temperature is significantly lowered by the catalysis of CuO-Fe2O3, and ARB can be oxidized completely without volatile organic compound by-product; in comparison, in the absence of CuO-Fe2O3, the temperature needed for oxidation of ARB is higher and the reaction is incomplete with some N-containing harmful compounds produced. The reusability of CuO-Fe2O3 is also studied in successive seven adsorption-regeneration cycles.     

Simultaneously catalytic removal of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and particulate matter on diesel particulate filter

Diesel engines combine a high fuel economy with high durability and low maintenance costs and are, there-fore, used on a large scale for transportation purposes.However, the environmental pollution by diesel-engine exhausts has become more and more serious in the lastdecade, and currently the regulation of diesel emissions becomes tightened especially with respect to nitrogen ox-ides (NOx) and particulate matters (PM). Since the reduc-tion of both NOx and PM to the admitted level cannot be …     

Investigation on high magnetoresistance Ni0.81Fe0.19 films grown on （Ni0.81Fe0.19）1-xCrx underlayers

We have fabricated Ni0.18Fe0.19 films with (Ni0.18Fe0.19)1-xCrx films as underlayers by dc magnetron sputtering, the results show that larger anisotropic magnetoresistance (△R/R) values of Ni0.18Fe0.19 films are observed using the underlayers with Cr concentration of -36 at.% at an optimum underlayer thickness of -4.4 nm, the maximum AMR value is 3.35%. The results of atomic force microscope (AFM) and X-ray diffraction (XRD) show that the △R/R enhancement is attributed to the formation of large average grain size and the strong(111)texture in the Ni0.18Fe0.19 films.     

Fabrication and properties of aluminum silicate fibrous materials with <Emphasis Type="Italic">in situ</Emphasis> synthesized K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> whiskers

To improve their mechanical and thermal insulation properties, aluminum silicate fibrous materials with in situ synthesized K₂Ti₆O₁₃ whiskers were prepared by firing a mixture of short aluminum silicate fibers and gel powders obtained from a sol-gel process. During the preparation process, the fiber surface was coated with K₂Ti₆O₁₃ whiskers after the fibers were subjected to a heat treatment carried out at various temperatures. The effects of process parameters on the microstructure, compressive strength, and thermal conductivity were analyzed systematically. The results show that higher treatment temperatures and longer treatment durations promoted the development of K₂Ti₆O₁₃ whiskers on the surface of aluminum silicate fibers; in addition, the intersection structure between whiskers modulated the morphology and volume of the multi-aperture structure among fibers, substantially increasing the fibers' compressive strength and reducing their heat conduction and convective heat transfer at high temperatures.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O2-H2O-CO2 system:products,reaction kinetics,and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O₂-H₂O-CO₂ environment at various temperatures and O₂-CO₂ partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100℃ and increased sharply when the temperature exceeded 100℃. In the absence of O₂, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and FeCO₃ was the main corrosion product. When O₂ was introduced into the system, various forms of Fe₂O₃ appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O₂ was added; this phenomenon is related to the non-uniform distribution of Cr in 3Cr.     

One-pot synthesis of PVP-coated Ni<Subscript>0.6</Subscript>Fe<Subscript>2.4</Subscript>O<Subscript>4</Subscript> nanocrystals

Novel poly(N-vinyl-2-pyrrolidone) (PVP)-coated nickel ferrite nanocrystals were prepared by simultaneously pyrolyzing nickel(II) acetylacetonate (Ni(acac)₂) and iron(III) acetylacetonate (Fe(acac)₃) in N-vinyl-2-pyrrolidone (NVP). The PVP coating was formed in situ through polymerization of NVP. The crystalline structure of the resultant nickel ferrite was analyzed by high-resolution transmission electron microscopy, electron diffraction patterns, and powder X-ray diffraction. In addition, the valence state of Ni and the metal contents of Ni and Fe in different valence states were analyzed by X-ray photoelectron spectroscopy (XPS), atomic absorption and the phenanthroline method. The surface coating layer of PVP and its binding states were characterized by Fourier transform infrared spectroscopy in combination with XPS. Colloidal stability experiments revealed that the nanocrystals could be dispersed well in both phosphate-buffered saline and Dulbecco’s Modified Eagle Medium.     

Shear-thinning behavior of the CaO-SiO2-CaF2-Si3N4 system mold flux and its practical application

Satisfying the mold-flux performance requirements for high-speed continuous casting necessitates the development of a new non-Newtonian-fluid mold flux with shear-thinning behavior, i.e., a mold flux whose viscosity is relatively high under lower shear rates and relatively low under higher shear rates. In this work, a mold flux that exhibits shear-thinning behavior was developed by adding different amounts of Si₃N₄ to the CaO-SiO₂-CaF₂ mold flux. The shear-thinning behavior was investigated using a rotational viscometer. In addition, the microstructure of the newly prepared slags was studied by high-temperature Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that the mechanism of shear-thinning was attributable to a temporary viscosity loss caused by the one-way shear stress, whereas the corresponding magnitude of shear-thinning was closely related to the degree of polymerization (DP). Finally, the non-Newtonian fluid mold flux was used for laboratory casting tests, which revealed that the mold flux could reduce slag entrapment and positively affect the continuous casting optimization.     

Micro-arc oxidization fabrication and ethanol sensing performance of Fe-doped TiO<Subscript>2</Subscript> thin films

In-situ pure TiO₂ and Fe-doped TiO₂ thin films were synthesized on Ti plates via the micro-arc oxidation (MAO) technique. The as-fabricated anatase TiO₂ thin film-based conductometric sensors were employed to measure the gas sensitivity to ethanol. The results showed that Fe ions could be easily introduced into the MAO-TiO₂ thin films by adding precursor K₄(FeCN)₆·3H₂O into the Na₃PO₄ electrolyte. The amount of doped Fe ions increased almost linearly with the concentration of K₄(FeCN)₆·3H₂O increasing, eventually affecting the ethanol sensing performances of TiO₂ thin films. It was found that the enhanced sensor signals obtained had an optimal concentration of Fe dopant (1.28at%), by which the maximal gas sensor signal to 1000 ppm ethanol was estimated to be 7.91 at 275°C. The response time was generally reduced by doped Fe ions, which could be ascribed to the increase of oxygen vacancies caused by Fe³⁺ substituting for Ti⁴⁺.     

Novel mechanism for the modification of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al₂O₃-based inclusions during secondary refining. The results showed that Al₂O₃-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition,[Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO-MgO-Al₂O₃ multi-component inclusions. Thermodynamic analysis confirmed that the reaction between[Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3wt% and the temperature is higher than 1843 K.     

La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> TBCs toughened by Pt particles prepared by cathode plasma electrolytic deposition

La₂Zr₂O₇ thermal barrier coatings (TBCs) with dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED) with ceramic balls added to the cathode region. Compared with the conventional CPED, when ceramic balls are used in the cathode region, the plasma discharge ignition current density decreases approximately 62-fold and the stable plasma discharges occur at the whole cathode surface. Such TBCs with a thickness of 100 μm exhibit a crack-free surface and are composed of pyrochlore-structured La₂Zr₂O₇. Cyclic oxidation, scratching, and thermal insulation capability tests show that such TBCs not only exhibit high resistance to oxidation and spallation but also provide good thermal insulation. These beneficial effects are attributed to the excellent properties of TBCs, such as good thermal insulation because of low thermal conductivity, high-temperature oxidation resistance because of low-oxygen diffusion rate, and good mechanical properties because of the toughening effect of Pt particles.     

Effect of diboron trioxide on the crushing strength and smelting mechanism of high-chromium vanadium-titanium magnetite pellets

The effect of diboron trioxide (B₂O₃) on the crushing strength and smelting mechanism of high-chromium vanadium-titanium magnetite pellets was investigated in this work. The main characterization methods were X-ray fluorescence, inductively coupled plasma-atomic emission spectroscopy, mercury injection porosimetry, X-ray diffraction, metallographic microscopy, and scanning electron microscopy-energy-dispersive X-ray spectroscopy. The results showed that the crushing strength increased greatly with increasing B₂O₃ content and that the increase in crushing strength was strongly correlated with a decrease in porosity, the formation of liquid phases, and the growth and recrystallization consolidation of hematite crystalline grains. The smelting properties were measured under simulated blast furnace conditions; the results showed that the smelting properties within a certain B₂O₃ content range were improved and optimized except in the softening stage. The valuable element B was easily transformed to the slag, and this phenomenon became increasingly evident with increasing B₂O₃ content. The formation of Ti(C,N) was mostly avoided, and the slag and melted iron were separated well during smelting with the addition of B₂O₃. The size increase of the melted iron was consistent with the gradual optimization of the dripping characteristics with increasing B₂O₃ content.     

Ce对Cu-Cr合金内氧化层组织和性能的影响

利用不同Ce含量的Cu-0.4Cr-Ce合金进行包埋内氧化处理,对所得的Cu/Cr2O3复合材料进行了显微组织观察,测定了内氧化层深、显微硬度、电导率及抗拉强度。结果表明:随着内氧化时间的延长,复合材料的内氧化层深增加;Ce的加入,不仅细化了晶粒,而且内氧化层深也相应加深,最高达770μm;同时Ce含量增加,也提高了Cu/Cr2O3显微硬度、电导率及抗拉强度,分别达到HV128、80%IACS和400MPa。