Novel Al2O3‐C Refractories with Less Residual Carbon Due to Nanoscaled Additives for Continuous Steel Casting Applications

A new generation of thermal shock resistant Al₂O₃‐C refractories with approximately 30% less residual carbon and functionalized due to nanoscaled additives based on carbon nanotubes (CNTs) and alumina nanosheets (α‐Al₂O₃) were developed and investigated after coking at 1000 and 1400 °C. With the aid of electron backscatter diffraction analyses (EBSD) on fracture surfaces of the carbon bonded samples, Al₃CON was identified on the nanosheet shapes already at 1000 °C coking temperature. The Al₃CON new phase based on the reaction between alumina nanosheets and CNTs offers a chemical interconnecting phase for the carbon as well as for the oxide alumina filler. The new refractory composite structure presents excellent thermo‐mechanical properties in spite the lower carbon content. In addition, due to EDS and EBSD analyses amorphous whiskers and platelets within the system of Si? O were observed in samples coked at 1000 °C, that were transformed to crystalline β‐SiC‐whiskers in samples coked at 1400 °C.     

含碳耐火材料酚醛树脂结合剂的研究现状与展望

含碳耐火材料不仅热导率较高,具有较好的抗热冲击性能,而且与熔渣不润湿,具有良好的抗侵蚀性能,因此大量生产并在冶金工业中广泛应用。酚醛树脂因具有与石墨润湿、残碳率高、环境友好、结合强度较高的特点而广泛用作含碳耐火材料结合剂。然而,酚醛树脂热解碳为脆性的非晶结构,不仅在应力作用下易脆性断裂,而且在高温下容易氧化。很多研究致力于酚醛树脂的化学改性。为提高酚醛热解碳的抗氧化性能或力学性能,提高酚醛树脂残碳率,通常添加过渡金属化合物、纳米碳、半导体陶瓷作为催化剂以提高热解碳的有序度,或者在其酚醛树脂热解碳基体中生成具有较高石墨化度的碳纳米管、碳纳米纤维以及Si C纳米线。     

碳纤维/TiO2改性树脂复合材料的制备及力学性能

针对环氧树脂脆性大、与碳纤维形成的界面性能较差等问题,本文选用纳米TiO₂对5284环氧树脂进行改性,并以角联锁机织物为增强体制备了碳纤维/环氧树脂复合材料。使用FT-IR、旋转流变仪、表面张力仪等设备对TiO₂/环氧树脂进行表征,并研究了树脂改性对复合材料压缩与层间剪切性能的影响。研究表明：TiO₂的羟基与环氧树脂的环氧基和羟基发生了反应;经1wt.%TiO₂改性的树脂复数黏度为0.066 Pa·s,纤维与树脂间接触角为28.85°,浸润效果较好;相较于未改性复合材料,树脂改性的复合材料纵向压缩强度与模量分别提高了7.46%和11.03%,横向压缩强度与模量分别提高了6.99%和4.96%,纵向、横向的剪切强度分别提高了6.88%和4.65%。TiO₂改性环氧树脂提高了复合材料的承载能力,改善了界面结合强度。     

Oxides reactions with a High-chrome sesquioxide refractory

In slagging coal-gasifier systems, the combination of oxides present as impurities in coal and combustion temperatures that can exceed 1650°C restrict the use of liner materials in the coal combustion chambers to refractories. In this study, the slag-refractory interactions of a new high chrome sesquioxide refractory was characterized. High-temperature cup tests showed that the molten oxides infused into the refractory and that the sesquioxide refractory reacts with the oxides in a manner similar to spinel phase refractories. Studies of the coal slag's individual oxide components showed CaO reacts with the chrome refractory to form a low melting Ca(CrO₂)₂. FeO reacts with the sesquioxide to form a interface layer of (Cr,Fe)₃O₄ spinel phase. Results of this study now make it possible to design studies for improving corrosion resistance to increase refractory life.     

Effect of binders on microstructure and photoelectrochemical properties of the TiO2 film photoelectrodes

In order to obtain thick, crack-free TiO₂ film photoelectrodes, the screen-printed method was employed by using ethylene glycol and ethylene glycol monomethylether (EGME) as binder. The surface morphology of TiO₂ film observed by scanning electron microscope (SEM) is porous and coarse. SEM results also show that TiO₂ films with binder are crack-free in the microstructure. Optical absorption spectra show that films with binder have stronger ability to adsorb dye molecules than that without binder. I–V curves show that films with binder have better photoelectrochemical (PEC) property than films without binder. Moreover, EGME improves the PEC property of the sample stronger than ethylene glycol.     

Constitution and properties of ceramized fireclay refractories: II. Properties

Low-grade fireclay refractories contain large amounts of glassy phase. The properties, e.g. mechanical strength, thermal-shock resistance, refractoriness-under-load, refractoriness and also porosity and bulk density of these refractories before and after ceramization of their glassy phase were investigated. The glassy phase was ceramized by incorporating Cr₂O₃, V₂O₅ and TiO₂ into the refractories as nucleating agents and subsequent heat-treatment. Significant improvement in mechanical strength and thermal-shock resistance of the ceramized refractories was observed.     

Effects of TiO2�CSiO2 fillers on thermal and dielectric properties of bismuth glass microcomposite dielectrics for plasma display panel

The combined effects of TiO₂ and SiO₂ fillers on thermal and dielectric properties of new lead-free environmental friendly zinc bismuth borate, ZnO?CBi₂O₃?CB₂O₃ (ZBIB) glass microcomposite dielectrics have been investigated from the viewpoint of application as rear glass dielectric layer of plasma display panels (PDPs). The interaction of fillers with glass occurred during firing has also been explored by XRD, SEM and FTIR spectroscopic analyses. All the properties are found to be regulated by the covalent character (a fundamental property) of resultant microcomposite dielectrics. In this work, the co-addition of TiO₂?CSiO₂ filler to ZBIB glass is found to be more effective to adjust the required properties to employ with PD200 glass substrate in PDP technology.     

Crystallization of glass in fireclay refractories: part II: Detailed study on the mullite crystal content of the ‘synthetic’ glass

A glass of composition similar to that found in fireclay refractories was synthesized and subsequently nucleated with Cr₂O₃, V₂O₅ and TiO₂. These glasses were heat-treated for crystallization of the mullite phase. The mullite content, the crystallization of mullite and the effect of temperature on the rate were investigated. The concentration of the nucleating oxides and the size and charge of their cations influence both the mullite content obtained and the crystallization rate.     

Effect of Binder Composition on the Shrinkage of Chemically Bonded Sand Cores

Modern foundries increasingly use chemically bonded no-bake sand cores and molds because they provide ease of molding, good surface finish, and collapsibility. One of the most popular binder systems is alkyd oil urethane no-bake system comprising three parts: alkyd resin, catalyst, and crosslinking agent. Their amounts and ratios can influence mold shrinkage, and thereby dimensional quality of the resulting casting. With rising emphasis on net-shape casting, there is a need to optimize the binder composition to minimize dimensional errors, while achieving the desired bench life, stripping time and hardness. This work investigates the effect of binder composition on the dimensions of chemically bonded sand cores with respect to time. The maximum shrinkage of 0.15% over length was observed when resin content was 2.4% by weight of sand. The rate of shrinkage increased with the amount of catalyst. Measurement of core hardness and reduction in weight, followed by SEM studies, provided a better understanding of the underlying phenomena, especially formation of resin bridges between compacted sand particles and evaporation of solvent. This work is expected to aid in selection of the most appropriate binder composition for a given set of molding process constraints and cast product requirements.     

The effect of additives on Al2O3–SiO2–SiC–C ramming monolithic refractories

Abstract

The aim of this study is to describe the effect of containing additives on increasing cold crushing strength (CCS) and bulk density (BD) of Al₂O₃–SiO₂–SiC–C monolithic refractories. Two series of carbon containing monolithics were prepared from Iranian chamotte (Samples A) and Chinese bauxite (Samples B), as 65 wt.% in each case together with, 15wt.% SiC-containing material regenerates (crushed sagger), 10 wt.% fine coke (a total of 90% aggregate) and 10 wt.% resole (phenol formaldehyde resin) as a binder. Different types of additives (such as silicon and ferrosilicon metal) are added to a batch of 100 g of mixture and the physical and mechanical properties (such as BD, apparent porosity and CCS) are measured after tempering at 200°C for 2 h and firing at 1100°C and 1400°C for 2h. After low temperature tempering at 200°C, silicon and ferrosilicon contribute to the formation of stronger cross linking in the resulting structure and provides CCS values as high as 65 MPa. After high temperature sintering, at 1400°C, SiC whiskers of nano sized diameter are formed due to the presence of Si and FeSi₂ and increases the CCS values of the refractories as high as 3–4 times in sample containing 6wt.% ferrosilicon metal as additive, compared to the material without additive. The temperature of 1100°C is a transient temperature, used in high temperature sintering.     

Effects of hybrid fillers on the electromagnetic interference shielding effectiveness of polyamide 6/conductive filler composites

The effects of hybrid conductive fillers on the electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of polyamide 6 (PA6)/conductive filler composites were investigated. Nickel-coated carbon fiber (NCCF) was used as the main filler and multi-walled carbon nanotube (MWCNT), nickel-coated graphite, carbon black, and titanium dioxide (TiO₂) were used as the second fillers in this study. From the results of morphological studies of the PA6/NCCF/second filler composites, NCCF easily formed an electrical pathway since it has a high aspect ratio and random orientation, and the second fillers seemed to disperse evenly in the PA6 matrix. The electrical conductivity and EMI SE of the PA6/NCCF composites were increased with the increase of NCCF content. Among the second fillers used in this study, TiO₂ appeared to be the most effective second filler with regard to increasing the EMI SE and electrical conductivity of the PA6/NCCF composite. This was probably because TiO₂ has a high dielectric constant with dominant dipolar polarization, consequently leading to greater shielding effectiveness due to the absorption of electromagnetic waves. From the above results of EMI SE and electrical conductivity, it was suggested that the TiO₂ produced a synergistic effect when it was hybridized with the NCCF of the PA6/NCCF/TiO₂ composites.     

Improvement of epoxy resin properties by incorporation of TiO2 nanoparticles surface modified with gallic acid esters

Epoxy resin/titanium dioxide (epoxy/TiO₂) nanocomposites were obtained by incorporation of TiO₂ nanoparticles surface modified with gallic acid esters in epoxy resin. TiO₂ nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO₂ nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO₂ nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO₂ nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO₂ nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO₂ nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO₂ nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO₂ nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO₂ nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.     

Preparation of porous sheet composite impregnated with TiO<Subscript>2</Subscript> photocatalyst by a papermaking technique

Titanium dioxide (TiO₂) powder-containing sheet composites, called TiO₂ sheet, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO₂ powders were homogeneously scattered over the fiber-mix networks tailored within the catalyst sheet. Under UV irradiation, the TiO₂ paper could decompose p-hydroxyacetophenone (p-HAP), although the degradation efficiency by the TiO₂ sheet was lower than that by the TiO₂ powder. Scanning electron microscopy revealed that coverage of the TiO₂ particles inside the sheet by alumina binder which was used to improve the sheet strength caused the deterioration of the photocatalytic performance. Internal addition of alumina binder made the TiO₂ sheet porous and such a TiO₂ sheet exhibited high photocatalytic performance equivalent to that of TiO₂ powder. The porous structure of TiO₂ sheet might contribute to effective transport of p-HAP to the surface of TiO₂ particles inside the sheet, resulting in high degradation performance. In addition, TiO₂ sheet prepared using TiO₂ sol showed higher photocatalytic efficiency than TiO₂ powder and it was indicated that the porous sheet structure might provide suitable conditions for TiO₂ catalysis for photodecomposition.     

Preparing of nanostructured Al2O3–TiO2–ZrO2 composite powders and plasma spraying nanostructured composite coating

Nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders for plasma spraying were prepared by spray drying granulation technology. The effects of processing parameters on the microstructure and properties of composite powders were investigated. The results show that with increasing the slurry solid content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the binder content, the particle size of powders increases, and the bulk density of powders increases, and the flowability of powders increases firstly and then decreases. With increasing the spray drying temperature, the particle size of powders increases, and the bulk density and flowability of powders increases firstly and then decreases. The most appropriate spray drying parameters are the slurry solid content of 40 wt.%, the binder content of 2.0 wt.% and the spray drying temperature of 250 °C. The nanostructured composite coating was successfully prepared by using the as-prepared nanostructured Al₂O₃–TiO₂–ZrO₂ composite powders as feedstocks. The nanostructured coating possessed higher hardness and toughness compared with the conventional microstructured one, which was attributed to the use of the nanostructured composite powders feedstocks.     

Photocatalytic Carbon‐Nanotube–TiO2 Composites

The literature and advances in photocatalysis based on the combination of titania (TiO₂) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect‐rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixtures and chemically bonded CNT–TiO₂ composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with organic, inorganic, and biological agents. Finally, various applications and challenges for these composite materials are reported.     

Photocatalytic CO<Subscript>2</Subscript> conversion over Au/TiO<Subscript>2</Subscript> nanostructures for dynamic production of clean fuels in a monolith photoreactor

Global economic development intensifies the consumption of fossil fuels which results in increase of carbon dioxide (CO₂) concentration in the atmosphere. The technologies for carbon capture and utilization to produce cleaner fuels are of great significance. However, phototechnology provides one perspective for economical CO₂ conversion to cleaner fuels. In this study, CO₂ conversion with H₂ to selective fuels over Au/TiO₂ nanostructures using environment friendly continuous monolith photoreactor has been investigated. Crystalline nanoparticles of anatase TiO₂ were obtained in the Au-doped TiO₂ samples. The Au deposited over TiO₂ in metal state produced plasmonic resonance. CO₂ was efficiently converted to CO as the main product over Au/TiO₂ with a maximum yield rate of 4144 µmol g-catal.^?1 h^?1, 345 fold-higher than using un-doped TiO₂ catalyst. The significantly enhanced photoactivity of Au/TiO₂ catalyst was due to hindered charges recombination rate and Au metallic-interband transition. The photon energy in the UV range was high enough to excite the d-band electronic transition in the Au to produce CO, CH₄, and C₂H₆. The quantum efficiency over Au/TiO₂ catalyst for CO was considerably improved in the continuous monolith photoreactor. At higher space velocity, the yield rates of CO gradually reduced, but the initial rates of hydrocarbon yields increased. The stability of the recycled Au/TiO₂ catalyst was sustained in cyclic runs. Thus, Au-doped TiO₂ supported over monolith channels is promising for enhanced CO₂ photoreduction to high energy products. This provides pathway that phototechnology to be explored further for cleaner and economical fuels production.     

Effects of binders on dimensional accuracy and mechanical properties of SiC particulates preforms fabricated by selective laser sintering

SiC preforms were produced by selective laser sintering and thermal treatment sintering at 700 °C for fabricating near-net-shape composites. The dimensional accuracy and mechanical properties were investigated. The results show that dimensional accuracy 98.42% of preforms was obtained. After sintering at 700 °C, the dimensional accuracy of preforms using the binder of epoxy resin was decreased obviously, but that using the binder of epoxy resin and NH₄H₂PO₄ was maintained. The tensile and bend strength of preforms using epoxy resin and NH₄H₂PO₄ as binder were higher than that using epoxy resin, and enough to support the external load. When the epoxy resin was decompounded at 700 °C, the reaction product of SiP₂O₇ phase can form an effective bonding for maintaining the dimensional accuracy and supporting mechanical properties of preforms by using the binder of epoxy resin and NH₄H₂PO₄.     

Assessing the environmental impact of five Pd-based catalytic technologies in removing of nitrates

Emerging technologies involving chemical catalytic processes to remove nitrate from water have proven efficient and cost-effective. However, the environmental impact of noble metals and metals at the nanoscale used in these processes has become a topic of serious concern. The aim of this research was to develop a system for evaluating the environmental impact of technologies associated with Pd-based catalytic denitrification. This research performed life cycle assessment (LCA) based on a detailed analysis of the technologies to examine the environmental burden associated with all stages of the removal process. We then applied analytical hierarchy process (AHP) to determine the weights of various burdens. We implemented the proposed system to determine the relative environmental friendliness of 5 processes used for the removal of nitrate. These five methods use Cu-Pd/TNTs, H₂ + Pd-Cu/TiO₂, Pd-Cu/TiO₂, Pd/ZnO, and Pd-Cu/FeO as catalysts for the removal of nitrate. The results indicate that the use of palladium and the consumption of electricity have a major environmental impact; while the use of Pd-Cu/TiO₂ as catalyst was the most environmentally friendly of the five processes evaluated.     

Scalable synthesis of TiO<Subscript>2</Subscript> crystallites embedded in bread-derived carbon matrix with enhanced lithium storage performance

TiO₂/carbon (C/TiO₂) composites have been synthesized via an in-situ pyrolysis method using bread as carbon source and investigated as anodes for lithium-ion batteries. As a cheap and common staple food with a sponge-like structure, bread contains a certain amount of moisture, enabling the hydrolysis of tetrabutyl orthotitanate. It is characterized that TiO₂ nanocrystallites are embedded in bread-derived carbon matrix, and their synergetic effect on improving electrochemical properties is demonstrated as well. Partially surface lithium storage of ultrasmall TiO₂ particles is credited to the unique embedment structure. Meanwhile, the carbon species are of importance in enhancing reversible capacities and accelerating interfacial charge transfer. It delivers a reversible capacity of 231 mAh g^?1 at a specific current of 100 mA g^?1 after 200 cycles for the resultant C/TiO₂ composite with 38.8 wt.% carbon. This work presents a facile strategy toward scalable and eco-friendly preparation of metal oxides compositing with carbonaceous materials.     

Green and reusable Ag/AgCl-TiO2 nanocomposites for visible light-triggered dye degradation

Ag/AgCl-TiO₂ plasmonic nanocomposites (NCs) are endowed with excellent visible-light photocatalytic activity. However, only a few studies investigated environmentally friendly approaches to their synthesis. In this work, Ag/AgCl-TiO₂ NCs at five different compositions were prepared in a single-step process by a green and cost-effective route, using Satureja khuzistanica Jamzad aqueous extract. The role of the aqueous plant extract as a reducing and stabilizing agent, and the formation of the NCs were evidenced by several techniques, including FT-IR, EDS, SEM, HRTEM, elemental mapping, and XRD. The morphological analysis demonstrated that the NCs formed nanoaggregates with an average size of 30 nm. The synthesized Ag/AgCl-TiO₂ NCs displayed a remarkable photoactivity in the visible light region, as confirmed by the significantly higher degradation rates of methyl orange (MO) compared to TiO₂. In particular, the 15% Ag/TiO₂ molar ratio sample revealed a MO degradation efficiency higher than 99% under visible light, and retained high photocatalytic activity even after several degradations runs. Overall, the green, cost-effective, and scalable synthesis of Ag/AgCl-TiO₂ NCs herein reported provides a novel, more sustainable strategy for the high-efficiency modification of TiO₂ photocatalyst in engineering and other environmental applications.