Interfacial factors affecting the incidence of defects in ceramic mouldings

Ceramic injection moulding suspensions consisting of two alumina powders of surface area 9.5 m² g^–1 and 0.3 m² g^–1 were prepared at 60 vol % ceramic loading in the same organic composition. Cylinders of various diameters of each suspension were companion fired on an identical temperature ramp in nitrogen. For the fine powder, bloating occurred for all diameters above 8 mm. The coarse powder cylinders of 25 mm diameter could be prepared free from internal voids. The problems presented by fine powders during binder removal are discussed in terms of adsorbed layers, water emission and catalytic degradation.     

Influence of solids loading on the green microstructure and sintering behaviour of ceramic injection mouldings

The influence of solid loading of ceramic injection mouldings containing 45–60 vol % submicrometre zirconia powders on the green microstructure and sintering behaviour was investigated. The mouldings with lower solids content exhibit a coarser green microstructure, which, in turn, shows lower sintering activity. The sintering activity is largely improved by increasing the solids loading to 60% at which a sintered density of 99% theoretical can easily be attained at 1400°C, which is primarily because of the evolution of a finer green microstructure. The green microstructure of the mouldings, along with the sintering behaviour, was found to be well correlated with the average pore diameter, rather than the most-frequent pore diameter in the pore-size frequency distribution of the green compacts. The moulded compacts, although containing considerable amount of agglomerates, show isotropic shrinkage behaviour. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of different extraction agents on metal and organic contaminant removal from a field soil

This paper presents an evaluation of different extracting solutions for the removal of phenanthrene, lead and zinc from a contaminated soil obtained from a former manufactured gas plant site. The field soil contained 50%-88% sand, 11%-35% fines, 2.7%-3.7% organic matter and high concentrations of phenanthrene (260 mg/kg), lead (50.6 mg/kg) and zinc (84.4 mg/kg). A series of batch extraction experiments were conducted using the field soil with different extracting solutions at various concentrations to investigate the removal efficiency and to optimize the concentration of each extractant. The results showed that removal efficiencies of different flushing systems were significantly influenced by their affinity and selectivity for the contaminants in the soil matrix. Non-ionic surfactants (Igepal CA720 and Tween 80) were found to be effective in removing phenanthrene, but they were ineffective in removing lead and zinc. Chelating agents (ethylenediamine tetra acetic acid, EDTA and diethylene triamine penta acetic acid, DTPA) and selected acids were effective in removing lead and zinc, but they were ineffective for the phenanthrene removal. Co-solvents and cyclodextrins were not effective for removal of any of the contaminants. A sequential use of the 0.2 M EDTA followed by 5% Tween 80 or 5% Tween 80 followed by 1 M citric acid was found to be effective for the removal of lead, zinc, and phenanthrene. Overall, it can be concluded that sequential use of different extracting solutions is required for the removal of both heavy metals and organics from field contaminated silty sand soils.     

Modelling of the adhesive layer in mixed ceramic/metal armours subjected to impact

The effect of the adhesive layer, used to bond ceramic tiles to a metallic plate, on the ballistic behaviour of ceramic/metal mixed armours is analysed mathematically and experimentally. Two types of adhesives, polyurethane (soft adhesive) and rubber-modified epoxy resin (rigid adhesive), and different thicknesses, are considered in the study. Numerical simulations were made of low calibre projectiles impacting on alumina tiles backed by an aluminium plate, using a commercial finite difference code. Full-scale tests were carried out to check the influence of the adhesive. An engineering model was also developed to provide a preliminary design tool taking account of the influence of the adhesive.     

Hydrogen sulfide removal from coal gas by the metal-ferrite sorbents made from the heavy metal wastewater sludge

The metal-ferrite (chromium-ferrite and zinc-ferrite) sorbents made from the heavy metal wastewater sludge have been developed for the hydrogen sulfide removal from coal gas. The high temperature absorption of hydrogen sulfide from coal gas with the metal-ferrite sorbent in a fixed bed reactor was conducted in this study. The metal-ferrite powders were the products of the ferrite process for the heavy metal wastewater treatment. The porosity analysis results show that the number of micropores of the sorbents after sulfidation and regeneration process decreases and the average pore size increases due to the acute endothermic and exothermic reactions during the sulfidation–regeneration process. The FeS, ZnS, and MnS peaks are observed on the sulfided sorbents, and the chromium extraction of the CFR6 can fulfill the emission standard of Taiwan EPA. The suitable sulfidation temperature range for chromium-ferrite sorbent is at 500–600 °C. In addition, effects of various concentrations of H₂ and CO were also conducted in the present work at different temperatures. By increasing the H₂ concentration, the sulfur sorption capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction.     

The effect of inert gas ion bombardment on the oxidation of metal surfaces

The results of a systematic AES study of the kinetics of oxygen interaction at O₂ exposures up to 5000 L with Cu, Ni, Fe, Co surfaces irradiated with Ar ions in the dose range 10¹⁴–10¹⁸ cm⁻² and ion energy range 1–8 keV are presented. The kinetics of oxygen chemisorption at different temperatures of implanted Cu has been studied. The oxygen chemisorption on irradiated metals is shown to be retarded as compared to that on the non-irradiated ones, the degree of the chemisorption supression being a function of metal nature, dose and oxygen exposure. The character of the kinetics of oxygen chemisorption on irradiated surfaces depends on the ion bombardment dose, ion energy and the temperature of the implanted sample and changes with intervals of O₂ exposure. A model is proposed to explain the obtained results, based on the assumption of competition between the effect of radiation defects and implanted atoms on the adsorption process.     

The effect of the skin thickness and spherulite size on the mechanical properties of injection mouldings

In this work are studied the relationships between the microstructure and the mechanical properties of an injection moulded propylene-ethylene copolymer. Distinct microstructures were obtained by processing, through a moulding programme that includes the variation of the injection and the mould temperatures and the injection flow rate. They were characterized by the skin ratio (measured by polarised light microscopy) and the spherulite size (evaluated by small angle light scattering system). Tensile tests were carried out at two different constant loading velocities: 2 mm/min (3.33 × 10^–5 m/s) and 3 m/s, in order to assess the initial modulus, the yield stress, the strain and the energy at break. The results are presented in terms of the relationships between the chosen microstructural parameters and the selected tensile properties. The skin thickness is evidenced as an important microstructural feature. The role of the core spherulite size is secondary or even negligible. The results also show that other microstructural parameters must be considered to establish more general microstructure-properties relationships.     

Direct oxidation route from metal to ceramic: Study on cobalt oxide

The study deals with the direct-oxidation kinetics of micronic-cobalt metal particles and its simulation for the complete transition from metal to ceramic. The simulation was also experimentally verified. All the three possible interfaces, Co/CoO, CoO/Co₃O₄ and Co₃O₄/O₂ (air), have been taken into consideration for the simulation. The complete oxidation kinetics has been investigated from the thermogravimetric studies under isothermal conditions in the temperatures 973–1173 K. A quantitative interpretation based on the diffusion of Co or oxygen ions through the grown oxide layer has been proposed. The activation energy for the oxidation kinetics calculated from the Arrhenius law was 161 ± 20 kJ mol⁻¹.     

Studies of the effect of metal particles on the fracture toughness of ceramic matrix composites

The purpose of this study was to describe the influence of metal particles on the fracture toughness of ceramic matrix composites. Here, alumina matrix composites with molybdenum particles have been investigated. The results presented show that the change of fracture toughness of a ceramic–metal composite can be controlled by the volume fraction of metallic phase and size of metal particles.

The model proposed in this paper describes the change of crack length and as a consequence, the change of K_IC value. The results of modelling calculations have been compared with experimentally measured K_IC values. This model is useful for simulation of crack length changes in the composites and to design a material with an optimum fracture toughness.     

MOFs材料合成及其对有机气体吸附研究进展

讨论了金属有机骨架(MOFs)材料的不同合成方法,并结合国内外研究现状分别分析了IRMOFs、MILs、ZIFs和PCN等系列MOFs材料对有机气体吸附的研究进展,比较其性能及分析研究中的难点,对MOFs材料在有机气体吸附领域的应用进行了展望。     

Review on nanoadsorbents: a solution for heavy metal removal from wastewater

Elimination of heavy metals from contaminated streams is of prime concern due to their ability to cause toxic chaos with the metabolism of flora and fauna alike. Use of advanced nano‐engineered technologies such as the innovative combination of surface chemistry, chemical engineering fundamentals and nanotechnology opens up particularly attractive horizons towards treatment of heavy metal contaminated water resources. The obtained product of surface engineered nanoadsorbent produced has successfully proven to show rapid adsorption rate and superior sorption efficiency towards the removal of a wide range of defiant heavy metal contaminants in wastewater. The use of these materials in water treatment results in markedly improved performance features like large surface area, good volumetric potential, extra shelf‐lifetime, less mechanical stress, stability under operational conditions with excellent sorption behaviour, no secondary pollution, strong chelating capabilities and they are easy to recover and reuse. This review intends to serve as a one‐stop‐reference by bringing together all the recent research works on nanoparticles synthesis and its advantages as adsorbents in the treatment of heavy metal polluted wastewater that have so far been undertaken, thereby providing researchers with a deep insight and bridging the gap between past, present and future of the elegant nanosorbents.Inspec keywords: wastewater treatment, nanotechnology, adsorption, contaminationOther keywords: heavy metal removal, wastewater, contaminated streams, nanoengineered technology, surface chemistry, chemical engineering fundamentals, nanotechnology, heavy metal contaminated water resources, surface‐engineered nanoadsorbent, rapid adsorption rate, sorption efficiency, heavy metal contaminants, water treatment, surface area, volumetric potential, shelf‐lifetime, mechanical stress, stability, sorption behaviour, chelating capabilities     

Plasma cleaning and the removal of carbon from metal surfaces

In an investigation of the plasma cleaning of metals and the plasma etching of carbon, a mass spectrometer was used as a sensitive process monitor. CO₂ produced by the plasma oxidation of carbon films or of organic contamination and occluded carbon at the surfaces of metals proved to be the most suitable gas to monitor. A good correlation was obtained between the measured etch rate of carbon and the resulting CO₂ partial pressure monitored continuously with the mass spectrometer.The rate of etching of carbon in an oxygen-argon plasma at 0.1 Torr was high when the carbon was at cathode potential and low when it was electrically isolated in the plasma, thus confirming the findings of previous workers and indicating the importance of ion bombardment in the etching process. Superficial organic contamination on the surfaces of the metals aluminium and copper and of the alloy Inconel 625 was quickly removed by the oxygen-argon plasma when the metal was electrically isolated and also when it was at cathode potential. Occluded carbon (or carbides) at or near the surfaces of the metals was removed slowly and only when the metal was at cathode potential, thus illustrating again the importance of ion bombardment.     

Comparison of organic and inorganic packing materials in the removal of ammonia gas in biofilters

Two organic and two inorganic packing materials were compared with regard to the removal of ammonia gas in a biofilter inoculated with night-soil sludge. By gradually increasing the inlet load of ammonia, the complete removal capacity, which was defined as the inlet load of ammonia that was completely removed, and the maximum removal capacity of ammonia, which was the value when the removal capacity leveled off for each packing material, were estimated. Both values which were based on a unit volume of packing material, were higher for organic packing materials than inorganic ones. By using kinetic analysis, the maximum removal rate of ammonia, V(m), and the saturation constant, K(s), were determined for all packing materials and the values of V(m) for organic packing materials were found to be larger. By using the kinetic parameters, the removal rates for ammonia were compared among the four packing materials, and the organic packing materials showed superior performance for the removal of ammonia in the concentration range of 0-300 ppm as compared to inorganic packing materials.