Characterisation of structure of iron ore sinter and its behaviour during reduction at low temperatures

Abstract

Various sinter microstructures were produced in the laboratory using the same iron ore blend, varying only the sinter basicity and the carbon content of the blend via limestone and coke additions, respectively. The sinter cakes were subjected to low temperature, size degradation tests and their structural composition was determined. A relationship has been established between sinter structural composition and its size degradation under low temperature reducing conditions. Also, varying the gas composition led to development of a new reduction test procedure, which is more sensitive to microstructural variations than the conventional standard test (reduction degradation index, RDI).     

Oxidation of MCrAlY coatings on Ni based superalloys

Abstract

Industrial gas turbine engines used for power generation generally employ Ni based superalloys for the turbine blades. The operating conditions for these blades are very arduous with high temperatures (>900°C) leading to oxidation and corrosion. Therefore in order to increase the service life of components, coatings are employed which allow the use of Ni based superalloys at higher temperatures and therefore more efficient engines. These systems are very complicated and in order to understand coating performance and service life, many modelling approaches have been utilised. However, there is still a lack of understanding of the thermally grown oxide (TGO) with regards to its chemistry, microstructure, adhesion strength and mechanical properties. Therefore a more detailed understanding of the TGO would be useful for both empirical and computational modelling. The effect of compositional changes in the MCrAlY bond coat and their effect on the TGO have been studied. Two different MCrAlY coatings have been examined after aging at representative operation temperatures. A number of analytical techniques have been used including, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray and electron backscattered diffraction. A dual beam scanning electron microscope has also been utilised for both TEM sample preparation and microstructural evaluation. These techniques will allow a better understanding of the microstructure of the TGO, ultimately leading to improved predictions of coating behaviour and service life.     

Using heterogeneous silane patterns to maintain adhesion and decrease water penetration into epoxy/aluminum interfaces

Silanes are used for surface modification to improve dispersion, bind biomaterials, improve adhesion, etc. Their use in improving adhesion in composite materials is widespread, and for these systems there is a growing need for both increased adhesion performance and resistance to water penetration across polymer/oxide interfaces. The present work reports adhesion results obtained using patterned, binary combinations of adhesion-promoting and non-adhesion-promoting silanes patterned onto an oxide surface. The effects of pattern shape, texture (feature size) and the fractional coverage of the adhesion promoter are explored for the bonding of epoxy matrices to aluminum oxide surfaces using combinations of γ-glycidoxypropyltrimethoxysilane (GPS), an adhesion promoter, and either octadecyltrichlorosilane (ODTS) as a hydrophobic non-adhesion promoter, or vinyltrimethoxysilane (VMS) as a water scavenger. In addition to dry tests, samples are submerged in boiling water for 48 h, and in 50°C water for 4 h to determine if water penetrated into the interface, thereby reducing the adhesion. Climbing drum peel tests reveal that heterogeneity of silane primer substrates can influence the adhesion and increase the durability to water penetration. Adhesion enhancement is attributed to the blocking of lateral diffusion of water by barriers due to the presence of the hydrophobic silane. Results show that due to exposure to water at 50°C for 4 h, the adhesion is reduced by 46% in the homogeneous samples but only by 20% in the heterogeneous samples. In contrast, the use of VMS was ineffective in preventing the loss of adhesion due to water penetration.     

Atmospheric-Pressure Plasma Amination of Polymer Surfaces

Using dielectric barrier discharges (DBDs) in suitable gas atmospheres, appreciable densities of amino groups can be generated on polymer surfaces. After the introduction and a few remarks on analytical methods for the determination of functional groups densities, this paper presents a short summary of recent studies on the mechanism of the polymer surface amination from nitrogen and nitrogen/hydrogen mixtures, and possible relevant precursor species. Combination of chemical derivatization with quantitative FT-IR spectroscopy was employed for the determination of primary amino groups densities introduced on polyolefin surfaces in DBD afterglows in N₂ and N₂ + H₂ mixtures. Owing to the possibility to generate atmospheric-pressure plasmas in sub-mm³ volumes, DBD plasmas can be used to modify polymer surfaces area selectively: a new process termed 'plasma printing' can be applied for the achievement of micropatterned surface modifications, such as hydrophilization/hydrophobization or chemical functionalization. Direct-patterning polymer surface modification processes are of interest for biochemical/biomedical applications as well as for polymer electronics. Two examples are presented in more detail: ? the area-selective plasma amination of carbon-filled polypropylene minidiscs to manufacture microarrays with peptide libraries utilizing parallel combinatorial chemical synthesis, and ?the continuous treatment of polymer foils by means of reel-to-reel patterned plasma amination for the subsequent electroless copper metallization, leading to a fast and highly efficient process for the manufacture of structured metallizations for flexible printed circuits or RFID antennas.     

Dynamics of the wetting process on dielectric barrier discharge (DBD)-treated wood surfaces

Protection and preservation of wood properties in exterior environments can only be ensured if the surface is coated with a paint or varnish. In our experiments a dielectric barrier discharge (DBD) was used as a wood surface pretreatment for improvement of the subsequent deposition of thin paint layers from solutions onto these surfaces. As the adsorption, interfacial interactions and adhesion of paints are strongly dependent on surface wettability, the dynamics of the wetting process were analyzed. The results show that the water contact angle decreases after the DBD treatment, proving a more wettable surface. Additionally, the spreading of paint solution on the DBD-treated surface is more isotropic, showing a lower tendency to elongate along the wood fiber orientation.     

Knowledge transfer mechanisms for advanced surface engineering technologies

Abstract

A breakthrough in the area of PVD/CVD coating technologies, as in other surface engineering technologies, requires not only technical innovation but also innovative technological and organisational support. The cohesion of these diverse areas forms a basis for obtaining theoretical and physical models, which give rise to prototypes for the rapid application of breakthrough solutions. Mechanisms and structures aimed at reaching breakthrough research objectives are presented, taking as an example the investigation and application of new materials, particularly using surface engineering PVD plasma technologies. The advanced technology of thermal barrier coatings (TBC) is described and the associated process development, including the design and construction of a unique hybrid device for TBC creation, are presented. By means of this example, a combination of breakthrough and incremental research is explored and a real path for balancing research and knowledge transfer, leading to innovative solutions and technologically advanced product application, is demonstrated.     

Wetting Transitions on Rough Substrates: General Considerations

General properties of wetting transitions for droplets on rough substrates are analyzed theoretically. The energy barrier to be surpassed for wetting transitions is much lower than the heat of evaporation of the droplet; this makes wetting transitions possible. It is shown that the energy curve of the transition state, i.e., the dependence of the interfacial part of the Gibbs free energy on the apparent contact angle in this state, as well as the energy barriers, can be expressed through the contact angles in the initial and final states without going into the geometric details of the given substrate relief. On this basis, the reason for the irreversibility of the Cassie–Wenzel transitions is elucidated: the energy barrier of the reverse transition is shown to be much higher. The scheme is also applicable to the substrates with disordered reliefs. Time-scaling arguments are important for understanding wetting transitions.     

毛纺行业面临的"绿色壁垒"和我们的对策

文中阐述了作者在第５届全国毛染整经验交流会上，对我国加入ＷＴＯ后毛纺行业面临的“绿色壁垒”和我们对对策提出的一些看法和建议，介绍并分析了纺织品的生态标准、禁用环境荷尔蒙的危害性及其对纺织品的影响，详细探讨了禁用染料、助剂的代用方案。     

Ultra-Thin Polymer Layer Deposition by Aerosol–Dielectric Barrier Discharge (DBD) and Electrospray Ionization (ESI) at Atmospheric Pressure

Polyolefins are chemically inert and do not adhere well to metals, polymers or inorganics. To overcome this problem, polyolefin surfaces were modified thermally, plasmachemically, or by flame treatment with different oxygen-containing groups, however, unfortunately, such treatments were accompanied by undesired, adhesion lowering polymer degradation. To solve this dilemma, solutions of synthetic polymers and copolymers were prepared, sprayed into the barrier discharge or electrosprayed without discharge and deposited as thin adhesion-promoting layers. The deposited polymer layers from poly(vinylamine), poly(ethylene glycol)–poly(vinyl alcohol) copolymers and poly(acrylic acid) were endowed with monotype functional groups. Using the aerosol — dielectric barrier discharge only a fraction of functional groups survived the deposition process in contrast to the electrospray in which all functional groups were retained.     

Bond coat oxidation and its significance for life expectancy of thermal barrier coating systems

Abstract

The time and temperature dependent evolution of the microstructure of thermal barrier coating systems under isothermal conditions between 950 and 1100 ° C up to 5000 h are investigated for two APS - TBC systems and two EB-PVD systems. Kinetics for the thermally grown oxide thickness values, the β phase depletion underneath the oxide scale and the physical defects in and around the thermally grown oxide are determined by extensive SEM and subsequent interactive image analysis. In the case of physical defects, the size of pores, interacting pore populations and maximum crack lengths are measured. Additionally, the latter are classified with respect to their local orientation in the thermally grown oxide or its vicinity. Finally, the results are discussed with regard to their significance in lifetime modelling of gas turbine components.