Magnetic resonance imaging of water absorption by highly porous ceramic materials

By using the magnetic resonance imaging method the nontrivial character of water absorption was demonstrated for the first time in highly porous ceramic materials. The effect of hygroscopic memory was found out which is that the preferable concentration of absorbed water in certain areas within the sample persists regardless the subsequent sample wetting history. Coating the oxide fibres with fluorine-containing hydrocarbons in supercritical CO2 in order to hydrophobize the material has been shown to affect substantially the water transport within the sample that can be referred to as an effective approach to protect the porous materials from humid environment. The results obtained demonstrate the advantages of the magnetic resonance imaging in studying the water absorption processes and visualization of water pathways in highly porous ceramic materials.

Empirical modelling and optimization of pressure-coupled infusion gyration parameters for the nanofibre fabrication

Pressure-coupled infusion gyration (PCIG) is a novel promising technique for economical and effective mass production of nanofibres with desirable geometrical characteristics. The average diameter of spun fibres significantly influences the structural, mechanical and physical properties of the produced fibre mats. Having a comprehensive understanding of the significant effects of PCIG experimental variables on the spun fibres is beneficial. In this work, response surface methodology was used to explore the interaction effects and the optimal PCIG experimental variables for achieving the desired morphological characteristics of fibres. The effect of experimental variables, namely solution concentration, infusion (flow) rate, applied pressure and rotational speed, was studied on the average fibre diameter and standard deviations. A numerical model for the interactional influences of experimental variables was developed and optimized with a nonlinear interior point method that can be used as a framework for selecting the optimal conditions to obtain poly-ethylene oxide fibres with desired morphology (targeted average diameter and narrow standard deviation). The adequacy of the models was verified by a set of validation experiments. The results proved that the predicted optimal conditions were able to achieve the average diameter that matched the pre-set desired value with less than 10% of difference.

Preparation for the Hollow Nickel Fibres of the Positive Current Collector by Electroless Plating Technique

In this experiment, electroless plating method was used to obtain the hollow nickel fibres. Polyacrylonitrile fibres with the diameter about 10μm and 3mm length were chosen as the templates of electroless-plating through screening and optimizing various fibres. Low temperature alkaline solution with the sodium hypophosphite as the reducer was adopted and the optimal parameters were determined. Polyacrylonitrile composite fibres with a dense nickel coating about 5~7 μm thickness were obtained. The plated fibres were then sintered in the air to remove the organic templates. It had been found that the sintering temperature had great influences on the formation of the hollow fibres. The Polyacrylonitrile fibres could not be removed completely at low temperature (300°C), and when the temperature increased to 400°C, no organic fibres could be observed from SEM and the hollow nickel oxide fibres with dense wall were obtained. However, when the sintering temperature further increased to 500°C, great changes had been found, the hollow fibres with brittle porous wall were obtained. A dense and uniform hollow nickel fibres with nickel content higher than 90% were finally obtained after the hydrogen reduction treatment at the temperature of 750°C for 2 hours.