Preparation and characterization of electroless nickel-coated cellulose fibres
The aim of this project was to fabricate electroless nickel-coated cellulose fibres. Ultimately, these nickel-coated cellulose fibres will be used to develop a cost-effective polymer composite for electromagnetic interference (EMI) shielding and/or electrostatic discharge (ESD) applications. An attempt has been made to impart electrical conductivity onto cellulose fibres via an electroless nickel plating process. The aim was to achieve a homogeneous, continuous layer of Ni on the cellulose fibres, and the plating conditions were optimized to achieve this. The relationship between the coating morphology and the performance of the coated fibre was also of interest. Testing was carried out using cellulose filter paper and then loose cellulose fibres. Scanning electron microscopic (SEM) images of nickel-coated filter paper showed that nickel particles are bonded to the cellulose fibres. The coating appeared more compacted and continuous as plating time increased, corresponding to lower surface resistivity. This observation suggested a correlation between morphology and electrical conductivity of the coating. For nickel-coated cellulose fibres, after optimization of plating conditions, a uniform deposition of nickel particles around the cellulose surfaces was confirmed by SEM images. EDS and XRD results confirmed similar coating could be produced on filter paper and cellulose fibres. SEM images of cross-sectioned nickel-coated cellulose fibres illustrated nickel particles had penetrated into the inner walls of the cellulose fibres. This impregnation of the fibres should act to increase the bonding between nickel coating and cellulose fibres. These nickel-impregnated cellulose fibres could now be incorporated into a polymer matrix to create an electrically conducting composite with the right processing parameters.
Conductive Papers Containing Metallized Polyester Fibers for Electromagnetic Interference Shielding
Conductive papers were developed for preventing or reducing electromagnetic interference (EMI), and their shielding efficiency was evaluated. This type of conductive paper consists of wood pulp, synthetic pulp and metallized polyester fibers (0.5–2.0 mm long and 14 μm in diameter) whose surfaces are coated with nickel alone (Ni-PET) or copper and nickel double layers (Ni-Cu-PET) by electroless plating. In this report, the effect of the characteristics of these metallized fibers, such as their conductivity, geometry and the concentration of fibers in paper, which lead to high efficiency for shielding effectiveness is discussed. For instance, one of the conductive papers (80 g/m2) which was prepared by mixing 40% Ni-Cu-PET and 60% synthetic polyethylene pulp showed over 40 dB shielding effectiveness between 10 MHz and 1 GHz.
State-of-the-Art of Thermal Spray Coatings for Corrosion Protection
ABSTRACT Thermal-spray coatings are widely used in marine structures including offshore pipelines without external cathodic protection (CP). Al, Zn and Zn-Al thermal-spray coatings protect steel by acting both as barrier coatings and as sacrificial anodes at local defects where corrosion would otherwise occur. Zn provides better galvanic protection whereas Al is better as a less-reactive barrier layer. Zn-Al alloys appear to combine the protective properties of both Zn and Al. Although further research is required in order to specify the optimal alloy compositions for specific applications, 85% Zn-15% Al alloy is widely used. The best long-term protection is provided by suitably primed, sealed, and painted thermal-spray coatings. Thermal-spray coatings of acceptable structures and properties can be produced by flame spraying (wire or powder), arc spraying or plasma processing. However, due to economical reasons low melting point metals and their alloys are sprayed either by arc or flame. Surface preparation is considered to be a key factor in the production of uniform high quality coatings with maximum bond strength. Also of equal importance are the control of process facilities, equipment selection, and quality of consumable material for applying thermal-spray coatings. Well-bonded, relatively dense, sealed coatings have the ability to provide effective long term corrosion protection (10-20 years), with minimum periodic maintenance. Standards for evaluating thermal spray coatings have recently been developed.