Alan Hynes

Comparison of pilot and industrial scale atmospheric pressure glow discharge systems including a novel electro-acoustic technique for process monitoring

A comparison of a pilot and industrial scale atmospheric pressure polymer processing plasma system has been carried out using process-monitoring diagnostic tools during treatment of amorphous polyethylene terephthalate. These systems have been compared using optical emission spectroscopy (OES), photodiode (PD) analysis and multi-variate analysis of the applied electrical and emitted electro-acoustic signals to facilitate scale up operations from the pilot to the industrial scale system. The voltage, current, electro-acoustic intensity and frequency of the plasma systems were found to change systematically with an increase in applied plasma power and addition of oxygen (O2) into a helium (He) plasma. The plasma drive frequency was pulled by the plasma reactance from approximately 26 to 16 kHz on the pilot system and from approximately 36 to 32 kHz on the industrial system, for an increase in applied plasma power and addition of O2. The OES analysis revealed a number of peaks associated with nitrogen (N2) species between 250 and 450 nm due to the presence of air within the He plasma. Temporally resolved analysis of the discharge emission carried out using a PD showed an increase in the number of discharge events per power cycle with an increase in power and a decrease in emission intensity for addition of O2 into the He plasma for both the pilot and industrial scale systems. Using these diagnostic tools both plasma stability and run to run variations were assessed. A visual analysis of the 1.2 m wide plasma was also carried out where a more homogeneous plasma was observed at higher powers.

Comparing Deposition Properties in an Atmospheric Pressure Plasma System Operating in Uniform and Nonuniform Modes

A large-scale atmospheric pressure plasma has been generated in helium, and the time-resolved optical and electrical properties have been shown to produce a homogeneous dielectric barrier discharge. Introducing tetraethyl orthosilicate as a liquid aerosol into this plasma produced clear, uniform, and smooth plasma polymerized coatings. Optical imaging studies have shown that adding 1% oxygen to the gas mixture induced a switch from a homogeneous plasma to a filamentary or microdischarge mode of operation, and this has been shown to dramatically alter the morphology of the deposited coatings. Surface analysis reveals significant particulate inclusions in coatings deposited from the filamentary mode of operation.

Plasma power can slash small run sintering times

A group of Irish researchers have demonstrated that rapid discharge sintering can dramatically reduce sintering times for processing small numbers of green compacts. But while mainstream sintering technologies have the upper hand for the time being, commercial prospects for plasma are being assessed…

Evaluation of real-time non-invasive diagnostic tools for the monitoring of a pilot scale atmospheric pressure plasma system

A set of real-time non-invasive multivariate analysis tools were evaluated using LabVIEW software for the process monitoring of an atmospheric pressure plasma system. During system operation, it was observed that the optical and electrical properties are subject to a deterministic jitter effect caused by momentary changes in the discharge characteristics. This temporal jitter in the voltage, current and frequency of the applied power to an atmospheric pressure plasma was monitored to assess the plasma processing conditions. Electrical diagnostic tools were used to determine the transition of the plasma from the primary glow mode to the secondary glow mode and were correlated with photo diode (PD) analysis of the plasma. Intensified charge-coupled device (ICCD) imaging of the plasma was also used to distinguish between glow and Townsend discharge properties at low applied powers (400 W). The electrical observations were recorded in real time, plotted on a principal component analysis (PCA) loading plot and analysed using non-parametric cluster analysis (NPCA). It was observed from the plotted electrical parameters that data clusters were formed which relate to both the geometry of the atmospheric plasma chambers and the mode of plasma operation. The development of these tools facilitates real-time analysis of this reel-to-reel atmospheric pressure plasma processing system.

Comparison of thermal and microwaveassisted plasma sintering of nickel–diamond composites

There is considerable interest in processing technologies which can lead to more energy efficient sintering of metal powders. Microwave sintering has been shown to reduce energy usage as volumetric heating is more efficient than resistance heating. Plasma sintering meanwhile delivers heat via uniform excitation of the processing gas. The use of a rapid, novel microwave-assisted plasma sintering (MaPS) technology has been evaluated for processing nickel-diamond composites. Discs fired in a low pressure microwave plasma under a hydrogen atmosphere were compared with discs sintered in a conventional tube furnace. MaPS is very rapid, with full disc strength being achieved within 10 min, compared with 8 h for furnace treatment. MaPS produced similar or superior mechanical properties to furnace sintering but with sintering cycle time reduced by up to 95%.