(159b) Changes in the Wettability of Calcium Pyrophosphate Induced by Glow-Discharge Radio Frequency Plasma and Muffle Furnace Heating

The ceramic compound calcium pyrophosphate (Ca₂P₂O₇) has been studied extensively over the years. The major applications for this material have been in the development of bio-ceramics, in the form of bone re-generation, luminescence, and more recently with the view to use in mobile telephones as a high quality microwave dielectric.

For all these applications, the knowledge of the wettability of the particles is of importance in the construction of the required structures. Of equal importance is an understanding of how to alter this characteristic for better processing, and if there are any further adverse effects to this in terms of compound/suspension stability. In this paper, the wettability of calcium pyrophosphate is investigated using two techniques, namely that of traditional contact angle measurements (Kruess Tensiometer) and by a gravimetric vapour sorption technique (Dynamic Vapour Sorption Advantage, SMS UK Ltd.). To alter the surface chemistry of the calcium pyrophosphate two methods were utilised. One was a muffle furnace, and the other was by radio frequency glow-discharge plasma. In the muffle furnace, the calcium pyrophosphate was heated at 200, 400, 600 and 800 ^oC for 1 hour before the wettability was investigated. The plasma treatment was at a set power for increasing periods of time. The vapour sorption technique showed that the mass percentage uptake of water increased after plasma treatment, indicating an increase in the wettability of the calcium pyrophosphate. Conversely, increasing the temperature in the muffle furnace led to a decrease in the mass percentage uptake. This is indicative of a decrease in the wettability. Contact angle measurements were performed to confirm this effect. From contact angle data obtained from measurements in different wetting liquids such as ethylene glycol or di-iodomethane surface energies were calculated according to three different methods: 1)Wu, 2)Neumann and 3)Owens & Wendt. The surface energy of the powder investigated is relatively low: 1) 17.7 mJ m^-2, 2) 20.8 mJ m^-2 and 3) 14.8 mJ m^-2. The Owens & Wendt and Wu approach enables the calculation of the total surface energy, as well as the dispersive and polar components themselves. While according to the Neumann method, only the total surface energy can be calculated. The surface energy of the calcium pyrophosphate is dominated by the dispersive component (Owens & Wendt: dispersive component was 14.2 mJ m^-2 and the polar component 0.6 mJ m^-2; calculations according to Wu: dispersive component was 16.3 mJ m and the polar component 1.4 mJ m^-2). Small surface tensions enable better incorporation and acceptance in the body.