With developments of electronics, heat radiation of circuit boards and components are also showing an increasing level, which result in more and more studies on heat radiation materials for high efficiency. Alumina is very suitable for fabricating heat radiation materials because of its high thermal conductivity and low electrical conductivity. In particular, if alumina rods are lined up in the direction of thermal conduction, high thermal conductivity can be obtained.

Electrospinning is one of the routes for preparing high purity ceramic fiber, in which ceramic and polymer com pounds are used as raw materials. Although alumina nanofibers can be prepared by electrospinning, only limited information is available on spinning and calcination conditions for preparing alumina rods and fibers. Therefore, in this study, the different forms of ASB/PVP composite fibers prepared under various electro-spinning conditions are observed, and identify adequate calcination conditions for preparing α phase alumina rod from composite fibers.

After mixing aluminum sec-butoxide(ASB) with ethanol and distilled water in a ratio of 1:16:0.6 at 80℃ for 45mins, acetic acid was added to obtain an alumina gel. PVP solutions was prepared using ethanol as the solvent at concentrations of 5%, 10% and 15% subsequently, the PVP solution and mixed gel were blended in a ratio of 3:1 for 24 hours.

For electrospinning, the ASB/PVP solution was injected using a plastic syringe through a blunt needle tip at a constant flow rate using syringe pump.  The value of positive voltage applied to the polymer solution was increased gradually within the range of 10-25 kV.

A grounded counter electrode was connected to the collector covered with an aluminum foil. After curing at 300-500℃ for 24 hours, the nanofibers were heated at 800-1100℃ in a muffle furnace. Finally, calcined α phase alumina was ground in an agate mortar to form α phase alumina rod.

Diameter of ASB/PVP composite fibers decreased with decrease of polymer concentration, because viscosity of the solution at low concentration is lower than the surface tension. As the voltage applied throughout the syringe needle increased, the excessively high voltage resulted in undesirable stretching, resulting in markedly low fiber diameters.

Because when voltage higher than the critical value is applied, charge density increases, and consequently, the viscosity of the spinning solution decreases and the Taylor cone becomes unstable. As the flow rate of the spinning solution increased, average diameter also increased. However, when the flow rate was excessively high, the unstable Taylor cone failed to stretch.

In order to obtain α phase alumina from the ASB/PVP composite fibers. PVP must be removed from the fibers by calcination. Thermo gravimetric analysis of fibers indicates that moisture is removed from the fibers at temperatures in the range 25-120℃, and PVP in the composite fiber decomposes at temperatures between 200 and 800°C. A strong peak was observed at 340.78℃, resulting from decomposition of PVP, which is highly exothermic reaction. ASB/PVP composite fibers heated to 1000℃ melted, and the fiber form was no longer identifiable.

When calcination temperature was increased, the stretching vibration peak of Al-O became stronger, which means that when the calcination temperature was increased, PVP decomposed and alumina was formed.

The optimum composite fibers (300-500nm in diameter) were obtained when the voltage, flow rate, TCD, and PVP concentration were 15kV, 0.025ml/min. 15cm, and 10%, respectively. After the ASB/PVP composite fibers were cured at 500℃ for 24 hours, they were heated at 1000℃ and subsequently ground to obtain α phase alumina rods, and this preparation method can be also used for factory mass production.