Microwave heating of ceramics and its application to joining

Abstract

A new butt joining method for ceramics by microwave heating was developed. Ceramics were heated in a rectangular cavity, and a klystron of maximum 3 kW at 6 GHz was used as the power amplifier. The heating system can control an iris, a plunger, and the microwave power to maintain the power efficiency up to 90% and the accuracy within ±10°C at 1800 °C. This system was applied to alumina-alumina direct joining. The average strength of alumina rods (92% purity) joined for 3 min was 420 MPa, which was equal to the original strength. The joined boundary line at the interface was not observed, and there was little difference in microstructure between before and after joining. This suggests that sintering aids in the grain boundary phase were preferentially heated and melted, resulting in the sound joining of ceramics. Next, silicon nitride ceramics containing yttrium were indirectly joined with an intermediate, which was a sintered ceramic sheet having lower purity and larger dielectric loss factor than the base material. The microwave energy was concentrated on the ceramic sheet, so that only the joining area was locally heated. The strength of the joined rods was in excess of 70% of the base material, but a deficient layer of yttrium occurred in the area of the joined boundary.

Stability of localized structures in non-local reaction-diffusion equations

“…Second, f(u) must be equal to e ClU where ci > 0. The exponential form of f(u) is widely used in ceramic applications [8], including the one of interest in this paper. Thus it is natural to exploit its properties.…”

“…where u denotes a dimensionless temperature along the axis, L(u) models heat loss at the surface of the fiber due to convection and radiation, and the exponential function f(u) represents the effective electrical conductivity of a low-loss ceramic, such as alumina [8]. The parameters D, (3, and x are assumed to be sufficiently small, which is true for fibers, and p is the dimensionless power which is proportional to the square of the amplitude of the mode which excites the cavity.…”

Novel joining of dissimilar ceramics in the Si3N4–Al2O3 system using polytypoid functional gradients

“…Moreover, microwave joining of alumina to magnesia was attempted, and the maximum bending 5 strength of the joint was about 60% of the strength of the raw MgO specimen and the reaction layer was formed at the joining interface [38]. Fukushima [39]. Although interest in microwave processing has grown dramatically in the last decade, this technology is still largely in a developmental stage.…”

“…The joining of similar ceramics has been demonstrated using various techniques, such as brazing [22][23][24][25][26][27][28][29][30][31][32][33][34][35], diffusion welding [36], microwave joining [37][38][39][40] and Transient Liquid Phase methods [41][42][43]. However, the joining of dissimilar ceramics has been more difficult and problematic for several reasons.…”

Fabrication of Reliable Joints of Alumina Ceramics by Microwave-Assisted Reactive Brazing Technique

“…The first report on microwave joining was published by Meek and Blake in 1986 11) that was followed by significant work performed by Palaith and Silberglitt. 12) Joining of oxides, carbides and nitrides was achieved in both single and multimode applicators wherein filler alloys were used that are better microwave absorbers than the substrate materials.…”