Single-Mode Microwave Sintering of Traditionally Resistant Materials
Abstract
Microwaves can be effectively exploited and controlled by designing a sample chamber with a resonant cavity that produces a standing wave in which the electric and magnetic field components are spatially separated. This can lead to distinct regions in which the sample can be positioned for exposure to a specific set of microwave conditions (100 electric, 100 magnetic, mixed ratio of electric-to-magnetic). Processing of ceramics under microwave frequencies has been pursued for several decades, but success has been dictated by the limited number of ceramics that readily couple with microwave fields. Compatible ceramics generally have high dielectric losses, which cause heat to build up in the material, promoting uniform densification and fine grain structures. However, most materials are not microwave-susceptible and require an external susceptor to harness the microwave energy and transfer the heat to the sample. Alternatively, internal susceptors can provide localized heating of microwave-transparent ceramics, thereby reducing sintering times and helping to maintain a finer grain size. In this work, efforts to blend hybrid ceramic materials composed of microwave-transparent materials and ferromagnetic materials (which act as internal susceptors) are pursued to obtain dense materials with fine microstructures. Microwave sintering of alumina using microwave-susceptible nickel ferrite plate yielded a density only 8 greater than the original green density, whereas use of nickel ferrite as an internal susceptor forming a ceramic composite increased density by 22 at a lower temperature than the external susceptor sintering method.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2018
- Accession Number
- AD1059385
Entities
People
- Michael Kornecki
- Raymond E. Brennan
- Selva V. Raju
- Victoria L. Blair
Organizations
- United States Army Research Laboratory