Isolating Field Effects in Sintering via Ultrahigh Temperature In Situ Nanomechanics

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Most ceramic products and devices originate from crystalline powders consolidated at high temperatures; a process called sintering. Traditional sintering typically requires a large input of energy, significant equipment costs, and relatively long manufacturing times. Application of electric fields during sintering can greatly reduce these costs and processing times. Unfortunately, electric field effects remain poorly understood owing in large part to (1) the great geometrical complexity of sintering and (2) a poor understanding of atomic motion and bonding at crystal surfaces where powder bonds during sintering. The lack of scientific understanding impairs engineers' ability to design optimal manufacturing conditions and produce new materials. This project develops a new methodology that efficiently isolates the physical properties of the material from particle geometry effects. As a result, unprecedented information about how electric fields affect bonding and atomic motion on surfaces can be obtained. This information can define which parameters are most important during electric field assisted sintering, and as a result, strategies to optimize manufacturing conditions. The work is technologically relevant to development of new ultrahigh temperature aerospace materials, advanced optical ceramics, and ceramics in microelectronics. The project supports the training of a graduate student in materials science and engineering. Graduates then typically work in industrial research laboratories in large manufacturing firms. The project also provides research opportunities for underrepresented high school students and pre-service teachers, and outreach activities targeted towards K-12 students. These activities are intended to attract students to science and engineering careers. TECHNICAL DETAILS: Electric fields can dramatically accelerate sintering kinetics, as is often observed during spark plasma sintering or flash sintering. However, the mechanisms underlying these processes remain highly controversial and poorly understood. The lack of fundamental knowledge derives from the complexity of the sintering process and the coupling of the electric field to all relevant diffusional and thermodynamic coefficients. The experiments isolate these effects by (1) measuring electrocapillarity coefficients of grain boundaries and surfaces in zirconia using a nanoscale zero creep experiment in applied fields, (2) quantifying electric field dependent grain boundary and surface diffusion coefficients via nanoscale single grain boundary Coble creep and surface smoothing experiments, respectively, and (3) controlling for anisotropy by using representative low and high energy bicrystal geometries. The work emerges from the development of novel ultra-high temperature in situ transmission electron microscopy based nanomechanical testing methods. The transformational impacts on the discipline are a new mechanistic understanding of electric field effects on sintering, new insights into field dependent interface thermodynamics in oxides, and the development of novel experimental methodologies useful for addressing many problems in ceramic science. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.