Dustin M. Hulbert

The Absence of Plasma in "Spark Plasma Sintering"

Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.

Spark plasma sintering and forming of transparent polycrystalline Al 2 O 3 windows and domes

Spark plasma sintering(SPS) method was used to produce transparent alumina and it proved to be a cost-effective method due to short processing cycle. It was found that the optical transmittance of alumina is greatly influenced by SPS sintering parameters. A maximum transmittance of 85% has been achieved by sintering at 1300°C for 5min. Annealing in air at 1250°C for 24h significanly increased mid-infrared transmission. Utilizing SPS, transparent polycrystalline alumina domes have been successfully produced by combining sintering and forming into one step in minutes instead of hours needed when using conventional methods. This is a near-net-shape forming method such that only a minor amount of machining or polishing is needed. The present forming method provides an unprecedented opportunity to make optically transparent domes at much lower costs.

Mechanical Properties of Nanocomposite Materials

Publisher Summary This chapter discusses the mechanical properties of nanocomposite materials. It describes an attractive processing methodology—spark plasma sintering (SPS); by using this as a processing tool, microstructures of ceramic-based nanocomposites that have either much improved fracture toughness or significantly enhanced superplastic formability, or much improved creep resistance, can be engineered. It has been shown that the ability to design the mechanical properties of new materials in the nanocrystalline range depends upon the design and production of novel microstructures. This requires control of grain size and grain size distribution, reinforcement-particle (or fiber) morphology, and the amount and distribution of dopants and reinforcement elements. In metal-based nanocomposites, designed nanostructure might be obtained by various methods that include crystallization from amorphous state. The results present in the chapter provide new insights to the strengthening mechanisms operative in nanoscale multilayered materials.