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FF Lange

Publications and source records attributed to FF Lange.

4 recordsLinked to original sources
PubMed1999

Laminar Ceramics That Exhibit a Threshold Strength.

Thin compressive layers within a laminar ceramic arrest large cracks (surface and internal) and produce a threshold strength. This phenomenon increases the damage tolerance of ceramics and will allow engineers to design reliable ceramic components for structural applications. The stress intensity factor derived for a crack sandwiched between two compressive layers suggests that the threshold strength is proportional to the residual compressive stress and the thickness of the compressive layer and is inversely proportional to the distance between the compressive layers. Laminates composed of thick alumina layers (605 +/- 11 micrometers) and thin mullite/alumina compressive layers (37 +/- 1.4 micrometers) fabricated for this study had a threshold strength of 482 +/- 20 megapascals, in fair agreement with the theory.

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PubMed1997

Plastic-to-Brittle Transition of Consolidated Bodies: Effect of Counterion Size

The effect of ion size on the force necessary to remove counterions from the surface when particles are forced into contact (primary minimum) was investigated. Alumina slurries dispersed at pH 12 and then coagulated with 0.5 M Li+, Cs+, and tetraethylammonium (TEA+) chlorides were consolidated by pressure filtration at different applied pressures. Uniaxial compression tests were performed to determine the plastic-to-brittle transition pressure for bodies formulated with each of the different counterions. Brittle bodies are produced when particles are pushed together to form a strong touching network. The force required to push particles together is related to the slope of the repulsive potential barrier, with steeper slopes requiring greater force. The consolidation pressure necessary for brittle behavior was greater for slurries with small counterions such as Li+ as compared with Cs+ and TEA+. The results presented here show that the resistance to pushing particles into contact is related to the size of the bare counterion in weakly attractive (salt-coagulated) slurries. That is, the slope of the potential barrier produced when the slurry is formulated with smaller ions is steeper. This result is consistent with the idea that smaller counterions are more strongly bound to the surface, as well as the fact that the repulsion due to the finite size of the ion occurs at smaller interparticle separation distances for the smaller counterions. Copyright 1997Academic Press

Journal Article↗
PubMed1996

Chemical Solution Routes to Single-Crystal Thin Films

Epitaxial thin films of inorganic single crystals can be grown on single-crystal substrates with a variety of different solution chemistries. This review emphasizes chemical solution deposition, in which a solution is used to deposit a layer of precursor molecules that decompose to low-density, polycrystalline films during heating. Ways to control film cracking during deposition and heat treatment and why many precursors synthesize metastable crystalline structures are discussed, and the different mechanisms that convert the polycrystalline film into a single crystal are reviewed. Hydrothermal epitaxy, in which single crystal thin films are directly synthesized on templating substrates in an aqueous solution at temperatures <150&deg;C, is also discussed.

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