Neutral emission from fracture

Neutral emission accompanying fracture has two origins (a) basically degassing from a freshly exposed surface of gases that are trapped in the material (within voids, grain boundaries, inclusions, etc.) and (b) species resulting from bond scissions (sometimes referred to as... 

J. T. Dickinson and L. C. Jensen, Neutral emission from the fracture of epoxy, J. Appl. Phys. (to be submitted). 

Significant neutral emission is also observed during and after fracture. When analyzing the time dependence of the observed NE, one must take into account both the time dependence of the emission itself and the time-of-flight of the neutral species (associated with Boltzmann velocity distributions) from the source to the mass spectrometer. We expect NE intensities to be much higher than the PIE intensities of the same molecular species due to the high probability of reneutralization as ions leave the surface. NE will be discussed more fully in the following section. 

Neutral emission of species other than atomic Mg from MgO is a strong function of impurity content or microstructure (4). Samples with a cloudy appearance due to the presence of brucite (Mg(OH)2) precipitates, displayed especially high NE intensities of O2, CO, H2O, and CH4. The cloudy MgO is nominally as pure as the clear with respect to metallic impurities. Single crystals of MgO are often grown in an arc furnace, with water and carbon as minor impurities. Small amounts of brucite can precipitate in portions of the crystal mass. The precipitate/MgO interface can serve as a sink for many species which are then emitted as these interfaces are exposed in fracture. The cloudy MgO is more typical of geologic materials than clear MgO, implying that NE from geologic materials can be quite intense and rich. 

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

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