In-Situ Microstructure Characterization of Sintering of Controlled Porosity Materials

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177 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society

there are incoherent multiple scattering events that cannot be interpreted in the conventional manner. Developments (5,6) and implementation (7) of multiple small-angle neutron scattering (MSANS) theory has extended the measurable feature size range to 80-10,000 nm in non-dilute (> 2 %) thick samples; i.e., the size, density range, and geometric form most relevant to ceramics. Data treatment involves the analysis of the low q (scattering wavevector) regime where multiple scattering dominates and the scattering curve exhibits beam broadening as a function of wavelength. In-situ multiple scattering data obtained from a ceramic system during sintering are shown in figure 1, where the ordinary transmitted beam is represented by the "blank" data with no sample present. There is clearly significant broadening when compared to the blank curve. The effective pore radius, Reff, is directly obtained from an analysis of broadened curves such as those shown in figure 1. The large q or Porod region of the scattering curve has been shown (5) to be stable against multiple scattering events, thus the conventional derivation of total surface area at large q is also available. Our ability to interpret multiple scattering curves as well as conventional single scattering data, including their respective Porod regimes, enables us to perform a comprehensive analysis of synthesis schemes and thermal treatments of ceramics

whose voids extend from the micropore (< 2 nm) to macropore range (i.e., 50-10,000 nm). Until recently, it has been difficult to perform in-situ microstructure investigations because of the lack of instrumentation for the noninterruptive measurement of the kinetics of microstructure development. Hot-stage microscopy (8) and loaded dilatometry (9) have been employed to obtain in-situ data on particle and pore morphology and shrinkage during sintering, respectively. SANS combines the major advantages of these aforementioned techniques. Specifically, like dilatometric measurements, the data from small-angle neutron scattering are representative of the bulk. Analogous to microscopy, SANS affords particular microstructural details such as particle or pore morphology and size information. The in-situ small-angle scattering furnace offers the opportunity to measure microstructural changes heretofore unattainable by conventional ceramics characterization techniques. 9k

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Q (nm") Figure 1: Multiple small-angle neutron scattering curves taken at X 1.4 nm as a function of sintering time illustrating the evolution of beam broadening as sintering proceeds.

178

EXPERIMENT Furnace Design A number of furnaces have been constructed and successfully applied to neutron scattering research, and a good review article (10) is available of the earlier work. The unique feature of the furnace described here and illustrated in figure 2 is that it has

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