The microstructures of thick plasma-sprayed yttria-stabilized zirconia (8% mass fraction yttria) deposits were studied in a series of Porod small-angle neutron scattering (SANS) and multiple small-angle neutron scattering (MSANS) experiments. Three main void components were identified in the deposits: intrasplat cracks, interlamellar planar pores, and globular pores. The SANS and MSANS measurements were analyzed using the traditional theory for Porod scattering and a recently developed three-component model for MSANS evaluation. The average size, volume fraction, internal surface area, and orientation distribution for each void component within the deposits were determined. This study focused on gaining a better understanding of the effects of initial feedstock particle size and annealing temperatures on the microstructure of deposits sprayed under equivalent particle-impact conditions. Quantitative results are presented for each of four deposit samples: one prepared using the as-received feedstock particle wide-size distribution and three prepared from feedstock powder of different and relatively narrow particle size ranges with average sizes of 32, 47, and 88 μm. Except for the coarse (88 μm) feedstock powder, only mild monotonic variations were found in the microstructural anisotropies, the porosities (13 ± 1%), and the internal surface areas in the as-sprayed deposits. The internal surface area was independent of the feedstock particle size, even with the coarse feedstock. When the deposits were annealed at high temperatures (1100 and 1400 °C), the microstructures were altered with a reduction of the total internal surface area and a mild coarsening of the voids. These changes in the microstructural evolution were well-captured and described by the three-component model. The results were compared and related with those obtained from scanning electron microscopy images and elastic moduli measurements.

The role of 12.4 vol% ZrO2 addition in the microstructure evolution of alumina compacts during the intermediate and final stages of sintering was investigated by means of small-angle neutron scattering measurements and stereological analysis. Both the pore-size evolution results and the grain-growth data indicate a narrowly defined onset density for the transition to the final sintering stage. The presence of ZrO2 as a second phase apparently maintains the stability of the intermediate sintering stage out to significantly higher density than in single-phase alumina and plays an important role in inhibiting grain growth and in preventing pore–grain boundary separation. The influence of the ZrO2 second phase on pore evolution, grain growth, and sinterability of the alumina–zirconia composite is discussed and compared to the behavior of single-phase alumina. The samples were prepared from commercially available powders, with naturally occurring porosity distributions, rather than from artifact(model) pore compacts prepared from nominally pure research-grade materials. The goal was to gain an improved understanding of microstructure development in real materials.

Processing-microstructure relationships in a silica gel system, based on mixtures of colloidal sol and soluble potassium silicate, have been studied. Quantitative microstructural information regarding colloidal cluster sizes, size distributions, surface areas, and pore-size distribution from the nanopore range to the macropore range was determined via small-angle scattering and transmission electron microscopy. The colloid cluster size distribution varies systematically, with gels fabricated with the least colloidal fraction possessing the most polydisperse microstructure. It is shown that the porosity over the entire range can be tailored by selecting the appropriate starting chemistry; under the same pH conditions, the ratio of the two silicate ingredients controls the average size, the polydispersity of sizes, and the connectivity of the pores. A population of fine (2 nm) uniformly dispersed nanopores, which result from leaching, is responsible for large increases in surface area. The leaching process can be controlled by the surrounding macropore void size, which determines alkali transport. The product material consists of 85% large, open pores, with fine pores within the gel skeleton, making this gel an ideal candidate for controlled-porosity applications such as catalyst supports and magnetic composites.

Poly(methyl methacrylate) (PMMA) based orthopaedic bone cements contain 1-3 Pim size radiopacifier particles. Incomplete dispersion of these particles leads to the presence of 50-200 μm size agglomerates. These large defects are sites of high-stress concentration that reduce the fracture toughness of PMMA. In this study, the micrometer-sized radiopacifying particles of a commercial bone cement were replaced by nanosized fillers. Both, commercial and nanocomposite PMMA bone cements were characterized using ultra-small angle x-ray scattering and low voltage scanning electron microscopy; mechanical properties were evaluated using ASTM standard tensile testing. The results showed a substantial reduction of particle agglomerate size and a significant increase in tensile properties of the nanocomposite over that of the standard microcomposite bone cement.

Studies of microstructure evolution as a function of sintering parameters are necessary to better control the microstructure of nanophase ceramic compacts during processing. Small-angle scattering provides a comprehensive probe of the statistically-representative microstructures present in nanophase ceramics. A complete characterization includes complementary density, electron microscopy, nitrogen desorption and x-ray diffraction measurements. Small-angleneutron and ultra-small-angle x-ray scattering have been used to determine the effects of different sintering temperatures, pressures and additives during sintering of nanophase zirconia compacts. The samples were of sufficient size and uniformity to permit absolute calibration of the scattering data, making it possible to confirm that scattering from the pore/grain interface dominates the total scattering cross-section. A quantitative microstructural model was developed for this system, resulting in the determination of specific pore surface area, total pore volume fraction, pore number size distribution and grain size as a function of sintering parameters.

An enhanced multiple small-angle neutron scattering (MSANS) formulation has been developed to interpret the beam-broadening, arising from coarse, concentrated pore/grain microstructures in porous ceramics and similar materials. Prolific scattering from such systems precludes single-scattering studies (apart from Porod surface determinations). Previous MSANS techniques, which have been developed to extract the mean pore dimensions, either treat a range of scattering morphologies, while assuming that the scattering is in the diffraction limit, or they consider refraction effects, while assuming that the scattering features are spherical. Many systems of interest violate both these assumptions. In the enhanced formulation, the previous method, which allowed fully for refraction, is extended to non-spherical scattering morphologies. Applications of the MSANS formulation to sintering studies of Si3N4 and silica gels, and to the microstructural characterization of plasma-spray coatings are currently of interest.

The isothermal sintering behavior of a colloidal gel with a well-characterized pore structure was studied using a newly commissioned in-situ small-angle neutron scattering furnace. The apparatus enables small-angle scattering measurements to be performed on monolithic samples during heat treatment in an oxidizing, reducing, or neutral environment at temperatures up to 1700°C. In-situ, quantitative measurements of the pore size evolution within a gel possessing a bimodal pore size distribution is discussed. Also reported is the in-situ measurement of the gel's surface area evolution which is an important microstructural parameter in understanding the sintering behavior of highly porous materials.