Neutron Diffraction Measurements of the Residual Stresses in Al2O3-ZrO2 (CeO2) Ceramic Composites

High-resolution neutron powder diffraction was used to study the residual stresses in Al₂O₃-ZrO₂ (12 mol% CeO₂) ceramic composites containing 10, 20, and 40 vol% ZrO₂ (CeO₂). The diffraction data were analyzed using the Rietveld structure refinement technique. The analysis shows that for all samples, the CeO₂-stabilized tetragonal ZrO₂ particles are in tension and the Al₂O₃ matrix is in compression. For both the ZrO₂ particles and the Al₂O₃ matrix, the average lattice strains are anisotropic and increase approximately linearly with a decrease in the corresponding phase content. It is shown that these features can be qualitatively understood by taking into consideration the thermal expansion mismatch between the ZrO₂ and Al₂O₃ grains. Also, for all composite samples, the diffraction peaks are broader than the instrumental resolution, indicating that the strains in these samples are inhomogeneous. From an analysis of the refined peak shape parameters, the average root-meansquare strain, which describes the distribution of the inhomogeneous strain field, was determined. Finally, the average residual stresses were evaluated from the experimentally determined average lattice strains and compared with recent results of X-ray measurements on similar composites.     

Evaluation of a direct immunofluorescence cytospin assay for the detection of herpes simplex virus in clinical samples

A comparison between a direct immunofluorescence assay (DFA) and the shell-vial culture (SVC) was conducted to evaluate their efficacies according to the quality and origin of the sample and the type of herpes simplex (HSV) responsible for the infection. The SVC detected all 58 HSV-infected samples, while the DFA detected only 49 (84.5%) positive samples. The DFA detected HSV type 1 in 22 of 89 samples (24.7%) and HSV type 2 in 27 of 96 samples (28.1%). Compared with the SVC, the DFA had a sensitivity of 75.8% for HSV type 1 and 93.1% for HSV type 2. The sensitivity of the DFA depends on the quality of the sample. Thus, while DFA is recommendable as a screening method, the SVC remains the method of choice for obtaining the maximum diagnostic yield from the sample.     

Phase-transformation study of metastable tetragonal zirconia powder

The rate of the transformation from the metastable tetragonal to the monoclinic phase of ZrO2 was measured in air from 850°C to 1000°C by neutron diffraction. This rate was found to be temperature dependent, and its measured values were considerably lower then those reported previously. The kinetics of this phase transformation is discussed in terms of a modified crystallite growth-martensitic transformation model' that includes the distribution of crystallite sizes.