.S. Hay et al. /Journal of the European Ceramic Society 20 (2000)589-597 2 nm t山Hd WAlNi w Mus Kev(x100) Fig 8. TEM picture of an area around a monazite coating -fiber interface analyzed by TEM. The EDS spectra of spots 1, 2, and 3 on the image are shown to the right. Spot 3 at an alumina-mullite interphase boundary shows trace lanthanum. increase in coating mass loss observed at about 950.C. Although the temperature interval does not exactly match, the heating rate was higher during coating than during the DTA/TGA measurements, so the corre- ponding mass loss during coating should be at a higher temperature. However, there are alternative explana tions for this strength drop that will be discussed in the next section Coating fibers with monazite at 900 C using this par- ticular precursor preserves most of the original tensile strength. However, this would not eliminate tensile strength degradation if composites with these coated fibers were processed or used at or above 1200.C, as shown by tensile strengths of 900C coated fiber heat treated at 1200C(Fig. 10). However, control experiments on uncoated fiber heat -treated at 1200 c have tensile strengths nearly as low as coated fibers. Beneath 1300C grain growth is insignificant in Nextel 720.38 The sensi Fig. 9. High resolution TEM micrograph of a monazite-alumina- tivity of tensile strength to heat-treatment or coating ng mullite triple junction at a coating-fiber interface. No evidence of a atmosphere (Table 1)suggests that degradation is most wetting phase at the interface or triple junction was foundincrease in coating mass loss observed at about 950C. Although the temperature interval does not exactly match, the heating rate was higher during coating than during the DTA/TGA measurements, so the corre￾sponding mass loss during coating should be at a higher temperature. However, there are alternative explana￾tions for this strength drop that will be discussed in the next section. 4. Discussion Coating ®bers with monazite at 900C using this par￾ticular precursor preserves most of the original tensile strength. However, this would not eliminate tensile strength degradation if composites with these coated ®bers were processed or used at or above 1200C, as shown by tensile strengths of 900C coated ®ber heat￾treated at 1200C (Fig. 10). However, control experiments on uncoated ®ber heat-treated at 1200C have tensile strengths nearly as low as coated ®bers. Beneath 1300C grain growth is insigni®cant in Nextel 720.38 The sensi￾tivity of tensile strength to heat-treatment or coating atmosphere (Table 1) suggests that degradation is most Fig. 8. TEM picture of an area around a monazite coating Ð ®ber interface analyzed by TEM. The EDS spectra of spots 1, 2, and 3 on the image are shown to the right. Spot 3 at an alumina±mullite interphase boundary shows trace lanthanum. Fig. 9. High resolution TEM micrograph of a monazite±alumina± mullite triple junction at a coating±®ber interface. No evidence of a wetting phase at the interface or triple junction was found. R.S. Hay et al. / Journal of the European Ceramic Society 20 (2000) 589±597 593