R.S. Hay et al. Journal of the European Ceramic Society 20(2000)589-597 DTA TGA Fig. 2. DTA/TGA of monazite precursor Scale for DTA trace is not 100nm ictures of typical coating anomalies: (a) Debonded n, poorly crystallize coating;(c) Broken filament to filament bridge. 3.3 The most obvious change in the coatings as deposi tion temperature increased from 900 to 1300C was a 100 300500700 decrease in pore volume fraction and an increase in pore size from 8 to 25 nm in diameter(Fig. 5). There were Temperature(C) other more subtle differences in coating microstructure. For coatings deposited at 900C, SAD patterns from Fig 3. Mass spectrometry of gas evolution from monazite precurso the coatings were roughly consistent with monazite, but diffraction spots were diffuse and streaked, and a fine <50 nm)grain size was inferred from the patterns Diffraction contrast did not change abruptly across DTA exotherm at about 450 C. The mass spectrometry grains as the sample was tilted; instead, diffuse diffraction specimen was black after the measurement, suggesting contrast swept irregularly across the coating, and iden- incomplete oxidation of carbonaceous species in the tification of specific grains was difficult. Evidently the argon environment. monazite coating grains were highly defective, but the defects could not be identified. For coatings deposited 3.2. Coatings-general at 1300C, diffraction patterns were sharp, with individual grains easily identifiable. Defects other than intra Coating thickness and morphology was similar to that granular porosity were not observed. The coating grain observed previously for this precursor. Coating cover- size was often much greater than the coating thickness age was continuous. Coating bridges between filaments thin poorly crystallized coatings, and debonded or 3.3.1. 1200C heat-treatments buckled"coatings were occasionally observed(Fig. 4) Coatings deposited at 900C and then heat-treated at Significant place to place variations in pore volume 1200oC had somewhat different microstructures. Two fraction and size were also observed. Coating thicknes hours at 1200.C changed the defective, porous, and averaged about 80 nm, with variations between 30 and poorly crystallized monazite grains(Fig. 5)to small( 120 common. Although a small amount of La PO, was nm diameter), well crystallized monazite grains with a observed by X-ray, no evidence of any phase other than small amount of porosity(Fig. 6). One hundred hours monazite was found in fiber coatings by tEM at 1200C caused grain growth to 100 nm diameterDTA exotherm at about 450C. The mass spectrometry specimen was black after the measurement, suggesting incomplete oxidation of carbonaceous species in the argon environment. 3.2. Coatings Ð general Coating thickness and morphology was similar to that observed previously for this precursor.6 Coating cover￾age was continuous. Coating bridges between ®laments, thin poorly crystallized coatings, and debonded or ``buckled'' coatings were occasionally observed (Fig. 4). Signi®cant place to place variations in pore volume fraction and size were also observed. Coating thickness averaged about 80 nm, with variations between 30 and 120 common. Although a small amount of La3PO7 was observed by X-ray, no evidence of any phase other than monazite was found in ®ber coatings by TEM. 3.3. Coating temperature The most obvious change in the coatings as deposi￾tion temperature increased from 900 to 1300C was a decrease in pore volume fraction and an increase in pore size from 8 to 25 nm in diameter (Fig. 5). There were other more subtle di€erences in coating microstructure. For coatings deposited at 900C, SAD patterns from the coatings were roughly consistent with monazite, but di€raction spots were di€use and streaked, and a ®ne (<50 nm) grain size was inferred from the patterns. Di€raction contrast did not change abruptly across grains as the sample was tilted; instead, di€use di€raction contrast swept irregularly across the coating, and iden￾ti®cation of speci®c grains was dicult. Evidently the monazite coating grains were highly defective, but the defects could not be identi®ed. For coatings deposited at 1300C, di€raction patterns were sharp, with individual grains easily identi®able. Defects other than intra￾granular porosity were not observed. The coating grain size was often much greater than the coating thickness. 3.3.1. 1200C heat-treatments Coatings deposited at 900C and then heat-treated at 1200C had somewhat di€erent microstructures. Two hours at 1200C changed the defective, porous, and poorly crystallized monazite grains (Fig. 5) to small (40 nm diameter), well crystallized monazite grains with a small amount of porosity (Fig. 6). One hundred hours at 1200C caused grain growth to 100 nm diameter Fig. 2. DTA/TGA of monazite precursor. Scale for DTA trace is not given. Fig. 3. Mass spectrometry of gas evolution from monazite precursor. Fig. 4. TEM pictures of typical coating anomalies: (a) Debonded coating; (b) Thin, poorly crystallize coating; (c) Broken ®lament to ®lament coating bridge. R.S. Hay et al. / Journal of the European Ceramic Society 20 (2000) 589±597 591