S Ji et al. /Journal of the European Ceramic Society 25(2005)301-317 Hot-pressed particulate composite 001 [100] (50%Qt,50%CAS J12-QA N=300 Mean grain size: 2.1 om L。ower L001] [100 Fig. 5. Preferred orientations of triclinic CAS(0 10)[100] and [001] Grain size, dm for undeformed, hot isostatical pressed, pure CAS aggregate(sample J7) Notice that the whole sphere, rather than a hemisphere, is necessary to J12-QA represent the distribution of the positive directions. Projections on the lower(a)and upper(b) hemispheres. Stereonets are equal-area plots: 130 measurements are used N=300 Mean aspect ratio: 2.2 (3)TEM(Philips CM200, GFZ-Potsdam, Germany)op- erating at 200 kV shows that the grain boundaries in the CAs aggregates are coherent and high-angle ones They are straight and clean, suggesting that the crystal lization and compaction of samples were well done16 Very little melt(<<0.5%)were found to occur in the triple- junctions. CAS grains in the HIPed samples are characterized by closely spaced growth twin lamellae with low dislocation densities(10 m-).The twins Aspect ratio have their composition planes parallel to(0 10) and are Fig. 4. Grain size distribution of CAs in hot pressed particulate com mainly albite, Carlsbad and Carlsbad-albite types. The posite(sample J12-QA)consisting of 50 vol. Qtz and 50 vol. CAS). ge fibres in CAS spherulites are actually composed Measurements were made from SEM micrographs. of very small grains (4) EBSD patterns of CAs and Qtz were measured and indexed using a SEM(Philips XL30)at Liverpool University, and the software package Channel + from size ranging from 0. 4 to 9 um with a mean value of HKL Software Company. The patterns were recorded at 2. 1 um(Fig 4a) 30kV acceleration voltage and nominal beam currents (2)Both optical and sEM observations show that Qtz grains of 80 HA. No carbon coat was used on the thin sec- in the PC aggregates form almost rigid clasts dispersed tions, which were chemically-mechanically polished to homogeneously within a relatively continuous matrix of emove specimen surface damage, because the coat de- CAS(Fig 2a). Spherulites with radial fibres of CAs(not teriorated the eBsd image quality. In most cases, more shown in Fig. 2)are occasionally observed in the pure than five or six bands were detected, allowing the bands CAS aggregates and the CAs layers of laminated com- indexed unambiguously by the computer simulation posites. In the spherulites, CAS fibres are generally tab- The measurement uncertainty was given by the software ular on 010) with an elongation mainly along [001 as a mean angular deviation(MAD) between detected and to a lesser extent along [100]. However, no CAs bands and simulated patterns. The indexing was not spherulites occur in particulate composites(Fig. 2a) accepted if the MAd value was larger than 2. EBSD It is generally accepted that spherulite texture results measurements showed a random crystallographic pre where the rate of crystal growth exceeds that of crystal ferred orientation(CPO)of either CAS(Fig. 5)or Qtz in nucleation2-27. The spherulite is a typical texture for HIPed samples, as expected for hydrostatic conditions crystallization of Cas glass that generally starts from a (5)FTIR measurements using a Bruker IFS-66v(GFZ nucleation centre where the water content is relatively Potsdam, Germany) show that the HIPed samples have high. The volume fraction of spherulites in CAS aggre a water content ranging from 8000 to 20.000 H/106 gates is about 10% on average with an average value of 13,000 H/10oSi( 0.08 wt %304 S. Ji et al. / Journal of the European Ceramic Society 25 (2005) 301–311 Hot-pressed particulate composite (50% Qtz, 50% CAS) 0 20 40 60 80 100 Grain size, m Number of measurements 0 1 2 3 4 5 6 7 8 9 10 N=300 Mean grain size: 2.1 ∝m CAS J12-QA 0 10 20 30 40 50 60 Aspect ratio Number of measurements 0 1.0 2.0 3.0 4.0 5.0 6.0 N=300 Mean aspect ratio: 2.2 J12-QA CAS (a) ∝ (b) Fig. 4. Grain size distribution of CAS in hot pressed particulate com￾posite (sample J12-QA) consisting of 50 vol.% Qtz and 50 vol.% CAS). Measurements were made from SEM photomicrographs. size ranging from 0.4 to 9
m with a mean value of 2.1
m (Fig. 4a). (2) Both optical and SEM observations show that Qtz grains in the PC aggregates form almost rigid clasts dispersed homogeneously within a relatively continuous matrix of CAS (Fig. 2a). Spherulites with radial fibres of CAS (not shown in Fig. 2) are occasionally observed in the pure CAS aggregates and the CAS layers of laminated com￾posites. In the spherulites, CAS fibres are generally tab￾ular on {010} with an elongation mainly along [0 0 1] and to a lesser extent along [1 0 0]. However, no CAS spherulites occur in particulate composites (Fig. 2a). It is generally accepted that spherulite texture results where the rate of crystal growth exceeds that of crystal nucleation25–27. The spherulite is a typical texture for crystallization of CAS glass that generally starts from a nucleation centre where the water content is relatively high. The volume fraction of spherulites in CAS aggre￾gates is about 10% on average. Fig. 5. Preferred orientations of triclinic CAS (0 1 0), [1 0 0] and [0 0 1] for undeformed, hot isostatical pressed, pure CAS aggregate (sample J7). Notice that the whole sphere, rather than a hemisphere, is necessary to represent the distribution of the positive directions. Projections on the lower (a) and upper (b) hemispheres. Stereonets are equal-area plots; 130 measurements are used. (3) TEM (Philips CM200, GFZ-Potsdam, Germany) op￾erating at 200 kV shows that the grain boundaries in the CAS aggregates are coherent and high-angle ones. They are straight and clean, suggesting that the crystal￾lization and compaction of samples were well done.16 Very little melt (<<0.5%) were found to occur in the triple-junctions. CAS grains in the HIPed samples are characterized by closely spaced growth twin lamellae with low dislocation densities (∼1011 m−2). The twins have their composition planes parallel to (0 1 0) and are mainly albite, Carlsbad and Carlsbad-albite types. The large fibres in CAS spherulites are actually composed of very small grains.22 (4) EBSD patterns of CAS and Qtz were measured and indexed using a SEM (Philips XL30) at Liverpool University, and the software package Channel + from HKL Software Company. The patterns were recorded at 30 kV acceleration voltage and nominal beam currents of 80
A. No carbon coat was used on the thin sec￾tions, which were chemically–mechanically polished to remove specimen surface damage, because the coat de￾teriorated the EBSD image quality. In most cases, more than five or six bands were detected, allowing the bands indexed unambiguously by the computer simulation. The measurement uncertainty was given by the software as a mean angular deviation (MAD) between detected bands and simulated patterns. The indexing was not accepted if the MAD value was larger than 2◦. EBSD measurements showed a random crystallographic pre￾ferred orientation (CPO) of either CAS (Fig. 5) or Qtz in HIPed samples, as expected for hydrostatic conditions. (5) FTIR measurements using a Bruker IFS-66v (GFZ￾Potsdam, Germany) show that the HIPed samples have a water content ranging from 8000 to 20,000 H/106Si with an average value of 13,000 H/106Si (∼0.08 wt.%)