C -H. Chao, H.Y. Lu/Materials Science and Engineering 4328(2002)267-276 temperature polymorph of crystalline silica, B-cristo 19.5 balite, has apparently been stabilized and retained 1100℃/48h metastably to room temperature in the y= 19.5 samples with 4.65 mol% of both Na,O and Al,O3(Table 1) The lattice spacing of d=0.4069 nm(C-1)does not match exactly with that of either the a- or B-phase given by the JCPDS files, but falls between dIor C-2C- 0.4039 nm and d11B=0.4110 nm. However, the C 102aC4 reflection in Fig. l(a)can be deconvoluted to two peaks corresponding to the lattice spacings of 0.4084 and 0.4058 nm and representing(101)a and(lID),respec- 20(deg) tively. This is shown in Fig. 1(b). The co-existence of a-cristobalite and the untransformed B-cristobalite can be discerned. It is also noted that no peak splitting(of the C-l reflection in Fig. I(c) was detected before the 20 1100℃/48h sintered samples had been pulverized again to powders a-cristobalite (C-l(a) in Fig. I(c). The C-4 peak(Fig. I(a))at 26 35.80 corresponding to a lattice spacing of d=0. 2506 nm again lies amongst d12a =0.2467 nm, d200 =0.2487 nm and d220B=0.2530 nm(JCPDS 27-605 for B-cristo balite). Similarly, it implies the co-existence of a-and B-cristobalite in the sintered mixture. The later is appar 20.521.021.5 022523.023 ently the untransformed high temperature B-phase 20(dee) which has been retained metastably to room 35 temperature. Sintered samples re-ground to powder were passed 1100℃/48h through a 45 um sieve prior to XRD analysis. The characteristic feature of the re-ground samples is the peak splitting of the initially Gaussian-type reflections of C-1(also given in Fig. I(c))and C-4. The C-l peak 20=21.8%(of Fig. 1(a)) has splitted of dup=0.4086 nm at 20=21.75 and d1ola=0.4058 nm at 20=21.90. They are again not completely in 20.521.021.522.022.52 3.524.0 accordance with the d-spacings(of d1B=0.4110 nm 20(deg) and dIola=0.4039 nm)given by the JCPDS files. The 111)B reflection shown in Fig. 1(c)for both as-sintered ng. I. XRD traces of (a)as-sintered surface of the y= 19.5 sample and re-ground samples remains almost unchanged in C for 24 h,(b) deconvoluded peak, and (c)re- position. However, the (101), reflection shifting to- higher 20-angles) from that (of <5 wt %)and beyond the detection by XRD, if of the as-sintered sample surface can be easily discerned they exist at all in the mixture from Fig. I(c) The reflections of C-l at 20=21.8 and C4 at 35.8 3. 1.2. Composition with y=24.6 may include both a- and B-cristobalite since the respec For powder compacts containing a smaller amount tive 20-angles are very close to each other(as indicated of Al,Oa and Na,o(e.g. y=24.6 of 3. 76 mol% as given in Fig. I(a). Investigating the peak areas of C-I and in Table 1), sintering at 1100C for 24 h results in C-4 in Fig. I(a)reveals that the sample may also mixture of a-and B-cristobalite. The XRd trace resem contain B-cristobalite. The relative intensities of C-l to bles that of the y=19.5 samples (of Fig. I()). The C-4 by integrating the peak areas are 1045: 24: 41: 236 20=21.8 reflection approximated to a Gaussian-type Normalizing them on the basis of the C-2 peak (i.e. peak locating between(101)a and(Ill)e is again ob (lID)a) intensity following the JCPDS file 39-1425, the tained. and which is also designated to C-1 in Fig. 2 mixture containing only a-cristobalite would give a Similar peak splitting and shift are observed from the peak ratio of 300: 24: 27: 51. The discrepancy of excess y=246 samples re-ground to 45-38 Hm, shown by intensities by A=745 for the C-l peak and 4=185 for C-1(a)in Fig. 2. When the same sample was pulverized the C-4 peak indicates the co-existence of B-cristobalite further down to particle size of 38 um, not only that with the a-phase in the crystalline mixture. The high the peak splitting had become more distinctive, theC.-H. Chao, H.-Y. Lu / Materials Science and Engineering A328 (2002) 267–276 269 Fig. 1. XRD traces of (a) as-sintered surface of the y=19.5 sample sintered at 1100 °C for 24 h, (b) deconvoluded peak, and (c) re￾ground powder showing
-cristobalite. temperature polymorph of crystalline silica,
-cristo￾balite, has apparently been stabilized and retained metastably to room temperature in the y=19.5 samples with 4.65 mol% of both Na2O and Al2O3 (Table 1). The lattice spacing of d=0.4069 nm (C-1) does not match exactly with that of either the - or
-phase given by the JCPDS files, but falls between d101= 0.4039 nm and d111
=0.4110 nm. However, the C-1 reflection in Fig. 1(a) can be deconvoluted to two peaks corresponding to the lattice spacings of 0.4084 and 0.4058 nm and representing (101) and (111)
, respec￾tively. This is shown in Fig. 1(b). The co-existence of -cristobalite and the ‘untransformed’
-cristobalite can be discerned. It is also noted that no peak splitting (of the C-1 reflection in Fig. 1(c)) was detected before the sintered samples had been pulverized again to powders (C-1(a) in Fig. 1(c)). The C-4 peak (Fig. 1(a)) at 2
= 35.8° corresponding to a lattice spacing of d=0.2506 nm again lies amongst d112=0.2467 nm, d200=0.2487 nm and d220
=0.2530 nm (JCPDS 27-605 for
-cristo￾balite). Similarly, it implies the co-existence of - and
-cristobalite in the sintered mixture. The later is appar￾ently the untransformed high temperature
-phase which has been retained metastably to room temperature. Sintered samples re-ground to powder were passed through a 45 m sieve prior to XRD analysis. The characteristic feature of the re-ground samples is the peak splitting of the initially Gaussian-type reflections of C-1 (also given in Fig. 1(c)) and C-4. The C-1 peak at 2
=21.8° (of Fig. 1(a)) has splitted into two peaks of d111
=0.4086 nm at 2
=21.75° and d101=0.4058 nm at 2
=21.90°. They are again not completely in accordance with the d-spacings (of d111
=0.4110 nm and d101=0.4039 nm) given by the JCPDS files. The (111)
reflection shown in Fig. 1(c) for both as-sintered and re-ground samples remains almost unchanged in position. However, the (101) reflection shifting to￾wards smaller d-spacings (higher 2
-angles) from that of the as-sintered sample surface can be easily discerned from Fig. 1(c). 3.1.2. Composition with y=24.6 For powder compacts containing a smaller amount of Al2O3 and Na2O (e.g. y=24.6 of 3.76 mol% as given in Table 1), sintering at 1100 °C for 24 h results in a mixture of - and
-cristobalite. The XRD trace resem￾bles that of the y=19.5 samples (of Fig. 1(a)). The 2
=21.8° reflection approximated to a Gaussian-type peak locating between (101) and (111)
is again ob￾tained, and which is also designated to C-1 in Fig. 2. Similar peak splitting and shift are observed from the y=24.6 samples re-ground to 45–38 m, shown by C-1(a) in Fig. 2. When the same sample was pulverized further down to particle size of 38 m, not only that the peak splitting had become more distinctive, the (of 5 wt.%) and beyond the detection by XRD, if they exist at all in the mixture. The reflections of C-1 at 2
=21.8° and C-4 at 35.8° may include both - and
-cristobalite since the respec￾tive 2
-angles are very close to each other (as indicated in Fig. 1(a)). Investigating the peak areas of C-1 and C-4 in Fig. 1(a) reveals that the sample may also contain
-cristobalite. The relative intensities of C-1 to C-4 by integrating the peak areas are 1045:24:41:236. Normalizing them on the basis of the C-2 peak (i.e. (111)) intensity following the JCPDS file 39-1425, the mixture containing only -cristobalite would give a peak ratio of 300:24:27:51. The discrepancy of excess intensities by =745 for the C-1 peak and =185 for the C-4 peak indicates the co-existence of
-cristobalite with the -phase in the crystalline mixture. The high