CRYSTALLO-CHEMICAL AND COLLOIDAL PROPERTIES OF SYNTHETIC FLUORINE MICA FROM TALC

Transcription

1 Clay Science 8, (1992) CRYSTALLO-CHEMICAL AND COLLOIDAL PROPERTIES OF SYNTHETIC FLUORINE MICA FROM TALC HIROSHI TATEYAMA, SATOSHI NISHIMURA, KINUE TSUNEMATSU Government Industrial Research Institute, Kyushu, Shuku-machi, Tosu city, Saga Prefecture, 841, Japan and MITSURU KIMURA CO-OP Chemicals Co. LTD Chiyoda-ku, Tokyo, 102, Japan (Accepted July 1, 1992) ABSTRACT Fluorine were synsized using talc and K2SiF6 at 900 Ž for 1 hour in an electric furnace. With increasing K2SiF6/talc ratio, b and c unit cell parameters syntic fluorine were decreased. This result may be interpreted in terms shrinkage octahedral sheet by loss Mg2 + from octahedral site. Infrared absorption spectra syntic showed splitting absorption band Si-O stretching, which indicates that some alkali ions migrate into interlayer site silicate skeleton. The one dimensional Fourier synsis showed that with increase K2SiF6/talc ratio electron density K + in interlayer site syntic increased and that Mg2 + from octahedral site decreased. These analytical data indicate that fluorine are mainly formed by transformation from talc without entire disruption original atomic arrangement by intercalation process alkali ion into interlayer site talc and partially formed by solid state reactions. The negative zeta potential syntic fluorine decreased in magnitude as with increasing K2SiF6/talc ratio. It indicates that zeta potential syntic fluorine is closely connected with ir net layer charge. Key words: Fluorine, Talc, Synsis, Intercalation, Zeta potential. Fluorine have been synsized from melts at Ž or by solid sate reactions at Ž (Nagai, 1941; Noda and Saito, 1943; Reichmann and Middel, 1941; Daimon, 1952; Hatch et al., 1957; Matsushita, 1960; Shell and Ivey, 1969; Sugimori, 1986). Daimon et al. (1967) succeeded to synsize fluorphlogopite and or excellent quality and made a single crystal which was 10 cm long and 5 cm width. Tateyama et al. (1990) reported expandable and non-expandable synsized at Ž for one hour from mixture talc and alkali silicluoride in an electric furnace. The formation process from talc to expandable was analyzed by Tateyama et al. (1992).

2 242 H. Tateyama et al. In present study, crystallo-chemical properties syntic non-expandable fluorine were investigated by rmal, X-ray powder diffraction, nuclear magnetic resonance, and zeta potential analyses. EXPERIMENTAL METHODS The talc used in this study was from Kanshi deposit in China and milled in a vibrating ball mill. The milled talc was prepared into two particle size ranges using an air cyclone in order to investigate effects particle size on formation fluorine ; one was 4.6 ƒêm in average particle size and or 6.6 ƒêm. The chemical composition talc is shown in Table 1 (Tateyama et al., 1992). The K2SiF6 used was a reagent grade chemical. The mixing ratio talc and K2SiF6 is shown in Table 2. The mixtures were n placed in a platinum crucible with a lid to minimize volatilization gaseous SiF4. The crucible was heated at Ž in an electric furnace under following conditions; heating rate was 10 Ž/min., and holding time was 1 hour. The mixtures were analyzed by rmogravimetric and differential rmogravimetric TABLE 1. Chemical composition talc used TABLE 2. Batch compositions mixture and estimated structural formulae syntic fluorine (A) Batch compositions (B) Syntic products

3 Syntic Fluorine Mica from Talc 243 analysis (TGA, DTG). Infrared heating furnace was used with a Shinku-Rico TA-1500 Thermal Analyzer. They were placed in a Pt capsule with a lid under same heating conditions as experiment in electric furnace. All products were analyzed with CuKƒ radiation by a Phillips APD-15 X-ray Powder Diffractometer. Infrared absorption spectra syntic were recorded with a Nihon-Bunko IR-810 Spectrophotometer using KBr method. A JEOL JEM-200CX Electron Microscope was operated at 120 kv to obtain electron optical data. All 29Si NMR spectra talc and syntic were recorded on a Bruker AC-200 NMR Spectrometer at MHz using a wide-bore s.c. magnet 4.7T. The electrophoretic mobilities syntic were measured with a Pen Kern System 3000 Automated Electrokinetics Analyzer. The measured electrophoretic mobility was converted to zeta potential by Smoluchowski equation. RESULTS AND DISCUSSION Formation fluorine from talc The mixtures (TM-3) talc (4.6 and 6.6 ƒêm) and K2SiF6 were analyzed by TGA and DTG. Two prominent weight loss events are encountered in Figures 1(A) and 1(B). To analyze chemical reaction between talc and K2SiF6, mixture was air quenched from 300 to 1000 Ž at each 50 Ž temperature interval. X-ray powder diffraction patterns air quenched samples are shown in Figure 2. The reflections K2SiF6 remained until structure collapsed at about 600 Ž when reflections nearly disappeared and those KMgF3 appeared. The 2.8% weight loss between 400 Ž and FIG. 1. Thermogravimetric data for mixture (TM-3) (A) The mixture talc (4.6 ƒêm) and 0.5K2SiF6 (B) The mixture talc (6.6 ƒêm) and 0.5K2SiF6

4 244 H. Tateyama et al. (A) 500 Ž (B) 600 Ž (C) 700 Ž (D) 800 Ž (E) 900 Ž (F)1000 Ž FIG. 2. X-ray powder diffraction patterns air quenched products. TA, Talc; KS, K2SiF6; KM, KMgF3; MC, Fluorine mica 700 Ž was due to decompositions K2SiF6 and talc. The decomposition K2SiF6 could be expressed as follows: The total weight loss K2SiF6 in mixture (TM-3), which is supposed to be completely collapsed below 700 Ž, was calculated to be 10.6%. The calculated weight loss did not

5 Syntic Fluorine Mica from Talc 245 correspond to observed one, which showed that K2SiF6 decomposed to mainly amorphous potassium silicluoride and partially KMgF3. The peak intensity 001 reflection talc at each reaction temperature decreases from about 6000 cps at Ž to about 2500 cps at 700 Ž as shown in Figure 3. These results indicate that partial removal structural water in talc occurs and KMgF3 is formed below 700 Ž. Figure 1(B) shows DTG pattern mixture talc (6.6 ƒêm) and K2SiF6 in which mixing ratio is same as TM-3. In region Ž two peaks are recognized on DTG pattern; first at 560 Ž is assigned to be decomposition K2SiF6 because decomposition temperature is same as that pure K2SiF6, and second at about 610 Ž is decompositions K2SiF6 and talc. These results indicate that weight loss in Ž includes both SiF4 (g) from K2SiF6 and H2O (g) from talc. Continued heating up to 800 Ž led to reaction between talc and resultant amorphous potassium silicluoride, which yielded fluorine with a c-spacing being 10.0A. The X-ray powder diffraction pattern mixture heated at FIG. 3. Each peak intensity air quenched products TA, 9.2A reflection talc; KS, 2.88 A reflection K2SiF6; KM, 1.99 A reflection KMgF3; MC, 10.0A reflection fluorine

6 H Ž showed treatments that at crystallization According are converted loss in to raw charge form between indicate solid that state site consists talc and outer structure, et al., platelets with plate-like potassium ion partly entire in talc intercalates shown regular fluorine is mainly is interlayer maintained Si4+ particles in Figure with shape may 4. Fluorine but, irregular be shape by outlines. outline formed by The particles. are talc most These crystallization (B) TP-2 (C) TP-3 (D) SAD TP-3 Electron structure into replacement outlines, (A) TP-1 4. by disruption reactions. FIG. Heat caused by Mg ). are is fluorine persisted. be analyses, without OH- fluorine and still may diffraction talc that syntic means site fluorine fluorine parts octahedral X-ray from while KMgF3 which rearrangement. and transformation but KMgF3, structural which (Tateyama hexagonal ten balance micrographs, rmogravimetric mica into considerable by from tetrahedral materials point with et al. decomposition arrangement, The Mg2+ transformed above in to formed to F- Electron in atomic talc. mostly led mainly original site talc 1000 Ž Tateyama micrographs syntic fluorine mainly used as different results with

7 Syntic Fluorine Mica from Talc 247 Crystallo-chemical properties syntic fluorine The estimated structural formulae syntic fluorine are shown in Table 2(B). For example, in case TP-2, chemical equation talc and K2SiF6 could be roughly expressed as follows: The constituents gas components, however, must be determined quantitatively to obtain exact reaction process. In present report, structural formula tetrahedral sheet was assumed to be Si4O10F2 in place Si4 _4O11F2,4. Then net positive layer charge TP-2 in interlayer sheet was obtained from equation The net negative layer charge in octahedral sheet was estimated from equation (A) TP-1 (s) TP-2 (c) TP-3 (D) TP-4 FIG. 5. X-ray powder diffraction patterns products heated at 900 Ž for 1 hour MC, Fluorine mica; ES, Enstatite; CR, Cristobalite; KM, KMgF3

8 248 H. Tateyama et al. X-ray powder diffraction patterns syntic products are shown in Figure 5. TP-1 includes a small amount enstatite as impurities, TP-2 and TP-3 contain a very small amount cristobalite, and TP-4 has cristobalite and KMgF3. Each reflection powder lines for fluorine could be indexed using unit cell parameters a 1M polytype mica. The unit cell parameters fluorine from TP-1 to TP-4 are refined by a least squares method using eight reflections not being overlapped as shown in Table 3. With increasing K2SiF6/talc ratio, b and c unit cell parameters were decreased. Hazen and Wones (1972) noted that octahedral substitutions different size R2+ cations affect only b parameter. Toraya (1981) showed that octahedral flattening angle is expressed with b-axis length and mean length octahedra. The present result may be interpreted in terms shrinkage octahedral sheet by loss Mg2+ from octahedral site. Figure 6(A) shows infrared absorption spectrum talc. Two strong bands in cm-1 region were assigned to be Si-O stretching mode near 1030 cm-1 and Si-O bending mode near 460 cm-1. Figures 7(B) and 7(C) show infrared spectra TP-2 and TP-3, respectively, which are very similar to those Al-free magnesium (Tateyama et al., 1976). The band at 1140 cm-1 fluorine was attributed to Si-O (apical oxygen) stretching vibrations, large band at 970 cm-1 to Si-O (basal oxygen) stretching vibrations (Serratosa, 1960; Farmer, 1974; Tateyama et al., 1976). Splitting absorption band Si-O stretching indicates that some alkali ions migrate into interlayer site silicate skeleton (Tettenhorst, 1962). The one dimensional Fourier synses fluorine using eleven orders reflections given in Figure 7 show atomic distribution normal to basal plane. With increase K2SiF6/talc ratio electron density K + in interlayer site increases and that Mg2 + in octahedral site decreases. It is evident that loss Mg2 + from octahedral site increases as with increasing K2SiF6/talc ratio. The 29Si NMR spectra talc and fluorine are shown in Figure 8. The 295i chemical shifts natural aluminosilicates depend mainly on number Al atoms in second coordination sphere Si atoms (Lippmaa et al., 1980). The 29Si spectrum talc consists one single sharp line at -98.0ppm, which is complete agreement with that earlier works (Smith et al., 1983; Magi et al., 1984; Kinsey et al., 1985). The intensity distributions 29Si NMR line fluorine corresponding to unsubstituted Si(0Al) units, which are assigned to Si surrounded by three Si, became broad as compared with that talc. The 29Si chemical shifts all syntic were nearly close to TABLE 3. Unit cell parameters syntic fluorine

9 Syntic Fluorine Mica from Talc 249 (A) Talc (B) TP-2 (C) TP-3 FIG. 6. Infrared absorption spectra talc and syntic fluorine that (-91 ppm) phlogopite Si(OAl) units (Sanz and Serratosa, 1984). The 29Si chemical shifts were increased from to ppm in accordance with increasing K2SiF6/talc ratio from TM-1 to TM-4. Magi et al. (1984) pointed out that distortion SiO4 tetrahedra is anor factor that affects 29Si chemical shifts in silicate, and y indicated that shift difference between a-quartz and ƒ -cristobalite correlated with slight increase in Si-O-Si bond angles. The displacement chemical shifts

10 250 H. Tateyama et al. (A)TP-1 (B)TP-3 (C)TP-4 FIG. 7. One dimensional Fourier synsis syntic fluorine syntic may correlate with distortion SiO4 tetrahedra in tetrahedral sheet. Colloidal properties fluorine The zeta potential is electric potential in double layer at interface between a particle which moves in an electric filed and surrounding liquid. The zeta potential

11 Syntic Fluorine Mica from Talc 251 FIG Si NMR spectra talc and syntic fluorine is computed from electrophoretic mobility colloid particles. Its magnitude was considered a measure particle repulsion. The results for zeta potential measurements fluorine are shown in Figure 9 as a function concentrations in aqueous K+ chloride solution. In pure water negative zeta potential TP-1 is highest in magnitude among all four syntic, and increases on increasing

12 252 H. Tateyama et al. FIG. 9. Zeta potential syntic fluorine as a function concentrations in aqueous K + chloride solution concentration KC1 to about 10-3 M. The negative zeta potential TP-2 has a maximum at 10-3 M, and those TP-3 and TP-4 have maximum at 10-2 M. The zeta potential usually decreases upon addition an electrolyte. However, all data for measured zeta potential show maximum with increase in concentration. This is explained that concentration an electrolyte below 10-4 M is low to calculate zeta potential using Smoluchowski equation, because this equation can be used when thickness diffuse double layer is very thin as compared with size particles (Kitahara and Watanabe, 1972). The zeta potential, however, decreases with an excess amount an electrolyte because a shift counter ions toward Stern layer when diffuse double layer is compressed. Therefore optimum condition for electrolyte concentration is kept at 10-3 M KCl solution in present experiment. Figure 10 shows zeta potential as a function ph in 10-3 M KCl solution. All data indicate ph dependence. There are not so much differences in zeta potential above ph 8, but are remarkable differences below ph 8 between each syntic fluorine

13 Syntic Fluorine Mica from Talc 253 FIG. 10. Zeta potential syntic fluorine as a function ph in 10-3 M KCl solution mica. The negative zeta potential TP-1 which has lowest net layer charge (nearly 0.6) is higher than that TP-4 which has highest net layer charge (nearly 1.0). The negative zeta potential fluorine decreases with increasing net layer charge fluorine. The zeta potential is usually not equal to surface potential, because seat zeta potential is shearing plane or slipping plane between bulk liquid and an envelope water which moves with particle. But it is to some extent comparable with Stern potential. The Stern potential is defined to be potential at Stern layer whose position is inside slipping plane (Kitahara and Watanabe, 1972). Then se results zeta potential measurements show that zeta potential fluorine is closely connected with ir net layer charge. CONCLUSIONS Fluorine were synsized using talc and K2SiF6 at 900 Ž for 1 hour in an

14 254 H. Tateyama et al. electric furnace. The mixture talc and K2SiF6 shows two prominent weight loss on TG analysis; X-ray powder diffraction patterns air quenched samples show that reflections K2SiF6 remained until structure collapsed at about 600 Ž when reflections KMgF3 appeared. Continued heating up 800 Ž led to reaction talc with resultant amorphous potassium silicluoride, which yielded fluorine with a c-spacing being 10.0A. Below 900 Ž talc mostly transformed to fluorine, but KMgF3 still persisted. After heat treatments at 1000 Ž KMgF3 disappeared, which may be caused by crystallization fluorine with considerable structural rearrangement. Infrared absorption spectra syntic show splitting absorption band Si-O stretching, which indicates that some alkali ions migrate into interlayer site silicate skeleton. The one dimensional Fourier synsis shows that with increase K2SiF6/talc ratio electron density K+ in interlayer site syntic increases and that Mg2+ from octahedral site decreases. Electron micrographs syntic show similar morphological features kaolinite with hexagonal shape. According to se analytical data, fluorine are mainly formed by transformation from talc without entire disruption original atomic arrangement by intercalation process alkali ion into interlayer site talc. However, fluorine may be partially formed by solid state reactions with atomic rearrangements original structure. The negative zeta potential fluorine increased as with increasing net layer charge fluorine. It indicates that zeta potential fluorine is closely connected with ir layer charge. ACKNOWLEDGEMENTS The writers would like to thank Drs. K. Jinnai and N. Hara Governmental Industrial Research Institute Kyushu for ir useful discussion. REFERENCES DAIMON, N. (1952) J. Chem. Soc. Japan, Ind. Chem. Sec., 55, DAIMON, N., TATE, I., HIRAO, M. and AMANO, T. (1967) J. Chem. Soc. Japan, Ind. Chem. Sec., 70, FARMER, V.C. (1974) Layer silicates, V.C. Farmer, ed., Mineral. Soc. Monograph 4, London, HATCH, R.A., HUMPHREY, R.A., EITEL, W. and COMEFORO, J.E. (1957) U.S. Bur. Mines, Rept. Invest., 5337, HAZEN, R.H. and WONES, D.R. (1972) Amer. Mineral., 57, KINSEY, R.A., KIRKPATRICK, R.J., HOWER, J., SMITH, K.A. and OLDFIELD, E. (1985) Amer. Mineral., 70, KITAHARA, A. and WATANABE, A. (1972) Electrical Phenomena at Interfaces, Kyoritsu Shuppan, (in Japanese). LIPPMAA, E., MAGI, M., SAMOSON, A., ENGELHARDT, G. and GRIMMER, A.-R. (1980) J. Am. Chem. Soc., 102, MAGI, M., LIPPMAA, E., SAMOSON, A., ENGELHARDT, G. and GRIMMER, A.-R. (1984) J. Phys. Chem., 88, MATSUSHITA, T. (1960).1. Chem. Soc. Japan, Ind. Chem. Soc., 63,

15 Syntic Fluorine Mica from Talc 255 NAGAI, S. (1941) J. Ceram. Assoc. Japan, 49, NODA, T. and SAITO, S. (1943) J. Soc. Chem. Ind., 46, REICHMANN, R. and MIDDEL, V. (1941) Siemens and Schuckert Rept., 653, SANZ, J. and SERRATOSA, M. (1984) J. Am. Chem. Soc., 106, SERRATOSA, J.M. (1960) Am. Mineral., 45, SELL, H.R. and IVEY, K.H. (1969) U.S. Bur. Mines, Bull., 647, SMITH, K.A., KIRKPATRICK, R.J., OLDFIELD, E. and HENDERSON, D.M. (1983) Amer. Mineral., 68, SUGIMORI, K. (1986) Nendo Kagaku, 26, (in Japanese with English abstract). TATEYAMA, H., NISHIMURA, S., TSUNEMATSU, K., JINNAI, K., ADACHI, Y. and KIMURA, M. (1992) Clays & Clay Minerals, 40, TATEYAMA, H., SHIMODA, S. and SUDO, T. (1976) N. Jahrb. Mineral., Monatsch., 3, TATEYAMA, H., TSUNEMATSU, K., HIROSUE, H., KIMURA, K., FURUSAWA, T. and ISHIDA, Y. (1990) Pro. 9th Int. Clay Conf., Strasbourg, France, V.C. Farmer and Y. Tardy, eds., Vol. II, TETTENHORST, R. (1962) Amer. Miner., 47, TORAYA, H. (1981) Z. Kristallogr., 157,