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Aqueous sol–gel synthesis of nanosized ceramic composite powders with metal-formate precursors
Materials Science and Engineering C 16 Ž2001. 113–117 www.elsevier.comrlocatermsec
Aqueous sol–gel synthesis of nanosized ceramic composite powders with metal-formate precursors N.N. Ghosh a,) , P. Pramanik b a
Chemistry Group, Biria Institute of Technology and Science, Rajasthan, India Department of Chemistry, Indian Institute of Technology, Kharagpur, India
b
Abstract In the present investigation, a series of multicomponent silicate systems have been prepared by using an aqueous sol–gel method, where water-soluble metal formates were used as precursors. Tetraethoxy silane and metal formates were used as precursors and water was used as solvent. The gels prepared using these precursors were calcined at different temperatures and characterized by using XRD, IR, DTA, TGA. Transmission electron microscope ŽTEM. was used to measure the average particle size of the calcined powders. It was observed that the average particle sizes of the powders are in nanometer scale with a narrow size distribution. In this method the replacement of metal alkoxides by metal formates and the use of water as solvent instead of alcohol, which is commonly used as solvent in all alkoxide sol–gel route facilitated the reduction of cost of the product. This processing route provides the basis for a low-cost, low-temperature method for the preparation of homogeneous nanometer-sized multicomponent ceramic powders compared with other conventional methods. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Sol–gel; Ceramic; Spodumene; Mullite; Eucryptite; Zirconia
1. Introduction The design of advanced ceramics depends on the availability of powders with outstanding properties in terms of composition, purity and size distribution. The sol–gel method for synthesis of glass, ceramics, and glass–ceramics has received much attention in recent years w1–5x. Sol–gel process refers to a process in a liquid medium to obtain a solid matter, which does not settle under gravity—that is to say, which does not precipitate. This solid matter can be composed of single network spreading throughout the liquid matrix, which is the definition of gel. Roy et al. w6–8x had used the sol–gel technique for the preparation of highly homogeneous glasses and ceramics with the use of different metal-alkoxides. As this procedure allows the mixing of precursors at the molecular level, there is a better control over the whole process, facilitating synthesis of Atailor-madeB materials. Based on the knowledge of sol–gel conversions, it is possible to prepare fibers, films, and composites. Multicomponent alkoxides have been used
)
Corresponding author. E-mail address: [email protected] ŽN.N. Ghosh..
to prepare a wide variety of ultra-fine and high-purity powders, which are difficult to prepare by conventional ceramic processing. However, for the synthesis of multicomponent systems from single metal alkoxides, chemical homogeneity is of great importance. Different hydrolysis rates of individual alkoxides may result in chemical inhomogeneity that leads to a higher crystalline temperature or the formation of undesired crystalline phases w9x. To overcome these limitations, several approaches have been attempted, including matching of hydrolysis rates by chemical modifications with chelating ligands, or synthesis of multication alkoxides, or partial prehydrolysis of an alkoxide w10–12x. As metal alkoxides that used in all alkoxides sol–gel routes are costly, and the preparations in laboratory are complex in nature, the objective of the present work was to develop an efficient and low-cost processing of the sol–gel route w13–21x. The sol–gel method has been modified by using metal formates instead of metal alkoxides, and water as reaction medium instead of alcohol, in the preparation of multicomponent ceramic composite powders. In this paper, the synthesis of a series of multicomponent ceramic composite systems are Ži. 3Al 2 O 3 –2SiO 2 –ZrO 2 Žmullite– zirconia., Žii. Li 2 O–Al 2 O 3 –2SiO 2 –ZrO 2 Žeucryptite– zirconia., Žiii. Li 2 O–Al 2 O 3 –4SiO 2 –ZrO 2 Žspodumene–
0928-4931r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 8 - 4 9 3 1 Ž 0 1 . 0 0 2 8 4 - 3
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N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
zirconia. and Živ. 2MgO–Al 2 O 3 –5SiO 2 –ZrO 2 Žcordierite–zirconia..
2. Experimental procedures 2.1. Preparation of gels The starting materials were aluminium nitrate nonahydrate Ž98.5 wt., SD Fine Chemicals., lithium carbonate Ž) 98% purity, BDU Chemicals., zirconium oxychloride octahydrate Ž98 wt. Aldrich., and tetraethoxy silane ŽTEOS. ŽFluka Chemicals.. Fresh precipitated aluminium hydroxide, magnesium hydroxide, and zirconium hydroxide were prepared by adding ammonium hydroxide to the aqueous solutions of aluminium nitrate, magnesium nitrate, and zirconium oxychloride, respectively. The solutions were then filtered out and precipitates were washed with distilled water several times. These hydroxides were then reacted with aqueous formic acid solution Ž50%. to give the corresponding metal formate solutions. Lithium formate solution was prepared by reacting lithium carbonate with aqueous solution of formic acid. Metal formate solutions that contained the required amount of metal ions were then added to TEOS according to the compositions. The specific conditions and compositions are listed in Table 1. At the start of mixing, TEOS and the aqueous solutions of metal formates were immiscible. A homogeneous solution was obtained after about 30 min of hydrolysis of TEOS, under rapid stirring using a magnetic stirrer. Slow stirring was continued until the formation of gels. The gels were dried at 100 8C for 24 h over a water bath and ground to powders. These powders were gradually heated at 5 8C miny1 and were calcined in air to temperatures ranging from 500 8C to 1200 8C.
2.2. Characterization of calcined powders The crystalline phase was identified by XRD with the use of a Philips X-ray diffractometer PWIS40 and CuK a radiation. IR spectra were recorded by using Perkin Elmer 883 spectrophotometer. The IR samples were prepared by using KBr pellet method. TGA and DTA were carried out at a heating rate of 10 8C miny1 in air using a Shimadzu Thermal Analyzer DT-40. Electron microscopic examination of powders was carried out by transmission electron microscope Phillips CM12.
3. Results and discussion The TGA of all dried gel powders exhibited weight losses in two steps. The total weight loss being ; 65 wt.%. There was no significant weight change above 500 8C. The DTA curve showed an endothermic peak at 110 8C, which can be explained by the removal of water from gel, and an exothermic peak at ; 375 8C, which is attributed to the decomposition and oxidation of formate salts. XRD patterns were taken for all the samples calcined at different temperatures. The crystalline phases formed during calcination at different temperatures are summarized in Table 2. From the XRD patterns, the following observations were made. All the dried gel powders were amorphous in nature. The samples MZ25, MZ35, MZ50 were amorphous in nature when calcined up to 1100 8C for 1 h. XRD peaks corresponding to mullite and tetragonal zirconia were observed when the samples were calcined at 1200 8C or higher temperatures. Some selected XRD patterns are shown in Fig. 1.
Table 1 Gel preparation compositions Target composition
3Al 2 O 3 –2SiO 2 with 25 mol% ZrO 2 3A1 2 O 3 –2SiO 2 with 35 mol% ZrO 2 3A1 2 O 3 –2SiO 2 with 50 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 5 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 10 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 15 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 5 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 10 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 15 mol% ZrO 2 2MgO–Al 2 O 3 –5SiO 2 with 5 mol% ZrO 2 2MgO–Al 2 O 3 –5SiO 2 with 15 mol% ZrO 2
Sample
MZ25 MZ35 MZ50 EZ5 EZ10 EZ15 SZ5 SZ10 SZ15 CZ5 CZ15
Molar ratio
Tgel Žh.
TEOS
Zrf
Alf
Lif
Mgf
1 1 1 1 1 1 2 2 2 5 5
0.25 0.35 0.5 0.05 0.1 0.15 0.025 0.05 0.075 0.05 0.15
3 3 3 1 1 1 1 1 1 4 4
– – – 1 1 1 1 1 1 – –
– – – – – – – – – 3 3
8 8 8 5 5 5 3 3 3 3 3
TEOS s tetraethoxy silane; Zrf s zirconium formate; Alf s aluminium formate; Lif s lithium formate; Mgf s magnesium formate; Tg s gel formation time in hours at 60 8C.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
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Table 2 Summary of XRD results Sample
MZ25 MZ35 MZ50 EZ5 EZ10 EZI5 SZ5 SZ10 SZ15 CZ5 CZ15
Calcination temperature Ž8C. 600
700
800
900
1000
1100
1200
1300
A A A a q be a q be a q be A A A A A
A A A a q be qT a q be qT a q be qT A A A A A
A A A a q be qT a q be qT a q be qT bs q T bs q T bs q T A A
A A A
A A A
A A A
MqT MqT MqT
MqT MqT MqT
m q S q T q X q ac m q S q T q X q ac
m q S q T q X q ac m q S q T q X q ac
ac q T ac q T
m q S q T q X q ac m q S q T q X q ac
A s amorphous; M s mullite; S s spinel; T s tetragonal zirconia; X s crystabolite; a s a-eucryptite; be s b-eucryptite; b s b-spodumene; m s mcordierite; ac s a-cordierite.
a and b eucryptite phases were formed when the samples EZ5, EZ10, and EZ15 were calcined at 600 8C for 2 h. Tetragonal zirconia phase appeared along with a and b eueryptite phases when the samples were calcined at 700 8C and 800 8C. The XRD patterns of samples calcined at different temperatures are shown in Fig. 2. Samples SZ5, SZ10, and SZ15 were amorphous in nature when calcined at 600 8C and 700 8C for 2 h. XRD peaks corresponding to b spodumene phase and tetragonal zirconia phase were observed when the samples were calcined at 800 8C ŽFig. 3..
Fig. 1. Powder X-ray diffractograms of sample MZ25, MZ35, and MZ50 after calcination at different temperatures. Ža. MZ25 at 1000 8C, Žb. MZ25 at 1100 8C, Žc. MZ35 at 1100 8C, Žd. MZ25 at 1200 8C, Že. MZ35 at 1200 8C, Žf. MZ50 at 1200 8C; Ž`. mullite, Ž^. tetragonal zirconia.
Samples CZ5 and CZ15 were amorphous up to the calcination temperature 800 8C. CZ5 and CZ15 produce spinel m-cordierite, and tetragonal zirconia as initial phase when calcined for l h at 900 8C. When the samples were calcined at 1200 8C for 1 h, m-cordierite started to convert
Fig. 2. Powder X-ray diffractograms of sample EZ5, EZ10, and EZ15 after calcination at different temperatures. Ža. EZ15 at 500 8C, Žb. EZ10 at 500 8C, Žc. EZ5 at 600 8C, Žd. EZ15 at 600 8C, Že. EZ10 at 600 8C, Žf. EZ5 at 700 8C, Žg. EZ15 at 700 8C, Žh. EZ10 at 800 8C, Ži. EZ15 at 800 8C; a s a-eucryptite, bsb-eucryptite, t s tetragonal zirconia.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
116
The principal absorption band of the formate group at 1380 cmy1 was observed in the IR spectra in the all gel powders dried at 100 8C. The intensity of the band diminished to zero when the gel powders were calcined at 500 8C. The samples MZ25, MZ35, and MZ5O exhibited the characteristic bands of mullite at 1175, 1125, 814, 750, 560 and 450 cmy1 , along with the characteristic band of
Fig. 3. Powder X-ray diffractograms of sample SZ5, SZ10, and SZ15 after calcination at different temperatures. Ža. SZ15 at 700 8C, Žb. SZ10 at 700 8C, Žc. SZ5 at 800 8C, Žd. SZ15 at 800 8C, Že. SZ10 at 800 8C; Ž`. b-spodumene, Ž^. tetragonal zirconia.
to a-cordierite. Small amount of spinel and crystabollite were still present, though. The complete formation of a-cordierite with disappearance of spinel and crystabolite were observed when the calcination temperature was 1300 8C. The observed IR frequencies of all the materials are in good agreement with the values reported in literature w22x. The most striking features of the IR spectra on increase in calcination temperatures were as follows. Table 3 Average particle size Ž"10 nm. of calcined powders as measured from TEM Sample
Calcination temperature Ž8C. 600
MZ25 MZ35 MZ50 EZ5 EZ10 EZ15 SZ5 SZ10 SZ15 CZ5 CZ15
155 175 200 160 175 190
700
185 210 245 200 190 230
800
900
1000
1100
1200
1300
A A A
76 110 115
84 122 125
108 135 135
118 146 150
110 112
117 120
124 126
128 130
225 265 285 310 330 275 Fig. 4. TEM micrograph of samples: Ža. MZ25 at 1200 8C, Žb. EZ10 at 800 8C, Žc. SZ10 at 800 8C.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
tetragonal zirconia at 600 cmy1 when calcined at 1200 8C and higher temperature. Calcination for 2 h at 600 8C or higher of the samples EZ5, EZ10, and EZ15 caused the IR bands at 1015, 755, 720, and 705 cmy1 , which are the characteristic bands of eucryptite and also the characteristic bands of tetragonal zirconia. The characteristic IR bands of b-spodumene at 1017, 765, and 560 cmy1 and the IR band of tetragonal zirconia were observed when SZ5, SZ10, and SZ15 were calcined for 2 h at 600 8C. From the IR-spectra of the samples CZ5 and CZ15, calcined at 1300 8C, the characteristic IR bands of cordierite and tetragonal zirconia were observed. The average particle size of all the ceramic composite powders calcined at different temperatures as measured by TEM are listed in Table 3. It was observed that particles were nanosized with a narrow size distribution. The average size increased with the increase in calcination temperatures. Some of the selected TEM micrographs are shown in Fig. 4Ža,b,c..
4. Conclusions A series of multicomponent ceramic composite powders were prepared by using the aqueous sol–gel method. Here, metal formates and TEOS were used as precursor compounds instead of metal alkoxides, and water was used as the reaction medium instead of conventionally used solvent alcohol. The advantages of this aqueous sol–gel method are as follows: Ži. A series of nanosized ceramic composite powders can easily be obtained by this method. Žii. The replacement of metal alkoxides by metal formates, and the use of water as reaction medium instead of alcohol, which is commonly used as solvent in all-al-
117
koxides sol–gel route, facilitate the reduction in the cost of the product. Žiii. This processing route provides the basis for a technically simple and cost-effective method for the synthesis of nanosized ceramic composite powders compared with other conventional methods.
References w1x w2x w3x w4x
w5x w6x w7x w8x w9x
w10x w11x w12x w13x w14x w15x w16x w17x w18x w19x w20x w21x w22x
D.R. Ulrich, J. Non-Cryst. Solids 100 Ž1988. 174. H. Schmidt, J. Non-Cryst. Solids 100 Ž1988. 51. L.L. Hench, J.K. West, Chem. Rev. 90 Ž1990. 33. C.J. Brinker, G.W. Scherer, Sol–Gel science: The Physics and Chemistry of Sol–Gel Processing. Academic Press, New York, 1990. A.L. Plere, Ceram. Bull. 70 Ž1991. 1281. R. Roy, J. Am. Ceram. Soc. 52 Ž1969. 344. R. Roy, Science 238 Ž1987. 1664. R. Roy, D.W. Hoffmann, S. Komarneni, Am. Ceram. Soc. Bull. 63 Ž1984. 459. A.B. Hardy, G. Gowda, G. McMahon, T.J. Riman, Rhine, H.K. Bowen, Ultrastructure Processing of Advanced Ceramics. Wiley, New York, 1988, p. 407. F. Babonneau, L. Coury, J.I. Ivage, J. Non-Cryst. Solids 121 Ž1990. 153. U. Selvaraj, S. Komarneni, R. Roy, J. Am. Ceram. Soc. 73 Ž1990. 3663. B.E. Yoldas, J. Mater. Sci. 14 Ž1979. 1843. N.N. Ghosh, P. Pramanik, Br. Ceram. Trans. 95 Ž1996. 209. N.N. Ghosh, P. Pramanik, Br. Ceram. Trans. 95 Ž1996. 267. N.N. Ghosh, P. Pramanik, Bull. Mater. Sci. 20 Ž1997. 247. N.N. Ghosh, P. Pramanik, Bull. Mater. Sci. 20 Ž1997. 283. N.N. Ghosh, P. Pramanik, Mater. Sci. Eng., B. 49 Ž1997. 79. N.N. Ghosh, P. Pramanik, Eur. J. Solid State Inorg. Chem. 34 Ž1997. 905. N.N. Ghosh, P. Pramanik, Br. Ceram. Trans. 96 Ž1997. 155. N.N. Ghosh, P. Pramanik, Nanostruct. Mater. 8 Ž1997. 1041. N.N. Ghosh, S.K. Saha, P. Pramanik, Br. Ceram. Trans. 97 Ž1998. 180. J.A. Gadsden, Infrared Spectra of Minarals and Related Inorganic Compounds. Butterworth, London, 1975.
Aqueous sol–gel synthesis of nanosized ceramic composite powders with metal-formate precursors N.N. Ghosh a,) , P. Pramanik b a
Chemistry Group, Biria Institute of Technology and Science, Rajasthan, India Department of Chemistry, Indian Institute of Technology, Kharagpur, India
b
Abstract In the present investigation, a series of multicomponent silicate systems have been prepared by using an aqueous sol–gel method, where water-soluble metal formates were used as precursors. Tetraethoxy silane and metal formates were used as precursors and water was used as solvent. The gels prepared using these precursors were calcined at different temperatures and characterized by using XRD, IR, DTA, TGA. Transmission electron microscope ŽTEM. was used to measure the average particle size of the calcined powders. It was observed that the average particle sizes of the powders are in nanometer scale with a narrow size distribution. In this method the replacement of metal alkoxides by metal formates and the use of water as solvent instead of alcohol, which is commonly used as solvent in all alkoxide sol–gel route facilitated the reduction of cost of the product. This processing route provides the basis for a low-cost, low-temperature method for the preparation of homogeneous nanometer-sized multicomponent ceramic powders compared with other conventional methods. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Sol–gel; Ceramic; Spodumene; Mullite; Eucryptite; Zirconia
1. Introduction The design of advanced ceramics depends on the availability of powders with outstanding properties in terms of composition, purity and size distribution. The sol–gel method for synthesis of glass, ceramics, and glass–ceramics has received much attention in recent years w1–5x. Sol–gel process refers to a process in a liquid medium to obtain a solid matter, which does not settle under gravity—that is to say, which does not precipitate. This solid matter can be composed of single network spreading throughout the liquid matrix, which is the definition of gel. Roy et al. w6–8x had used the sol–gel technique for the preparation of highly homogeneous glasses and ceramics with the use of different metal-alkoxides. As this procedure allows the mixing of precursors at the molecular level, there is a better control over the whole process, facilitating synthesis of Atailor-madeB materials. Based on the knowledge of sol–gel conversions, it is possible to prepare fibers, films, and composites. Multicomponent alkoxides have been used
)
Corresponding author. E-mail address: [email protected] ŽN.N. Ghosh..
to prepare a wide variety of ultra-fine and high-purity powders, which are difficult to prepare by conventional ceramic processing. However, for the synthesis of multicomponent systems from single metal alkoxides, chemical homogeneity is of great importance. Different hydrolysis rates of individual alkoxides may result in chemical inhomogeneity that leads to a higher crystalline temperature or the formation of undesired crystalline phases w9x. To overcome these limitations, several approaches have been attempted, including matching of hydrolysis rates by chemical modifications with chelating ligands, or synthesis of multication alkoxides, or partial prehydrolysis of an alkoxide w10–12x. As metal alkoxides that used in all alkoxides sol–gel routes are costly, and the preparations in laboratory are complex in nature, the objective of the present work was to develop an efficient and low-cost processing of the sol–gel route w13–21x. The sol–gel method has been modified by using metal formates instead of metal alkoxides, and water as reaction medium instead of alcohol, in the preparation of multicomponent ceramic composite powders. In this paper, the synthesis of a series of multicomponent ceramic composite systems are Ži. 3Al 2 O 3 –2SiO 2 –ZrO 2 Žmullite– zirconia., Žii. Li 2 O–Al 2 O 3 –2SiO 2 –ZrO 2 Žeucryptite– zirconia., Žiii. Li 2 O–Al 2 O 3 –4SiO 2 –ZrO 2 Žspodumene–
0928-4931r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 8 - 4 9 3 1 Ž 0 1 . 0 0 2 8 4 - 3
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N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
zirconia. and Živ. 2MgO–Al 2 O 3 –5SiO 2 –ZrO 2 Žcordierite–zirconia..
2. Experimental procedures 2.1. Preparation of gels The starting materials were aluminium nitrate nonahydrate Ž98.5 wt., SD Fine Chemicals., lithium carbonate Ž) 98% purity, BDU Chemicals., zirconium oxychloride octahydrate Ž98 wt. Aldrich., and tetraethoxy silane ŽTEOS. ŽFluka Chemicals.. Fresh precipitated aluminium hydroxide, magnesium hydroxide, and zirconium hydroxide were prepared by adding ammonium hydroxide to the aqueous solutions of aluminium nitrate, magnesium nitrate, and zirconium oxychloride, respectively. The solutions were then filtered out and precipitates were washed with distilled water several times. These hydroxides were then reacted with aqueous formic acid solution Ž50%. to give the corresponding metal formate solutions. Lithium formate solution was prepared by reacting lithium carbonate with aqueous solution of formic acid. Metal formate solutions that contained the required amount of metal ions were then added to TEOS according to the compositions. The specific conditions and compositions are listed in Table 1. At the start of mixing, TEOS and the aqueous solutions of metal formates were immiscible. A homogeneous solution was obtained after about 30 min of hydrolysis of TEOS, under rapid stirring using a magnetic stirrer. Slow stirring was continued until the formation of gels. The gels were dried at 100 8C for 24 h over a water bath and ground to powders. These powders were gradually heated at 5 8C miny1 and were calcined in air to temperatures ranging from 500 8C to 1200 8C.
2.2. Characterization of calcined powders The crystalline phase was identified by XRD with the use of a Philips X-ray diffractometer PWIS40 and CuK a radiation. IR spectra were recorded by using Perkin Elmer 883 spectrophotometer. The IR samples were prepared by using KBr pellet method. TGA and DTA were carried out at a heating rate of 10 8C miny1 in air using a Shimadzu Thermal Analyzer DT-40. Electron microscopic examination of powders was carried out by transmission electron microscope Phillips CM12.
3. Results and discussion The TGA of all dried gel powders exhibited weight losses in two steps. The total weight loss being ; 65 wt.%. There was no significant weight change above 500 8C. The DTA curve showed an endothermic peak at 110 8C, which can be explained by the removal of water from gel, and an exothermic peak at ; 375 8C, which is attributed to the decomposition and oxidation of formate salts. XRD patterns were taken for all the samples calcined at different temperatures. The crystalline phases formed during calcination at different temperatures are summarized in Table 2. From the XRD patterns, the following observations were made. All the dried gel powders were amorphous in nature. The samples MZ25, MZ35, MZ50 were amorphous in nature when calcined up to 1100 8C for 1 h. XRD peaks corresponding to mullite and tetragonal zirconia were observed when the samples were calcined at 1200 8C or higher temperatures. Some selected XRD patterns are shown in Fig. 1.
Table 1 Gel preparation compositions Target composition
3Al 2 O 3 –2SiO 2 with 25 mol% ZrO 2 3A1 2 O 3 –2SiO 2 with 35 mol% ZrO 2 3A1 2 O 3 –2SiO 2 with 50 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 5 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 10 mol% ZrO 2 Li 2 O–Al 2 O 3 –2SiO 2 with 15 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 5 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 10 mol% ZrO 2 Li 2 O–Al 2 O 3 –4SiO 2 with 15 mol% ZrO 2 2MgO–Al 2 O 3 –5SiO 2 with 5 mol% ZrO 2 2MgO–Al 2 O 3 –5SiO 2 with 15 mol% ZrO 2
Sample
MZ25 MZ35 MZ50 EZ5 EZ10 EZ15 SZ5 SZ10 SZ15 CZ5 CZ15
Molar ratio
Tgel Žh.
TEOS
Zrf
Alf
Lif
Mgf
1 1 1 1 1 1 2 2 2 5 5
0.25 0.35 0.5 0.05 0.1 0.15 0.025 0.05 0.075 0.05 0.15
3 3 3 1 1 1 1 1 1 4 4
– – – 1 1 1 1 1 1 – –
– – – – – – – – – 3 3
8 8 8 5 5 5 3 3 3 3 3
TEOS s tetraethoxy silane; Zrf s zirconium formate; Alf s aluminium formate; Lif s lithium formate; Mgf s magnesium formate; Tg s gel formation time in hours at 60 8C.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
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Table 2 Summary of XRD results Sample
MZ25 MZ35 MZ50 EZ5 EZ10 EZI5 SZ5 SZ10 SZ15 CZ5 CZ15
Calcination temperature Ž8C. 600
700
800
900
1000
1100
1200
1300
A A A a q be a q be a q be A A A A A
A A A a q be qT a q be qT a q be qT A A A A A
A A A a q be qT a q be qT a q be qT bs q T bs q T bs q T A A
A A A
A A A
A A A
MqT MqT MqT
MqT MqT MqT
m q S q T q X q ac m q S q T q X q ac
m q S q T q X q ac m q S q T q X q ac
ac q T ac q T
m q S q T q X q ac m q S q T q X q ac
A s amorphous; M s mullite; S s spinel; T s tetragonal zirconia; X s crystabolite; a s a-eucryptite; be s b-eucryptite; b s b-spodumene; m s mcordierite; ac s a-cordierite.
a and b eucryptite phases were formed when the samples EZ5, EZ10, and EZ15 were calcined at 600 8C for 2 h. Tetragonal zirconia phase appeared along with a and b eueryptite phases when the samples were calcined at 700 8C and 800 8C. The XRD patterns of samples calcined at different temperatures are shown in Fig. 2. Samples SZ5, SZ10, and SZ15 were amorphous in nature when calcined at 600 8C and 700 8C for 2 h. XRD peaks corresponding to b spodumene phase and tetragonal zirconia phase were observed when the samples were calcined at 800 8C ŽFig. 3..
Fig. 1. Powder X-ray diffractograms of sample MZ25, MZ35, and MZ50 after calcination at different temperatures. Ža. MZ25 at 1000 8C, Žb. MZ25 at 1100 8C, Žc. MZ35 at 1100 8C, Žd. MZ25 at 1200 8C, Že. MZ35 at 1200 8C, Žf. MZ50 at 1200 8C; Ž`. mullite, Ž^. tetragonal zirconia.
Samples CZ5 and CZ15 were amorphous up to the calcination temperature 800 8C. CZ5 and CZ15 produce spinel m-cordierite, and tetragonal zirconia as initial phase when calcined for l h at 900 8C. When the samples were calcined at 1200 8C for 1 h, m-cordierite started to convert
Fig. 2. Powder X-ray diffractograms of sample EZ5, EZ10, and EZ15 after calcination at different temperatures. Ža. EZ15 at 500 8C, Žb. EZ10 at 500 8C, Žc. EZ5 at 600 8C, Žd. EZ15 at 600 8C, Že. EZ10 at 600 8C, Žf. EZ5 at 700 8C, Žg. EZ15 at 700 8C, Žh. EZ10 at 800 8C, Ži. EZ15 at 800 8C; a s a-eucryptite, bsb-eucryptite, t s tetragonal zirconia.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
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The principal absorption band of the formate group at 1380 cmy1 was observed in the IR spectra in the all gel powders dried at 100 8C. The intensity of the band diminished to zero when the gel powders were calcined at 500 8C. The samples MZ25, MZ35, and MZ5O exhibited the characteristic bands of mullite at 1175, 1125, 814, 750, 560 and 450 cmy1 , along with the characteristic band of
Fig. 3. Powder X-ray diffractograms of sample SZ5, SZ10, and SZ15 after calcination at different temperatures. Ža. SZ15 at 700 8C, Žb. SZ10 at 700 8C, Žc. SZ5 at 800 8C, Žd. SZ15 at 800 8C, Že. SZ10 at 800 8C; Ž`. b-spodumene, Ž^. tetragonal zirconia.
to a-cordierite. Small amount of spinel and crystabollite were still present, though. The complete formation of a-cordierite with disappearance of spinel and crystabolite were observed when the calcination temperature was 1300 8C. The observed IR frequencies of all the materials are in good agreement with the values reported in literature w22x. The most striking features of the IR spectra on increase in calcination temperatures were as follows. Table 3 Average particle size Ž"10 nm. of calcined powders as measured from TEM Sample
Calcination temperature Ž8C. 600
MZ25 MZ35 MZ50 EZ5 EZ10 EZ15 SZ5 SZ10 SZ15 CZ5 CZ15
155 175 200 160 175 190
700
185 210 245 200 190 230
800
900
1000
1100
1200
1300
A A A
76 110 115
84 122 125
108 135 135
118 146 150
110 112
117 120
124 126
128 130
225 265 285 310 330 275 Fig. 4. TEM micrograph of samples: Ža. MZ25 at 1200 8C, Žb. EZ10 at 800 8C, Žc. SZ10 at 800 8C.
N.N. Ghosh, P. Pramanikr Materials Science and Engineering C 16 (2001) 113–117
tetragonal zirconia at 600 cmy1 when calcined at 1200 8C and higher temperature. Calcination for 2 h at 600 8C or higher of the samples EZ5, EZ10, and EZ15 caused the IR bands at 1015, 755, 720, and 705 cmy1 , which are the characteristic bands of eucryptite and also the characteristic bands of tetragonal zirconia. The characteristic IR bands of b-spodumene at 1017, 765, and 560 cmy1 and the IR band of tetragonal zirconia were observed when SZ5, SZ10, and SZ15 were calcined for 2 h at 600 8C. From the IR-spectra of the samples CZ5 and CZ15, calcined at 1300 8C, the characteristic IR bands of cordierite and tetragonal zirconia were observed. The average particle size of all the ceramic composite powders calcined at different temperatures as measured by TEM are listed in Table 3. It was observed that particles were nanosized with a narrow size distribution. The average size increased with the increase in calcination temperatures. Some of the selected TEM micrographs are shown in Fig. 4Ža,b,c..
4. Conclusions A series of multicomponent ceramic composite powders were prepared by using the aqueous sol–gel method. Here, metal formates and TEOS were used as precursor compounds instead of metal alkoxides, and water was used as the reaction medium instead of conventionally used solvent alcohol. The advantages of this aqueous sol–gel method are as follows: Ži. A series of nanosized ceramic composite powders can easily be obtained by this method. Žii. The replacement of metal alkoxides by metal formates, and the use of water as reaction medium instead of alcohol, which is commonly used as solvent in all-al-
117
koxides sol–gel route, facilitate the reduction in the cost of the product. Žiii. This processing route provides the basis for a technically simple and cost-effective method for the synthesis of nanosized ceramic composite powders compared with other conventional methods.
References w1x w2x w3x w4x
w5x w6x w7x w8x w9x
w10x w11x w12x w13x w14x w15x w16x w17x w18x w19x w20x w21x w22x
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