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Preparation of phosphoric acid-based porous geopolymers
Applied Clay Science 50 (2010) 600–603
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Note
Preparation of phosphoric acid-based porous geopolymers Liu Le-ping, Cui Xue-min ⁎, Qiu Shu-heng, Yu Jun-li, Zhang Lin School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, PR China
a r t i c l e
i n f o
Article history: Received 1 February 2010 Received in revised form 4 September 2010 Accepted 1 October 2010 Available online 5 November 2010 Keywords: Geopolymers Porosity Phosphoric acid Thermal stability
a b s t r a c t We report a porous geopolymer synthesized from metakaolin, α-Al2O3, Al powder and phosphoric acid at 80 °C for 5 h. The Al powder served as a foaming agent to control porosity, pore size and pore distribution producing a porosity ranging from 40% to 83% and a pore size of approximately 1 mm .The compressive strength was N 6 MPa. The phases of the geopolymers were determined by X-ray diffraction and their thermal properties investigated by TG-DTA and thermal shrinkage analysis. The porous geopolymer consisted of an amorphous phase and minor amounts of quartz, and showed an excellent thermal stability at a high temperature, with a linear shrinkage of only 5.3% at 1450 °C. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Porous inorganic materials were widely used in numerous applications such as thermal retardation, filtering, purification, acoustics, and electric pole materials (Madhavi et al., 2005; Buchwald et al., 2009; Rodriguez et al., 2009). Generally, these materials are fabricated via sintering above 1000 °C. Recently, a new type of porous geopolymer has been extensively studied due to its low cost, sinter-free fabrication, acid resistance, good thermal properties and environmentally friendly nature (Wang et al., 2005a,b; Okada et al., 2009). These geopolymer materials, initially reported by Davidovits, were synthesized by activating an aluminosilicate with alkali metal hydroxide, silicate or phosphoric acid solutions at an ambient temperature or slightly above (Davidovits et al., 1994). For the alkali-based geopolymers, activated aluminosilicate materials were rapidly dissolved by an alkali solution with formation of lowpolymeric [SiO4] and [AlO4] tetrahedral units which were then linked to form three-dimensional structures. Balance of the negative charges on the [AlO4] tetrahedra was achieved by Na+ and K+ ions (Davidovits et al., 1989). However, due to the presence of the alkali ions, the thermal stability was not ideal, and the geopolymers underwent phase transformations between 800 °C and 1000 °C. The transformations depended on the chemical composition of the polymer and the type of alkali ions (Barbosa and Mackensie, 2003; Duxson et al., 2006; Provis et al., 2009). In phosphoric acid-based geopolymers, the positive charges on of the [PO4] tetrahedra were balanced by the negative charges of the [AlO4] tetrahedra, so that neutrality was maintained. In comparison to the sodium silicate-base
⁎ Corresponding author. Tel.: + 86 771 3233718. E-mail address: [email protected] (C. Xue-min). 0169-1317/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2010.10.004
geopolymers, phosphoric acid-based geopolymers had superior performance with good mechanical, thermal and dielectric properties. When the reaction system contains a low-concentration of [SiO4] and [AlO4] tetrahedra, these units are bound by [PO4] groups forming geopolymers. In aqueous dispersion of phosphoric acid and metakaolin, between the Al–O layers of metakaolin react with phosphoric acid. Formation of Al–O–P bonds was confirmed by FTIR and NMR. (Hipedinger et al., 2004; Cao et al., 2005) In this study, porous phosphoric acid-based geopolymers were synthesized at 80 °C using metakaolin, α-Al2O3 and phosphoric acid, and Al powder as a pore-forming agent. 2. Experimental methods 2.1. Materials Kaolin (obtained from Beihai in Guangxi Province, China) was calcined at 800 °C for 2 h to produce metakaolin. The chemical composition of the metakaolin as measured by EDS was (mass%): SiO2 56.91, Al2O3 42.35, Fe2O3 0.22, and K2O 0.49. The average particle size was 47–55 μm. Industrial grade (99.9 mass%) α-Al2O3 with an average particle size of 35–50 μm was used in the experiments. Both phosphoric acid (85 mass%) and aluminum powder (99 mass%) were analytical reagents. Distilled water was used throughout the experiments. 2.2. Sample preparation Metakaolin, α-Al2O3, distilled water and phosphoric acid were mixed in a mixer for 30 min to obtain an aqueous slurry having molar ratios: Al2O3/SiO2 = 1:1, H3PO4/Al2O3 = 1.4:1, and H3PO4 /H2O = 3:2 where Al2O3 comprised Al2O3 of metakaolin and α-Al2O3. Al powder
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
90
14
60 8 50
13 12 11 10 9 8 7
40
6
6 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22
0
300
600
900
1200
1500
Temperature(°C)
Mass content of Al powder/%
Fig. 3. Compressive strength of the calcined geopolymers.
Fig. 1. Influence of the Al powder content on porosity and compressive strength.
was added at a mass fraction of 0.06%, 0.08%, 0.10%, 0.12% and 0.20%. The mixtures were stirred for 1 min. The aqueous slurry was then poured into cubic molds of 20 mm × 20 mm × 20 mm and when filled, sealed to prevent water loss. The cubes were cured at 80 °C for 5 h, while non-molded samples were cured at 40 °C and 90% R.H. for 7 days. Sample fragments collected from compression tests were used for XRD, TG-DTA and thermal shrinkage analyses. Other samples were cured in a closed oven at 150 °C for 12 h, and then calcined at 950 °C, 1250 °C, 1450 °C and 1500 °C for 1 h.
2.3. Characterization The compressive strength was measured by a DNS100 electronic Universal tester. Six samples of each formulation were measured and the averaged values were reported. The loading was set at a rate of 0.5 mm/min for all measurements. X-ray diffraction (XRD) patterns were was recorded on automated D/Max 2500 V X-ray diffractometers: 40 kv, 100 mA, CuKα radiation, and scanning from 10° to 70° (2θ) at a rate of 10° per min. The pore size and pore size distribution were analyzed on a GL-99 T Stereo microscope. Thermal analysis was conducted on a STA409PC TG-DTA instrument in air with a heating rate of 5 °C/min. Thermal shrinkage was assessed utilizing a KSF1600X high temperature oven with a heating rate of 5 °C/min.
3. Results and discussion 3.1. Porosity, shrinkage and compressive strength Fig. 1 illustrates the effect of the amount of pore-forming Al powder on the porosity and compressive strength of the synthesized geopolymer. The higher the Al content, the higher the porosity of the samples and the lower the compressive strength. The maximum porosity value was 83% and the corresponding compressive strength 7 MPa. The compressive strength of the geopolymer is related to its porosity, pore size and pore distribution which is controlled by the Al content. In addition, the water content also plays an important role with regard to pore size and porosity. The lower the water content in the slurry, the higher the viscosity, and the smaller the final pore size. If the water content was high and the viscosity of the slurry was quite low, all pores disappeared. Therefore, the molar ratio of H3PO4 to H2O was fixed at 3:2. Below 150 °C, the volume and length decreased to 11.1% and 3.6%, (Fig. 2) due to the loss of absorbed water in the samples. The volume and length decreased with an additional 1–2% between 150 °C and 950 °C due to dehydroxylation, although the rate of shrinkage remained unchanged from 950 °C to 1450 °C. However, an abrupt volume decrease of 45.52% occurred between 1450 °C and 1500 °C due to phase transformation. The compressive strength changed little between 80 °C and 1450 °C (Fig. 3), but the compressive strength increased significantly between 1450 °C and 1500 °C due to the shrinkage of the pores.
50 Volume shrinkage rate linear shrinkage rate
45
102
40
TG DTA
98
35
142.92
96 30
exo
0.6 0.4
94
TG (%)
Shrinkage rate (%)
0.8
100
25 20
92
0.2
90 268.92
88
15
0.0
86
10
1002.92
84 5
-0.2
82
0
80 0
400
800 1200 Temperature(°C)
Fig. 2. Shrinkage of samples prepared with 0.2 mass% Al.
1600
0
300
600
900
1200
Temperature(°C) Fig. 4. TG-DTA curves of the geopolymers calcined in air.
-0.4
DTA(uv· mg-1)
Porosity/%
porosity 70
Compressive strength /MPa
10
Compressive strength(MPa)
compressive strength 80
601
602
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
reaction. The phosphoric acid dissolved rapidly the metakaolin and α-Al2O3 forming a three-dimensional polymeric Si–O–Al–O–P unit.
(b) geopolymer (a) metakaolin 10
20
30
40
50
60
70
2θ(°) Fig. 5. XRD patterns: (a) metakaolin and (b) geopolymers. ● — quartz, ◆ — aluminum phosphate.
3.4. Optical microscopy analysis The porosity of the geopolymers fabricated with 0.06 mass% or 0.10 mass% Al content is low as shown in Fig. 6A and B. The pore size was small and the pore size distribution was non-uniform in these samples. Geopolymers fabricated with 0.2 mass% Al powder and cured at 80 °C for 5 h (Fig. 6C) had larger pores and porosity. The pore size decreased after being calcined at 1250 °C (Fig. 6D), and the pore size distribution is far more uniform being with pores approximately 1 mm. 4. Conclusions
3.2. Thermal analysis The thermal analysis result is shown in Fig. 4. A mass loss of approximately 15% occurred due to dehydration of absorbed water below 300 °C. A sharp endothermic peak was seen between 142 °C and 144 °C. From 300 °C to 1000 °C the mass remained almost constant although a small exothermic peak, assignable to spine formation, was found between 1002 °C and 1005 °C. Between 1005 °C and 1300 °C, the mass and quantity of heat remained nearly constant. 3.3. XRD analysis The XRD patterns of metakaolin (Fig. 5a) revealed that the main phase was amorphous, and several reflections of quartz between 15 and 27º (2θ) were seen. The geopolymer showed a diffuse peak indicating that it is an amorphous nature as shown in Fig. 5b. Several sharp reflections between 20º and 28º (2θ) belonged to quartz and aluminum phosphate. α-Al2O3 was not detected. Quartz was an associated mineral of kaolin, and did not take part in the chemical
Porous phosphoric acid-based geopolymers were fabricated from metakaolin, phosphoric acid, α-Al2O3 and Al powder as a poreforming agent. The geopolymers consisted of an amorphous phase with minor amounts of quartz and aluminum phosphate. The phase composition of these geopolymers was similar to that of sodium silicate-based geopolymers. The pore size and pore volume fraction were controlled by the content of Al powder and/or water. The porosity varied from 40% to 83%. The compressive strength of these geopolymers was N6.0 MPa with the maximum compressive strength reaching 13.7 MPa. These polymers displayed an excellent thermal stability and showed nearly constant compressive strength or shrinkage by heating up to 1450 °C. Acknowledgements This work was supported by the Chinese Natural and Science fund (grant: 50602006 and 50962002) and by the Program for Excellent Talents in Guangxi Higher Education institutions.
Fig. 6. Optical images of the geopolymers prepared with: (A) 0.06 mass% Al; (B) 0.10 mass% Al cured at 80 °C for 5 h; (C) 0.20 mass% Al cured at 80 °C for 5 h; and (D) 0.20 mass% Al sample calcined at 1250 °C for 1 h.
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
References Barbosa, V.F.F., Mackensie, K.J.D., 2003. Synthesis and thermal behavior of potassium sialate geopolymers. Mater. Lett. 57, 1477–1482. Buchwald, A., Vicent, M., Kriegel, R., et al., 2009. Geopolymeric binders with different fine fillers-phase transformations at high temperature. Appl. Clay Sci. 46, 190–195. Cao, D., Su, D., Lu, B., et al., 2005. Synthesis and structure characterization of geopolymeric material based on metakaolinite and phosphoric acid. J. Chin. Ceram. Soc. 33, 1385–1389. Davidovits, J., et al., 1989. Geopolymers geopolymer new materials. J. Therm. Anal. 35 (2), 429–444. Davidovits, J., et al., 1994. Geopolymer: man-made rocks geosynthesis and the resulting development of very early high strength cement. J. Mater. Educ. 16, 91–139. Duxson, P., Lukey, G.C., Van Deventer, J.S., et al., 2006. Thermal evolution of metakaolin geopolymers: Part1 — physical evolution. J. Non-Cryst. Solids 352, 5541–5555.
603
Hipedinger, N.E., Scian, A.N., Aglietti, E.F., 2004. Magnesia–ammonium phosphatebonded cordierite refractory castables: phase evolution on heating and mechanical properties. J. Cem. Concr. Res. 34, 157–164. Madhavi, S., Ferraris, C., White, T.J., 2005. Synthesis and crystallization of macroporous hydroxyapatite. J. Solid State Chem. 178, 2838–2845. Okada, K., Ooyama, A., Isobe, T., et al., 2009. Water retention properties of porous geopolymers for use in cooling applications. J. Eur. Ceram. Soc. 29, 1917–1923. Provis, J.L., Chong, C.Z., Duxson, P., van Deventer, J.S., 2009. Correlating mechanical and thermal properties of sodium silicate-ash geopolymers. Colloids Surf. A 336, 57–63. Rodriguez, R., Estevez, M., Vargas, S., et al., 2009. Synthesis and characterization of HApbased porous materials. J. Mater. Lett. 63, 1588-1561. Wang, H., Li, H., Yan, F., 2005a. Synthesis and tribological behavior of metakaolin-based geopolymer composites. Mater. Lett. 59, 3976–3978. Wang, H., Li, H., Yan, F., 2005b. Synthesis and mechanical properties of metakaolinbased geopolymer. Colloids Surf. A Physicochem. Eng. Aspects 268, 1–6.
Contents lists available at ScienceDirect
Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Note
Preparation of phosphoric acid-based porous geopolymers Liu Le-ping, Cui Xue-min ⁎, Qiu Shu-heng, Yu Jun-li, Zhang Lin School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, PR China
a r t i c l e
i n f o
Article history: Received 1 February 2010 Received in revised form 4 September 2010 Accepted 1 October 2010 Available online 5 November 2010 Keywords: Geopolymers Porosity Phosphoric acid Thermal stability
a b s t r a c t We report a porous geopolymer synthesized from metakaolin, α-Al2O3, Al powder and phosphoric acid at 80 °C for 5 h. The Al powder served as a foaming agent to control porosity, pore size and pore distribution producing a porosity ranging from 40% to 83% and a pore size of approximately 1 mm .The compressive strength was N 6 MPa. The phases of the geopolymers were determined by X-ray diffraction and their thermal properties investigated by TG-DTA and thermal shrinkage analysis. The porous geopolymer consisted of an amorphous phase and minor amounts of quartz, and showed an excellent thermal stability at a high temperature, with a linear shrinkage of only 5.3% at 1450 °C. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Porous inorganic materials were widely used in numerous applications such as thermal retardation, filtering, purification, acoustics, and electric pole materials (Madhavi et al., 2005; Buchwald et al., 2009; Rodriguez et al., 2009). Generally, these materials are fabricated via sintering above 1000 °C. Recently, a new type of porous geopolymer has been extensively studied due to its low cost, sinter-free fabrication, acid resistance, good thermal properties and environmentally friendly nature (Wang et al., 2005a,b; Okada et al., 2009). These geopolymer materials, initially reported by Davidovits, were synthesized by activating an aluminosilicate with alkali metal hydroxide, silicate or phosphoric acid solutions at an ambient temperature or slightly above (Davidovits et al., 1994). For the alkali-based geopolymers, activated aluminosilicate materials were rapidly dissolved by an alkali solution with formation of lowpolymeric [SiO4] and [AlO4] tetrahedral units which were then linked to form three-dimensional structures. Balance of the negative charges on the [AlO4] tetrahedra was achieved by Na+ and K+ ions (Davidovits et al., 1989). However, due to the presence of the alkali ions, the thermal stability was not ideal, and the geopolymers underwent phase transformations between 800 °C and 1000 °C. The transformations depended on the chemical composition of the polymer and the type of alkali ions (Barbosa and Mackensie, 2003; Duxson et al., 2006; Provis et al., 2009). In phosphoric acid-based geopolymers, the positive charges on of the [PO4] tetrahedra were balanced by the negative charges of the [AlO4] tetrahedra, so that neutrality was maintained. In comparison to the sodium silicate-base
⁎ Corresponding author. Tel.: + 86 771 3233718. E-mail address: [email protected] (C. Xue-min). 0169-1317/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2010.10.004
geopolymers, phosphoric acid-based geopolymers had superior performance with good mechanical, thermal and dielectric properties. When the reaction system contains a low-concentration of [SiO4] and [AlO4] tetrahedra, these units are bound by [PO4] groups forming geopolymers. In aqueous dispersion of phosphoric acid and metakaolin, between the Al–O layers of metakaolin react with phosphoric acid. Formation of Al–O–P bonds was confirmed by FTIR and NMR. (Hipedinger et al., 2004; Cao et al., 2005) In this study, porous phosphoric acid-based geopolymers were synthesized at 80 °C using metakaolin, α-Al2O3 and phosphoric acid, and Al powder as a pore-forming agent. 2. Experimental methods 2.1. Materials Kaolin (obtained from Beihai in Guangxi Province, China) was calcined at 800 °C for 2 h to produce metakaolin. The chemical composition of the metakaolin as measured by EDS was (mass%): SiO2 56.91, Al2O3 42.35, Fe2O3 0.22, and K2O 0.49. The average particle size was 47–55 μm. Industrial grade (99.9 mass%) α-Al2O3 with an average particle size of 35–50 μm was used in the experiments. Both phosphoric acid (85 mass%) and aluminum powder (99 mass%) were analytical reagents. Distilled water was used throughout the experiments. 2.2. Sample preparation Metakaolin, α-Al2O3, distilled water and phosphoric acid were mixed in a mixer for 30 min to obtain an aqueous slurry having molar ratios: Al2O3/SiO2 = 1:1, H3PO4/Al2O3 = 1.4:1, and H3PO4 /H2O = 3:2 where Al2O3 comprised Al2O3 of metakaolin and α-Al2O3. Al powder
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
90
14
60 8 50
13 12 11 10 9 8 7
40
6
6 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22
0
300
600
900
1200
1500
Temperature(°C)
Mass content of Al powder/%
Fig. 3. Compressive strength of the calcined geopolymers.
Fig. 1. Influence of the Al powder content on porosity and compressive strength.
was added at a mass fraction of 0.06%, 0.08%, 0.10%, 0.12% and 0.20%. The mixtures were stirred for 1 min. The aqueous slurry was then poured into cubic molds of 20 mm × 20 mm × 20 mm and when filled, sealed to prevent water loss. The cubes were cured at 80 °C for 5 h, while non-molded samples were cured at 40 °C and 90% R.H. for 7 days. Sample fragments collected from compression tests were used for XRD, TG-DTA and thermal shrinkage analyses. Other samples were cured in a closed oven at 150 °C for 12 h, and then calcined at 950 °C, 1250 °C, 1450 °C and 1500 °C for 1 h.
2.3. Characterization The compressive strength was measured by a DNS100 electronic Universal tester. Six samples of each formulation were measured and the averaged values were reported. The loading was set at a rate of 0.5 mm/min for all measurements. X-ray diffraction (XRD) patterns were was recorded on automated D/Max 2500 V X-ray diffractometers: 40 kv, 100 mA, CuKα radiation, and scanning from 10° to 70° (2θ) at a rate of 10° per min. The pore size and pore size distribution were analyzed on a GL-99 T Stereo microscope. Thermal analysis was conducted on a STA409PC TG-DTA instrument in air with a heating rate of 5 °C/min. Thermal shrinkage was assessed utilizing a KSF1600X high temperature oven with a heating rate of 5 °C/min.
3. Results and discussion 3.1. Porosity, shrinkage and compressive strength Fig. 1 illustrates the effect of the amount of pore-forming Al powder on the porosity and compressive strength of the synthesized geopolymer. The higher the Al content, the higher the porosity of the samples and the lower the compressive strength. The maximum porosity value was 83% and the corresponding compressive strength 7 MPa. The compressive strength of the geopolymer is related to its porosity, pore size and pore distribution which is controlled by the Al content. In addition, the water content also plays an important role with regard to pore size and porosity. The lower the water content in the slurry, the higher the viscosity, and the smaller the final pore size. If the water content was high and the viscosity of the slurry was quite low, all pores disappeared. Therefore, the molar ratio of H3PO4 to H2O was fixed at 3:2. Below 150 °C, the volume and length decreased to 11.1% and 3.6%, (Fig. 2) due to the loss of absorbed water in the samples. The volume and length decreased with an additional 1–2% between 150 °C and 950 °C due to dehydroxylation, although the rate of shrinkage remained unchanged from 950 °C to 1450 °C. However, an abrupt volume decrease of 45.52% occurred between 1450 °C and 1500 °C due to phase transformation. The compressive strength changed little between 80 °C and 1450 °C (Fig. 3), but the compressive strength increased significantly between 1450 °C and 1500 °C due to the shrinkage of the pores.
50 Volume shrinkage rate linear shrinkage rate
45
102
40
TG DTA
98
35
142.92
96 30
exo
0.6 0.4
94
TG (%)
Shrinkage rate (%)
0.8
100
25 20
92
0.2
90 268.92
88
15
0.0
86
10
1002.92
84 5
-0.2
82
0
80 0
400
800 1200 Temperature(°C)
Fig. 2. Shrinkage of samples prepared with 0.2 mass% Al.
1600
0
300
600
900
1200
Temperature(°C) Fig. 4. TG-DTA curves of the geopolymers calcined in air.
-0.4
DTA(uv· mg-1)
Porosity/%
porosity 70
Compressive strength /MPa
10
Compressive strength(MPa)
compressive strength 80
601
602
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
reaction. The phosphoric acid dissolved rapidly the metakaolin and α-Al2O3 forming a three-dimensional polymeric Si–O–Al–O–P unit.
(b) geopolymer (a) metakaolin 10
20
30
40
50
60
70
2θ(°) Fig. 5. XRD patterns: (a) metakaolin and (b) geopolymers. ● — quartz, ◆ — aluminum phosphate.
3.4. Optical microscopy analysis The porosity of the geopolymers fabricated with 0.06 mass% or 0.10 mass% Al content is low as shown in Fig. 6A and B. The pore size was small and the pore size distribution was non-uniform in these samples. Geopolymers fabricated with 0.2 mass% Al powder and cured at 80 °C for 5 h (Fig. 6C) had larger pores and porosity. The pore size decreased after being calcined at 1250 °C (Fig. 6D), and the pore size distribution is far more uniform being with pores approximately 1 mm. 4. Conclusions
3.2. Thermal analysis The thermal analysis result is shown in Fig. 4. A mass loss of approximately 15% occurred due to dehydration of absorbed water below 300 °C. A sharp endothermic peak was seen between 142 °C and 144 °C. From 300 °C to 1000 °C the mass remained almost constant although a small exothermic peak, assignable to spine formation, was found between 1002 °C and 1005 °C. Between 1005 °C and 1300 °C, the mass and quantity of heat remained nearly constant. 3.3. XRD analysis The XRD patterns of metakaolin (Fig. 5a) revealed that the main phase was amorphous, and several reflections of quartz between 15 and 27º (2θ) were seen. The geopolymer showed a diffuse peak indicating that it is an amorphous nature as shown in Fig. 5b. Several sharp reflections between 20º and 28º (2θ) belonged to quartz and aluminum phosphate. α-Al2O3 was not detected. Quartz was an associated mineral of kaolin, and did not take part in the chemical
Porous phosphoric acid-based geopolymers were fabricated from metakaolin, phosphoric acid, α-Al2O3 and Al powder as a poreforming agent. The geopolymers consisted of an amorphous phase with minor amounts of quartz and aluminum phosphate. The phase composition of these geopolymers was similar to that of sodium silicate-based geopolymers. The pore size and pore volume fraction were controlled by the content of Al powder and/or water. The porosity varied from 40% to 83%. The compressive strength of these geopolymers was N6.0 MPa with the maximum compressive strength reaching 13.7 MPa. These polymers displayed an excellent thermal stability and showed nearly constant compressive strength or shrinkage by heating up to 1450 °C. Acknowledgements This work was supported by the Chinese Natural and Science fund (grant: 50602006 and 50962002) and by the Program for Excellent Talents in Guangxi Higher Education institutions.
Fig. 6. Optical images of the geopolymers prepared with: (A) 0.06 mass% Al; (B) 0.10 mass% Al cured at 80 °C for 5 h; (C) 0.20 mass% Al cured at 80 °C for 5 h; and (D) 0.20 mass% Al sample calcined at 1250 °C for 1 h.
L. Le-ping et al. / Applied Clay Science 50 (2010) 600–603
References Barbosa, V.F.F., Mackensie, K.J.D., 2003. Synthesis and thermal behavior of potassium sialate geopolymers. Mater. Lett. 57, 1477–1482. Buchwald, A., Vicent, M., Kriegel, R., et al., 2009. Geopolymeric binders with different fine fillers-phase transformations at high temperature. Appl. Clay Sci. 46, 190–195. Cao, D., Su, D., Lu, B., et al., 2005. Synthesis and structure characterization of geopolymeric material based on metakaolinite and phosphoric acid. J. Chin. Ceram. Soc. 33, 1385–1389. Davidovits, J., et al., 1989. Geopolymers geopolymer new materials. J. Therm. Anal. 35 (2), 429–444. Davidovits, J., et al., 1994. Geopolymer: man-made rocks geosynthesis and the resulting development of very early high strength cement. J. Mater. Educ. 16, 91–139. Duxson, P., Lukey, G.C., Van Deventer, J.S., et al., 2006. Thermal evolution of metakaolin geopolymers: Part1 — physical evolution. J. Non-Cryst. Solids 352, 5541–5555.
603
Hipedinger, N.E., Scian, A.N., Aglietti, E.F., 2004. Magnesia–ammonium phosphatebonded cordierite refractory castables: phase evolution on heating and mechanical properties. J. Cem. Concr. Res. 34, 157–164. Madhavi, S., Ferraris, C., White, T.J., 2005. Synthesis and crystallization of macroporous hydroxyapatite. J. Solid State Chem. 178, 2838–2845. Okada, K., Ooyama, A., Isobe, T., et al., 2009. Water retention properties of porous geopolymers for use in cooling applications. J. Eur. Ceram. Soc. 29, 1917–1923. Provis, J.L., Chong, C.Z., Duxson, P., van Deventer, J.S., 2009. Correlating mechanical and thermal properties of sodium silicate-ash geopolymers. Colloids Surf. A 336, 57–63. Rodriguez, R., Estevez, M., Vargas, S., et al., 2009. Synthesis and characterization of HApbased porous materials. J. Mater. Lett. 63, 1588-1561. Wang, H., Li, H., Yan, F., 2005a. Synthesis and tribological behavior of metakaolin-based geopolymer composites. Mater. Lett. 59, 3976–3978. Wang, H., Li, H., Yan, F., 2005b. Synthesis and mechanical properties of metakaolinbased geopolymer. Colloids Surf. A Physicochem. Eng. Aspects 268, 1–6.