ARTICLE pubs.acs.org/IECR
A General and Scalable Formulation of Pure CaAl-Layered Double Hydroxide via an Organic/Water Solution Route Sailong Xu, Bowen Zhang, Zhanrui Chen, Jianhui Yu, David G. Evans, and Fazhi Zhang* State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China
bS Supporting Information ABSTRACT: CaAl-layered double hydroxide (CaAl-LDH) has recently been proposed as potential concrete hardening accelerators, because of the similarity in the AFm phase (a family of hydrated calcium aluminate phases) that occurs in hydrated cement. The applications of the promising materials require synthesis routes to be capable of producing large-scale, byproduct-free, and easy-to-handle CaAl-LDH. Herein, we report a general and scalable synthesis of pure CaAl-LDH via an organic/water solution. The possibility of the formation of CaAl-LDH is addressed in terms of the prevention of ethanol from the generation of CaCO3 byproduct. The morphology and crystallinity of CaAl-LDH are tuned by varying different pH value, ethanol/water volumetric content, crystallization time, and temperature. A proper synthesis condition (for example, an ethanol/water volume ratio of 4:1, a pH value of 10.511.5, an aging time of 24 h, and a crystallization temperature of 70 °C) are optimized, and further readily scaled up, by a factor of up to 20, with respect to the initial starting materials. Our results of pure CaAl-LDH in different organic/water solutions may open up a means to produce promising concrete hardening accelerators in large amounts.
1. INTRODUCTION Layered double hydroxides (LDHs), which also are known as anionic layered clay materials, have been widely investigated in many industries, such as high-performance catalysts and catalyst supports, adsorbents, separation materials, additives in plastics, and biological and pharmaceutical materials.17 LDHs are typically represented by the general formula [MII1xMIIIx(OH)2]xþ(An)x/n 3 yH2O. The identities of the divalent and trivalent cations (MII and MIII, respectively) and the interlayer anion (An), together with the value of the stoichiometric coefficient (x), may be varied over a wide range, giving rise to a large class of isostructural materials.5 The flexibility in composition, which is one of their most attractive features, allows LDHs with a wide variety of properties to be prepared.6,7 CaAl-LDH has recently been proposed as promising concrete hardening accelerators, because it contains the Ca2þ cation. The formula of CaAl-LDH811 can be illustrated as [Ca2Al(OH)6]An 3 yH2O (where An represents OH, Cl, NO3, (CO32)0.5, (SO42)0.5, or Al(OH)4), indicating the similarity in composition to the currently commercial hardening accelerators in concrete (such as calcium nitrate and calcium chloride). In the case of the alumina, ferric oxide, and monosulfate involving the AFm phase that occurs in hydrated cement, CaAl-LDH is considered to be a crystal seed, which accelerates cement hydration and improves the mechanical properties. We have recently demonstrated the promising application of the pure CaAl-LDH as a hardening accelerator in concrete, with a result of the greatly enhanced performances in early compressive strength and early flexural strength, compared to the pristine concrete specimen.12 The addition of CaAl-LDH was found to result in an increased amount of calcium silicate hydrate (C-S-H) gel, underlying the improved strength of cement hydration products. r 2011 American Chemical Society
Concrete currently is the building material used in the largest amount; the worldwide consumption of concrete is more than 11 billion m3/yr, and this has especially increased remarkably in developing countries.13,14 Concrete additives, which are widely used to improve concrete properties, are needed both in increasingly larger quantities and with greater performance. Previous literature reports of CaAl-LDH have shown the difficulties in preparing pure CaAl-LDH. The laboratory-level synthesis was performed with the necessities to employ protective conditions to avoid the formation of large amounts of calcium carbonate (CaCO3) byproduct.811 However, the silver capsule equipment employed was a time-consuming operation.8,9 The adopted protection of decarbonated deionized water and nitrogen was also a rigid control of solution pH value.10,11,15,16 These synthesis methods are inconvenient and cost-consuming in the context of an industrial process; therefore, it is essential to develop a facile and scalable approach to prepare highly pure CaAl-LDH. In our previous study, the CaAl-LDH was prepared only in an ethanol/water solution at a certain volume ratio without the byproduct of CaCO3.12 In this present study, however, we report on how the synthesis route may be extended to prepare pure CaAl-LDH in general organic/water solutions, such as methanol, ethanol, n-propyl alcohol, n-butyl alcohol, acetone, and tetrahydrofuran (THF). The engineering of morphology and crystallinity of CaAl-LDH was performed by varying different pH value, ethanol/water volumetric content, crystallization time and temperature. The synthesis conditions were optimized, involving ethanol/water volume ratio of 4:1, pH value from 10.5 to 11.5, Received: October 21, 2010 Accepted: April 18, 2011 Revised: April 18, 2011 Published: April 18, 2011 6567
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aging time 24 h, and crystallization temperature 70 °C, which were easily utilized to produce pure CaAl-LDH by scaling up by a factor of up to 20, with respect to the initial starting materials.
2. EXPERIMENTS 2.1. Preparation of CaAl-LDH. All reactions were performed using analytical-grade chemicals without further purification. Organic solvents that were used included methanol, ethanol (different ratio to water), n-propyl alcohol, n-butyl alcohol, acetone, and THF. All water used was decarbonated deionized water. A separate nucleation and aging steps (SNAS) method was used to prepare CaAl-LDH with Cl in the interlayers.17,18 For a typical preparation procedure, CaCl2 3 2H2O and AlCl3 3 6H2O (with Ca2þ/Al3þ ratios of 2.00 and a Ca2þ concentration of 0.66 M) were dissolved in organic/water mixtures to give solution A. NaOH (with a concentration of 2.30 M) was dissolved in organic/water mixtures to form a base solution B. Solution A (100 mL) and solution B (100 mL) were simultaneously added to a colloid mill with a rotor speed of 5000 rpm and mixed for 1 min and at pH values of 10.512.5. The resulting slurry was then removed from the microreactor and further crystallized under different conditions, such as varying temperatures (70160 °C) and times (5168 h). Finally, the resulting precipitate was washed by centrifugation and dried in vacuum for 24 h at room temperature. Different organic solvents, involving methanol, n-propyl alcohol, n-butyl alcohol, acetone, and THF, were respectively added into the distilled water with a volume ratio of 1:4 to give solution A again. CaAl-LDH was then synthesized in a diverse organic/ water solution by replacing ethanol. Large-scale production of the CaAl-LDH was performed in an ethanol/water system as the molar ratio of the starting materials increased by a factor of up to 20. 2.2. Characterization. The products were characterized using powder X-ray diffraction (Rigaku XRD-6000 diffractometer, Cu KR radiation: 40 kV, 30 mA, λ = 0.15406 nm). The samples were step-scanned in steps of 0.04° (2θ) in the range of 3° 70°, using a count time of 10 s/step. Analysis of the composition of metallic elements was performed using inductively coupled plasma (ICP) emission spectroscopy on a Shimadzu Model ICPS-7500 instrument. All samples were dissolved in dilute nitric acid. The morphology of CaAl-LDH was investigated by scanning electron microscopy (SEM) (Hitachi, Model S-4700, 20 kV).
3. RESULT AND DISCUSSIONS 3.1. Synthesis in Ethanol/Aqueous with Control of Aqueous Solution. Preparation of pure CaAl-LDH was attempted
initially in a decarbonated aqueous solution using a SNAS method without the need for N2 protection. The raw materials of CaCl2 3 2H2O, AlCl3 3 6H2O, and NaOH were dissolved in deionized water, and the pH values of the reactants were kept at 10.5, 11.0, 11.5, 12.0, and 12.5, respectively. Figure 1 shows that the characteristic peaks with high reflection intensity were observed for the five samples, which correspond to (002), (004), and (020) planes of the CaAl-Cl-LDH, respectively.12,16 In the case of pH 12.0 and 12.5 (Figures 1d and 1e), we can see that the intensity of the characteristic (002) peak decreased for the samples synthesized in the case of pH 12.0 and pH 12.5, and that two additional weak peaks were discerned at 17° and 19°, corresponding to the characteristic peaks of Ca(OH)2 and
Figure 1. XRD patterns of the CaAl-LDH synthesized in water solution at different pH values: (a) pH 10.5, (b) pH 11, (c) pH 11.5, (d) pH 12.0;, and (e) pH 12.5. The inset shows the strong reflection peaks corresponding to the formation of CaCO3 byproduct.
Al(OH)3, respectively. In contrast, in the case of pH 10.5, 11, and 11.5 (Figures 1a, 1b, and 1c), neither Ca(OH)2 nor Al(OH)3 were observed for the resulting CaAl-LDH. Also, comparison of the above XRD patterns of the five samples clearly shows that a peak corresponding to the (104) reflection of CaCO3 was visible at ∼29.4° at different pH values (see inset of Figure 1). This strongly suggests that the byproduct of CaCO3 cannot be avoided only in the water solution system; this is analogous to the situations reported previously in the literature.10,11,15,16 Based on the above results, pure CaAl-LDH without a CaCO3 byproduct was prepared using a ethanol/water system via the introduction of ethanol, as reported in our recent study.12 A tentative explanation of the formation of pure CaAl-LDH could be addressed herein, in terms of the solubility of carbon dioxide (CO2), which was not illustrated in our recent study.12 Basically, the solubility of CO2 in the mixture of alcohol and water, especially in ethanol, is lower than that in the distilled water. In our case of LDH synthesis, the amount of CO2 dissolved is remarkably reduced, in comparison with pure water. In addition, ethanol could favor decomposition of the carbonate anions (CO32) generated by dissolving a small quantity of CO2 in water, and thereby the liberation of CO2.19 Similar situation was also reported for glycerol in a previous literature,20 which shows that the CO32 ions between the layers of hydroxide can be deintercalated by NO3, Cl, and SO42 in the presence of glycerol. Therefore, one can hypothesize that no CaCO3 byproduct could be attributed to the low solubility of CO2 in our mixed ethanol/water system, even without the protective nitrogen condition. 3.2. General Synthesis of CaAl-LDH in Different Organic/ Water Solutions. We have extended the synthesis method to a general situation, based on the possible formation of pure CaAlLDH. We chose a diverse organic/water synthesis medium with certain conditions of volume ratio (1:4), temperature (70 °C), and aging (24 h), involving methanol/water, n-propyl alcohol/ water, n-butyl alcohol/water, acetone/water, and THF/water to prepare pure CaAl-LDH. All the XRD patterns (Figure 2) clearly show that no (104) peak characteristic of CaCO3 was indeed observed for the samples obtained in the above-mentioned different organic/water synthesis medium. This strongly reveals 6568
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Figure 2. XRD patterns of the CaAl-LDH synthesized in different organic/ water systems with a volume ratio of 1:4: (a) methanol, (b) n-propyl alcohol, (c) n-butyl alcohol, (d) acetone, and (e) tetrahydrofuran (THF).
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to 9/10. SEM observations clearly show that the CaAl-LDH platelets, synthesized at R values of 1/4 and 1/2, exhibited a hexagonal or quasi-hexagonal morphology (Figures 3a and 3b). We can also see that the samples, obtained at R values of 3/4 and 9/10, exhibited an unusual irregular lamellar morphology (shown in Figures 3c and 3d), in marked contrast to the typical hexagonal platelet obtained in pure water (Figure 3e). The sample prepared at a R value of 3/4 (Figure 3c) was found to be thicker and smaller in size, and the sample prepared at a R value of 9/10 (Figure 3d) displayed an almost rotundity. We also compared the compositions and the values of crystallite sizes calculated from the Scherrer formula for the CaAl-LDH synthesized in aqueous and ethanol/water solutions. The Ca/Al molar ratios (summarized in Table 1) in the final products were determined to be close to the values used in the starting materials (2.00). However, the CaAl-LDH synthesized in aqueous solution gave a relatively higher Ca/Al molar ratio (2.5) than those prepared in the above ethanol/water media with R values of 1/4, 1/2, 3/4, and 9/10 (2.23, 2.24, 2.23, and 1.44) respectively. This indicates a lower level of Al3þ substitution in the products obtained in the ethanol/water media. The average crystallite size (L) in the c-direction (the stacking direction, perpendicular to the layers2) was estimated from the values of the full width of half maximum (fwhm) of the (002) and (004) diffraction peaks by means of the Scherrer equation: L¼
Figure 3. Scanning electron microscopy (SEM) images of the CaAlLDH synthesized with different R values in ethanol/water solutions: (a) 1/4, (b) 1/2, (c) 3/4, (d) 9/10, and (e) synthesized in water solution. R is the volume ratio of ethanol/(water þ ethanol).
that the above organic/water solutions were able to be utilized to produce pure CaAl-LDH free of CaCO3 byproduct, which, in turn, supports the above hypothesis on the possible formation of pure CaAl-LDH. 3.3. Controllable Synthesis in an Ethanol/Water Solution with Various Volume Ratios. To optimize the scalable synthesis conditions, we first evaluated the influence of volume ratios on the CaAl-LDH morphology and crystallinity of CaAl-LDH prepared in an ethanol/water solution. CaAl-LDH were prepared in an ethanol/water solvent at pH 11.0 with various volume ratios R (R is defined as the volume ratio of ethanol/(water þ ethanol); R = 1/4, 1/2, 3/4, and 9/10). Figure 3 shows SEM images of the LDH samples synthesized with the above different ethanol/ water solvents. In the case of pure water, the LDH synthesized displayed the large particle size (Figure 3e). With increasing amounts of ethanol, a decrease in the mean size of LDH particles was clearly observed over a range of R values, from 1/4, 1/2, 3/4,
0:89λ βðθÞ cos θ
where L is the crystallite size, λ the wavelength of the radiation used, θ the Bragg diffraction angle, and β(θ) the fwhm. The average values of L, i.e., 34.9, 29.6, 29.1, 23.9 (summarized in Table 1) showed that the crystallite size in the c-direction decreased as the ethanol content increased. Although the average crystallite size in the a-direction may be estimated from the fwhm of the (020) peak, the low intensity of this peak, coupled with the approximations inherent in the Scherrer formula, introduced a large uncertainty into the calculated value. 3.4. Controllable Synthesis by Varying the Crystallization Time and Temperature. To examine the effect of crystallization time on the purity of LDH product, an ethanol/water mixture with a R value of 1:4 was chosen for different crystallization durations at pH 11.0. Figure 4 displays the XRD patterns of CaAl-LDH with different crystallization times in ethanol/water system at 70 °C. No (104) diffraction peak of CaCO3 formation was observed over a range in different crystallization times from 0, 5, 10, 24, 72, 120, to 168 h (inset of Figure 4). For the sample without further aging (i.e., 0 h of aging), the intensities of the (002) and (004) diffraction peaks of LDH were clearly identified (Figure 4a). The discernable diffraction peaks strongly suggest the hydrotalcite-like characterizations, indeed consistent with the previous studies of SNAS including an initial step of very rapid nucleation under a high shearing force in this process.12,17 After 10 h of aging, the intensities of the (002) and (004) diffraction peaks of LDH were slightly increased. As the aging duration increased, the intensities of the characteristic peaks of LDH were enhanced significantly (see Figures 4c, 4d, 4e, and 4f) when taking into account the possible experimental error. The enhancement can be clearly identified by plotting the intensity of the (002) diffraction peak against aging time (see Figure S1a in the Supporting Information), suggesting the conventional evolution of crystalline LDH from initial nucleation to successive 6569
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Table 1. Properties of the CaAl-LDH Synthesized in Aqueous and Ethanol/Water Solution In Ethanol/Water Solution with Different Volume Ratios Ra property 2þ
3þ
Ca /Al
ratio
b
L in c-directionc (nm)
in aqueous solution
R = 1/4
R = 1/2
R = 3/4
R = 9/10
2.50
2.23
2.24
2.23
1.44
34.3
34.9
29.6
29.1
23.9
R is the volume ratio of ethanol/(water þ ethanol). b Determined by inductively coupled plasma (ICP) analysis. c Value calculated from the Scherrer formula (see text). a
Figure 4. XRD patterns of the CaAl-LDH synthesized via separate nucleation and aging steps (SNAS) with different crystallization times: (a) 0 h, (b) 5 h, (c) 10 h, (d) 24 h, (e) 72 h, (f) 120 h, and (g) 168 h.
growth. Based on the above-mentioned successive growth of LDH crystalline from 0 h (nucleation), through 10, 24, 72, 120, to 168 h (the aging durations), viz., a dependence of over a temperature range, we tried to fit the kinetic data for the nucleation/growth using a widely employed JohnsonMehl AvramiKolmogorov (JMAK) equation:2123 R ¼ 1 expð kt n Þ
ð1aÞ
ln½ lnð1 RÞ ¼ ln k þ n ln t
ð1bÞ
or
where k and n are both empirical model parameters, R is the fraction of transformation, and t is the reaction time. In accordance with eq 1b, the loglog plot of our experimental data was shown in Figure S1b in the Supporting Information. The Avrami exponent (n, i.e., the slopes of the curves) was determined to be almost constant, implying the validity of the JMAK equation. Other models were also used, including standard first-order reaction utilized to describe the phase transformation,24 a model for one-dimensional, linear and branching nuclei, and constant growth,25 and a model for random nucleation and rapid growth.24,25 The results obtained show that none of the models involved was able to elucidate the kinetics for the nucleation/ growth of nanometer-sized LDH samples. The influence of crystallization temperature was then evaluated based on the crystallinity of pure CaAl-LDH by starting from 70 °C. A condition of 24 h crystallization time was chosen,
Figure 5. XRD patterns of the CaAl-LDH synthesized with different crystallization temperatures: (a) 70 °C, (b) 100 °C, (c) 130 °C, (d) 140 °C, (e) 150 °C, and (f) 160 °C.
due to the high crystallinity but a short duration in comparison with the other longer one. Figure 5 shows that no byproduct of CaCO3 were observed for all the CaAl-LDH samples synthesized under the crystallization temperature from 70 °C to 160 °C (see inset of Figure 5). The intensities of the diffraction peaks of LDH increased as the crystallization temperature increased, from 70 °C to 130 °C (see Figures 5a, 5b, and 5c). Surprisingly, at the elevated temperatures (>130 °C), the intensities of the diffraction peaks of LDH decreased rapidly (see Figures 5d, 5e, and 5f). Comparison of the intensities of the (002) peak between the above different samples clearly shows that the crystallization of CaAl-LDH was increased as the time increased and temperature increased (below 130 °C). Note that the synthesis conditions of CaAl-LDH upon 168 h of crystallization at 130 °C was indeed time- and energy-consuming compared with the other conditions mentioned above. To realize the formulization of the above pure CaAl-LDH, an optimized condition should be time-saving, have low energy cost, and be convenient. In this context, the conditions were optimized to be an ethanol/water solvent with a volume ratio at 1:4, aging for 24 h at 70 °C with pH form 10.5 to 11.5. 3.5. Large-Scale Production of CaAl-LDH under the Optimized Condition. Large-scale production of pure CaAl-LDH was performed with the molar ratio of the starting materials increased by a factor of up to 20, under the above-optimized condition. XRD patterns indeed confirm the primary deflection peaks of CaAl-LDH, without observation of the (104) peak of CaCO3 byproduct (see Figure 6). In this case, the formation of pure CaAl-LDH obtained is in very good agreement with our previous study,12 strongly suggesting the good reproducibility 6570
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’ ACKNOWLEDGMENT This work was financially supported by the National Natural cience Foundation of China, the 973 Program (No. 2009CB939802), the Program for New Century Excellent Talents in Universities (No. NCET-07-0055), the Beijing Nova Program (No. 2007B021), and the Fundamental Research Funds for the Central Universities (No. ZZ1128). ’ REFERENCES
Figure 6. XRD patterns of the CaAl-LDH prepared with the amount of the starting materials increased by a factor of up to 19 in an ethanol/ water system (1/4, v/v), using SNAS preparation, followed by 24 h of aging.
and the possible scaleup of our synthesis concept. As reported previously,17,26 the LDH synthesized via the SNAS method showed attractive features, such as very high crystallinity and a much narrower range of particle sizes and shapes, in comparison with those produced via the traditional coprecipitation approach. Recently, the SNAS process for preparation of MgAl-LDH based on a microreactor has been successfully scaled up, making use of a pilot-plant facility (on the scale of 100 tonnes annum1) in our laboratory, and two production lines have been established in Yixing in Jiangsu province, China (1000 and 10000 tonnes annum1).26 Therefore, we expect that this production of pure CaAl-LDH may be capable of being scaled up in an organic/ water solution system using the SNAS method.
4. CONCLUSIONS We have demonstrated that the extended general organic/ water synthesis route could avoid the generation of CaCO3 in the progress of CaAl-LDH production. It is possible to steer the morphology and crystallinity of CaAl-LDH particles by varying the conditions of organic/water solvent, crystallization time, and temperature. Large-scale synthesis of CaAl-LDH without the CaCO3 byproduct was readily achieved in organic/water mixture media, using the SNAS method in a scalable microreactor. Our results involving the formation of pure CaAl-LDH in different organic/water solutions may open up a means to produce large amounts of promising concrete hardening accelerator. ’ ASSOCIATED CONTENT
bS
Supporting Information. Plot showing the intensity of the (002) diffraction peak against aging time (Figure S1a) and a loglog plot of our experimental data (Figure S1b). This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Tel.: þ86 10 64425105. Fax: þ86 10 64425385. E-mail address:
[email protected].
(1) Oh, J.-M.; Biswick, T. T.; Choy, J.-H. Layered nanomaterials for green materials. J. Mater. Chem. 2009, 19, 2553. (2) Williams, G. R.; O’Hare, D. Towards understanding, control and application of layered double hydroxide chemistry. J. Mater. Chem. 2006, 16, 3065. (3) Braterman, P. S.; Xu, Z. P.; Yarberry, F. Handbook of Layered Materials; Marcel Dekker: New York, Basel, Switzerland, 2004; p 373. (4) Li, F.; Duan, X. Applications of layered double hydroxide. Struct. Bonding (Berlin) 2006, 119, 193. (5) Evans, D. G.; Slade, R. C. T. Structural aspects of layered double hydroxide. Struct. Bonding (Berlin) 2006, 119, 1. (6) Leroux, F.; Taviot-Gueho, C. Fine tuning between organic and inorganic host structure: New trends in layered double hydroxide hybrid assemblies. J. Mater. Chem. 2005, 15, 3628. (7) Chen, T.; Xu, S. L.; Zhang, F. Z.; Evans, D. G.; Duan, X. Formation of photo- and thermo-stable layered double hydroxide films with photo-responsive wettability by intercalation of functionalized azobenzenes. Chem. Eng. Sci. 2009, 64, 4350. (8) Renaudin, G.; Francois, M.; Evrard, O. Order and disorder in the lamellar hydrated tetracalcium monocarboaluminate compond. Cem. Concr. Res. 1999, 29, 63. (9) Renaudin, G.; Rapin, J. P.; Humbert, B.; Francois, M. Thermal behaviour of the nitrated AFm phase Ca4Al2(OH)12(NO3)2 3 4H2O and structure determination of the intermediate hydrate Ca4Al2(OH)12(NO3)2 3 2H2O. Cem. Concr. Res. 2000, 30, 307. (10) Vieille, L.; Rousselot, I.; Leroux, F.; Besse, J.-P.; Taviot-Gueho, C. Hydrocalumite and its polymer derivatives. 1. Reversible thermal behavior of Friedel’s salt: A direct observation by means of hightemperature in situ powder X-ray diffraction. Chem. Mater. 2003, 15, 4361. (11) Millang, F.; Walton, R. I.; Lei, L. X.; O’Hare, D. Efficient separation of terephthalate and phthalate anions by selective ionexchange intercalation in the layered double hydroxide Ca2Al(OH)6 3 NO3 3 2H2O. Chem. Mater. 2000, 12, 1990. (12) Xu, S. L.; Chen, Z. R.; Zhang, B. W.; Yu, J. H.; Zhang, F. Z.; Evans, D. G. Facile preparation of pure CaAl-layered double hydroxide and their application as a hardening accelerator in concrete. Chem. Eng. J. 2009, 155, 881. (13) Allen, A.; Thomas, J.; Jennings, A. Composition and density of nanoscale calcium-silicate-hydrate in cement. Nat. Mater. 2007, 6, 311. (14) Birchall, J. D.; Howard, A. J.; Kendall, K. Flexural strength and porosity of cements. Nature 1981, 289, 388. (15) Raki, L.; Beaudoin, J. J.; Mitchell, L. Layered double hydroxidelike materials: Nanocomposites for use in concrete. Cem. Concr. Res. 2004, 34, 1717. (16) Vieille, L.; Taviot-Gueho, C.; Besse, J.-P.; Leroux, F. Hydrocalumite and its polymer derivatives. 2. Polymer incorporation versus in situ polymerization of styrene-4-sulfonate. Chem. Mater. 2003, 15, 4369. (17) Zhao, Y.; Li, F.; Zhang, R.; Evans, D. G.; Duan, X. Preparation of layered double-hydroxide nanomaterials with a uniform crystallite size using a new method involving separate nucleation and aging steps. Chem. Mater. 2002, 14, 4286. (18) Feng, Y. J.; Li, D. Q.; Wang, Y.; Evans, D. G.; Duan, X. Synthesis and characterization of a UV absorbent-inercalated Zn-Al layered double hydroxide. Polym. Degrad. Stab. 2006, 91, 789. 6571
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Industrial & Engineering Chemistry Research
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(19) Grodijo, C. R.; Constantino, V. R. L.; Silva, D. O. Evidences for decarbonation and exfoliation of layered double hydroxide in N,Ndimethylformamideethanol solvent mixture. J. Solid State Chem. 2007, 180, 1976. (20) Hansen, H. C. B.; Taylor, R. M. The use of glycerol intercalates in the exchange of CO32 with SO42, NO3 or Cl in pyroaurite-type compounds. Clay Miner. 1991, 26, 311. (21) Christian, J. W. The Theory of Transformation in Metals and Alloys, 2nd ed.; Pergamon Press: New York, 1975; p 525. (22) Borg, R. J.; Dienes, G. J. The Physical Chemistry of Solids; Academic Press: Boston, 1992; p 525. (23) Williams, G. R.; Khan, A. I.; O’Hare, D. Mechanistic and kinetic studies of guest ion intercalation into layered double hydroxides using time-resolved, in-situ X-ray powder diffraction. Struct. Bonding (Berlin) 2006, 119, 161. (24) Gennari, F. C.; Pasquevich, D. M. Kinetics of the anataserutile transformation in TiO2 in the presence of Fe2O3. J. Mater. Sci. 1998, 33, 1571. (25) Shannon, R. D.; Pask, A. Kinetics of the anataserutile transformation. J. Am. Ceram. Soc. 1965, 48, 391. (26) Evans, D. G.; Duan, X. Preparation of layered double hydroxide and their applications as additives in polymers, as precursors to magnetic materials and in biology and medicine. Chem. Commun. 2006, 485.
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