Why Mineral Interfaces Matter Andrew Putnis Science 343, 1441 (2014); DOI: 10.1126/science.1250884
This copy is for your personal, non-commercial use only.
If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here.
Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://www.sciencemag.org/content/343/6178/1441.full.html This article cites 11 articles, 3 of which can be accessed free: http://www.sciencemag.org/content/343/6178/1441.full.html#ref-list-1 This article appears in the following subject collections: Geochemistry, Geophysics http://www.sciencemag.org/cgi/collection/geochem_phys Materials Science http://www.sciencemag.org/cgi/collection/mat_sci
Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2014 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS.
Downloaded from www.sciencemag.org on April 5, 2014
The following resources related to this article are available online at www.sciencemag.org (this information is current as of April 5, 2014 ):
PERSPECTIVES
A good looker. When the Atacama Large Millimeter/submillimeter Array (ALMA) is completed in Chile later this year, it will consist of 54 12-m and 12 7-m antennae, spread over an area of 16 km in diameter.
migrated to their present location by gravitational interaction with other planets or the disk, or to have been formed in place through gravitational collapse (6). The planets in the two Dent et al. scenarios argue for migration, because Mars-size planets are too small to be formed by typical gravitational collapse models (9), and the alternative scenario requires the planet to migrate in order to produce the enhanced collision rate of icy bodies (10).
The planet signature found by Dent et al. is much more subtle than the massive warp caused by β Pic b. What made the mapping of CO in the disk possible is the giant submillimeter radio observatory being constructed in the Atacama desert in northern Chile, named the Atacama Large Millimeter/submillimeter Array (ALMA). Even in its half-completed state a year ago, ALMA was already the most powerful observatory of its kind. In the years to come, with a fully operational ALMA, we will no doubt witness an explosion of detailed observations of disk structure, giving another measure of how diverse planetary systems can be.
References 1. A. N. Youdin, Astrophys. J. 742, 38 (2011). 2. W. R. F. Dent et al., Science 343, 1490 (2014); 10.1126/ science.1248726. 3. B. A. Smith, R. J. Terrile, Science 226, 1421 (1984). 4. D. Mouillet, J. D. Larwood, J. C. B. Papaloizou, A. M. Lagrange, Mon. Not. R. Astron. Soc. 292, 896 (1997). 5. A.-M. Lagrange et al., Science 329, 57 (2010). 6. C. Baruteau et al., Protostars and Planets VI (Univ. of Arizona Press, Tucson, 2014). 7. M. Mayor, D. Queloz, Nature 378, 355 (1995). 8. D. Lafrenière, R. Jayawardhana, M. H. van Kerkwijk, Astrophys. J. 689, L153 (2008). 9. K. M. Kratter, C. D. Matzner, Mon. Not. R. Astron. Soc. 373, 1563 (2006). 10. M. C. Wyatt, Astrophys. J. 598, 1321 (2003). 10.1126/science.1251123
MATERIALS SCIENCE
Why Mineral Interfaces Matter Andrew Putnis
CREDIT: BABAK TAFRESHI
T
hroughout Earth, rocks respond to changing physical and chemical conditions by converting one rock type to another. These conversions have conventionally been described in terms of solidstate mechanisms, in which new minerals nucleate and grow through exchange of elements by diffusion. The slow rates of solidstate diffusion suggested geological time scales for these processes. However, rocks in Earth’s crust are not dry (1), and even very low concentrations of aqueous solutions can increase reaction rates substantially (2). In the presence of a fluid phase, mineral conversions turn out to proceed not via solidInstitut für Mineralogie, University of Münster, Münster, Germany. E-mail: [email protected]
state diffusion but through dissolution and recrystallization at the mineral-fluid interface (3). Well beyond mineralogy, these insights may prove useful in developing new methods of materials synthesis, for carbon removal from the atmosphere, and for safe nuclear waste storage. Depending on the chemical composition of the aqueous solution, the dissolution of even a few monolayers of a mineral surface can supersaturate an interfacial layer of solution with respect to another solid phase. If this phase can nucleate and grow on the parent substrate, inside the diffusion distance in the fluid, a feedback between the dissolution rate and the growth rate couples the two processes. This feedback allows the parent solid phase to be replaced by a product phase with
Reactions at mineral-fluid interfaces play a key role in processes ranging from the deep Earth to materials synthesis and nuclear waste storage.
different composition while maintaining its original dimensions. Such a “pseudomorphic” replacement was long thought to require a solid-state mechanism, especially given that crystallographic orientations from the parent can be transferred to the product phase. However, an interface-coupled dissolution-precipitation mechanism (4) can transfer crystallographic information via structural matching (epitaxy) when the product nucleates on the parent substrate. Depending on the degree of structural matching, a single parent crystal can be pseudomorphically replaced by a single crystal or a polycrystalline product through an interface-coupled mechanism. For the complete replacement of one phase by another, surface coverage by the
www.sciencemag.org SCIENCE VOL 343 28 MARCH 2014 Published by AAAS
1441
A
B
1 µm
1 µm
Interfacial processes. (A) Carbonated solution produces triangular dissolution etch-pits on the surface of brucite, Mg(OH)2, reflecting the trigonal symmetry of this mineral. Each step in this atomic force microscope image is a molecular monolayer (3). (B) Brucite dissolution is coupled to the precipitation of nanoparticles of a magnesium carbonate phase (13).
new phase should not armor the parent from further reaction; the product must have porosity and hence permeability to allow continued fluid access to the parent phase. The generation of porosity depends on the relative molar volumes of parent and product phases, as well as their relative solubility in the interfacial fluid. The product phase is more stable than the parent (and hence less soluble in the specific aqueous solution), meaning that more of the parent is dissolved than product precipitated within the same external dimensions; this generates porosity. Because of the close coupling between dissolution and precipitation, only the interfacial layer of fluid needs to be supersaturated with respect to the product phase. The interaction of aqueous solutions with solids is ubiquitous throughout Earth, from chemical weathering at the surface to reactions deep in the crust (5). The dynamics of these large-scale processes ultimately depend on nanoscale mechanisms at the mineral-fluid interface, and the coupling of dissolution and precipitation forms the basis of our understanding of element transport in the crust. Understanding the nanoscale mechanisms of fluid-mineral interaction can be exploited to discover geo-inspired routes for the synthesis of functional materials. For example, Reboul et al. have exploited the inheritance of morphology during a replacement process, which can be controlled in the laboratory by parameters such as fluid composition and temperature, to synthesize predefined architectures of porous coordination polymer (PCP) crystal networks (6). The method relies on pseudomorphically replacing a porous, three-dimensionally patterned aluminum (Al) oxide parent, which acts as
1442
both the metal source and the architecturedirecting agent, by an identically shaped AlPCP product. The local dissolution of the Al oxide by reaction with a solution containing organic ligands provides the metal ions that supersaturate the interfacial solution with respect to the Al-based PCP. An advantage of this method is the hierarchical nature of the porosity in the final product, combining the porosity of the original alumina architecture with the secondary porosity in the PCP due to the replacement mechanism. The method holds considerable promise for the design of porous coordination polymer architectures for use in catalysis, sensing, and adsorption separation (6). Xia et al. (7) have used a similar strategy to synthesize three-dimensional ordered arrays of nanocrystals of the zeolite analcime (NaAlSi2O6.H2O) by pseudomorphic replacement of natural leucite (KAlSi2O6), which contains an inherent three-dimensional ordered pattern of nanosized lamellar twins. After reaction in NaCl solutions, these patterns are preserved in the resulting array of analcime nanocrystals, the size of which can be tuned by changing the pH of the solution. The same authors have also used this method to synthesize complex metal sulfides with low thermal stability (8). At low temperatures, traditional synthesis from the elements is far too slow compared to pseudomorphically replacing a preexisting precursor sulfide using an appropriate aqueous solution. The same principles may apply to carbon capture and storage by mineral carbonation. The idea is that reaction of carbonated fluids with magnesium- and calcium-rich rocks supplies metal ions by dissolution, resulting in the precipitation of a metal carbonate. For
28 MARCH 2014 VOL 343
example, dissolution of brucite, Mg(OH)2, a natural constituent of altered mantle rocks, is coupled to the precipitation of a magnesium carbonate phase (see the figure) (9). Understanding the chemical controls on this coupling is a necessary prerequisite to using this strategy of carbon capture and storage. During the dissolution of many silicate minerals by carbonated fluids, metal ions are preferentially released into solution. This results in the formation of silica-rich surface layers (“leached layers”) that may have a substantial effect on the reaction kinetics (10). The differential extraction of metal ions from minerals by treatment with aqueous solutions (leaching) is routinely used in industrial processes (e.g., the production of titanium dioxide from ilmenite, FeTiO3). The mechanism of leaching has been the subject of debate, especially in relation to chemical weathering on Earth, with the consensus moving toward a dissolution-precipitation mechanism as opposed to diffusional exchange (11). The same questions concern the mechanism of aqueous alteration of glass used to encapsulate radioactive nuclear waste. The currently accepted models, based on diffusional exchange of ions between the glass and the solution, are being challenged by new models based on coupled dissolution-precipitation mechanisms (12). Understanding fluid-solid interaction mechanisms is important to diverse fields of Earth science, materials science, and chemistry. Knowledge of the chemical controls on the feedback mechanisms that couple dissolution and precipitation are a necessary prerequisite for predictive numerical modeling. Currently, this knowledge is limited. Studying mineral-fluid reactions in synthetic systems, as well as in Earth’s natural laboratory, will continue to supply some of the answers. References 1. J. J. Ague, in Treatise on Geochemistry 3.06, H. D. Holland, K. K. Turekian, Eds. (Elsevier, Amsterdam, 2003), p. 195. 2. R. Milke, G. Neusser, K. Kolzer, B. Wunder, Geology 41, 247 (2013). 3. C. V. Putnis, E. Ruiz-Agudo, Elements 9, 177 (2013). 4. A. Putnis, Rev. Mineral. Geochem. 70, 87 (2009). 5. D. Harlov, H. Austrheim, Eds., Metasomatism and the Chemical Transformation of Rock (Springer, Berlin/ Heidelberg, 2012). 6. J. Reboul et al., Nat. Mater. 11, 717 (2012). 7. F. Xia et al., Cryst. Growth Des. 9, 4902 (2009). 8. F. Xia et al., Chem. Mater. 20, 2809 (2008). 9. J. Hövelmann, C. V. Putnis, E. Ruiz-Agudo, H. Austrheim, Environ. Sci. Technol. 46, 5253 (2012). 10. D. Daval et al., Chem. Geol. 284, 193 (2011). 11. R. Hellmann et al., Chem. Geol. 294, 203 (2012). 12. L. Dohmen et al., Int. J. Appl. Glass Sci. 4, 357 (2013). 13. J. Hövelmann, C. V. Putnis, E. Ruiz-Agudo, H. Austrheim, Environ. Sci. Technol. 46, 5253 (2012).
SCIENCE www.sciencemag.org
Published by AAAS
10.1126/science.1250884
IMAGES: J. HÖVELMANN/UNIVERSITY OF MÜNSTER; REPRODUCED WITH PERMISSION FROM (3) (PANEL A) AND (13) (PANEL B)
PERSPECTIVES
This copy is for your personal, non-commercial use only.
If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here.
Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://www.sciencemag.org/content/343/6178/1441.full.html This article cites 11 articles, 3 of which can be accessed free: http://www.sciencemag.org/content/343/6178/1441.full.html#ref-list-1 This article appears in the following subject collections: Geochemistry, Geophysics http://www.sciencemag.org/cgi/collection/geochem_phys Materials Science http://www.sciencemag.org/cgi/collection/mat_sci
Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2014 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS.
Downloaded from www.sciencemag.org on April 5, 2014
The following resources related to this article are available online at www.sciencemag.org (this information is current as of April 5, 2014 ):
PERSPECTIVES
A good looker. When the Atacama Large Millimeter/submillimeter Array (ALMA) is completed in Chile later this year, it will consist of 54 12-m and 12 7-m antennae, spread over an area of 16 km in diameter.
migrated to their present location by gravitational interaction with other planets or the disk, or to have been formed in place through gravitational collapse (6). The planets in the two Dent et al. scenarios argue for migration, because Mars-size planets are too small to be formed by typical gravitational collapse models (9), and the alternative scenario requires the planet to migrate in order to produce the enhanced collision rate of icy bodies (10).
The planet signature found by Dent et al. is much more subtle than the massive warp caused by β Pic b. What made the mapping of CO in the disk possible is the giant submillimeter radio observatory being constructed in the Atacama desert in northern Chile, named the Atacama Large Millimeter/submillimeter Array (ALMA). Even in its half-completed state a year ago, ALMA was already the most powerful observatory of its kind. In the years to come, with a fully operational ALMA, we will no doubt witness an explosion of detailed observations of disk structure, giving another measure of how diverse planetary systems can be.
References 1. A. N. Youdin, Astrophys. J. 742, 38 (2011). 2. W. R. F. Dent et al., Science 343, 1490 (2014); 10.1126/ science.1248726. 3. B. A. Smith, R. J. Terrile, Science 226, 1421 (1984). 4. D. Mouillet, J. D. Larwood, J. C. B. Papaloizou, A. M. Lagrange, Mon. Not. R. Astron. Soc. 292, 896 (1997). 5. A.-M. Lagrange et al., Science 329, 57 (2010). 6. C. Baruteau et al., Protostars and Planets VI (Univ. of Arizona Press, Tucson, 2014). 7. M. Mayor, D. Queloz, Nature 378, 355 (1995). 8. D. Lafrenière, R. Jayawardhana, M. H. van Kerkwijk, Astrophys. J. 689, L153 (2008). 9. K. M. Kratter, C. D. Matzner, Mon. Not. R. Astron. Soc. 373, 1563 (2006). 10. M. C. Wyatt, Astrophys. J. 598, 1321 (2003). 10.1126/science.1251123
MATERIALS SCIENCE
Why Mineral Interfaces Matter Andrew Putnis
CREDIT: BABAK TAFRESHI
T
hroughout Earth, rocks respond to changing physical and chemical conditions by converting one rock type to another. These conversions have conventionally been described in terms of solidstate mechanisms, in which new minerals nucleate and grow through exchange of elements by diffusion. The slow rates of solidstate diffusion suggested geological time scales for these processes. However, rocks in Earth’s crust are not dry (1), and even very low concentrations of aqueous solutions can increase reaction rates substantially (2). In the presence of a fluid phase, mineral conversions turn out to proceed not via solidInstitut für Mineralogie, University of Münster, Münster, Germany. E-mail: [email protected]
state diffusion but through dissolution and recrystallization at the mineral-fluid interface (3). Well beyond mineralogy, these insights may prove useful in developing new methods of materials synthesis, for carbon removal from the atmosphere, and for safe nuclear waste storage. Depending on the chemical composition of the aqueous solution, the dissolution of even a few monolayers of a mineral surface can supersaturate an interfacial layer of solution with respect to another solid phase. If this phase can nucleate and grow on the parent substrate, inside the diffusion distance in the fluid, a feedback between the dissolution rate and the growth rate couples the two processes. This feedback allows the parent solid phase to be replaced by a product phase with
Reactions at mineral-fluid interfaces play a key role in processes ranging from the deep Earth to materials synthesis and nuclear waste storage.
different composition while maintaining its original dimensions. Such a “pseudomorphic” replacement was long thought to require a solid-state mechanism, especially given that crystallographic orientations from the parent can be transferred to the product phase. However, an interface-coupled dissolution-precipitation mechanism (4) can transfer crystallographic information via structural matching (epitaxy) when the product nucleates on the parent substrate. Depending on the degree of structural matching, a single parent crystal can be pseudomorphically replaced by a single crystal or a polycrystalline product through an interface-coupled mechanism. For the complete replacement of one phase by another, surface coverage by the
www.sciencemag.org SCIENCE VOL 343 28 MARCH 2014 Published by AAAS
1441
A
B
1 µm
1 µm
Interfacial processes. (A) Carbonated solution produces triangular dissolution etch-pits on the surface of brucite, Mg(OH)2, reflecting the trigonal symmetry of this mineral. Each step in this atomic force microscope image is a molecular monolayer (3). (B) Brucite dissolution is coupled to the precipitation of nanoparticles of a magnesium carbonate phase (13).
new phase should not armor the parent from further reaction; the product must have porosity and hence permeability to allow continued fluid access to the parent phase. The generation of porosity depends on the relative molar volumes of parent and product phases, as well as their relative solubility in the interfacial fluid. The product phase is more stable than the parent (and hence less soluble in the specific aqueous solution), meaning that more of the parent is dissolved than product precipitated within the same external dimensions; this generates porosity. Because of the close coupling between dissolution and precipitation, only the interfacial layer of fluid needs to be supersaturated with respect to the product phase. The interaction of aqueous solutions with solids is ubiquitous throughout Earth, from chemical weathering at the surface to reactions deep in the crust (5). The dynamics of these large-scale processes ultimately depend on nanoscale mechanisms at the mineral-fluid interface, and the coupling of dissolution and precipitation forms the basis of our understanding of element transport in the crust. Understanding the nanoscale mechanisms of fluid-mineral interaction can be exploited to discover geo-inspired routes for the synthesis of functional materials. For example, Reboul et al. have exploited the inheritance of morphology during a replacement process, which can be controlled in the laboratory by parameters such as fluid composition and temperature, to synthesize predefined architectures of porous coordination polymer (PCP) crystal networks (6). The method relies on pseudomorphically replacing a porous, three-dimensionally patterned aluminum (Al) oxide parent, which acts as
1442
both the metal source and the architecturedirecting agent, by an identically shaped AlPCP product. The local dissolution of the Al oxide by reaction with a solution containing organic ligands provides the metal ions that supersaturate the interfacial solution with respect to the Al-based PCP. An advantage of this method is the hierarchical nature of the porosity in the final product, combining the porosity of the original alumina architecture with the secondary porosity in the PCP due to the replacement mechanism. The method holds considerable promise for the design of porous coordination polymer architectures for use in catalysis, sensing, and adsorption separation (6). Xia et al. (7) have used a similar strategy to synthesize three-dimensional ordered arrays of nanocrystals of the zeolite analcime (NaAlSi2O6.H2O) by pseudomorphic replacement of natural leucite (KAlSi2O6), which contains an inherent three-dimensional ordered pattern of nanosized lamellar twins. After reaction in NaCl solutions, these patterns are preserved in the resulting array of analcime nanocrystals, the size of which can be tuned by changing the pH of the solution. The same authors have also used this method to synthesize complex metal sulfides with low thermal stability (8). At low temperatures, traditional synthesis from the elements is far too slow compared to pseudomorphically replacing a preexisting precursor sulfide using an appropriate aqueous solution. The same principles may apply to carbon capture and storage by mineral carbonation. The idea is that reaction of carbonated fluids with magnesium- and calcium-rich rocks supplies metal ions by dissolution, resulting in the precipitation of a metal carbonate. For
28 MARCH 2014 VOL 343
example, dissolution of brucite, Mg(OH)2, a natural constituent of altered mantle rocks, is coupled to the precipitation of a magnesium carbonate phase (see the figure) (9). Understanding the chemical controls on this coupling is a necessary prerequisite to using this strategy of carbon capture and storage. During the dissolution of many silicate minerals by carbonated fluids, metal ions are preferentially released into solution. This results in the formation of silica-rich surface layers (“leached layers”) that may have a substantial effect on the reaction kinetics (10). The differential extraction of metal ions from minerals by treatment with aqueous solutions (leaching) is routinely used in industrial processes (e.g., the production of titanium dioxide from ilmenite, FeTiO3). The mechanism of leaching has been the subject of debate, especially in relation to chemical weathering on Earth, with the consensus moving toward a dissolution-precipitation mechanism as opposed to diffusional exchange (11). The same questions concern the mechanism of aqueous alteration of glass used to encapsulate radioactive nuclear waste. The currently accepted models, based on diffusional exchange of ions between the glass and the solution, are being challenged by new models based on coupled dissolution-precipitation mechanisms (12). Understanding fluid-solid interaction mechanisms is important to diverse fields of Earth science, materials science, and chemistry. Knowledge of the chemical controls on the feedback mechanisms that couple dissolution and precipitation are a necessary prerequisite for predictive numerical modeling. Currently, this knowledge is limited. Studying mineral-fluid reactions in synthetic systems, as well as in Earth’s natural laboratory, will continue to supply some of the answers. References 1. J. J. Ague, in Treatise on Geochemistry 3.06, H. D. Holland, K. K. Turekian, Eds. (Elsevier, Amsterdam, 2003), p. 195. 2. R. Milke, G. Neusser, K. Kolzer, B. Wunder, Geology 41, 247 (2013). 3. C. V. Putnis, E. Ruiz-Agudo, Elements 9, 177 (2013). 4. A. Putnis, Rev. Mineral. Geochem. 70, 87 (2009). 5. D. Harlov, H. Austrheim, Eds., Metasomatism and the Chemical Transformation of Rock (Springer, Berlin/ Heidelberg, 2012). 6. J. Reboul et al., Nat. Mater. 11, 717 (2012). 7. F. Xia et al., Cryst. Growth Des. 9, 4902 (2009). 8. F. Xia et al., Chem. Mater. 20, 2809 (2008). 9. J. Hövelmann, C. V. Putnis, E. Ruiz-Agudo, H. Austrheim, Environ. Sci. Technol. 46, 5253 (2012). 10. D. Daval et al., Chem. Geol. 284, 193 (2011). 11. R. Hellmann et al., Chem. Geol. 294, 203 (2012). 12. L. Dohmen et al., Int. J. Appl. Glass Sci. 4, 357 (2013). 13. J. Hövelmann, C. V. Putnis, E. Ruiz-Agudo, H. Austrheim, Environ. Sci. Technol. 46, 5253 (2012).
SCIENCE www.sciencemag.org
Published by AAAS
10.1126/science.1250884
IMAGES: J. HÖVELMANN/UNIVERSITY OF MÜNSTER; REPRODUCED WITH PERMISSION FROM (3) (PANEL A) AND (13) (PANEL B)
PERSPECTIVES
