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Making windows more flexible
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porosity of the material, the better it will adsorb,’ he explains. ‘So people have been synthesizing materials to maximize both. It turns out that’s kind of a dead area of research because once you get to a critical number, no matter how high you get after that, they don’t improve absorption.’ He and his colleagues have essentially cooked up a recipe for how to make the optimal carbon capture materials. The team’s experimental data was based on a range of porous carbons made from sources as diverse as pulverized coconut shells and sawdust and treated them with potassium hydroxide to pit these grains with nanoscopic pores. Some batches were
Materials Today Volume 19, Number 10 December 2016
treated with nitrogen others with sulfur as additives aimed at making them more adsorbent. Chemical activation was carried out at a range of temperatures from 500 to 800 degrees Celsius. Carbon dioxide adsorption capacity was measured at pressures from zero to 30 times atmospheric pressure. Tests suggest adsorption plateaus with materials with a minimum surface area of 2800 square meters per gram and a pore volume of 1.35 cubic centimeters. ‘Once you get to a certain point, no matter what you do, you’re not going to get any better with a certain material,’ Barron says. They also found that a material with less than 90 percent carbon and enhanced by
oxygen, rather than nitrogen or sulfur, worked best for both carbon capture and methane selectivity, especially for materials activated at close to 800 degrees Celsius. Indeed, there is a tradeoff between adsorption of carbon dioxide as opposed to methane. An ideal material would capture all the carbon dioxide and let all the energy-containing methane pass through for use as fuel. ‘The barrier where it doesn’t help you any more is different for the total uptake of carbon dioxide than it is for the selectivity between carbon dioxide and methane,’ Barron adds. David Bradley
clothing, windows, in paints and as fuel cell catalysts. In this latter application it is the vast surface area per unit volume and high porosity that make the materials useful as catalytic components. The Washington State team has now created a series of bimetallic aerogels, that combine the relatively inexpensive transition metal copper with the precious noble metal which is needed in a smaller quantity in their aerogels. The team made the bimetallic aerogel system using their one-step, high-temperature
reduction method to first create a hydrogel exploiting enhanced gelation kinetics. The hydrogel is, to all intents and purposes, the liquid-filled form of the aerogel. The liquid component can subsequently be removed by careful drying to leave behind the seemingly delicate three-dimensional network of the aerogel. The novel synthesis has reduced the standard manufacturing time of a hydrogel from three days to just six hours. ‘‘This will be a great advantage for large scale production,’’ explains WSU’s Zhu. The research was undertaken as part of WSU’s Grand Challenges, a suite of research initiatives aimed at large societal issues. It is particularly relevant to the challenge of sustainable resources and its theme of energy. ‘‘The resultant PdCu aerogel with ultrathin nanowire networks exhibits excellent electrocatalytic performance toward ethanol oxidation, holding promise in fuel-cell applications,’’ the team reports in the journal Advanced Materials [Zhu, et al., Adv. Mater. (2016) doi:10.1002/adma. 201602546]. David Bradley
a low-temperature acid-catalyzed condensation of polyniobate clusters process for making depositing a smart coating on to a plastic substrate. The same approach also allows ‘nanocrystal-in-glass’ composites, i.e. tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass to be prepared. The method gives researchers an alternative
to attempting to make transparent composites with glass itself. The team has demonstrated their flexible electrochromic device, which responds to a 4 V input to lighten or darken the material and affect the degree to which it transmits near-infrared radiation. The work was carried out in collaboration with scientists at the European Synchrotron
Noble aerogel goes catalytic A new aerogel nanomaterial that reduces the amount of noble metals, such as platinum or palladium, needed to make fuel cells should reduce the cost of such devices making them more commercially viable according to researchers in the USA and China. The aerogel could also improve efficiency. Chengzhou Zhu, Qiurong Shi, Shaofang Fu, Junhua Song, Dan Du, and Yuehe Lin of the Department of Mechanical and Materials Engineering, at Washington State University, Pullman and Haibing Xia of the State Key Laboratory of Crystal Materials, Shandong University, Jinan, have developed a rapid synthesis of aerogels that avoids the need for noble metals. The materials could find use in hydrogen-powered fuel cells as a novel component of this promising environmentally friendly energy solution for the generation of electricity. Aerogels are solids that are certainly worthy of their colloquial name of solid smoke in that they are 92 percent air by volume. They are powerful insulators and have found applications in diving wet suits, firefighting equipment and protective
Making windows more flexible A smart window material that is also flexible could revolutionize architecture and vehicle design allowing control of heat and light to improve efficiency as well as potentially opening new solutions to as yet unrecognized problems. Delia Milliron of the University of Texas at Austin, USA, and colleagues have devised 556
Radiation Facility and CNRS in France, and Ikerbasque in Spain. [Milliron, et al., Nature Mater. (2016) doi:10.1038/nmat4734]. The nanostructured material, niobium oxide, in common with those made using sputtering techniques or by solution coating with high temperature annealing at high temperature is amorphous but has a unique local arrangement of linear chains of atoms. These chains allow ions to flow in and out of the material. ‘There’s relatively little insight into amorphous materials and how their properties are impacted by local structure,’ Milliron explains. ‘But, we were able to characterize with enough specificity what the local arrangement of the atoms is, so that it sheds light on the differences in properties in a rational way.’ UT’s Graeme Henkelman adds that the determination of the atomic structure for amorphous materials is far more difficult than for crystalline materials and so the team had to use a combination of X-ray scattering and spectroscopic characterization to obtain an atomic structure that
was consistent with both experiment and computer simulations. ‘Such collaborative efforts that combine complementary techniques are, in my view, the key to the rational design of new materials,’ he suggests. The same insights that have emerged from this work might also be exploited in the design of other amorphous materials for a wide range of engineering applications such as the development of supercapacitors for storing electrical energy from sustainable but intermittent or periodic generation sources such as wind and solar power.
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The team’s next challenge will be to optimize the flexible material so that their low-temperature process makes substances that exceed the performance of conventional electrochromic materials. ‘We want to see if we can marry the best performance with this new low-temperature processing strategy,’ Milliron says. ‘The next step is to apply the newly developed low temperature process to materials which have enhanced optical performance,’ Milliron told Materials Today. ‘Specifically, we want to be able to block more infrared and tint the windows to a darker hue than is possible using the materials that we used in our proof-ofconcept study just published’. We have demonstrated enhanced optical coloration previously but it required multiple high temperature processing steps, so we need to figure out how to use the low temperature process on these other, improved materials. David Bradley
3D printing makes bone scaffolds a better fit Serious injury or damage to the face and head can require bone grafts. But 3D printing is emerging as an option to tailor artificial bone scaffolds to fit the patient’s needs exactly. And if those scaffolds can be made from biodegradable metals, patients can avoid removal surgeries at a later stage. Now researchers from the University of Pittsburgh, Robert Morris University, Ort Braude College in Israel, and ExOne Company think they have come up with the ideal mix of metals to create an alloy that will degrade without eliciting a toxic response [Hong, et al., Acta Biomater. (2016), doi:10.1016/j.actbio.2016.08.032]. ‘Mg is by far the most popular and attractive metal of choice as a biodegradable or bioabsorbable system since it has properties very similar to bone,’ explains Prashant N. Kumta of the University of Pittsburgh. ‘The only limitation is that it degrades very rapidly.’ To overcome this problem, researchers have investigated other metals like Fe, which degrades very slowly. A combination, however, of Mg and Ca alloyed with Fe–Mn could offer a solution. The team created Fe–Mn–Mg/Ca alloys using a process known as high energy
A scaled down porous human mandible made out of the alloy using the binder jetting approach.
mechanical milling (HEMM) or high energy mechanical alloying (HEMA) in which powders of each element are pulverized together by stainless steel balls in a mill. A scaffold of any shape can then be built up layer-bylayer via a 3D printing process called binder-jetting where a liquid binder is ejected through a nozzle, holding the alloy powder together. A curing step after the structure is created removes the binder, while subsequent heating joins the alloy powder particles together.
‘The Fe–Mn–Mg/Ca alloys are unique and [this] is the first demonstration that introducing Mg and Ca can accelerate corrosion,’ says Kumta. ‘The alloy is also cytocompatible without eliciting any toxic response.’ While the results demonstrate that the Fe–Mn–Mg/Ca alloys can be easily 3D printed using the binder jetting approach, other additive manufacturing methods should work just as well, say the researchers. The resulting alloys have just the right combination of strength, ductility, and controlled, rapid corrosion for use as degradable bone scaffolds. ‘These alloys could be more acceptable than Mg-based alloys, which exhibit rapid corrosion leading to hydrogen pockets that can cause toxicity of the local tissue,’ explains Kumta. The only problem is that the alloy particles produced by milling tend to vary in size and shape. This can produce structures that are quite porous — which is good from the corrosion point of view but less advantageous in terms of strength. The researchers believe that atomization and quenching strategies, which would produce more spherical alloy particles, could overcome this shortcoming. Cordelia Sealy
557
NEWS
Materials Today Volume 19, Number 10 December 2016
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porosity of the material, the better it will adsorb,’ he explains. ‘So people have been synthesizing materials to maximize both. It turns out that’s kind of a dead area of research because once you get to a critical number, no matter how high you get after that, they don’t improve absorption.’ He and his colleagues have essentially cooked up a recipe for how to make the optimal carbon capture materials. The team’s experimental data was based on a range of porous carbons made from sources as diverse as pulverized coconut shells and sawdust and treated them with potassium hydroxide to pit these grains with nanoscopic pores. Some batches were
Materials Today Volume 19, Number 10 December 2016
treated with nitrogen others with sulfur as additives aimed at making them more adsorbent. Chemical activation was carried out at a range of temperatures from 500 to 800 degrees Celsius. Carbon dioxide adsorption capacity was measured at pressures from zero to 30 times atmospheric pressure. Tests suggest adsorption plateaus with materials with a minimum surface area of 2800 square meters per gram and a pore volume of 1.35 cubic centimeters. ‘Once you get to a certain point, no matter what you do, you’re not going to get any better with a certain material,’ Barron says. They also found that a material with less than 90 percent carbon and enhanced by
oxygen, rather than nitrogen or sulfur, worked best for both carbon capture and methane selectivity, especially for materials activated at close to 800 degrees Celsius. Indeed, there is a tradeoff between adsorption of carbon dioxide as opposed to methane. An ideal material would capture all the carbon dioxide and let all the energy-containing methane pass through for use as fuel. ‘The barrier where it doesn’t help you any more is different for the total uptake of carbon dioxide than it is for the selectivity between carbon dioxide and methane,’ Barron adds. David Bradley
clothing, windows, in paints and as fuel cell catalysts. In this latter application it is the vast surface area per unit volume and high porosity that make the materials useful as catalytic components. The Washington State team has now created a series of bimetallic aerogels, that combine the relatively inexpensive transition metal copper with the precious noble metal which is needed in a smaller quantity in their aerogels. The team made the bimetallic aerogel system using their one-step, high-temperature
reduction method to first create a hydrogel exploiting enhanced gelation kinetics. The hydrogel is, to all intents and purposes, the liquid-filled form of the aerogel. The liquid component can subsequently be removed by careful drying to leave behind the seemingly delicate three-dimensional network of the aerogel. The novel synthesis has reduced the standard manufacturing time of a hydrogel from three days to just six hours. ‘‘This will be a great advantage for large scale production,’’ explains WSU’s Zhu. The research was undertaken as part of WSU’s Grand Challenges, a suite of research initiatives aimed at large societal issues. It is particularly relevant to the challenge of sustainable resources and its theme of energy. ‘‘The resultant PdCu aerogel with ultrathin nanowire networks exhibits excellent electrocatalytic performance toward ethanol oxidation, holding promise in fuel-cell applications,’’ the team reports in the journal Advanced Materials [Zhu, et al., Adv. Mater. (2016) doi:10.1002/adma. 201602546]. David Bradley
a low-temperature acid-catalyzed condensation of polyniobate clusters process for making depositing a smart coating on to a plastic substrate. The same approach also allows ‘nanocrystal-in-glass’ composites, i.e. tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass to be prepared. The method gives researchers an alternative
to attempting to make transparent composites with glass itself. The team has demonstrated their flexible electrochromic device, which responds to a 4 V input to lighten or darken the material and affect the degree to which it transmits near-infrared radiation. The work was carried out in collaboration with scientists at the European Synchrotron
Noble aerogel goes catalytic A new aerogel nanomaterial that reduces the amount of noble metals, such as platinum or palladium, needed to make fuel cells should reduce the cost of such devices making them more commercially viable according to researchers in the USA and China. The aerogel could also improve efficiency. Chengzhou Zhu, Qiurong Shi, Shaofang Fu, Junhua Song, Dan Du, and Yuehe Lin of the Department of Mechanical and Materials Engineering, at Washington State University, Pullman and Haibing Xia of the State Key Laboratory of Crystal Materials, Shandong University, Jinan, have developed a rapid synthesis of aerogels that avoids the need for noble metals. The materials could find use in hydrogen-powered fuel cells as a novel component of this promising environmentally friendly energy solution for the generation of electricity. Aerogels are solids that are certainly worthy of their colloquial name of solid smoke in that they are 92 percent air by volume. They are powerful insulators and have found applications in diving wet suits, firefighting equipment and protective
Making windows more flexible A smart window material that is also flexible could revolutionize architecture and vehicle design allowing control of heat and light to improve efficiency as well as potentially opening new solutions to as yet unrecognized problems. Delia Milliron of the University of Texas at Austin, USA, and colleagues have devised 556
Radiation Facility and CNRS in France, and Ikerbasque in Spain. [Milliron, et al., Nature Mater. (2016) doi:10.1038/nmat4734]. The nanostructured material, niobium oxide, in common with those made using sputtering techniques or by solution coating with high temperature annealing at high temperature is amorphous but has a unique local arrangement of linear chains of atoms. These chains allow ions to flow in and out of the material. ‘There’s relatively little insight into amorphous materials and how their properties are impacted by local structure,’ Milliron explains. ‘But, we were able to characterize with enough specificity what the local arrangement of the atoms is, so that it sheds light on the differences in properties in a rational way.’ UT’s Graeme Henkelman adds that the determination of the atomic structure for amorphous materials is far more difficult than for crystalline materials and so the team had to use a combination of X-ray scattering and spectroscopic characterization to obtain an atomic structure that
was consistent with both experiment and computer simulations. ‘Such collaborative efforts that combine complementary techniques are, in my view, the key to the rational design of new materials,’ he suggests. The same insights that have emerged from this work might also be exploited in the design of other amorphous materials for a wide range of engineering applications such as the development of supercapacitors for storing electrical energy from sustainable but intermittent or periodic generation sources such as wind and solar power.
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The team’s next challenge will be to optimize the flexible material so that their low-temperature process makes substances that exceed the performance of conventional electrochromic materials. ‘We want to see if we can marry the best performance with this new low-temperature processing strategy,’ Milliron says. ‘The next step is to apply the newly developed low temperature process to materials which have enhanced optical performance,’ Milliron told Materials Today. ‘Specifically, we want to be able to block more infrared and tint the windows to a darker hue than is possible using the materials that we used in our proof-ofconcept study just published’. We have demonstrated enhanced optical coloration previously but it required multiple high temperature processing steps, so we need to figure out how to use the low temperature process on these other, improved materials. David Bradley
3D printing makes bone scaffolds a better fit Serious injury or damage to the face and head can require bone grafts. But 3D printing is emerging as an option to tailor artificial bone scaffolds to fit the patient’s needs exactly. And if those scaffolds can be made from biodegradable metals, patients can avoid removal surgeries at a later stage. Now researchers from the University of Pittsburgh, Robert Morris University, Ort Braude College in Israel, and ExOne Company think they have come up with the ideal mix of metals to create an alloy that will degrade without eliciting a toxic response [Hong, et al., Acta Biomater. (2016), doi:10.1016/j.actbio.2016.08.032]. ‘Mg is by far the most popular and attractive metal of choice as a biodegradable or bioabsorbable system since it has properties very similar to bone,’ explains Prashant N. Kumta of the University of Pittsburgh. ‘The only limitation is that it degrades very rapidly.’ To overcome this problem, researchers have investigated other metals like Fe, which degrades very slowly. A combination, however, of Mg and Ca alloyed with Fe–Mn could offer a solution. The team created Fe–Mn–Mg/Ca alloys using a process known as high energy
A scaled down porous human mandible made out of the alloy using the binder jetting approach.
mechanical milling (HEMM) or high energy mechanical alloying (HEMA) in which powders of each element are pulverized together by stainless steel balls in a mill. A scaffold of any shape can then be built up layer-bylayer via a 3D printing process called binder-jetting where a liquid binder is ejected through a nozzle, holding the alloy powder together. A curing step after the structure is created removes the binder, while subsequent heating joins the alloy powder particles together.
‘The Fe–Mn–Mg/Ca alloys are unique and [this] is the first demonstration that introducing Mg and Ca can accelerate corrosion,’ says Kumta. ‘The alloy is also cytocompatible without eliciting any toxic response.’ While the results demonstrate that the Fe–Mn–Mg/Ca alloys can be easily 3D printed using the binder jetting approach, other additive manufacturing methods should work just as well, say the researchers. The resulting alloys have just the right combination of strength, ductility, and controlled, rapid corrosion for use as degradable bone scaffolds. ‘These alloys could be more acceptable than Mg-based alloys, which exhibit rapid corrosion leading to hydrogen pockets that can cause toxicity of the local tissue,’ explains Kumta. The only problem is that the alloy particles produced by milling tend to vary in size and shape. This can produce structures that are quite porous — which is good from the corrosion point of view but less advantageous in terms of strength. The researchers believe that atomization and quenching strategies, which would produce more spherical alloy particles, could overcome this shortcoming. Cordelia Sealy
557
NEWS
Materials Today Volume 19, Number 10 December 2016