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Robert M.H.,State University of Campinas | Silva R.R.,IFSP Federal Institute of Education
Archives of Materials Science and Engineering | Year: 2015

Purpose: To explore a new route to produce metallic foams which results in a structure of closed micro porous. High energy milling is employed to incorporate particles of foaming agents in metallic powders to promote homogeneous distribution of micro gas bubbles during foaming. Design/methodology/approach: AA2014 powders were mixed with TiH2 particles as gas releasing agent, through high energy milling, producing composite powders. Powders were compacted and obtained compacted precursors were heated to promote foaming of the metal. Effect of processing conditions in the expansion of the metal, structural characteristics, density and mechanical properties under compression, of obtained foams was analyzed. Findings: Foaming composite powders of AA2014/TiH2 produced by high energy milling is a promising route to produce micro porous aluminium foams. The best foaming condition among the conditions investigated, occurs for the highest milling time (17 h) and highest heating rate (3°C/s) imposed during foaming, resulting in 140% of maximum expansion and foams with relative density of 0.44. Research limitations/implications: Main limitation of the proposed process is the long time required to produce composite powders by high energy milling, which can justify the process for specific purposes where micro porous are required. However, as all new development, further works can lead to the optimization of processing parameters, mainly concerning reduction of processing time, to make the process compatible to wider industrial applications. Practical implications: New products can be developed for specific applications requiring porous with micro scale. Originality/value: The use of the foaming agent structurally incorporated in the metal powder to produce precursors for foaming is original. © International OCSCO World Press. All rights reserved. 2015.


News Article
Site: www.cemag.us

An adaptive material invented at Rice University combines self-healing and reversible self-stiffening properties. The Rice material called SAC (for self-adaptive composite) consists of what amounts to sticky, micron-scale rubber balls that form a solid matrix. The researchers made SAC by mixing two polymers and a solvent that evaporates when heated, leaving a porous mass of gooey spheres. When cracked, the matrix quickly heals, over and over. And like a sponge, it returns to its original form after compression. The labs of Rice materials scientists Pulickel Ajayan and Jun Lou led the study that appears in the American Chemical Society journal ACS Applied Materials and Interfaces. They suggested SAC may be a useful biocompatible material for tissue engineering or a lightweight, defect-tolerant structural component. Other “self-healing” materials encapsulate liquid in solid shells that leak their healing contents when cracked. “Those are very cool, but we wanted to introduce more flexibility,” says Pei Dong, a postdoctoral researcher who co-led the study with Rice graduate student Alin Cristian Chipara. “We wanted a biomimetic material that could change itself, or its inner structure, to adapt to external stimulation and thought introducing more liquid would be a way. But we wanted the liquid to be stable instead of flowing everywhere.” In SAC, tiny spheres of polyvinylidene fluoride (PVDF) encapsulate much of the liquid. The viscous polydimethylsiloxane (PDMS) further coats the entire surface. The spheres are extremely resilient, Lou said, as their thin shells deform easily. Their liquid contents enhance their viscoelasticity, a measure of their ability to absorb the strain and return to their original state, while the coatings keep the spheres together. The spheres also have the freedom to slide past each other when compressed, but remain attached. “The sample doesn’t give you the impression that it contains any liquid,” Lou says. “That’s very different from a gel. This is not really squishy; it’s more like a sugar cube that you can compress quite a lot. The nice thing is that it recovers.” Ajayan said making SAC is simple, and the process can be tuned — a little more liquid or a little more solid — to regulate the product’s mechanical behavior. “Gels have lots of liquid encapsulated in solids, but they’re too much on the very soft side,” he says. “We wanted something that was mechanically robust as well. What we ended up with is probably an extreme gel in which the liquid phase is only 50 percent or so.” The polymer components begin as powder and viscous liquid, said Dong. With the addition of a solvent and controlled heating, the PDMS stabilizes into solid spheres that provide the reconfigurable internal structure. In tests, Rice scientists found a maximum of 683 percent increase in the material’s storage modulus — a size-independent parameter used to characterize self-stiffening behavior. This is much larger than that reported for solid composites and other materials, they say. Dong said sample sizes of the putty-like material are limited only by the container they’re made in. “Right now, we’re making it in a 150-milliliter beaker, but it can be scaled up. We have a design for that.” Co-authors are Rice postdoctoral researchers Bo Li, Yingchao Yang, Hua Guo, Liehui Ge, and Liang Hong; graduate student Sidong Lei; undergraduate students Bilan Yang and Qizhong Wang; alumnus Phillip Loya; Emilie Ringe, an assistant professor of materials science and nanoengineering and of chemistry; Robert Vajtai, a senior faculty fellow in materials science and nanoengineering, and Ming Tang, an assistant professor of materials science and nanoengineering; Mircea Chipara, an assistant professor of physics and geology at the University of Texas-Pan American, and postdoctoral researchers Gustavo Brunetto and Leonardo Machado and Douglas Galvao, a professor at the State University of Campinas, Brazil. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. Lou is a professor of materials science and nanoengineering and of chemistry and associate chair of the Department of Materials Science and NanoEngineering. The Air Force Office of Scientific Research and the Department of Defense supported the research.


News Article
Site: www.materialstoday.com

Materials scientists at Rice University have succeeded in making nanodiamonds and other forms of carbon by smashing nanotubes against a target at high speeds. Nanodiamonds won't make anyone rich, but the process of making them will enrich the knowledge of engineers who design structures that can resist damage from high-speed impacts. The diamonds are the result of a detailed study into the ballistic fracturing of carbon nanotubes at different velocities. The results, which are reported in a paper in ACS Applied Materials and Interfaces, showed that such high-energy impacts caused atomic bonds in the nanotubes to break and then sometimes recombine to form different structures. Led by the labs of materials scientists Pulickel Ajayan at Rice and Douglas Galvao at the State University of Campinas in Brazil, the study is intended to help aerospace engineers design ultralight materials for spacecraft and satellites that can withstand impacts from high-velocity projectiles like micrometeorites. Knowing how the atomic bonds of nanotubes can recombine will give scientists clues for developing such lightweight materials by rearranging those bonds, said co-lead author and Rice graduate student Sehmus Ozden. "Satellites and spacecraft are at risk of various destructive projectiles, such as micrometeorites and orbital debris," Ozden explained. "To avoid this kind of destructive damage, we need lightweight, flexible materials with extraordinary mechanical properties. Carbon nanotubes can offer a real solution." The researchers packed multiwalled carbon nanotubes into spherical pellets and fired them at an aluminum target from a two-stage light-gas gun at Rice, and then analyzed the results of impacts at three different speeds. At what the researchers considered a low velocity of 3.9 kilometers per second, a large number of nanotubes were found to remain intact. Some even survived higher velocity impacts of 5.2 kilometers per second. But very few were found among samples smashed at a hypervelocity of 6.9 kilometers per second. The researchers found that many, if not all, of the nanotubes split into nanoribbons, confirming earlier experiments. Co-author Chandra Sekhar Tiwary, a Rice postdoctoral researcher, noted the few nanotubes and nanoribbons that did survive the impact were often welded together, as observed in transmission electron microscope images. "In our previous report, we showed that carbon nanotubes form graphene nanoribbons at hypervelocity impact," Tiwary said. "We were expecting to get welded carbon nanostructures, but we were surprised to observe nanodiamond as well." According to Ajayan, the orientation of the nanotubes, both to each other and in relation to the target, and the number of tube walls were as important to the final structures as the velocity. "The current work opens a new way to make nanosize materials using high-velocity impact," said co-lead author Leonardo Machado from the State University of Campinas. This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Home > Press > Graphene oxide 'paper' changes with strain: Rice researchers say material is more or less brittle, depending on how hard it's pulled Abstract: The same slip-and-stick mechanism that leads to earthquakes is at work on the molecular level in nanoscale materials, where it determines the shear plasticity of the materials, according to scientists at Rice University and the State University of Campinas, Brazil. A video shows computer models of graphene oxide paper under strain. At top, under more pressure, the material remains brittle as one layer of graphene oxide is pulled away. Under less strain, the layers separate more easily as oxygen molecules on the surfaces stick and slip against each other. Credit: Ajayan Research Group/Douglas Galvão The Rice lab of materials scientist Pulickel Ajayan found that random molecules scattered within layers of otherwise pristine graphene affect how the layers interact with each other under strain. Plasticity is the ability of a material to permanently deform when strained. The Rice researchers, thinking about future things like flexible electronics, decided to see how graphene oxide "paper" would handle shear strain, in which the sheets are pulled by the ends. Such deep knowledge is important when making novel advanced materials, said Chandra Sekhar Tiwary, a lead author of the new paper in the American Chemical Society journal Nano Letters and a Rice postdoctoral research associate. "We want to build three-dimensional structures from two-dimensional materials, so this kind of study is useful," he said. "These structures could be a thermal substrate for electronic devices, they could be filters, they could be sensors or they could be biomedical devices. But if we're going to use a material, we need to understand how it behaves." The graphene oxide paper they tested was a stack of sheets that lay atop each other like pancakes. Oxygen molecules "functionalized" the surfaces, adding roughness to the otherwise atom-thick sheets. In experiments and computer models, the team found that with gentle, slow stress, the oxides would indeed catch, causing the paper to take on a corrugated form where layers pulled apart. But a higher strain rate makes the material brittle. "The simulation performed by our collaborators in Brazil provides insight and confirms that if you pull it very fast, the layers don't interact, and only one layer comes out," Tiwary said. "After this study, we now know there are some functional groups that are useful and some that are not. With this understanding we can choose the functional groups to make better structures at the molecular level." ### Rice graduate student Soumya Vinod is a lead author of the paper. Co-authors are Rice graduate student Sehmus Ozden and undergraduates Juny Cho and Preston Shaw; postdoctoral researcher Leonardo Machado and Professor Douglas Galvão of the State University of Campinas, Brazil; and Robert Vajtai, a senior faculty fellow in materials science and nanoengineering at Rice. Ajayan is chair of Rice's Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. The Department of Defense and Air Force Office of Scientific Research supported the research. About Rice University Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. Follow Rice News and Media Relations via Twitter @RiceUNews. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | January 19, 2016
Site: phys.org

The same slip-and-stick mechanism that leads to earthquakes is at work on the molecular level in nanoscale materials, where it determines the shear plasticity of the materials, according to scientists at Rice University and the State University of Campinas, Brazil.


News Article | September 6, 2016
Site: www.cemag.us

Superman can famously make a diamond by crushing a chunk of coal in his hand, but Rice University scientists are employing a different tactic. Rice materials scientists are making nanodiamonds and other forms of carbon by smashing nanotubes against a target at high speeds. Nanodiamonds won’t make anyone rich, but the process of making them will enrich the knowledge of engineers who design structures that resist damage from high-speed impacts. The diamonds are the result of a detailed study on the ballistic fracturing of carbon nanotubes at different velocities. The results showed that such high-energy impacts caused atomic bonds in the nanotubes to break and sometimes recombine into different structures. The work led by the labs of materials scientists Pulickel Ajayan at Rice and Douglas Galvao at the State University of Campinas, Brazil, is intended to help aerospace engineers design ultralight materials for spacecraft and satellites that can withstand impacts from high-velocity projectiles like micrometeorites. The research appears in the American Chemical Society journal ACS Applied Materials and Interfaces. Knowing how the atomic bonds of nanotubes can be recombined will give scientists clues to develop lightweight materials by rearranging those bonds, says co-lead author and Rice graduate student Sehmus Ozden. “Satellites and spacecraft are at risk of various destructive projectiles, such as micrometeorites and orbital debris,” Ozden says. “To avoid this kind of destructive damage, we need lightweight, flexible materials with extraordinary mechanical properties. Carbon nanotubes can offer a real solution.” The researchers packed multiwalled carbon nanotubes into spherical pellets and fired them at an aluminum target in a two-stage light-gas gun at Rice, and then analyzed the results from impacts at three different speeds. At what the researchers considered a low velocity of 3.9 kilometers per second, a large number of nanotubes were found to remain intact. Some even survived higher velocity impacts of 5.2 kilometers per second. But very few were found among samples smashed at a hypervelocity of 6.9 kilometers per second. The researchers found that many, if not all, of the nanotubes split into nanoribbons, confirming earlier experiments. Co-author Chandra Sekhar Tiwary, a Rice postdoctoral researcher, noted the few nanotubes and nanoribbons that survived the impact were often welded together, as observed in transmission electron microscope images. “In our previous report, we showed that carbon nanotubes form graphene nanoribbons at hypervelocity impact,” Tiwary says. “We were expecting to get welded carbon nanostructures, but we were surprised to observe nanodiamond as well.” The orientation of nanotubes both to each other and in relation to the target and the number of tube walls were as important to the final structures as the velocity, Ajayan says. “The current work opens a new way to make nanosize materials using high-velocity impact,” says co-lead author Leonardo Machado of the Brazil team. Machado is a graduate student at the State University of Campinas, Brazil, and the Federal University of Rio Grande do Norte, Brazil. Co-authors are Rice’s Robert Vajtai, an associate research professor, and Enrique Barrera, a professor of materials science and nanoengineering, and Pedro Alves da Silva of the State University of Campinas and the Federal University of ABC, Santo Andre, Brazil. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. The research was supported by the Department of Defense, the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, NASA’s Johnson Space Center, the Sao Paulo Research Foundation, the Center for Computational Engineering and Sciences at Unicamp, Brazil, and the Brazilian Federal Agency for Support and Evaluation of Graduate Education.


Home > Press > 3-D graphene has promise for bio applications: Rice University-led team welds nanoscale sheets to form tough, porous material Abstract: Flakes of graphene welded together into solid materials may be suitable for bone implants, according to a study led by Rice University scientists. The Rice lab of materials scientist Pulickel Ajayan and colleagues in Texas, Brazil and India used spark plasma sintering to weld flakes of graphene oxide into porous solids that compare favorably with the mechanical properties and biocompatibility of titanium, a standard bone-replacement material. The discovery is the subject of a paper in Advanced Materials. The researchers believe their technique will give them the ability to create highly complex shapes out of graphene in minutes using graphite molds, which they believe would be easier to process than specialty metals. "We started thinking about this for bone implants because graphene is one of the most intriguing materials with many possibilities and it's generally biocompatible," said Rice postdoctoral research associate Chandra Sekhar Tiwary, co-lead author of the paper with Dibyendu Chakravarty of the International Advanced Research Center for Powder Metallurgy and New Materials in Hyderabad, India. "Four things are important: its mechanical properties, density, porosity and biocompatibility." Tiwary said spark plasma sintering is being used in industry to make complex parts, generally with ceramics. "The technique uses a high pulse current that welds the flakes together instantly. You only need high voltage, not high pressure or temperatures," he said. The material they made is nearly 50 percent porous, with a density half that of graphite and a quarter of titanium metal. But it has enough compressive strength -- 40 megapascals -- to qualify it for bone implants, he said. The strength of the bonds between sheets keeps it from disintegrating in water. The researchers controlled the density of the material by altering the voltage that delivers the highly localized blast of heat that makes the nanoscale welds. Though the experiments were carried out at room temperature, the researchers made graphene solids of various density by raising these sintering temperatures from 200 to 400 degrees Celsius. Samples made at local temperatures of 300 C proved best, Tiwary said. "The nice thing about two-dimensional materials is that they give you a lot of surface area to connect. With graphene, you just need to overcome a small activation barrier to make very strong welds," he said. With the help of colleagues at Hysitron in Minnesota, the researchers measured the load-bearing capacity of thin sheets of two- to five-layer bonded graphene by repeatedly stressing them with a picoindenter attached to a scanning electron microscope and found they were stable up to 70 micronewtons. Colleagues at the University of Texas MD Anderson Cancer Center successfully cultured cells on the material to show its biocompatibility. As a bonus, the researchers also discovered the sintering process has the ability to reduce graphene oxide flakes to pure bilayer graphene, which makes them stronger and more stable than graphene monolayers or graphene oxide. "This example demonstrates the possible use of unconventional materials in conventional technologies," Ajayan said. "But these transitions can only be made if materials such as 2-D graphene layers can be scalably made into 3-D solids with appropriate density and strength. "Engineering junctions and strong interfaces between nanoscale building blocks is the biggest challenge in achieving such goals, but in this case, spark plasma sintering seems to be effective in joining graphene sheets to produce strong 3-D solids," he said. Co-authors of the paper are graduate student Sruthi Radhakrishnan of Rice and at MD Anderson; researcher Soumya Vinod and graduate student Sehmus Ozden of Rice; Pedro Alves da Silva of the State University of Campinas, Brazil, and the Federal University of ABC, Santo Andre, Brazil; Autreto Cristano Woellner and Professor Douglas Galvão of the State University of Campinas, Brazil; Sanjit Bhowmick and Syed Asif of Hysitron Inc. of Minneapolis; and Sendurai Mani of MD Anderson. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. The research was supported by the Department of Defense, the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, the Sao Paulo Research Foundation, the Center for Computational Engineering and Sciences at Unicamp, Brazil, and the Government of India Department of Science and Technology. About Rice University Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice’s undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger’s Personal Finance. To read “What they’re saying about Rice,” go to tinyurl.com/RiceUniversityoverview. Follow Rice News and Media Relations via Twitter @RiceUNews For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Home > Press > 3-D graphene has promise for bio applications: Rice University-led team welds nanoscale sheets to form tough, porous material Abstract: Flakes of graphene welded together into solid materials may be suitable for bone implants, according to a study led by Rice University scientists. A molecular dynamics simulation shows how graphene oxide layers stack when welded by spark plasma sintering. The presence of oxygen molecules at left prevents the graphene layers from bonding, as they do without oxygen at right. Credit: Ajayan Group/Rice University and Galvão group/Unicamp, Brazil The Rice lab of materials scientist Pulickel Ajayan and colleagues in Texas, Brazil and India used spark plasma sintering to weld flakes of graphene oxide into porous solids that compare favorably with the mechanical properties and biocompatibility of titanium, a standard bone-replacement material. The discovery is the subject of a paper in Advanced Materials. The researchers believe their technique will give them the ability to create highly complex shapes out of graphene in minutes using graphite molds, which they believe would be easier to process than specialty metals. "We started thinking about this for bone implants because graphene is one of the most intriguing materials with many possibilities and it's generally biocompatible," said Rice postdoctoral research associate Chandra Sekhar Tiwary, co-lead author of the paper with Dibyendu Chakravarty of the International Advanced Research Center for Powder Metallurgy and New Materials in Hyderabad, India. "Four things are important: its mechanical properties, density, porosity and biocompatibility." Tiwary said spark plasma sintering is being used in industry to make complex parts, generally with ceramics. "The technique uses a high pulse current that welds the flakes together instantly. You only need high voltage, not high pressure or temperatures," he said. The material they made is nearly 50 percent porous, with a density half that of graphite and a quarter of titanium metal. But it has enough compressive strength -- 40 megapascals -- to qualify it for bone implants, he said. The strength of the bonds between sheets keeps it from disintegrating in water. The researchers controlled the density of the material by altering the voltage that delivers the highly localized blast of heat that makes the nanoscale welds. Though the experiments were carried out at room temperature, the researchers made graphene solids of various density by raising these sintering temperatures from 200 to 400 degrees Celsius. Samples made at local temperatures of 300 C proved best, Tiwary said. "The nice thing about two-dimensional materials is that they give you a lot of surface area to connect. With graphene, you just need to overcome a small activation barrier to make very strong welds," he said. With the help of colleagues at Hysitron in Minnesota, the researchers measured the load-bearing capacity of thin sheets of two- to five-layer bonded graphene by repeatedly stressing them with a picoindenter attached to a scanning electron microscope and found they were stable up to 70 micronewtons. Colleagues at the University of Texas MD Anderson Cancer Center successfully cultured cells on the material to show its biocompatibility. As a bonus, the researchers also discovered the sintering process has the ability to reduce graphene oxide flakes to pure bilayer graphene, which makes them stronger and more stable than graphene monolayers or graphene oxide. "This example demonstrates the possible use of unconventional materials in conventional technologies," Ajayan said. "But these transitions can only be made if materials such as 2-D graphene layers can be scalably made into 3-D solids with appropriate density and strength. "Engineering junctions and strong interfaces between nanoscale building blocks is the biggest challenge in achieving such goals, but in this case, spark plasma sintering seems to be effective in joining graphene sheets to produce strong 3-D solids," he said. ### Co-authors of the paper are graduate student Sruthi Radhakrishnan of Rice and at MD Anderson; researcher Soumya Vinod and graduate student Sehmus Ozden of Rice; Pedro Alves da Silva of the State University of Campinas, Brazil, and the Federal University of ABC, Santo Andre, Brazil; Autreto Cristano Woellner and Professor Douglas Galvão of the State University of Campinas, Brazil; Sanjit Bhowmick and Syed Asif of Hysitron Inc. of Minneapolis; and Sendurai Mani of MD Anderson. Ajayan is chair of Rice's Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. The research was supported by the Department of Defense, the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, the Sao Paulo Research Foundation, the Center for Computational Engineering and Sciences at Unicamp, Brazil, and the Government of India Department of Science and Technology. About Rice University Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to tinyurl.com/RiceUniversityoverview. Follow Rice News and Media Relations via Twitter @RiceUNews For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Home > Press > Nanodiamonds in an instant: Rice University-led team morphs nanotubes into tougher carbon for spacecraft, satellites Abstract: Superman can famously make a diamond by crushing a chunk of coal in his hand, but Rice University scientists are employing a different tactic. A simulation shows how nanotubes deform when shot at a solid target at 5.2 kilometers per second. Experiments and calculations by researchers at Rice University and in Brazil showed the formation of nanodiamonds and other carbon structures. Credit: Galvao Group/State University of Campinas Rice materials scientists are making nanodiamonds and other forms of carbon by smashing nanotubes against a target at high speeds. Nanodiamonds won't make anyone rich, but the process of making them will enrich the knowledge of engineers who design structures that resist damage from high-speed impacts. The diamonds are the result of a detailed study on the ballistic fracturing of carbon nanotubes at different velocities. The results showed that such high-energy impacts caused atomic bonds in the nanotubes to break and sometimes recombine into different structures. The work led by the labs of materials scientists Pulickel Ajayan at Rice and Douglas Galvao at the State University of Campinas, Brazil, is intended to help aerospace engineers design ultralight materials for spacecraft and satellites that can withstand impacts from high-velocity projectiles like micrometeorites. The research appears in the American Chemical Society journal ACS Applied Materials and Interfaces. Knowing how the atomic bonds of nanotubes can be recombined will give scientists clues to develop lightweight materials by rearranging those bonds, said co-lead author and Rice graduate student Sehmus Ozden. "Satellites and spacecraft are at risk of various destructive projectiles, such as micrometeorites and orbital debris," Ozden said. "To avoid this kind of destructive damage, we need lightweight, flexible materials with extraordinary mechanical properties. Carbon nanotubes can offer a real solution." The researchers packed multiwalled carbon nanotubes into spherical pellets and fired them at an aluminum target in a two-stage light-gas gun at Rice, and then analyzed the results from impacts at three different speeds. At what the researchers considered a low velocity of 3.9 kilometers per second, a large number of nanotubes were found to remain intact. Some even survived higher velocity impacts of 5.2 kilometers per second. But very few were found among samples smashed at a hypervelocity of 6.9 kilometers per second. The researchers found that many, if not all, of the nanotubes split into nanoribbons, confirming earlier experiments. Co-author Chandra Sekhar Tiwary, a Rice postdoctoral researcher, noted the few nanotubes and nanoribbons that survived the impact were often welded together, as observed in transmission electron microscope images. "In our previous report, we showed that carbon nanotubes form graphene nanoribbons at hypervelocity impact," Tiwary said. "We were expecting to get welded carbon nanostructures, but we were surprised to observe nanodiamond as well." The orientation of nanotubes both to each other and in relation to the target and the number of tube walls were as important to the final structures as the velocity, Ajayan said. "The current work opens a new way to make nanosize materials using high-velocity impact," said co-lead author Leonardo Machado of the Brazil team. Machado is a graduate student at the State University of Campinas, Brazil, and the Federal University of Rio Grande do Norte, Brazil. Co-authors are Rice's Robert Vajtai, an associate research professor, and Enrique Barrera, a professor of materials science and nanoengineering, and Pedro Alves da Silva of the State University of Campinas and the Federal University of ABC, Santo Andre, Brazil. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry. The research was supported by the Department of Defense, the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, NASA's Johnson Space Center, the Sao Paulo Research Foundation, the Center for Computational Engineering and Sciences at Unicamp, Brazil, and the Brazilian Federal Agency for Support and Evaluation of Graduate Education. About Rice University Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice’s undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger’s Personal Finance. To read “What they’re saying about Rice,” go to tinyurl.com/RiceUniversityoverview. Follow Rice News and Media Relations via Twitter @RiceUNews For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Makishi P.,University of Campinas | Thitthaweerat S.,Mahidol University | Sadr A.,University of Washington | Shimada Y.,Tokyo Medical and Dental University | And 3 more authors.
Dental Materials | Year: 2015

Abstract Objectives To evaluate the sealing ability and the microtensile bond strength (MTBS) of different adhesive systems bonded to dentin in class I cavities. Methods Round tapered dentin cavities (3-mm diameter, 1.5-mm height) prepared in extracted human molars were restored using composite resin (Clearfil Majesty Posterior) with two-step etch-and-rinse adhesive system (Adper Single Bond 2: ASB2), two-step self-etch adhesive (Clearfil SE Bond: CSEB), all-in-one adhesives (G-Bond Plus: GBP; Tri-S Bond Plus: TSBP), or no adhesive (Control), or bonded using low-shrinkage composite with its proper adhesive (Filtek Silorane, Silorane Adhesive System: FSS). After 24-h water storage or 10,000 cycles of thermal stress, the specimens were immersed into a contrast agent. Two and three-dimensional images were obtained using optical coherence tomography (OCT). The mean percentage of high brightness (HB%) at the interfacial zone in cross-sectional images was calculated as an indicator of contrast agent or gap at the interface. The specimens were then sectioned into beams and the MTBS measured. Results The HB% (ASB2 = TSBP = CSEB < FSS = GBP) and MTBS (CSEB = ASB2, CSEB > TSBP = GBP = FSS, ASB2 > FSS) differed significantly among the adhesives. After aging, HB% increased for GBP and FSS specimens, and the MTBS decreased for FSS specimens (ANOVA, Tukey's post hoc, p < 0.05). The HB% and MTBS were significantly and negatively correlated (p = 0.002). Confocal laser scanning and scanning electron micrographs confirmed contrast agent infiltration within the gap. Significance There was a significant correlation between sealing performance and bond strength of the adhesives in the whole cavity. After aging, the two-step systems showed equal or superior performance to the all-in-one and Silorane systems. © 2015 Academy of Dental Materials.

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