For years, in the weight-critical auto and aerospace industries, the challenge has been how to make reliable use of magnesium, the lightest of all structural metals. Magnesium components can be 30% lighter than aluminum, and 75% lighter than steel, without compromising strength. The metal has other attractive characteristics for manufacturers, as well; these include a low melting temperature, which saves casting time, fast and effective machining, and castability to finer tolerances, which also reduces the amount of required machining. However, magnesium also has disadvantages: it is chemically very reactive, corroding easily and seriously, and the soft material is very susceptible to scratching. It can be coated, but the standard processes of anodizing involving (typically) chromic, hydrofluoric, or phosphoric acid offer limited protection, at high environmental cost. Recently, a magnesium coating process, originally developed at Moscow State University, has been commercially launched — with a little help from the British government — by Keronite Ltd, Cambridge, UK. The process bonds magnesium atomically, making it considerably tougher, and thus avoiding nearly all of the known disadvantages of this metal. The process uses plasma electrolytic oxidation to build a microscopically thin, yet very hard, ceramic oxide coating on the magnesium, all within a completely non-toxic environment. The coating is suited for products including bicycle frames, wheelchairs, and children’s pushchairs. In other applications, Keronite can be applied even to a mesh surface. Engineers are finding the coating’s strength suitable for such applications as belt pulleys, engine oil pumps, pistons and other engine components. Its scratch resistance makes it an attractive alternative for portable (read: ‘dingable’) consumer products. The fashion world, too, is not oblivious to the advantages of strength with lightness; already a number of companies are selling premium sunglasses made from coated magnesium.
Chemists at UC San Diego have developed minute grains of silicon that spontaneously assemble, orient and sense their local environment, a first step toward the development of robots the size of sand grains that could be used in medicine, bioterrorism surveillance and pollution monitoring. In a paper published last month in the Proceedings of the National Academy of Sciences, Michael Sailor, a professor of chemistry and biochemistry at UCSD, and Jamie Link, a graduate student in his laboratory, report the design and synthesis of tiny silicon chips, or “smart dust,” consisting of two colored mirrors, green on one side and red on the other. Each mirrored surface is modified to find and stick to a desired target, subsequently changing color slightly to let the observer know what has been found. “This is a key development in what we hope will one day make possible the development of robots the size of a grain of sand,” Sailor explains. “The vision is to build miniature devices that can move with ease through a tiny environment, such as a vein or an artery, to specific targets, then locate and detect chemical or biological compounds and report this information to the outside world. Such devices could be used to monitor the purity of drinking or sea water, to detect hazardous chemical or biological agents in the air or even to locate and destroy tumor cells in the body.” To create the smart dust, the researchers chemically etch one side of a silicon chip, generating a colored mirrored surface with tiny pores. They then bind a hydrophobic chemical to this porous surface. The other side of the chip is etched to create a porous reflective surface of a different color, and expose the surface to air so that it becomes hydrophilic. Vibrations are used to break the chip into pieces about the size of the diameter of a human hair. The resulting tiny sensors can then detect oily substances via the hydrophobic surface. “As the particle comes in contact with the oil drop, some of the liquid from the target is absorbed into it,” Sailor explains. “The liquid only wicks into the regions of the particle that have been modified chemically. The presence of the liquid in the pores causes a predictable change in the color code, signaling to the outside observer that the correct target has been located.” Link, the first author on the paper, says the dual-sided particles have the additional benefit of being able to collect at a target and then self-assemble into a larger, more visible reflector that can be seen from a distance.
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For years, in the weight-critical auto and aerospace industries, the challenge has been how to make reliable use of magnesium, the lightest of all structural metals. Magnesium components can be 30% lighter than aluminum, and 75% lighter than steel, without compromising strength. The metal has other attractive characteristics for manufacturers, as well; these include a low melting temperature, which saves casting time, fast and effective machining, and castability to finer tolerances, which also reduces the amount of required machining. However, magnesium also has disadvantages: it is chemically very reactive, corroding easily and seriously, and the soft material is very susceptible to scratching. It can be coated, but the standard processes of anodizing involving (typically) chromic, hydrofluoric, or phosphoric acid offer limited protection, at high environmental cost. Recently, a magnesium coating process, originally developed at Moscow State University, has been commercially launched — with a little help from the British government — by Keronite Ltd, Cambridge, UK. The process bonds magnesium atomically, making it considerably tougher, and thus avoiding nearly all of the known disadvantages of this metal. The process uses plasma electrolytic oxidation to build a microscopically thin, yet very hard, ceramic oxide coating on the magnesium, all within a completely non-toxic environment. The coating is suited for products including bicycle frames, wheelchairs, and children’s pushchairs. In other applications, Keronite can be applied even to a mesh surface. Engineers are finding the coating’s strength suitable for such applications as belt pulleys, engine oil pumps, pistons and other engine components. Its scratch resistance makes it an attractive alternative for portable (read: ‘dingable’) consumer products. The fashion world, too, is not oblivious to the advantages of strength with lightness; already a number of companies are selling premium sunglasses made from coated magnesium.
Chemists at UC San Diego have developed minute grains of silicon that spontaneously assemble, orient and sense their local environment, a first step toward the development of robots the size of sand grains that could be used in medicine, bioterrorism surveillance and pollution monitoring. In a paper published last month in the Proceedings of the National Academy of Sciences, Michael Sailor, a professor of chemistry and biochemistry at UCSD, and Jamie Link, a graduate student in his laboratory, report the design and synthesis of tiny silicon chips, or “smart dust,” consisting of two colored mirrors, green on one side and red on the other. Each mirrored surface is modified to find and stick to a desired target, subsequently changing color slightly to let the observer know what has been found. “This is a key development in what we hope will one day make possible the development of robots the size of a grain of sand,” Sailor explains. “The vision is to build miniature devices that can move with ease through a tiny environment, such as a vein or an artery, to specific targets, then locate and detect chemical or biological compounds and report this information to the outside world. Such devices could be used to monitor the purity of drinking or sea water, to detect hazardous chemical or biological agents in the air or even to locate and destroy tumor cells in the body.” To create the smart dust, the researchers chemically etch one side of a silicon chip, generating a colored mirrored surface with tiny pores. They then bind a hydrophobic chemical to this porous surface. The other side of the chip is etched to create a porous reflective surface of a different color, and expose the surface to air so that it becomes hydrophilic. Vibrations are used to break the chip into pieces about the size of the diameter of a human hair. The resulting tiny sensors can then detect oily substances via the hydrophobic surface. “As the particle comes in contact with the oil drop, some of the liquid from the target is absorbed into it,” Sailor explains. “The liquid only wicks into the regions of the particle that have been modified chemically. The presence of the liquid in the pores causes a predictable change in the color code, signaling to the outside observer that the correct target has been located.” Link, the first author on the paper, says the dual-sided particles have the additional benefit of being able to collect at a target and then self-assemble into a larger, more visible reflector that can be seen from a distance.