UNIT 13 Modern Materials and the Solid State Unit Overview This unit explores advances in modern materials in the context of their underlying chemistry. Many common materials represent significant technological advances but are still based on basic chemical principles. Therefore, an understanding of chemistry is an excellent entry point not only to understand how a material behaves or a device works, but also to understand the ways in which cutting-edge advances are made. Learning Objectives and Applicable Standards Participants will be able to: 1. Differentiate between types of solid structures in terms of atomic interactions and order (or lack thereof) in the structure. 2. Recognize the conditions that influence phase changes in materials. 3. Identify different types of alloys in terms of their constituents and behavior. 4. Recognize and characterize the different allotropes of carbon. 5. Identify various naturally occurring and synthetically created polymers. Key Concepts and People 1. Modern Materials: The chemistry of matter in the solid state and the applications of solid materials are areas of some of the most cutting-edge research in chemistry and engineering. 2. What Is a Solid?: Both the identity of the elements and the arrangement of atoms in a solid affect the properties of the solid. At the most basic level, solids are classified as either amorphous or crystalline, depending on whether or not they exhibit long-range order at the atomic level. 3. Ionic and Covalent-Network Solids: Coulombic forces hold together ionic solids while covalent bonds hold together covalent solids. 1 UNIT 13 Modern Materials and the Solid State 4. Molecular Solids: Molecular solids, such as ice, are held together by intermolecular interactions of the molecules themselves. These interactions are weaker than the ionic or covalent interactions in ionic and covalent solids, and the physical characteristics of the solids reflect this. 5. Metallic Solids: Metals have readily accessible valence electrons, and in metallic solids the electrons are shared readily between atoms. Metals can be used in their pure form but can also combine to form alloys, whose properties are influenced by the identity and proportion of the components. 6. Phase Changes in Solids: Temperature and pressure influence the state of matter in which a material will be found. Phase diagrams summarize the behavior of materials under different temperature and pressure conditions. 7. Natural and Synthetic Polymers: Carbon is not only the basis of life but also the basis of polymer chemistry. Both naturally-occurring and synthetically-created polymers are tremendously important materials in modern life. 8. Alloys: Metals form alloys by combining in various proportions, and occasionally with trace amounts of non-metals. Video While chemical reactions in gases and liquids are essential to the understanding of chemistry, the chemistry of solid-state materials characterizes most of the interactions we have with matter on a daily basis. Chemists take advantage of the complexity of solids to engineer new materials, including nanoparticles, polymers, and advanced metal alloys. These new materials have many potential applications in sensors, advanced drug delivery systems, and space exploration. Today, modern materials are following a heritage—one that can be traced back to earlier civilizations— in which the properties of solids are manipulated to advance human needs. VIDEO CONTENT Host Science Introduction Materials scientist and science writer Dr. Ainissa Ramírez, introduces the unique properties of solid-state materials through the example of a “memory metal,” an alloy that can be deformed at room temperature, but then returns to its original shape when heated. This segment emphasizes a central idea of the unit: The observable properties of bulk solid materials are the result of the interactions of their molecular components at the microscopic level. Real World Example “Atomic Arrangements” Dr. Raquel Alonso Pérez, curator of the Mineralogical and Geological Museum at Harvard University, uses examples from the minerals in her collection to point out the different types 2 UNIT 13 Modern Materials and the Solid State of bonding that hold solids together. Comparing the different forms of carbon - diamond and graphite - which differ greatly in their properties because of differences in their internal bonding arrangements, she reinforces that the external properties of solids result from these atomic and molecular structures. Current Chemistry Research “Carbon Nanotube Sensors” Joseph Azzarelli’s research in the Swager group at MIT focuses on developing new sensors for agricultural, food, industrial, and environmental applications. He has found ways to use carbon nanotubes, yet another molecular form of carbon, as the heart of a sensor that can measure ethylene gas, a plant hormone that controls the ripening of fruit. History of Chemistry “Early Plastic” In the 1800s, Leominster, Massachusetts became known as the “Comb City,” because factories there specialized in the manufacture of combs and other items made from natural materials, such as bone and horn. Paul Benoit, a curator at the Leominster Historical Society, describes how Leominster switched to man-made materials shortly after the turn of the 20th century. One of the first plastics was celluloid, a polymer that could be molded and cooled to make objects of many different shapes. Leominster made important contributions to the rise of today’s multi-billion dollar plastics industry. Laboratory Demonstration “Making Polymers” One of the best-known plastics is nylon, which, like all polymers, is formed from linking together smaller molecules, or monomers, into large molecules. Harvard University Lecture Demonstrator Daniel Rosenberg shows how to react two monomers, diacid chloride and hexamethylenediamine, and come away with a long strand of nylon. Current Chemistry Research “Polymer Research in the Pharmaceutical Industry” Dr. Trevor Castor, Chief Scientist at Aphios Corporation, is enveloping insulin inside biodegrad- able polymers. The polymer protects the insulin, a protein, from the harsh chemical environment in the digestive system. There, the encapsulated nanoparticles are so small that they are absorbed directly into the bloodstream. Once inside the blood, the polymer degrades, releasing the insulin. This technology has the potential to deliver insulin without injections, thereby improving quality of life for millions of people with diabetes. Current Chemistry Research “High Temperature Alloys” Engineers at the Smithsonian Astrophysical Observatory are building components for a new spacecraft, one that will travel close enough to the Sun to take actual samples of the Sun’s corona. During the mission, the spacecraft will experience solar radiation that is 500 times more intense than it is on Earth, so the materials used must be able to withstand extremely high 3 UNIT 13 Modern Materials and the Solid State temperatures. Smithsonian Astrophysicist Dr. Anthony Case and technology and product devel- opment manager Stephen McCrossan of Plansee USA, describe how alloys of molybdenum with tungsten and zirconium have the necessary characteristics. Unit Text Content Overview The unit begins with a brief review of chemical bonding to introduce chemistry as the founda- tion for the performance of materials in the solid state. The development of solid materials, and the behavior of naturally occurring solid materials, depends not only on the chemistry but also the structure of the solid itself. Different types of solids exhibit different types of atomic inter- actions and different microscale geometry, and these both influence the behavior of the solids. At the very basic level, solids may be either amorphous or crystalline. Within those broad definitions, however, particularly for crystalline solids, a vast array of geometric arrangements and chemical interactions are possible. Alloys such as bronze and steel are among the earliest examples of the engineering of solids, but the development of new alloys continues, and remains a significant contributor to industry. Carbon is not only the centerpiece of organic chemistry but also polymer chemistry, and is therefore another centerpiece of industrial and commercial applications. Both naturally occur- ring and synthetically created polymers are relevant to such applications. The production and the recycling of these products are major contributors to industry. Sidebar Content 1. The Chemistry of Steelmaking: The chemical composition of steel dramatically affects its properties. Beginning in the mid-19th century with the Bessemer converter, production methods for steel have become significantly more controlled allowing for more variations on the composition of the alloy. 2. Recycling Plastics: Plastics can be recycled, but because the polymers that make them come in a wide range of chemical structures, different types must be processed differently. Interactives Historical Timeline of Chemistry This interactive illustrates how different discoveries build upon, disprove, or reinforce previous theories. This not only reinforces basic chemistry concepts, but also emphasizes the nature of science. Scientists mentioned in this unit are listed on the timeline. It is interesting to note that even before the era of modern chemistry, advances in materials science helped shape civilization (e.g., Bronze Age, Iron Age). 4 UNIT 13 Modern Materials and the Solid State Control a Haber-Bosch Ammonia Plant