The Amazing Nacre (Mother of Pearl)

 

Nacre, also known as mother of pearl, is an organic–inorganic composite material produced by some molluscs as an inner shell layer. It comprises 95% calcium carbonate (aragonite) which, due to its layered microstructure, yields tensile strength, toughness and ductility levels as well as barrier and durability characteristics that far exceed those of monolithic aragonite or artificial inorganic materials such as concrete.

The superior engineering properties of nacre result from its controlled microstructure fored during a biomineralization process. This process involves controlled through-solution crystallization of amorphous materials (mostly calcium carbonate) to form intricate microstructures tailored towards serving structural, protective and other purposes.

Can we learn from biomineralization of nacre to produce improved material for construction of longer-lasting, safer and more sustainable infrastructure systems?

Morphing Aircraft: The Need for Flexible Skin

 

The morphing aircraft attempts to break out of the confines of rigid structures with the intention of creating vehicles with multiple functional equilibria. The morphing aircraft is a multirole platform that changes its state substantially to adapt to changing operation environments, and is viewed as part of a revolutionary transformation from large, expensive piloted aircraft to smaller, autonomous types with combined roles and increased functionality. 

Flexible skins constitute an enabling technology for morphing aircraft. The skin must be able to handle large in-plane deformations and out-of-plane aerodynamic loads while simultaneously carrying some shear loads. There are numerous design concepts that can be used for morphing aircraft, but most designs cannot effectively integrate skins. Elastomers constitute a promising group of materials for flexible skins; they are capable of elastically deforming by very large amounts without permanent changes in shape. The occasional cross-links within elastomers define an original shape which will be restored upon unloading.

Since elastomers are generally insulating, elastomeric skins can become charged in service; they could then behave as a capacitor and discharge in a single event causing considerable damage to the surrounding materials and the electronics on the vehicle. To mitigate electrostatic charge buildup, the surface resistivity of the skin should be lowered below a threshold level, which should be retained even under large elastomeric deformations. The conductivity of the elastomeric skin would also provide a level of protection against lightning strike.

New Cement and Concrete Materials for a Sustainable Future

 

The global consumption of concrete, estimated at 30 billion tons per year, is second only to water. The desired balance of performance and cost offered by concrete has led to its prevalence as the most widely used material of construction. Concrete is the defining feature of our vast transportation, sewer, water, energy, defense, building and other infrastructure systems. While the structural performance and economics of concrete have led to its prevalent role in infrastructure systems for more than two centuries, the durability and sustainability of concrete are receiving increasing scrutiny. The rising cost of maintaining vast infrastructure systems in developed nations have led to growing demands for realizing improvements in service life and life-cycle economy by enhancing concrete durability. The hydraulic cement developed in this project offers twice the service life of today’s prevalent Portland cement at about half the production cost.

Our generation is also concerned with preserving the energy and natural resources as well as the environment for future generations. Production of cement and concrete account for about 5% of energy use, 10% of anthropogenic CO₂ emissions and 30 billion tons/yr consumption of valuable natural resources worldwide. Improvements in the sustainability of cement and concrete production, while maximizing the use of market-limited industrial wastes, have emerged as major priorities within cement and concrete industries. Refined cement chemistries promise to have about 70% less energy content than today’s prevalent Portland cement, and a net negative carbon footprint. The tremendous volumes of cement consumed annually offer opportunities for value-added use of large CO₂ volumes as a raw material in manufacturing of hydraulic cements with refined chemical composition. Tailoring of cement chemistry and its production condition can enable use of 1.5 billion tons/yr of carbon dioxide directly from combustion emissions or other abundant sources of CO₂. Broad market transition of these technologies would reduce global energy use and anthropogenic CO₂ emissions by about 3.5% and 10%, respectively.

The new classes of cement and concrete materials can replace close to 3.5 billion tons/yr of valuable natural resources used as raw materials in production of Portland cement with landfill-bound (or landfilled) raw materials such as market-limited grades of coal and biomass combustion ash, and metallurgical slags, in addition the CO₂ content of combustion emissions. The emphasis on the use of landfill-bound and landfilled industrial wastes requires careful consideration of the safety attributes of the resulting concrete materials. The chemistry and structure of the hydration products of some of these new cements are particularly effective in immobilization of heavy metals and other hazardous wastes.

The market appeal of the next generation of sustainable hydraulic cements will be enhanced by their favorable economics, improved performance, and compatibility with common methods of concrete design, production and field construction. The compatibility of the new hydraulic cements with Portland cement will enable development of blended cements that would readily meet the specifications accepted by states and municipalities for seamless and expedient transition to construction markets.

Sustainable Processing of High-Temperature Ceramics Using Microwave Energy

 

Processing of industrial ceramics for use in high-temperature service environments is currently accomplished by conventional heating that is energy-intensive and polluting. Microwave renders thermal and non-thermal effects that significantly benefit processing of ceramics. Microwave processing is adopted in industrial applications for realizing time, energy and cost savings, and for improving the end product quality and uniformity.

The heating mechanisms are different in conventional and microwave processing of materials. Conventional methods heat the surface and then rely on conduction, convection and radiation for transfer of heat into the material. Microwave, on the other hand, directly interacts with the material across its volume. Given the surface heat losses, heat transport under microwave radiation is from the core towards surface. The specific mechanisms and efficiency of microwave heating depend upon the material type. Microwave radiation also renders non-thermal effects that benefit diffusion, chemical reaction and densification phenomena.

Some advantages of microwave processing are: (i) reduced processing time, temperature and power consumption, and enhanced diffusion and reaction rates; (ii) finer, more uniform and nearly fault-free microstructures, yielding improved and more consistent physical and mechanical properties; (iii) reduced thermal stresses and heat-affected zones; and (iv) improved interfacial qualities resulting from selective hating of phases with higher microwave absorption. These advantages can reduce the energy demand and the corresponding polluting effects of processing ceramics by the currently prevalent conventional heating.