Rapid advances in nuclear medicine and the growth of nuclear power as a primary energy source in developed countries have driven a growing need for cost-effective radiation shielding and nuclear containment solutions. Whereas metals like lead are strong and resistant to various forms of radiation, they can be very expensive, and performance tends to degrade over time from prolonged exposure. One alternative, concrete, is highly durable and inexpensive, but weakens at elevated temperatures and do not effectively shield uncharged neutrons. There is a thus a clear demand for a shielding technology that blocks all forms of radiation, yet is durable and inexpensive to produce. (more...)

Rapid prototyping materials that have durable characteristics are extremely expensive. Where traditional 3-D printing technology is reserved for small-scale prototyping in a limited number of fields at an exorbitant cost, 3-D Printed Structural Translucent Concrete introduces the notion that this same technology could be employed to fabricate structural building components at very little cost for a wide range and scales of applications.      Researchers at the University of California, Berkeley has developed a 3-D Printable Structural Translucent Concrete that uses traditional 3-D printing technology to produce building components with compressive and tensile strength up to 70% greater than standard concrete. This process introduces a new level of control over how modular building blocks are considered and derived. This material allows for high degrees of variability and specificity to be imbedded in building components that are structurally strong, water resistant, and inexpensive. The cost of production is over 90% less expensive than standard rapid prototyping processes and it shares similar strengths to concrete with thin-shell capabilities not unlike fiberglass. The material has the potential to entirely redefine how we consider rapid prototyping, and when related to architecture, the degree to which buildings can be responsive and unique to their climate, client and context. (more...)

The separation of CO2 from H2 is highly significant in the context of two distinct applications: (i) the capture of CO2 emissions like those produced from coal-fired power plants, and (ii) the purification of hydrogen gas, which is synthesized on megaton scales annually. Pressure-swing adsorption (PSA) is advantageous over other separations techniques such as liquid absorbents, membrane or cryogenic separation due to the high purity and yield of hydrogen that can be produced. In a PSA system, CO2 adsorbs onto a surface at high pressure in the presence of other gases, and the porous material can be regenerated for another purification cycle by simply dropping the pressure to ambient conditions. Porous materials such as zeolites and activated carbons are used in PSA systems for CO2/H2 separations, however due to the maturity of these technologies only modest improvements in CO2/H2 separation performance can be expected in the future. For PSA to be the most economical separation technique in all scenarios, much greater efficiencies must be achieved than what can be realized with these adsorbents. To address this need, investigators at University of California at Berkeley have investigated a novel group of adsorbents, metal-organic frameworks, for PSA separation of CO2 from H2 and other gases such as CH4. Metal-organic frameworks are a group of porous crystalline materials composed of metal cations or clusters joined by multifunctional organic linkers.  The high surface area and low bulk densities of these materials result in both large gravimetric and volumetric capacities for CO2. Five metal-organic frameworks have been studied by the investigators, where single-component CO2, H2 and CH4 adsorption isotherms were measured at 313 °K at pressures up to 40 bar. Mixtures of CO2, H2 and CH4 were simulated using these single-component data as a starting point. The best-performing materials exhibited much higher selectivities and working capacities for CO2 than activated carbons and zeolites. (more...)

The strength of brittle materials, including ceramics and glasses, must be described by statistical parameters because they contain an unknown variety of cracks and crack-like flaws inadvertently introduced during processing. Typical flaws found at fracture origins include large voids produced by organic inclusions (e.g. human hair) and inorganic inclusions (e.g. dust particles). The lack of plastic deformation in ceramics causes their strength to be inversely dependent on the size of very small cracks, which generally cannot be detected except by failure itself. For this reason, ceramic components frequently have a high probability of failure. (more...)

Ceramic matrix composites (CMCs) contain strong, reinforcing fibers embedded in a ceramic matrix. CMCs exhibit superior toughness and strength and are especially tolerant of impact and thermal shock. The fabrication of current CMCs employs a third material to create a weak interaction between the fibers and the matrix. When cracks form within the matrix, they are deflected along the weak interface without propagating through the fibers. The fibers bridge the crack and enable the composite to continue supporting the load through the fibers. Current manufacturing methods are expensive and material systems are limited because it is difficult to create this weak interface and the current belief is that the density of the ceramic matrix must be high. In addition to manufacturing difficulties, current CMCs may exhibit bonding of the fibers to the matrix when the composite is used in oxidizing environments at moderate temperatures. This fiber-matrix bonding severely degrades the mechanical properties of the composite material. (more...)

Transition metal carbides, nitrides and carbonitrides hold considerable commercial interest because of their properties of hardness, corrosion resistance and thermal stability. The manufacture of the whole class of materials has, however, remained cumbersome and costly up to now. The conventional synthesis of Titanium carbonitride involves three steps: Formation of a carbide phase, a nitride phase, and an homogenization of the two conducted at high temperatures over the course of several hours. Materials scientists at the University of California have recently developed a technique for the direct synthesis of titanium carbonitride. Their procedure takes place in a single, rapid step. Under the conditions of the procedure, a 2000 degree Celsius, self-sustaining combustion wave passes through and converts reactants at a velocity of 9 mm per second. Following propagation of the initial wave, the reaction is complete after approximately 1.7 seconds. The synthesis technique has all the attractive features of combustion syntheses in general, including straight-forwardness, high purity of products, and easy applicability to the manufacture of large items. UC investigators have submitted their products to X-ray analysis, and have found that the synthesis converts reactants completely to a single, cubic, NaCl-type crystal phase with lattice parameters of 0.4269-0.4309 nm. No other phases, by-products, or regions of nonhomogeneity appear in the reacted mixtures. The high temperature at which conversion to titanium carbonitride takes place indicates the high thermal stability of this material. A quality that has attracted additional attention to this particular transition-metal carbonitride is the affinity with which it conjugates with nickel. Titanium carbonitride/nickel cermets have the advantages of tungsten carbide/cobalt cermets but are considerably less costly to produce, given the low cost of nickel relative to cobalt. The development of a direct synthesis by UC researchers makes titanium carbonitride the most desirable material of its type. (more...)