Crack Proof Cement Made with Carbon Nanotubes, Technology Licenses Available

Northwestern researchers invented a process to use multi-walled carbon nanotubes (MWCNTs) at very low levels in conjunction with additives and mixing methods that provide excellent MWCNT dispersion in cement matrixes and afford significant improvement in cured mechanical properties. An aqueous MWCNT (0.08 wt% cement basis) additive solution, after suitable mixing, is blended into cement under ASTM procedures, cast and cured. Scanning electron microscopy (SEM) analysis of fracture surface specimens after 18 hours reveals isolated MWCNT fibers with a high degree of dispersion in the matrix. The uniform MWCNT distribution contributes to the observed increase in cured cement mechanical properties. Over 45% increase in the 28 day flexural strength is realized at the 0.08 wt% MWCNT loading versus the unmodified control. This modest MWCNT addition inhibits cracking at the nanoscale level and provides a cement matrix essentially “crack free”. The current invention promises a cost effective technology to provide high strength cements in a direct and scalable process.

Most construction cements today are hydraulic, and generally based on Portland cement, composed primarily of limestone, certain clay minerals and gypsum. Effort to mitigate structural failures in cement is a constant endeavor that has employed a range of materials. Although microfiber reinforcement has led to significant improvement of cement mechanical properties, flaws at the nanoscale remain. Carbon nanotubes (CNTs) have been added to cementitious matrices at 0.5 to 1.0 wt% loadings to overcome such defects but suffered from poor dispersion and cost.

Northwestern researchers Surendra P. Shah, Maria S. Konsta-Gdoutos, and Zoi S. Metaxa were able to overcome the major obstacle to the manipulation and use of carbon nanotubes for reinforcement in cementitious materials which has been their poor dispersion in cement. A composite cement material was prepared from cement material and carbon nanotubes from about 0.02 wt % to about 0.10 wt % based on weight of cement material. The process for preparing such cement compositions includes sonicating a mixture of a surfactant, water, and carbon nanotubes; blending the dispersion and the cement material to form a cementitious paste. The composite cement materials are useful in a variety of cement applications where a reduction in nanoscale flaws and fractures is desired.

The nanocomposite cementitious material exhibits a reduction of autogenous shrinkage of at least 30% after 96 hours from casting as compared to the same cementitious material without carbon nanotubes. The nanocomposite cementitious material exhibits a modified nanostructure so that the average values of stiffness and hardness of C-S-H, as determined by nanoindentation tests, are higher compared to the same cementitious material without carbon nanotubes. The nanocomposite cementitious material exhibits an increase of the Young's modulus of at least 15% up to about 55% as compared to the same cementitious material without carbon nanotubes. The nanocomposite cementitious material exhibits an increase in flexural strength of at least of 8% up to about 40%. as compared to the same cementitious material without carbon nanotubes.

CNT cement composites are expected to find wide application for highway structures, bridges, pavements, runways for airports, continuous slab-type sleepers for high speed trains and in general in all applications of conventional and high strength concrete, as well as in manufactured precast elements for residential and commercial buildings.

Further details of the invention are revealed in United States Patent Application 20090229494. The technology is available for licensing from Northwestern University. Interested parties should contact Technology Transfer @ Northwestern 1800 Sherman Avenue - Suite 504 Evanston, IL 60201 Phone: 847-491-3005 Fax: 847-491-3625 E-mail: jcowan(at) northwestern.edu

Gallium Used to Control Nanocarbon Shapes

University of Louisville Institute for Advanced Materials and Renewable Energy (IAM-RE) Director Dr. Mahendra Kumar Sunkara and Intel Process Engineer Gopinath Bhimarasetti developed a technique to synthesize, control and fine tune the morphology of tubular carbon nano structures. Their invention provides a means to control the inner and outer diameter of the tubes and provides the means of controlling the wall thickness of the tubes. Different morphologies of tubular carbon such as tubes, cones, nozzles, funnels, tapered tubes, barbells, Y-junctions and multijunction tubes, can be synthesized reliably. The technique is based on the wetting behavior of gallium with carbon in different gas phase growth environments.

The walls of the various nanocarbon shapes exhibit a very unique structure. Unlike multi-walled carbon nanotubes (MWNTs), the wall is not comprised of graphene sheets rolled into a cylinder. Instead, the wall is made of parallel sets of nanocrystals of graphite in the size range of 2-5 nanometers (nm). The internal diameters of the carbon tubular structures can be varied from a few nm to as high as about 25 microns. The wall thickness is about 10-20 nm. The carbon tubular structures can be formed open on both ends and are directly applicable to micro-fluidics.

The figure illustrates a variety of shapes created by using methane as a carbon source and gallium as the wetting agent. The University of Louisville Research Foundation, Inc. (Louisville, KY) received U.S. Patent 7,597,941 for the work.

The carbon tubular structures have use as nano fluid delivery systems, absorption and percolation medium, electronic devices such as junction diodes made of multi-junction tubular structures, lithium exchange medium in batteries, ink delivery systems for printer cartridges, and hollow funnels or nano-crucibles for metal alloy production permitting the containment and handling of very small amounts of material such as for combinatorial synthesis, and for micro-reactors for combinatorial synthesis.

Furthermore, the tubular carbon nano/micro structures having tunable internal diameters and conical angles can provide flow channels, flow distribution channels, control valves/throttle valves in microfluidic devices. The materials also provide a medium for lithium intercalation electrodes, pico-liter dispensers, templates for synthesis of similar morphologies of other materials systems, micro-reactors, and nano test tubes to study fluid flow behavior and materials behavior at various length scales.

The process is based on changing the wetting behavior of a low melting metals such as gallium, indium, and aluminum with carbon using a growth environment of different gas phase chemistries. In the presence of oxygen or nitrogen, gallium wets carbon, thus forming a flatter meniscus during growth. Based on this behavior of gallium various morphologies of carbon nano-structures can be successfully controlled and synthesized. Gallium that partially fills the carbon structures can be removed from the tubes by simple heating in vacuum at temperature above 600.degree C. Gallium required for the growth of the carbon tubes can be supplied either as a thin film on the substrate or could be supplied through the gas phase with different precursors such as Tri-methyl gallium.

The nanostructures can be synthesized using any kind of gas phase excitation such as microwave excitation, hot filament excitation, thermal excitation and Radio Frequency (RF) excitations. This growth concept can be extended to synthesize tubular morphologies of other material systems.