August 03, 2008

Graphene enhanced plastics

Comparison of xGnP (graphene additive) to other nanocomposite additives.

Michigan state University is using the recent discovery that graphene is the strongest material ever and using graphene additives to make stiffer, stronger and lighter plastics.

The material – xGnP Exfoliated Graphite NanoPlatelets - can an either be used as an additive to plastics or by itself it can make a transformational change in the performance of many advanced electronic and energy devices,” Drzal said. “It can do so because it’s a nanoparticle with a unique shape made from environmentally benign carbon, and it can be made at a very reasonable cost.”

The key to the new material’s capabilities is a fast and inexpensive process for separating layers of graphite (graphene) into stacks less than 10 nanometers in thickness but with lateral dimensions anywhere from 500 nm to tens of microns, coupled with the ability to tailor the particle surface chemistry to make it compatible with water, resin or plastic systems.

* Could be used to make lighter, more fuel-efficient aircraft and car parts, and stronger wind turbines, medical implants and sports equipment.
* Is a good electrical conductor attractive for lithium ion batteries and could be used to make transparent conductive coatings for solar cells and displays.
* Can make gasoline tanks lightweight and leak tight and plastic containers that keep food fresh for weeks.

Drzal and his partners (former students Hiroyuki Fukushima, Inhwan Do and XG Sciences CEO Mike Knox) are already looking ahead to more uses for the product – like recyclable, economical or lightweight units to store hydrogen for the next generation of fuel cell-powered autos.

The startup XG Sciences is commercializing the material

xGnP is a platelet consisting of several sheets of graphene with an overall thickness of approximately 5 nanometers (ranging from 1 nm to 15nm) and particle diameters that can range from sub-micron to 100+ microns.

Density: ~2.0g/cm 3
Chemical Composition: Graphene
Electrical Resistivity: ~ 50 x 10-6 Ω cm
Thermal Conductivity: 3000 W/m K
Tensile Modulus: ~1.0 TPa
Tensile Strength: ~10-20 GPa

Mechanical strength characteristics compared to other carbon materials

Comparing electrical conductance

Thermal properties of different additive materials compared

Oxygen permeability compared

XG Sciences describes the applications

xGnP™ can be used to significantly lower costs by replacing carbon nanotubes in many composite applications where electrical conductivity or stiffness are required.

xGnP™ can also be used to replace nano-clays in applications where barrier properties or thermal stability are desired, with the added benefits of electrical conductivity and improved mechanical properties.

In general, xGnP™ has been found to compare favorably with competitive materials in the following applications:

* Fuel tank and fuel line coatings – the unique shape of xGnP particles imparts high barrier properties that, when coupled with its electrical conductivity, make this an ideal additive to Nylon for fuel tank linings.
* Electronic enclosures – xGnP adds electrical conductivity to polymers at low densities of 1% to 3%. xGnP can also be used to provide EMI or RFI shieldingto a variety of polymers.
* Automotive parts – a composite made with xGnP can be painted electrostatically, thereby saving costs.
* Aerospace – graphite has long been used in aerospace composites. xGnP can be combined with other additives to reinforce stiffness, add electrical conductivity, add RFI shielding, etc.
* Appliances – xGnP fortified polymers provide superior thermal and electrical conductivity, thereby saving the costs of separate heat dissipation mechanisms.
* Sporting goods – graphite-based composites are stronger and stiffer and lighter than comparable materials.
* Coatings and paints – xGnP can be dispersed in a wide variety of materials to add electrical conductivity and surface durability.
* Batteries – xGnP increases the effectiveness of Lithium-ion batteries when used as a surface coating on anodes or cathodes.
* Fuel cells – both bi-polar plate and electrode efficiencies can be improved with xGnP.


Will Brown said...

I wonder how successfully this substance can be added to polyethylene-based (plastic) structural siding and roofing materials? I would think the increased thermal insulation (and to a lessor extent electrical as well) achieved, along with the increased structural strength, would be considered a positive factor, even at some appreciable added cost over traditional materials.

In light of your recent post on radioactivity protection from structural design and materials Brian, any information as to graphene's radiocative shielding qualities?

bw said...

Discussion of materials for shielding against ionizing radiation. The more hydrogen in the materials the better the radiation shielding.

Lithium hydride is a popular shield material for nuclear power reactors, but is generally not useful for other functions. The graphite nanofiber materials heavily impregnated with hydrogen or any composite thereof may well represent a viable multifunctional component in future space structures. In this case study of the graphite nanofiber, hydrogen content is ~ 68% wt while in laboratory in single-walled carbon nanotubes (SWNT) hydrogen storage has been achieved ~ 10% wt.

So hydrogen added to graphite and graphene would be good regular physical shielding material. Probably not that helpful for widespread use but for some hardened sites it could be affordable and helpful.

Revolutionary methods of radiation shielding

A discussion about how much magnetic and other electric fields are needed to stop radiation.

(1) Active (electromagnetic) shield concepts:
• Electric fields.
• Magnetic fields (attached coils).
• Magnetic fields (deployed large-diameter coils or shields bearing magnets).
• Plasma methods (expand magnetic field, produce electric field).
Common elements:
• Many previous studies of physics for most; some studies of engineering.
• Requires space power to develop fields; requires superconducting magnets.
• To shield against GCRs one must have either very high fields or very extended fields.
• ∫ L BXdl
> 1,000 G km or V > 10**10 V.
Proposed figures of merit/discriminators:
• ∫ L BXdl
> 1,000 G km or V > 10**10 V.
• Smallest stored energies in field.
• Minimized effects of fields on crew and equipment (<2,000 G).
• Perceived practicality.
• Hazards.

(3) Novel materials concepts:
• Quasi-crystal H absorbers.
• Palladium, alloys as H absorbers.
• Carbon nano-material absorbers.
• Solid H.
• Metal hydrides.
• Borated CH2 and other compounds.
Common elements:
• Mass shielding.
• Goal is lowest average atomic mass achievable (polyethylene, CH2 is current “standard”).
• Dual use would modify the lowest average atomic mass rule.
• Neutron absorption.
• Structural or other use.
• Volumetric considerations.
Proposed figures of merit/discriminators:
• Average atomic mass number.
• Mass fraction of H.
• Dual use as construction material, neutron absorber, fuel, etc.
• Perceived practicality (fabrication, mechanical properties).
• Hazards.

Dave Salcido and Scott Moyes said...

Could graphene be the impetus for electromagnetic propulsion and the actual electro-framework for an aviation device such as a so-called "flying saucer"?