CNT Composites for MEMS Mechanical Structural Applications : A Systems Approach

Transcription

1 CNT Composites for MEMS Mechanical Structural Applications : A Systems Approach Ranga Komanduri and Satish Bukkapatnam Oklahoma State University Stillwater, OK Workshop on Research Challenges for Nanomanufacturing Systems National Science Foundation Arlington, VA February 11-12, 2008

2 GRAPHENE SHEET, SWNT AND MWNT

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4 Unique Mechanical Properties of CNT Quite stiff, exceptionally strong, and resilient. Young s modulus of SWNT is ~0.75 TPa Strength of SWNT is ~37 GPa CNT are extremely flexible under large elastic strains and resist failure under repeated bending. Small diameter CNT can be extended elastically to ~ 5.8% before breaking Low density (1.1 to 1.5 g/cm 3 ), hallow structure, large aspect ratio, nanometric dimensions Density normalized modulus and strength of typical SWNT are ~19 and ~56 times that of steel wire, respectively Very high damping coefficient

5 CNT before and after nanoindentation

6 Engineer s s Dream Material They can be considered as engineer s dream material as no material to date has such unique combination of desirable properties. The mechanical properties alone make CNTs, a unique material as they are stiff at the same time highly flexible, strong yet highly deformable. They perform much better in compression than carbon fibers and do not fracture easily. SWNTs can be bent, twisted, flattened and can be made into small circles without breaking. We have also observed that CNTs do not undergo any permanent deformation when indented with an AFM probe.

7 Features An engineer s approach for the synthesis of CNT composites for MEMS mechanical structural applications with high stiffness and damping. Can also be used for structural health monitoring, for CNT can also be used as sensors. The focus is not on composites with pure SWCNTs but on composites with highly-aligned bundles of MWCNTs with the ends closed and the catalyst sealed inside the tubes for structural composite applications. The focus is not on macro structural applications, such as hydrogen storage batteries for automobile, aerospace structural applications, it will focus on micro structural applications, such as MEMS components, power supply. This way, the high cost and large volume requirements will not be factors in their application to MEMS.

8 Approach Develop CTC composites with highly aligned CNT bundles for structural applications with significant increase in stiffness/damping for potential MEMS mechanical structural applications. There are numerous MEMS applications where this approach would be more than adequate and the conventional approaches would not be cost effective. The analogy would be instead of considering composites for aerospace applications, where quality is a prime requisite, our approach will be tantamount to considering reinforced concrete for structural applications (e.g. roads, buildings, bridges) where the requirements are not as stringent but used extensively all around the world.

9 Approach Also, instead of applications requiring large volumes of CNTs (macro), the research work will focus on micro (MEMS) systems. Consequently, the cost or volume requirements of CNTs will be a minor issue similar to platinum coating on razor blades. Significant cost reductions can accrue from using the asgrown, highly-aligned multiwalled CNT bundles for advanced composite applications as subsequent processing costs are minimal and large quantities of CNTs are not required.

10 Mechanical Structures Cast Iron Easy to cast complicated structures Believed to have high damping Inexpensive Low elastic modulus (10 x 10 6 psi) or stiffness Welded steel High elastic modulus (30 x 10 6 psi) or stiffness Low damping More expensive Granite-epoxy: machine tools for HSM Low modulus More damping Ceramic structures for UPM High modulus High precision Thermally more stable Low damping

11 CNT Composites for Structural Applications High modulus High stiffness High damping Built-in sensors for structural health monitoring Ideal for MEMS structural applications Reasonable cost

12 EXCIMER LASER PLD SETUP Schematic of PLD setup Photograph of PLD setup

13 MICROWAVE CVD SYSTEM FOR SYNTHESIS OF CNTs

14 TANGLED CARBON NANOTUBES

15 TEM OF CNT

16 100 μm

17 100 μm

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19 THANK YOU