H.E. Misak

Functionalization of carbon nanotube yarn by acid treatment

Carbon nanotube (CNT) yarn was functionalized using sulfuric and nitric acid solutions in 3:1 volumetric ratio. Successful functionalization of CNT yarn with carboxyl and hydroxyl groups (e.g., COOH, COO–, OH, etc.) was confirmed by attenuated total reflectance spectroscopy. X-ray diffraction revealed no significant change to the atomic in-plane alignment in the CNTs; however, the coherent length along the diameter was significantly reduced during functionalization. A morphology change of wavy extensions protruding from the surface was observed after the functionalization treatment. The force required to fracture the yarn remained the same after the functionalization process; however, the linear density was increased (310%). The increase in linear density after functionalization reduced the tenacity. However, the resistivity density product of the CNT yarn was reduced significantly (234%) after functionalization.

The use of carbon nanotube yarn as a filter medium to treat nitroaromatic-contaminated water

Abstract Carbon nanotube yarn (CNTY) is a promising material for the removal of organic contaminants from aqueous waste streams owing to its extraordinary mechanical strength, chemical stability, thermal stability and high surface area. CNTY was used to treat water contaminated with a model nitroaromatic compound, 2,4-dinitrotoluene (DNT). The isotherms and kinetics of DNT adsorption onto CNTY were investigated. The adsorption capacities of DNT were compared with the literature values of alternative sorbents. SEM-EDX, HRTEM, Raman spectroscopy and XPS were used to characterize the size, surface morphology and surface chemistry of the CNTY before and after DNT adsorption. Results indicate that adsorption isotherm of DNT onto CNTY could be fitted by the Freundlich isotherm with a Freundlich constant, KF, of 55.0 mg/g (L/mg)1/n and a Freundlich exponent, 1/n, of 0.737. Adsorption kinetics can be formulated by the pseudo-second order kinetic model. This study demonstrates the ability of CNTY to remove organic contaminants from water.

Crack Initiation from Corrosion Pit in Three Aluminum Alloys Under Ambient and Saltwater Environments

Corrosion-pit-to-crack transition behaviors of three aluminum alloys using two pit configurations were investigated under ambient and saltwater environments. Fatigue stress ranges for crack initiation from a through-pit were less than that from a corner-pit in both environments in all three materials, while stress intensity factor ranges showed the opposite trend. Further, stress ranges or stress intensity factor ranges for crack initiation were less in saltwater than that in ambient environment for both pit configurations. Fatigue damage mechanisms in a test environment were similar for both pit configurations in all three materials. An empirical relationship is proposed to estimate pit-to-crack transition fatigue cycles.

Tensile behavior of carbon nanotube multi-yarn coated with polyester

The behavior of a carbon nanotube (CNT) multi-yarn consisting of 30 yarns and coated with a thin layer of polyester is investigated under tensile loading condition. The coated and uncoated CNT multi-yarns are loaded until fracture occurred inside a scanning electron microscope. In situ photographs were undertaken to investigate the helix angle, diameter, yarn twist, and damage and failure mechanisms. The coated CNT multi-yarn has a higher ultimate tensile strength than the uncoated counterpart. The coated multi-yarn fails at a single location and remains tight after the failure. The uncoated yarn fails at multiple locations along its length and also unravels. The adhesive coating adheres to the CNT yarn surface and does not penetrate into the yarn. These results provide insights into how CNT multi-yarn would behave when used as the reinforcement in the nanocomposites.

Investigation into Corrosion Pit-to-Fatigue Crack Transition in 7075-T6 Aluminum Alloy

Transition of corrosion pit to crack under fatigue condition was investigated in high-strength 7075-T6 aluminum alloy. The pit was formed at the edge of a hole in a specimen. Specimen was subjected to a constant stress during the pit formation. Two types of corrosion pit were considered: corner-pit and through-pit. Two sizes were tested for each pit type. Also, the baseline data of cycles to initiate a 250-µm-long crack were established when the corrosion pit was created without any applied stress on the specimen, i.e., Sapplxa0=xa00. The cycles to initiate a 250-µm-long crack initially decreased with increasing Sappl relative to the baseline value and then increased with increasing Sappl such that this increase was significant with higher value of Sappl. The transition between this increase and decrease occurred when the Sappl was greater or less than a value which caused the onset of plastic deformation at the root of the pit, respectively. Microstructural analysis showed that this decrease in cycles to initiate the crack was due to microcracks at the pit front which developed at the lower level of Sappl, and the increase was due to plastic deformation at the higher levels of Sappl.

Thermal Transport Properties of Dry Spun Carbon Nanotube Sheets

The thermal properties of carbon nanotube- CNT- sheet were explored and compared to copper in this study. The CNT-sheet was made from dry spinning CNTs into a nonwoven sheet. This nonwoven CNT-sheet has anisotropic properties in in-plane and out-of-plane directions. The in-plane direction has much higher thermal conductivity than the out-of-plane direction. The in-plane thermal conductivity was found by thermal flash analysis, and the out-of-plane thermal conductivity was found by a hot disk method. The thermal irradiative properties were examined and compared to thermal transport theory. The CNT-sheet was heated in the vacuum and the temperature was measured with an IR Camera. The heat flux of CNT-sheet was compared to that of copper, and it was found that the CNT-sheet has significantly higher specific heat transfer properties compared to those of copper. CNT-sheet is a potential candidate to replace copper in thermal transport applications where weight is a primary concern such as in the automobile, aircraft, and space industries.