Retention Of Carbon Nanotubes Research Articles

In Situ Growth of Carbon Nanotubes on Ti Powder for Strengthening of Ti Matrix Composite via Nanotube–Particle Dual Morphology

In situ synthesis of carbon nanotubes (CNTs) on Ti powder decorated with Ni catalyst enabled us to obtain a high-quality CNTs/Ti composite powder via fluidized bed chemical vapor deposition (FBCVD) process. The composite powder was characterized by a combination of high structural integrity and uniform dispersion of CNTs, which is not obtained by traditional ball-milling route. These advantages enabled the retention of CNTs in the near-fully dense titanium matrix composite (TMC), together with the uniform dispersion of TiC particles. The CNTs and TiC particles coordinated with each other and contributed to a synergistic effect involving load transfer from the matrix to CNTs and dispersion strengthening of TiC particles. The nanotube–particle-reinforced TMC exhibited superior mechanical properties in comparison to single-phase-reinforced TMCs. The catalytic behavior of Ni, controllable synthesis of CNTs, the retention behavior of CNTs, and the formation mechanism of TiC particles during the sintering process are discussed in detail.

Tailoring the thermal shock resistance of titanium carbide by reinforcement with tungsten carbide and carbon nanotubes

Titanium carbide (TiC) is reinforced with 3.5wt% of tungsten carbide (WC) and 2wt% of carbon nanotubes (CNTs) in order to improve its thermal shock resistance and mechanical integrity of oxide layer. Three pellets namely, TiC (T-SD), TiC-3.5wt% WC (TW-SD) and TiC-3.5wt% WC-2wt% CNT (TWC-SD) were thermally shocked at 1700°C in an open atmosphere for 10 numbers of thermal cycles. Raman spectra confirmed the retention of CNTs after thermal cycling, which could be attributed to the thermal shielding offered by the molten TiC to CNTs. HR-TEM image infers the collapse of some of the CNTs into carbon structure after the thermal shocks. The mass loss % of T-SD, TW-SD and TWC-SD pellets were found to be 41.5%, 33.3% and 15.13%, respectively after the 10 numbers of thermal cycles. The rate of mass change in T-SD sintered pellet was found to be ~1.4 × 10−3g/min., which got reduced to ~0.4 × 10−3g/min. on addition of 3.5wt% of WC and 2wt% of CNT. Furthermore, reinforcement of 3.5wt% WC and 2wt% CNTs in TiC matrix showed the dramatic increase of 89% in thermal shock resistance parameter (Rst) compared to T-SD pellet. This significant improvement in thermal shock resistance of TWC-SD pellet is mainly attributed to the following three factors viz. (i) higher fracture toughness (ii) higher density and (iii) homogeneous dispersion of CNTs, which hinders the movement of oxygen atoms along the grain boundaries. Hardness of the thermally shocked TWC-SD pellet was found to be 5.1GPa, which was 1.3GPa i.e. ~74% higher compared to thermally shocked T-SD pellet. This increased hardness of thermally shocked TiC matrix has been shown to suppress the crack formation and restrict oxidation.

Transport and retention of carbon dots (CDs) in saturated and unsaturated porous media: Role of ionic strength, pH, and collector grain size

Carbon-based engineered nanoparticles (ENPs) are widely used in consumer products due to their small size and unique physicochemical properties. Therefore, their release and distribution into the surface and subsurface environment is a subject of concern. Several studies have evaluated the transport and retention of carbon nanotubes and fullerenes, but none investigated the transport and retention of carbon dots (CDs). The aim of this research is to fill this knowledge gap by evaluating the transport and retention of CDs in saturated and unsaturated porous medium. Here, we investigate the effects of solution ionic strength (IS, 1–700 mM NaCl) and pH (4–9), the initial concentration of CDs (50–200 mg L−1), and porous media grain size (0.20–0.50 mm, 0.50–1 mm, 1–1.5 mm and 1.5–2 mm grain diameters) on the transport and retention of CDs in saturated (upward flow) and unsaturated (downward flow) quartz porous media. A mathematical model based on the advection-dispersion equation coupled with the second-order kinetics was used to fit the breakthrough curves and to calculate the attachment and straining rates under the different experimental conditions. These analyses were underpinned by characterization of CD surface functional groups, surface charge and aggregation under the different experimental conditions, calculation of CD-CD and CD-quartz sand interaction potential according to DLVO theory.Transport and retention of CDs in quartz porous media are consistent with those observed for other types of carbon-based ENPs such as fullerenes and carbon nanotubes. Mobility of CDs in both saturated and unsaturated porous media increases with the decrease in ionic strength, increase in pH, and increase in collector grain size. Retention of CDs increases with the increase in IS, decrease in pH and decrease in grain size. Generally, CDs mobility was higher under saturated than under unsaturated flow conditions, for the same experimental conditions. Overall, CDs tend to be highly mobile and could travel for long distances at a wide range of environmental conditions.

Transport of Surface-modified Carbon Nanotubes through a Soil Column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Transport of surface-modified carbon nanotubes through a soil column.

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Separation of carbon nanotubes by frit inlet asymmetrical flow field-flow fractionation.

Flow field-flow fractionation (flow FFF), a separation technique for particles and macromolecules, has been used to separate carbon nanotubes (CNT). The carbon nanotube ropes that were purified from a raw carbon nanotube mixture by acidic reflux followed by cross-flow filtration using a hollow fiber module were cut into shorter lengths by sonication under a concentrated acid mixture. The cut carbon nanotubes were separated by using a modified flow FFF channel system, frit inlet asymmetrical flow FFF (FI AFIFFF) channel, which was useful in the continuous flow operation during injection and separation. Carbon nanotubes, before and after the cutting process, were clearly distinguished by their retention profiles. The narrow volume fractions of CNT collected during flow FFF runs were confirmed by field emission scanning electron microscopy and Raman spectroscopy. Experimentally, it was found that retention of carbon nanotubes in flow FFF was dependent on the use of surfactant for CNT dispersion and for the carrier solution in flow FFF. In this work, the use of flow FFF for the size differentiation of carbon nanotubes in the process of preparation or purification was demonstrated.