RESUMO
In hostile environments, sensing is critical for many industries such as chemical and oil/gas. Within this industry, the deposition of scales or minerals on various infrastructure components (e.g., pipelines) forms a reliability hazard that needs to be monitored. Therefore, the approach adopted in this study to tackle this issue relies on the use of real-time sensing of specific ions in brine, the natural trigger for ions deposition. In order to do so, electrochemical sensors based on carbon nanotubes (CNTs) are developed, taking advantage of their unique properties facilitated by different synthesis and fabrication methods. One of these promising synthesis methods is inkjet printing of CNT films since in general, it has exceptional benefits over other approaches that are used to print CNTs. Furthermore, it does not need the use templates. In addition, it is a very fast technique with consistent printing results for many applications along with very low cost on various shapes/formfactors. As these sensors are exposed to a hostile environment (chemical, temperature, etc.), the stability of the CNT films is of great importance. In this study, a comprehensive investigation of the stability of CNT surfaces upon exposure to elements is presented. Accordingly, the several impacts of this interaction on physical properties of the surfaces as a function of interaction time and brine chemical composition are assessed. Moreover, the approach used for investigating the impact of this exposure involves the following: surface electrical resistance change using four probe measurements; surface roughness/topography using Atomic Force Microscopy (AFM) along Scanning Electron Microscopy (SEM); quality of CNT through Raman spectroscopy and wettability using the sessile drop method. The sensing capabilities of the devices are investigated by looking at the sensing selectivity of target ions, resetting capabilities, and sensing sensitivity manifested in the electrical resistance change. Consequently, our results indicate that while inkjet films are very promising sensor material, the fabrication and long term stability require further optimization of the films along with the process to make them meet reliability and lifetime requirements in the oil/gas hostile operational environments.
RESUMO
In this paper, a new type of sensor and associated system for complete online monitoring of scale deposition with great accuracy and reliability is fabricated and characterized. The system is based on carbon nanotubes (CNTs), which have unique sensing/electronic properties along with physical and chemical stability in corrosive and hostile environments required for the oil and gas application. CNTs inkjet printing technique is used to fabricate the CNTs sensor. The sensitivity of the films, real time monitoring of brine solution, stability of the films in various solvents and fluids and the ability of setting and resetting of the sensor are studied. The results of these studies indicate that adding of one brine solution on the surface of the CNTs inkjet printing increases the resistance from 0.50 kΩ to 1.50 kΩ. The CNTs inkjet printing sample is found to be stable even after 48 hours of soaking the whole sample in DI-water. This sensor not only shows good sensing response for detection of the deposition of brine, but can also be easily reset back many times by just wash it with DI-water. This simple sensor is ideally suited for real time monitoring and the response time of the film is found to be from 1530 s.
RESUMO
Despite the current interest in the scientific community in exploiting divergent surface properties of graphitic carbon allotropes, conclusive differentiation remains elusive even when dealing with parameters as fundamental as adhesion. Here, we set out to provide conclusive experimental evidence on the time evolution of the surface properties of highly oriented pyrolytic graphite (HOPG), graphene monolayer (GML) and multiwalled carbon nanotubes (MWCNTs) as we expose these materials to airborne contaminants, by providing (1) statistically significant results based on large datasets consisting of thousands of force measurements, and (2) errors sufficiently self-consistent to treat the comparison between datasets in atomic force microscopy (AFM) measurements. We first consider HOPG as a model system and then employ our results to draw conclusions from the GML and MWCNT samples. We find that the surface properties of aged HOPG are indistinguishable from those of aged GML and MWCNT, while being distinct from those of cleaved HOPG. Herein, we provide a sufficient body of evidence to disregard any divergence in surface properties for multidimensional sp (2) carbon allotropes that undergo similar aging processes.
