Oil fly ash has been reported to be a good source for the production of carbon nanotubes (CNTs). Recently, these CNTs were evaluated as lubricant additives in sunflower base oil and were found to exhibit excellent tribological properties. In this work, these CNTs were tested as lubricant additives in 100SN, 500SN and 150BS Saudi Aramco base oils. The results on other commercial carbon nanostructures like multiwall and single wall CNTs and graphene are also included in this study for comparison. Excellent tribological performance was obtained with CNTs of fly ash at a very small concentration. The observed reduction in values of the friction coefficient between two metallic surfaces using these CNTs was found to be superior to those of other carbon nanomaterials. The value of the friction coefficient was reduced by around 20% at a concentration of 0.1 wt%. These values were also investigated as a function of load, speed and temperature. The rheological behaviour showed that the viscosity of the 0.1 wt% CNTsimpregnated 500SN oil is almost invariant compared to that of the pure one. It is therefore suggested that CNTs of fly ash may be a good lubricant additive to minimize the friction and improve the fuel economy.

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Metal oxide semiconductor (MOS) gas sensors show poor selectivity when exposed to mixed gases. This is a challenge in gas sensors and limits their wide applications. There is no efficient way to detect a specific gas when two homogeneous gases are concurrently exposed to sensing materials. The p–n nanojunction of xSnO2–yCr2O3 nanocomposites (NCs) are prepared and used as sensing materials (x/y shows the Sn/Cr molar ratio in the SnO2–Cr2O3 composite and is marked as Sn x Cr y for simplicity). The gas sensing properties, crystal structure, morphology, and chemical states are characterized by employing an electrochemical workstation, an X-ray diffractometer, a transmission electron microscope, and an X-ray photoelectron spectrometer, respectively. The gas sensing results indicate that Sn x Cr y NCs with x/y greater than 0.07 demonstrate a p-type behavior to both CO and H2, whereas the Sn x Cr y NCs with x/y < 0.07 illustrate an n-type behavior to the aforementioned reduced gases. Interestingly, the Sn x Cr y NCs with x/y = 0.07 show an n-type behavior to H2 but a p-type to CO. The effect of the operating temperature on the opposite sensing response of the fabricated sensors has been investigated. Most importantly, the mechanism of selectivity opposite sensing response is proposed using the aforementioned characterization techniques. This paper proposes a promising strategy to overcome the drawback of low selectivity of this type of sensor.