This study presents the sensitivity of graphene nanoribbon (GNR) when exposed to ammonia gas at room temperature. Alumina were used as a substrate and coated with GNR as sensing film for ammonia gas detection. Four different concentration of GNR in the category of maximum, high, low, and minimum were prepared. Each category of GNR will be dispersed on alumina substrate with area of 1cm2 and 4cm2. 30nm of gold contacts are sputtered on both ends of the sensing film. The ammonia gas can be detected by measuring the changes in resistance. The GNR as ammonia sensor shows good responses at room temperature. In repeatability test, maximum GNR shows least variation when exposed to ammonia with the value of 1.01% (4cm2) and 2.12% (1cm2). In a sensitivity test, 0.25% to 1.00% of ammonia gas was used and tested on maximum GNR. Maximum GNR on 4cm2 substrate shows higher sensitivity as compared to 1cm2. Reaction time of GNR on ammonia gas decreased as the concentration of ammonia increased. Larger surface area of sensing element required lesser reaction time.
Various production methods have been developed for graphene production, but each of them falls short in either the economic or quality aspect. In this paper, we present the flame deposition method, a modified chemical vapor deposition (CVD) that uses an open-flame. In this method, resulting carbon deposits were found to be graphitic in nature, thereby suggesting multilayer graphene growth in a very short reaction time of 5 min. Furthermore, the deposits were transferred onto a cyanoacrylate plastic substrate and its sheet resistance was measured to be 81 ohm/square. The results showed that open-flame deposition exhibits high potential for low-cost, low-energy and high-quality production of graphene.
Top-Oil Temperature (TOT) is one of the basic components to estimate the Hot-Spot temperature (HST) of the transformers. This paper presents an alternative TOT model based on the heat transfer theory that utilises Nonlinear Thermal Resistance (NTR) and Lumped Capacitance (LC) approaches. It is applied in a thermal-electrical analogy and the heat transfer equivalent equation is determined. This model is tested on a measured TOT of 250 MVA ONAF and 400 MVA ONAF transformers obtained from IEC 60076-7 and previous research. A comparison of TOT is carried out with the existing models IEC 60076-7 exponential and IEEE Loading Guide clause 7 methods. It is found that the thermal model based on the NTR and LC approach could determine the measured TOT closer than the existing methods available in the standards.