ABSTRACT
Sensors for pH evaluation of concrete were made by a sol-gel process with alizarin yellow as pH indicator. The optical absorbance was measured with a visible spectrophotometer coupled with optical fibers. Results showed that the sensors had good reversibility, reproducibility, and fast response time.
Subject(s)
Azo Compounds/chemistry , Carbon/chemistry , Phase Transition , Calibration , Chemistry Techniques, Analytical , Gels , Hydrogen-Ion Concentration , Materials Testing , Microscopy, Electron, Scanning , Optical Fibers , Reproducibility of Results , Spectroscopy, Fourier Transform Infrared , Temperature , X-Ray DiffractionABSTRACT
Humidity sensors are widespread in many industrial applications, ranging from environmental and meteorological monitoring, soil water content determination in agriculture, air conditioning systems, food quality monitoring, and medical equipment to many other fields. Thus, an accurate and reliable measurement of water content in different environments and materials is of paramount importance. Due to their rich surface chemistry and structure designability, carbon materials have become interesting in humidity sensing. In addition, they can be easily miniaturized and applied in flexible electronics. Therefore, this short review aims at providing a survey of recent research dealing with carbonaceous materials used as capacitive and resistive humidity sensors. This work collects some successful examples of devices based on carbon nanotubes, graphene, carbon black, carbon fibers, carbon soot, and more recently, biochar produced from agricultural wastes. The pros and cons of the different sensors are also discussed in the present review.