Ceramic humidity sensors

Ceramic materials have an advantage in terms of mechanical strength and thermal and chemical stability. A number of investigations have been carried out on humidity sensors utilizing porous ceramic elements. There have been a number of reviews of ceramic humidity sensors [1, 5], and some examples of recent developments are introduced in this chapter. 

FIGURE 30.10 Electrical response of three ceramic humidity sensors at room temperature and 1 kHz. 

Seiyama T, Yamazoe N, Aral H (1983) Ceramic humidity sensors. Sens Actuators 4 85-96... 

She Y-E, Jiang B-Y, Liu J-Z (1994) Si-Mg-Al-O system ceramic humidity sensor. Sens Actuators A 40 151-153 Shimizu Y, Arai H, Seiyama T (1985) Theoretical studies on the impedance-humidity characteristics of ceramic humidity sensors. Sens Actuators 7 11-22... 

Yarkin DG (2003) Impedance of humidity sensitive metal/porous silicon/n-Si structures. Sens Actuators A 107 1-6 Yeh Y, Tseng T, Chang D (1989) Electrical properties of porous titania ceramic humidity sensors. J Am Ceram Soc 72 1472-1475... 

Surface conduction is monitored in most humidity sensors through the use of porous ceramics of MgCr204—Ti02 that adsorb water molecules which then dissociate and lower the electrical resistivity. 

Humidity sensors consist of two major types, i.e., one which measures relative humidity and the other which detects dew condensation. The sensors for relative humidity made of ceramic or organic polymers are produced in amounts exceeding one million. They are applied to controling systems in air conditioning, micro wave ovens, and so on... 

Amdur, E. J. Nelson, D. E. "A Ceramic Relative Humidity Sensor", Paper 38, ibid. 

Fundamental concepts of the molecular layering method have been developed and applied by the team headed by Professor Valentine Aleskovsky in Russia. This method, similar to atomic layer epitaxy and atomic layer deposition, has been used to create monolayers on oxides and polymers as humidity sensors, flame retardants, and agents to enhance sintering in ceramic materials. 

A. Bearzotti, J. M. Bertolo, P. Iimocenzi, P. Falcaro, E Travers, Humidity sensors based on mesoporous silica thin films synthesized by block copolymers, J. Eur. Ceram. Soc. 24, 1969-1972 (2004). 

In many traditional applications for ceramics, particularly in structural and electrical applications, the sintered ceramic component is required to have minimum porosity. However, in a growing number of applications, for example, in ceramic humidity and gas sensors, porosity is not just desirable, it is required. Several different methods can be used to produce porous structures. 

Besides the applications for lighting and domes, transparent nanostructured Y-AI2O3 ceramics have various other applications, such as a humidity sensor of Y-AI2O3 [75]. Nanostructured Y AlaOs ceramics were prepared from Al-Sec-Butoxide (C12H27AIO3) by using a sol-gel process. The sensors had a long term stability of up to two years. 

The range of available ceramic sensors for measuring humidity in industrial process environments can be classified into four categories (1) ionic, (2) electronic, (3) solid electrolyte, and (4) rectifying-junction types. A solid electrolyte humidity sensor that uses doped strontium cerate has been reported... 

---