Inorganic ceramic membranes

The ceramic membrane has a great potential and market. It represents a distinct class of inorganic membrane. In particular, metallic coated membranes have many industrial applications. The potential of ceramic membranes in separation, filtration and catalytic reactions has favoured research on synthesis, characterisation and property improvement of inorganic membranes because of their unique features compared with other types of membrane. Much attention has focused on inorganic membranes, which are superior to organic ones in thermal, chemical and mechanical stability and resistance to microbial degradation. 

The vast increase in the application of membranes has expanded our knowledge of fabrication of various types of membrane, such as organic and inorganic membranes. The inorganic membrane is frequently called a ceramic membrane. To fulfil the need of the market, ceramic membranes represent a distinct class of inorganic membrane. There are a few important parameters involved in ceramic membrane materials, in terms of porous structure, chemical composition and shape of the filter in use. In this research, zirconia-coated y-alumina membranes have been developed using the sol-gel technique. 

We have successfully developed a new inorganic ceramic membrane coated with zirconium and alumina. A thin film of alumina and zirconia unsupported membrane was also fabricated. The successful method developed was the sol-gel technique. 

Although inorganic (ceramic) membranes offer many advantages they do suffer from a few limitations at the present state of technology development... 

INORGANIC MEMBRANES SYNTHESIS AND APPLICATIONS Table 2.3. Advantages and Disadvantages of Inorganic (Ceramic) Membranes... 

Inorganic membranes commercially available today are dominated by porous membranes, particularly porous ceramic membranes which are essentially the side-products of the earlier technical developments in gaseous diffusion for separating uranium isotopes in the U.S. and France. Summarized in Table 3.1 are the porous inorganic membranes presently available in the market (Hsieh 1988). They vary greatly in pore size, support material and module geometry. 

For efficient separation, porous inorganic membranes need to be crack-free and uniform in pore size. An important reason for the increasing acceptance of ceramic membranes introduced in recent years is the consistent quality as exemplified in a scanning electron micrograph of the surface of a 0.2 micron pore diameter alumina membrane (Figure 3.3). 

Gillot, J., R. Soria, and D. Garcera. 1990. Recent developments in the Membralox ceramic membranes. Proc. 1st. Inti. Conf. Inorganic Membranes 3-6 July pp. 379-81, Montpellier. 

Armor, J. N. 1989. Catalysis with fiermselective inorganic membranes. Appl. Catai 49 1-25. Anderson, M. A., M. J. Giesclmann and Q. Xu. 1988. Titania and alumina ceramic membranes. J. Membrane Science 39 243-258. 

Uhlhom, R. J. R., M. H. B. J. Huis in t Veld, K. Keizer and A. J. Burggraaf. 1989a. Theory and experiments on transport of condensable gases in microporous ceramic membrane systems. Proc. 1st Inti Cong, Inorganic Membrane, 3-6 July, 323-328, Montpellier. 

While considerable progress has been made in the preparation of ceramic membranes by sol-gel processing, the development of membranes from hybrid polymers is in its infancy (see also Section V). This is, nevertheless, a very promising area of development, because the possibility of forming mechanically stable membranes by inorganic polycondensation is implemented by the possibility to incorporate organic functions. 

Refs. [i] Rickert H (1982) Electrochemistry of solids. An introduction. Springer, Berlin [ii] Schmalzried H (1963) Z phys Chem 38 87 [in] Bouwmeester HJM, Burggraaf A) (1996) Dense ceramic membranes for oxygen separation. In Burggraaf A), Cot L (eds) Fundamentals of inorganic membrane science and technology. Elsevier, Amsterdam, pp 435-... 

Because of the unique characteristics of inorganic membranes mentioned above, the search for inorganic membranes of practical significance has been continuing for several decades. With the advent of ceramic membranes with superior stabilities coming to the separation markets, the potentials for inorganic membranes as separators and/or reactors are being explored at an accelerated rate never wimessed before. 

Much of the impetus for the awakened interest and utilization of inorganic membranes recently came hom a history of about forty or fifty years of some large scale successes of porous ceramic membranes for gaseous diffusion to enrich uranium in the military weapons and nuclear power reactor applications. In the gaseous diffusion literature, the porous membranes are referred to as the porous barriers. For nuclear power generation, uranium enrichment can account for approximately 10% of the operating costs (Charpin and Rigny, 1989]. 

In addition to the U.S. and France, other countries such as the Soviet Union, China and England were also involved in using presumably inorganic membranes for its gaseous diffusion opierations although little has been documented. Ceramic membranes were also made by the anodic oxide process (to be discussed later in Chapter 3) in Sweden for military and nuclear applications. 

The methods of preparing inorganic membranes with tortuous pores vary enormously. Some use rigid dense solids as the templates for creating porous structures while many others involve the deposition of one or more layers of smaller pores on a premanufactured microporous support with larger pores. Since ceramic membranes have been studied, produced and commercialized more extensively than any other inorganic membrane materials, more references will be made to the ceramic systems. 

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