Titanium membranes

The sol—gel technique has been used mosdy to prepare alumina membranes. Figure 18 shows a cross section of a composite alumina membrane made by sHp coating successive sols with different particle sizes onto a porous ceramic support. SiUca or titanium membranes could also be made by the same principles. Unsupported titanium dioxide membranes with pore sizes of 5 nm or less have been made by the sol—gel process (57). 

The latitude that titanium affords the cell designer has made a wide variety of monopolar and bipolar membrane cell designs possible. 

Sodium nitrite has been synthesized by a number of chemical reactions involving the reduction of sodium nitrate [7631-99-4] NaNO. These include exposure to heat, light, and ionizing radiation (2), addition of lead metal to fused sodium nitrate at 400—450°C (2), reaction of the nitrate in the presence of sodium ferrate and nitric oxide at - 400° C (2), contacting molten sodium nitrate with hydrogen (7), and electrolytic reduction of sodium nitrate in a cell having a cation-exchange membrane, rhodium-plated titanium anode, and lead cathode (8). 

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

Operation of cells at higher temperatures such as 80°C, as in membrane fuel cells, is not encouraged here because of the corrosion instability of the hardware, manufactured from titanium or titanium alloy. Even without such constraints, however, this high temperature would be unwelcome as the water produced is present as steam - without the conductive bridge of the liquid phase it would be necessary to bond the catalytic particles to the membrane with all the associated problems of technology and cost. 

In this chapter brief information on the origin and cost of titanium will be discussed. A definition of the term unique properties will be given and how these properties are exploited in the membrane, diaphragm and in the mercury cell processes will be considered and miscellaneous applications touched upon. The chapter will conclude with a summary of the financial benefits which, after all, propel the use of this challenging material. 

Figure 23.7 illustrates a model of a membrane cell header where the battery voltage can be as high as 600 V. By proper design of titanium-based electrodes, this voltage can be reduced. 

Typical areas where titanium has found widespread industrial use in membrane technology are cells, anodes, anolyte headers, anolyte containers, filters, heat exchangers, chlorate removal systems and various parts of the brine system. 

Other typical uses of titanium in a membrane cell process are in the pipelines for hot anolyte and in the anolyte collecting tanks as well as dechlorination systems that normally work under vacuum and sometimes limit the use of loose linings. 

The anodes are platinized titanium (titanium plated with 5 microns of platinum) the cathodes are also titanium plated with 2.5 microns of platinum. All gaskets are Viton GF (peroxide grade), and the cell membranes are DuPont Nation 324. Flow through the cells is in parallel using manifolds with /4-inch fluid-flow inlet port orifices to provide equal flow to all cells. 

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