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First samples of perfluorinated cation exchange membranes were obtained in 1971. They were tested for use in the diaphragm process as a replacement for asbestos diaphragms. However, the special features of these membranes led to the decision to develop special new membrane electrolysis cells. A patent was sought for the first new cell design in 1975. After extensive material testing and many improvements, the HOECHST bipolar membrane cell was produced, consisting of an electrolyzer made up of individual elements, i.e. individual sealed electrolysis cells. Starting in 1982, this cell type was developed further in cooperation with UHDE GmbH. In 1983 it was installed for the first time in an industrial electrolysis plant. Despite strong competition, the bipolar HOECHST-UHDE membrane cell has now gained an important market share. In 1998 it will be installed worldwide in 43 electrolysis plants, with a total NaOH capacity then amounting to 2.5 million mtpa.

State of Development of Alkali Chloride Electrolysis (II). Electrochemical Quantities, Economics. The first part of this rewiew article described cells, membranes, electrolytes and products of the membrane cell process. The second part, presented below, deals with cell voltages, current efficiences and energy consumption, as well as with plant construction and plant conversion with membrane cells. A brief look at the connection between the discussion on chlorine chemistry and the introduction of the membrane cell process concludes this review.

State of the Art in Alkali Chloride Electrolysis (I). Cells, Membranes, Electrodes, Electrolytes, Products. The state of the art in the field of alkali chloride electrolysis for the production of chlorine, alkali hydroxide and hydrogen is characterized by the state of development of the membrane cell process. By 1996 about 230 membrane electrolysis plants with a combined NaOH capacity of about 11 million metric tons will be on line worldwide. This amounts to roughly one fourth of the world's caustic soda production by electrolysis. In this review the main membrane cell technologies, the ion exchange membranes of different suppliers and anodes and cathodes of the membrane cells are described. This first part of the review ends with a look at the problems of brine quality for the membrane cells and a description of the products chlorine, caustic soda solution and hydrogen.

JENOPTIK Laser, Optik, Systeme GmbH (JO L.O.S.) enlarged its product range in the field of cylinder lenses and crystal optics. These components are used in optical measuring technology and in various laser applications. The new cylinder components are a result of the state of the art manufacturing technology. For applications, where the quality of standard cylinders with a surface deviation of PV~Lambda/2 to ~Lambda/5 @632,8nm and tested with a reference glass only is not sufficient, the surface shape can be improved to PV Lambda/10 @632,8nm. The presentation deals with Jenoptik's current state to produce cylinder optics, to reduce remaining surface shape deviations of semi-finished cylinder optics and to test these elements. Based on in-house developed machinery, cylinders are manufactured by means of blocking or drum. The required surface quality in the range of PV~Lambda/10 @632,8nm for cylindrical lenses can be reached by computer aided correction using mrf-polishing techniques in connection with an interferometer test set-up. Therefore, the polishing machine is equipped with an additional axis of movement. The interferometer measurement of the residual surface deviation is done by Computer Generated Holograms (CGH), which are designed and manufactured in-house. CGHs from JO L.O.S. for testing cylindrical lenses can be custom designed starting with F#1.0. They are related to the typical rectangular geometry of cylinder components. Using these measurement techniques, testing is no longer the limiting factor in achieving high quality cylindrical surfaces. JO L.O.S. has all the capabilities of effective manufacturing, testing and correcting cylindrical lenses. Latest results achieved in series production are shown.

Alkali chloride electrolysis using the membrane process. Some 300,000 tonnes per year of chlorine are currently produced by the membrane process; the installed capacity will have tripled by 1984; a further increase is certain owing to the advantages of this new process as compared to the mercury and diaphragm processes. After a description of the different ion-exchange membranes and cell types these advantages of the membrane cell process are elucidated in a comparison with the other two electrolysis processes. Subsequently recent development trends in respect of the membrane cell process are described which concern a further lowering of the energy consumption such as reduction of the hydrogen overvoltage at the cathode, the use of air-consuming cathodes in the place of the hydrogen-evolving cathodes, membrane electrolysis under pressure and the SPE process or zero-gap electrolysis.

Progress in the field of alkali chloride electrolysis. In the field of alkali chloride electrolysis, new developments are restricted almost solely to the membrane cell process, and no longer concern the conventional mercury and diaphragm processes. At present, the membrane process has a roughly 10% share of the world's caustic soda production capacity of about 48 million t NaOH/a. This share includes membrane cells and retrofit diaphragm cells. After dealing with electrolytes and electrolysis products, this review then turns to a discussion of the optimum current density, of cell voltages, current efficiency, and energy consumption. Subsequently, economic aspects are considered in relation to energy and capital expenditure costs as well as to plant construction. Finally, the most recent developments are discussed, especially in the field of oxygen consuming cathodes in membrane cells.