Window materials, desirable properties

Figure 10-3 shows the basic features of a hollow cathode lamp source. Here A is the anode (the plus electrode) and C is the cathode, terminated in the lamp as a hollow cup. The anode can be a wire, such as tungsten, and the cathode cup may be constructed from the element whose spectrum is desired or it may be an inert material into which the desired element or a salt of the desired element is placed. The lamp envelope is made of glass and IT is a window of suitable properties. If an ultraviolet line spectrum is desired, the window may be quartz or a high silica glass. The hollow cathode has an inert gas present, usually neon or argon, at low pressure. 

There are a number of other glass recipe variations that may be used to yield desired properties. Most likely, these formulations were discovered by accident or in a trial-and-error manner, using materials from their locale and measuring the resultant properties. For instance, the Europeans were the first to discover that K2O, obtained locally from plant ash, could also be combined with lime and quartz to yield a potash-lime glass, later exploited for stained-glass windows. Another popular variation substitutes boric oxide (B2O3) for lime and soda to yield... 

Commercial development of this field was aided by a fortuitous set of circumstances. Maleic anhydride became available commercially shortly prior to World War II and cheap styrene for synthetic rubber during this conflict. Glass fibers in woven cloth form appeared at about the same time. A demand for radomes for aircraft caused a search for a strong lastic material which literally would be a window for radar waves. Glass cloth-reinforced unSaturated polyester resins provided the strength necessary as well as the desired electrical properties. From this commercial start "in 1944, the imsaturated polyester resin production has grown to an estimated 70 million lb in 1956. The major part of the resin is used with reinforcing fibers of some tj e. 

Borgschulte et al. [84] concluded from photoemission and scanning tunneling microscopy studies (STM/STS) that this critical cap layer thickness is related to inactivation of Pd by encapsulation of the Pd islands by yttrium oxide or hydroxide strong metal-support interaction (SMS I effect). The substitution of Pd by cheaper, preferably transparent, catalytic cap layers is desirable, especially for smart window devices. In this respect, the catalytic properties of transition metal oxides [85] for storage materials could also prove to be useful for smart windows. 

Because the performance of spinel windows is also very sensitive to the quality of the precursor materials (both purity and morphology), there have been researches that can be found in the open literature. To produce better spinel precursor powders, various methods have been developed. For example, a new method has been used to synthesize spinel powders from boehmite, in which Mg " ion was metal exchanged onto the surface of boehmite particles [208]. In this method, particle size, size distribution, purity, and stoichiometry of the Mg-doped boehmite powders could be well controlled. Such powders exhibited good sinterability and resulted in spinel ceramics with desired optical properties. 

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