Chemically sensitive materials

Chemically sensitive materials, smart, 22 708t, 716-717, 721t Chemical manganese dioxide (CMD),... 

Liq chromatography is conducted at ambient temps. Therefore, efficient separation and identification of chemically sensitive materials is now state of the art. Liq chromatography of NG, TNT, HMX and RDX using dichloroethane as solvent and 2% isopropanol in heptane as eluent has been reported (Ref 52). Separation of RDX from HMX was demonstrated using 40% l,2dichloroethane in heptane. The use of HPLC for the study of unstable compds is still in its infancy and major advances in the technique are anticipated 6.3 Mass Spectrometry... 

An optical fiber chemical sensor and biosensor are devices that can selectively detect the presence and concentration of chemical and bio species, respectively. The development of such sensors can be performed in three major steps (or tasks) (a) sensor design (b) sensor development and processing, which involves (1) selection and characterization of chemical sensitive material, such as polyaniUne... 

Using a modified cladding as the chemical sensitive material. Two types are recorded in many applications the single fiber strucmre and the dual fiber (parallel or twisted) structure, as shown before in Figs. 5 and 6. The single fiber strucmre will be explained in detail in this chapter, with samples of application... 

Various techniques are used for the fabrication of semiconductor sensors. Conductance sensors from structurized sintered polycrystalline ceramics can be produced by thick- or thin-film technology. Chemically sensitive materials in the form of single crystals or whiskers can be attached to electrodes by thin- or thick-film techniques as well. Mass production of sensors requires that the resulting devices be characterized by a defined level of conductance. For example, the conductance of polycrystalline Sn02 can be adjusted by subsequent thermal treatment >800°C under a controlled partial pressure of oxygen. Another approach to defined conductance involves doping the semiconductor with antimony or fluorine. The reproducibility and stability of a sensor signal... 

The most often used subphase is water. Mercury and otlier liquids [12], such as glycerol, have also occasionally been used [13,14]. The water has to be of ultrapure quality. The pH value of tire subphase has to be adjusted and must be controlled, as well as tire ion concentration. Different amphiphiles are differently sensitive to tliese parameters. In general it takes some time until tire whole system is in equilibrium and tire final values of pressure and otlier variables are reached. Organic contaminants cannot always be removed completely. Such contaminants, as well as ions, can have a hannful influence on tire film preparation. In general, all chemicals and materials used in tire film preparation have to be extremely pure and clean. 

By far the most widely known classes of pH-sensitive materials are the classes of chemical compounds that iaclude the acids, bases, and iadicators. The most interesting of these are the iadicators. These materials change colors as a function of pH and usually are totally reversible (see Hydrogen-ION concentration). 

Soluble impurities can be extracted by washing with deionized or distilled water foUowed by filtration (1,12,26). Powders prepared by wet chemical synthesis are often washed and filtered for purification prior to use. The dewatering (qv) process can be enhanced by pressure filtration. Organic solvents can be used to remove water-insoluble impurities and wash-water sensitive materials. 

Because silver, gold and copper electrodes are easily activated for SERS by roughening by use of reduction-oxidation cycles, SERS has been widely applied in electrochemistry to monitor the adsorption, orientation, and reactions of molecules at those electrodes in-situ. Special cells for SERS spectroelectrochemistry have been manufactured from chemically resistant materials and with a working electrode accessible to the laser radiation. The versatility of such a cell has been demonstrated in electrochemical reactions of corrosive, moisture-sensitive materials such as oxyhalide electrolytes [4.299]. 

Chemical Reactivity - Reactivity with Water Dissolves to form an alkaline solution. The reaction is non-violent Reactivity with Common Materials Forms explosion-sensitive materials with some metals such as lead, silver, mercury, and copper Stability During Transport Stable but must not be in contact with acids Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

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