Water purification electrically conducting

Since minerals form ions in solution, they increase the electrical conductivity of the solution. Conversely, water that is low in dissolved ions has higher resistance to current flow. For example, the calculated resistivity of chemically pure water is 18.3 million Cl (megohms) over a distance of 1 cm at 25°C. In fact, 18 Mfl-cm is the upper limit of current water-purification technology. 

Solvent purification has been discussed by many, and recommended procedures have been listed by Kratochvil. Molecular and volatilizable impurities are best measured by gas chromatography, and ionic impiuities by electrical conductivity. The commonest and most troublesome impurity, because of its leveling action, is water it can be measured by the Karl Fischer method (Section 19-8) among others. 

All silanes were obtained from commercial production at Huls America. Ultra-pure water was prepared in a Millipore purification unit. FTIR studies were conducted with a Nicolet Model 740 Spectrometer using ATR (attenuated total reflectance) of samples in a zinc selenide cell. NMR spectra were obtained using a General Electric QE-plus 300 MHz NMR Spectrometer. 

Electric current leads to degradation of a LCM and reduces the lifetime of the display. Impurities influence the stability of the material and accelerate electrodegradation. Therefore a multistage purification, consisting for example of recrystallization, and column chromatography, to remove conducting impurities (intermediate products, water, and CO2), is necessary. Usually the specific conductivity of a LCM is lower than 10 -10 Cm/cm and corresponds to the intrinsic conductivity. 

For the preparation of samples suitable for electrical measurements, special types of purification methods are employed. Reduction of the self-conductivity of the sample requires removal of traces of water and of particles from the liquid samples and from the walls of the test cell and filling tubes. Powerful drying agents used are activated silica gel or molecular sieves, phosphorus pentoxide, or alkali metals, especially sodium-potassium alloys. The liquid samples are either percolated through columns of silica gel or molecular sieves in an atmosphere of dry argon or nitrogen gas, or they are refluxed in a container with sodium potassium alloys for many hours. In order to remove adsorbed water from the walls of the test equipment, circulation of purified liquid and continuous drying are necessary. 

A reasonably simple first example is the purification of copper. Its purification is hugely important for electrical applications because its conductivity is severely impaired if impurities are present because, like boulders in a stream, they inhibit the electron flow. To visualize the process, think of one electrode, the anode, as impure copper metal and the other electrode, the cathode, as pure copper. Both electrodes are immersed in a solution of blue copper sulfate in water. Copper sulfate solution consists of positively charged copper ions, Cu (Cu denotes copper, cuprum) and negatively charged sulfate ions, 804 , i, all of them free to migrate through the water. Sulfate ions are sturdy, and are just inert, disinterested spectators in all that follows. 

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