Ionic contamination

Semiconductor devices are particularly sensitive to ions, and the levels of ionic extractables in electronics packaging materials are becoming more important as devices become increasingly smaller. Again, as is illustrated in Table 7.11, some LCPs, owing to the use of high-purity monomers and small amounts of catalyst, exhibit very low levels of ionic extractables. This relative purity also has positive implications for the employment of LCPs in many other application areas. 

In 1990 the worldwide market for engineering polymers for electrical and electronic components was about 900 million. By 1995 an increase to about 1300 million is expected, which will represent about 25% of the total engineering polymers sold [9]. 

The trend towards miniaturization, higher-temperature assembly and harsher end-use environments is changing the requirements for the 

Methyl ethyl ketone 1 week under reflux 96 

In the electrical, electronic, optoelectronic and fibre-optic application areas, thermotropic LCPs are being specified commercially because of their high mechanical properties in thin-walled parts, high impact 

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The carbon black in semiconductive shields is composed of complex aggregates (clusters) that are grape-like stmctures of very small primary particles in the 10 to 70 nanometer size range (see Carbon, carbon black). The optimum concentration of carbon black is a compromise between conductivity and processibiUty and can vary from about 30 to 60 parts per hundred of polymer (phr) depending on the black. If the black concentration is higher than 60 phr for most blacks, the compound is no longer easily extmded into a thin continuous layer on the cable and its physical properties are sacrificed. Ionic contaminants in carbon black may produce tree channels in the insulation close to the conductor shield. 

Phospholipids. For the removal of ionic contaminants from raw zwitterionic phospholipids, most lipids were purified twice by mixed-bed ionic exchange (Amberlite AB-2) of methanolic solutions. (About Ig of lipid in lOmL of MeOH). With both runs the first ImL of the eluate was discarded. The main fraction of the solution was evaporated at 40°C under dry N2 and recryst three times from n-pentane. The resulting white powder was dried for about 4h at 50° under reduced pressure and stored at 3°. Some samples were purified by mixed-bed ion exchange of aqueous suspensions of the crystal/liquid crystal phase. [Kaatze et al. J Phys Chem 89 2565 7955.]... 

Desalination of sea water, or purification to eliminate dangerous ionic contaminants from industrial waste water involves important technological, scientific and financial risks. Most of them are related to the development of cheaper smart membranes that can mimic biological membranes. 

The simplest estimate of the overall salinity of water (its ionic impurity content) is obtained by measuring its conductivity. Such measurements can be useful, for instance, when checking the purity of rinsing waters from the plating and metalfinishing industries. A quantitative estimate of the degree of contamination is possible via conductometry when the qualitative composition of the ionic contaminants is known and does not change. 

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

Kuhn, M. Silversmith, D. 1971. Ionic contamination and transport of mobile ions in MOS structures. J. Electrochem. Soc. 118 966-970. 

The removal of ionic contaminants from ion chromatographic eluents is often necessary and has traditionally been accomplished using trap columns that contain ion-exchange resins of appropriate functionality. 

Chapter 2 mentioned that the adsorption of charged ionic compounds on the solid phase is a result of a combination of chemical binding forces and electric fields at the interface. Here, we extend the discussion on this topic, focusing mainly on aspects relevant to behavior of ionic contaminants in the subsurface environment. 

Cation exchange capacity and selectivity are among the most important processes that control the fate of charged (ionic) contaminants in the subsurface. These processes... 

High concentration of nontargeted ionic contaminants may reduce the efficiency of the 3M Empore extraction disk. Due to the high loading capabilities of the Empore membranes, the radionuclide concentration on the filters must be monitored to ensure that the membranes do not exceed the limits for low-level radioactive waste. 

Pool Process electrokinetic remediation (Pool Process) is a patented, commercially available technology for the removal of heavy metals and other ionic contaminants. The technology uses a series of electrodes placed in contaminated media to recover ionic contaminants in situ or ex situ from soils, muds, groundwater, dredgings, and other materials. The Pool Process can also be used to enhance bioremediation of media contaminated with a combination of ionic and nonionic organic contaminants. 

Geokinetics International, Inc., has developed other applications for this technology as weU. It can be set up as an electrokinetic ring fence to recover ionic contamination from groundwater as it flows past the electrodes. It may also be used as a soil heating element in conjunction with soil vapor or groundwater extraction to remove organics from soil. 

ISOTRON s ELECTROSORB C technology applies an electric field to induce migration of ionic contaminants from within porous concrete. This process provides an in situ alternative to concrete decontamination, thereby eliminating physical or mechanical damage of the concrete and allowing reuse of the structure or facility. The process generates minimal secondary waste and no airborne particulates common to conventional scabbUng or physical abrasion techniques. 

Fluor Daniel GTl, Inc. (now part of the IT Corporation), has developed in situ geochemical fixation technology to immobilize metallic contaminants in soil, sediment, sludge, and groundwater. The technology uses a site- and contaminant-specific combination of reagents to convert ionic contaminants to less soluble forms. In situ geochemical fixation has been used to remediate sites contaminated with chromium, uranium, molybdenum, and copper. 

Exchange resins may have an affinity for other ionic contaminants such as sulfates. Waste streams with these competing ionic contaminants may have lower removal efficiencies and these treatment systems may require more frequent resin regeneration or disposal. Ion exchange treatment does not destroy targeted contaminants. In some cases, waste disposal costs may render the technology cost prohibitive. 

Offers the ability to selectively adsorb both negatively charged and positively charged ionic contaminants. 

For incorporation of crown ethers and cryptates into the RTV encapsulant system as sodium and potassium ion scavengers, the total ionic contaminants must first precisely be determined. Atomic absorption is used to measure these ions in commercial silicone RTVs and silicone fluids. Values of "10 ppm for sodium and potassium were obtained in the best samples. Chloride level was determined by potentiometric titration of the silicone with AgN03. A quantity of ion trap (either crown ethers or cryptates) was then added to the RTV silicone encapsulant, and its molar concentration was equal to the combined sodium and potassium contaminant levels. 

There has been considerable interest in the determination of ions at trace levels as, for example, in applications need high-purity water as in semiconductor processing and the determination of trace anions in amine treated waters. For this investigation, we will define "trace" as determinations at or below 1 pg/1 (ppb) levels. The Semiconductor Equipment and Materials International (SEMI) recommended the use of IC for tracking trace ionic contaminants from 0.025 to 0.5 pg/1 [18]. In addition, the Electric Power Research Institute (EPRI) has established IC as the analytical technique for determining of trace level concentrations of sodium, chloride and sulfate down to 0.25 pg/1 in power plant water [19]. 

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