Ionic impurities corrosion

The quality of the ethanol has a strong influence on its corrosive effects. Three categories of problems have been identified general corrosion (caused by ionic impurities, mainly chloride ions and acetic acid), dry corrosion due to ethanol polarity, and wet corrosion caused by azeotropic water. Corrosion inhibitors should thus be incorporated in ethanol-diesel blends. 

It is well known that in the presence of moisture, ionic impurities, and electric fields, the delicate integrated circuitry is very vulnerable to corrosion. Since no polymer is impermeable to moisture, it is impossible to completely exclude moisture from the packaged device. 

Typical transfer molding compositions for encapsulation of electronic devices are mixtures of an epoxy novolac resin, a phenolic resin hardener, a catalyst, large amounts of inorganic filler (e.g., Si02) flame-retardant ingredients, internal lubricants, carbon black, and sometimes other additives such as getters to trap ionic impurities (34,35), corrosion-protection materials, and stress-relief ingredients. 

A novel method of improving the reliability of plastic packaged semiconductor devices has been developed. One of the major causes of failure in such devices is corrosion due to moisture permeating through the encapsulant, transporting small amounts of ionic impurity and condensing at the chip surface to form an aggressive electrolyte. 

Epoxies became popular for the first generation of electrically conductive adhesives introduced in the mid-to-late 1960s. The early adhesive formulations contained organic solvents, which often became trapped in the bondhne during cure and resulted in voids, especially under large chips and substrates. These early adhesives also contained large amounts of ionic impurities, notably chloride ions, which, in the case of nonconductive adhesives, resulted in reduced electrical resistivity, ion migration, and corrosion, especially in humid environments. Early epoxies were also... 

W.E. Ruther, W.K. Soppet, T.F. Kassner, Effect of temperamre and ionic impurities at very low concentrations on stress corrosion cracking of AISI304 stainless steel. Corrosion 44 (1988) 791—799. 

The steam produced in the reactor pressure vessel is directed to the high-pressure part of the turbine downstream, the condensate formed on the high-pressure turbine is separated and directed to the heater drains. The residual steam powers the low-pressure part of the turbine and, finally, is completely condensed in the main condenser. The main condensate is purified in the condensate demineralizers where corrosion products and ionic impurities are retained. The feedwater then is recycled via preheaters to the reactor pressure vessel. In older BWR plants, all the condensates are purified in the condensate polishing system in the newer, forward-pumped plants only the main condensate is purified there, while the heater drains are directly pumped to the feedwater tank. In some of the BWR plants the feed-water tank is equipped with an electromagnetic filter for removal of suspended corrosion products (mainly iron oxides). 

The failure due to the cathodic corrosion of aluminum is also accelo ted ionic impurities existing in the water film on the bonding pad area. Ion chromatographic analysis showed that the extracts from molding compound into water were hydrolyzed products such as R—COO" and inorganic ions from polymer. leakage current... 

Effect of Temperature and Ionic Impurities at Very Low Concentrations on Stress Corrosion Cracking of AISI 304 Stainless Steel... 

The condensate polishing system chemically cleans up the condensate by passing it through ion exchange resins to remove corrosion products and ionic impurities. It is required during start-up, imtil the desired water quality is attained, but during power operation would be used only when abnormal secondary conditions exist, such as a continuous condenser tube leak. 

The hypothetical polarization curve shown in Figure 5.2 illustrates a near-realistic industrial condition since most corroding solutions contain more than one oxidizing agent. Normally, ferric-ferrous salts and other ionic impurities are contained in acid solutions due to contamination from corrosion products and existing oxidizers [4]. Nevertheless, the electrochemical situation shown in Figure 5.2 implies that... 

Ionic impurities such as Cl, Na", and can cause corrosion of A1 bond pads and other metallization, loss in oxide dielectric strength in FET circuits, and other problems in high reliability (high rel) ICs. Until recently, most conductive epoxy adhesives contained very high levels of extractable chloride ions and other ionic impurities. The adhesives of Table 3, for example, would typically yeild over 600 ppm Cl and over 200 ppm Na, after a 24 hour extraction in neutral water at 100 C. 

The most direct effect of defects on tire properties of a material usually derive from altered ionic conductivity and diffusion properties. So-called superionic conductors materials which have an ionic conductivity comparable to that of molten salts. This h conductivity is due to the presence of defects, which can be introduced thermally or the presence of impurities. Diffusion affects important processes such as corrosion z catalysis. The specific heat capacity is also affected near the melting temperature the h capacity of a defective material is higher than for the equivalent ideal crystal. This refle the fact that the creation of defects is enthalpically unfavourable but is more than comp sated for by the increase in entropy, so leading to an overall decrease in the free energy... 

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