Silicones contaminants

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

Fig. I. Silicone contamination, as measured by XPS, as a function of distance from the edge of a silicone tape after a heal treatment to simulate a curing cycle. The dashed line represents the silicone level that would produce delamination. Adapted from Ref. [11).

A number of alternative precursors have been used and include trimethylsilyl azide, Me3SiN3 (Figure 23a), used in combination with Me3Al films of AIN were grown under atmospheric pressure MOCVD conditions between 300 °C and 450 °C. No silicon contaminants were detected in the as-grown AIN films.128... 

In ultra pure crystalline silicon, there are no extra electrons in the lattice that can conduct an electric current. If however, the silicon becomes contaminated with arsenic atoms, then there will be one additional electron added to the silicon crystal lattice for each arsenic atom that is introduced. Upon heating, some of those "extra electrons will be promoted into the conduction band of the solid. The electrons that end up in the conduction band are able to move freely through the structure. In other words, the arsenic atoms increase the conductivity of the solid by providing additional electrons that can carry a current when they are promoted into the conduction band by thermal excitation. Thus, by virtue of having extra electrons in the lattice, silicon contaminated with arsenic will exhibit greater electrical conductance than pure silicon at elevated temperatures. 

The survey summaries show that zeoHte adsorbents are most often employed for non-aqueous systems. This is because the material generally used as a binder to fabricate an agglomerated zeoHte, is a clay comprising silicon dioxide and aluminum oxide which tends to dissolve in water. This dissolution results in negative changes in physical characteristics of the adsorbent as well as silicon contamination of the solution which manifests itself as turbidity in the product. 

The outlines are cerium/alumina particles the bright white dots represent silicon. Qualitatively, silicon contamination increases with time. 

Five and twenty-three hundredths grams of germanium(IV) oxide (0.05 mol) is dissolved in 15 ml. of a concentrated aqueous solution of hydrofluoric acid (47 %). A platinum evaporating dish or a polyethylene plastic beaker is used to keep silicon contamination to a minimum. A solution of 10.5 g. of barium chloride (0.05 mol) in 50 ml. of water is added. Barium hexafluorogermanate forms as a white, granular precipitate, which is filtered and washed free of chloride. The product is dried by heating to 300° in vacuo and is stored in a desiccator over phosphorus(V) oxide. The yield is 15.24 g. (94%). 

Silicon contaminated with carbon can be obtained by reduction ot silica, SiOs, with carbon in an electric furnace. An alloy of iron and silicon, called ferrosilicon, is obtained by reducing a mixture of iron oxide and silica with carbon. 

Serum silicon levels correlate with the degree of renal failure [49] and once enrolled in a dialysis program patients not only accumulate the element via the oral intake of high silicon drinking water but especially by the use of silicon contaminated dialysis fluids [19,50,51]. Contamination of the dialysis fluid... 

Direct reaction of the elements can also be achieved in a sealed quartz ampule, with a hand torch to control the reaction . Besides the obvious hazard, it is difficult to assure completion, and silicon contamination from the quartz can be expected. A better approach is the reaction of a vapor stream of the metal with a chalcogenide hydride. 

Typical XPS spectra are shownoin Figure 5. This technique samples a greater depth (about 30 A) and is able to give some detailed chemical state information about the composition ( ). Survey scans of the polymer reveal trace amounts of silicon contaminant, but represent only about 2% of the total surface area and can be subtracted from the final spectra. Silicones are... 

H.S. Gandhi, W.B. Williamson, R.L. Goss, L.A. Mareotty and D. Lewis, "Silicon Contamination of Automotive Catalysts," Society of Automotive Engineers Paper No. 860565 (February, 1986). 

Silicone contamination has been implicated as a cause of failure in telephone switching systems and other devices that contain relay switch contacts (507). Analysis of airborne particulates near telephone switching stations showed the presence of silicones at these locations. Where the indoor use of silicones is intentionally minimized, outdoor levels were found to be higher than inside concentrations (508). Samples of particulates taken at two New Jersey office buildings revealed silicone levels that were considerably higher indoors than outdoors. In these cases, indoor silicone aerosols are believed to be generated primarily by photocopiers, which use silicone fuser oils. 

Surface contamination can take a number of forms. We are surrounded by a complex mixture of hydrocarbon molecules as a consequence of both our industrial and natural environments. Low surface energy silicones (e.g., vacuum greases and pump oils) are commonly present in the laboratory environment. Silicone contamination is particularly troublesome and is found on many surfaces because few materials have surface energies lower than silicone compounds. 

Features Reduces coeff. of friction creates color uniformity eliminates fear of silicone contamination eliminates orange peel, fisheye cratering minimizes pigment mobility will not affect gloss or clarity Reguiatory EDA 21CER 175.320,182.1978 Properties Pale amber liq. sp.gr. 0.86 dens. 7.1 Ib/gal vise. 600-1000 cps b.p. > 316 C flash pt. > 121 C 100% cone. 

A summary is presented of topics discussed at a conference on adhesive tapes organised in Athens by AFERA. These included the use of iodopropynyl butyl carbamate for the protection of water-based adhesives from biological attack, the formulation of NR latex based adhesives with tackifiers in aqueous dispersion, the effects of silicon contamination on adhesion to plastics film supports treated in different ways, possible harmful effects... 

Silicone contamination has been implicated as a cause of failure in telephone switching systems and other devices that contain relay switch contacts... 

Mitigation approaches with respect to silicon contamination include avoiding the use of silicon-containing materials in FC designs, or using silicone materials that are highly stable under the aggressive chemical and electrochemical environment of the FC. 

Note 5—CAUTION —Isolate silicones from other bituminous testing equipment and samples to avoid contamination, and wear disposable rubber gloves whenever handling silicones or apparatus coated with them. Silicone contamination can produce erroneous results... 

Its sensitivity and surface specificity make it ideal in the detection of very low levels of contamination/ modification. For example, the detection of a monolayer of silicone contamination of a plastic part that was hampering the wetting of a paint. It can also be used to analyse particulate impurities, fibres and defects in surface coatings. 

Features Reduces coeff. of friction creates color uniformity eliminates fear of silicone contamination eliminates orange peel, fisheye cratering minimizes pigment... 

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