Sodium contamination

Carbon The solubility of carbon in sodium has been measured it is considered lower than the corresponding value for oxygen (2 p.p.m. of carbon at 520°C) but is sufficiently high to give rise to undesirable effects. Carburisation of refractory metals and of austenitic stainless steels has been observed in sodium contaminated with carbon e.g. oil, grease or a low alloy ferritic steel the source of which can be either decomposed organic material, e.g. oil, or a ferritic steel of low or zero alloy content. The latter is an example of... 

The sulfate level in the reactor water is a good indicator of sodium contamination, and it may be observed by an increase in the pick-up rate of sulfate, from perhaps 0.2 to 0.4 ppb to 3 to 4 ppb. 

Figure 5.49. (a) STM image (unfiltered) of the initially sodium-contaminated Pt(l 1 l)-(2x2)-0 adlattice (b) corresponding Fourier transform spectrum (c) Fourier-filtered STM image of the overlapping Pt(l 1 l)-(2x2)-0 and Pt(111)-(12x12)-Na adlayers (bias Ut = 80 mV, tunelling current I, = 10 nA, total scan size 319 A).78 Reprinted with permission from Elsevier Science. 

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

Sodium contamination and drift effects have traditionally been measured using static bias-temperature stress on metal-oxide-silicon (MOS) capacitors (7). This technique depends upon the perfection of the oxidized silicon interface to permit its use as a sensitive detector of charges induced in the silicon surface as a result of the density and distribution of mobile ions in the oxide above it. To measure the sodium ion barrier properties of another insulator by an analogous procedure, oxidized silicon samples would be coated with the film in question, a measured amount of sodium contamination would be placed on the surface, and a top electrode would be affixed to attempt to drift the sodium through the film with an applied dc bias voltage. Resulting inward motion of the sodium would be sensed by shifts in the MOS capacitance-voltage characteristic. 

NOTE Solution (either water or sample) must be continuously aspirated into the flame. Therefore, ensure that the sample delivery tube is immersed in solution at all times. Rinse all glassware with distilled or de-ionized water before preparing standards to avoid sodium contamination. Ensure that you have prepared all of your standards before proceeding with the experiment. 

To examine the ability of membranes to prepare samples with known contaminants, we contaminated the above peptide and protein solution with 5% glycerol and 500 mM NaCl. In addition to preventing effective crystallization of analyte samples with matrix on conventional stainless steel surfaces, glycerol and sodium contaminants are frequently present in biological samples. Doped samples were prepared for MALDI-TOF analysis by saturating the membrane with MeOH, immediately followed by the addition of 1 ul of the sample. The membrane was washed 3 times with 3-6 ml 70% methanol in water and allowed to dry after each wash. Once dry, lul saturated matrix solution was added to the sample spot. 

The appearance of ESI mass spectra depends on the solvent conditions, especially on the extent of sodium contamination. Sodiated molecules were observed as the base peak for chlortoluron, isoproturon, diuron, linuron, and diflubenzuron [34], while protonated molecules and only weak sodiated molecules were observed for monuron, diuron, and neburon [14], Some phenylureas can also be analysed in negative-ion ESI, where deprotonated molecules as well as acetate or formate adducts can be observed, depending on the mobile-phase composition [9],... 

Diffused conductors maintain the hermeticity of the sealed cavity, but, due to the large sodium contamination of the silicon-glass interface, large leakage currents destroy the electrical insulation between the different conductors. 

Stock standard NaCl solution (1000ppm Na). Dry about 1 g NaCl at 120°C for 1 h and cool for 30 min. Weigh and dissolve 0.254 g NaCl in water and dilute to 1 L. Care must be taken to avoid sodium contamination, especially from the water and glassware. A blank must be run to correct for sodium in the water. 

Note the change in flame color, shape, and size. With each flame measure the emission at 589.0 and 589.5 nm. This is from sodium contamination in the flame gases and from dust in the atmosphere. Aspirate into the flame (a) deionized water from a plastic container, (b) deionized water from a soda-lime glass container (your typical glass jar or bottle), and (c) deionized water from a borosilicate glass container (e.g., Pyrex or Kimax ). (Allow water to sit in each container overnight). Compare with freshly drawn deionized water. Compare the relative sodium contamination of the water by the containers (emission intensity at 589.0 nm). 

The mineral bauxite, which is a mixed hydroxide of iron and aluminum, is the raw material at the origin of the industrial chemistry of aluminum compounds. Bauxite is transformed into sodium-contaminated gibbsite in the so-called Bayer process (32,33). Industrial Bayer-type gibbsite can be redissolved in acids or in strongly basic solutions, and from these solutions aU other aluminum compounds are produced including aluminum hydroxides and oxides (34,35). 

Experimental difficulties, theoretical uncertainties, and poor planning have so conspired together as to frustrate most attempts to determine the conductances or excess conductances of the electrons in amine solvents. One of the main problems in the laboratory has been the low chemical stability of the alkali metal solutions. Their blue colour gradually fades as the solutions decompose with the formation of hydrogen, a process catalysed by impurities and especially by the platinum electrodes of the cell itself. Pyrex vessels, it was recently discovered, cause sodium contamination, and for this reason much of the early research is now of doubtful worth. The experimental problems are exacerbated in the case of methylamine, whose volatility demands the use of low temperatures at which the metals dissolve but slowly. A further problem arises in the extrapolation of the data to infinitesimal ionic strength, for the appropriate conductance function to be applied depends upon the kind of species which the solution contains. And when, after all these hazards, the limiting conductance of an alkali metal solution has finally been obtained, it turns out as often as not that it can neither be compared with values for other metals because each experimenter has worked at a different temperature, nor with the conductances of normal salts because in the excitement their measurement has been overlooked. 

Sodium ions are a common impurity in solvents used for ESI. Analyte samples (especially proteins) are often contaminated by sodium ions in the production process, while sample solution storage in glass vessels also contributes to the sodium contamination. The extensive evaporation of solvent in the ESI process promotes solution ion-pairing reactions. When the analyte is a protein, ion-pairing reactions will involve Na and the ionized acid residues of the protein, see Eq. (1.16a). Similarly, impurity anions such as Cl will ion pair with ionized basic residues of the protein (see Eq. (1.16b)). 

---