Moisture getter

The main difficulty is to prevent pyrohydrolysis over the long experimental periods. (Moisture is removed by "gettering with hot lanthanides or actinides.) The potentials of M/MF reference electrodes have also been used to study activities of metals in alloys, carbides, and borides (208). The accuracy is limited by reproducibility of potentials (2 1 mV) as a fraction of the cell potential and indeterminate errors. The latter can be avoided by checking for internal consistency (e.g., measuring emfs of two cells against a common third electrode). 

Protection of the molten metals from air and moisture The protection of the molten metals has always been an essential point. Fusion under vacuum or an inert atmosphere (pure He or Ar, possibly gettered) is systematically used. In the past, also for small scale laboratory preparations, fusion under a protective layer of molten non-reactive salts was often used. Low density salt mixtures having low-melting point and high-boiling point were generally employed (for instance eutectic mixtures of anhydrous stable alkali halides). 

The addition of various corrosion inhibitors to the epoxy encapsulant formulation to prevent corrosion was also evaluated (8). This procedure basically adds compounds or complexing agents to neutralize or "getter corrosion accelerating impurities or adds hydro-phobic agents to reduce the moisture permeation of the plastic. 

In stoppered vials we could follow quite easily the transfer of moisture from the stopper toward the plug, which acted as a getter pump until a new equilibrium was reached (Figure 21). This allowed us, for instance, to understand why in a certain BCG vaccine the Karl Fischer titration went up when the equilibrium water vapor went down reaching condensation points as low as -50°C. 

In Case 7, a thermoplastic die-attach adhesive was used. The large amount of carbon dioxide indicates decomposition, but the small amount of moisture indicates that moisture may have been generated, but gettered by oxides or metals in the package. Often when moisture is expected to be high, but is low, and hydrogen is present, the moisture is believed to have reacted with oxides or metals to produce hydrogen. 

The requirement of a helium-leak test for a MEMS device package with an internal volume of around 0.001 cc or below for chronic implantation (>10 years) is definitely beyond the capability of any current helium-leak detector. That is where getter materials come into play. A getter material can absorb various gaseous species and can be used to extend the effective lifetime of a medical device by absorbing moisture and other detrimental gas species, such as hydrogen [104—106] and oxygen [40]. 

NaK (contamination control) An alloy of sodium (20-50%) and potassium that is liquid at room temperature and is used to getter oxygen and moisture in an inert gas dry box. 

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