Occlusion of gases

Blowholes Occlusion of gases (i) Increased venting (ii) Elimination of materials that can react to produce gas (ill) Degassing Avoid feed systems which have high flow velocities... 

Some interferences appear to be vapour-phase effects and are presumably due to occlusion of analyte elements into particles of matrix. The use of platforms in furnaces (see Section 3.6.3), the use of reactive purge gases (e.g. hydrogen) and dispersion of the matrix, e g. by using an organic acid such as ascorbic acid, can in some cases reduce such interferences. 

Molten copper absorbs hydrogen9 and sulphur dioxide,10 the occluded gases being eliminated on cooling. The liquid metal does not absorb nitrogen. It combines with oxygen to form cuprous oxide, so that fall of temperature is not attended by evolution of the gas. It decomposes hydrocarbons such as methane and ethane, with occlusion of hydrogen and separation of carbon. 

The compositional characteristics of an icy planetesimal source in comet accretion models for Venus, discussed below, require occlusion of nebular noble gases with approximately unfractionated elemental ratios for Ar Kr Xe but much lower Ne. Thermodynamic modeling suggests that noble gases incorporated in clathrates do indeed have low Ne/Ar ratios, but do not reflect ambient gas-phase compositions for Xe/Ar and Kr/Ar and instead are strongly enriched in the heavier species (Lunine and Stevenson... 

In Rocks.—In a state of "occlusion, or molecular condensation, hydrogen is to be found in most igneous rocks in association with other gases, the total volume of occluded gases being on the average about 4 5 times the volume of the rock. 

The most common sample forms used for the measurement of electrical properties are pressed pellets, thin films, and single crystals. Electrical measurements on pellets are often difficult to interpret because of the presence of polycry staUinity, grain boundaries, large surface area, and unknown amounts of adsorbed gases. Films are useful in some instances, but in many cases also cause uncertainties because of poly cry staUinity. Electrical properties are most easUy and reUably interpreted with single crystals free from unintentional impurities and solvent occlusions. 

It is important to realise that mass spectrometric measurements in TG-MS are not performed directly on the polymer but only evolved gases are detected and identified. Factors influencing component loss from polymeric matrices are volatility, rate of diffusion, solubility in the polymeric matrix, flow-rate, temperature, AT, sample thickness, etc. Therefore, information about the polymeric matrix is obtained in an indirect way, and concerns especially the thermal stability, degradation mechanism and kinetics, performance behaviour, reactivity, and analysis of volatile additives, residuals, monomer occlusions... 

In handling rare gases, especially tracer amounts, one does well to remember that contact with liquids or solids (including system walls) or condensation from the gas phase of other liquids or solids may result in removal of rare gases from the gas phase through solution, adsorption or physical occlusion. Thus in quantitative work rare gas carriers are usually added for essentially the same reasons that carriers are added for species to be separated from solutions. 

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