Vapour retarders

Details are given of water penetration and moisture characteristics of barrier Exterior Insulation Finish Systems clad walls. The study includes results from a field investigation, laboratory experiments and computer simulations. The system includes a PE vapour retarder and PS foam. 2 refs. 

European Commission Expert Team for Vapour Retarding Additives Effectiveness of Vapour Retardants in Reducing Risks to Human Health from Paint Strippers containing Dichloromethane, Final Report published by the European Commission, Brussels, Belgium, 2004. 

Faraday, who gives a long abstract, says I cannot form a distinct idea of the power to which he refers the phenomena . Faraday also brings in Dalton s idea (see Vol. Ill, p. 766) that one gas is a vacuum towards another gas , and his speculations are far from clear. He does not explain why the effects are specific to platinum and why other solids do not behave in the same way. He found that it is essential that the platinum shall be clean and found that ethylene, carbon monoxide, carbon disulphide and ether vapours, retard the combination of hydrogen and oxygen on platinum, but the metal acts when put into a pure gas mixture. Sulphuretted hydrogen and phosphoretted hydrogen, however, permanently inactivated the platinum unless treated with hot concentrated sulphuric acid or fused caustic potash and washed with water. 

The most commonly applied vapour retarder materials in lightweight envelope parts are polyethylene film and bituminous or aluminium kraftpaper. In flat membrane roofs, the bituminous membranes applied for water-tighmess are also used as a vapour retarder. A new... 

In the Belgian design guides, four vapour retarding classes have been developed, depending on the resistance to water vapour diffusion of a vapour retarder (expressed as the diffusion thickness or equivalent air layer thickness pd). Table 4.2 gives the boundaries of the vapour retarding classes, and some examples of materials. 

As illustrated by the previous example, other factors than purely physical considerations play an important role in condensation control. The properties of air barriers or vapour retarders are not the only concerns in preventing condensation problems. Different condensation control strategies may be combined in order to create condensation control systems with a greater probability of effectiveness in building practice. 

The reaction mechanisms are quite complicated in these syntheses, the kinetics depending on inter-diffusion rates in neighbouring particles, the formation of transient liquid phases, and in some cases, the vapour transport of a reactant. The presence of the latter can be detected by dre retarding effect of increased pressure in an inert surrounding atmosphere. 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

In considering the heat that is transferred, the method first put forward by NussELT(%i and later modified by subsequent workers is followed. If the vapour condenses on a vertical surface, the condensate film flows downwards under the influence of gravity, although it is retarded by the viscosity of the liquid. The flow will normally be streamline and the heal flows through the film by conduction. In Nusselt s work it is assumed that the temperature of the film at the cool surface is equal to that of the surface, and at the other side was at the temperature of the vapour. In practice, there must be some small difference in temperature between the vapour and the film, although this may generally be neglected except where non-condensable gas is present in the vapour. 

Touching on drawbacks of vapour-liquid method, we should note that among those there is a lack of control of the thickness of condensed liquid layer on detector surface which may result (for fairly thick liquid layers) in diffusion retardation of oxygen chemisorbtion. The diffusion... 

This explanation advanced by Iredale cannot be considered as adequate or even thermodynamically possible. The change in density of the mercury vapour at the surface of the drop due to retardation of diffusion by the gas admitted, as well as alteration of the orientation of the surface layers may prove important factors. 

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