Permeability to liquids and gases

Glazes for ceramic bodies and porcelain enamels for metallic substrates are coatings that are applied to these surfaces with a variety of purposes chemical inertness, zero permeability to liquids and gases, cleanability, smoothness and resistance to abrasion and scratching, mechanical strength, and decorative and aesthetic considerations [12]. 

Aromatic amorphous or semicrystalline polyamides, PARA, such as copolyamide from caprolactam, hexamethylenediamine and iso- and tere-phthalic acids, PA-6IT6, or copolyphthalamide, PPA, are frequent components of polymer blends. Their advantage is low permeability to liquids and gases, stiffness and high HDT. Several blends of PP with PARA have been described, e.g. with either PP-MA, PE-MA, or PP grafted either with acrylic acid or GMA. Usually, these blends must be heat stabilized with phosphite ester or hydrazine. The alloys are often reinforced by addition of glass fibers and talc. 

Temperature plays a part in all environmental tests but it was convenient to separate into Chapter 15 those tests which are particularly concerned with thermal resistance alone and to consider here the other types of environment to which rubbers may be exposed. This includes resistance to liquids and gases other than permeability tests (permeability is covered in Chapter 17). 

Wood Quality. The relative number of thin-walled and thick-walled fibers in softwoods and hardwoods, and the vessel size and number in hardwoods, have a major impact on wood characteristics that often dictate the wood s end use. Such characteristics include the mechanical properties of wood, the type of surface resulting from wood machining, the permeability of wood to liquids and gases, wood weatherability, and perhaps others. In essence, the types and pro-... 

The volume ratio of vessels to fibers and fiber wall thickness are two important factors influencing the hardness and density of different hardwood species and the permeability of these woods to liquids and gases. Wood grain is also partly a function of these two parameters. 

The moisture content of heartwood in softwood trees is reduced to a level much lower than that of normal sap-wood (2, 24), During the moisture reduction period, the membranes of bordered pits in sapwood fibers have a strong tendency to become aspirated. This situation, together with that of pit membrane incrustation, greatly reduces the natural permeability of heartwood tissue to liquids and gases. 

Polymers are used a great deal as barriers to liquids and gases in such areas as damp-proof membranes, food packaging, and balloons. For these applications, the permeability will be a prime consideration in the selection of materials. 

Microbial synthesis of cellulosic fibres affords the opportunities to create products with unique properties suitable for practical application in human and veterinary medicine. Due to its high water absorption capacity, high mechanical strength in the wet state, substantial permeability for liquids and gases, wet cellulose can be used as a temporary artificial skin to treat severe skin burns. 

Nanocomposites based on thermoplastic matrix and containing natural, laminated inorganic structures are referred to as laminated nanocomposites. Such materials are produced on the basis of ceramics and polymers however with the use of natinal laminated inorganic structiues such as, montmorillonite or vermiculite which are present for example, in clays. A layer of filler 1 tun thick is satinated with monomer solution and later polymerized. The laminated nanocomposites in comparison with initial polymeric matrix possess much smaller permeability for liquids and gases. These properties allow applying them to medical and food processing indnstry. Snch materials can be used in manufactine of pipes and containers for the carbonated beverages. 

Permeability. The low density of plastics is an advantage in many situations but the relatively loose packing of the molecules means that gases and liquids can permeate through the plastic. This can be important in many applications such as packaging or fuel tanks. It is not possible to generalise about the performance of plastics relative to each other or in respect to the performance of a specific plastic in contact with different liquids and gases. 

Porosity bears but little connection to permeability. The permeability is a measure of the rate of diffusion of liquids and gases through the refractory. It is understandable that the... 

Polymers are permeable to liquids having similar solubility parameters. Several different celts have been designed to measure the permeability of membranes to gases and vapors. 

Because it is a saturated aliphatic hydrocarbon, LLDPE does not conduct electricity, and so is widely used for wire and cable insulation. LLDPE is poorly permeable to water and inorganic gases and only slightly more so to organic compounds, whether liquid or gas. 

Abstract In this contribution, the coupled flow of liquids and gases in capillary thermoelastic porous materials is investigated by using a continuum mechanical model based on the Theory of Porous Media. The movement of the phases is influenced by the capillarity forces, the relative permeability, the temperature and the given boundary conditions. In the examined porous body, the capillary effect is caused by the intermolecular forces of cohesion and adhesion of the constituents involved. The treatment of the capillary problem, based on thermomechanical investigations, yields the result that the capillarity force is a volume interaction force. Moreover, the friction interaction forces caused by the motion of the constituents are included in the mechanical model. The relative permeability depends on the saturation of the porous body which is considered in the mechanical model. In order to describe the thermo-elastic behaviour, the balance equation of energy for the mixture must be taken into account. The aim of this investigation is to provide with a numerical simulation of the behavior of liquid and gas phases in a thermo-elastic porous body. 

Permeable—Having small openings that allow liquids and gases to pass through. 

Other convenient units for pointwise permeability are g-moles/ cm -sec-atm/cm., applicable to both liquids and gases. The conversion for gaseous pointwise permeabihty utilizes the value of 22,414 cm (STP) per gram-mole, and a value of 76 cm Hg/atm. Thus... 

It is possible to measure the partial pressure of any gas in a mixture directly if there is a membrane that is permeable to that gas alone for example, palladium is permeable to hydrogen and certain types of glass are permeable to helium. The fact that at present only a few such membranes are known does not destroy the physical reality of the concept of partial pressure. Later it will be shown that in chemical equilibria involving gases and in physical equilibria such as solubility of gases in liquids and solids, it is the partial pressures of the gases in the mixture that are significant (further confirmation of the physical content of the concept). 

---