Relative humidity effects conductivity

Antistatic agents require ambient moisture to function. Consequently their effectiveness is dependent on the relative humidity. They provide a broad range of protection at 50% relative humidity. Much below 20% relative humidity, only materials which provide a conductive path through the bulk of the plastic to ground (such as carbon black) will reduce electrostatic charging. 

Schmidt and Anderson (op. cit.) and Anderson [Physics, 3, 23 (July 1932)] claim that resistivity of the collected dust may be a controlling factor which is very sensitive to moisture. They state that an increase in relative humidity of 5 percent may double the precipitation rate because of its effect on the conductivity of the collected dust layer. 

Trace contaminants are also significant at charged solid surfaces, affecting both the charging process and the surface conductivity. In ambient air atmospheres their effect is often determined by interaction with adsorbed water vapor, whose dominant concentration may be sufficiently large to form a monolayer. Topical antistatic agents for solids typically rely on interaction with adsorbed water and can lose effectiveness at low relative humidity (4-2.1). 

The effect of Oj, SOj, NOj, HjS, CI2, CO and NH3 on Sn/50%Pb in atmospheres of different relative humidity were investigated but only SO2 and NO2 were active at low concentrations (<100 ppm). An XPS study of Sn/50 7oPb solder exposed to O2, HjO and NO2 was conducted to establish both the surface species formed and the ratio of the concentration of each metal in the surface. Previous XPS studies had only considered the interaction of tin/lead solder with the air . 

Kagawa and Toyama in Tokyo followed 20 normal 11-yr-old school children once a week from June to December 1972 with a battery of pulmonary-function tests. Environmental factors studied included oxidant, ozone, hydrocarbon, nitric oxide, nitrogen dioxide, sulfur dioxide, particles, temperature, and relative humidity. Temperature was found to be the most important environmental factor affecting respiratory tests. The observers noted that pulmonary-function tests of the upper airway were more susceptible to increased temperature than those of the lower airway. Although the effect of temperature was the most marked, ozone concentration was significantly associated with airway resistance and specific airway conductance. Increased ozone concentrations usually occur at the same time as increased temperature, so their relative contributions could not be determined. 

Eontanella and co-workers studied the effect of high pressure variation on the conductivity as well as the H, H, and O NMR spectra of acid form Nafionl 17 membranes that were exposed to various humidities. Variation of pressure allows for a determination of activation volume, A V, presumably associated with ionic and molecular motions. Conductivities (a) were obtained from complex electrical impedance diagrams and sample geometry, and A V was determined from the slope of linear isothermal In a versus p graphs based on the equation A E = —kJ d In a/d/j] t, where p is the applied pressure. At room temperature, A Ewas found to be 2.9 cm mol for a sample conditioned in atmosphere and was 6.9 cm mol for a sample that was conditioned in 25% relative humidity, where the latter contained the lesser amount of water. 

The effect of humidity on conductivity of thin films of poly(dG)-poly(dC) and poly(dA)-poly(dT) in air was also investigated. It was found that above 20% relative humidity (RH) the conductance increases exponentially with RH [68]. It was concluded that the resistance of the films is not determined by that of the DNA, but rather by conduction through the hydration layers surrounding the DNA molecules in the film [68]. 

Coefficients of friction between several polymers and different surfaces are listed in Table 2.19 [49]. However, when dealing with polymers, the process of two surfaces sliding past each other is complicated by the fact that enormous amounts of frictional heat can be generated and stored near the surface due to the low thermal conductivity of the material. The analysis of friction between polymer surfaces is complicated further by environmental effects such as relative humidity and by the likeliness of a polymer surface to deform when stressed, such as shown in Fig. 2.65 [49], The top two figures illustrate metal-metal friction, wheareas the bottom figures illustrate metal-polymer friction. 

Schatz and Koopman (1990) reported on the Hawk series, 87 tests conducted at the DOE Nevada test site. These experiments were large-scale chamber releases of HF, as well as laboratory experiments. The objective of these tests was to study the effect of the water-to-HF ratio, water spray geometry, water application via a fire monitor, acid type (anhydrous HF and alkylation unit acid (AUA)), acid temperature and pressure, water additives, relative humidity, wind speed, and steam as an acid jet dispersant on HF removal efficiency. Figure 4.2 shows removal efficiencies ranging from 25 to 90% for water-to-HF volumetric flow ratios ranging from 6 1 to 40 1. Fire monitors provided removal efficiencies comparable to those of water sprays. Some of the conclusions reached by the authors were ... 

Occlusion of the skin, seen with application of water-impermeable drug vehicles or patches, alters the rate and extent of toxicant absorption. As the skin hydrates, a threshold is reached where transdermal flux dramatically increases (approximately 80% relative humidity). When the skin becomes fully hydrated under occlusive conditions, flux can be dramatically increased. This occlusive effect must be accounted for when extrapolating toxicology studies conducted under occlusive conditions to field scenarios where the ambient environmental conditions are present. Hydration may also markedly affect the pH of the skin, which varies between 4.2 and 7.3. Therefore, dose alone is often not a sufficient metric to describe topical doses when the method of application and surface area become controlling factors. Dose must be expressed as mg/cm2 of exposed skin. 

Experiments conducted in the large 335-ft irradiation chamber also showed that in most cases the effect of ambient concentrations of CO on the oxidation rate of NO to NO2 is negligible. The results for three series of runs, one involving only paraffins, one involving paraffins and more reactive hydrocarbons, and one involving no hydrocarbons, are shown in Table III. The various hydrocarbons and their relative concentrations were chosen to represent the Los Angeles atmosphere as determined by Kopczynski and co-workers 14). All runs were conducted at 50% relative humidity. 

Another factor augmectting the heat conductivuty of plastic foams under conditions is the absorbed moisture. For example, for CCljF-foamed polyurethane at 25 °C and a relative humidity of 65%, the ambient moisture diffusion rate is 10-20 g/m for 24 h. Especially strong is the effect of moisture on heat conductivity if the temperature differential across the sample is considerable. For example, in plastic foams used in cryogenic technology, the inner layers are exposed to low temperatures the water vapor first condenses and is then convected into ice. Since the thermoconductivity of water and ice are 0.5 and 1.5 kcal/m x h °C, respectively, even minor tunounts have a considerable detrimental effect of the heat insulating capacity of a foam material... 

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