Hygroscopic Coefficient

The amount of moisture taken up by a diy soil when kept in contact with an atmosphere saturated with water vapour (100% relative humidity) at a given temperature is known as the hygroscopic coefficient of the soil at that temperature and is usually expressed on the dry weight basis. 

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Figure 10.13 shows the cumulative release of pore water for three soils tested with increasing pressure (Di Bonito, 2005). The dotted line represents the pressure corresponding to the hygroscopic coefficient, that is, the upper limit for the capillary water. This illustrates the capability of squeezing to reach a wider range of pores. This pressure value should also correspond to most of the available water in the soil. 

Figure 10.13 Cumufative voiume of pore water extracted for the three soifs tested with increasing pressure the dotted line represents the pressure corresponding to the hygroscopic coefficient, that is, the upper limit for the capillary water.

Briggs and Shantz defined an upper limit of hygroscopic moisture which is determinable by experiment. If a soil is placed in a water-saturated atmosphere, it will absorb water vapor until a condition of approximate equilibrium is reached. The moisture content of a soil under these conditions is called the1 hygroscopic coefficient of that soil. Determination of the hygroscopic coefficient is subject to error unless carried out with considerable care. It has been pointed out that hygroscopic moisture is tenacious and difficult to drive off even at elevated temperatures. For this reason, and also because the equilibrium... 

Moisture-equivalent = hygroscopic coefficient X 2.71 = (moistureholding capacity — 21) X 0.635 = 0.02 percent sand + 0.22 percent silt + 1.05 percent clay Eq (14-6)... 

Moisture-holding capacity = (moisture-equivalent X 1.57) + 21 = (hygroscopic coefficient X 4.26) + 21 = 0.03 percent sand + 0.35 percent silt + 1.65 percent clay + 21 Eq (14-7)... 

Hygroscopic coefficient = moisture-equivalent X 0.37 =. (moisture-holding capacity — 21) X 0.234 = 0.007 percent sand + 0.082 percent silt + 0.39 percent clay Eq (14-8)... 

Calculate the moisture percentage at hygroscopic coefficient after oven drying at 105°C for 24 hours. 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

Hygroscopic (moisture) effects arise for polymer materials such as some epoxies that absorb moisture chemically after curing and therefore expand. These effects are directly analogous to thermal effects and are characterized by coefficients of moisture expansion and p2 in principal material coordinates in direct analogy to a.( and 02 for coefficients of thermal expansion. All calculations for thermal effects with the a can be replaced by or supplemented with analogous terms for moisture expansion. 

Thermogravimetry Hygroscopicity Solubility Characteristics Partition Coefficients Ionization Constants Micromeritic Properties... 

Tang, I. N., Chemical and Size Effects of Hygroscopic Aerosols on Light Scattering Coefficients, J. Geophys. Res., 101, 19245-19250 (1996). 

Hygroscopicity Tests. Hygroscopicity is the affinity of a substance for water vapor. It is a complex phenomenon which is controlled by the rate of diffusion of water across the vapor-liquid interface. This rate depends on temperature, surface area, liquid depth, and liquid and vapor film coefficients. Inasmuch as it is impractical to measure the effect of all these variables, simplified empirical tests have been... 

Agar gel is a hygroscopic medium for w < 60% [7], In this range, the equation (10) allows the determination of de from the chemical potential of water given by the desorption isotherm. Assuming that the two-phase structure of the medium is conserved, the coefficient (3 can be expressed by (3 = 1/3 (a I w), where a is the ratio between the specific mass of the water and the specific mass of the solid. This expression is confirmed by experimental tests (fig. 4). The coefficient Kw (fig. 5) was measured for a plate of gel placed in a PEG solution [6]. Dw and De (fig. 6) are deduced from ... 

By the time the clinical program has entered phase 3, the sponsor should provide a full description of the physical, chemical, and biological characteristics of the drug substance. For example, most of the following should be evaluated and submitted solubility and partition coefficient, pKa, hygroscopicity, crystal properties/morphology, thermal evaluation, X-ray diffraction, particle size, melting point, and specific rotation stereochemical consideration. Proof... 

Each of the components, polymer and metal, has both thermal and hygroscopic expansion coefficients which may differ between components by orders of magnitude. Thus, the very act of fabrication introduces internal stresses into the device. If permitted to act, these stresses are capable of ripping apart the device, destroying it Such destruction is prevented by strong interfacial adhesion, maintained at every step during manufacture, as well as throughout the use life of the device. 

The vitreous B2O3 is colourless, transparent and hygroscopic. It can be prepared by dehydration of H3BO3 at 266 °C —270 C under a reduced pressure of 130 — 260 Pa. The removal of water by heating H3BO3 in air is quite difficult and even the melt contains considerable amounts of residual water.The final H2O content after fusion at 700,1100 and 1200 °C is 0.25, 0.17 and 0.14% respectively (Poch, 1964). As a result of the H2O content, the data on the basic properties (e.g. those on viscosity and thermal expansion coefficient) exhibit some differences. The viscosity curve shown in Fig. 7 should serve for rough orientation only. More detailed data are reported by Bruckner (1964), for example. 

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