Relative humidity bentonite

The reaction of neomycin with many compounds has been described in Section 3, hence numerous reports of neomycin incompatibility may be expected. Dale and Rundman have extensively reviewed the compatibility of neomycin with substances that may be encountered by the formulation pharmacist. Kudalker et al 03 have described the incompatibility of the antibiotic with rancid oils, and the incompatibility with bentonite, a montomorill-onite clay, has been reported by Danti and Guth306. The incompatibility with lactose, causing a discoloration of the mixture has been studied by Hammouda and Salakawy- 0 . The amount of browning produced was shown to be dependant on the initial pH of the solution. The rate of discoloration of the lactose/neomycin powder was directly related to the temperature of storage and the relative humidity of the atmosphere. Discoloration was overcome by addition of sodium bisulphite. 

Insoluble solids, regardless of particle size, that have a relatively low interfacial tension and are readily wetted by water are called hydrophilic solids. These solids include clays (bentonite, kaolin, talc, magnesium aluminum silicate) bismuth salts, barium sulfate, carbonates, hydroxides, or oxides of calcium, magnesium, zinc, and aluminum and titanium dioxide. The hydro-philicity of a powder surface can be investigated with the help of moisture absorption studies in which the solid particles are exposed to varying relative humidities. Insoluble powders that absorb moisture below relative humidities of 70-80% at room temperature are said to be hydrophilic solids. 

Based on the characterization of the bentonite and on the details of the process of test installation, a thermo-hydro-mechanical model for the bentonite barrier and the heaters was to be prepared. Using this model, the thermo-hydro-mechanical response of the bentonite barrier as a result of the heat released by the heaters and the hydration from the host rock was required. Local field variables such as temperature, relative humidity, pore water pressure, stresses and displacements, as well as global... 

The three fully coupled models (CNS, SKI, and SKB) behaved in general terms in a quite satisfactory manner. They predicted quite accurately the evolution of relative humidities inside the barrier. Stress prediction, however, has proved to be a more difficult task. There is always some concern about the actual reliability of measuring procedures. It appears that the measured radial stresses, which are essentially induced by the progressive hydration of the bentonite, are higher and develop faster than predictions, especially at the end of the considered period. 

Abstract Coupled THM simulation of the FEBEX, which is the full-scale in-situ Engineered Barrier System Experiment performed in Grimsel Test Site in Switzerland, is one Task in the international cooperation project DECOVALEX III. In the Task, the simulation of the thermal, hydraulic and mechanical behaviour in the buffer during heating phase is required, e.g. the evolutions and the distributions of stress, relative humidity and temperature at the specified points in bentonite buffer material. 

Figure 8 shows the variation in relative humidity as function of time in the section of El in bentonite. In the section of El, the measured relative humidity near the point of the surface of heater... 

Figure 8 presents simulated and measured evolutions of the moisture content (relative humidity) at three points located along a vertical monitoring section between the two heaters (HG, HC and HH in Figure 7). Figure 8 shows that the wetting of the bentonite starts at the drift wall (Point HG located a few centimeters from the rock surface) as soon as the bentonite is installed in that section. At this monitoring point, the relative... 

At point HH, condensation of vapor caused a slight wetting during the first 100 days. For the period between 100 to 300 days, the water content decreased slightly because of drying induced by the heat. After 3(X) days, the relative humidity increased again as a result of capillary driven liquid flow from the outer regions of the bentonite. 

The space between the drift and the heaters is fdled by blocks of compacted bentonite with a smectite content in the range of 88%-96%. The test is heavily instrumented with measurements of temperatures, relative humidity (equivalent to total suction), pore pressures, displacements, and stresses. 

Based on the characterization of the bentonite and the granite a 2D model which represents a cut through heater 2 has been applied to model the saturation process of the bentonite. The evaporation of water in the vicinity of the heaters has been modelled with a boundary condition for saturation evaluated from the measured relative humidity evolution. As this approach does not represent the phase transitions this model can just give an impression of the saturation process. Figure 8 shows the calculated distributions of saturation and temperature in the bentonite 1000 d after the heaters have been turned on. 

After the installation of each heater, the bentonite blocks, the instrumentation and backfilling of the surrounding area, the corresponding system was switched on. That is, heaters were turned on according to the installation time schedule. First heater started last September 2001 (Goudarzi Bbrgesson, 2003). Since that dale, temperature, relative humidity, total pressure and water pressure from the instrumentation have been collected. 

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