Controlled relative humidity

Unpigmented paint samples were brushed onto a potassium bromide crystal or polyethylene sheet (paint film thickness about 5 microns) and stored at controlled relative humidity using saturated salt solutions in closed vessels or a climate controlled room. 

Generation of water sorption/desorption isotherms in a controlled relative humidity environment can be carried out either gravimetrically or volumetrically. Gravimetric methods require... 

Methods. The wide and small angle x-ray patterns were recorded in a flat film camera at controlled relative humidity using Ni-filtered CuKa radiation generated at 40 kV and 15 mA. 

The hygroscopicity of atorvastatin calcium, Form-I, was determined by exposing the samples to controlled relative humidity (RH) conditions (21-92% RH) at ambient temperature, and after 7 days the percent weight change was recorded. The substance was found to show less than 0.1%... 

Originally, water activity could not be measured directly. One method was to measure the weight loss of a product held at a range of controlled relative humidities, which also has the effect of holding the product over a range of water activities. If a product is held at its own water activity it neither gains nor loses weight, and this point is described as its equilibrium water activity. 

Native DNAs and polynucleotides can be stretched out as films or fibers. Sealed inside cells with IR transparent windows or in glass capillaries for Raman studies, films and fibers may be expo.sed to an atmosphere with a controlled relative humidity. This is achieved by simply placing small vessels with known saturated salt solutions at the bottom of the cell or by bringing them in contact with the capillary. Changing the relative humidity induces conformational transitions in the sample (Secs. 4.7.1.3.1 and 4.7.1.3.2). Raman studies of polynucleotides have thus been correlated with X-ray diffraction results obtained from the same fibers (Erfurth et al., 1975 Goodwin and Brahms, 1978). 

Most individuals recognize hysteresis in terms of a substance having different moisture contents at a specified relative humidity (CD in Fig. 3). The implications of this situation are obvious the moisture content of a material depends on its history of exposure to different relative humidity conditions. Controlling relative humidity can only insure that the moisture content lies within the range specified by the isotherm. The other aspect of hysteresis is that substances with equal moisture contents can have adsorbed water with different chemical activity (AB in Fig. 3). 

The manufacturing process requires a very low and controlled relative humidity (about 20% or less, if necessary) as well as a controlled ambient temperature close to 25°C. Generally, effervescent powders are made by classical wet granulation of the acid and carbonate part separately or mixed with water-ethanol or isopropanol. Special care must be taken in the case of... 

Attaining and measuring an equilibrium weight of sorbed water vapor. Gravimetric measurement of moisture uptake can occur continuously or discontinuously. Continuous measurement usually involves placing a sample on a balance in a temperature- and relative humidity-controlled environment. Microbalances in closed systems have been used successfully for this purpose, " and commercial systems are now available that can accurately and precisely control relative humidity and simultaneously monitor sample weight. 

Although there is no bulk liquid with which adsorbed cations can be exchanged in the experiments made in atmospheres of controlled relative humidity, successive experiments can be made with different adsorbed cation populations, and it is found that the succession of dehydration steps varies with size and hydration energy of the cation (Posner and Quirk, 1964). There is also a dependence upon the type and extent of substitution in the aluminosilicate framework White (1958), for example, observed that two montmorillonites with the same cation-exchange capacity, loaded with the same cation, may have different water sorption and swelling properties. 

Dried slices with 10 g water/100 g sample were further equilibrated at different moisture contents in chambers at 20°C with controlled relative humidity, using saturated salt solutions P2O5 = 0, LiCl = 0.11 and CH3COOK = 0.22 (Katz and Labuza, 1981). 

Water-sorption isotherms were obtained at 30°C by keeping the samples in desiccators under the controlled relative humidity (RH) prepared with saturated inorganic salt solutions. The weight increase of the samples was measured after 3 weeks. 

For adsorption isotherms, pear cubes (10 mm X 10 mm) were frozen at — 40°C and freeze-dried (Telstar Lioalfa-6 lyophyliser) at 10 Pa. Afterwards, samples were placed in chambers with controlled relative humidity (RH) up to equilibrium was reached. Desorption isotherms were obtained in pear slices with skin (with approximately 8 cm diameter and 10 mm thickness), partially dehydrated in a conventional dryer at 45°C for different times to ensure different final water contents in the samples. After the drying treatment, samples were kept in plastic bags under refrigeration to ensure the internal moisture equilibration and then their water activity was measured. Experiments were carried out in triplicate for each sample. 

It Is very difficult to control relative humidity precisely at high temperatures and for that reason 80 and 90 C may be considered excessive. 

For the formulation, there is a significant problem of increasing the mass of powder during blending and especially for spheronisation, since a large mass can break down fragile spheres. Powder processing is usually carried out at controlled relative humidity (RH), usually <50 percent RH. 

Barrow (see above) used ageing in an oven for 72 hours at 100°C to replicate the effects of natural ageing of paper for 25 years. Nowadays, this assumption is still used, but regarded as simplistic and not applicable to all types of paper. Many laboratories prefer to perform their paper ageing in an oven at a controlled relative humidity and at a lower temperature. There is no consensus, but a... 

A gas manifold for proportioning gases and controlling relative humidity was constructed. 

S-35, a Philadelphia Quartz sodium silicate solution, into polyethylene molds (1 1/2" diameter) to a depth approximating one millimeter and storing in controlled relative humidity desiccators at room temperature. Dehydration of the S-35 solution produced solid glass samples. Thicker S-35 hydrosilicate was produced by dehydration in an autoclave to avoid wrinkled surfaces. 

Nb NbCls + template in EtOH PE-co-PB-b-PE Dip coating under controlled relative humidity (15-20 %) Calc. (600 °C)... 

Shirazi, A., Cameron, A.C. (1992). Controlling relative humidity in modified-atmosphere packages of tomato fruit. HortScience, Vol. 27, pp. 336-339. 

In order to overcome hyperhydricity, several strategies have been proposed, basically related to environmental issues that help to control relative humidity and water availability through the manipnilation of solutes in de growth medium (Maene Debergh, 1987). Plantlets with well developed leaves under low humidity and high irradiance show a photosynthetic and metabolic normal activity. 

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