Moisture, in solids

Pypee JW (1985) The determination of moisture in solids - a selected review. Anal Chim Acta 170 159-175. 

Very little is known about the resistance to flow of moisture in solids. If this problem were to be solved, it would be possible to design driers for material where the major resistance is in the solid phase. 

Moisture. In NIR, as in the MIR, water has the strongest absorption of light. It stands to reason that moisture in solid products would be an important assay. For instance, Warren et al. used NIR to determine the amount of water in glycerides. Transmission spectra of standard... 

Moisture in solid that exerts vapor pressure equal to that of pure liquid at the same temperature. 

The dififusivity of moisture in solids is a function of both temperature and moisture content. For strongly shrinking materials, the mathematical model used to define must account for the changes in diffusion path as well. The temperature dependence of diffusivity is adequately described by the Arrhenius equation as follows ... 

Moisture in solids such as wood, foods, and textiles can be measured. However, such determinations are more often made by instruments designed to directly measure the dielectric changes between two parallel plates of a condenser. 

Moisture in solid sugars is determined generally by oven drying in liquid products, by Karl Fischer titration. Inorganic content is determined by either conductivity in solution, or sulfated ash gravimetric procedures. 

Bound moisture in a solia is that hquid which exerts a vapor pressure less than that of the pure hquid at the given temperature. Liquid may become bound by retention in small capillaries, by solution in cell or fiber walls, by homogeneous solution throughout the sohd, and by chemical or physical adsorption on solid surfaces. 

Capillary Flow Moisture which is held in the interstices of solids, as liquid on the surface, or as free moisture in cell cavities, moves by gravity and capiUarity, provided that passageways for continuous flow are present. In diying, liquid flow resulting from capiUarity appUes to liquids not held in solution and to aU moisture above the fiber-saturation point, as in textiles, paper, and leather, and to all moisture above the equiUbrium moisture content at atmospheric saturations, as in fine powders and granular solids, such as paint pigments, minerals, clays, soU, and sand. 

Liquid Diffusion The movement of liquids by diffusion in soUds is restricted to the equihbrium moisture content below the point of atmospheric saturation and to systems in which moisture and solid are mutually soluble. The first class apphes to the last stages in the diying of clays, starches, flour, textiles, paper, and wood the second class includes the diying of soaps, glues, gelatins, and pastes. 

Special designs of direct rotaiy dryers, such as the Renneburg DehydrO-Mat (Edward Renneburg Sons Co.), are constructed especially to provide lower retention during the falling-rate diy-ing period for the escape of internal moisture from the solids. The DehydrO-Mat is a cocurrent diyer employing a smaU-diameter shell at the feed end, where rapid evaporation of surface moisture in the stream of initially hot gas is accomplished with low holdup. At the solids- and gas-exit end, the shell diameter is increased to reduce gas velocities and provide increased holdup for the solids while they are exposed to the partially cooled gas stream. 

Moisture content. The moisture content of solid wastes usually is expressed as the mass of moisture per unit mass of wet or diy material. In the wet-mass method of measurement, the moisture in a sample is expressed as a percentage of the wet mass of the material in the diy-mass method, it is expressed as a percentage of the diy mass of the material. In equation Form, the wet-mass moisture content is expressed as follows ... 

One part by weight of propyl-methyl-carbinyl allyl barbituric acid is added to enough alcohol to facilitate handling, in this case conveniently about six times its weight. To this is added a solution of sodium hydroxide, preferably carbonate-free or substantially so, containing °%38 parts by weight of sodium hydroxide, which is the amount of sodium hydroxide necessary to combine in equal molecular proportions with the propyl-methyl-carbinyl allyl barbituric acid. This solution is filtered clear, and is then evaporated under vacuum until the sodium propyl-methyl-carbinyl allyl barbiturate (alternatively named sodium allyl 1-methyl-butyl barbiturate) separates out in solid form. The salt as thus obtained in solid form contains a varying amount of moisture. 

Many of the compounds in higher oxidation states are reactive, and for moisture-sensitive solids that cannot be crystallized, some of the bond lengths quoted in Table 2.1 are from EXAFS measurements [24], Raman spectroscopy is likewise well suited to studying such reactive compounds, and vibrational data for halometallates are given in Table 2.2 trends illustrated include the decrease in frequency as the oxidation state of the metal decreases, and similarly a decrease in vibrational frequency, for a given oxidation state, with increasing mass of the halogen. 

In solid form, Mg is difficult to ignite because heat is conducted rapidly away from the source of ignition it must be heated above its mp before it will bum. However, in finely divided form it may be ignited by a spark dr the flame of a, match. Mg fires do not flare up violently unless there is moisture present. Therefore it must be kept away from w, moisture, etc. It m y. be ignited by a spark, match flame, or even spontaneously when the Mg is finely divided and damp, particularly with w-oil emulsion. Also, Mg reacts with moisture, acids, etc to evolve H2 which is a highly dangerous fire arid explosion hazard (Ref 23)... 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Figure 5 Pectinase activity in solid substrates of wheat bran, rice bran and rice husk at different ratios of substrates. Initial moisture content 66 % Incubation temperature 32°C Initial pH 5.7...

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