Measurement of bound water

The and Na" are present in the cement partly as sulphates and partly in the major clinker phases (Section 3.5.6). When the phases containing them react, the accompanying anions enter products of low solubility and equivalent quantities of OH are produced. The K, Na and OH" ions are partitioned between the pore solution and the hydration products. Early estimates of the fractions remaining in solution were too high because non-evaporable water was used as a measure of bound water and the quantity of pore solution thereby overestimated. 

NMR (Nuclear Magnetic Resonance) (i> > ) This technique detects the mobility of protons in various energy states. The hydrogen atoms in bound water are at different energy levels than the hydrogen atoms in free water. These energy levels are measured and recorded in the form of NMR spectra. The bound water can be calculated from the NMR spectrum. NMR measurements may be done at any temperature. While NMR may be the most basic method for the measurement of bound water, it requires expensive equipment, trained personnel, and considerable preparation for each experiment. These requirements are not frequently available to the researcher in the paper industry. 

The phenomenon of non-freezing water is well documented and is often considered as a measure of bound water. Typically the amount of non-freezing water is a strong function of initial water content. This appears inconsistent with the bound water concept as it would be expected that, above the bound water threshold, the amount of bound water, hence non-freezing water, would remain constant. An alternative model is one in which that non-freezing water arises because the biopolymer/water system is not at thermodynamic equilibrium. As the system is cooled water crystallises out and, if it were an equilibrium S5 tem, at sufficiently low temperatures biopolymer would crystallise out in a eutectic. 

Thermogravimetric analysis (TGA) is a widely applied technique in the field of cement science. Measurements of bound water and portlandite content by TGA are often used to follow the reaction of portland cement or to evaluate the reactivity of supplementary cementitious materials (SCMs), such as fly ash and blast furnace slags. TGA is able to identify X-ray amorphous hydrates, such as C-S-H or AHj, and can be used complementarily to other techniques such as X-ray diffraction (XRD). 

The relative error of measurement of bound water or the amount of hydrates between several independent preparations of hydrated cement paste is observed to be between 5% and 10% (Deschner et al. 2012 Gruskovnjak et al. 2011 Lothenbach and Winnefeld 2006). This error is related to the heterogeneity of the paste samples and the relative small amount weighted in, typically 10 to 50 mg and to the errors introduced by the deconvolution of the TGA as discussed in Section 5.4.4. Because of the heterogeneity even in paste samples, a minimal weight of approximately 50 mg is recommended for hydrated cement paste samples. 

A typical field test involves several steps (a) transporting the mobile unit to the site (b) instrument warmup (c) system check out, consisting of mobile unit measurements of distilled water and a 1-ppm stock phenol solution and (d) in situ measurements of the well water, repeated three times for statistical analysis. Signal levels recorded at a field site may be reported as equivalents of phenol (or other calibrant) using the calibration curves. Therefore, this method allows us to report the upper bounds of pollution levels. 

According to TG and TGA measurements for all obtained samples (Figure 2) two steps of mass loss were observed. The first step in 80-190°C temperature range is an effect of bound water loss ... 

It should be clear that the RM measured in this way, e. g. 0,1 %, must not be identical with residual moisture contents measured with other methods (see Section 1.3.1) because there will be always some water which cannot be desorbed at the end temperature of the drying. This content of bound water for one product and one temperature is a stable value which can be taken from the measurements of absorption isotherms. 

Slade, L. and Levine, H. 1985. Intermediate moisture systems concentrated and supersaturated solutions pastes and dispersions water as plasticizer the mystique of bound water thermodynamics versus kinetics (Number 24). Presented at Faraday Division, Royal Society of Chemistry Discussion Conference - Water Activity A Credible Measure of Technological Performance and Physiological Viability Cambridge, July 1-3. 

The Flory-Huggins interaction parameter, x, indicates the water affinity of the polymer while Ch is a measure of the fraction of bound water in the... 

The mole fractions of labeled water at t = 0 and at equilibrium are noted as Xq and Xoo, respectively (Pig. 4). In the end, the signal of bound water becomes small and difficult to quantify. But, this does not influence the quality of the measured rate constant because the mole fraction at equilibrium, x, is known from the concentration of the metal ion and the coordination number. These experiments can be performed at variable temperature and at variable pressure to obtain activation enthalpies and entropies as well as activation volumes. 

The chemical shift measured on the bulk water signal and normalized by the mole fraction of bound water, Pm, is given by Eq. (10), where m and mA are the observed chemical shifts with and without the paramagnetic compound and ffios is the shift originating from water molecules outside the first coordination shell. 

Water in food products can be described as being free or bound. The definition of what consitiutes bound water is far from clear (see Fennema, 1985) but it can be considered as that part of the water in a food which does not freeze at — 40°C and exists in the vicinity of solutes and other non-aqueous constituents, has reduced molecular mobility and other significantly altered properties compared with the bulk water of the same system (Fennema, 1985). The actual amount of bound water varies in different products and the amount measured is often a function of the assay technique. Bound water is not permanently immobilized since interchange of bound water molecules occurs frequently. 

Moisture in coal takes three forms (l)free or adherent moisture, essentially surface water (2) physically bound or inherent moisture (thai moisture held by vapor pressure and other physical processes) and (3) chemically bound water (water of hydration or combined" water). The ASTM defines total moisture as a loss in weight in an air atmosphere under rigidly controlled conditions of temperature, time, and air flow. Total moisture represents a measurement of all water not chemically combined. Total moisture is determined by a two-slep procedure, involving air-drying for removal of surface moisture from the gross sample, division and reduction of Ihc gross sample, and determination of residual moisture in the prepared sample. An algebraic calculation is used to obtain the total moisture value. 

The structure proposed by Bradley (1940) has three forms of water a zeolitic water, bound water (at the edges of the octahedral sheet), and structural hydroxyls. Using thermogravimetric curves, Caillere and Henin (1961a) attempted to measure the amount of these three types of water for several attapulgites (Table LV). The amount of bound water and hydroxyls differs considerably from that calculated on the basis of the ideal structure (column 5) and suggests there are more structural hydroxyls than proposed for the ideal structure. 

Characteristic frequencies may be found from dielectric permittivity data or, even better, from conductivity data. The earlier data by Herrick et al. (6) suggest that there is no apparent difference between the relaxation frequency of tissue water and that of the pure liquid (7). However, these data extend only to 8.5 GHz, one-third the relaxation frequency of pure water at 37°C (25 GHz), so small discrepancies might not have been uncovered. We have recently completed measurements on muscle at 37°C and 1°C (where the pure water relaxation frequency is 9 GHz), up to 17 GHz. The dielectric properties of the tissue above 1 GHz show a Debye relaxation at the expected frequency of 9 GHz (8 ) (Figure 3). The static dielectric constant of tissue water as determined at 100 MHz compares with that of free water if allowance is made for the fraction occupied by biological macromolecules and their small amount of bound water (1, 9). 

Weight loss determinations associated with the loss of bound water were obtained in the course of gravimetric adsorption studies of various vapors on these surfaces. Quartz springs of 250-mg. capacity and sensitivities near 1 mg. per mm. were used in the above system. Outgassing in the 300° to 400° C. temperature range required 4 to 9 days to obtain the required low pressure measurement. 

Table 23.1a. Fraction of bound water in hen egg white lysozyme and hemoglobin as measured by different experimental techniques [810]... 

The hydration of starch evokes thermal effects which are obviously also dependent on the starch variety. This is true because the external temperature does not affect426 the macrostructure and microstructure of starch below 140°C. An estimation of the heat of sorption is useful in determining the concentration of bound water.426-434 The heat of adsorption ranges from 0.255 to 0.100 kJ/mol and depends not only on the variety of starch, but also on the mode of drying of starch prior to measurement (Table XVIII).426... 

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