Parameterized Modeling of Unfrozen Water in Frozen Soil Based on the Freezing Characteristics of Multicomponent Cation Solutions and the Electrical Double‐Layer Theory of Clay Colloids

The pulsed nuclear magnetic resonance (P-NMR) method is commonly used to determine unfrozen water content in frozen soils. Traditionally, unfrozen water content is calculated using first return data from the free induction decay (FID) signal intensity (SI); however, these data may contain both ice and liquid water responses, thus overestimating unfrozen water. To address this, the authors used the normalization method for calculating unfrozen water. First, the authors refined a P-NMR testing system for greater temperature control. Next, testing using two P-NMR instruments at different facilities yielded repeatable unfrozen water measurements to within 2.6% of each other. Results from a desorption test indicated excellent agreement (with an average difference of 0.33%) between P-NMR-derived unfrozen water and physical gravimetric water content data. Finally, comparing results from the normalization method to the first return data indicated that calculated unfrozen water in a frozen soil is up to 3.3 times greater for a given temperature using the first return data versus the normalization method. Because this difference is significant, the authors recommend further investigation using an independent method to confirm the results.

To understand wintertime controls of biogeochemical processes in high latitude soils it is essential to distinguish between direct temperature effects and the effects of changes in water availability mediated by freezing. Efforts to separate these controls are hampered by a lack of adequate methods to determine the proportion of unfrozen water. In this study we present a high-field 2H2O NMR method for quantifying unfrozen water content in frozen soil. The experimental material consisted of the humic layer of a boreal spruce forest soil mixed with varying proportions of quartz sand and humidified with deuterium-enriched water. The relative standard deviation of unfrozen water content (measured as NMR signal integral) was less than 2% for repeated measurements on a given sample and 3.5% among all samples, based on a total of 16 measurements. As compared to 1H NMR, this 2H NMR method was found to be superior for several reasons: it is less sensitive to field inhomogeneity and paramagnetic impurities, it gives a bigger line shape difference between the ice and liquid signal, it shows a sharper response to water fusion, and it excludes the possibility of hydrogen in the organic material interfering with the measurement.

Unfrozen soil water affects the physical, chemical, hydrological, and mechanical properties of frozen soils, and climate change makes these relationships more complicated. The objective of this study was to investigate the research status of unfrozen soil water using scientometrics. Publications on unfrozen water in frozen soil (UWFS) retrieved from the Web of Science were analyzed with scientometric software tools including VOSviewer, CiteSpace, and HistCite Pro. The annual publication trend, co-authorship of authors, organizations, and countries, and the co-occurrence of keywords were analyzed. The most utilized journals and high-impact publications were identified. The results showed that 2007 (the year the “Bali Road Map” was released) represents a turning point (from slow to rapid) in the development of research on unfrozen water in frozen soil. Researchers and organizations from China and the United States are the major contributors, while Cold Regions Science and Technology is the most utilized journal for publishing research pertaining to UWFS. Currently, there is still a lack of reliable and user-friendly methods and techniques for measuring unfrozen water content. Future efforts are required to understand the mechanisms governing the magnitude of unfrozen water content and to develop new approaches to accurately and rapidly measure unfrozen water content in both laboratory and in situ.

Unfrozen water content significantly affects the thermal‐hydro‐mechanical characteristics of frozen soil. Currently, theoretical explanations for the presence of unfrozen water include capillary action, surface effects, adsorption forces, and the electrical double layer. However, the relationships between unfrozen water and these actions are not well explained, except for capillary forces. In addition, although frost heave experiments indicate that the electrical double‐layer solution on a clay particle contains the main portion of unfrozen water, the electrical double‐layer theory which produces a cation solution has not previously been used to calculate unfrozen water content. In this paper, it is assumed that the residual unfrozen water at very low temperatures (below −18°C) is held within the adsorption‐layer solution and that the remaining unfrozen water within the influence of surface effects is the cationic solution in the diffuse layer. Based on these assumptions, a theoretical model of unfrozen water is established with independent variables of temperature, specific surface area, and electrical double‐layer parameters. While the input parameters of the theoretical model are numerous and difficult to obtain, the theoretical model is simplified as a parametric model. Results of the parametric model are strongly consistent with experimental data within a certain temperature range, supporting the hypothetical conditions. The similarity in the underlying mathematical structure of the derived theoretical and parametric models to current semi‐empirical models further suggests that the surface effects of clay are the main causes of unfrozen water in frozen soil.

Controlling the hardness of ice cream, gelato and similar frozen desserts

Extreme low-temperature freezing process and characteristic curve of icy lunar regolith simulant

A simplified freezing point depression (FPD) equation was derived for calculating water activity (a w ) of food systems. The a w values as calculated by FPD data agreed with literature data for a variety of foods to within ± 0.01 a w units. The FPD equation was found particularly useful for calculating a w values of frozen foods at temperatures between 273.1.5–233.15 °K (0 to −40°C).

Measurement of unfrozen water content and relative permittivity of frozen unsaturated soil using NMR and TDR

Core Ideas A triaxial apparatus is developed to measure stress‐dependent SFCC. Unfrozen water content of clay and sand increases with increasing confining stress. Stress effects on the SFCC of clay are more significant than sand. The soil freezing characteristic curve (SFCC) defines the relationship between soil temperature and unfrozen water content. This curve is important for predicting water flow and heat conduction in frozen soils, as well as freezing heave and thawing settlement. So far, SFCCs reported in the literature were usually determined at zero stress. To investigate stress effects on SFCC, a stress‐ and temperature‐controlled triaxial apparatus was developed in this study. The unfrozen volumetric water content was measured using a newly developed noninvasive time domain reflectometry (TDR) probe. The new apparatus was used to measure SFCCs of two typical soils (i.e., clay and sand) at different stress conditions (i.e., 30, 100, and 200 kPa). Each specimen was subjected to compression, and then a cycle of freezing and thawing. As expected, for both soils, the saturated water content prior to freezing was smaller at higher stresses because of compression. During the subsequent freezing and thawing, the soil specimen at a higher stress was able to retain more liquid water than that at a lower stress. The higher unfrozen water retention capacity at higher stresses is mainly because the pore size of a soil specimen becomes smaller during compression. Hence, more water can retain a liquid state due to the enhanced capillarity. On the other hand, stress effects on the SFCC were found to be more significant for clay than for sand. This is likely because the stress‐induced change in pore size distribution is larger in clay due to its higher compressibility.

An extended equation was derived relating the relative partial molar free energy of water in a soil to its freezing point depression and relative partial molar heat content. The equation was used to prepare a table from which each of these three quantities can be ascertained if the other two are known. The table was used with experimental data to obtain a curve of freezing point depression versus water content for Na‐Wyoming bentonite. Provided the activity of the liquid water in the clay is a single‐valued function of the liquid water content, and that the ice has the properties of pure bulk ice, this curve also represents the relationship between freezing point depression and unfrozen water in the partially frozen clay. An equation for the heat capacity of a partially frozen soil was also derived. This equation was employed to calculate the heat capacities of the clay at different water contents and sub‐zero temperatures. A comparison of the calculated unfrozen water contents and heat capacities of the partially frozen Na‐Wyoming bentonite with the available experimental data indicated satisfactory agreement, especially as regards the unfrozen water contents.

The aim of the study was to investigate the effect of oil-salt pollution on moisture due to unfrozen water in clay and to identify methodological peculiarities when working with soils containing oil. The object of the study was a model clay soil, and tests were conducted on model samples. The research was conducted for "clean," saline, and oil-contaminated soils, as well as soils with oil-salt pollution. The authors pay special attention to aspects such as the preparation of soil pastes, as laboratory modeling of such a complex system as "soil-water-ice-salt-oil" is associated with a number of methodological peculiarities. The authors also highlight the requirements and methods traditionally used in conducting engineering and geological surveys in accordance with regulatory documentation. The tests were carried out using standard contact and cryoscopic methods. For comparison, tests were conducted using nuclear magnetic resonance (NMR) method. The moisture due to unfrozen water in a wide temperature range for soils with oil-salt pollution was investigated for the first time. When examining this characteristic, not only was the dependence of unfrozen water content on temperature obtained, but the limitations of standard methods for determining moisture due to unfrozen water were also identified. It was established that the contact method for determining moisture due to unfrozen water cannot be applied when investigating unsalinated and saline soils containing oil. To obtain correct results, methods should be used that do not change the ratio of oil, water (or solution), and ice. The results of the cryoscopic and NMR methods showed that the effect of oil-salt pollution on the content of unfrozen water is identical to the effect of salinity, with a discrepancy of less than 8%.

Study on the Unfrozen Water Quantity of Maximally Freeze-Concentrated Solutions for Multicomponent Lyoprotectants

Mainly located in the Sichuan Basin, known as the ‘Land of Plenty’, purple soils (developed from purple sandstone and shale) have been long noted as highly productive in spite of their rocky texture. However, information on the physicochemical properties (including mineral properties) of purple soils remained obscure for the scientific community. For example, it is not clear what causes the purple color of the soils. In this study, eight soil profiles of the Jiufeng (JF, acidic), Shibao (SB, neutral), and Yanting (YT, calcareous) areas, representing the three most widely distributed purple soils in Sichuan Basin, were individually sampled under both cropland and forestland, and then analyzed using common chemical analysis and conventional X-ray diffraction to clarify the effects of clay mineral and anthropogenic influences on the typical soils. The results show that considerable variability of soil pH and cation-exchange capacity (CEC) exists between soil types (p < 0.05). Organic matter, total nitrogen, and CEC of forestland are higher than those of farmland, while farmland has a higher content of Olsen-P, indicating significant farming effects on nutrient status. Acidic and neutral purple soils had higher total P contents than calcareous soils while calcareous soils had higher TN, clay, and CaCO3 contents. OM, TN, TP, and Olsen-P decreased with soil depth both in farmland and forestland soil profiles. Vertical distribution of organic-bound Fe-oxides (Fep) and clay particles also shows the anthropogenic interference on farmland. Illite, chlorite, kaolinite, goethite, and trace amounts of an illite–chlorite mixing layer in clay fractions were identified for typical purple soils. Hematite was observed in the coarser fractions of the calcareous pedons, confirming that the purple soil color was mainly derived from the parent rocks. Understanding of the physicochemical properties and mineral species of soil profiles can shed light on the sustainable uses of typical purple soils in subtropical area.

The unfrozen water content and its distribution are of importance to the macro mechanical behaviors of frozen soil. In this study, the phase field method was used to deeply investigate and model the evolution of the microstructure of different saturated soils during the freezing process. Particle size distribution and freezing point depression were considered in the simulation of freezing of the soil. The soil freezing characteristic curves of the soil with different particle sizes were well predicted by the phase field method. Moreover, the unidirectional freezing test was used to validate the proposed method. The simulation results successfully predicted the inhibition effect of soil particles on the spread of pore ice during the cooling process. A series of mesoscale characteristics can be well simulated, such as unfrozen water film, retardation effect of soil particles, nonhomogeneous freezing front, and isolated ice and unfrozen water. Our results provide a deeper insight into the freezing process of porous media, including the formation of pore ice, and the movement of the freezing front on a mesoscale.

The freezing and moisture characteristics of porous media are difficult to measure. We have designed an instrument to measure the freezing characteristic of a porous medium in the range −20 to 0°C. Because of the similarity between the freezing characteristic and the moisture characteristic, the data obtained can be used to infer the moisture characteristic from about −30 to −23,600 J kg−1. Temperatures and unfrozen water contents are measured with a thermistor and a spiral‐shaped transmission line connected to an oscillator, respectively. Temperatures are converted to water potential using the Clapeyron equation. Experimental results obtained with the freezing technique were compared with vapor pressure methods. The four test media used, a silt loam soil, a silty‐clay loam, a clay, and a sandstone, showed good agreement between freezing and standard methods. The freezing technique described here has a water potential resolution of about −11 J kg−1. An entire characteristic can be determined within 24 hours.