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1.
The understanding of the temporal and spatial dynamics of soil moisture and hydraulic property is crucial to the study of several hydrological and ecological processes. Karst environments are extremely fragile because of thin soil and small soil water holding capacity. A marked intensification of agricultural land use and deforestation due to increase of population and thus expansion of agricultural areas has made the karst environment even more delicate. In this study, the soil moisture contents (SMC) and hydraulic conductivities (K) along four karst hillslopes were measured in situ by time domain reflectometry and the Guelph Permeameter, respectively, at test plots, each of which has a different vegetative cover, landform, land surface slope, soil property and content of rock fragment. The statistical results from the measurements show that land cover changes strongly affect the distribution of soil moisture and hydraulic properties. Compared with SMC in the bare soil areas, SMC values are 30.5, 20.1 and 10.2% greater in the forest, shrub and grass areas, respectively. Vegetation roots significantly increase permeability of low-layer silt soils. Measured K values were 0.8, 0.6 and 0.01 cm/min for the forest, agriculture and bare soil areas, respectively. When the forest was destroyed by fire or cut to become an agricultural area or bare soils, SMC would be reduced by 13.1 and 32.1%, respectively. If deforestation leads to strong rock desertification, SMC was reduced by 70%. Bedrock fractures significantly reduce the SMC in the overlying layer, but increase K values. SMC values of 30–45% would be reduced to 17–30% for the soil layer embedding rocks with and without fractures, respectively. K values could be increased from 1.0 to 8.5 cm/min. SMC are sensitive to terrain. A slope angle increase of 1° would reduce SMC about 0.82%. These changes resulting from land cover and land use alterations offer useful information to further investigate the response of ecosystem evolution to hydrodynamic processes.  相似文献   

2.
Calculated phase equilibria involving minerals and H2O–CO2–NaCl fluid lead to predictions of how infiltration of rock by H2O–NaCl fluids with X NaCl in the range 0–0.3 (0–58 wt% NaCl) drives the reactions calcite + quartz = wollastonite + CO2 and dolomite = periclase + calcite + CO2. Calculations focus on metamorphism in four aureoles that together are representative of the normal P–T conditions and processes of infiltration-driven contact metamorphic reactions. The effect of salinity on the spatial extent of oxygen isotope alteration was also computed. The time-integrated input fluid flux (q°) that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing X NaCl. For input fluids with salinity up to approximately five times that of seawater (X NaCl ≤ 0.05), values of q° required to explain the spatial extent of decarbonation reaction are no more than 1.1–1.5 times that computed assuming the input fluid was pure H2O. For more saline fluids, values of q° may be up to 1.4–7.9 times that for pure H2O. Except for reaction in the presence of halite and vapor (V), infiltration of H2O–NaCl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction. The expansion is significant only for saline fluids with X NaCl ≥ ~0.1. Immiscible fluid phase separation and differential loss of the liquid (L) or V phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of L or V. Decarbonation reactions driven by infiltration of fluids with even modest seawater-like salinity can explain the occurrence of salt-saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks.  相似文献   

3.
This paper presents the results of laboratory experiments showing the effects of rock fragments contained in three different purple soils of the Sichuan basin of southwest China. The experiments investigated how these rock fragments alter the soil’s physical, chemical, and agronomical characteristics such as infiltration and evaporation. We found that the infiltration rate, whether horizontal or vertical, in the three soils has the following order: gray brown purple soil < reddish brown purple soil < brown purple soil. With increasing rock fragment contents the accumulated infiltration decreases, while the total time decreases first and then increases. The minimum occurs at approximately 10–20% of fragment content by weight. The infiltration rate also changes with the distance. In the 0–5 cm range, the initial infiltration rate increases with increasing rock fragment contents, while in the 5–10 cm range, the slope of infiltration curve increases with increasing rock fragment contents. With increasing distance, the slope gradually decreases and finally reaches a stable value. The presence of rock fragments reduces soil water content, the minimal value appearing when the rock fragments were on top of the soil column (soil + rock sample), decreasing with increasing rock fragments for other samples mixed with fragments. Under the constant 40°C temperature, the accumulated evaporation and evaporation rate are minimal for soils covered by rock fragments, and the accumulated evaporation decreases with increasing rock fragment for other soil samples. However, the evaporation rate increases with increasing rock fragments in the first 4 days and decreases thereafter.  相似文献   

4.
Diagenetic effects upon the hydraulic parameters of dolomite aquifers were examined. Results indicate that dolomites affected only by late (burial) diagenesis are economically more interesting to exploit than those formed first by early and then also affected by late diagenesis, as the values of most studied hydraulic parameters (transmissivity, specific capacity, linearized specific capacity and maximum yields) are higher in the former group. Data were collected from the hydrogeological reports of 298 wells in dolomites from Permian to Cretaceous age in Slovenia, classified in a relational hydrogeological database and analyzed by statistical methods. The studied parameters are hydraulic conductivity K, transmissivity T, specific capacity q (=Q/s), linearized specific capacity Ql (=q/d) and maximum yields Q max. Values of the studied parameters are distributed log-normally according to most normality tests and span several orders of magnitude. Statistical tests show significant differences between the “late” and “early + late” groups for parameters q, Ql and T, and non-significant differences for K and Q max.  相似文献   

5.
The thermoelastic parameters of synthetic Ca3Al2Si3O12 grossular garnet were examined in situ at high-pressure and high-temperature by energy dispersive X-ray diffraction, using a Kawai-type multi-anvil press apparatus coupled with synchrotron radiation. Measurements have been conducted at pressures up to 20 GPa and temperatures up to 1,650 K: this P, T range covered the entire high-P, T stability field of grossular garnet. The analysis of room temperature data yielded V 0,300 = 1,664 ± 2 ?3 and K 0 = 166 ± 3 GPa for K￠0 K^{\prime}_{0} fixed to 4.0. Fitting of our P–V–T data by means of the high-temperature third order Birch–Murnaghan or the Mie–Grüneisen–Debye thermal equations of state, gives the thermoelastic parameters: (∂K 0,T /∂T) P  = −0.019 ± 0.001 GPa K−1 and α 0,T  = 2.62 ± 0.23 × 10−5 K−1, or γ 0 = 1.21 for fixed values q 0 = 1.0 and θ 0 = 823 (Isaak et al. Phys Chem Min19:106–120, 1992). From the comparison of fits from two different approaches, we propose to constrain the bulk modulus of grossular garnet and its pressure derivative to K T0 = 166 GPa and K￠T0 K^{\prime}_{T0}  = 4.03–4.35. Present results are compared with previously determined thermoelastic properties of grossular-rich garnets.  相似文献   

6.
Physical and hydraulic properties of sediment from two karst aquifers were measured to determine (1) the similarity of sediment between karst aquifer systems and (2) the importance of sediment in modeling flow through karst aquifers. The sediment from the two systems was similar in size and composition. Within both aquifers, the silt-sized sediment was composed primarily of quartz, with minor amounts of plagioclase and clays. Hydraulic conductivity of the sediment measured directly (falling-head test) ranged from 1.61×10−7 to 1.33×10−6 m s–1 and estimated using the Campbell equation ranged from 8.30×10−8 to 8.98×10−7 m s–1. These values of hydraulic conductivity fall within the span of hydraulic conductivities for carbonate rocks, indicating that the sediment and carbonate matrix could be represented as one mathematical unit in modeling flow through karst aquifers. Statistical agreement in the hydraulic conductivity values generated by the two methods indicates that the estimation technique could be used to calculate hydraulic conductivities; thus allowing karst scientist to collect bulk sediment samples instead of having to collect cores from within karst aquifers. Electronic Publication  相似文献   

7.
Batch experiments were performed to investigate cephapirin (a widely used veterinary antibiotic) adsorption on various size sands of low total organic carbon content (0.08–0.36 wt%). In the aqueous concentration range investigated (11–112 μmol/L cephapirin), adsorption to nearly pure quartz filter sands (0.50–3.35 mm diameter) is low. Isotherms are S-shaped and most display a region of minimum adsorption, where decreased adsorption occurs with increasing solution concentration, followed by increased adsorption at higher concentrations. Cephapirin adsorption to quartz-rich, feldspar-bearing dune sands (0.06–0.35 mm diameter), and the smallest quartz filter sand investigated (0.43–0.50 mm), can be described by linear sorption isotherms over the range of concentrations investigated. Distribution coefficients (K d) range from 0.94 to 3.45 L/kg. No systematic relationship exists between grain size and amount of adsorption for any of the sands investigated. Cephapirin adsorption is positively correlated to the feldspar ratio (K-feldspar/(albite + Ca-plagioclase). Feldspar-ratio normalization of distribution coefficients was more effective than organic carbon normalization at reducing variability of K d values in the dune sands investigated.  相似文献   

8.
In this study, the impact of correlation length (λ) of hydraulic conductivity (K) heterogeneity on pump-and-treat (P&T) remediation period (time-to-compliance) for a mass transfer-limited aquifer is evaluated. Additionally, impacts of variance (σ 2), different distributions of high and low K zones and different initial contaminant masses are explored. Two different P&T policies including different number of wells pumping at different rates are employed for the investigation. Simulation–optimization approach in which a genetic algorithm (GA) is linked with a groundwater flow and contaminant transport model is used. Results show that K heterogeneity, in terms of λ ln K , sln K2 \sigma_{\ln \,K}^{2} and respective locations of low and high K zones, significantly impacts the time-to-compliance. Contaminant presence at low K zones can increase the time required to clean up the aquifer. Lower variation is observed in time-to-compliance for the remediation design utilizing higher number of wells pumping at slower rates compared to the design with a single well pumping at a higher rate. Higher number of wells increases the robustness of P&T remediation system when aquifer is heterogeneous in K.  相似文献   

9.
The thermo-elastic behavior of a natural epidote [Ca1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction. No phase transition has been observed within the temperature and pressure range investigated. P–V data fitted with a third-order Birch–Murnaghan equation of state (BM-EoS) give V 0 = 458.8(1)Å3, K T0 = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance–covariance matrix of K T0 and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the “Eulerian finite strain” vs “normalized stress” yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated with a linearized BM-EoS are: a 0 = 8.8877(7) Å, K T0(a) = 117(2) GPa, and K′(a) = 3.7(4) for the a-axis; b 0 = 5.6271(7) Å, K T0(b) = 126(3) GPa, and K′(b) = 12(1) for the b-axis; and c 0 = 10.1527(7) Å, K T0(c) = 90(1) GPa, and K’(c) = 8.1(4) for the c-axis [K T0(a):K T0(b):K T0(c) = 1.30:1.40:1]. The β angle decreases with pressure, βP(°) = βP0 −0.0286(9)P +0.00134(9)P 2 (P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α0 + α1 T −1/2. The refined parameters for epidote are: α0 = 5.1(2) × 10−5 K−1 and α1 = −5.1(6) × 10−4 K1/2 for the unit-cell volume, α0(a) = 1.21(7) × 10−5 K−1 and α1(a) = −1.2(2) × 10−4 K1/2 for the a-axis, α0(b) = 1.88(7) × 10−5 K−1 and α1(b) = −1.7(2) × 10−4 K1/2 for the b-axis, and α0(c) = 2.14(9) × 10−5 K−1 and α1(c) = −2.0(2) × 10−4 K1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α0(a): α0(b): α0(c) = 1 : 1.55 : 1.77. The β angle increases continuously with T, with βT(°) = βT0 + 2.5(1) × 10−4 T + 1.3(7) × 10−8 T 2. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out.  相似文献   

10.
Hydraulic properties of the crystalline basement   总被引：1，自引：1，他引：1  
Hydraulic tests in boreholes, up to 4.5 km deep, drilled into continental crystalline basement revealed hydraulic conductivity (K) values that range over nine log-units from 10−13−10−4 m s−1. However, K values for fractured basement to about 1 km depth are typically restricted to the range from 10−8 to 10−6 m s−1. New data from an extended injection test at the KTB research site (part of the Continental Deep Drilling Program in Germany) at 4 km depth provide K=5 10−8 m s−1. The summarized K-data show a very strong dependence on lithology and on the local deformation history of a particular area. In highly fractured regions, granite tends to be more pervious than gneiss. The fracture porosity is generally saturated with Na–Cl or Ca–Na–Cl type waters with salinities ranging from <1 to >100 g L−1. The basement permeability is well within the conditions for advective fluid and heat transport. Consequently, fluid pressure is hydrostatic and a Darcy flow mechanism is possible to a great depth. Topography-related hydraulic gradients in moderately conductive basement may result in characteristic advective flow rates of up to 100 L a−1 m−2 and lead to significant advective heat and solute transfer in the upper brittle crust. An erratum to this article can be found at  相似文献   

11.
The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) Å up to 11.8 GPa. A fit to the Birch–Murnaghan equation of state (EoS) based on the P–V data gives: K 0 = 209 (13) GPa, K′ = 4.0 (fixed), and V 0 = 588 (1) Å3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe–O and Cr–O bond distances decreasing from 1.996 (6) to 1.949 (7) Å and from 1.997 (3) to 1.969 (7) Å, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K 0 = 147 (9) GPa, K′ = 4.0 (fixed), V 0 = 4.07 (1) Å3 and K 0 = 275 (24) GPa, K′ = 4.0 (fixed), V 0 = 10.42 (2) Å3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd-[`3]{\overline{3}} m) to a tetragonal structure (space group I41 /amd). At the phase transition boundary, the two Cr–O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) Å and the other four Cr–O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) Å. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a “stretched” tetrahedral geometry. It is proposed that the Jahn–Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn–Teller effect observed in this structure and its role in the pressure-induced phase transition.  相似文献   

12.
CH4 and CO2 fluxes from a high-cold swamp meadow and an alpine meadow on the Qinghai-Tibetan Plateau, subject to different degrees of degradation, were measured over a 12-month period. Air temperature, soil temperature and moisture, and the depths of the water table and thawing-freezing layer were determined. For swamp meadows, the greater the degradation, the lesser the carbon efflux. CH4 emissions at the nondegraded swamp meadow site were 1.09–3.5 and 2.5–11.27 times greater, and CO2 emissions 1.08–1.69 and 1.41–4.43 times greater, respectively, than those from moderately and severely degraded sites. For alpine meadows, the greater the degradation, the greater the CH4 consumption and CO2 emissions. CH4 consumption at the severely degraded alpine meadow site was 6.6–21 and 1.1–5.25 times greater, and CO2 emissions 1.05–78.5 and 1.04–6.28 times greater, respectively, than those from the nondegraded and moderately degraded sites. The CH4 and CO2 fluxes at both sites were significantly correlated (R 2 > 0.59, P < 0.05) with air temperature, soil temperature, and topsoil (0–5 cm depth) moisture, indicating these to be the main environmental factors affecting such fluxes.  相似文献   

13.
The low-temperature heat capacity (C P) of stishovite (SiO2) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol−1 K−1, which is considerably smaller (by 2.86 J mol−1 K−1) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007).  相似文献   

14.
Surface water resources play a crucial role in the domestic water delivery system in Ghana. In addition, sustainable food production is based on the quality and quantity of water resources available for irrigation purposes to supplement rain-fed agricultural activities in the country. The objective of this research was to determine the main controls on the hydrochemistry of surface water resources in the southern part of Ghana and assess the quality of water from these basins for irrigation activities in the area. R-mode factor and cluster analyses were applied to 625 data points from 6 river basins in southern Ghana after the data had been log transformed and standardized for homogeneity. This study finds that surface water chemistry in the south is controlled by the chemistry of silicate mineral weathering, chemistry of rainfall, fertilizers from agricultural activities in the area, as well as the weathering of carbonate minerals. A Gibb’s diagram plotted with total dissolved solids (TDS) on the vertical axis against (Na+ + K+)/(Ca2+ + K+ + Na+) on the horizontal axis indicates that rock weathering plays a significant role in the hydrochemistry. Activity diagrams for the CaO–Na2O–Al2O–SiO2–H2O and CaO–MgO–Al2O3–SiO2–H2O systems suggest that kaolinite is the most stable clay mineral phase in the system. In addition, an assessment of the irrigation quality of water from these basins suggests that the basins are largely low sodium—low to medium salinity basins, delivering water of acceptable quality for irrigation purposes.  相似文献   

15.
Soil properties of major landslides that occurred recently on the mid-altitude slopes of Mount Elgon, eastern Uganda were analysed. A mudflow, located at the Kitati protected forest site, and two deep debris flows on the Nametsi and Buwabwala deforested steep slopes (36°–58°) were surveyed. In order to test the hypothesis that ‘soils at the landslide sites are particularly ‘problem soils’ and thus prone to landslides’, the following analyses were undertaken: particle size distribution, Atterberg limits, shear strength and factor of safety (Fs). Soils at the Kitati and Buwabwala sites exhibited expansive potential, owing to clay contents well above 20%. A clay content exceeding 32% was identified at the Nametsi debris flow site implying an extremely high expansive potential of the soil. High liquid limits (LLs) at Kitati (59%) and Buwabwala (53%) meant that the soils qualified as vertisols susceptible to landslides. High plasticity indices (PIs) (averaging 33%) also confirmed the vertic nature of soils at the Nametsi debris flow site. Whereas the value of F s  < 1 for the Kitati site signifies an inherently unstable slope, Nametsi and Buwabwala are supposedly stable slopes (F s  > 1). Despite this finding, the stable sites could be described as only conditionally stable because of the interplay of various physical, pedological and anthropogenic factors. The results point to the fact that soils at the landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Therefore, the hypothesis that soils at three landslide sites are inherently ‘problem soils’ and prone to landslides, is accepted.  相似文献   

16.
The high-pressure X-ray diffraction study of a natural arsenopyrite was investigated up to 28.2 GPa using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at National Synchrotron Light Source, Brookhaven National Laboratory. The 16:3:1 methanol–ethanol–water mixture was used as a pressure-transmitting medium. Pressures were measured using the ruby-fluorescence method. No phase change has been observed up to 28.2 GPa. The isothermal equation of state (EOS) was determined. The values of K 0, and K′ 0 refined with a third-order Birch–Murnaghan EOS are K 0 = 123(9) GPa, and K′ 0 = 5.2(8). Furthermore, we confirm that the linear compressibilities (β) along a, b and c directions of arsenopyrite is elastically isotropic (β a  = 6.82 × 10−4, β b  = 6.17 × 10−4 and β c  = 6.57 × 10−4 GPa−1).  相似文献   

17.
Measurement of streambed hydraulic conductivity and its anisotropy   总被引：17，自引：0，他引：17  
 A method is described for the measurement of streambed hydraulic conductivity. Unlike permeameter methods, this method applies straight and l-shaped standpipes directly to streambeds for measurements of in-situ hydraulic conductivity in the vertical (K v ) and horizontal (K h ) directions, as well as in other oblique directions (K s ). This method has advantages in determination of K v values over grain-size analysis, permeameter tests, or slug test methods. Also unique to this method is that it provides K s values of a streambed. The measured results can be used to construct a hydraulic conductivity ellipse and to evaluate the anisotropy of streambed sediments. Field examples from the Republican River, Nebraska, demonstrated the usefulness of this method in the determination of streambed hydraulic conductivity and anisotropy along or across a river channel. Results indicate that the K h is about three to four times larger than K v , whereas K s values are larger than K v but smaller than K h . Received: 6 March 2000 · Accepted: 18 April 2000  相似文献   

18.
The ratios M R = E/σ c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ c < 100 MPa) and very strong (σ c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus (E = 6100–82300 MPa), uniaxial compressive strength (σ c = 14–273.9 MPa), Poisson's ratio (ν = 0.13–0.49), and dry bulk density (ρ = 1.7–2.7 g/cm3). The observed range of M R = 60.9–1011.4 and mean value of M R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20, 1968) for limestones and dolomites, and the statistical analysis of M R distribution is performed. Mutual relations between E, σ c, ρ, M R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus and M R in very strong carbonate samples are more correlated with ρ−σ c combination and ε a max, respectively, than in weak to strong samples. The relation between M R and maximum axial strain (ε a max) for all studied rock samples (weak-to-strong and very strong) is discussed.  相似文献   

19.
The heat capacity at constant pressure, C p, of chlorapatite [Ca5(PO4)3Cl – ClAp], and fluorapatite [Ca5(PO4)3F – FAp], as well as of 12 compositions along the chlorapatite–fluorapatite join have been measured using relaxation calorimetry [heat capacity option of the physical properties measurement system (PPMS)] and differential scanning calorimetry (DSC) in the temperature range 5–764 K. The chlor-fluorapatites were synthesized at 1,375–1,220°C from Ca3(PO4)2 using the CaF2–CaCl2 flux method. Most of the chlor-fluorapatite compositions could be measured directly as single crystals using the PPMS such that they were attached to the sample platform of the calorimeter by a crystal face. However, the crystals were too small for the crystal face to be polished. In such cases, where the sample coupling was not optimal, an empirical procedure was developed to smoothly connect the PPMS to the DSC heat capacities around ambient T. The heat capacity of the end-members above 298 K can be represented by the polynomials: C pClAp = 613.21 − 2,313.90T −0.5 − 1.87964 × 107 T −2 + 2.79925 × 109 T −3 and C pFAp = 681.24 − 4,621.73 × T −0.5 − 6.38134 × 106 T −2 + 7.38088 × 108 T −3 (units, J mol−1 K−1). Their standard third-law entropy, derived from the low-temperature heat capacity measurements, is S° = 400.6 ± 1.6 J mol−1 K−1 for chlorapatite and S° = 383.2 ± 1.5 J mol−1 K−1 for fluorapatite. Positive excess heat capacities of mixing, ΔC pex, occur in the chlorapatite–fluorapatite solid solution around 80 K (and to a lesser degree at 200 K) and are asymmetrically distributed over the join reaching a maximum of 1.3 ± 0.3 J mol−1 K−1 for F-rich compositions. They are significant at these conditions exceeding the 2σ-uncertainty of the data. The excess entropy of mixing, ΔS ex, at 298 K reaches positive values of 3–4 J mol−1 K−1 in the F-rich portion of the binary, is, however, not significantly different from zero across the join within its 2σ-uncertainty.  相似文献   

20.
A barrier system based on the hydraulic trap design concept for a landfill was proposed. To study the field scenario in which a clay liner is underlain by a granular layer functioning as a secondary leachate drain layer, a laboratory advection–diffusion test was performed to investigate factors controlling the transport of contaminants in a two-layer soil system. The soils used for this study were Ariake clay and, the underlying layer, Shirasu soil from the Kyushu region of Japan. Potassium (K+) was selected as the target chemical species with an initial concentration of 905 mg L−1. The effective diffusion coefficients (D e) of K+ for Ariake clay and Shirasu soil were back-calculated using an available computer program, Pollute V 6.3. Values of D e derived from this experiment are consistent with previously published ones. The Ariake clay has lower D e than the Shirasu soil. The hypothesis that mechanical dispersion can be considered negligible is reasonable based on both the observation that the predicted values well fit the experimental data and the analyses of two dimensionless parameters. Parametric analyses show that transport of K+ through soils is controlled by advection–diffusion rather than diffusion only, whereas at low Darcy velocity (i.e., ≤10−9 m s−1), transport of K+ will be controlled by diffusion. Applications of the test results and parametric analysis results in practical situations were reviewed.  相似文献   

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