The basal spacing of a set of smectites, with layer charges between 0.74 and 1.14 electrons per unit cell, have been measured while the smectites were in equilibrium with NaCl solutions having concentrations of 0.25 to 2.5 molal. Except for the most highly charged smectites, an expansion from ~15.5 to ~18.5 Å occurred as the NaCl concentrations were reduced. This expansion (or “crystalline swelling”) corresponds to the transition from two to three sheets of water between the silicate layers. A random interstratification of 15.5 and 18.5 Å structure units was present during the change and gave rise to broad diffraction peaks for the 001 reflections. A balance between cation hydration forces, interlamellar electrostatic forces, and van der Waals forces was apparently the basis of the relationship between surface charge and swelling. The results can be expressed in terms of the relative vapor pressures at which the transitions were half complete; these pressures increased with surface density of charge, and over the range of surface charge studied, the P/P0 values ranged from 0.943 to 0.974.

Samples of Na-saturated, Upton montmorillonite were prepared with different contents of water (H2O or D2O) by: (1) adsorption of water from the vapor phase at a specific value of p/p°, the relative humidity, (2) adsorption of water from the vapor phase at p/p° = 1.0 followed by desorption of the water into the vapor phase at a specific p/p° < 1.0, and (3) adsorption of water from the liquid phase followed by desorption of the water into the vapor phase at a specific p/p° < 1.0. Water adsorbed initially from the vapor phase was called V-adsorbed water, and water adsorbed initially from the liquid phase was called L-adsorbed water. The water contents of these samples were determined by gravimetric analysis, the c-axis spacings by X-ray powder diffraction, the O-D stretching frequencies by IR spectroscopy, and the heats of immersion by differential microcalorimetry. No difference was found between V-adsorbed and L-adsorbed water; however, if the final water content was established by adsorption, the system was in a different state than if the final water content was established by desorption. In particular, hysteresis was observed in the following properties: the relative humidity of the adsorbed water, the O-D stretching frequency in this water, and the degree of order in the stacking of the clay layers. The only property that did not exhibit hysteresis was the heat of immersion. Apparently, hysteresis occurred because the orderliness of the system was not reversible, and, thus, any property that depended on orderliness was hysteretic.

The swelling property of smectite is dominated by the hydration of exchangeable cations in the interlayer spacing (‘interlayer hydration’). By investigating systematically the swelling behavior of various exchangeable cations with different valences and ionic radii, the interlayer hydration of smectite was explored. The swelling behavior of Li+-, K+-, Rb+-, Cs+-, Mg2+-, Sr2+-, Ba2+-, and La3+- montmorillonites in undersaturated conditions was measured precisely over the range 50–150°C by in situ X-ray diffraction (XRD) analyses. The systematic swelling behavior of ten homocationic montmorillonites, the aforementioned eight homoionic montmorillonites, plus Na+ and Ca2+ from a previous study, and the cation hydration energies were analysed by studying the changes occurring in the basal spacing and the 001 peak width. With decreasing cation hydration energy, swelling curves (i.e. plots of basal spacing vs. relative humidity (RH)) change from continuous (Mg2+, La3+, and Ca2+) to stepwise (Sr2+, Li+, Ba2+, and Na+) to one-layer only (K+, Rb+, and Cs+). For the first two groups, the RH at the midpoint between the one- and two-layer hydration states increased as the cation hydration energy decreased. Under low RH, with increasing temperature, the basal spacings of Mg-, La-, Ca-, Sr-, Li-, and Ba-montmorillonites decreased continuously to the zero-layer hydration state, whereas Na-, K-, Rb-, and Cs-montmorillonites swelled from the zero-layer hydration state even at the lowest temperature (50°C). A decrease in the basal spacing at the same RH but at different temperatures suggests the existence of metastable states or that the layer-stacking structure changes with temperature. The systematics of the swelling behavior of various homocationic montmorillonites as functions of RH and temperature (<150°C) at 1 atmare reported here.

The effects of temperature on the swelling properties of smectites are important for a variety of different geological conditions, but studies on this topic have been rather limited. The purpose of this study was to investigate the swelling behavior of Na- and Ca-montmorillonite at various temperatures greater than room temperature, up to 150°C, using in situ X-ray diffraction (XRD) analysis. A sample chamber was designed, the temperature and humidity of which were controlled precisely, for environmental in situ measurements. The XRD measurements were performed at small relative humidity (RH) intervals for precise observation of the swelling behavior.

The swelling behavior of Na-montmorillonite showed distinct zero-, one-, and two-layer hydration states. The basal spacings of Na-montmorillonite changed continuously with RH for various temperatures in the transition region between the zero- and one-layer hydration states, and the swelling curves of the transition region moved to greater degrees of RH with increasing temperature. The basal spacings jumped from the one- to two-layer hydration states for all temperatures at almost the same RH.

The basal spacings of Ca-montmorillonite changed continuously from the zero- to the two-layer hydration states at all temperatures. This behavior is remarkably different from that of Na-montmorillonite. At low-RH conditions, the d001 value of Ca-montmorillonite decreased with increasing temperature. The swelling curves of Ca-montmorillonite did not show a plateau at any temperature for the one-layer hydration state. The swelling curves of Ca-montmorillonite moved to greater RH with temperature, similar to the transformation region between the zero- and one-layer hydration states in Na-montmorillonite. These differences between Na- and Ca-montmorillonite are related to the hydration powers of exchangeable cations.

A principal mode of corrosion in combustion or fuel cell environments is the formation of volatile hydroxides and oxyhydroxides from metal or oxide surfaces at high temperatures. It is important to determine the degree of volatility and accurate thermodynamic properties for these hydroxides. Significant gaseous metal hydroxides/oxyhydroxides are discussed, along with available experimental and theoretical methods of characterizing species and determining their thermodynamic properties.

The ARS Pesticide Properties Database (PPD) is a compendium of chemical and physical properties of a collection of widely used pesticides. At present, there are 92 compounds in the database and we have focused on 19 of the most important properties impacting on groundwater and atmospheric quality. The PPD relies upon experimentally determined data points. With the help of the National Agricultural Chemicals Association (NACA) we have been communicating directly with manufacturers to obtain the original experimental data with which they characterize pesticide properties and fulfill requirements for federal and state regulations. This provides the basis for the PPD which is augmented with data from the scientific literature. Features of the PPD are: 1. 19 parameters are provided for each pesticide. 2. References are given for all data. 3. When there are several values for a given property, all are cited. 4. All data have been verified and provide the latest, most reliable figures available.

Roots or shoots of oats (Avena sativa L. ‘Dal’) and peas (Pisum sativum L. ‘Early Perfection’) were exposed to vapors of 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6 dinitro-N-propyl-4-(trifluoromethyl)aniline], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). All of the dinitroaniline herbicides except oryzalin were absorbed by roots and shoots of germinating oats and peas. Some root-shoot translocation of the herbicides was observed in peas, but no shoot-root transport could be detected in either peas or oats. In peas, 14C from root-absorbed benefin, fluchloralin, profluralin and trifluralin was detected in shoots, and 14C from benefin and trifluralin was detected in cotyledons. In general, vapor absorption was correlated with rates of herbicide volatilization.

Common lambsquarters is an important annual weed of many crops world-wide. Ascochyta caulina is a plant pathogenic fungus that, under natural conditions, causes necrotic spots on the leaves and stems of Chenopodium species. The objective of this study was to evaluate the effect of weed growth stage, relative humidity, dew period, and temperature on the infection of A. caulina isolates against common lambsquarters. In greenhouse experiments, replicated groups of common lambsquarters plants were sprayed with different isolates of A. caulina 2, 3, 4, 5, and 6 wk after emergence. Both disease severity and pathogen-induced dry weight reduction decreased with plant age. The efficacy of all isolates tested was reduced by high leaf-to-air vapor-pressure deficit. Disease severity was more responsive to relative humidity than temperature. However, a minimum dew period of 6 h was required to cause significant disease severity in common lambsquarters. Among all tested A. caulina isolates, W90–1 gave the highest disease scores under all conditions, with the exception of temperatures ≤15 C.

Study of the acid bake-leach process has shown potential advantages for the treatment ofenargite (Cu3AsS4) concentrates. Among the most important advantages of theprocess is the transformation of enargite to water-soluble copper sulfate and highlysoluble arsenic trioxide (arsenolite). Because arsenic is retained in the condensed phaseduring the baking, the vapor pressure of arsenic trioxide should be estimated at typicalbaking temperatures (e.g. 473 K). To that end, the vapor pressure of As4O6 (g) was estimated under thebaking conditions based on published thermodynamic values. The vapor pressure ofarsenolite at 473 K was found to be approximately 9.03 × 10-4 atm. Based on thelinear regression analysis of the published vapor pressure values for arsenolite in thetemperature range 366−579 K,the equation for the best fit line was found to be as follows, with a correlationcoefficient of 0.9973:

logPArsenolite(atm) = (-5780.7)/(T (K))+9.16.

Available information on arsenic trioxide does not allow a definite conclusion regardingthe arsenolite/claudetite transformation temperature and their exact melting points.However, the transition temperature has been reported to be in the wide range of240−506 K in differentreferences. Furthermore, the thermodynamic information concerning arsenolite/claudetite issparse and at times not consistent. An effort has been made in this paper to compile themost reliable thermodynamic information for arsenic trioxide (arsenolite and claudetite).

In this article, ZnO microtube was prepared using mixed powder of Zn, ZnO, and carbon as source via chemical vapor deposition method. The growth process was discussed in detail, and the high Zn vapor pressure and high growth temperature were considered as two crucial factors determining the formation of tubular structure. A two-step growth model was proposed, namely initial deficient-oxidation and followed by second-volatilization. Four another experiments were further conducted to analyze the growth behavior of reagent species under different Zn vapor pressure and growth temperature, respectively. These experimental results indicated that the formation of Zn-rich structure under enough high Zn vapor pressure and second-volatilization of these abundant interstitial Zn under high growth temperature were important to form tubular structure. Our experimental method provided a feasible route to prepare other hollow structures, such as oxide, sulfide, etc. Furthermore, these synthesized ZnO microtube might have potential application as functional blocks in nanodevices.

We have developed a QCM (Quartz Crystal Microbalance) based method for direct gravimetric determination of water adsorption on PuO2 surrogate surfaces, especially CeO2, under conditions representative of those in a typical PuO2 storage can. In this application, the method of transduction of the QCM relies upon the linear relationship between the resonant frequency of piezoelectrically active quartz crystals and the mass adsorbed on the crystal surface. The spurious effect of high temperatures on the resonant frequency of coated QCM crystals has been compensated for by modeling the temperature dependence of the frequency response of the surrogate coated-QCM crystal in the absence of water. Preliminary results indicate that water is readily adsorbed from the vapor phase into porous metal oxide structures by capillary condensation, an observation that may have important ramifications for water uptake within the packed powder beds that may obtain in PuO2 storage cans.

In this study, ZnO f ilms heavily doped with Al or Ga were grown on a polarity-controlled buffer layer using pulsed laser deposition. The films prepared using a 1 mol% Al-doped target with the buffer layer grown at 700 °C had the c(+)-face, whereas the films with the buffer layer grown at 400 °C had the c(-)-face, which means that the polarity control can be successfully carried out using the buffer layer. However, the films prepared using targets doped with more than 1 mol% Al or Ga had the c(+)-face regardless of the polarity of the buffer layer. The 1 mol% Al-doped ZnO film with the c(+)-face had lower electron concentration and higher growth rate than the film with the c(-)-face. This result indicates that the Al content in the film with the c(-)-face was larger than that in the film with the c(+)-face.

Growth orientation and type of internal structures are both observed to change abruptly as a function of growth temperature in catalyst free growth of gallium nitride nanowires. In the present work, corresponding temperature-dependent changes in the growth matrix substrate that can affect the availability of nucleation sites and influence the reactivity of constituent adatom materials in catalyst-free nanowire growth are investigated. The influence of Ga vapor pressure and an abrupt change in the availability of single versus molecular adatom constituents is identified as a possible controlling parameter.

The effect of salt concentration on swelling pressure of water-saturated bentonite was modelled based on the thermodynamic data of water at montmorillonite surface and of water in solutions of various salinities coming in contact with the montmorillonite. Activities of water at montmorillonite surface were obtained as a function of water content and temperature at montmorillonite densities of 0.6 and 0.9Mg/m3 by a vapor pressure method, and the relative partial molar Gibbs free energies (dGw) were determined. Water affected from the montmorillonite surface was estimated to be almost all interlayer water. Swelling pressure vs. montmorillonite partial density was estimated for solutions of various salinities and compared to data measured for various montmorillonite contents and different silica sand contents of bentonites. The calculated swelling pressure clearly decreased with increasing salinity. The effect of salinity on swelling pressure was not clear in the measured data and was within the range of the scattering in the measured data. This cause is presumed to be due to the increase of the ionic strength of porewater by dissolution of soluble minerals in the bentonite.

The purpose of this paper is to report the results of a new model study critically examining the high temperature nuclear waste disposal concept at Yucca Mountain using MULTIFLUX, an integrated in-drift- and mountain-scale thermal-hydrologic model. In addition to new results the paper summarizes results of a previous study. The results show that a large amount of vapor flow into the drift is expected during the period of above-boiling temperatures in the emplacement drift. This phenomenon makes the emplacement drift a water/moisture attractor for thousands of years during the above-boiling temperature operation.

The evaporation of the percolation water into the drift gives rise to salt accumulation in the rock wall, especially in the crown of the drift for about 1500 years in the example. The deposited salts over the drift footprint, almost entirely present in the fractures, may enter the drift either by rock fall or by water drippage. During the high temperature operation mode the barometric pressure variation creates fluctuating relative humidity in the emplacement drift with a time period of approximately 10 days. Potentially wet and dry conditions and condensation on the surfaces over salt-laden drift wall sections are unfavorable to the storage environment. Corrosive salt accumulation during the above-boiling temperature operation must be sufficiently addressed to fully understand the waste package environment during the thermal period. Until the questions are resolved, a below-boiling repository design is favored where the Alloy-22 will be less susceptible to localized corrosion.