Sublimation Rate Research Articles

Sublimation of vertically oriented paradichlorobenzene cylinders in a natural convection environment

Paradichlorobenzene cylinders were cast, then suspended vertically and allowed to sublimate in air. Data on mass versus time were measured, and a sublimation rate was calculated. Three cylinders of different diameters were used: 1 inch (2.54 cm), 1.5 inch (3.81 cm), and 2 inch (5.08 cm). The length of all three cylinders was 10 in. (25.4 cm). Calculations indicate that the Schmidt number was constant. The Sherwood number ranged from 23 to 26, and Rayleigh numbers varied from 11 × 103 to 88 × 103. The objective of this study was to develop a correlation for determining the mass transfer coefficient of vertically suspended paradichlorobenzene cylinders in a natural convection environment. An equation relating Sherwood and Rayleigh numbers was derived.

Effects of shelterbelts on snow distribution and sublimation

On the Canadian Prairies and the northern US Great Plains, snow is an important component of annual precipitation, sometimes constituting over 40% of the total, although there is much annual and regional variability. Much of this snow is transported by wind, causing substantial sublimation losses, which are reduced by obstacles and topographic features on the landscape that reduce snow transport and trap snow. Agroforestry configurations trap snow and reduce the amount and distance of snow movement and, because of this, reduce the amount of moisture lost to sublimation. The planning of agroforestry measures should therefore take into account their effects on snow hydrology. In this study, the effects of shelterbelts on snow quantity and distribution are shown over multiple years, including a number of locations in Manitoba and Saskatchewan. Results show that snow transport reached equilibrium in 400 m or less (i.e., that sublimation rates were at their maximum beyond 400 m leeward of a shelterbelt). Also, in a paired landscape inventory, the landscape with shelterbelts had 29% more snow water equivalent (SWE) than the unsheltered landscape. Site-specific meteorological data was used in the Prairie Blowing Snow Model, now a component of the Cold Regions Hydrological Model, to calculate the effects of agroforestry configurations on snow water conservation. Modeled snow distribution agreed well with measured snow at Conquest, Saskatchewan, in the winter of 2009/2010. Using actual weather data for the same location for the period 1996–2011, the model calculated the annual sublimation from 200 m wide fields protected by shelterbelts to be up to 12.5 mm less than similar unsheltered fields.

Distributed temperature-index snowmelt modelling for forested catchments

► We adapt extended temperature-index snowmelt algorithms for forested catchments. ► A simple model for canopy interception reasonably predicts snow accumulation. ► Extended temperature-index algorithms can be as accurate as an energy balance model. ► Accounting for cold-content was required to realize the increased performance. ► One algorithm is also capable of simulating the diurnal cycle of meltwater outflow. This work was motivated by the need to understand the hydrologic consequences of rapid and widespread forest disturbance to assist forest management and operational forecasting. The objective was to compare three extended temperature-index-based melt models to a basic temperature-index model, as well as to the physically based snow model in the Distributed Hydrology-Soil-Vegetation Model (DHSVM). One model uses ad hoc parameterizations to represent the variation of the melt factor with slope-aspect, forest cover and time of year. The other two incorporate either potential direct or measured solar radiation; they were originally developed for open sites and were adapted to account for the effects of forest cover. The models were calibrated and tested using lysimeter data and spatially distributed snow surveys conducted at the Cotton Creek Experimental Watershed located in southeast British Columbia, Canada. A model for canopy interception that included a maximum canopy storage and a fixed sublimation rate provided reasonable predictions of peak snow accumulation. Accounting for cold content in the upper layer of a two-layer snowpack model was required to realize the increased predictive performance of the extended temperature-index melt models, compared to the most basic model. The model that incorporated measured solar radiation provided the best performance, and was almost as accurate as the DHSVM snow model. The model that uses potential direct radiation also performed well in spatial testing and, in addition, closely matched day-time highs and night-time lows of the measured lysimeter outflow. The model with ad hoc representations did not perform as well as the other extended temperature-index models outside the calibration period. Spatially distributed snowpack measurements assisted in constraining the parameters in the extended temperature-index models. Further research should test the extended temperature-index melt models at the catchment scale, particularly in catchments where there have been rapid and well documented changes in forest cover.

CO2gas fluidization in the initiation and formation of Martian polar gullies

[1] Martian gully landforms, indicative of rapid flow of sediment down steep slopes, have been cited as evidence of the action of near-surface liquid water in Mars' recent past. Gullies in polar regions cannot involve pure liquid water because ambient temperatures are too low. Here, we show that polar gullies could be initiated by fluidization of sediment over a subliming seasonal deposit of CO2 frost, as has been proposed previously. For gullies in sand, the gas speed and CO2 sublimation rate required for fluidization is calculated with the semi-empirical Ergun relation (as validated in industrial applications). For gullies in dust, the gas speed and sublimation rate required for fluidization are estimated from laboratory experiments with comparable materials. To determine if those rates can be achieved, we compute diurnal and seasonal surface (and subsurface) temperatures through a Martian year (including CO2 condensation and sublimation) using the MARSTHERM one-dimensional finite difference thermal model. Models were run without sediment, and with layers of sand or dust 10−4–10−1 m thick deposited over a seasonal layer of CO2 frost. The simulations show that, in the spring, sufficient heat reaches the CO2 frost, underlying the surface sediment layer, to fluidize them. This result confirms that Martian gullies may have diverse origins – and that polar and mid-latitude gullies can be initiated on steep slopes by the fluidization of loose sediment on a sublimating seasonal deposit of CO2 gas.

Thermo-optical determination of vapor pressures of TNT and RDX nanofilms

Accurate thermodynamic parameters of thin films of explosives are important for understanding their behavior in the nanometer scale as well as in standoff detection. Using UV-absorbance spectroscopy technique, accurate thermodynamic parameters such as activation energies of sublimation, sublimation rates, and vapor pressures of the explosives cyclotrimethylenetrinitramine (RDX) and 2,4,6-trinitrotoluene (TNT) were determined. The values of these parameters are in excellent agreement with those reported using traditional experiments based on gravimetry. In terms of the Clapeyron equation, the dependence of RDX and TNT vapor pressures on temperature can be described by the relations LnP (Pa)=39.6−15459/T (K) and LnP (Pa)=34.9−12058/T (K), respectively. Heats of sublimation of RDX and TNT were also determined to be 128kJ/mol and 100.2kJ/mol, respectively.

Large area and structured epitaxial graphene produced by confinement controlled sublimation of silicon carbide

After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. It was long known that graphene mono and multilayers grow on SiC crystals at high temperatures in ultrahigh vacuum. At these temperatures, silicon sublimes from the surface and the carbon rich surface layer transforms to graphene. However the quality of the graphene produced in ultrahigh vacuum is poor due to the high sublimation rates at relatively low temperatures. The Georgia Tech team developed growth methods involving encapsulating the SiC crystals in graphite enclosures, thereby sequestering the evaporated silicon and bringing growth process closer to equilibrium. In this confinement controlled sublimation (CCS) process, very high-quality graphene is grown on both polar faces of the SiC crystals. Since 2003, over 50 publications used CCS grown graphene, where it is known as the "furnace grown" graphene. Graphene multilayers grown on the carbon-terminated face of SiC, using the CCS method, were shown to consist of decoupled high mobility graphene layers. The CCS method is now applied on structured silicon carbide surfaces to produce high mobility nano-patterned graphene structures thereby demonstrating that EG is a viable contender for next-generation electronics. Here we present for the first time the CCS method that outperforms other epitaxial graphene production methods.

Determination of sublimation rate of 2,4,6-trinitrotoluene (TNT) nano thin films using UV-absorbance spectroscopy

We report the in situ measurements of the sublimation rate and activation energy of continuous nanofilms of 2,4,6-trinitrotoluene (TNT) in air using UV absorbance spectroscopy. The films were prepared using acetone-dissolved TNT by simple spin coating deposition technique. Unlike traditional mass loss techniques, this new method is independent of the surface area of the sample which contributes to errors in determining physical parameters accurately in both bulk and thin films of materials. The calculated activation energy and temperature-dependent sublimation rates agree well with the reported values for TNT thin films. The results suggest that UV absorbance spectroscopy is an efficient tool in measuring thermodynamic properties in the nanometer scale for materials with absorbance in the UV region of the electromagnetic spectrum.

Initial Ice Microparticle Sublimation Measurements from the Levitating Upper-Tropospheric Environmental Simulator (LUTES)

Abstract Initial ice particle sublimation data are presented from the new Levitating Upper-Tropospheric Environmental Simulator (LUTES) at The College of New Jersey. This experimental system mimics the conditions of a typical cirrus cloud in order to evaluate the phase-change kinetics of single ice particles. These ice particles are charged and then trapped in a levitating electrodynamic balance where they can be observed as they sublimate in a subsaturated atmosphere. Levitation and sublimation take place within a vacuum chamber, which is contained in a freezer at a temperature of −40° to −80°C and is capable of a reduced pressure of 10 mb. The sublimation rates of the ice particles are observed at a variety of temperature, humidity, and pressure conditions and are compared to sublimation rates predicted by particle-scale diffusion models. Initial measurements suggest that the diffusion models are capturing the essential sublimation behavior of the particles, but further measurements promise to inform lingering questions about the fundamental thermodynamics and surface processes of sublimating and growing ice particles under cirrus conditions.

Spontaneous Crystalline-to-Amorphous Phase Transformation of Organic or Medicinal Compounds in the Presence of Porous Media, Part 1: Thermodynamics of Spontaneous Amorphization

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal molecules in the presence of mesoporous materials has been observed, for which pathway was suggested to be via the vapor phase, that is, sublimation of the crystalline molecules followed by adsorption on the porous media. The objective of this paper is to rigorously evaluate this amorphization pathway and to study the thermodynamics of spontaneous amorphization. Mesoporous silicon dioxide (SiO(2)) was used as a model system. Physical mixtures of SiO(2) and crystalline compounds were prepared and stored at 0% relative humidity (RH) and 40 °C. Loss of crystallinity of the model compounds was confirmed using powder X-ray diffraction and polarized light microscopy. Adsorption chamber was set up, in which naphthalene and SiO(2) were stored, without physical contact, under reduced pressure at 0% RH and 40 °C. Data confirmed that the rate and extent of sublimation and adsorption of naphthalene were significant for amorphization to occur on a pharmaceutically relevant timescale. Furthermore, a thermodynamic model has been developed to explain spontaneous amorphization. This unique phase transformation phenomenon can be a simple and effective method to improve the aqueous solubility and bioavailability of poorly soluble drug molecules.

Sublimation’s impact on temporal change of albedo dichotomy on Iapetus

Iapetus, one of the saturnian moons, has an extreme albedo contrast between the leading and trailing hemispheres. The origin of this albedo dichotomy has led to several hypotheses, however it remains controversial. To clarify the origin of the dichotomy, the key approach is to investigate the detailed distribution of the dark material. Recent studies of impact craters and surface temperature from Cassini spacecraft data implied that sublimation of H 2O ice can occur on Iapetus’ surface. This ice sublimation can change the albedo distribution on the moon with time. In this study, we evaluate the effect of ice sublimation and simulate the temporal change of surface albedo. We assume the dark material and the bright ice on the surface to be uniformly mixed with a certain volume fraction, and the initial albedo distribution to incorporate the dark material deposits on the surface. That is, the albedo at the apex is lowest and concentrically increases in a sinusoidal pattern. This situation simulates that dark materials existed around the Iapetus’ orbit billions of years ago, and the synchronously rotating Iapetus swept the material and then deposited it on its surface. The evolution of the surface albedo during 4.0 Gyr is simulated by estimating the surface temperature from the insolation energy on Iapetus including the effect of Saturn’s eccentricity and Iapetus’ obliquity precession, and evaluating the sublimation rate of H 2O ice from the Iapetus’ surface. As a result, we found that the distribution of the surface albedo changed dramatically after 4.0 Gyr of evolution. The sublimation has three important effects on the resultant surface albedo. First, the albedo in the leading hemisphere has significantly decreased to approach the minimum value. Second, the albedo distribution has been elongated along the equator. Third, the edge of the low albedo region has become clear. Considering the effect of ice sublimation, the current albedo distribution can be reconstructed from the sinusoidal albedo distribution, suggesting the apex–antapex cratering asymmetry as a candidate for the origin of the albedo dichotomy. From the model analysis, we obtained an important aspect that the depth of the turn-over layer where the darkening process proceeded for 4 Gyr should be an order of 10 cm, which is consistent with evaluation from the Cassini radar observations.

In situ observation of the formation of hollow zinc oxide shells

Single crystal zinc particles, 1–2 μm in diameter, were observed in situ with transmission electron microscopy during sublimation. The rate of sublimation is strongly dependent on the presence of a surface oxide layer. Near 375 °C, minimally oxidized Zn surfaces sublime in tens of seconds, consistent with a model in which the particle behaves similarly to an isolated microscale effusion cell. By contrast, zinc particles fully enclosed by oxide sublime less than one-tenth as quickly. These results provide new insight into the synthesis mechanisms of hollow ZnO microspheres and related structures formed from metallic zinc at elevated temperatures.

Outgassing of icy bodies in the Solar System – I. The sublimation of hexagonal water ice through dust layers

Our knowledge about the physical processes determining the activity of comets were mainly influenced by several extremely successful space missions (Giotto, Deep Space I, Stardust, Deep Impact and EPOXI), the predictions of theoretical models and the results of laboratory experiments. However, novel computer models should not be treated in isolation but should be based on experimental results and should be verified and calibrated by experimental work. Therefore, a new experimental setup was constructed to investigate the temperature dependent sublimation properties of hexagonal water ice and the gas diffusion through a dry dust layer covering the ice surface. We show that this experimental setup is capable to reproduce known gas production rates of pure hexagonal water ice. The reduction of the gas production rate due to an additional dust layer on top of the ice surface was measured and compared to the results of another experimental setup in which the gas diffusion through dust layers at room temperature was investigated. We found that the relative permeability of the dust layer is inversely proportional to its thickness, which is also predicted by theoretical models. However, the measured absolute weakening of the gas flow was smaller than predicted by models. This lack of correspondence between model and experiment may be caused by an ill-determination of the boundary condition in the theoretical models, which further demonstrates the necessity of laboratory investigations. Furthermore, the impedance of the dust layer to the ice evaporation was found to be similar to the impedance at room temperature, which means that the temperature profile of the dust layer is not influencing the reduction of the gas production. Finally, we present the results of an extended investigation of the sublimation coefficient, which is an important factor for the description of the sublimation rate of water ice and, thus, an important value for thermophysical modeling of icy bodies in the Solar System. The achieved results of this laboratory investigations demonstrate that experimental works are essential for the understanding of the origin of cometary activity.

Self-Disproportionation of Enantiomers via Sublimation; New and Truly Green Dimension in Optical Purification

This Review article presents all available in the literature data on optical purification of enantiomerically enriched organic compounds via simple procedure of sublimation. The material is arranged in a chronological order from early publications to current research. Relatively small amount of the results reported in the literature suggest that this area of research is still in its infancy it terms of commonly accepted experimental procedures, generalizations, interpretation or prediction of the stereochemical outcome of sublimation. On the other hand, the available data clearly show the potential of sublimation as most economical and greener alternative to the conventional optical purification techniques such as chromatography on chiral stationary phase or fractional crystallization. Another important goal of this Review is to bring to the attention of scientific community a warning that special care should always be taken in evaluation of the stereochemical outcome of enantioselective reactions. Thus, due to the always different sublimation rates of racemic and enantiomerically pure crystals, such a routine procedure as drying reaction products in vacuum or even removal of solvents under reduced pressure can significantly alter the true enantiomeric composition (% ee) of a compound under study and lead to erroneous results. Keywords: Sublimation, chiral purification, self-disproportionation of enantiomers, non-linear effects, green methodology, optical purification, chromatography, fractional crystallization, enantioselective resctions, biocatalysis

Coincident measurements of PMSE and NLC above ALOMAR (69° N, 16° E) by radar and lidar from 1999–2008

Abstract. Polar Mesosphere Summer Echoes (PMSE) and Noctilucent Clouds (NLC) have been routinely measured at the ALOMAR research facility in Northern Norway (69° N, 16° E) by lidar and radar, respectively. 2900 h of lidar measurements by the ALOMAR Rayleigh/Mie/Raman lidar were combined with almost 18 000 h of radar measurements by the ALWIN VHF radar, all taken during the years 1999 to 2008, to study simultaneous and common-volume observations of both phenomena. PMSE and NLC are known from both theory and observations to be positively linked. We quantify the occurrences of PMSE and/or NLC and relations in altitude, especially with respect to the lower layer boundaries. The PMSE occurrence rate is with 75.3% considerably higher than the NLC occurrence rate of 19.5%. For overlapping PMSE and NLC observations, we confirm the coincidence of the lower boundaries and find a standard deviation of 1.26 km, hinting at very fast sublimation rates. However, 10.1% of all NLC measurements occur without accompanying PMSE. Comparison of occurrence rates with solar zenith angle reveals that NLC without PMSE mostly occur around midnight indicating that the ice particles were not detected by the radar due to the reduced electron density.

Stability Study of a Magnesium β-Diketonate As Precursor for Chemical Vapor Deposition of MgO

On the basis of the study of the thermal behavior of [Mg(tmhd)2(TMEDA)] (1; tmhd =2,2,6,6-tetramethyl-3,5-heptanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), a novel procedure for magnesium oxide thin film growth has been developed for chemical vapor deposition (CVD) applications. Complementary studies (thermogravimetric measurements and IR and NMR spectroscopy) enabled revelation of the dissociation of TMEDA from 1, confirmed by the detection of both free TMEDA in the vapor phase and less volatile [Mg2(tmhd)4] (2) as a residue after sublimation. The effect of this dissociation is an unwanted changeable sublimation rate of the precursor 1 during the CVD process. The endeavor of a constant deposition rate by simultaneously exploiting the good volatility of 1 was achieved through its synthesis in situ by using 2 with a diamine enriched carrier. Laser reflectance interferometry (LRI) measurements testified that such a method ensured a good and constant deposition rate throughout the growth experim...

Synthesis and thermal energy storage properties of ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides as novel solid–liquid phase change materials

Ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides were synthesized as novel solid–liquid phase change materials (PCMs) via condensation of ethylene diamine with the respective carboxyl chlorides (lauroyl chloride, myristoyl chloride, and palmytoyl chloride). The synthesized ethylene dilauroyl amide (EDLA), ethylene dimyristoyl amide (EDMA), and ethylene dipalmytoyl amide (EDPA) were characterized structurally by FT-IR and 1H NMR spectroscopy techniques. Latent heats of melting and freezing determined using DSC technique were found to be 127.83 and −118.30 J/g for EDLA, 129.95 and −132.40 J/g for EDMA, and 150.66 and −145.22 J/g for EDPA, respectively. Phase change temperatures of these PCMs were ranged between 38.5 and 52.5 °C. The synthesized PCMs were tested for durability by accelerated thermal cyclings including 1000 melting/freezing cycles. Besides the thermal endurance of the PCMs were determined by TG analysis. Based on the results it was concluded that EDLA, EDMA, and EDPA compounds synthesized as novel solid–liquid PCMs have considerable amount of thermal energy storage potential in terms of suitable phase change temperatures, high latent heats, thermal reliability, and thermal stability. Moreover, the other advantages of the synthesized PCMs over the fatty acids used are better odor, low corrosivity, and low sublimation rates.

Degradation of glacial deposits quantified with cosmogenic nuclides, Quartermain Mountains, Antarctica

AbstractMany glacial deposits in the Quartermain Mountains, Antarctica present two apparent contradictions regarding the degradation of unconsolidated deposits. The glacial deposits are up to millions of years old, yet they have maintained their meter‐scale morphology despite the fact that bedrock and regolith erosion rates in the Quartermain Mountains have been measured at 0·1–4·0 m Ma−1. Additionally, ground ice persists in some Miocene‐aged soils in the Quartermain Mountains even though modeled and measured sublimation rates of ice in Antarctic soils suggest that without any recharge mechanisms ground ice should sublimate in the upper few meters of soil on the order of 103 to 105 years. This paper presents results from using the concentration of cosmogenic nuclides beryllium‐10 (10Be) and aluminum‐26 (26Al) in bulk sediment samples from depth profiles of three glacial deposits in the Quartermain Mountains. The measured nuclide concentrations are lower than expected for the known ages of the deposits, erosion alone does not always explain these concentrations, and deflation of the tills by the sublimation of ice coupled with erosion of the overlying till can explain some of the nuclide concentration profiles. The degradation rates that best match the data range 0·7–12 m Ma−1 for sublimation of ice with initial debris concentrations ranging 12–45% and erosion of the overlying till at rates of 0·4–1·2 m Ma−1. Overturning of the tills by cryoturbation, vertical mixing, or soil creep is not indicated by the cosmogenic nuclide profiles, and degradation appears to be limited to within a few centimeters of the surface. Erosion of these tills without vertical mixing may partially explain how some glacial deposits in the Quartermain Mountains maintain their morphology and contain ground ice close to the surface for millions of years. Copyright © 2010 John Wiley & Sons, Ltd.

Surface exciton in thiophene oligomer single crystals

AbstractA new type of surface exciton has been observed on large grown single‐crystal surfaces of the bc plane in bithiophene, quarterthiophene, and quinquethiophene and of the ab plane in terthiophene, by reflection measurements. These surfaces are well‐grown flat surfaces. The surface exciton absorption intensities decrease with time and are faster in the order of bithiophene, terthiophene, quarterthiophene, and quinquethiophene. This is the same order as their sublimation rates. The present new type of surface exciton is not confined in a surface layer potential like other ones reported before. The energy is lowered by twisting the molecular form between cis and trans forms. The surface exciton absorption band was not observed on the other side walls of the thick crystals, which are the ab and the ac planes in bithiophene, quarterthiophene, and quinquethiophene single crystals (SCs) and the bc and ac planes in a terthiophene SC. Vibronic exciton absorption bands were observed directly by the reflection measurements on these side walls.

Water ice sublimation-related landforms on Mars

Abstract Sublimation-related landforms are ubiquitous on Mars, especially at mid to high latitudes. This paper reviews the main landforms interpreted to form due to sublimation of subsurface ice on Mars. Pits, knobs and dissected terrains are classical landforms thought to form due to subsurface ice sublimation as observed with high-resolution imagery. Sublimation-related processes on Mars are strongly latitude dependent, with sublimation being increasingly important from high (>60°) to low latitudes (down to 25°) due to correspondingly higher mean annual temperatures. Equatorial regions (within 25° latitude) are mainly devoid of any sublimation-related landforms, reflecting an ice-free shallow subsurface. Mean temperatures and water vapour pressure strongly control the sublimation rate, but diffusion and water adsorption are fundamental and vary depending on the regolith porosity and composition, leading to variations in the theoretical depth at which water ice becomes stable. From a geomorphological point of view, this review highlights the importance of subsurface structure (fractures, layering) in the shaping of landforms and in the control of sublimation rates, in addition to usual physicochemical parameters.

Sublimation and surface energy budget of Taylor Glacier, Antarctica

AbstractTaylor Glacier, an outlet of the East Antarctic ice sheet, flows through the Transantarctic Mountains and terminates in the Dry Valleys. Understanding how this glacier fluctuates is important for studies of glacial geology, paleoclimate, ice dynamics and ecology. Sublimation is the primary mass-loss process for most of the glacier. Four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cm a−1. We used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate. Calculated and measured ablation rates agree to within uncertainties, indicating that wind speed and vapour pressure gradient (a function of temperature and humidity) are the governing variables, as expected from theory. Measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier. On average, sublimation is about two times faster in summer than winter. Rapid sublimation occurs during storms and katabatic wind events, but such periods contribute less to the annual total than do slow, persistent losses. Spatially, sublimation reaches a maximum midway along the glacier, where descending surface air currents are focused by the topography of the aptly named tributary, Windy Gully.