Preparation of Low-Density Aerogels at Ambient Pressure

1992 ◽  
Vol 271 ◽  
Author(s):  
Douglas M. Smith ◽  
Ravindra Deshpande ◽  
C. Jeffrey Brinke
Keyword(s):  
Capillary Pressure ◽  
High Pressures ◽  
High Efficiency ◽  
Ambient Pressure ◽  
Silica Gels ◽  
Low Density ◽  
Additional Advantage ◽  
Commercial Viability ◽  
Critical Point Drying ◽  
Density Surface

ABSTRACTLow density aerogels have numerous unique properties which suggest a number of applications such as ultra high efficiency thermal insulation. However, the commercial viability of these materials has been limited by the high costs associated with drying at high pressures (supercritical), low stability to water vapor, and low mechanical strength. Normally, critical point drying is employed to eliminate the surface tension and hence, the capillary pressure, of the pore fluid to essentially zero. However, we show that by employing a series of aging and surface derivatization steps, the capillary pressure and gel matrix strength may be controlled such that gel shrinkage is minimal during rapid drying at ambient pressure. The properties (density, surface area, pore size, SAXS) of aerogel monoliths prepared from base catalyzed silica gels using this technique, supercritical CO2 drying, and supercritical ethanol drying are compared. An additional advantage of this approach is that the final gels are hydrophobic.

Effect of ambient pressure on low-density nozzle plumes

1995 ◽  
Author(s):  
Chan-Hong Chung ◽  
Kenneth D ◽  
Robert Stubbs
Keyword(s):  
Ambient Pressure ◽  
Low Density

Molecular Dynamics Simulations on Melting of Aluminum

2013 ◽  
Vol 423-426 ◽  
pp. 935-938 ◽  
Author(s):  
Ji Feng Li ◽  
Xiao Ping Zhao ◽  
Jian Liu
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Molecular Dynamics Simulations ◽  
High Pressures ◽  
Ambient Pressure ◽  
Initial Porosity ◽  
Equilibrium Melting Point ◽  
Porosity Effect ◽  
Dynamics Simulations ◽  
Experimental Melting Point

Molecular dynamics simulations were performed to calculate the melting points of perfect crystalline aluminum to high pressures. Under ambientpressure, there exhibits about 20% superheating before melting compared to the experimental melting point. Under high pressures, thecalculated melting temperature increases with the pressure but at a decreasing rate, which agrees well with the Simon's melting equation. Porosity effect was also studied for aluminum crystals with various initial porosity at ambient pressure, which shows that the equilibrium melting point decreases with the initial porosity as experiments expect.

scholarly journals Pressure-Dependent Clustering in Ionic-Liquid-Poly (Vinylidene Fluoride) Mixtures: An Infrared Spectroscopic Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2099
Author(s):  
Teng-Hui Wang ◽  
Wei-Xiang Wang ◽  
Hai-Chou Chang
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Vinylidene Fluoride ◽  
Ambient Pressure ◽  
Infrared Spectroscopic Study ◽  
Research Attention ◽  
Nanoscale Structures ◽  
Local Structures ◽  
Poly Vinylidene Fluoride ◽  
Hydrogen Bonded

The nanostructures of ionic liquids (ILs) have been the focus of considerable research attention in recent years. Nevertheless, the nanoscale structures of ILs in the presence of polymers have not been described in detail at present. In this study, nanostructures of ILs disturbed by poly(vinylidene fluoride) (PVdF) were investigated via high-pressure infrared spectra. For 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HEMIm][TFSI])-PVdF mixtures, non-monotonic frequency shifts of the C4,5-H vibrations upon dilution were observed under ambient pressure. The experimental results suggest the presence of microheterogeneity in the [HEMIm][TFSI] systems. Upon compression, PVdF further influenced the local structure of C4,5–H via pressure-enhanced IL–PVdF interactions; however, the local structures of C2–H and hydrogen-bonded O–H were not affected by PVdF under high pressures. For choline [TFSI]–PVdF mixtures, PVdF may disturb the local structures of hydrogen-bonded O–H. In the absence of the C4,5–H⋯anion and C2–H⋯anion in choline [TFSI]–PVdF mixtures, the O–H group becomes a favorable moiety for pressure-enhanced IL–PVdF interactions. Our results indicate the potential of high-pressure application for designing pressure-dependent electronic switches based on the possible changes in the microheterogeneity and electrical conductivity in IL-PVdF systems under various pressures.

scholarly journals Barothermal Processing of Animal Feed Ingredients

2019 ◽  
Vol 29 (3) ◽  
pp. 428-442 ◽  
Author(s):  
Vladimir I. Syrovatka ◽  
Natalya V. Zhdanova ◽  
Aleksandr N. Rasskazov ◽  
Dmitriy I. Toropov
Keyword(s):  
Heat Treatment ◽  
Superheated Steam ◽  
High Pressures ◽  
High Efficiency ◽  
Animal Feed ◽  
Raw Materials ◽  
Digital Technologies ◽  
Feed Ingredients ◽  
System P ◽  
User Friendly

Introduction. The article substantiates the need for high-temperature processing of feed ingredients. Principles of operation and design features of the applied methods and equipment for feed production are considered. Phase transitions, along with advantages and energy, technological, and technical drawbacks are highlighted. The aim of the study is to justify a possibility of creating high-efficiency production lines using heat treatment of feeds by application of heat valves ensuring continuous loading of raw materials into a reactor and discharge of the treated feed at high pressures and temperatures. Materials and Methods. It is proposed to transfer the process of barothermal processing to a higher zone of the phase diagram of the system p,t (pressure and temperature). This is a section of the superheated steam zone with temperature 300–374 °C, pressure 12–21 MPa and treatment exposure 30–60 seconds, which replaces costly processes of normalizing, expansion, extrusion and granulation. The change in enthalpy in the pressure range 0–21 MPa and temperature range 0–600 °C is shown. Thermal modes are presented as formulas which is the basic condition for the use of digital technologies. Results. The design of the reactor with a thermal gate for loading and unloading, being the main unit of the production line of the feed heat treatment, was proposed. The results of the study are fundamental for the development of the sample flow low-capacity line. Discussion and Conclusion. The transfer of the process of barothermic processing of feed into the zone of superheated steam allows for the transfer of poorly digestible elements of grain and legumes in easily digestible, pathogen-free feed. Advantages of the reactor and line include the user-friendly design, energy saving and possibility of implementation of advanced digital technologies.

scholarly journals Iterative fractionation of recycling receptors from lysosomally destined ligands in an early sorting endosome.

1989 ◽  
Vol 109 (6) ◽  
pp. 3303-3314 ◽  
Author(s):  
K W Dunn ◽  
T E McGraw ◽  
F R Maxfield
Keyword(s):  
Digital Image Analysis ◽  
High Efficiency ◽  
Low Density Lipoproteins ◽  
Low Density ◽  
Recycling Endosomes ◽  
Double Label ◽  
Fluorescent Ligands ◽  
Endocytic Vesicles ◽  
Endocytic Compartments ◽  
Very High

To study the fusion and separation of endocytic compartments, we have used digital image analysis to quantify the accumulation of fluorescent ligands in endosomes during continuous endocytosis for periods of 1-20 min. Fluorescently labeled transferrin (Tf) and low density lipoproteins (LDL) were used as markers of recycling receptors and lysosomally directed ligands respectively. By measuring the intensity of individual endosomes, we found that the amount of LDL per endosome increases 30-40-fold between 1 and 10 min and then plateaus. In contrast, the amount of Tf per endosome reaches a steady state within 2 min at a level that is only three to four times that at 1 min. We used pulse-chase double label methods to demonstrate that Tf cycles through the compartment in which the LDL accumulates. When both Tf and LDL are added to cells simultaneously for 2 min, nearly all endosomes contain both labels. With 2-4 min further incubation in the absence of external ligands, LDL-containing compartments become depleted of Tf as Tf is directed to para-Golgi recycling endosomes. However, if Tf is added to the medium 2-4 min after a pulse with LDL, most of the LDL-containing endosomes become labeled with Tf. The data indicate that at least 30-40 endocytic vesicles containing both Tf and LDL fuse with an endosomal compartment over a period of 5-10 min. LDL accumulates within this compartment and Tf is simultaneously removed. Simple mathematical models suggest that this type of iterative fractionation can lead to very high efficiency sorting.

scholarly journals X-ray studies of the transformation from high- to low-density amorphous water

2019 ◽  
Vol 377 (2146) ◽  
pp. 20180164 ◽  
Author(s):  
Daniel Mariedahl ◽  
Fivos Perakis ◽  
Alexander Späh ◽  
Harshad Pathak ◽  
Kyung Hwan Kim ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Structural Evolution ◽  
High Energy ◽  
Real Space ◽  
High Density ◽  
Low Density ◽  
X Ray ◽  
Amorphous Ice ◽  
Density State ◽  
Amorphous States

Here we report about the structural evolution during the conversion from high-density amorphous ices at ambient pressure to the low-density state. Using high-energy X-ray diffraction, we have monitored the transformation by following in reciprocal space the structure factor S OO ( Q ) and derived in real space the pair distribution function g OO ( r ). Heating equilibrated high-density amorphous ice (eHDA) at a fast rate (4 K min –1 ), the transition to the low-density form occurs very rapidly, while domains of both high- and low-density coexist. On the other hand, the transition in the case of unannealed HDA (uHDA) and very-high-density amorphous ice is more complex and of continuous nature. The direct comparison of eHDA and uHDA indicates that the molecular structure of uHDA contains a larger amount of tetrahedral motives. The different crystallization behaviour of the derived low-density amorphous states is interpreted as emanating from increased tetrahedral coordination present in uHDA. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

The concentration and pressure dependent diffusion of carbon dioxide in nitrile rubbers

1992 ◽  
Vol 339 (1655) ◽  
pp. 497-519 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Diffusion Coefficient ◽  
High Pressures ◽  
Ambient Pressure ◽  
Weight Fraction ◽  
Gas Pressure ◽  
Time Dependent ◽  
Initial Increase ◽  
Parametric Function ◽  
Ambient Gas

The paper reports the results of an experimental and associated analytical study of the time dependent adsorption of carbon dioxide gas into two nitrile elastomers. The mass gas sorption has been measured using a device based on a vibrating reed to a weight fraction accuracy of ca . 0.05 % at 47 °C in the ambient gas pressure range 0.1-34 MPa. The experimental method is described and data are provided. These data are used to compute the most effective description of the diffusion process by invoking a number of different diffusion coefficient, D(θ), characteristics, where θ denotes lapsed time, ambient pressure and local ambient gas concentration within the elastomers. The numerical procedures adopted to perform the fitting of the experimental data with various D(θ) characteristics are described and the quality of the fit is assessed. The D(θ) characteristics chosen have no particular physical basis but follow established empirical precedents. The characteristics of the parameters associated with the various D(θ) functions generally indicate that as the gas is embibed with progressively increasing ambient pressures the diffusion coefficient increases. At high pressures the diffusion is arrested and the coefficient decreases. We have associated the initial increase with gas induced plasticization and the eventual decreases with the effect of the hydrostatic component of the ambient gas pressure. The parameter fitting also indicates that the diffusion is arrested with lapsed time which is tentatively associated with time dependent volumetric relaxations. These interpretations apart, the data and analyses clearly indicate that the transport is not simply fickian and a relatively complex parametric function to describe the sensitivity of the diffusion coefficient to time, concentration and pressure is necessary for these systems.

PRESSURE-INDUCED ELECTRONIC PHASE TRANSITIONS AND SUPERCONDUCTIVITY IN TITANIUM

2009 ◽  
Vol 23 (05) ◽  
pp. 723-741 ◽  
Author(s):  
K. IYAKUTTI ◽  
C. NIRMALA LOUIS ◽  
S. ANURATHA ◽  
S. MAHALAKSHMI
Keyword(s):  
High Pressure ◽  
Band Structure ◽  
Fermi Surface ◽  
High Pressures ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Normal Pressure ◽  
Orbital Method ◽  
Superconducting Transition ◽  
Electronic Band

The electronic band structure, density of states, structural phase transition, superconducting transition and Fermi surface cross section of titanium ( Ti ) under normal and high pressures are reported. The high pressure band structure exhibits significant deviations from the normal pressure band structure due to s → d transition. On the basis of band structure and total energy results obtained using tight-binding linear muffin-tin orbital method (TB LMTO), we predict a phase transformation sequence of α( hcp ) → ω (hexagonal) → γ (distorted hcp) → β (bcc) in titanium under pressure. From our analysis, we predict a δ (distorted bcc) phase which is not stable at any high pressures. At ambient pressure, the superconducting transition occurs at 0.354 K. When the pressure is increased, it is predicted that, Tc increases at a rate of 3.123 K/Mbar in hcp–Ti . On further increase of pressure, Tc begins to decrease at a rate of 1.464 K/Mbar. The highest value of Tc(P) estimated is 5.043 K for hcp–Ti , 4.538 K for ω– Ti and 4.85 K for bcc – Ti . From this, it is inferred that the maximum value of Tc(P) is rather insensitive to the crystal structure of Ti . The nonlinearities in Tc(P) is explained by considering the destruction and creation of new parts of Fermi surface at high pressure. At normal pressure, the hardness of Ti is in the following order: ω- Ti > hcp - Ti > bcc- Ti > γ- Ti .

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