scholarly journals Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane

2017 ◽  
Vol 114 (7) ◽  
pp. E1046-E1053 ◽  
Author(s):  
Nancy Birkner ◽  
Alexandra Navrotsky
Keyword(s):  
Surface Energy ◽  
Surface Area ◽  
Oxidation State ◽  
Manganese Oxides ◽  
Lower Surface ◽  
Surface Energies ◽  
Surface Areas ◽  
Bulk Thermodynamics ◽  
Lower Surface Energy

Manganese oxides with layer and tunnel structures occur widely in nature and inspire technological applications. Having variable compositions, these structures often are found as small particles (nanophases). This study explores, using experimental thermochemistry, the role of composition, oxidation state, structure, and surface energy in the their thermodynamic stability. The measured surface energies of cryptomelane, sodium birnessite, potassium birnessite and calcium birnessite are all significantly lower than those of binary manganese oxides (Mn3O4, Mn2O3, and MnO2), consistent with added stabilization of the layer and tunnel structures at the nanoscale. Surface energies generally decrease with decreasing average manganese oxidation state. A stabilizing enthalpy contribution arises from increasing counter-cation content. The formation of cryptomelane from birnessite in contact with aqueous solution is favored by the removal of ions from the layered phase. At large surface area, surface-energy differences make cryptomelane formation thermodynamically less favorable than birnessite formation. In contrast, at small to moderate surface areas, bulk thermodynamics and the energetics of the aqueous phase drive cryptomelane formation from birnessite, perhaps aided by oxidation-state differences. Transformation among birnessite phases of increasing surface area favors compositions with lower surface energy. These quantitative thermodynamic findings explain and support qualitative observations of phase-transformation patterns gathered from natural and synthetic manganese oxides.

ROLE OF LOW SURFACE AREA FEW LAYER GRAPHENE IN ENHANCING MECHANICAL PROPERTIES OF POLY (1,4-CIS-ISOPRENE) RUBBER NANOCOMPOSITES

2020 ◽  
Vol 93 (1) ◽  
pp. 172-182 ◽  
Author(s):  
Vineet Kumar ◽  
Najib Alam ◽  
Dong-Joo Lee ◽  
Ulrich Giese
Keyword(s):  
Mechanical Properties ◽  
Surface Area ◽  
Lower Surface ◽  
Elongation At Break ◽  
Layer Graphene ◽  
Surface Areas ◽  
Series Of Experiments ◽  
Rubber Nanocomposites ◽  
Few Layer Graphene

ABSTRACT Nanofillers of type few layer graphene (FLG) characterized with “low” surface area (<40 m2/g) were studied as reinforcing agents in poly (1,4-cis-isoprene) (IR matrix), and their roles in enhancing mechanical properties of rubber nanocomposites were demonstrated. The adsorption isotherms show that FLG surface areas were 13.8 m2/g for SFG6, 23.8 m2/g for KS4, and 39.5 m2/g for EXG 9840. All FLG had remarkable in-plane crystallinity and were characterized by a lower number of layers stacked (45–48) in the crystalline domain. Rheometric curves were studied to estimate the scorch time (t′05) and curing time (t′90). Tensile and dynamic–mechanical analyses show that FLG forms filler networks at low filler content. Tensile properties show that EXG 9840/IR has a lower reinforcing factor and elongation at break than KS4 FLG nanofiller. A series of experiments shows the dependency surface area of FLG in enhancing mechanical properties of nanocomposites. The work suggests that lower surface area should be selected in order to have lower dissipation of energy and efficient filler networking.

Molecular Dynamics Studies of Surface Nucleation and Crystal Growth of Si on SiO2 Substrates

2005 ◽  
Vol 899 ◽  
Author(s):  
Byoung-Min Lee ◽  
Hong Koo Baik ◽  
Takahide Kuranaga ◽  
Shinji Munetoh ◽  
Teruaki Motooka
Keyword(s):  
Thin Film ◽  
Molecular Dynamics ◽  
Crystal Growth ◽  
Surface Energy ◽  
Md Simulations ◽  
Lower Surface ◽  
Surface Nucleation ◽  
Lower Surface Energy ◽  
Potential Parameters ◽  
Si Thin Film

AbstractMolecular dynamics (MD) simulations of atomistic processes of nucleation and crystal growth of silicon (Si) on SiO2 substrate have been performed using the Tersoff potential based on a combination of Langevin and Newton equations. A new set of potential parameters was used to calculate the interatomic forces of Si and oxygen (O) atoms. It was found that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the surface of MD cell. The values surface energy for (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J/m2, respectively. This result suggests that, the nucleation leads to a preferred (111) orientation in the poly-Si thin film at the surface, driven by the lower surface energy.

Comparison on the Characteristics of Bio-Based Porous Carbons by Physical and Novel Chemical Activation

2014 ◽  
Vol 554 ◽  
pp. 22-26 ◽  
Author(s):  
Jibril Mohammed ◽  
Noor Shawal Nasri ◽  
Muhammad Abbas Ahmad Zaini ◽  
Usman Hamza Dadum ◽  
Murtala Musa Ahmed
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Chemical Activation ◽  
Value Added ◽  
Potassium Acetate ◽  
Lower Surface ◽  
Physical Activation ◽  
Porous Carbons ◽  
Surface Areas ◽  
Agricultural Materials

There is significantly abundant portion of waste agricultural materials in the world serving as environmental challenge, however, they could be converted into useful value added products like activated carbon. Coconut shell based carbons were synthesized using physical activation by CO2 and chemical activation with potassium hydroxide and potassium acetate. The BET surface areas and pore volumes are 361m2/g and 0.19cm3/g for physical activation, 1353m2/g and 0.61cm3/g for activation with KOH and 622m2/g and 0.31cm3/g for potassium acetate activated carbon. From the Fourier Transform Infrared Spectroscopy analysis, hydroxyls, alkenes and carbonyl functional groups were identified with more prominence on the chemically activated porous carbons. Thermogravimetric analysis (TGA) results showed occurrence of moisture pyrolysis at 105°C, the pyrolysis of hemicellulose and cellulose occurred at 160–390°C and lignin at (390-650°C). Carbonization at 700°C and 2hrs had highest yield of 32%. Physical activation yielded lower surface area with approximately 88% micropores. On the other hand, chemically activation yielded higher surface area with elevated mesopores. The porous carbons can be applied to salvage pollution challenges.

THE SURFACE ENERGIES OF CALCIUM OXIDE AND CALCIUM HYDROXIDE

1956 ◽  
Vol 34 (6) ◽  
pp. 729-742 ◽  
Author(s):  
Stephen Brunauer ◽  
D. L. Kantro ◽  
C. H. Weise
Keyword(s):  
Surface Energy ◽  
Specific Surface ◽  
Calcium Hydroxide ◽  
Calcium Oxide ◽  
Surface Energies ◽  
Surface Areas ◽  
C 23 ◽  
Cell Dimensions ◽  
Specific Surface Areas ◽  
Unit Cell Dimensions

The total surface energies (or surface enthalpies) of calcium oxide and calcium hydroxide were determined by measuring the heats of solution in 2 N nitric acid of calcium oxide and calcium hydroxide having high and low specific surface areas, and by determining the surface areas by the B.E.T. method, using nitrogen as adsorbate. The molecular area of nitrogen was taken to be 16.2 Å2 at 77.3 °K. Precision determinations of the lattice parameters indicated that the high and low surface substances had the same unit cell dimensions, and X-ray line broadening measurements indicated that the crystals were perfect or nearly perfect. The surface energy of calcium oxide at 23 °C. was found to be 1310 ± 200 erg/cm.2, which compares well with the theoretical value of 1100 erg/cm.2 The surface energy of calcium hydroxide at 23 °C. was found to be 1180 ± 100 erg/cm.2 The heat of the reaction CaO (c, 23°) + H2O (l, 23°) = Ca(OH)2 (c, 23°), for crystals having negligible specific surface areas, was found to be −15,620 cal.

Bulk and (001) Surface Properties of TiAl3 Compound

2011 ◽  
Vol 299-300 ◽  
pp. 417-421
Author(s):  
Li Wang ◽  
Jian Hong Gong ◽  
Jun Gao
Keyword(s):  
Surface Energy ◽  
Structural Relaxation ◽  
Density Functional ◽  
Dominant Role ◽  
Lower Surface ◽  
Heat Of Formation ◽  
Lattice Constants ◽  
Structural And Electronic Properties ◽  
The Stability ◽  
Lower Surface Energy

The structural and electronic properties of bulk and (001) surface of TiAl3 have been examined by the first-principles total-energy pseudopotential method based on density functional theory. The lattice constants and heat of formation of bulk TiAl3 we obtained are in good agreement with the experimental and other theoretical values. The calculated bulk properties indicates that bonding nature in TiAl3 is a combination of metallic and ionic, in which the metallic bonding become the predominate one. the strongest hybridization exist in the DO22 structure, the Al-3p and Ti-3d bonding of TiAl3 play the dominant role in hybridization. The structural relaxation and surface energy for (001) slab have been simulated to make sure the stability of slabs with different atomic layers. Compared to TiB2 (0001) slab, TiAl3 surfaces shows smaller structural relaxation and lower surface energy, furthermore, the charge redistribution of (001) slab shows almost the same characteristics as bulk TiAl3, which confirms structural stability of TiAl3 with (001) slab. This present work makes a beneficial attempt at exploring TiAl3 surface as an ab initio method for studying possible nucleation mechanism of Aluminum on it.

scholarly journals INVESTIGATIONS OF RESISTANCE TO SEIZING OF LASER-TEXTURED ELEMENTS

1970 ◽  
pp. 3-6
Author(s):  
Bogdan Antoszewski
Keyword(s):  
Surface Energy ◽  
Lower Surface ◽  
Texture Effect ◽  
Lower Surface Energy

The paper presents results of experiments concerning the assessment of the texture effect on scuffing resistance. The results showed that texturing  causes an increase in scuffing resistance. In addition, textures showing lower surface energy and having higher volume were found  to form surfaces more resistant to scuffing.

Efficiency of the Conversion of Work of Drainage to Surface Energy for Sandstone and Carbonate

2007 ◽  
Vol 10 (04) ◽  
pp. 338-347 ◽  
Author(s):  
Siddhartha Seth ◽  
Norman R. Morrow
Keyword(s):  
Surface Energy ◽  
Capillary Pressure ◽  
Surface Area ◽  
Pressure Curve ◽  
Thin Sections ◽  
Surface Areas ◽  
Capillary Pressure Curve ◽  
Phase Saturation ◽  
Interfacial Areas ◽  
Random Packings

Summary The increase in surface energy resulting from drainage of a wetting phase from a porous medium is often equated to the work of displacement determined from the area under its capillary pressure curve. However, capillary pressure vs. saturation relationships are not reversible and do not represent quasistatic displacement. The increase in surface energy is less than the work done because of inherent capillary instabilities that are the basic cause of capillary pressure hysteresis. Nevertheless, relating the area under a capillary pressure curve to the thermodynamic work of displacement can be justified by interpreting the curve as a series of alternating isons (reversible displacements) and rheons (spontaneous redistribution at constant saturation). The efficiency of conversion of work to surface energy, Ed, depends on the increase in surface area that accompanies drainage. Surface areas of nonwetting phase/solid and nonwetting phase/wetting phase have been determined through displacement of a colored low-viscosity liquid resin that can be solidified so that thin sections reveal the distribution of phases and surfaces within the pore space of the rock. Two-dimensional images obtained from thin sections were analyzed using stereology to obtain estimates of saturations and interfacial areas in three dimensions. For drainage of Berea sandstone to 20% wetting-phase saturation, Ed was 36%, which was less than one-half of the efficiency of 85% for the same range of change in saturation determined previously for random packings of equal spheres. Values of Ed for the tested carbonate were approximately one-half of those for sandstone. The wide variation is explained in terms of a simple pore model that relates Ed to aspect ratio. Introduction Changes in fluid saturations during multiphase displacements in porous media are accompanied by changes in interfacial surface area between the phases. Interfacial areas are directly related to surface energy and are fundamental to spontaneous-imbibition phenomena, to multiphase transport properties such as relative permeability, and to processes that involve mass transfer between phases (Haines 1930; Leverett 1941; Rapoport and Leas 1951; Payne 1953; Rootare and Prenzlow 1967; Hassanizadeh and Gray 1993; Reeves and Celia 1996; Kim et al. 1997; Alpak et al. 1999; Schaefer et al. 2000a, 2000b; Beliaev and Hassanizadeh 2001; Wan and Tokunaga 2002; Jain et al. 2003; Cheng et al. 2004). The relationship between work of displacement from capillary pressure data to changes in surface energy from direct measurements of surface areas has been reported in detail for drainage, imbibition, and secondary drainage for random packings of equal spheres (Morrow 1970a). The first measurements of relationships between work and increase in surface energy for porous rocks are reported here for primary drainage of a sandstone and a limestone.

Filler—Elastomer Interactions. Part III. Carbon-Black-Surface Energies and Interactions with Elastomer Analogs

1991 ◽  
Vol 64 (5) ◽  
pp. 714-736 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff ◽  
Jean-Baptiste Donnet
Keyword(s):  
Surface Energy ◽  
Carbon Black ◽  
Surface Area ◽  
Particle Interaction ◽  
Crystallographic Structure ◽  
Specific Component ◽  
Dispersive Component ◽  
Carbon Blacks ◽  
Surface Energies ◽  
Very High

Abstract The surface energies, both the dispersive component, γsd, and the specific component, γssp, of dry- and wet-pelletized carbon blacks, ranging from N110 to N990, were evaluated by inverse gas-solid chromatography at infinite dilution. The results indicate that the dispersive components of the surface energy of carbon blacks increase with increasing surface area. This dependence may essentially reflect an effect of microstructure on the surface energies, which can be confirmed by the relationship between the crystallographic parameters of crystallites and the graphitization of the carbon blacks. It was found that smaller crystallites characterized by a lower value of Lc lead to higher surface energy, whereas graphitization of the carbon black points toward lower surface energy, perhaps resulting from the growth of the quasi-graphite structure. Surface area dependence of the specific component of the surface energy characterized by the specific energy of adsorption of a polar probe follows the same pattern as was observed for the dispersive component, i.e., γsd increases with surface area. This is believed to be related to the crystallographic structure and the surface chemistry. Studies on adsorption energies of the low-molecular-weight analogs of elastomers generally show that the interactions between carbon blacks and rubbers depend not only on filler surface energies but also on the structure of the elastomers. Due to their polar functional groups, NBR and SBR show a stronger interaction with blacks than unsaturated rubbers. Among the rubbers simulated, IIR would have the lowest interaction with the filler. A comparison of the surface energies of carbon blacks and silicas points toward a very high γsd, for blacks which may show strong interaction with nonpolar- or low-polar polymers, while the very high Sf value of the silicas, especially precipitated silicas, a measure of the relative polarity of their surface, is considered to be representative of strong particle-particle interaction, leading to the formation of a filler network.

THE SURFACE ENERGIES OF AMORPHOUS SILICA AND HYDROUS AMORPHOUS SILICA

1956 ◽  
Vol 34 (10) ◽  
pp. 1483-1496 ◽  
Author(s):  
Stephen Brunauer ◽  
D. L. Kantro ◽  
C. H. Weise
Keyword(s):  
Surface Energy ◽  
Amorphous Silica ◽  
Liquid Water ◽  
Bound Water ◽  
Adsorbed Water ◽  
Heat Of Hydration ◽  
Molecular Area ◽  
Surface Energies ◽  
Average Dimension ◽  
Surface Areas

The total surface energies (or, more strictly, surface enthalpies) of amorphous silica and hydrous amorphous silica were determined by measuring the heats of solution in a mixture of nitric acid and hydrofluoric acid of samples having differing specific surface areas and bound water contents, and by measuring the surface areas by the B.E.T. method, using nitrogen as adsorbate. The molecular area of nitrogen was taken to be 16.2 Å2 at 77.3 °K. The surface energy of amorphous silica of zero water content (or the energy of the pure siloxane surface) at 23 °C. was found to be 259 ± 3 ergs/cm.2 The heat of hydration by liquid water of the siloxane surface to silanol surface at 23 °C. was found to be 258.6 ± 13.0 cal./gm. of water. From these two values, with the added assumption that the molecular area of bound water was 25 Å2, the surface energy of hydrous amorphous silica with a completely hydrated surface (or the energy of pure silanol surface) at 23 °C. was calculated to be 129 ± 8 ergs/cm.2 This value is only slightly greater than the surface energy of liquid water. Surface area determinations were also made by water vapor adsorption at 25 °C. The packing of physically adsorbed water appeared to be determined by the geometry of the surface. The cross-sectional area of the adsorbed water molecule was found to be 12.5 Å2. The density of amorphous anhydrous silica was 2.28 to 2.29 gm./cc. Silica particles having an average dimension of 37 Å were dehydrated at lower temperatures and sintered at lower temperatures than particles having an average dimension of 64 Å.

Sign in / Sign up

Export Citation Format

Share Document