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.

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.

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.

scholarly journals Evolution Mechanism of Metallic Dioxide MO2 (M = Mn, Ti) from Nanorods to Bulk Crystal: First-Principles Research

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Pengsen Zhao ◽  
Guifa Li ◽  
Bingtian Li ◽  
Haizhong Zheng ◽  
Shiqiang Lu ◽  
...  
Keyword(s):  
Surface Energy ◽  
Electronic Properties ◽  
Surface Effect ◽  
Mulliken Charge ◽  
Mulliken Population ◽  
Evolution Mechanism ◽  
Surface Energies ◽  
Surface Areas ◽  
Nanometer Materials ◽  
Intrinsic Mechanism

Using first-principle calculations, the surface energy, cohesive energy, and electronic properties of α-MnO2 and rutile TiO2 nanorods and microfacets were investigated and clarified to, in the first instance, determine the evolution mechanism. The results show that the surface energies of α-MnO2 nanorods and microfacets conform to function 1.0401 Jm−2 + N × 0.608 Jm−2, while the surface energies of the rutile TiO2 nanorods and microfacets are governed by a 1.0102 × 1.1997 rule. Their electronic properties, such as the Mulliken population and Mulliken charge, can only be normalized by their surface areas to attain a linear function. Meanwhile, the surface energy of α-MnO2 with the nanostructure closely conforms to the function for normalized Mulliken population and Mulliken charge as f(x)=102.9×x+0.101 with an R2 value of 0.995. Thus, our research into the evolution mechanism affecting the surface effect of nanometer materials will be useful for investigating the intrinsic mechanism of the nanometer effect and doping process of metallic dioxide catalysts.

THE SURFACE ENERGY OF TOBERMORITE

1959 ◽  
Vol 37 (4) ◽  
pp. 714-724 ◽  
Author(s):  
Stephen Brunauer ◽  
D. L. Kantro ◽  
C. H. Weise
Keyword(s):  
Surface Energy ◽  
Room Temperature ◽  
Geometric Mean ◽  
Adsorbed Water ◽  
Tricalcium Silicate ◽  
Dicalcium Silicate ◽  
Total Surface Energy ◽  
Cross Sectional ◽  
Surface Areas ◽  
Negative Surface

The total surface energy (or surface enthalpy) of a calcium silicate hydrate, tobermorite, having the composition of Ca3Si2O7•2H2O, was determined at 23.5 °C. The tobermorite was obtained from the room-temperature hydration of tricalcium silicate, Ca3SiO5, or β-dicalcium silicate, β-Ca2SiO4, two of the most important constituents of portland cements. The hydration reactions were carried out in three different ways, and 14 preparations were obtained. For each preparation the heats of solution in a mixture of nitric acid and hydrofluoric acid were measured at 23.5 °C, and the surface areas were determined by the B.E.T. method, using water vapor at 25 °C as the adsorbate. The cross-sectional area of the adsorbed water molecule was taken to be 11.4 Å2. The surface energy of tobermorite at 23.5 °C was found to be 386 ± 20 ergs/cm2. It is close to the geometric mean of the surface energies of calcium hydroxide and hydrous amorphous silica, previously reported.Nitrogen adsorption did not measure the true surface area of most tobermorite preparations. This was indicated by negative surface energy values in a number of instances.

scholarly journals Numerical Investigation of the Deformable Porous Media Treated by the Intermittent Microwave

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 757
Author(s):  
Tianyi Su ◽  
Wenqing Zhang ◽  
Zhijun Zhang ◽  
Xiaowei Wang ◽  
Shiwei Zhang
Keyword(s):  
Porous Media ◽  
Heat Transport ◽  
Liquid Water ◽  
Von Mises Stress ◽  
Temperature Deformation ◽  
Local Maxima ◽  
Whole Process ◽  
Surface Areas ◽  
Pulse Ratio ◽  
Von Mises

A 2D axi-symmetric theoretical model of dielectric porous media in intermittent microwave (IMW) thermal process was developed, and the electromagnetic energy, multiphase transport, phase change, large deformation, and glass transition were taken into consideration. From the simulation results, the mass was mainly carried by the liquid water, and the heat was mainly carried by liquid water and solid. The diffusion was the dominant mechanism of the mass transport during the whole process, whereas for the heat transport, the convection dominated the heat transport near the surface areas during the heating stage. The von Mises stress reached local maxima at different locations at different stages, and all were lower than the fracture stress. A material treated by a longer intermittent cycle length with the same pulse ratio (PR) tended to trigger the phenomena of overheat and fracture due to the more intense fluctuation of moisture content, temperature, deformation, and von Mises stress. The model can be extended to simulate the intermittent radio frequency (IRF) process on the basis of which one can select a suitable energy source for a specific process.

scholarly journals Vertical Orientation of Liquid Crystal on 4-n-Alkyloxyphenoxymethyl-Substituted Polystyrene Containing Liquid Crystal Precursor

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 736
Author(s):  
Kyutae Seo ◽  
Hyo Kang
Keyword(s):  
Molecular Structure ◽  
Liquid Crystal ◽  
Surface Energy ◽  
Polymer Films ◽  
Ultraviolet Irradiation ◽  
Molar Fraction ◽  
Side Chain ◽  
Polymer Modification ◽  
Vertical Orientation ◽  
Surface Energies

We synthesized a series of polystyrene derivatives that were modified with precursors of liquid crystal (LC) molecules, such as 4-ethyloxyphenol (homopolymer PEOP and copolymer PEOP#; # = 20, 40, 60, and 80, where # indicates the molar fraction of 4-ethyloxyphenoxymethyl in the side chain), 4-n-butyloxyphenol (PBOP), 4-n-hexyloxyphenol (PHOP), and 4-n-octyloxyphenol (POOP), via polymer modification reaction to investigate the orientation of LC molecules on polymer films, exhibiting part of the LC molecular structure. LC molecules showed a stable and uniform vertical orientation in LC cells fabricated with polymers that have 4-ethyloxyphenoxymethyl in the range of 40–100 mol%. In addition, similar results were obtained in LC cells fabricated with homopolymers of PEOP, PBOP, PHOP, and POOP. The vertical orientation of LC molecules in LC cells fabricated with polymer films correlated to the surface energy of polymer films. For example, vertical LC orientation was observed when the total surface energies of the polymer films were lower than approximately 43.2 mJ/m2. Good alignment stabilities were observed at 150 °C and 20 J/cm2 of ultraviolet irradiation for LC cells fabricated with PEOP film.

SURFACE ENERGY ENGINEERING OF Cu SURFACE BY STRAIN: FIRST-PRINCIPLES CALCULATIONS

2013 ◽  
Vol 20 (06) ◽  
pp. 1350054 ◽  
Author(s):  
L. HE ◽  
Y. W. LIU ◽  
W. J. TONG ◽  
J. G. LIN ◽  
X. F. WANG
Keyword(s):  
Surface Energy ◽  
First Principles ◽  
Strain Distribution ◽  
First Principles Calculations ◽  
Surface Energies ◽  
Energy Engineering

Surface energies of strained Cu surfaces were studied systematically using first-principles methods. Results showed that the strain-stabilization of Cu surface was anisotropic and strongly related to the strain distribution. This strain-induced approach could be used as an effective way to engineer the surface energies of metals.

scholarly journals Snow specific surface area simulation using the one-layer snow model in the Canadian LAnd Surface Scheme (CLASS)

2013 ◽  
Vol 7 (3) ◽  
pp. 961-975 ◽  
Author(s):  
A. Roy ◽  
A. Royer ◽  
B. Montpetit ◽  
P. A. Bartlett ◽  
A. Langlois
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Liquid Water ◽  
Land Surface ◽  
Surface Energy Balance ◽  
Liquid Water Content ◽  
Canadian Land Surface Scheme ◽  
Snow Model ◽  
Surface Scheme ◽  
The One

Abstract. Snow grain size is a key parameter for modeling microwave snow emission properties and the surface energy balance because of its influence on the snow albedo, thermal conductivity and diffusivity. A model of the specific surface area (SSA) of snow was implemented in the one-layer snow model in the Canadian LAnd Surface Scheme (CLASS) version 3.4. This offline multilayer model (CLASS-SSA) simulates the decrease of SSA based on snow age, snow temperature and the temperature gradient under dry snow conditions, while it considers the liquid water content of the snowpack for wet snow metamorphism. We compare the model with ground-based measurements from several sites (alpine, arctic and subarctic) with different types of snow. The model provides simulated SSA in good agreement with measurements with an overall point-to-point comparison RMSE of 8.0 m2 kg–1, and a root mean square error (RMSE) of 5.1 m2 kg–1 for the snowpack average SSA. The model, however, is limited under wet conditions due to the single-layer nature of the CLASS model, leading to a single liquid water content value for the whole snowpack. The SSA simulations are of great interest for satellite passive microwave brightness temperature assimilations, snow mass balance retrievals and surface energy balance calculations with associated climate feedbacks.

γ-Alumina and Amorphous Silica–Alumina: Structural Features, Acid Sites and the Role of Adsorbed Water

2017 ◽  
Vol 60 (19-20) ◽  
pp. 1554-1564 ◽  
Author(s):  
Vicente Sanchez Escribano ◽  
Gabriella Garbarino ◽  
Elisabetta Finocchio ◽  
Guido Busca
Keyword(s):  
Amorphous Silica ◽  
Adsorbed Water ◽  
Structural Features ◽  
Acid Sites ◽  
Silica Alumina

scholarly journals Surface energies emerging in a microscopic, two-dimensional two-well problem

2017 ◽  
Vol 147 (5) ◽  
pp. 1041-1089 ◽  
Author(s):  
Georgy Kitavtsev ◽  
Stephan Luckhaus ◽  
Angkana Rüland
Keyword(s):  
Surface Energy ◽  
Two Dimensional ◽  
Direct Control ◽  
First Order ◽  
Surface Energies ◽  
Energy Scaling ◽  
Continuous Analogue ◽  
Dimensional Shape ◽  
Set Up ◽  
Microscopic Modelling

In this paper we are interested in the microscopic modelling of a two-dimensional two-well problem that arises from the square-to-rectangular transformation in (two-dimensional) shape-memory materials. In this discrete set-up, we focus on the surface energy scaling regime and further analyse the Hamiltonian that was introduced by Kitavtsev et al. in 2015. It turns out that this class of Hamiltonians allows for a direct control of the discrete second-order gradients and for a one-sided comparison with a two-dimensional spin system. Using this and relying on the ideas of Conti and Schweizer, which were developed for a continuous analogue of the model under consideration, we derive a (first-order) continuum limit. This shows the emergence of surface energy in the form of a sharp-interface limiting model as well the explicit structure of the minimizers to the latter.

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