scholarly journals PASCal: a principal axis strain calculator for thermal expansion and compressibility determination

2012 ◽  
Vol 45 (6) ◽  
pp. 1321-1329 ◽  
Author(s):  
Matthew J. Cliffe ◽  
Andrew L. Goodwin
Keyword(s):  
Thermal Expansion ◽  
Lattice Parameter Data ◽  
Principal Axis ◽  
Molecular Conformation ◽  
Variable Temperature ◽  
Lattice Parameter ◽  
Mechanical Anisotropy ◽  
Variable Pressure ◽  
Coordination Polyhedra ◽  
Compressibility Effect

This article describes a web-based tool (PASCal; principal axis strain calculator; http://pascal.chem.ox.ac.uk) designed to simplify the determination of principal coefficients of thermal expansion and compressibilities from variable-temperature and variable-pressure lattice parameter data. In a series of three case studies,PASCalis used to reanalyse previously published lattice parameter data and show that additional scientific insight is obtainable in each case. First, the two-dimensional metal–organic framework [Cu2(OH)(C8H3O7S)(H2O)]·2H2O is found to exhibit the strongest area negative thermal expansion (NTE) effect yet observed; second, the widely used explosive HMX exhibits much stronger mechanical anisotropy than had previously been anticipated, including uniaxial NTE driven by thermal changes in molecular conformation; and third, the high-pressure form of the mineral malayaite is shown to exhibit a strong negative linear compressibility effect that arises from correlated tilting of SnO6and SiO4coordination polyhedra.

Thermal Expansion Of GaN And Ain

1997 ◽  
Vol 482 ◽  
Author(s):  
Kai Wang ◽  
Robert R. Reeber
Keyword(s):  
Experimental Data ◽  
Residual Stress ◽  
Thermal Expansion ◽  
Lattice Parameter Data ◽  
Equations Of State ◽  
Lattice Parameter ◽  
Epitaxial Films ◽  
Residual Stress Distribution ◽  
Interatomic Potentials ◽  
Semiempirical Models

AbstractThe temperature dependence of the thermal expansion and the bulk modulus are critical for predicting the residual stress distribution in epitaxial films and provides information relevant for interatomic potentials and equations of state. The thermal expansions of aluminum nitride (AIN) and gallium nitride (GaN) are calculated with two models that employ the limited elastic and lattice parameter data. These semiempirical models allow prediction of the thermal expansions to higher temperatures. Calculated results are compared with experimental data.

Reduction in Wear Rate of α-Alumina and Silicon Nitride by Diffusional Surface Modification

1988 ◽  
Vol 140 ◽  
Author(s):  
A.K. Gangopadhyay ◽  
M.E. Fine ◽  
H.S. Cheng
Keyword(s):  
Wear Resistance ◽  
Thermal Expansion ◽  
Surface Modification ◽  
Silicon Nitride ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Surface Region ◽  
Lattice Parameter ◽  
Lower Thermal Expansion ◽  
Wear Modes

AbstractThe surface regions of α-alumina and hot pressed silicon nitride were modified by suitable alloying in order to improve their wear resistance. The surface modification in polycrystalline α-alumina was done by diffusing chromia into the surface region which resulted in the formation of a thin layer of A12O3 - Cr9O3 solid solution which has a lower thermal expansion coefficient than pure α-alumina. Also Cr2O3 has a larger lattice parameter than α-alumina thus during cooling the surface was put into compression. The surface region of hot pressed silicon nitride was modified by diffusing α-alumina into the surface which resulted in the formation of a thin sialon layer. A surface compressive stress was again introduced due to the lower thermal expansion coefficient and larger latticeparameter of sialon compared to silicon nitride.Wear tests were conducted against 52100 steel under both lubricated and unlubricated sliding contact using a block on ring apparatus. The wear resistance of chromia surface alloyed α-alumina was improved considerably over unalloyed α-alumina under both lubricated and unlubricated conditions. The wear resistance of alumina surface alloyed silicon nitride was also improved over unalloyed silicon nitride under both lubricated and unlubricated conditions.Different wear modes were identified by examining the worn surfaces under the scanning electron microscope.

Using Variable Temperature Powder X-ray Diffraction To Determine the Thermal Expansion Coefficient of Solid MgO

2007 ◽  
Vol 84 (5) ◽  
pp. 818 ◽  
Author(s):  
Nicholas C. Corsepius ◽  
Thomas C. DeVore ◽  
Barbara A. Reisner ◽  
Deborah L. Warnaar
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Variable Temperature ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2150 ◽  
Author(s):  
Ondřej Socha ◽  
Martin Dračínský
Keyword(s):  
Acetic Acid ◽  
Gas Phase ◽  
Low Temperatures ◽  
Variable Temperature ◽  
Glass Tube ◽  
Variable Pressure ◽  
Liquid Phases ◽  
Donor And Acceptor ◽  
Moller Plesset ◽  
Triple Excitation

Due to the nature of the carboxylic group, acetic acid can serve as both a donor and acceptor of a hydrogen bond. Gaseous acetic acid is known to form cyclic dimers with two strong hydrogen bonds. However, trimeric and various oligomeric structures have also been hypothesized to exist in both the gas and liquid phases of acetic acid. In this work, a combination of gas-phase NMR experiments and advanced computational approaches were employed in order to validate the basic dimerization model of gaseous acetic acid. The gas-phase experiments performed in a glass tube revealed interactions of acetic acid with the glass surface. On the other hand, variable-temperature and variable-pressure NMR parameters obtained for acetic acid in a polymer insert provided thermodynamic parameters that were in excellent agreement with the MP2 (the second order Møller–Plesset perturbation theory) and CCSD(T) (coupled cluster with single, double and perturbative triple excitation) calculations based on the basic dimerization model. A slight disparity between the theoretical dimerization model and the experimental data was revealed only at low temperatures. This observation might indicate the presence of other, entropically disfavored, supramolecular structures at low temperatures.

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