Molecular Dynamics Simulations of the Effect of the Composition of Calcium Alumino-Silicate Intergranular Films on Alumina Grain Growth

Zhang, Shenghong; Garofalini, Stephen H.

doi:10.1021/jp0531053

Cited by 19 publications

(31 citation statements)

References 39 publications

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“…The modified-BMH potential was employed to describe the atomic behavior of silicon oxide, which was developed by Garofalini et al [16,17,[28][29][30], to fit into certain interatomic angles and coulombic forces of the amorphous phase. The total energy of the system V is modeled as a sum of the twobody and three-body interaction terms as follows:…”

Section: Potential Energy Functionmentioning

confidence: 99%

“…Note that the modified-BMH potential was originally developed to characterize the amorphous silicon oxide [16,17] by considering the angle dependency in describing interatomic forces. It is versatile in including other elements, such as nitrogen and aluminum [28][29][30]. It should also be pointed out that basic studies with computational methods using MD techniques have been seldom performed, especially on crystalline phases and grain boundaries, despite the great interest in SiO 2 materials.…”

Section: Introductionmentioning

confidence: 99%

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Effects of temperature and tilt angle on the grain boundary structure in silicon oxide: Molecular dynamics study

2010

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Molecular Dynamic (MD) simulations on a crystalline and amorphous silicon oxide were performed by using modified-Born-Mayer-Huggins (modified-BMH) potential. Comparison of the lattice parameters and analyses of the RDF for five different bulk phases of silicon oxide showed that the modified-BMH potential was properly able to describe crystalline phases, as well as the amorphous phase. When a polycrystalline model system that was composed of two β-cristobalite grains with a tilt grain boundary was annealed, an amorphouslike grain boundary region formed. The thickness of the grain boundary region was practically identical, regardless of the annealing temperature within the MD calculation time, which showed a very early stage of grain boundary amorphization. The atomic distribution in the grain boundary region became more uniform as the annealing temperature increased due to the faster relaxation. On the other hand, the atomic configuration and the thickness of the grain boundary region hardly depended on the grain boundary tilt angle.

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Section: Potential Energy Functionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of temperature and tilt angle on the grain boundary structure in silicon oxide: Molecular dynamics study

2010

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“…Owing to the low solubility limit of common impurities in alumina such as calcia and silica, liquid phases with Ca/Si concentrations far in excess of the bulk level form at grain boundaries 3–6 that preferentially adsorb to certain crystalline planes 7,8 . Computational studies have been able to simulate this behavior and offer a geometric and energetic explanation for this preferential adsorption and the anisotropic grain growth that results; 9 however, considerably less attention has been paid to the opposite effect of preferential dissolution of crystallographic planes that are commonly exposed to the liquid phase during the sintering process.…”

Section: Introductionmentioning

confidence: 99%

“…In order to address these concerns, the molecular dynamics simulation technique was applied to examine the dissolution behavior of differently oriented alumina crystals into silicate melts of varying composition using interatomic potentials applied in previous computational studies of grain growth 9 …”

Section: Introductionmentioning

confidence: 99%

Anisotropic Dissolution of α‐Alumina (0001) and (1120) Surfaces into Adjoining Silicates

Lockwood

Zhang

Garofalini

2008

Journal of the American Ceramic Society

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The dissolutions of the (0001) and (1120) orientations of α‐Al2O3 into calcium silicate, aluminosilicate, and calcium aluminosilicate melts were modeled using molecular dynamics simulations. In all cases, it was found that the (1120) surface of the crystal destabilizes and melts at a lower temperature than does the (0001) surface. This anisotropy in dissolution counters the anisotropy in grain growth, in which the outward growth of the (1120) surface occurs more rapidly than that on the (0001) surface, causing platelets. However, anisotropic dissolution occurred only at a certain temperature range, above which dissolution behavior was isotropic. The presence of calcium in the contacting silicate melt plays an important role in this anisotropic dissolution, similar to its role in anisotropic grain growth observed previously. However, anisotropic dissolution also occurs in the silicate melts not containing calcium, indicating the importance of the different surface energies. In combination with previous simulations of anisotropic grain growth in alumina, these simulations reveal a complex kinetic competition between preferential adsorption and growth versus preferential dissolution of the (1120) orientation in comparison with the (0001) orientation as a function of temperature and local composition. This, in turn, indicates potential processing variations in which to design morphology in alumina.

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“…It was also found that the films' properties can change depending on structure and thickness of the film. However, due to microscopy limitations the structure of the film was not fully resolved and considered to be mainly disordered (amorphous), although order was predicted in the films from both theoretical models and simulations [2]. Relatively recently IGFs were discovered to also exist at metal-ceramic interfaces, and the fundamental questions regarding the structure of the film remain the same.…”

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confidence: 99%

Order in Nanometer-Thick Intergranular Films at Au-Sapphire Interfaces

2011

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The existence of intergranular film (IGFs) at ceramic grain boundaries was observed over 30 years ago. IGFs were found to have a strong influence on material properties (e.g. enhancing fracture toughness or degrading high temperature strength). Recently it was proposed that interfaces can be treated in a manner similar to bulk phases and can have a distinct structure and composition at equilibrium (termed as "complexions") [1]. IGFs were identified as one type of complexion. It was also found that the films' properties can change depending on structure and thickness of the film. However, due to microscopy limitations the structure of the film was not fully resolved and considered to be mainly disordered (amorphous), although order was predicted in the films from both theoretical models and simulations [2]. Relatively recently IGFs were discovered to also exist at metal-ceramic interfaces, and the fundamental questions regarding the structure of the film remain the same. In addition, the reason for the stability of the film at equilibrium is still not fully clear. While it is the common opinion that IGFs reduce interfacial energy, this was never experimentally proven in a direct manner.A model experiment was used to form equilibrated Au particles in contact with sapphire, in the vicinity of small droplets of anorthite glass (CaO-2SiO 2 -Al 2 O 3 ) [3]. This method provided specimens from which the interface energy could be measured, and correlated with the local atomistic structure and chemistry. The local structure was characterized using aberration corrected transmission electron microscopy (TEM) from site-specific cross-section specimens prepared by a modified technique in a dual-beam focused ion beam system [4]. Quantitative aberration corrected HRTEM analysis was conducted where negative spherical aberration (Cs) and exit wave reconstruction were correlated with simulations to determine the atoms' location in the bulk, and the order in the film. One example of such an analysis is presented in Fig. 1. In addition, the equilibrium thickness of the films was measured from the amplitude and phase of the reconstructed wave function. It was found that since the amplitude and phase holds information on the chemistry and the crystallography respectively, their combination provides an accurate method to measure the IGF thickness.Order was indeed observed in the 1.2nm thick films adjacent to the sapphire crystal. From comparison to simulations [2] the order was concluded to be in the form of "Ca cages", experimentally demonstrating that ordering is an intrinsic part of IGFs, as predicted from molecular dynamics and diffuse-interface theory. This finding together with the measurement of the equilibrium thickness and interface energy offers additional experimental support to the perception of IGFs as complexions and their future incorporation in bulk phase diagrams.

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Molecular Dynamics Simulations of the Effect of the Composition of Calcium Alumino-Silicate Intergranular Films on Alumina Grain Growth

Cited by 19 publications

References 39 publications

Effects of temperature and tilt angle on the grain boundary structure in silicon oxide: Molecular dynamics study

Effects of temperature and tilt angle on the grain boundary structure in silicon oxide: Molecular dynamics study

Anisotropic Dissolution of α‐Alumina (0001) and (1120) Surfaces into Adjoining Silicates

Order in Nanometer-Thick Intergranular Films at Au-Sapphire Interfaces

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