9 research outputs found
Fracture Strength Evaluation of Agglomerates of Fatty Acid-Coated CaCO3 Nanoparticles by Nano-Indentation
Nanoparticles often form agglomerates during their manufacturing process. When nanoparticles form agglomerates, their inherent properties cannot be fully exploited. In this study, we attempted to establish a conventional method to evaluate the fracture strength of agglomerates into smaller parts. We used a commercially available nano-indentation instrument with a flat indenter tip. We chose calcium carbonate nanoparticles with stearic acid coatings as model materials. It was found that the more fatty acid that is coated on the particle surface, the stronger the agglomerates become. The technique we propose in this study can be used to rapidly evaluate the fracture strength of nanoparticle agglomerates
First-principles Analysis of Stearic Acid Adsorption on Calcite (104) Surface
Calcium carbonate nanoparticles are often surface-treated with organic compounds such as fatty acids. The activated calcium carbonates not only exhibit excellent application properties, but also can be applied as eco-friendly inorganic-organic hybrid materials. However, the microscopic adsorption structure of organic compounds on calcite surfaces is not yet well understood. In this study, we performed computational simulations based on density functional theory to investigate adsorption states of stearic acid (SA) on a calcite (104) surface. Based on the first-principles ionic relaxation and molecular dynamics simulations for several types of SA−SA and calcite−SA bonding models, a SA bilayer model on the calcite (104) surface is predicted to be a possible stable structure. The proposed structure model is well consistent with the experimentally predicted adsorption mechanism of SA on the calcite (104) surface
Fabrication of Single-Crystalline Calcite Needle-Like Particles Using the Aragonite–Calcite Phase Transition
Calcium carbonate (CaCO3) occurs in two major polymorphs: rhombohedral calcite and orthorhombic aragonite, the latter is thermodynamically metastable. In this study, we first prepared aragonite needle-like particles by introducing CO2-containing gas into Ca(OH)2 aqueous slurry. Then, the resulted aragonite particles were heat treated at 500 °C for 1 h, in order to induce the aragonite–calcite phase transition. Particle structures before and after the heat treatment were characterized mainly by powder X-ray diffractometry (XRD), field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). We found that single-crystalline calcite needle-like particles with zigzag surface structures can be fabricated using the phase transition
Formation of a Cr3+-rich luminescent thin phase along a grain boundary of alpha-Al2O3
An α-Al2O3 bicrystal doped with Cr3+ was fabricated by diffusion bonding at high temperatures. It was found that a ruby phase with approximately 200 nm thickness was formed along the grain boundary. This thin phase shows Cr3+:Al2O3-induced luminescence, confirmed by confocal micro-luminescence spectroscopy
Evolution of Calcite Nanocrystals through Oriented Attachment and Fragmentation: Multistep Pathway Involving Bottom-Up and Break-Down Stages
A nonclassical
multistep pathway involving bottom-up and break-down
stages for the evolution of calcite nanograins ∼50 nm in size
was demonstrated in a basic aqueous system. Calcite nanofibrils ∼10
nm wide were produced as the initial crystalline phase via amorphous
calcium carbonate through ion-by-ion assembly by the carbonation of
Ca(OH)<sub>2</sub> at a high pH of ∼13. Bundles ∼50
nm in diameter were then formed by the subsequent oriented attachment
of the nanofibrils. Monodispersed calcite nanograins were finally
obtained through spontaneous fragmentation of the fibrous forms via
a decrease in pH by further carbonation
Direct Observation of Impurity Segregation at Dislocation Cores in an Ionic Crystal
Dislocations,
one-dimensional lattice defects, are known to strongly interact with
impurity atoms in a crystal. This interaction is generally explained
on the basis of the long-range strain field of the dislocation. In
ionic crystals, the impurity–dislocation interactions must
be influenced by the electrostatic effect in addition to the strain
effect. However, such interactions have not been verified yet. Here,
we show a direct evidence of the electrostatic impurity–dislocation
interaction in α-Al<sub>2</sub>O<sub>3</sub> by visualizing
the dopant atom distributions at dislocation cores using atomic-resolution
scanning transmission electron microscopy (STEM). It was found that
the dopant segregation behaviors strongly depend on the kind of elements,
and their valence states are considered to be a critical factor. The
observed segregation behaviors cannot be explained by the elastic
interactions only, but can be successfully understood if the electrostatic
interactions are taken into account. The present findings will lead
to the precise and quantitative understanding of impurity induced
dislocation properties in many materials and devices