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Crystals, Volume 7, Issue 12 (December 2017)

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Cover Story (view full-size image) Our results demonstrate the important role of liquid in directing the mechanochemical synthesis [...] Read more.
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Open AccessArticle The Influence of Epitaxial Crystallization on the Mechanical Properties of Polyamide 66/Reduced Graphene Oxide Nanocomposite Injection Bar
Crystals 2017, 7(12), 384; https://doi.org/10.3390/cryst7120384
Received: 11 November 2017 / Revised: 16 December 2017 / Accepted: 18 December 2017 / Published: 20 December 2017
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Abstract
Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the
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Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the two-dimensional small angle X-ray scattering technique, were used to research the crystallization behavior in PA66/RGO nanocomposites. The results indicated that RGO was an effective nucleation agent for PA66. The presence of RGO could enhance the orientation degree of the PA66 crystals and did not influence the crystal structure of the PA66. The non-epitaxial crystals and the epitaxial crystals existed in PA66/RGO nanocomposites. The size of epitaxial crystals was much greater than that of the non-epitaxial crystals. Tensile test results showed that the presence of fewer epitaxial crystals can improve the mechanical properties of a polymer. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Far-field and Fresnel Liquid Crystal Geometric Phase Holograms via Direct-Write Photo-Alignment
Crystals 2017, 7(12), 383; https://doi.org/10.3390/cryst7120383
Received: 1 December 2017 / Revised: 15 December 2017 / Accepted: 18 December 2017 / Published: 20 December 2017
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Abstract
We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a
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We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a photo-alignment layer (PAL) using a direct-write laser scanner and coating the surface with a polymerizable liquid crystal (i.e., a reactive mesogen). We study various recording pixel sizes, down to 3 μm, that are easily recorded in the PAL. We characterize the fabricated elements and find good agreement with theory and numerical simulation. Because of the wavelength independent geometric phase, the (phase) fidelity of the replay images is preserved for all wavelengths, unlike conventional dynamic phase holograms. However, governed by the diffraction equation, the size and location of a reconstructed image depends on the replay wavelength for far-field and near-field GPHs, respectively. These offer interesting opportunities for white-light holography. Full article
(This article belongs to the Section Liquid Crystals)
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Open AccessReview Chemical Crystallography at the Advanced Light Source
Crystals 2017, 7(12), 382; https://doi.org/10.3390/cryst7120382
Received: 3 November 2017 / Revised: 11 December 2017 / Accepted: 12 December 2017 / Published: 18 December 2017
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Abstract
Chemical crystallography at synchrotrons was pioneered at the Daresbury SRS station 9.8. The chemical crystallography beamlines at the Advanced Light Source seek to follow that example, with orders of magnitude more flux than a lab source, and various in situ experiments. This article
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Chemical crystallography at synchrotrons was pioneered at the Daresbury SRS station 9.8. The chemical crystallography beamlines at the Advanced Light Source seek to follow that example, with orders of magnitude more flux than a lab source, and various in situ experiments. This article attempts to answer why a chemist would require synchrotron X-rays, to describe the techniques available at the ALS chemical crystallography beamlines, and place the current facilities in a historical context. Full article
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Open AccessArticle High-Pressure Synthesis, Structure, and Magnetic Properties of Ge-Substituted Filled Skutterudite Compounds; LnxCo4Sb12−yGey, Ln = La, Ce, Pr, and Nd
Crystals 2017, 7(12), 381; https://doi.org/10.3390/cryst7120381
Received: 18 October 2017 / Revised: 14 December 2017 / Accepted: 14 December 2017 / Published: 15 December 2017
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Abstract
A series of new Ge-substituted skutterudite compounds with the general composition of LnxCo4Sb12−yGey, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C.
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A series of new Ge-substituted skutterudite compounds with the general composition of LnxCo4Sb12−yGey, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C. They have a cubic unit cell and the lattice constant for each compound is 8.9504 (3), 8.94481 (6), 8.9458 (3), and 8.9509 (4) Å for the La, Ce, Pr, and Nd derivatives, respectively. Their chemical compositions, determined by electron prove microanalysis, are La0.57Co4Sb10.1Ge2.38, Ce0.99Co4Sb9.65Ge2.51, Pr0.97Co4Sb9.52Ge2.61, and Nd0.87Co4Sb9.94Ge2.28. Their structural parameters are refined by Rietveld analysis. The guest atom size does not affect the unit cell volume. The Co–Sb/Ge distance mainly determines the unit cell size as well as the size of guest atom site. The valence state of lanthanide ions is 3+. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle The Effect of the Vertex Angles of Wedged Indenters on Deformation during Nanoindentation
Crystals 2017, 7(12), 380; https://doi.org/10.3390/cryst7120380
Received: 30 September 2017 / Revised: 11 December 2017 / Accepted: 12 December 2017 / Published: 14 December 2017
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Abstract
In order to study the effect of the angle of wedged indenters during nanoindentation, indenters with half vertex angles of 60°, 70° and 80° are used for the simulations of nanoindentation on FCC aluminum (Al) bulk material by the multiscale quasicontinuum method (QC).
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In order to study the effect of the angle of wedged indenters during nanoindentation, indenters with half vertex angles of 60°, 70° and 80° are used for the simulations of nanoindentation on FCC aluminum (Al) bulk material by the multiscale quasicontinuum method (QC). The load-displacement responses, the strain energy-displacement responses, and hardness of Al bulk material are obtained. Besides, atomic configurations for each loading situation are presented. We analyze the drop points in the load-displacement responses, which correspond to the changes of microstructure in the bulk material. From the atom images, the generation of partial dislocations as well as the nucleation and the emission of perfect dislocations have been observed with wedged indenters of half vertex angles of 60° and 70°, but not 80°. The stacking faults move beneath the indenter along the direction [ 1 1 ¯ 0 ] . The microstructures of residual displacements are also discussed. In addition, hardness of the Al bulk material is different in simulations with wedged indenters of half vertex angles of 60° and 70°, and critical hardness in the simulation with the 70° indenter is bigger than that with the 60° indenter. The size effect of hardness in plastic wedged nanoindentation is observed. There are fewer abrupt drops in the strain energy-displacement response than in the load-displacement response, and the abrupt drops in strain energy-displacement response reflect the nucleation of perfect dislocations or extended dislocations rather than partial dislocations. The wedged indenter with half vertex angle of 70° is recommended for investigating dislocations during nanoindentation. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness) Printed Edition available
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Open AccessArticle Influence of Alkali Metal Substitution on the Phase Transition Behavior of CsGaQ2 (Q = S, Se)
Crystals 2017, 7(12), 379; https://doi.org/10.3390/cryst7120379
Received: 20 October 2017 / Revised: 27 November 2017 / Accepted: 4 December 2017 / Published: 14 December 2017
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Abstract
The formation of solid solution series Cs1−xMxGaQ2-mC64 (M = K, Rb; Q = S, Se; x = 0–1) was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of CsGa
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The formation of solid solution series Cs1−xMxGaQ2-mC64 (M = K, Rb; Q = S, Se; x = 0–1) was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of CsGaQ2-mC64 with RbGaQ2 and KGaSe2, and a large miscibility gap with KGaS2. All solid solution members exhibit similar Raman spectra, indicating the covalent Ga-Q bonding character. The similar optical band gaps likewise further contribute to this conclusion. Up to a certain degree of substitution, these solid solutions undergo a phase transition similar to CsGaQ2-mC64. The influence of the substitution parameter x on phase transition process was investigated in situ using high-temperature X-ray powder diffraction experiments. Phase-pure solid solutions of the high-temperature polymorphs Cs1−xMxGaQ2-mC16 were obtained up to xmax(K) = 0.1 and xmax(Rb) = 0.3. The crystal structures of these new CsGaQ2-mC16 analogous high-temperature phases were refined from synchrotron diffraction data by Rietveld-refinement. Full article
(This article belongs to the Special Issue Synthesis and Structural Investigations of Polymorphic Compounds)
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Open AccessArticle Thermal Stability of Epitaxial Graphene Electrodes for Conductive Polymer Nanofiber Devices
Crystals 2017, 7(12), 378; https://doi.org/10.3390/cryst7120378
Received: 21 November 2017 / Revised: 5 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to
[...] Read more.
We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to that of Au-nanofiber devices. We further checked the thermal stability of the graphene contacts to polyaniline devices by annealing up to T = 800 °C, the temperature at which polyaniline nanofibers are carbonized but the graphene electrode remains intact. The thermal stability and Ohmic contact of polymer nanofibers are demonstrated here, which together with the chemical stability and atomic flatness of graphene, make epitaxial graphene on SiC an attractive contact material for future all-carbon electronic devices. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessArticle Crystallization, Structure Determination and Reticular Twinning in Iron(III) Salicylate: Fe[(HSal)(Sal)(H2O)2]
Crystals 2017, 7(12), 377; https://doi.org/10.3390/cryst7120377
Received: 28 November 2017 / Revised: 7 December 2017 / Accepted: 11 December 2017 / Published: 14 December 2017
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Abstract
In this contribution, we present the first crystal structure of iron(III) salicylate without additional counterions. The octahedral complex contains two salicylate and two water molecules as ligands. One salicylate is mono-anionic while the other is di-anionic. Because of the centrosymmetry of the complex,
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In this contribution, we present the first crystal structure of iron(III) salicylate without additional counterions. The octahedral complex contains two salicylate and two water molecules as ligands. One salicylate is mono-anionic while the other is di-anionic. Because of the centrosymmetry of the complex, the acidic hydrogen atom is disordered on the midpoint between two salicylate oxygens. The structure determination of the tiny crystal indicates the presence of reticular twinning. The structure solution of the twin is shown and an explanation based on the crystal packing is provided. Full article
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Open AccessReview Aromatic C-Nitroso Compounds and Their Dimers: A Model for Probing the Reaction Mechanisms in Crystalline Molecular Solids
Crystals 2017, 7(12), 376; https://doi.org/10.3390/cryst7120376
Received: 8 November 2017 / Revised: 6 December 2017 / Accepted: 12 December 2017 / Published: 14 December 2017
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Abstract
This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation
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This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation or breaking of only one covalent bond between two nitrogen atoms. The crystalline molecular solids of nitroso dimers (azodioxides) dissociate by photolysis under the cryogenic conditions, and re-dimerize by slow warming. The thermal re-dimerization reaction is examined under the different topotactic conditions in crystals: disordering, surface defects, and phase transformations. Depending on the conditions, and on the molecular structure, aromatic C-nitroso compounds can associate to form one-dimensional polymeric structures and are able to self-assemble on gold surfaces. Full article
(This article belongs to the Special Issue Photocrystallography and Solid-State Structural Dynamics)
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Open AccessReview Defects in Static Elasticity of Quasicrystals
Crystals 2017, 7(12), 373; https://doi.org/10.3390/cryst7120373
Received: 27 October 2017 / Revised: 4 December 2017 / Accepted: 5 December 2017 / Published: 14 December 2017
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Abstract
A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The
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A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)
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Open AccessArticle Stable Stacking Faults Bounded by Frank Partial Dislocations in Al7075 Formed through Precipitate and Dislocation Interactions
Crystals 2017, 7(12), 375; https://doi.org/10.3390/cryst7120375
Received: 9 November 2017 / Revised: 10 December 2017 / Accepted: 11 December 2017 / Published: 13 December 2017
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Abstract
Through high-resolution electron microscopy, stacking faults (SFs) due to Frank partial dislocations were found in an aluminum alloy following deformation with low strain and strain rate, while also remaining stable during artificial aging. Extrinsic stacking faults were found surrounded by dislocation areas and
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Through high-resolution electron microscopy, stacking faults (SFs) due to Frank partial dislocations were found in an aluminum alloy following deformation with low strain and strain rate, while also remaining stable during artificial aging. Extrinsic stacking faults were found surrounded by dislocation areas and precipitates. An intrinsic stacking fault was found between two Guinier-Preston II (GP II) zones when the distance of the two GP II zones was 2 nm. Defects (precipitates and dislocations) are considered to have an influence on the formation of the SFs, as their appearance may cause local strain and promote the gathering of vacancies to lower the energy. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Influence of External Static Magnetic Fields on Properties of Metallic Functional Materials
Crystals 2017, 7(12), 374; https://doi.org/10.3390/cryst7120374
Received: 27 November 2017 / Revised: 9 December 2017 / Accepted: 11 December 2017 / Published: 13 December 2017
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Abstract
Influence of external static magnetic fields on solidification, solid phase transformation of metallic materials have been reviewed in terms of Lorentz force, convection, magnetization, orientation, diffusion, and so on. However, the influence of external static magnetic fields on properties of metallic functional materials
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Influence of external static magnetic fields on solidification, solid phase transformation of metallic materials have been reviewed in terms of Lorentz force, convection, magnetization, orientation, diffusion, and so on. However, the influence of external static magnetic fields on properties of metallic functional materials is rarely reviewed. In this paper, the effect of static magnetic fields subjected in solidification and/or annealing on the properties of Fe–Ga magnetostrictive material, high strength high conductivity Cu-based material (Cu–Fe and Cu–Ag alloys), and Fe–Sn magnetic material were summarized. Both the positive and negative impacts from magnetic fields were found. Exploring to maximize the positive influence of magnetic fields is still a very meaningful and scientific issue in future. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Phononic Crystal Made of Multilayered Ridges on a Substrate for Rayleigh Waves Manipulation
Crystals 2017, 7(12), 372; https://doi.org/10.3390/cryst7120372
Received: 6 November 2017 / Revised: 3 December 2017 / Accepted: 6 December 2017 / Published: 12 December 2017
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Abstract
We present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW). The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as
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We present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW). The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as one-dimensional phononic crystal which exhibits band gaps for elastic waves. The band gap allows the existence of resonance modes where the elastic energy is either confined within units in the free end of the ridge or the ones in contact with the substrate. We show that SAW interaction with localized modes in the free surface of the ridge gives rise to sharp attenuation in the SAW transmission, while the modes confined within the ridge/substrate interface cause broad band attenuations of SAW. Furthermore, we demonstrate that the coupling between the two kinds of modes within the band gap gives high SAW transmission amplitude in the form of Fano-like peaks with high quality factor. The structure could provide an interesting solution for accurate SAW control for sensing applications, for instance. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Vickers Hardness of Diamond and cBN Single Crystals: AFM Approach
Crystals 2017, 7(12), 369; https://doi.org/10.3390/cryst7120369
Received: 23 October 2017 / Revised: 4 December 2017 / Accepted: 5 December 2017 / Published: 12 December 2017
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Abstract
Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy
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Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy were used to study the structure of the material in the indents. It was found that Vickers indents in diamond has no sharp and clear borders. However, the phase contrast operation mode of the AFM reveals a new viscoelastic phase in the indent in diamond. Raman spectroscopy and Kelvin probe force microscopy revealed that the new phase in the indent is disordered graphite, which was formed due to the pressure-induced phase transformation in the diamond during the hardness test. The projected contact area of the graphite layer in the indent allows us to measure the Vickers hardness of type-Ib synthetic diamond. In contrast to diamond, very high plasticity was observed for 0.5 N load indents on the (001) cBN single crystal face. Radial and ring cracks were absent, the shape of the indents was close to a square, and there were linear details in the indent, which looked like slip lines. The Vickers hardness of the (111) synthetic diamond and (111) and (001) cBN single crystals were determined using the AFM images and with account for the elastic deformation of the diamond Vickers indenter during the tests. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness) Printed Edition available
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Open AccessArticle Hydrophobic Calcium Carbonate for Cement Surface
Crystals 2017, 7(12), 371; https://doi.org/10.3390/cryst7120371
Received: 14 November 2017 / Revised: 6 December 2017 / Accepted: 8 December 2017 / Published: 11 December 2017
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Abstract
This report describes a novel way to generate a highly effective hydrophobic cement surface via a carbonation route using sodium stearate. Carbonation reaction was carried out at different temperatures to investigate the hydrophobicity and morphology of the calcium carbonate formed with this process.
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This report describes a novel way to generate a highly effective hydrophobic cement surface via a carbonation route using sodium stearate. Carbonation reaction was carried out at different temperatures to investigate the hydrophobicity and morphology of the calcium carbonate formed with this process. With increasing temperatures, the particles changed from irregular shapes to more uniform rod-like structures and then aggregated to form a plate-like formation. The contact angle against water was found to increase with increasing temperature; after 90 °C there was no further increase. The maximum contact angle of 129° was obtained at the temperature of 60 °C. It was also found that carbonation increased the micro hardness of the cement material. The micro hardness was found to be dependent on the morphology of the CaCO3 particles. The rod like structures which caused increased mineral filler produced a material with enhanced strength. The 13C cross polarization magic-angle spinning NMR spectra gave plausible explanation of the interaction of organic-inorganic moieties. Full article
(This article belongs to the Special Issue Carbonates)
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