Flat Platelets Research Articles

First-principles study of interface stability and behaviors of He at the W/Y2O3 interface

In this study, we investigated the stability of the W/Y2O3 interface and the behaviors of He near the interface using the first-principles method. We reported that the termination structures had an essential effect on interfacial stability by calculating the adhesion energy and interface energy. The OW-terminated interface had better stability than the YW-terminated interface when O chemical potential ΔμO was larger than − 5.1 eV. The result of the segregation energy demonstrated that the W/Y2O3 interface could act as a strong trap to capture the He of the W layer, but it was extremely difficult to capture the He of the YO layer. By examining the effect of strain on the dissolution property of He in W and Y2O3 bulks, we reported that the strain caused by lattice matching would be the primary reason to affect the solution of He near the interface. A diffusion study reported a reaction region in the W layer near the interface, the thickness approached 0.3 nm. The interface was favorable to the release of the He because the trapped He preferred to diffuse along the interface plane, rather than to be filtered in the W and YO layers across the interface. In addition, we also reported that the configuration of the He cluster at the interface roughly presented as a flat platelet structure and accommodated up to three He atomic layers. Those calculation results agreed with experimental results and provided theoretical support to deeply understand the phase interface effects on the behaviors of He in the Y2O3 dispersion strengthened W.

Electronic gap stability of two-dimensional tin monosulfide phases: Towards optimal structures for electronic device applications

It is well known that tin monosulfide is a potential environment-friendly solar cell material that maximizes light-energy conversion efficiency, given its band gap at the peak of the solar emission spectrum. However, the presence of Sn and S vacancies at the surface of SnS hinders the performance of these solar cells. In the present work, we have prepared tin sulfide platelets on graphite using vapor phase deposition under a known temperature gradient. Remarkably, we observe two types of growth modes: (i) a dominant one with platelet-like flat crystals and (ii) a less favorable one, formed by spiral terraces. Both structures present a chemical composition compatible with SnS. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we observe that, whereas flat SnS platelets exhibit fluctuations in the band gap and doping, spiral platelets exhibit stable, homogeneous band gap, and negative doping. Using selected area electron diffraction (SAED), we determine that, whereas the platelets of the unstable phase are associated with the common orthorhombic structure of SnS, the minor stable spiral platelets are polycrystalline and are in the metastable cubic phase. The production of this less favorable phase on large surface areas is of potential interest for the production of more efficient tin sulfide-based solar cells. In addition, our analysis of solar cell materials using STM/STS and SAED provides a framework for the rapid determination of the suitability and applicability of 2D materials for other potential optoelectronic applications.

On mean Green operator and Eshelby tensor of hollow cylinders with length from infinite tubes to flat rings in isotropic elastic media

Using the (RT-IRT) Radon transform and inversion formula method, the author has previously reported the exact formal expressions for the mean shape function (mSF) of a finite solid cylinder of general aspect ratio in any infinite medium and for the related mean Green operator (mGO) and mean Eshelby tensor (mET) in cases of isotropic elastic-like (including dielectric-like) linear properties. Nearly exact solutions were obtained provided an accurate analytical approximation of an elliptic integral. Using the same RT-IRT method, the present work addresses the case of hollow cylinders with finite length in same isotropic property contexts. From examining the general formal mSF expression (and comparing with the limits of infinitely long cylinders and infinitely flat platelets) a simple accurate approximation is provided for the mSF, mGO and mET of "thin" hollow cylinders, from tubes to rings what covers a wide range of practical situations. The same expression being shown to hold on the thick side limit, the conjecture that it may be relevant over the whole thickness range is questioned.

Controlled Deposition of Lead Iodide and Lead Chloride Thin Films by Low-Pressure Chemical Vapor Deposition

Lead halide thin films, such as lead iodide (PbI2) and lead chloride (PbCl2), are used as precursor films for perovskite preparation, which is frequently achieved by vacuum thermal evaporation but rarely by the low-pressure chemical vapor deposition (CVD) method. Here, we report on the deposition of PbI2 and PbCl2 thin films on glass substrates by employing the low-pressure CVD method. The effect of the substrate temperature on the structure and morphology of the lead halide films is investigated. Crystalline films were realized for both lead halides, with PbI2 films showing high texture compared to the reduced texture of the PbCl2 films. Large lateral grain sizes were observed for the PbI2 films with a flat platelet grain morphology and an average grain size up to 734.2 ± 144.8 nm. PbCl2 films have columnar grains with an average grain size up to 386.7 ± 119.5 nm. The PbI2 films showed a band gap of about 2.4 eV, confirming its semiconducting properties, and the PbCl2 had a wide band gap of 4.3 eV, which shows the insulating properties of this material.

One pot facile transformation of CO2 to an unusual 3-D nano-scaffold morphology of carbon

An electrosynthesis is presented to transform CO2 into an unusual nano and micron dimensioned morphology of carbon, termed Carbon Nano-Scaffold (CNS) with wide a range of high surface area graphene potential usages including batteries, supercapacitors, compression devices, electromagnetic wave shielding and sensors. Current CNS value is over $323 per milligram. The morphology consists of a series of asymmetric 20 to 100 nm thick flat multilayer graphene platelets 2 to 20 µm long orthogonally oriented in a 3D neoplasticism-like geometry, and appears distinct from the honeycomb, foam, or balsa wood cell structures previously attributed to carbon scaffolds. The CNS synthesis splits CO2 by electrolysis in molten carbonate and has a carbon negative footprint. It is observed that transition metal nucleated, high yield growth of carbon nanotubes (CNTs) is inhibited in electrolytes containing over 50 wt% of sodium or 30 wt% of potassium carbonate, or at electrolysis temperatures less than 700 °C. Here, it is found that a lower temperature of synthesis, lower concentrations of lithium carbonate, and higher current density promotes CNS growth while suppressing CNT growth. Electrolyte conditions of 50 wt% sodium carbonate relative to lithium carbonate at an electrolysis temperature of 670 °C produced over 80% of the CNS desired product at 85% faradaic efficiency with a Muntz brass cathode and an Inconel anode.

The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance.

A surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface-enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI)-coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au3+ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the ultraviolet (UV)-absorption of the undulated Au@Ag nanoplatelets can be tuned depending on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4′-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by decoration with gold spikes.

Metal-free functionalized stilbene crystals exhibit silver luster

We herein report a new class of metal-free pigments based on low molecular weight functionalized stilbene derivatives that exhibit silver luster. These derivatives crystallize in very flat platelet shapes with the plain faces of the crystals easily stacked through the filtering process, resulting in multiply-stacked plain faces and high specular reflection over the entire visible wavelength range. Morphological characterization shows that the aspect ratio between the maximum diagonal and thickness of the plain face was at least 20, with surface roughness on the molecular scale. Crystal structure analyses suggest that preferential growth of the plain face is due to a large d-spacing between planar stilbene molecules that are arranged in a herringbone pattern. The specular reflectance of functionalized stilbene crystals was 10–16%, with color coordinates close to those of silver metal. These results suggest that crystals of the functionalized stilbene derivatives are promising dye or pigment materials for use in inks for printing applications.

Polystyrene-attached graphene oxide with different graft densities via reversible addition-fragmentation chain transfer polymerization and grafting through approach

Graphene oxide (GO) modified with double bond was utilized in grafting polystyrene chains to its surface through reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene. For this purpose, 3-(((2-aminoethyl)amino)dimethylsilyl)propyl methacrylate (OD) including double bond and amine groups was prepared and used for modification of GO in different grafting densities by a ring-opening nucleophilic reaction. Then, polystyrene-grafted GO was obtained by “grafting through” RAFT polymerization of styrene. Successful using of RAFT polymerization, efficiency of the grafting reaction, different characteristics of the graphene-attached and free polystyrene chains were investigated. Proton nuclear magnetic resonance spectroscopy confirmed successful synthesis of OD. Its grafting on GO was also confirmed by using X-ray photoelectron spectroscopy. The neat and modified GO layers were also investigated by Fourier transform infrared and Raman spectroscopies. Size exclusion chromatography was used to study molecular weight and polydispersity index of the attached polystyrene chains. Thermogravimetric analysis provides degradation temperature, char content, and grafting ratio of the modifier and polystyrene chains. Grafting ratio of OD was 10.3 and 4.4% for the modified GO layers with high and low grafting densities, respectively. Layers morphology was visually studied by scanning and transmission electron microscopies. Flat and smooth graphite platelets were changed to wrinkled layers after oxidation, and converted to opaque layers after grafting with polystyrene chains. High length of small molecule modifier in this study resulted in highly efficient grafting reaction.

Effects of Temperature and Particles Concentration on the Dynamic Viscosity of Graphene-NiO/Coconut Oil Hybrid Nanofluid: Experimental Study

In practice, lubricants are used to minimize the friction and wear of frictional surfaces. The disposal of mineral-based lubricating oil possesses environmental issues and forced the development of bio-degradable lubricating agents. The simultaneous mono-dispersion of metallic and metal oxides nanomaterials into lubricating agents may concurrently reveal superior thermo-physical and rheological characteristics. This paper proposes an experimental and theoretical investigation on the dynamic viscosity enhancement of flat platelets textured Graphene/NiO-coconut oil hybrid nanofluids. The results reveal that the dynamic viscosity enhancement of hybrid nanofluids increases with nanomaterial concentration and decreases with temperature. The squat hybrid nanomaterial concentration has less collusion probability and dynamic contact between the mono-dispersed hybrid nanomaterials as it has enough interfacing gaps to conquer superficial surface energy. The high nanomaterial concentration revamps the formation of lamellar-composite agglomerated particles and enhances the dynamic viscosity of base fluid. Further, a theoretical correlation is recommended to estimate the dynamic viscosity of hybrid nanofluid with minimum margin of deviation using artificial neural network (ANN).

Online condition monitoring of misaligned meshing gears using wear debris and oil quality sensors

PurposeThis paper aims to investigate the effect of misalignment on wear of spur gears and on oil degradation using online sensors.Design/methodology/approachThe misalignment effect on gears is created through a self-alignment bearing, and is measured using laser alignment system. Several online sensors such as Fe-concentration sensor, moisture sensor, oil condition sensor, oil temperature sensor and metallic particle sensor are installed in the gear test rig to monitor lubricant quality and wear debris in real time to assess gearbox failure.FindingsOffset and angular misalignments are detected in both vertical and horizontal planes. The failure of misaligned gear is observed at both the ends and on both the surfaces of the gear teeth. Larger-size ferrous and non-ferrous particles are traced by metallic particle sensor due to gear and seal wear caused by misalignment. Scanning electron microscope (SEM) images examine chuck, spherical and flat platelet particles, and confirm the presence of fatigue (pitting) and adhesion (scuffing) wear mechanism. Energy-dispersive X-ray spectroscopy analysis of SEM particles traces carbon (C) and iron (Fe) elements due to gear failure.Originality/valueGear misalignment is one of the major causes of gearbox failure and the lubricant analysis is as important as wear debris analysis. A reliable online gearbox condition monitoring system is developed by integrating wear and oil analyses for misaligned spur gear pair in contact.

Composites reinforced via mechanical interlocking of surface-roughened microplatelets within ductile and brittle matrices

Load-bearing reinforcing elements in a continuous matrix allow for improved mechanical properties and can reduce the weight of structural composites. As the mechanical performance of composite systems are heavily affected by the interfacial properties, tailoring the interactions between matrices and reinforcing elements is a crucial problem. Recently, several studies using bio-inspired model systems suggested that interfacial mechanical interlocking is an efficient mechanism for energy dissipation in platelet-reinforced composites. While cheap and effective solutions are available at the macroscale, the modification of surface topography in micron-sized reinforcing elements still represents a challenging task. Here, we report a simple method to create nanoasperities with tailored sizes and densities on the surface of alumina platelets and investigate their micromechanical effect on the energy dissipation mechanisms of nacre-like materials. Composites reinforced with roughened platelets exhibit improved mechanical properties for both organic ductile epoxy and inorganic brittle cement matrices. Mechanical interlocking increases the modulus of toughness (area under the stress–strain curve) by 110% and 56% in epoxy and cement matrices, respectively, as compared to those reinforced with flat platelets. This interlocking mechanism can potentially lead to a significant reduction in the weight of mechanical components while retaining the structural performance required in the application field.

Mineralization-related modifications in the calcifying tendons of turkey (Meleagris gallopavo)

The tendons of some birds undergo a physiological process of gradual mineralization, usually limited to the central portion of the tendon and resulting in an increase of the elastic modulus and the ultimate strength. The present study was carried out by light microscopy and scanning electron microscopy and was focused on the structural and ultrastructural modifications occurring in this tissue during biomineralization.In comparison with most other tendons, turkey tendons appeared to be more finely subdivided into thinner fascicles and to contain a greater amount of cell-rich endotenon tissue. The most obvious finding, however, was the complete disappearance of the crimps in the calcified portions of the tendon, while they were present with the usual morphology in the non-mineralized portion.The electron microscopy revealed in the mineralized tendon traces of pre-existing crimps, locked in the straightened-out position by the infiltrating mineral phase. This latter was composed of two different types of fine particles, respectively, growing inside and around the collagen fibrils and appearing as tightly packed platelets or as larger, flat platelets regularly arranged in phase with the D-period of collagen. The perifibrillar mineral could play a critical role in the mechanical coupling of adjoining fascicles and in the transmission of tensile loads along the tendon itself.

Spermatogenesis and spermatozoa ultrastructure of two Dipolydora species (Annelida: Spionidae) from the Sea of Japan

Spermatogenesis and the structure of the spermatozoa of two spionid polychaetes Dipolydora bidentata and Dipolydora carunculata are described by light and transmission electron microscopy. Both species are gonochoristic borers in shells of various molluscs. Proliferation of spermatogonia occurs in paired testes regularly arranged in fertile segments, and the rest of spermatogenesis occurs in the coelomic cavity. Early spermatogenesis occurs quite similarly in the two species but results in formation of tetrads of interconnected spermatids in D. bidentata and octads of spermatids in D. carunculata. Three consecutive stages of spermiogenesis are recognized according to the condensation of chromatin in nucleus: (1) early spermatids with heterogeneous, partly clumped chromatin, (2) middle spermatids with homogeneous, coarsely granular chromatin, and (3) late spermatids with homogeneous fibrillar chromatin. Moreover, late stage of spermatids is further classified into two stages, I and II, according to the position of the acrosome and shape of the nucleus. In late spermatids I, the acrosome is situated in the anterior invagination of the funnel-shaped to oval nucleus, whereas in late spermatids II the acrosome is situated on top of the elongated nucleus. Ultrastructural composition of cells at each stage of spermatogenesis is described and illustrated. The possible process of morphogenesis of organelles during spermato- and spermiogenesis is reconstructed for both species. The proacrosomal vesicle first appears in early spermatids near the Golgi complex and then migrates anteriorly; in the middle spermatids, the acrosome comes to lie in a deep anterior nuclear fossa. In late spermatids I, this fossa evaginates and a posterior fossa develops in the nucleus housing basal body and the anterior part of the axoneme. In late spermatids II, the mitochondria elongate and probably reduce in number due to fusion of some of them. The mature spermatozoa in both species are introsperm with the conical acrosome, subacrosomal plate, long nucleus with short posterior fossa, long midpiece with elongated mitochondria, and long flagellum with 9×2+2 organization of microtubules. Numerous flat rounded platelets with putative glycogen are present throughout most part of the nucleus and the midpiece. The process of spermatogenesis in D. bidentata and D. carunculata is similar to that in other Dipolydora, Polydora and Pseudopolydora species. Spermatozoa in these polydorin spionids have similar composition and differ mainly in size of the nucleus and the midpiece. Elongated spermatozoa are adapted for transfer in spermatophores and an internal fertilization which is characteristic for brooding species. Diversely modified spermatozoa among spionids may be signs of the diversity of fertilization biology within the Spionidae. The exact places where fertilization occurs in brooding spionids however remains unknown.

Two new paralcyoniid octocorals from Japan (Anthozoa: Alcyonacea).

Two new species of paralcyoniid octocorals are described from Japan. One of them, Ceeceenus retractus n. sp., is the fifth species of the genus, and the other, Nanalcyon sagamiense n. gen. n. sp., is proposed as a new genus. Nanalcyon is similar to the Mediterranean and Atlantic genera Maasella Poche, 1914 and Paralcyonium Milne Edwards and Haime, 1850, but the new genus clearly differs from these in having independent colonies not joined by stolons. The ultrastructure of the sclerites is compared among the new genus, Ceeceenus and Paralcyonium by means of SEM. All three genera display the same three main types of sclerites, flat platelets, rods and spindles, the ultrastructure of all consisting of non-branching fibrous crystals. In addition to these, two genera, Ceeceenus and Paralcyonium, have flat oval platelets with the ultrastructure showing branching dendritic crystals, lacking in Nanalcyon.

Effect of divalent cation substitution in the magnetoplumbite structured BaFe12O19 system

Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe12O19 system. The Ca2+ substituted Ba1−xCaxFe12O19 (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba1−xCaxFe12O19 system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe12O19 compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (MS) and remanent magnetization (MR) values drastically decreases for the Ba0.95Ca0.05Fe12O19 compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in MS and MR values for the Ba0.9Ca0.1Fe12O19 and Ba0.85Ca0.15Fe12O19 compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe3+–O–Fe3+ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe12O19 system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca2+ in the BaFe12O19 system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.

Characterizing industrially electrowon sticky zinc deposits

Physical, chemical, and microscopic characterization of industrially electrowon zinc was performed with a focus on cataloguing morphological differences between sticky and non-sticky zinc deposits. Preferred crystal deposition plane orientations were analyzed by XRD. The crystal orientations for the sticky samples reveal small angle growth (~ 25°) to the cathode surface. In non-sticky samples, the crystals were oriented at an average of ~ 44° to the cathode surface. Deposit microstructures were studied by SEM and optical microscopy. These revealed flat or basal zinc platelets with a number of pores for the sticky deposits whereas the non-sticky deposits were compact, sharp-edged and featured continuous grains with angular crystal plane depositions. No differences in deposit impurity contents were observed by elemental (ICP) and EDX analyses. Microhardness studies of the deposit cross-sections revealed that the sticky samples were, on average, softer than the non-sticky samples particularly at locations closer to the Al cathode.

Surface study of the building steps of enzymatic sol–gel biosensors at the micro- and nano-scales

We have studied, by scanning electron and atomic force (AFM) microscopies, how each step involved in the building process of massive carbon-based sol–gel enzymatic biosensors changes and determines the resulting surface morphology and nano-mechanical properties. The biosensor, selected as a model, is developed by the entrapment of glucose oxidase (GOx), a redox mediator and a material conferring conductivity (graphite powder, C) into a polymeric tridimensional network generated by sol–gel technology using tetraethoxysilane (TEOS) as precursor. The smooth TEOS morphology is formed by an irregular nanoporous network, which is very adequate for enzyme encapsulation. Upon addition of carbon powder to the system (TEOS/C), the surface morphology changes but it is still rather irregular since carbon powder micro-grains are found scattered on it. This morphology results in a rather rough surface at the micro- scale whereas at the nano- scale both atomically flat graphitic and nanoporous TEOS domains are found. In contrast, the final biosensing device surface is quite homogeneous and composed by flat platelets separated by deep crevices. On top of most of these platelets there is a soft, as assessed by AFM force indentation experiments, layer of globular structures whose dimensions are compatible with GOx molecules. The final device surface architecture results to be open and accessible both at the micro and nano scales, which turns it as adequate to enhance both the accessibility of the analytes to entrapped proteins and the mass-transfer rates. Finally, in order to show the applicability of the studied biosensor, its response was evaluated towards varying glucose concentrations, displaying a clear electrocatalytic activity.

Thermal-Induced Wear Mechanisms of Sheet Nacre in Dry Friction

Sheet nacre is a natural biocomposite with a multiscale structure including a mineral phase of calcium carbonate (97 wt.%) and two organic matrices (3 wt.%). The mineral phase is constituted by an arrangement of CaCO3 biocrystal nanograins (ca 40 nm in size) drowned in an ‘‘intracrystalline'' organic matrix (4 nm thick) in order to form a microsized flat organomineral aragonite platelet. These platelets are themselves surrounded by an ‘‘intercrystalline'' organic matrix (40 nm thick) building up a very tough materials. This microarchitecture referred to as ‘‘bricks and mortar'' nacre structure, is mainly studied for the creation of new organic/inorganic hybrid materials. Currently, only little is known about the nacre mechanical behaviour under dynamical loading and more particularly under tribological conditions which involve shocks and thermal effects simultaneously. This paper brings out the thermal-induced damage mechanisms effect on the wear of sheet nacre by the assessment of the thermal component of the friction with a scanning thermal microscope. Results reveal that the mean contact pressure is the main driving force involved in the degradation of the organic constituents. For the lowest mean contact pressure (\0.4 MPa), wear is rather weak because the friction-induced thermal component is not sufficient for degrading the organic matrices. In contrast, beyond 0.4 MPa, the friction-induced contact temperature rises up over the melting point of the organic matrices, and may even reach the temperature of the aragonite– calcite phase transformation increasing dramatically the wear of sheet nacre.

Suppressing and Enhancing Depletion Attractions between Surfaces Roughened by Asperities

By decorating the surfaces of smooth, flat platelets with hemispheroidal asperities and calculating the overlapping excluded volume of spherical depletion agents as two platelets approach face to face, we determine the depletion interaction potential for both ordered and disordered surface asperities. Depending on the surface morphologies, the depletion attraction between rough surfaces can be either dramatically reduced or amplified. A phase diagram of roughened Janus platelets is calculated and agrees well with prior experiments. This model explains the observed self-assembly of rough platelets and provides quantitative predictions of roughness-controlled depletion attractions for conditions that have not yet been explored experimentally.

Influence of AlF 3 and hydrothermal conditions on morphologies of α-Al 2O 3

Homogeneous α-Al 2O 3 platelets were synthesized by introducing AlF 3 to alumina precursor. The effects of AlF 3 additive on the phase transformation and morphology of the prepared α-Al 2O 3 platelets were investigated. The results show that a single phase of α-Al 2O 3 with an average particle size of 8 μm can be obtained at 900 °C with 2% AlF 3 additive. The transformation temperature decreasing is attributed to introduction of Al 3+ vacancy and to the formation of intermediate compound of AlOF, which is considered to accelerate the mass transportation from transitional Al 2O 3 to α-Al 2O 3. AlF 3 concentration and hydrothermal temperature can also affect the morphology of α-Al 2O 3. When hydrothermal temperature is 120 °C, the morphology of α-Al 2O 3 transforms from irregular to flat hexangular platelet with increasing AlF 3 concentration. As hydrothermal temperature increases, the morphology of α-Al 2O 3 with 2% AlF 3 additive changes from polyhedron to hexangular platelet and then to vermicular.