Experimental investigation of thermo-physical properties of platelet mesoporous SBA-15 silica particles dispersed in ethylene glycol and water mixture

This paper presents an experimental investigation of thermophysical properties of platelet mesoporous SBA-15 particles dispersed in 60:40 (v/v) ethylene glycol:water mixture. The effect of weight fraction of particles and temperature is studied on density, viscosity and thermal conductivity of nanofluids. The maximum measured thermal conductivity enhancement reaches up to 22% for the nanofluids containing 5 wt% of SBA-15 at 60 °C. The SBA-15 nanofluids show Newtonian behavior in the tested temperature range. Also, the relative density increases between 0.4% and 2.2% when the weight percent of the nanoparticles varies between 1 and 5 at 60 °C. Structural and morphological characterization of synthesized SBA-15 have been carried out using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N₂ adsorption–desorption isotherms methods.     

Synthesis and characterization of spray pyrolyzed mesoporous bioactive glass

Mesoporous bioactive glasses (MBGs) have recently been applied as important bone implant materials due to their high reactive surface areas and superior bioactivities. Various processes have been developed to fabricate MBGs. Among them, the sol–gel process is one of most popular. However, sol–gel has the drawbacks of discontinuous processing and long processing time, making it unsuitable for mass production. This study demonstrates a successful synthesis of MBGs using a spray pyrolysis (SP) method to overcome these problems. The bioactivities of the SP synthesized MBGs are correlated with the main SP processing parameter of calcination temperatures and their structures. Comparisons of the surface areas and bioactivities for the MBG particles prepared from the sol–gel and the SP process are included. Finally, the MBG formation mechanism using SP is proposed.     

Synthesis,microstructure and optical characterization of zirconium oxide nanostructures

Zirconium oxide (ZrO₂) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO₂ product is of pure monoclinic phase (m-ZrO₂) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of the m-ZrO₂. The UV–vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO₂ nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material.     

Hierarchically bimodal mesoporous silica fibers as building units for silica monolith with trimodal porous architecture

This work reports the controllable preparation of a unique kind of hierarchically mesoporous silica (HMS) fibers with bimodal porosities based on a simple TEOS/P123/HCl(aq.) templating system via the partitioned cooperative self-assembly (PCSA) process. Experimental results show that the formation of hierarchical mesostructures, especially the 2nd mode porous structure, depends on the interval time pertaining to the PCSA process. Synthetic conditions, including the interval time, temperature and stirring, are all found to be important in the evolution of fiber particle morphology. Moreover, such HMS fibers can be used as building units to prepare mesoporous silica monoliths with hierarchical trimodal pore systems via a simple gel-casting method, with additional (the 3rd modal) macropores originating from the packing of micron-sized HMS fibers. Such materials might further expand the application of both HMS fibers and HMS monoliths in various fields.     

The effect of silica template structure on the pore structure of mesoporous carbons

We have synthesized two kinds of mesoporous carbons using a spherical silica sol (SMC1 carbon) and an elongated silica sol (SMC3 carbon) as templates. Nitrogen isotherms and electrochemical experiments were performed to investigate the effect of the silica template structure on the pore structure of the resulting mesoporous carbons. When carbons produced using the same silica to resorcinol molar ratio were compared, both nitrogen isotherms and electrochemical studies revealed that the SMC3 carbons exhibit simpler pore connectivity than SMC1 carbons.     

Designing the morphology of ceria particles by precursor complexes

Ceria-based materials are widely used as catalysts, catalyst supports and electrolytes in many industrial applications. The morphological requirements of ceria particles vary depending on their applications. Here we show that complex morphologies of ceria particles can be achieved by using precursor complexes in the spray pyrolysis (SP) method. Three precursor complexes have been investigated: the complex of cerium acetate hydrate (CeA) and cerium nitrate hydrate (CeN); CeA and cerium ammonium nitrate (CeAN); and CeN and CeAN. Our results suggest that the morphological formation mechanism is highly correlated with the factors of precursor solubilities, solvent evaporation rates and precursor melting temperatures.     

Rheology of UV curable colloidal silica dispersions for rapid prototyping applications

Silica is a very promising material for micro-devices produced by rapid prototyping techniques due to its high transparency, thermal and chemical resistance. UV curable dispersions for rapid prototyping methods such as stereolithography should posses specific rheological properties which are crucial for such applications. We developed highly filled, low viscosity silica dispersions (up to 60 vol%) in UV curable, acrylate based systems. The influence of silica particle size, solid loading, temperature and shear rate on the viscosity of dispersions was investigated. The dispersions exhibited different types of shear thickening depending mainly on the size of particles. The critical shear rate defined as the onset of shear thickening, was found to be dependent on temperature, particle size, solid loading of the dispersions. The understanding of these rheological properties enables the design of new dispersions that meet rapid prototyping process requirements.     

Biomimetic deposition of hydroxyapatite on the surface of silica thin film covered steel tape

The biomimetic deposition of hydroxyapatite (HA) on the surface of SiO₂ thin film coated metal substrates was developed and investigated.     

Porous YSZ ceramics with unidirectionally aligned pore channel structure: Lowering thermal conductivity by silica aerogels impregnation

The previous report of this work has demonstrated the fabrication and properties of porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels. As a follow-up study, the present work aims at lowering the thermal conductivity of the porous YSZ ceramics by silica aerogels impregnation. The porous YSZ ceramics were immersed in an about-to-gel silica sol. Both the unidirectionally aligned pore channels and the inter-grain pores by grain stacking in the channel-pore wall of the porous YSZ ceramics were impregnated with the silica sol. After aging and supercritical drying, silica aerogels formed in the macroporous network of the porous YSZ ceramics with unidirectionally aligned pore channels. The influences of silica aerogel impregnation on the microstructure and properties of porous YSZ ceramics with unidirectional aligned pore channels were investigated. The porosity decreased after impregnation with silica aerogels. Both microstructure observation and pore size distribution indicated that both channel-pore size and inter-grain pore-size decreased significantly after impregnation with silica aerogels. Impregnating porous YSZ ceramics with silica aerogels remarkably lowered the room-temperature thermal conductivity and enhanced the compressive strength. The as-fabricated materials are thus suitable for applications in bulk thermal isolators.     

Regeneration of a solid waste from an edible oil refinery

This work presents a valorization of a solid waste originating from an edible oil refinery called spent bleaching earth (SBE). The SBE material is first impregnated with an ammonium chloride solution (3 M), then treated directly in furnace at 400 °C during an hour followed by a washing in the cold by HCl 1 M. To elucidate the changes in its crystalline structure, induced by the regeneration method, the obtained material (RSBE) is characterized by several physicochemical methods (X-ray diffraction, FTIR, thermal analysis, BET and SEM). The characterization results show that the heat treatment in furnace and the chemical treatment (decomposition of NH₄Cl) don’t affect the structure of montmorillonite of regenerated material (RSBE). The study of porous texture by the nitrogen adsorption technique at −196 °C shows that the specific surface area S_BET and the pore volume increased in the RSBE material compared to those of virgin bleaching earth VBE (unused) and their values are respectively of 145.68 against 115.5 m² g⁻¹ and of 0.287 against 0.234 cm³ g⁻¹. Calculations by the adsorption equations using BJH method, applied to both materials, show that the treatment generate an increase in the micropores in the RSBE material. We belonged the values of the micropores area of S_mic = 41.98 cm² g⁻¹ and of V_mic = 0.074 cm³ g⁻¹ for the volume.     

Structure and properties of short fibre reinforced silica matrix composite foams

Glass (GFC) and silica (SFC) fibre reinforced silica matrix composite foams with 84–90% porosity content have been developed through slurry-based processing, involving random dispersion of 10 wt.% fibres with aspect ratios of >1000 in hydrophobized silica-based suspensions, and direct foaming for air entrapment. Fibre entanglement has not been found either in the suspensions or in the sintered composite foams. Microstructural and mercury porosimetry studies of the composite foams have shown a trimodal size distribution with small (4–8 μm), medium (40–200 μm), and large (1 mm or more) pores. The pores appear spherical and interconnected, with the fibres embedded in cell-walls or struts. The dynamic Young's modulus of the silica-coated GFCs is found to be 3.5 and 5.2 times that of the coated and uncoated monolithic silica foams, respectively, confirming that both fibre-reinforcement and the presence of surface coating are beneficial for increase in stiffness of the composite foams.     

Preparation and pore control of highly mesoporous carbon from defluorinated PTFE

Porous carbon having more than 2000 m²/g of BET specific surface area was synthesized by defluorination of polytetrafluoroethylene (PTFE) at 473 K using sodium metal. The porous carbon as-prepared had a large amount of narrow mesopores 2-3 nm in pore width, together with micropores. Control of the pore structure was attempted by simple heat-treatment of the carbon in nitrogen, and change of the porous structures was characterized by nitrogen adsorption techniques. As a result, it was found that the ratio between micro- and mesopores was easily varied. Electric double layer capacitance was measured as one of the applications for the mesoporous carbon with specific porosity, and the effect of pore control on capacitance was investigated.     

Approach of phase transformations and densification in nanostructured and (Bi2O3, ZnO,TiO2) doped silica ceramics

The low temperature sintering of silica is studied under the influence of sintering aids and nanosized powders using X-Ray Diffractometry (XRD) and high-temperature environmental scanning electron microscopy analyses (HT-ESEM). Two particular aids were chosen to conduct this study, [Bi₂O₃–ZnO]_eutectic and titania. We report a lowering of the crystallization temperature when the former compound is introduced in the silica while a raise is observed when the latter is used. Moreover, the amorphous silica crystallization into cristobalite inhibits drastically the kinetics of densification of silica-based materials.     

Highly efficient green synthesis of highly pure microporous nanosilica from silicomanganese slag

Highly pure nanosilica was synthesized through a facile hydrometallurgy-based method from silicomanganese slag as a low cost silica source. The synthesis route included short-term nitric acid dissolution at room temperature, gelation, washing, drying, and calcination steps. The experimental dissolution conditions resulted in a dissolution efficiency of 98%. The crystalline structure, chemical composition, chemical bonding, microstructure and elemental analyses, particle size distribution, and surface area of the extracted silica were then studied by appropriate characterization techniques. The characterization findings indicated that the amorphous silica particles had a microporous nature with an average particle size of ~24 nm, exhibiting a high purity of more than 99% and a high specific surface area of ~474 m² g^?1. The overall results indicated that the proposed synthesis route is a promising feasible alternative method to produce highly pure microporous nanosilica from a low cost secondary resource. The proposed method can treat 98% of the slag and uses less chemicals than conventional methods and is therefore a greener nanosilica production process. The current process also competes with the traditional process and other recently introduced processes in terms of process economy and the quality of the produced product.     

Low hydrothermal temperature synthesis of porous calcium silicate hydrate with enhanced reactivity SiO2

This study presents a novel approach for the synthesis of porous calcium silicate hydrate (CSH) at a low hydrothermal temperature of 110 °C based on enhanced reactivity SiO₂ (i.e. silica/polyethylene glycol (PEG₂₀₀₀) composites) as the source silica material. The as-prepared CSH materials exhibited a porous microstructure with a large number of small mesopores. The porosity formation mechanism of CSH was apparent that cavitation, resulting from sonication, enabled PEG₂₀₀₀ (via intercalation on silica) to break apart Si–O–Si structural units, thereby enhancing SiO₂ reactivity at a low hydrothermal temperature. In addition, the presence of PEG₂₀₀₀ effectively prevented the aggregation of particles during the formation process of the porous CSH solid. The low temperature synthesis proposed herein represents a viable and effective method for the further development of porous CSH as a functional ceramic material.     

Workability and setting parameters evaluation of colloidal silica bonded refractory suspensions

The efficiency of colloidal silica as a binder agent for castable matrix suspension in the presence of different setting agents and curing temperatures was evaluated. The tests were carried out trough rheometric techniques according to a systemic approach specifically developed for ceramic systems (oscillatory and normal force tests). Colloidal silica performed well as a binder agent for refractory suspensions when a suitable additive was selected. Among the additives analyzed, magnesium oxide was the most suitable for the evaluated systems. MgO addition in the range of 0.3–0.6 wt% and curing temperature of 25 °C were the suggested parameters for alumina and microsilica systems.     

Solvothermal oxidation of gallium metal

Solvothermal oxidation of gallium metal in various organic solvents at 300 °C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300 °C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga₂O₃. The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga₂O₃ prepared by the conventional method.     

Manufacturing porous multi-channel ceramics by laser gelling

This article describes a novel layer manufacturing process for forming a ceramic part with porous multi-channel architecture by laser gelling under low laser energy. The process involves bonding silica powder by gelled silica sol after exposure by a CO₂ laser. Lower laser energy density of 0.8 J/mm² is required to produce ceramic parts by “gelling effect”. Therefore, the geometrical deflection and thermal distortion can be reduced after laser scanning. The inner porous structures were supported by ceramic slurries to prevent sagged deflection and to enhance dimensional accuracy due to optimal slurry suspension. The flexural strength of the green specimen was 4.7 MPa, while that of the gelled specimen was 12.5 MPa after heat-treatment at 1200 °C for 1.5 h. The proposed process has potential for fabricating complex interconnected porous ceramics for tissue engineering applications.     

Synthesis of lanthanum beta-alumina powders by the polymeric precursor technique

La-β-Al₂O₃ (LaAl₁₁O₁₈) powders were synthesized by the polymeric precursor technique using lanthanum nitrate and aluminum nitrate. The transformations during thermal treatment of the precursor solution with ethylene glycol and citric acid were evaluated by thermal analysis. Fourier transform infrared spectroscopy analysis was performed after calcinations of the polymeric resin for determination of residual carbon. The specific surface area was evaluated by the BET method. Fine powders with ∼121 m²/g specific surface area and 20 nm average particle size were obtained and observed by scanning and transmission electron microscopy. Nearly single phase LaAl₁₁O₁₈ was obtained after pressing and sintering these powders at 1600 °C with small additions of MgO. The sintered pellets were characterized by X-ray diffraction and scanning electron microscopy. Impedance spectroscopy measurements carried out in the 1000–1200 °C range show the electrolytic behavior of the La-β-Al₂O₃ pellets, suggesting their application as solid electrolytes in high temperature potentiometric oxygen sensors.