SiO2 Powder Research Articles

Investigating the Trimethylaluminium/Water ALD Process on Mesoporous Silica by In Situ Gravimetric Monitoring.

A low amount of AlOx was successfully deposited on an unordered, mesoporous SiO2 powder using 1–3 ALD (Atomic Layer Deposition) cycles of trimethylaluminium and water. The process was realized in a self-built ALD setup featuring a microbalanceand a fixed particle bed. The reactor temperature was varied between 75, 120, and 200 °C. The self-limiting nature of the deposition was verified by in situ gravimetric monitoring for all temperatures. The coated material was further analyzed by nitrogen sorption, inductively coupled plasma-optical emission spectroscopy, powder X-ray diffraction, high-resolution transmission electron microscopy, attenuated total reflection Fourier transformed infrared spectroscopy, and elemental analysis. The obtained mass gains correspond to average growth between 0.81–1.10 Å/cycle depending on substrate temperature. In addition, the different mass gains during the half-cycles in combination with the analyzed aluminum content after one, two, and three cycles indicate a change in the preferred surface reaction of the trimethylaluminium molecule from a predominately two-ligand exchange with hydroxyl groups to more single-ligand exchange with increasing cycle number. Nitrogen sorption isotherms demonstrate (1) homogeneously coated mesopores, (2) a decrease in surface area, and (3) a reduction of the pore size. The experiment is successfully repeated in a scale-up using a ten times higher substrate batch size.

NEAR INFRARED – EMITTING Zn2SiO4 POWDERS PRODUCED BY HIGH-ENERGY PLANETARY BALL MILLING TECHNIQUE

The near infrared-emitting Zn2SiO4 powders were produced by high-energy planetary ball milling of ZnO and SiO2 powders followed by annealing in air environment and at different temperatures. The surface morphology, crystal structure, chemical composition and optical properties of the obtained samples were investigated by means of field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Raman spectroscopy and photoluminescence measurements (PL) at room temperature. The analysis indicates the formation of Zn2SiO4 phase with annealing temperature of 1250 oC.°C. The size of Zn2SiO4 nanoparticles depends strongly on annealing temperature. Photoluminescence investigation reveals that the optimal annealing temperature for almost only near-infrared emission (~740 nm) is 1250 oC. The origin of this peak can be attributed to the energy transfer from non-bridging oxygen hole centers (NBOHs) to zinc interstialinterstitial (Zni) and oxygen vacancy (Vo) states in the Zn2SiO4 host lattice. These results demonstrate that we might be able to produce the Zn2SiO4 powders for applications in high CRI white light emitting diodes by a simple and low-cost method.

Synthesis of Si, N co-Doped Nano-Sized TiO₂ with High Thermal Stability and Photocatalytic Activity by Mechanochemical Method.

Τhe photocatalytic activity in the range of visible light wavelengths and the thermal stability of the structure were significantly enhanced in Si, N co-doped nano-sized TiO2, and synthesized through high-energy mechanical milling of TiO2 and SiO2 powders, which was followed by calcination at 600 °C in an ammonia atmosphere. High-energy mechanical milling had a pronounced effect on the mixing and the reaction between the starting powders and greatly favored the transformation of the resultant powder mixture into an amorphous phase that contained a large number of evenly-dispersed nanocrystalline TiO2 particles as anatase seeds. The experimental results suggest that the elements were homogeneously dispersed at an atomic level in this amorphous phase. After calcination, most of the amorphous phase was crystallized, which resulted in a unique nano-sized crystalline-core/disordered-shell morphology. This novel experimental process is simple, template-free, and provides features of high reproducibility in large-scale industrial production.

Effect of NaN<sub>3</sub> Addition Content on NaCl-NaF Medium Nitridation Synthesis β-Sialon Powders

β-Sialon powders were synthesized via salt-assisted nitridation synthesis from Al, Si, SiO2 powders and molten salt medium (NaCl and NaF) with the addition of different content of NaN3 at different temperature for 3 h. NaN3 were employed as auxiliary nitrogen source which effectively provide sufficient nitrogen. The results indicated that the growth of β-Sialon powders had better effect when the NaN3 was added. And the β-Sialon powders grew more completely and the morphology of β-Sialon powders showed the rod-like crystal with hexagonal smooth tips instead of conical tips. In addition, the products displayed different sizes when the content of NaN3 was changed. These results of this work suggested that β-Sialon could be synthesized with specific morphology by adding different content of NaN3.

Preparation of Consolidated Body Zeolite from Rice Husk Ash

Rice husks (RHs) are agricultural wastes which include approximately 20 mass% of silica (SiO2). In Thailand, RHs have been applied as fuel for thermal power generation systems and a large amount of ash (Rice husk ash: RHA) was produced. In addition, our research group has reported before that binder-free consolidated zeolite A could be obtained by using SiO2 powder with geopolymer reaction as a humidity conditioning material because zeolite A has been used as desiccant and builder for detergent with low silica content. Moreover, other kind of zeolite with high amount of SiO2 content, such as ZSM-5, was under interest due to its good properties as catalytic activity and a unique pore structure. But, it was not widely utilized because of the difficulty of consolidated body preparation. Therefore, in the present study, the possibility of the usage of RHA as raw materials for consolidated zeolite A and ZSM-5 was investigated for the high-value application of RHA under specific heat treatment condition, molar ratio and preparation technique. After specimens were obtained, XRD analysis and SEM were charactarized for consolidated bodies to confirm cystalline phases and observe microstructure, respectively. Consolidated zeolite A was synthesized with heat treatment above 60°C. The sample heat treated at 60°C for 24 h consisted of homogeneous zeolite A particles with the size smaller than 1 μm. In addition, consolidated ZSM-5 was synthesized with an usual method as TPABr (Tetra propyl ammonium bromide) technique and research method as S.C. (seed crystal) technique. The results showed that although around 10 μm seed crystal was used, around 4~5 μm of ZSM-5 particles were obtained by S.C. technique. This result led to the possibility to use RHA with S.C. technique to synthesize consolidated body and control ZSM-5 particle size.

Preparation of Si and O co-solution strengthened Ti alloys by using rice husks as SiO2 resource and quantitative descriptions on their strengthening effects

Ti alloys strengthened by both Si and O solutes were prepared by powder metallurgy method from pure Ti and amorphous SiO2 powder obtained by combusting rice husks. At the same time, Ti alloys singly strengthened by Si or O were also prepared for studying the strengthening effect of Si and O solutes. Results showed that amorphous SiO2 powder originated from rice husks could almost fully dissolve into pure Ti matrix when the content was not higher than 1.0 wt%, while higher content of SiO2 addition resulted in the formation of Ti5Si3 intermetallics. Si and O elements leaded to negative and positive distortion of Ti lattice, and the influencing degrees were −0.02 and +0.014 Å/wt% for lattice constant a, while −0.05 and +0.046 Å/wt% for constant c, respectively. Solid solution of Si and O would also result in the increase of hardness, which was 98.5 and 209.43 HV/wt%, respectively. When Si and O were co-exsited in Ti matrix, the negative and positive distortion cancelled each other, while the strengthening effect did not cancel but enhance each other.

Impurity effects on phase and microstructure stabilities of reactively-sintered porous MgTi2O5

Since the thermal-expansion anisotropy of pseudobrookite-type MgTi2O5 is not as prominent as isomorphic Al2TiO5, MgTi2O5 is thermally more stable than Al2TiO5. To realize the future structural applications of porous MgTi2O5, influence of impurities on the phase and microstructure stabilities should be studied. Here, impurity effects on phase and microstructure stabilities of reactively-sintered porous MgTi2O5 have been studied. As model impurities, Li2CO3 and amorphous SiO2 have been selected. Li2CO3 or SiO2 powder (0.1–4.0 wt%) was added to MgCO3 (basic) and TiO2 anatase powders with a molar ratio of 1:2. Uniaxially-pressed mixed powders were sintered at 1100 °C in air for 2 h to obtain porous MgTi2O5 bars. Appropriate Li2CO3 and SiO2 doping (~0.5 wt%) promoted uniform grain growth. However, with the excess amount of the impurities (> 2 wt%), the coefficient of thermal expansion of Li2CO3- and SiO2-doped MgTi2O5 ceramics decreased obviously above 900 °C and 950 °C due to the secondary sintering. To keep the fine-grained porous microstructure of Li2CO3- and SiO2-doped samples with preventing the secondary sintering, impurity levels should be preferably limited less than ~1.0 wt%.

The Raman Spectra and Molecular Relaxation Properties of Heterophase Glasses and Melts of K,Ca/CH3COO and Li,K,Cs/CH3COO

The Raman spectra and conductivity of KCH3COO–Ca(CH3COO)2 and LiCH3COO–KCH3COO–CsCH3COO vitrified acetate systems doped with fine Al2O3 and SiO2 powders at various concentrations were investigated. It was established that at temperatures below the glass formation temperature the addition of fine powders of Al2O3 and SiO2 increases the conductivity of heterophase glasses. It is shown that in the heterogeneous system there are two types of acetate ions differing in relaxation time.

Synthesis of Stable Bismuth Silicate with Sillenite Structure in the Na2O–Bi2O3–SiO2 System

A combined method for synthesizing a highly dispersed (0.8–2.5 μm) hydrophobic Na2O–Bi2O3–SiO2 powder (NBS powder) based on solutions of sodium methyl siliconate and bismuth nitrate is studied. The powder is synthesized at a reduced temperature (100°C). The microstructure and the phase composition of the resulting compounds in the Na2O–Bi2O3–SiO2 system at different processing temperatures are investigated. The structural phase transformations in the mineral phases of NBS powder are revealed in the temperature range of 100–500°C. The metastable bismuth silicate Bi2SiO5 at 400°C is transformed into stable sillenite with composition Bi12SiO20 having a cubic crystal structure (a = 10.1050 A). The synthesized NBS powder can be used as a filler to fabricate highly effective constructional radiation-shielding polymer composites with tailored properties.

Development and analysis of high density poly ethylene (HDPE) nano SiO2 and wood powder reinforced polymer matrix hybrid nano composites

ABSTRACTThe Hybrid composites are the emerging materials which uses two or more reinforced particles or fibres simultaneously. As potential applications of the composites, wood reinforced thermoplastic composites are commercially attractive for high volume applications, but their properties can be enhanced by adding Nano SiO2 particles. Wood powder and nano SiO2 were mixed with high density polyethylene as matrix material. Wood powder with fixed 5 wt. % and Nano SiO2 with varying weight % (3, 5, 7 wt. %) are reinforced in HDPE to manufacture composite materials by compression moulding process. Mechanical properties including tensile strength, flexural strength and Izod impact strength were evaluated and it was revealed that tensile strength and flexural strength were obtained maximum at 5 wt. % of Nano SiO2 and impact strength was obtained maximum at 3 wt. % of Nano SiO2.

Effect of heating parameters on sintering behaviors and properties of mullite whisker frameworks

Mullite whisker frameworks were fabricated by vapor–solid reaction with SiO2, Al2O3 and AlF3 powders as the whisker forming agent at high temperatures. The effects of heating temperature and soaking time on the weight loss, liner shrinkage, porosity, microstructure and compressive strength were investigated. The results showed that with the increasing of the sintering temperature and soaking time, the weight loss and liner shrinkage of the samples increased and the porosities decreased due to the accelerated vapor–solid reaction, resulting in strong bonding and grain growth of the mullite frameworks. The compressive strength of the samples increased with increasing the sintering temperature from 1500 to 1650 °C, and decreased with the soaking time extended to more than 5 h for 1500 °C and 2 h for 1650 °C. A maximum compressive strength of 142 MPa at a porosity of 62.3% was obtained for the mullite whisker framework heated at 1500 °C for 5 h. The enhanced strength was attributed to the strong bonding strength and fine mullite grains resulting from a relative lower heating temperature and a modest soaking time.

Effect of rubber compounding agent on adhesion strength between rubber and heat-assisted plasma-treated polytetrafluoroethylene (PTFE)

ABSTRACTAlthough heat-assisted plasma treatment enables drastic improvement of the adhesion property of polytetrafluoroethylene (PTFE), plasma-treated PTFE does not strongly adhere to any adherend. To clarify which rubber compounding agents positively affect the adhesion strength of a plasma-treated PTFE/rubber assembly, six types of unvulcanised rubbers were prepared and thermally compressed to a plasma-treated PTFE sheet. Thus, it was found that SiO2 addition to rubber drastically increased the adhesion strength of a plasma-treated PTFE/rubber assembly and cohesion failure of rubber occurred with large fractions of SiO2 although no adhesives were used. To confirm the reaction between plasma-treated PTFE and SiO2 powder, X-ray photoelectron spectroscopy (XPS) measurements were performed for the thermally compressed SiO2/PTFE assembly after repeated washing. The XPS results indicated that hydrophilic SiO2 powder strongly adhered to the plasma-treated PTFE, whereas hydrophobic SiO2 powder did not adhere to the PTFE. In this paper, a model was proposed for a possible mechanism of strong adhesion of a PTFE/rubber assembly through both hydrogen and covalent bonds between silanol groups of the SiO2 powder surface in the rubber and hydroxyl or carboxyl groups on the plasma-treated PTFE.

Interfacial effect of cyclodextrin inclusion complex on gas adsorption kinetics of dry water emulsion

Cyclodextrins (CD) solutions were mixed with hydrophobic SiO2 powders to form a dry-cyclodextrin-water (DCD) emulsion, and the effects of CDs with different concentrations and structures on gas adsorption kinetics were investigated, respectively. α-CD was found to enhance effectively both CH4 and CO2 gases adsorption capacity of DCD, while β-CD was generally negative to guest gas adsorption with one exception related to CH4 under lower concentration. Through analyzing dual interfacial effect of gas inclusion, the dominant competition between gas hydration and gas inclusion was speculated as the main reason for the different CD concentration dependence for CH4 and CO2 adsorption kinetics. Furthermore, based on considering the cooperative control of gas diffusion, hydration reaction, inclusion reaction and inclusion sedimentation, a diffusion-reaction-blocking model was suggested to describe the kinetic process. CH4 gases were found to prefer to exist in DCD with free form, while CO2 gases with adsorption form mainly. The selectiveness closely related to guest gas further illustrated the ‘CD concentration quenching’ appearing in CO2 adsorption rather than CH4 adsorption.

A broadband variable-temperature test system for complex permittivity measurements of solid and powder materials

A microwave test system to measure the complex permittivity of solid and powder materials as a function of temperature has been developed. The system is based on a TM0n0 multi-mode cylindrical cavity with a slotting structure, which provides purer test modes compared to a traditional cavity. To ensure the safety, effectiveness, and longevity, heating and testing are carried out separately and the sample can move between two functional areas through an Alundum tube. Induction heating and a pneumatic platform are employed to, respectively, shorten the heating and cooling time of the sample. The single trigger function of the vector network analyzer is added to test software to suppress the drift of the resonance peak during testing. Complex permittivity is calculated by the rigorous field theoretical solution considering multilayer media loading. The variation of the cavity equivalent radius caused by the sample insertion holes is discussed in detail, and its influence to the test result is analyzed. The calibration method for the complex permittivity of the Alundum tube and quartz vial (for loading powder sample), which vary with the temperature, is given. The feasibility of the system has been verified by measuring different samples in a wide range of relative permittivity and loss tangent, and variable-temperature test results of fused quartz and SiO2 powder up to 1500 °C are compared with published data. The results indicate that the presented system is reliable and accurate. The stability of the system is verified by repeated and long-term tests, and error analysis is presented to estimate the error incurred due to the uncertainties in different error sources.

A proton conductor electrolyte based on molten CsH5(PO4)2 for intermediate-temperature fuel cells.

Molten carbonate fuel cells have been commercialized as a mature technology. Due to the liquid electrolyte in molten carbonate fuel cells, gas seal and low contact resistance are easier to achieve than in other fuel cells. Herein, we report an investigation of the viability of a molten oxoacid salt as a novel type of fuel cell electrolyte. In comparison with molten carbonate electrolytes for MCFCs that operate at 500–700 °C, for which a ceramic support matrix is required, the molten proton conductor electrolyte has a lower working temperature range of 150–250 °C. The present study has shown that an electrolyte membrane, in which molten CsH5(PO4)2 is held in a matrix made of PBI polymer and SiO2 powder, has excellent thermal stability, good mechanical properties, and high proton conductivity. In addition, a molten proton conductor fuel cell equipped with such an electrolyte membrane operating at 200 °C showed an open-circuit voltage of 1.08 V, and a stable output voltage during continuous measurement for 150 h at a constant output current density of 100 mA cm−2.

Red, White and Blue Light Emission from Europium Doped Al2O3 Confined into a Silica Matrix

The main drawbacks of fluorescent activated lanthanide luminescent materials in practical optoelectronic applications are the high cost of raw material and the limitation of a specific color depending on the lanthanide ion. In this work, the synthesis of red, white and blue light emitting composite powders of Al2O3:Eu3+@SiO2 were successfully synthesized by the hydrolysis and condensation reactions of TEOS as the raw precursor of silica matrix on the Al2O3:Eu3+ surface. With the aim to change the CIE coordinates different weight ratios of Al2O3:Eu3+/SiO2 powders from 13Al/87Si to 5Al/95Si were prepared. Besides, various excitation wavelength from 280 to 340 nm was used in order to change the ratio intensity; Ired/Iblue, between the red emission coming from the 5D0→7F2 transition of Eu3+ ions and the blue band of silica matrix. Chemical evolution of the hydrolysis and condensation reaction of TEOS were conducted by FTIR spectroscopy. The results indicate that from 500°C a complete TEOS to SiO2 transformation is carried out.

Direct Electrochemical Preparation of Nanostructured Silicon Carbide and Its Nitridation Behavior

Silicon carbide was synthesized from mixtures of SiO2 and graphite by applying the concept of the FFC-Cambridge process and several fundamental aspects of the synthesis route were investigated. Porous disks composed of powders of SiO2 and graphite in molar ratios of 1:0.5, 1:1 and 1:1.5 were prepared by sintering in inert atmosphere and subjected to electro-deoxidation in molten CaCl2 at 1173 K under a range of experimental conditions. Disks of molar ratio 1:1.5, reduced at an applied voltage of 2.8 V for a duration of 6 h, yielded exclusively phase-pure SiC of nanowire morphology as the reaction product, while the other precursor compositions provided significant amounts of calcium silicides. Voltages lower than 2.8 V gave mixtures of SiC with elemental Si and graphite, and voltages higher than that gave CaSi alone. Shorter electro-deoxidation times led to incomplete reduction and allowed for the identification of CaSiO3 as a transient phase. Based on the experimental results a multipath reaction mechanism is proposed, consisting of the electrochemical reduction of SiO2 and CaSiO3 to Si and the subsequent in-situ carbonization of the Si formed to SiC. The effect of N2 at high temperature on the electrochemically synthesized SiC was investigated and the formation of nanowire Si2N2O was observed. Overall, the process presented is a facile single-step and low-temperature method for the synthesis of SiC with possible commercial prospects.

Preparation of metal doped SiO<sub>2</sub> films by magnetron sputtering deposition using metal oxide mixture powder target

Metal doped SiO2 thin films, which show strong luminescence by UV excitation, were prepared by a sputtering deposition method using metal oxide and SiO2 powder mixed targets. Electron density and temperature of the plasma using powder target was almost same independent for the mixture of powder target. However, peak intensity ratio of the plasma depends on the intensity of the powder target mixture. XPS measurements suggest that metal doped SiO2 thin films can be prepared using metal oxide and SiO2 mixture powder target, and their concentration ratio also depend on the powder target mixture.

Control of Silver Diffusion in Low-Temperature Co-Fired Diopside Glass-Ceramic Microwave Dielectrics.

Electrode material for low-temperature co-fired diopside glass-ceramic used for microwave dielectrics was investigated in the present work. Diffusion of silver from the electrode to diopside glass-ceramics degrades the performance of the microwave dielectrics. Two approaches were adopted to resolve the problem of silver diffusion. Firstly, silicon-oxide (SiO2) powder was employed and secondly crystalline phases were chosen to modify the sintering behavior and inhibit silver ions diffusion. Nanoscale amorphous SiO2 powder turns to the quartz phase uniformly in dielectric material during the sintering process, and prevents the silver from diffusion. The chosen crystalline phase mixing into the glass-ceramics enhances crystallinity of the material and inhibits silver diffusion as well. The result provides a method to decrease the diffusivity of silver ions by adding the appropriate amount of SiO2 and appropriate crystalline ceramics in diopside glass-ceramic dielectric materials. Finally, we used IEEE 802.11a 5.8 GHz as target specification to manufacture LTCC antenna and the results show that a good broadband antenna was made using CaMgSi2O6 with 4 wt % silicon oxide.

Bonding ZrB2-SiC-G ceramics using modified organic adhesive for engineering applications at ultra high temperatures in air

It is a challenge to bond ceramics for engineering applications at ultrahigh temperatures in air. In this paper, a high temperature organic adhesive (HTOA) was prepared using methylphenylsilicone resins (MPSR) as the matrix, trisilanolisobutyl-methylsilicone resin/polyhedral oligomeric silsesquioxane (POSS) as the modifier, ZrB2, SiO2 and Si powders as the inorganic fillers, and γ-aminopropyltriethoxysilane (KH550) as the curing agent. The synthesized HTOA was used to bond ZrB2-SiC-G ceramic (ZSG). The ceramic yield of MPSR was increased from 71% to 91% after being modified by trisilanolisobutyl-POSS. The average shear strength of ZSG joints bonded by HTOA was 13.2MPa at room temperature. After 1500°C/1h processing, the bonding strength between HTOA and ZSG ceramic was 53.8MPa. The inter-diffusion of elements between the HTOA and the ZSG occurred at 1500°C and ZrSiO4 compound was formed via the interface reaction. The excellent high-temperature performance of the prepared HTOA makes it one of the convenient and effective organic adhesive for joining ZSG for engineering applications at ultrahigh temperatures in air.