Al2O3 Tube Research Articles

Highly sensitive and low-temperature triethylamine sensor based on in situ growth of hierarchical α-MoO3 flowers

To challenge high working temperature of present triethylamine (TEA) sensor, well-defined hierarchical α-MoO3 flowers were in situ grown on Al2O3 tubes through a simple solvothermal method. The α-MoO3 flowers were about 3 μm in diameter consisted of overlapping nanosheets with average thickness of ∼30 nm, growing radially from the center of the flowers. The α-MoO3 flowers in situ grew on Al2O3 tubes to constitute the thin film sensors, which exhibited improved gas-sensing performance to TEA compared to the thick film sensors painted with the powder of α-MoO3 produced in the same reaction system. The average response value of the α-MoO3 thin film sensors to 10 ppm TEA was 243.5 at relatively low operating temperature of 133 °C, which was 4.5 times as high as that of the thick film sensors (54.2). And the detection limit of the thin film sensors to TEA is further decreased to 0.001 ppm compared to the α-MoO3 thick film ones. The superior TEA-sensing capability should be attributed to the hierarchical nanostructure grown in situ that supplies more active sites for gas molecule adsorption and electron transfer. The synthesized α-MoO3 flowers with hierarchical nanostructure are promising material for trace TEA detection in practical application.

Preparation of ionic liquid-immobilized siloxane membranes by vapor-phase transport and anion exchange

Using the sol-gel method, we developed ionic liquid (IL)-immobilized siloxane membranes from ionic alkoxysilanes (silylated ILs). The developed membranes were adapted for the separation of inorganic and organic gases and organic liquid mixtures. In this study, we developed a new method for preparing IL-immobilized siloxane membranes using vapor-phase transport and anion exchange techniques. First, a siloxane membrane containing chloropropyl groups was prepared in a porous Al2O3 tube. The membrane was brought into contact and reacted with 1-methylimidazole vapor at 353 K. AgCl precipitation, and Cl 2p3/2 X-ray photoelectron spectroscopy revealed that the chloropropyl group was successfully converted into an imidazolium-type IL structure. Next, the membrane was immersed in aqueous HN(SO2CF3)2 to exchange the anion from Cl− to (CF3SO2)2N−. The change in permselectivity through the membranes before and after the vapor-phase transport and anion-exchange treatments was confirmed by steam/H2 and toluene/N2 separation tests. The developed techniques exhibit excellent potential for preparing a wide variety of IL-immobilized siloxane membranes.

Preparation and characterization of ion-exchanged Ni-Na-β”-Al2O3 and Fe-Na-β”-Al2O3 solid electrolytes for applications in liquid metals

Accurate determinations of the thermochemical properties for the steel alloying elements (Fe, Cr, Ni, Co and Mn) dissolved as corrosion product impurities in Pb and Pb–Bi alloy (LBE) are relevant for the development of Lead-Cooled Fast Nuclear Reactors (LFRs). Ion-selective solid electrolytes are suitable for an electrochemical characterization of the dissolved impurities. Among these, ion-exchanged Ni-β”-Al2O3 and Fe-β”-Al2O3 are promising solid electrolytes for the selective detection of Ni and Fe dissolved in HLMs. In the present works we proposed a preliminary test of liquid and vapor ion-exchanges on commercial polycrystalline Na-β”-Al2O3 tubes at different conditions of temperature and reaction time with NiCl2 and FeCl2 salts, characterizing the effects on the material microstructure. The resulting Ni-Na-β”-Al2O3 and Fe-Na-β”-Al2O3 samples were only partially replaced by nickel or iron, extremely porous, damaged by molten salt corrosion, and contaminated by residual chlorides. When tested as selective sensors in molten LBE, they failed in detecting dissolved nickel or iron. Thus, ion-exchange procedure on polycrystalline Na-β”-Al2O3 substrates still needs to be improved by properly combining the liquid and vapor ion-exchange with optimized reaction conditions in order to increase the sodium replacement yield. Alternatively, efforts may be focused on the preparation and application of other different nickel and iron solid electrolytes.

High-temperature performance of thermal environmental barrier coatings in 90%H2O-10%O2 conditions at 1475 °C

The performance of 50HfO2-50SiO2/YxYb(2−x)Si2O7 thermal environmental barrier coating prepared using atmospheric plasma spraying was investigated in the Al2O3 tube furnace in 90%H2O-10%O2 conditions at 1475 °C. The results showed that YxYb(2−x)Si2O7 layer was contaminated by alumina impurities during the testing process. The thermally grown oxide layer was formed at the bond coat/SiC interface, it grew as the cycles increased. Furthermore, the (Y/Yb)2O3-HfO2 solid solution with a higher coefficient of thermal expansion was formed at YxYb(2−x)Si2O7/50HfO2-50SiO2 interface. The horizontal cracks were the principal factor that caused the failure of 50HfO2-50SiO2/YxYb(2−x)Si2O7. 50HfO2-50SiO2/YxYb(2−x)Si2O7 protected SiC for 25 cycles in steam conditions.

Direct Ink Writing of Tubular Al<sub>2</sub>O<sub>3</sub> Membrane Support Using Agar-Based Ink in 3D-Printing

Direct ink writing was used for 3D printing of tubular Al2O3 membrane support. Agar-based ink mixtures were prepared as a paste with a proper viscoelastic behavior in achieving printing. Using agar only for mixing with Al2O3 slurry in preparing the ink mixtures showed the flow behavior resulting in failure to print the Al2O3 tube due to too low viscosity of the ink mixture—100 Pa at 40°C. However, the introduction of Hydroxyethyl cellulose (HEC) as thickener and Polyethylene glycol 1500 (PEG 1500) as lubricant helped improve the behavior of the ink mixtures to be more proper paste for printing. The amounts of HEC were varied from 0 to 2wt% of solid loading. At 2wt% HEC, the ink mixture was able to be printed highest, compared to the other ink mixtures. However, the 2wt% HEC-using ink mixtures possessed the highest sintering shrinkage at 12%, while its relative density was highest at 70%. The results indicated that it was possible to print the alumina membrane tube if its fidelity was improved further.

Effect of clay addition to Al2O3-agar mixture on pore size and distribution of tubular Al2O3 membrane support fabricated byagar gelcasting

The addition of clay particles— kaolin or bentonite—into the mixture of Al2O3 slurry and agar solution was examined for creating pores with controllable size in tubular Al2O3 membrane. The mixtures were prepared and then molded out of glass tubes using the method of agar gelcasting. The green, gelcast Al2O3 tubes were sintered at 1350 °C for 1 h for membrane application. The effect of clay addition from 0 to 2 wt% into the mixture on pore size and structure of Al2O3 tubes was observed with SEM. The addition of bentonite provided less uniform pore size and distribution than that of kaolin. Additionally, the step of ball milling the clay particles to make complete dispersion prior to adding to the mixtures was needed to create more uniform pore size and distribution. The ball milling time of 60 min was the optimum condition for preparing Al2O3 membrane support.

A green synthesis of MOR zeolite membranes by wet gel conversion for dehydration of water-acetic acid mixtures

High performance mordenite (MOR) membranes were successfully synthesized by wet gel conversion (WGC) route using organic template-free and fluoride-free gels on seeded macroporous Al2O3 tubes. The seeded Al2O3 tubes were dipped into the gel solution with a composition of SiO2: 0.0045Al2O3: 0.19 Na2O: 27.76 H2O and then directly crystallized at 150 °C for 8 h without any extra solvent or solution in autoclave. The concentration of MOR seeds, crystallization time, composition of gels and crystallization way (hydrothermal growth or WGC) significantly influenced the membrane performance for dehydration of acetic acid (AA) mixtures by pervaporation. The prepared MOR membranes displayed a high water flux and good selectivity in long-term dehydration of 90 wt.% AA/H2O at 75 °C with the steay-state flux of 0.70 kg m−2 h−1 and separation factor increasing to 5000 after 200 h test. The WGC approach reduced the consumption of gel by about 96% with almost “zero” waste liquid. This WGC method is demonstrated as an efficient, green route to synthesze zeolite membranes and to possess potentiality for industrial dehydration applications.

Evaluation of tritium confinement performance of the assembly composed of zirconium and alumina simulating lithium rod

A high temperature gas cooled reactor is proposed as an external tritium source for stably starting up of fusion reactors. A Li rod coated with zirconium and alumina have been proposed to confine produced tritium. Although the tritium leakage from the Li rod has been estimated by the simulation, it is necessary to evaluate the tritium confinement performance experimentally. In this study, the test assembly simulating the Li rod composed of Inner Zr tube - Outer Zr tube - Al2O3 tube was built up, and tritium confinement experiments were conducted. The test assembly successfully confined tritium, which was contained in the Ar gas mainly as HTO and slightly as HT, for 12 h and 87 h at a high temperature of 700 °C. It was suggested that an oxide layer formed on the Zr tube contributed to suppress tritium permeation in HTO.

Good triethylamine sensing properties of Au@MoS2 nanostructures directly grown on ceramic tubes

Due to the extensive threat from TEA, the need for a simple and effective gas sensor for TEA detection is highly desired. Here, the design of the Au nanoparticles was deposited on the surface of the three-dimensional (3D) MoS2 nanostructures, and an excellent TEA gas sensor was successfully fabricated. The 3D MoS2 nanostructures are grown directly on the Al2O3 tubes with a simple and inexpensive hydrothermal process. Au nanoparticles are loaded on MoS2 nanostructures via DC-sputtering in a highly controllable and reproducible manner. Compared to the original MoS2 sensor, Au@MoS2 exhibits a remarkably higher response and faster recovery speed to TEA gas at 280 °C. The influence of the amount of Au on the device performance is also studied, which is controlled by changing the Au sputtering time (0, 30, 50, and 70 s). It is noteworthy that the Au@MoS2 sensor with a medium content (50 s) exhibits the highest response, which is about 4 times higher than that of original MoS2. The enhanced sensing property of the Au@MoS2 sensors is discussed with the semiconductor electron depletion layer model introduced by Au–MoS2 Schottky contact.

Microwave excitation of a low-energy atomic hydrogen

Performances of microwave driven compact neutral beam sources of different plasma excitation configurations have been compared in producing directed low energy atomic beams for biomolecular structural analyses. The beam sources include unique impedance matching systems in themselves for reducing the size of the source; a multi-turn spiral antenna successfully excited a hydrogen plasma in a 4 mm inner diameter Al2O3 tube by 2.45 GHz microwave power. A combination of a mirror magnetic field and electron cyclotron resonance has been found effective to realize a source operation at a low operating pressure (∼10−3 Pa). This magnetic field configuration produced a hydrogen plasma with the optical emission spectrum predominated by atomic lines indicating a high degree of dissociation. The plasma excited in this type of source exhibited a mode transition like behavior which was not confirmed in other source geometries.

Direct temperature measurement via thermocouples within an SPS/FAST graphite tool

Many publications investigate temperature distributions by simulations. Temperature is often not practically measured or only at a few locations inside the sintering tool using thermocouples. However, thermocouple temperature measurement is very sensitive to environmental conditions and can be extremely defective. This study investigates the feasibility of thermocouple temperature measurement at different measuring positions within a graphite tool during SPS/FAST. Three different graphite tool setups and three different thermocouples were used for the temperature measurements. The thermocouples were covered by an Al2O3 tube and placed directly inside a borehole in the setup. Process temperatures, measured by a vertical pyrometer, up to 1200 °C were realized. Experimental data at different temperature plateaus show significant temperature differences depending on the applied thermocouple and tool setup. It is shown that the temperature present is underestimated by the thermocouple and measuring errors vary drastically with the thermocouple length, which is inserted in the sintering tool.

Coating the porous Al2O3 substrate with a natural mineral of Nontronite-15A for fabrication of hydrogen-permeable palladium membranes

Substrate surface modification is a key pretreatment during fabrication of composite palladium membranes for hydrogen purification in hydrogen energy applications. The suspension of a natural porous material, Nontronite-15A mineral, without any organic additives was employed in dip-coating of the porous Al2O3 substrate. The Nontronite-15A mineral was characterized by SEM, XRD, TG−DSC and granulometry analysis. The surface and cross-section of the coated porous Al2O3 tubes were observed by SEM, and their pore size distribution and nitrogen flux were also measured. Palladium membranes were fabricated over the coated Al2O3 tubes by a suction-assisted electroless plating. The optimal loading amount of the Nontronite-15A mineral is just to fill in and level up the surface cavities of the Al2O3 substrate rather than to form an extra continuous layer. A thin and selective palladium membrane was successfully obtained, and its permeation performances were tested. The kinetic analyses on the hydrogen flux indicate that the hydrogen permeation behavior exhibits typical characteristics for most of the palladium membranes. During the stability test at 450 °C for 192 h, no membrane damage was detected, and the hydrogen flux increased slightly.

CO2/H2/H2O Hydrate Formation with TBAB and Nanoporous Materials

Nanoporous materials can significantly promote the formation process of gas hydrate by reducing the barrier of physical chemistry. In this work, the CO2/H2/H2O hydrates formation with tetra-n-butyl ammonium bromide (TBAB) and nano Al2O3 or carbon nano tube (CNT) were studied and compared in term of kinetic curves. It was found that both TBAB-Al2O3 and TBAB-CNT could promote the CO2/H2/H2O hydrate formation process. Furthermore, compared with TBAB-Al2O3, TBAB-CNT has the better promotion effect on the CO2/H2/H2O hydrate formation process. It is interesting that the CO2/H2/H2O hydrate formation process with TBAB-Al2O3 represents reformation phenomenon. It possibly forms sI CO2/H2/H2O hydrate firstly and finally forms semiclathrate CO2/H2/H2O hydrate.

Surface modification of macroporous Al2O3 tubes with carbon-doped TiO2 intermediate layer and preparation of highly permeable palladium composite membranes for hydrogen separation

ABSTRACTTo prepare H2-permeable palladium composite membranes, a novel carbon-doped microporous TiO2 intermediate layer was introduced to modify the surface of macroporous Al2O3 substrates. The Pd/TiO2–C/Al2O3 membrane was prepared via electroless plating, and thereafter, carbon residue in the intermediate layer was removed by calcination in air, yielding a Pd/TiO2/Al2O3 membrane. Experimental results indicate that the carbon residue shrinks the pore size of the intermediate layer and facilitates a decrease of membrane defects. Additionally, carbon removal induces a higher effective membrane area at the permeate side, which enhances hydrogen permeability. Furthermore, the apparent activation energy (EA) and stability of the as-prepared Pd/TiO2/Al2O3 membrane were investigated.

Preparation of highly crystalline NiO meshed nanowalls via ammonia volatilization liquid deposition for H2S detection

Novel NiO meshed nanowalls, with characteristics of open geometry, porosity, single crystal and highly crystalline framework, are grown in situ on different substrates (including Al2O3 tube, glass slide, ITO, stainless steel mesh, nickel foam and carbon cloth) via a simple ammonia volatilization liquid deposition process at room temperature and a postcalcination treatment. The calcination temperature can strongly influence the pore size and crystallinity of the product, leading to different gas-sensing performances. The product that obtained at 700 °C (NiO-700) has the advantage in the combination of the largest pore size and high crystallinity, and shows the highest response to H2S gas. In 0.01–100 ppm H2S gas, the NiO-700 meshed nanowalls based sensor can give evident and reversible response signals at a low optimal operating temperature of 50 °C, the response towards 100 ppm H2S can reach to 137.3, the detection limit is as low as 10 ppb. Furthermore, the sensor also exhibits excellent selectivity, repeatability, anti-humidity and long-term stability for H2S detection. The results of gas chromatograph-mass spectrometry (GC-MS) and infrared gas analysis (IRGA) reveal that the H2S gas can be oxidized to SO2 after interacting with NiO-700 meshed nanowalls material. Therefore, the possible H2S sensing mechanism should be proposed as: H2S gas molecules undergo a redox reaction with adsorbed oxygen anion on the surface of NiO-700 meshed nanowalls to form SO2; meanwhile, the electrons restricted by adsorbed oxygen return to the bulk and recombine with the holes, resulting in a decrease in effective carrier concentration of holes and thus generating a change in resistance.

A novel hetero-structure sensor based on Au/Mg-doped TiO2/SnO2 nanosheets directly grown on Al2O3 ceramic tubes

Chemiresistive gas sensors with novel nanostructures, high response and reliable fabrication process have been fabricated successfully by designing Au/Mg-doped TiO2/SnO2 nanosheets hetero-structures. Mg doping was used to decrease the work function of TiO2, which can lead to the electrons in TiO2 greatly depleted due to the formation of Schottky contact and n-n heterojunction. SnO2 nanosheets were directly grown on Al2O3 tube with a cost-effective hydrothermal process. By employing pulsed laser deposition (PLD) and direct current sputtering methods, the construction of gold (Au) nanoparticles-loaded Mg-doped TiO2/SnO2 heterostructure is highly controllable and reproducible. In comparison with pristine SnO2 and TiO2/SnO2, Mg-doped TiO2/SnO2 sensors exhibit high response (30.4) and short response time (9 s) to 50 ppm TEA gas, which is about 6 times higher than pure SnO2 sensor and 2 times higher than TiO2/SnO2 sensor at a working temperature of 260 °C. The mechanism for sensing property enhancing of the Au/Mg-doped TiO2/SnO2 sensor was also discussed in detail with the semiconductor depletion layer model introduced by Au-TiO2 Schottky contact and TiO2/SnO2n-n heterojunction.

Enhanced triethylamine sensing properties by fabricating Au@SnO2/α-Fe2O3 core-shell nanoneedles directly on alumina tubes

α-Fe2O3 nanoneedles were directly grown on the surface of Al2O3 tubes by a cost-effective hydrothermal method. In addition, the construction of Au nanoparticle-loaded SnO2/α-Fe2O3 core/shell heterostructure was fabricated by employing pulsed laser deposition (PLD) and DC-sputtering methods Gas sensors were fabricated from Au@SnO2/α-Fe2O3 core-shell nanoneedles on Al2O3 tubes, and their sensing properties have investigated for response to various target gases. The results indicated that the sensor based on Au@SnO2/α-Fe2O3 core-shell nanoneedles showed superior selectivity toward triethylamine (TEA) gas, giving a response of 39–100 ppm, which was higher than that of α-Fe2O3 nanoneedles and SnO2/α-Fe2O3 core-shell nanoneedles. Moreover, the sensor based on Au@SnO2/α-Fe2O3 core-shell nanoneedles showed an obvious better linearity (R = 0.9975) of sensing characteristics than of two other sensors. The enhanced sensing properties are discussed with the semiconductor depletion layer model along with the Schottky contact and N–N heterojunction theory.

Electrolytic Reduction of Solid Al2O3 to Liquid Al in Molten CaCl2

The electrochemical reduction of Al2O3 has been investigated in molten CaCl2 at 1123 K. To predict the electrochemical reduction behavior depending on the activity of O2− ions, the potential–pO2− diagram for the Al–Ca–O–Cl system is constructed from thermochemical data. In a Mo box-type electrode, an Al2O3 tube is successfully reduced to liquid Al with a maximum purity of 98 at%. However, in the electrolysis of Al2O3 powder in an Fe box-type electrode, Al2Ca is produced through the formation of Ca12Al14O33 as an intermediate product. The different electrochemical reduction behaviors of the tube and the powder are explained by the different diffusion path lengths for O2− ions from three-phase zone (Al2O3/CaCl2/cathode metal) to bulk CaCl2.

Enhanced triethylamine sensing properties by designing Au@SnO2/ZnO nanosheets directly on alumina tubes

A triethylamine (TEA) sensor working temperature of 280 °C with high sensitivity and selectivity for TEA gas has been successfully fabricated by building Au@SnO2/ZnO nanosheets. By introducing a seed layer, ZnO nanosheets have been directly grown on Al2O3 tubes with a facile hydrothermal method. The Au@SnO2/ZnO structure is formed by utilizing DC-sputtering and pulsed laser deposition (PLD) methods. Compared with the pristine ZnO and SnO2/ZnO nanosheets sensors, the Au@SnO2/ZnO nanosheets sensors measured at 280 °C get a higher response of 48.1 toward 50 ppm of TEA gas. Moreover, the Au@SnO2/ZnO nanosheets sensor exhibits excellent selectivity. The enhanced sensing properties of the Au@SnO2/ZnO nanosheets sensor are discussed with a model of semiconductor depletion layer on the basis of n–n heterojunction and Schottky contact.

Low-temperature in-situ growth of SnO2 nanosheets and its high triethylamine sensing response by constructing Au-loaded ZnO/SnO2 heterostructure

In this report, uniform SnO2 nanosheets (NSs) have been in-situ grew on the surface of Al2O3 tubes via a cost-efficient hydrothermal synthesis at low temperature. The nanostructures of ZnO/SnO2 were prepared by employing pulsed laser deposition (PLD) method. Furthermore, Au surface modification with DC-sputtering process is used to improve the sensitivity of ZnO/SnO2 NSs sensor to TEA gas. The Au@ZnO/SnO2 NSs exhibited high response (S = 115) to 100 ppm trimethylamine (TEA) gas at 300 °C, which was about 20 times higher than that of the pristine SnO2 NSs. The enhanced sensing properties of Au@ZnO/SnO2 NSs sensor are discussed from the points of Au@ZnO Schottky contact and ZnO/SnO2 n-n heterojunction on the basic of depletion layer model.