Low-pressure Method Research Articles

A simple low pressure method for the synthesis of TiO2 nanotubes and nanofibers and their application in DSSCs

TiO2 nanotubes were synthesized using a modified autoclave-free thermal method from as-prepared initial powders. The size of initial powders (IP) was found to be critical in determining the morphology and crystal structure of the final product. Oleylamine (OA) was used as the polymer agent in the preparation of initial powders with different mol ratios of OA/Ti: 1, 5, and 10. X-ray diffraction analysis depicted that the increase of mole ratio up to 10 resulted in smaller nanoparticles with the sizes of about 8 nm. It was also deliberated that low temperature thermally treated IP showed the characteristic diffraction pattern of titanate phase of nanotubes. Scanning electron microscope images showed nanorods, short nanotubes, and single-phase long and uniform nanofibers produced from initial powders. SEM cross-section of the anode cell of TiO2 nanofibers demonstrated the presence of uniformly closed net long fibers in the cell. Open circuit voltage measurements of the nanofiber cell demonstrated a several hundreds of seconds in the electron transport decay, which was significantly higher than that of the nanoparticles. IMPS/IMVS measurements of the nanofibers and nanotube solar cells showed electron transport enhancement and long life time compared to their nanoparticle counterparts. Open image in new window

Characteristics of a Frisch collar grid CdZnTe radiation detector grown by low-pressure Bridgman method

A single-polarity charge-sensing method was studied by using a CdZnTe Frisch collar grid detector grown by using a low-pressure Bridgeman furnace at the Korea Atomic Energy Research Institute (KAERI). The Frisch collar grid CdZnTe detector has an active volume of 5 × 5 × 10 mm3, and was fabricated from a single crystal, Teflon tape and copper tape used as a Frisch collar grid. A room-temperature energy resolution of 6% full width at half maximum (FWHM) was obtained for the 662keV peak of Cs-137 without any additional electrical corrections. The detector’s fabrication process is described, and its characteristics are discussed. Finally, the charge transport properties and gamma-ray energy resolution of the fabricated Frisch collar grid detector are compared with those of two other Frisch collar detectors grown by using different crystal growth methods and purchased from eV-products and Redlen technology.

Measuring System for Pressure Sensitive Paint (PSP) Calibration in the Range of Low Pressure Gains

The measurement by means of the PSP method in the range of low pressure gains (up to ±30kPa) may constitute a supplement to the low-pressure compressor stage research methods (pitot tubes, thermal anemometry, LDA). This paper presents an in-house PSP calibration system implemented in the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The tests were carried out using a calibration chamber co-operating with a measuring system controlled by an original handler operating in the LabView environment. The pressure-dependent luminous intensity of recorded light was determined at different values of temperature and levels of excitation illumination. The system makes it possible to calibrate pressure sensitive paints and perform measurements in the range of pressure values occurring in the systems of industrial fans.

Electromagnetic and microwave absorption properties of single-walled carbon nanotubes and CoFe2O4 nanocomposites

Abstract Single-walled carbon nanotubes were facilely and abundantly synthesized by low-pressure air arc discharge method (LPA-SWCNTs), and CoFe2O4 nanocrystals were synthesized by a nitrate citric acid sol–gel auto-ignition method. The electromagnetic and microwave absorption properties of LPA-SWCNTs, CoFe2O4 nanocrystals and their nanocomposites were investigated. The LPA-SWCNT/CoFe2O4 nanocomposites showed excellent microwave absorption properties. The minimum efficient reflection loss is −30.7 dB at 12.9 GHz for 10 wt% of LPA-SWCNTs in the nanocomposites, and an effective absorption bandwidth with a reflection loss below −10 dB is 7.2 GHz. The Debye equation and impedance matching were introduced to explain the microwave absorption properties. Compared with the single-component materials, the LPA-SWCNT/CoFe2O4 nanocomposites are an excellent candidate for microwave absorbers.

Measurement of thermal accommodation coefficients using a simplified system in a concentric sphere shells configuration

For heat transfer in the microscale, the interaction between the gas and the solid surface is characterized by the thermal accommodation coefficient, and is important owing to the large surface-to-volume ratio existing as a consequence of the small size. However, there are few data of the thermal accommodation coefficients on the nonmetal surfaces often employed in microdevices. In this research, a novel simplified system in a spherically symmetric configuration is proposed, achieving a low-cost measurement of the thermal accommodation coefficient for both metal and nonmetal surfaces. Tiny flat-plate samples on a heater are placed at the center of a spherical vacuum chamber, and the conductive heat flux is measured and analyzed under the assumption of a concentric spherical shells geometry based on the low-pressure method. An approximate relation for the heat flux is also employed to measure under the near free-molecular and the transitional flow regimes. The proposed novel measurement system is validated by measurements of the thermal accommodation coefficient on a platinum surface with helium, argon and xenon. The measured heat fluxes as a function of pressure are well fitted by the approximate relation, and the obtained thermal accommodation coefficients agree well with the data in the literature. Finally, the measurement is demonstrated on a nonmetal surface of glass, showing good feasibility of the measurement system.

Effect of Gas Pressure and Temperature on Stereometric Properties of Al+Al2O3 Composite Coatings Deposited by LPCS Method

Abstract The paper deals with effect of working gas pressure and temperature on surface stereometry of coatings deposited by low-pressure cold spray method. Examinations were focused on aluminium coatings which are commonly used to protect substrate against corrosion. A commercial Al spherical feedstock powder with admixture of Al2O3 (Al + 60vol.-% Al2O3), granulation -50+10 µm, was used to coat steel, grade S235JR. Thedeposited coatings were studied to determine their stereometry, i.e. roughness, transverse and longitudinal waviness, topography of surface and thickness as the functions of gas pressure and temperature. A profilometer and focal microscope were used to evaluate the stereometric properties. In order to reduce the number of variables, the remaining process parameters, i.e. shape and size of de Laval nozzle, nozzle-to-substrate distance, powder mass flow rate, linear velocity of spraying gun, were kept unchanged. The investigation confirmed influence of temperature and pressure on coating thickness as well as on the surface seterometry.

Effect of initial particle size and densification on AFEX-pretreated biomass for ethanol production.

Switchgrass (SG), corn stover (CS), and prairie cordgrass (PCG) pretreated with ammonia fiber expansion (AFEX) were densified using a novel low-temperature, low-pressure densification method. Simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) were performed with loose and densified AFEX-treated biomass to determine the effect of post-AFEX densification. Biomass particle size reduction before pretreatment increased 144-h SSF ethanol yields from densified material by 8-9 % although no significant differences were seen in the first 72 h. Grinding material after densification had no impact on final ethanol yields but increased production rates in the first 24-48 h. Low-pressure, post-AFEX densification had no adverse effects on SSF ethanol yields from SG or CS but reduced yields from densified PCG by 16 %. Glucose concentrations after hydrolysis (SHF) showed similar trends. Ethanol yields after SHF, however, showed that densification had no significant impact on CS or PCG but reduced final ethanol yields from SG.

Influence of the specific surface area of a porous nickel to the intermetallic compound generated by reaction of a porous nickel and aluminum

A new process is proposed to fabricate an intermetallic compound reinforced aluminum alloy matrix composite by using the reaction between porous nickel and molten aluminum alloy. The intermetallic compound reinforced aluminum alloy composite was manufactured with the low-pressure infiltration process method. The amounts of the intermetallic compounds under 3 different specific surface area of porous nickel and the porosity inside composites were investigated. Porous nickel reacted with molten aluminum alloy at 973 K, and the intermetallic compound of Al3Ni was generated on the surface of the porous nickel. The generated intermetallic compound Al3Ni, was delaminated according to the difference of thermal expiation coefficient with nickel. And the intermetallic compounds moves in the direction of aluminum matrix. The area fraction of the intermetallic compounds increased with the increasing specific surface area of porous nickel. In addition, the defect inside the composite decreased by the increasing specific surface area of porous nickel.

CO2-assisted synthesis of silk fibroin hydrogels and aerogels

Biocompatible and biodegradable porous materials based on silk fibroin (SF), a natural protein derived from the Bombyx mori silkworm, are being extensively investigated for use in biomedical applications including mammalian cell bioprocessing, tissue engineering and drug delivery applications. In this work, low-pressure, gaseous CO2 is used as an acidifying agent to fabricate SF hydrogels. This low-pressure CO2 acidification method is compared to an acidification method using high-pressure CO2 to demonstrate the effect of CO2 mass transfer and pressure on SF sol–gel kinetics. The effect of SF molecular weight on the sol–gel kinetics is determined using the low-pressure CO2 method. The results from these studies demonstrate that low-pressure CO2 processing proves to be a facile method for synthesizing 3-D SF hydrogels.

A Simple Low Temperature and Pressure Method for the Synthesis of Quasi-One Dimensional Nano Structures of TiO<sub>2</sub> for Dye Synthesized Solar Cells

In this work we have synthesized TiO2 nanostructures using a modified autoclave-free hydrothermal method from bulk powders. In the absence of pressure, Toluene was used as the dispersing agent to prohibit particle aggregation during the thermal treatment. Toluene to Ti mole ratio (X) was varied from 0 up to 30 to obtain different morphologies of TiO2. X-ray diffraction (XRD) analysis demonstrated the Anatase phase for all the samples. FTIR analysis indicated that samples are free of carbon rich compounds and carbon contaminants. SEM images showed that with the increase of Toluene to Ti ratio, the morphology of the powders change from spherical particles with an average size of about 45 nm for X=0 to broccoli-shape structure for X=10, nanotubes for X=20 and nanosticks/wires for X=30. The synthesized TiO2 nanotubes have been used as photoanode in a dye synthesized solar cell (DSSCs). The efficiency of the fabricated solar cell without any further modification was obtained about 2.3%.

Precise control of elastocapillary densification of nanostructures via low-pressure condensation

Capillary self-assembly of nanoscale filaments is an emerging means of fabricating complex and hierarchical surface textures. However, via conventional processing methods such as immersion in liquid and atmospheric pressure condensation of liquid onto the substrate, it is challenging to achieve uniform results over large areas and to adapt the process to structures with different dimensions and spacing. Here we study elastocapillary densification of carbon nanotube (CNT) microstructures via controlled low-pressure condensation of liquid and subsequent evaporation, with the structures placed on a temperature controlled substrate. We study the dynamics of liquid infiltration into the microstructures and achieve control over the liquid condensation rate within >1 μm s−1. We find that the extent of densification depends on the amount of liquid delivered to the substrate as well as the size and spacing of the microstructures. We also show that the low-pressure condensation method can be used to form large arrays of anisotropic CNT microstructures, including thin-walled slanted microwells and tilted microposts.

A Novel Low-Pressure Atomization Method for Burning Emulsified Crude Oil

ABSTRACT A novel, air-assisted atomizer designed for low-pressures and high viscosity fluids was used to produce and burn a spray of emulsified crude oil with different fractions of seawater. For a set of spray nozzles, the operational stability limits based on the crude oil flow rate, atomizing air ratio, seawater fraction, and co-flowing air characteristics were established. The droplet diameter and velocity distributions in the non-reacting spray plume were measured using phase Doppler interferometry. The low air and oil pressure requirements permit low power compressors and pumps with a minimal infrastructure footprint. This technology can be a scalable, effective, and fieldable remediation method for benthic spills or crude oil too emulsified for traditional in situ burning.

Characteristics of a planar-type Cd0.9Zn0.1Te radiation detector grown by using the low-pressure bridgman method

An indium-doped (7 ppm) Cd0.9Zn0.1Te single crystal for use in room-temperature radiation detectors has been grown using a low-pressure Bridgman (LPB) furnace at the Korea Atomic Research Institute. The single crystal has a (111) orientation and a high resistivity of ∼1 × 1012 Ω·cm. In addition, the mobility-lifetime products of the electrons and hole are 4.2 × 10−4 cm2/V and 5 × 10−5 cm2/V, respectively. These values are simply derived by using a Hecht and a neural equation and 5 MeV alpha particles emitted from an 241Am alpha source. To characterize the Cd0.9Zn0.1Te grown by using the LPB method, we fabricated planar detectors with volume of 10 × 10 × 2.5 mm3 from a 2-inch-diameter Cd0.9Zn0.1Te ingot.

Transparent and Conductive Fluorinated-Tin Oxide Prepared by Atmospheric Deposition Technique

Fluorinated tin oxide (FTO) is well known transparent conductive oxide which is widely applied for optoelectronic applications. Commercially, high-performance (FTO) film was fabricated by sputtering method or other low pressure methods. The product of these methods is expensive due to the high price of capital cost for the apparatus. To cut the price of FTO, atmospheric condition methods were developed and actively investigated using a simple device. By controlling the process conditions; such as processing temperature, precursor concentration, doping concentration, and reactor configuration; high performance FTO glass was successfully produced. The sheet resistance of the prepared FTO glass can be controlled from 9.55 – 63 Ω/□. In addition, its transparency is approximately 77 % which is ideal characteristics for the dye sensitized solar cell (DSSC) electrode application.

Effect of SiO2 amount on microstructures and tensile properties of alumina short fiber-reinforced composites by low-pressure infiltration method

The tensile properties of two types of alumina (Al2O3 and Al2O3–SiO2) and short fiber-reinforced A366 alloy composite created by low-pressure infiltration have been studied. The applied pressure and temperature of molten alloy are 0.4 MPa and 1073 K, respectively. The composite containing 10 vol.% of fiber preform was sectioned and the microstructure was observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Tensile properties of Al2O3 fiber-reinforced A366 alloy composites were investigated, in conjunction with investigation of effects of amounts of SiO2 sol added as binder to fabricated preform and effects of changed chemical composition of Al2O3 fiber. The composite with SiO2 sol of 8 mass% has higher relative density in comparison with composite with SiO2 sol of 2 mass%. SiO2 sol raised the relative density of composite by the reaction with aluminum. In addition, the ultimate tensile strength of composite which has Al2O3 fiber-reinforced A366 alloy composite containing SiO2 sol of 8 mass% was approximately 20% higher than that of Al2O3–SiO2 fiber-reinforced A366 alloy composite containing SiO2 sol of 8 mass%.

Filtration properties of activated sludge in municipal MBR wastewater treatment plants are related to microbial community structure

In the conventional activated sludge process, a number of important parameters determining the efficiency of settling and dewatering are often linked to specific groups of bacteria in the sludge – namely floc size, residual turbidity, shear sensitivity and composition of extracellular polymeric substances (EPS). In membrane bioreactors (MBRs) the nature of solids separation at the membrane has much in common with sludge dewaterability but less is known about the effect of specific microbial groups on the sludge characteristics that affect this process.In this study, six full-scale MBR plants were investigated to identify correlations between sludge filterability, sludge characteristics, and microbial community structure. The microbial community structure was described by quantitative fluorescence in situ hybridization and sludge filterability by a low-pressure filtration method. A strong correlation between the degree of flocculation (ratio between floc size and residual turbidity) and sludge filterability at low pressure was found. A good balance between EPS and cations in the sludge correlated with good flocculation, relatively large sludge flocs, and low amounts of small particles and single cells in the bulk phase (measured as residual turbidity), all leading to a good filterability. Floc properties could also be linked to the microbial community structure. Bacterial species forming strong microcolonies such as Nitrospira and Accumulibacter were present in plants with good flocculation and filtration properties, while few strong microcolonies and many filamentous bacteria in the plants correlated with poor flocculation and filtration problems. In conclusion this study extends the hitherto accepted perception that plant operation affects floc properties which affects fouling. Additionally, plant operation also affects species composition, which affects floc properties and in the end fouling propensity.

Sustainable Nanomaterials: A Greener Future Avenue?

The field of nanoscience has experienced a staggering number of advances in recent years with regards to a wide range of disciplines including physics, chemistry, materials science, biology and medicine [1]. Although most of these are still closely related to laboratory practices and yet far from entrepreneurial activities, many of these nanomaterials are currently commercially available (e.g. silica nanowires, silicon wafers, carbon nanotubes, graphene and derivatives) and have paved the way to enormous developments in the preparation of functional nanomaterials for various applications [1,2]. Generally speaking, environment and sustainable considerations around the synthetic protocols currently in place for the fabrication of nanoentities are scarce and nanosafety procedures in terms of toxicity, handling of nanomaterials and their environmental impact are still not yet sufficiently developed (in the available cases). Considering the synthesis of some of these nanomaterials, protocols often involve high temperatures and pressures, the use of hazardous reagents and/or solvents or include little details to be accounted for in terms of environmental considerations (e.g. environmental impact, green metrics, handling risks, toxicity). Taking into account the essentially different nature and properties (often unknown) of such nanoentities, an increasing number of restrictions, handling practices and safety procedures are currently present in several laboratories and working places in which nanomaterials are handled on a daily basis [3,4]. A complete set of new and updated information on characteristics and properties (as well as risks and toxicity issues in their manipulation) is truly needed to better understand and establish the most acceptable working practices for nanotechnologies. However, a benign by design concept should be promoted in all nano-related practices, aiming to target the development of future sustainable nanoprotocols and environmentally compatible nanomaterials [5,6]. This editorial contribution advocates for more thoughtful and carefully design methodologies that take into account environmentally sound protocols for nanomaterials development. These should range from low temperature ambient pressure methods, avoidance of hazardous chemicals, solvent-free protocols to alternative greener technologies such as mechanochemistry-ball milling-[7], microwave irradiation [2,8,9] and sonication [10] as well as life cycle and risks assessments (whenever possible and appropriate) [11] to analyse and considerate toxicity, risks and environmental impact of the synthesis, handling and utilization of nanomaterials in our daily practices in view of a future implementation of nanotechnologies in our future society [12].

Water purification of nitrates by low-pressure reverse osmosis method

The paper has investigated possibilities and basic regularities of water purification of nitrates by low pressure reverse osmosis. The negative influence of chlorides and sulfates on the process characteristic have bee shown. A conclusion has bee made on expediency of using the low pressure reverse osmosis method for purifying water of nitrates.

Electrochemical Mechanical Polishing of Copper with High Permittivity Abrasives

Electro-Chemical Mechanical Polishing (ECMP) is a promising low-pressure copper planarization method for the interconnection containing low-k material. ECMP utilizes anodic dissolution of copper to raise the material removal rate. However, the surface roughness is usually not acceptable in ECMP because the selective removal ability of electrochemical dissolution is poor. Different permittivity abrasives have different influence on surface quality in ECMP. High permittivity abrasives can enhance selective removal ability to get better polishing results through aggrandizing the potential drop in electrode/electrolyte interface. In this article, three abrasives with different permittivity are compared using polishing experiments. The results show that rutile TiO2, permittivity of which is larger than anatase TiO2 and SiO2, gets the best surface quality among the three abrasives. The composition of electrolyte with rutile TiO2 was also optimized to improve polishing performance. The chosen electrolyte contains 0.5 mol/L glycine, 0.1 mol/L TSA, 1 wt% rutile TiO2. The material removal rate got by using this electrolyte is 0.06 mg/min and the surface roughness is Ra8.9 nm.

Application of Pressure-Controlled Advanced Distillation Curve Analysis: Virgin and Waste Oils

One of the most important properties measured for liquid fuels is the volatility, usually expressed by the distillation curve. In previous work, we introduced the composition-explicit or advanced distillation curve (ADC) metrology, which we have applied to a wide variety of liquid fuels including biodiesel fuels. Application of this method to high-boiling-point fluids such as oils has required the addition of an inert-gas purge in the apparatus. Despite this precaution, there is clear evidence of thermal decomposition or polymerization at high distillation temperatures. To address this complication, a low-pressure version of the ADC was introduced. In this work, we have applied the low-pressure ADC method to the study of virgin and waste engine (motor) oils (5W-30, 10W-30, 20W-50), reclaimed comingled oil, reclaimed cutting oil, and used transformer oil. The results parallel similar measurements performed at atmospheric pressure, but with little evidence of chemical decomposition.