The Influence of Experimental Variables on the Development and Maintenance of Wear-Protective Oxides during Sliding of High-Temperature Iron-Base Alloys

1985 ◽  
Vol 199 (1) ◽  
pp. 35-41 ◽  
Author(s):  
J Glascott ◽  
G C Wood ◽  
F H Stott
Keyword(s):  
Room Temperature ◽  
Thermal Stresses ◽  
High Surface ◽  
Volume Ratio ◽  
Oxide Surface ◽  
Protective Oxide ◽  
Metal Debris ◽  
Wear Process ◽  
Metal Metal ◽  
Oxide Debris

An investigation has been carried out into the development and maintenance of wear-protective oxide on iron-12 per cent chromium-base alloys during sliding in air at 20–600°C, with particular reference to the effects of temperature, of intermittent changes in temperature, and of sliding speed. It has been established that the wear-protective surface develops on and from compacted oxide and oxide-coated metal debris and involves deformation of the oxide. The wear process in the early stages of sliding generates metallic wear debris particles. These are fractured and re-fractured until they have a high surface to volume ratio. These surfaces are oxidized at the ambient temperature, to produce considerable amounts of oxide debris. Additional amounts are generated by transient oxidation of the specimen surfaces and removal of this oxide during each transversal of the sliding action. The rate of production of such oxide debris is determined by the ease of fracture of the metal debris and the rate of oxidation. Under these sliding conditions, this results in a minimum in the time required to generate a wear-protective oxide surface at 400°C. Development of such a surface takes a longer period at higher and lower temperatures, and indeed it does not develop at all at room temperature. Once established, the wear-protective oxide remains adherent and stable during isothermal sliding at 300°C and higher temperatures. Thermal stresses imparted by cooling to room temperature and reheating to 300° C do not cause loss of effectiveness of the oxide on subsequent further sliding at 300°C. However, subsequent sliding at room temperature results in rapid breakdown of the oxide and metal-metal contact, presumably due to a decrease in plasticity of the fine oxide debris with decreasing temperature or to a decrease in the adhesion between the oxide and the metal substrate or in oxide cohesion.

scholarly journals Three-dimensional platinum nanoparticle-based bridges for ammonia gas sensing

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nishchay A. Isaac ◽  
Johannes Reiprich ◽  
Leslie Schlag ◽  
Pedro H. O. Moreira ◽  
Mostafa Baloochi ◽  
...  
Keyword(s):  
Room Temperature ◽  
Gas Sensing ◽  
Response Times ◽  
High Surface ◽  
Three Dimensional ◽  
Performance Testing ◽  
Volume Ratio ◽  
Platinum Nanoparticle ◽  
Ammonia Gas ◽  
Lift Off

AbstractThis study demonstrates the fabrication of self-aligning three-dimensional (3D) platinum bridges for ammonia gas sensing using gas-phase electrodeposition. This deposition scheme can guide charged nanoparticles to predetermined locations on a surface with sub-micrometer resolution. A shutter-free deposition is possible, preventing the use of additional steps for lift-off and improving material yield. This method uses a spark discharge-based platinum nanoparticle source in combination with sequentially biased surface electrodes and charged photoresist patterns on a glass substrate. In this way, the parallel growth of multiple sensing nodes, in this case 3D self-aligning nanoparticle-based bridges, is accomplished. An array containing 360 locally grown bridges made out of 5 nm platinum nanoparticles is fabricated. The high surface-to-volume ratio of the 3D bridge morphology enables fast response and room temperature operated sensing capabilities. The bridges are preconditioned for ~ 24 h in nitrogen gas before being used for performance testing, ensuring drift-free sensor performance. In this study, platinum bridges are demonstrated to detect ammonia (NH3) with concentrations between 1400 and 100 ppm. The sensing mechanism, response times, cross-sensitivity, selectivity, and sensor stability are discussed. The device showed a sensor response of ~ 4% at 100 ppm NH3 with a 70% response time of 8 min at room temperature.

Effect of current density on the porous silicon preparation as gas sensors**

2021 ◽  
Vol 30 (1) ◽  
pp. 257-264
Author(s):  
Muna H. Kareem ◽  
Adi M. Abdul Hussein ◽  
Haitham Talib Hussein
Keyword(s):  
Porous Silicon ◽  
Gas Sensors ◽  
Current Density ◽  
Room Temperature ◽  
Low Cost ◽  
High Surface ◽  
Volume Ratio ◽  
Etching Time ◽  
Force Microscopy ◽  
Materials Used

Abstract In this study, porous silicon (PSi) was used to manufacture gas sensors for acetone and ethanol. Samples of PSi were successfully prepared by photoelectrochemical etching and applied as an acetone and ethanol gas sensor at room temperature at various current densities J= 12, 24 and 30 mA/cm2 with an etching time of 10 min and hydrofluoric acid concentration of 40%. Well-ordered n-type PSi (100) was carefully studied for its chemical composition, surface structure and bond configuration of the surface via X-ray diffraction, atomic force microscopy, Fourier transform infrared spectroscopy and photoluminescence tests. Results showed that the best sensitivity of PSi was to acetone gas than to ethanol under the same conditions at an etching current density of 30 mA/cm2, reaching about 2.413 at a concentration of 500 parts per million. The PSi layers served as low-cost and high-quality acetone gas sensors. Thus, PSi can be used to replace expensive materials used in gas sensors that function at low temperatures, including room temperature. The material has an exceptionally high surface-to-volume ratio (increasing surface area) and demonstrates ease of fabrication and compatibility with manufacturing processes of silicon microelectronics.

scholarly journals Starch-Based Hybrid Nanomaterials for Environmental Remediation

2021 ◽  
Author(s):  
Ashoka Gamage ◽  
Thiviya Punniamoorthy ◽  
Terrence Madhujith
Keyword(s):  
Metal Oxide ◽  
Environmental Remediation ◽  
Membrane Filtration ◽  
Anthropogenic Activities ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Hybrid Nanomaterials ◽  
Metal Metal

Environmental pollution is becoming a major global issue with increasing anthropogenic activities that release massive toxic pollutants into the land, air, and water. Nanomaterials have gained the most popularity in the last decades over conventional methods because of their high surface area to volume ratio and higher reactivity. Nanomaterials including metal, metal oxide, zero-valent ions, carbonaceous nanomaterials, and polymers function as adsorbents, catalysts, photocatalysts, membrane (filtration), disinfectants, and sensors in the detection and removal of various pollutants such as heavy metals, organic pollutants, dyes, industrial effluents, and pathogenic microbial. Polymer-inorganic hybrid materials or nanocomposites are highly studied for the removal of various contaminants. Starch, a heteropolysaccharide, is a natural biopolymer generally incorporated with other metal, metal oxide, and other polymeric nanoparticles and has been reported in various environmental remediation applications as a low-cost alternative for petroleum-based polymers. Therefore, this chapter mainly highlights the various nanomaterials used in environmental remediation, starch-based hybrid nanomaterials, and their application and limitations.

scholarly journals Porous Gig-Lox TiO2 Doped with N2 at Room Temperature for P-Type Response to Ethanol

Chemosensors ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 12 ◽  
Author(s):  
Emanuele Smecca ◽  
Salvatore Sanzaro ◽  
Clelia Galati ◽  
Lucio Renna ◽  
Leonardo Gervasi ◽  
...  
Keyword(s):  
Tio2 Film ◽  
Room Temperature ◽  
Electrical Response ◽  
High Surface ◽  
Volume Ratio ◽  
Reactive Sputtering ◽  
Deposition Process ◽  
Deposition Method ◽  
Type Character ◽  
P Type

Nanostructured materials represent a breakthrough in many fields of application. Above all for sensing, the use of nanostructures with a high surface/volume ratio is strategic to raise the sensitivity towards dangerous environmental gas species. A new Dc-Reactive sputtering Deposition method has been applied to grow highly porous p-type nitrogen-doped titanium oxide layers by modifying the previously developed reactive sputtering method called gig-lox. The doping of the films was achieved at room temperature by progressive incorporation of nitrogen species during the deposition process. Two different amounts of N2 were introduced into the deposition chamber at flow rates of 2 and 5 standard cubic centimeter per minutes (sccm) for doping. It has been found that the N2 uptake reduces the deposition rate of the TiO2 film whilst the porosity and the roughness of the grown layer are not penalized. Despite the low amount of N2, using 2 sccm of gas resulted in proper doping of the TiO2 film as revealed by XPS Analyses. In this case, nitrogen atoms are mainly arranged in substitutional positions with respect to the oxygen atoms inside the lattice, and this defines the p-type character of the growing layer. Above this strategic structural modification, the multibranched spongy porosity, peculiar of the gig-lox growth, is still maintained. As proof of concept of the achievements, a sensing device was prepared by combining this modified gig-lox deposition method with state-of-the-art hot-plate technology to monitor the electrical response to ethanol gas species. The sensor exhibited a sensitivity of a factor of ≈2 to 44 ppm of ethanol at ≈200 °C as measured by a rise in the layer resistivity according to the p-type character of the material. At the higher temperature of ≈350 °C, the sensor turned to n-type as without doping. This behavior was related to a loss of nitrogen content inside the film during the annealing. It was indeed proved that p-type doping of a gig-lox sponge during growth is feasible, even at room temperature, without losing the layer porosity and the capability to host and detect environmental species. Moreover, the material integration on a device is simply done as the last production step. Easy TiO2 doping procedures, combined with porosity, are of general purpose and interest for several applications even on flexible substrates.

Room Temperature Recrystallization of Electroplated Copper Thin Films: Methods and Mechanisms

2000 ◽  
Vol 612 ◽  
Author(s):  
D. Walther ◽  
M. E. Gross ◽  
K. Evans-Lutterodt ◽  
W. L. Brown ◽  
M. Oh ◽  
...  
Keyword(s):  
Film Thickness ◽  
Sheet Resistance ◽  
Room Temperature ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
High Surface ◽  
Volume Ratio ◽  
Data Sets ◽  
Pole Figures ◽  
Electroplated Copper

AbstractWe report a comparison of the room temperature recrystallization of electroplated (EP) copper in blanket films as a function of thickness measured by focused ion beam (FIB) microscope images and sheet resistance measurements. Both sets of data show an increase in rate with film thickness from 0.75νm up to 5νm, while little recrystallization is observed in films thinner than 0.75νm. Interestingly, the recrystallization rates from FIB analysis are consistently faster than those from the sheet resistance measurements. These data suggest that the recrystallization is initiated close to the top surface of the EP Cu film, but that in thinner films a high surface-to-volume ratio allows surface inhibition or pinning to retard the transformation. A Johnson-Mehl-AvramiKolmogorov (JMAK) analysis of the two data sets yields unusually high values for the Avrami exponent μ of up to 7 for the FIB data, while lower values of around 4 are obtained for the sheet resistance data. X-ray diffraction pole figures of the films have also been collected and correlations between the crystallographic texture, film thickness and recrystallization are discussed.

scholarly journals Microbe-Mediated Biosynthesis of Nanoparticles: Applications and Future Prospects

Biomolecules ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 886
Author(s):  
Bhupendra Koul ◽  
Anil Kumar Poonia ◽  
Dhananjay Yadav ◽  
Jun-O Jin
Keyword(s):  
Size Structure ◽  
High Surface ◽  
Volume Ratio ◽  
Biological Properties ◽  
Medical Diagnostics ◽  
Chemical Compositions ◽  
Future Prospects ◽  
Synthesis Of Nanoparticles ◽  
Metal Metal ◽  
Characteristic Features

Nanotechnology is the science of nano-sized particles/structures (~100 nm) having a high surface-to-volume ratio that can modulate the physical, chemical and biological properties of the chemical compositions. In last few decades, nanoscience has attracted the attention of the scientific community worldwide due to its potential uses in the pharmacy, medical diagnostics and disease treatment, energy, electronics, agriculture, chemical and space industries. The properties of nanoparticles (NPs) are size and shape dependent. These characteristic features of nanoparticles can be explored for various other applications such as computer transistors, chemical sensors, electrometers, memory schemes, reusable catalysts, biosensing, antimicrobial activity, nanocomposites, medical imaging, tumor detection and drug delivery. Therefore, synthesizing nanoparticles of desired size, structure, monodispersity and morphology is crucial for the aforementioned applications. Recent advancements in nanotechnology aim at the synthesis of nanoparticles/materials using reliable, innoxious and novel ecofriendly techniques. In contrast to the traditional methods, the biosynthesis of nanoparticles of a desired nature and structure using the microbial machinery is not only quicker and safer but more environmentally friendly. Various microbes, including bacteria, actinobacteria, fungi, yeast, microalgae and viruses, have recently been explored for the synthesis of metal, metal oxide and other important NPs through intracellular and extracellular processes. Some bacteria and microalgae possess specific potential to fabricate distinctive nanomaterials such as exopolysaccharides, nanocellulose, nanoplates and nanowires. Moreover, their ability to synthesize nanoparticles can be enhanced using genetic engineering approaches. Thus, the use of microorganisms for synthesis of nanoparticles is unique and has a promising future. The present review provides explicit information on different strategies for the synthesis of nanoparticles using microbial cells; their applications in bioremediation, agriculture, medicine and diagnostics; and their future prospects.

Pd-Decorated Multi-Walled Carbon Nanotube Sensor for Hydrogen Detection

2021 ◽  
Vol 21 (7) ◽  
pp. 3707-3710
Author(s):  
Jae Keon Kim ◽  
Maeum Han ◽  
Yeongsam Kim ◽  
Hee Kyung An ◽  
Suwoong Lee ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Gas Sensors ◽  
High Performance ◽  
Room Temperature ◽  
Catalytic Effect ◽  
High Surface ◽  
Volume Ratio ◽  
Ambient Atmosphere ◽  
Low Concentrations ◽  
Multi Walled Carbon Nanotube

As hydrogen (H2) gas is highly reactive and explosive in ambient atmosphere, its prompt detection in industrial areas is imperative to prevent serious accidents. In particular, high-performance H2 sensors that can promptly detect even low-concentrations of H2 gas are necessary for safety. Carbon nanotubes (CNTs) have a large surface area and a high surface-to-volume ratio, and therefore, they are suitable for use as sensing materials in gas sensors. Moreover, gold, platinum, and palladium are known to be excellent catalyst metals that increase reactivity with H2 gas through the catalytic effect referred to as spill-over mechanism. In this study, a CNT felt sensor with a palladium (Pd) layer was fabricated, and its reactivity with H2 was evaluated. The sensitivity of a CNT felt sensor to H2 gas at room temperature was found to improve when coated with Pd layer.

scholarly journals Understanding Sulfur Redox Mechanisms in Different Electrolytes for Room-Temperature Na–S Batteries

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Hanwen Liu ◽  
Wei-Hong Lai ◽  
Qiuran Yang ◽  
Yaojie Lei ◽  
Can Wu ◽  
...  
Keyword(s):  
Room Temperature ◽  
High Surface ◽  
Reversible Capacity ◽  
High Loading ◽  
Side Reactions ◽  
Liquid Sulfur ◽  
Shuttle Effect ◽  
Loading Ratio ◽  
Solid Liquid ◽  
Sulfur Cathodes

Abstract This work reports influence of two different electrolytes, carbonate ester and ether electrolytes, on the sulfur redox reactions in room-temperature Na–S batteries. Two sulfur cathodes with different S loading ratio and status are investigated. A sulfur-rich composite with most sulfur dispersed on the surface of a carbon host can realize a high loading ratio (72% S). In contrast, a confined sulfur sample can encapsulate S into the pores of the carbon host with a low loading ratio (44% S). In carbonate ester electrolyte, only the sulfur trapped in porous structures is active via ‘solid–solid’ behavior during cycling. The S cathode with high surface sulfur shows poor reversible capacity because of the severe side reactions between the surface polysulfides and the carbonate ester solvents. To improve the capacity of the sulfur-rich cathode, ether electrolyte with NaNO3 additive is explored to realize a ‘solid–liquid’ sulfur redox process and confine the shuttle effect of the dissolved polysulfides. As a result, the sulfur-rich cathode achieved high reversible capacity (483 mAh g−1), corresponding to a specific energy of 362 Wh kg−1 after 200 cycles, shedding light on the use of ether electrolyte for high-loading sulfur cathode.

scholarly journals Electrospun Nanofibers for Sensing and Biosensing Applications—A Review

2021 ◽  
Vol 22 (12) ◽  
pp. 6357
Author(s):  
Kinga Halicka ◽  
Joanna Cabaj
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Toxic Metal ◽  
Volume Ratio ◽  
Electrospun Nanofibers ◽  
Clinical Diagnostics ◽  
Loading Capacity ◽  
Electrospun Nanofiber ◽  
Sensing Platforms ◽  
Different Types

Sensors and biosensors have found applications in many areas, e.g., in medicine and clinical diagnostics, or in environmental monitoring. To expand this field, nanotechnology has been employed in the construction of sensing platforms. Because of their properties, such as high surface area to volume ratio, nanofibers (NFs) have been studied and used to develop sensors with higher loading capacity, better sensitivity, and faster response time. They also allow to miniaturize designed platforms. One of the most commonly used techniques of the fabrication of NFs is electrospinning. Electrospun NFs can be used in different types of sensors and biosensors. This review presents recent studies concerning electrospun nanofiber-based electrochemical and optical sensing platforms for the detection of various medically and environmentally relevant compounds, including glucose, drugs, microorganisms, and toxic metal ions.

scholarly journals Study of the geometry of open channels in a layer-bed-type microfluidic immobilized enzyme reactor

2021 ◽  
Author(s):  
Cynthia Nagy ◽  
Robert Huszank ◽  
Attila Gaspar
Keyword(s):  
Immobilized Enzyme ◽  
High Surface ◽  
Volume Ratio ◽  
Volumetric Flow Rate ◽  
Enzyme Reactor ◽  
Channel Pattern ◽  
Immobilized Enzyme Reactor ◽  
Split Flow ◽  
Parallel Streams ◽  
Enzymatic Microreactors

AbstractThis paper aims at studying open channel geometries in a layer-bed-type immobilized enzyme reactor with computer-aided simulations. The main properties of these reactors are their simple channel pattern, simple immobilization procedure, regenerability, and disposability; all these features make these devices one of the simplest yet efficient enzymatic microreactors. The high surface-to-volume ratio of the reactor was achieved using narrow (25–75 μm wide) channels. The simulation demonstrated that curves support the mixing of solutions in the channel even in strong laminar flow conditions; thus, it is worth including several curves in the channel system. In the three different designs of microreactor proposed, the lengths of the channels were identical, but in two reactors, the liquid flow was split to 8 or 32 parallel streams at the inlet of the reactor. Despite their overall higher volumetric flow rate, the split-flow structures are advantageous due to the increased contact time. Saliva samples were used to test the efficiencies of the digestions in the microreactors. Graphical abstract

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