J. Ernesto Indacochea

High‐Quality Black Phosphorus Atomic Layers by Liquid‐Phase Exfoliation

P. Yasaei, Dr. B. Kumar, M. Asadi, Prof. A. Salehi-Khojin Department of Mechanical and Industrial Engineering University of Illinois at Chicago Chicago , IL 60607 , USA E-mail: salehikh@uic.edu T. Foroozan, Prof. J. E. Indacochea Department of Civil and Materials Engineering University of Illinois at Chicago Chicago , IL 60607 , USA C. Wang, Prof. R. F. Klie Department of Physics University of Illinois at Chicago Chicago , IL 60607 , USA D. Tuschel HORIBA Scientifi c HORIBA Scientifi c Inc. Edison , NJ 08820 , USA

Chemical reactions during submerged arc welding with FeO-MnO-SiO2 fluxes

Measurements have been made of the compositional changes of fluxes and weld metal during submerged arc flux welding with a series of synthetic MnO-FeO-SiO2 model fluxes containing 40 wt pct SiO2 and different ratios of MnO to FeO. Mechanisms for the transfer of Mn, O, Si, C, S, and P are discussed in terms of the thermodynamic driving forces and kinetic factors such as diffusion, nucleation, and segregation. One unique deduction is that interfacial, not bulk activities of components (such as FeO) govern transfer into (or out of) the metal phase. The concentrations of C, P, S, and possibly Si tend to be larger in the molten weld metal than in the base plate.

A comparison of two aluminizing methods for corrosion protection in the wet seal of molten carbonate fuel cells

The corrosion behavior of aluminized Type 310S stainless steel (SS) in the wet seal of molten carbonate fuel cells was investigated. Coupons of Type 310S SS were aluminized by two different aluminizing methods: thermal spray and slurry-coating. In both types of samples Fe and Cr diffused readily into the Al layer at 650thinsp{degree}C. At first this interdiffusion is limited to the interfacial area. With time, Fe and Cr aluminides precipitate in the Al layer. The slurry-coated layer contains a higher concentration of FeAl and Fe{sub 3}Al than does the thermal spray layer. Consequently, the slurry-coated layer also displays a greater degree of corrosion than the thermal spray layer. {copyright} {ital 1998 Materials Research Society.}

Interference color of anodized aluminum oxide (AAO) films for sensor application

Anodized aluminum oxide (AAO) membranes are fabricated under different anodization potentials in dilute sulfuric acid. Here we report the growth of AAO under 10, 15, 20, and 25V. These AAO membranes consist of nanopores with pore-to-pore distance from 35 to 69 nm. When AAO membranes are kept thin (less than ~500 nm), together with the unreacted aluminum substrate, interference colors are observed. The inference color of the membrane is changed by its thickness and the pore-to-pore distance, which is controlled by the anodization time and voltage, respectively. By using thin film interference model to analyze the UV-Vis reflectance spectra, we can extract the thickness of the membrane. Thus the linear growth of AAO membrane in sulfuric acid with time during the first 15 minutes is validated. Coating poly (styrene sulfonate) (PSS) sodium salt and poly (allylamine hydrochloride) (PAH) layer by layer over the surface of AAO membrane consistently shifts the interference colors. The red shift of the UV-Vis reflectance spectrum is correlated to the number of layers. This color change due to molecular attachment and increasing thickness is a promising method for chemical sensing.

Carbon Nanotube Structured Hydrogen Sensor

A nanostructured sensor based on double wall carbon nanotubes (DWNTs) was fabricated and assessed for hydrogen gas detection. DWNT networks were used as an active substrate material evaporated with layers of palladium nanoparticles of three thicknesses 1, 3 and 6 nm. The electrical resistance change of nanosensor with hydrogen gas exposure in compressed air at room temperature was monitored. The nanostructures were characterized using high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected at room temperature. Sensitivity values as high as 65% and response times of about 3 seconds were obtained. The results indicate that DWNT- based sensors exhibit comparable performance as that for SWNT-based high performance hydrogen sensors, but with potential improvement in mechanical and thermal resistance associated with the double layer structure.

Anodized aluminum oxide (AAO) based nanowells for hydrogen detection

A nanostructured sensing element based on anodic aluminum oxide (AAO) nanowells was fabricate and assessed for hydrogen gas sensing. AAO nanowells with an average diameter of 73 nm and depth proportional to the anodization time were immersed in a surfactant solution and coated with an 8 nm film of palladium nanoparticles. The electrical resistance change of the nanostructure with hydrogen gas exposure was used as the sensing parameter. The AAO nanowells-Pd nanostructures were characterized using atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM), and contact angle test. Hydrogen concentrations as low as 0.05 vol% (500 ppm) can be detected at room temperature. Response times as fast as 1.15 seconds were obtained. Compared to current devices and nanostructures in development, the AAO nanowell-Pd nanostructure is found to be considerably fast without compromising sensitivity and selectivity.

Effect of Lead on Passivation of Alloy 600 Surface

Abstract Effects of Pb on passivity of Alloy 600 surface were investigated in mild acidic aqueous solutions at 90°C using polarization, electrochemical impedance spectroscopy (EIS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results indicate that Alloy 600 surface consists of an inner oxide layer and outer hydroxide layer, containing Cr3+ and Ni2+. Pb is incorporated into the surface film and increases the electronic conductivity of Cr oxide in the surface film. Oxidation of Ni is inhibited by the presence of Pb.

Joining and Processing in Engineering Ceramics to Metallic Materials, in Biomorphic SiC Ceramics, and in Bioactive and Bioinert Ceramics

The need for improved efficiency in energy producing processes requires utilization and development of new advanced ceramic materials. Such materials must be capable to withstand considerably higher temperatures in more demanding environments. Moreover , many of these components cannot be built as large monolithic pieces or complex shapes ; they can only be fabricated by joining smaller pieces together. Under certain circumstances some joints include dissimilar materials. The joints must also be capable to re sist these stringent conditions. Joints fabricated using metallic filler materials, can only be bonded i f the liquid metal reacts with the ceramic substrate, but the extent of these reactions will impa ct the quality and performance of the joint. Silicon carbide brazes produced with CuAgSnTi filler metal f oils showed that the higher the processing temperature the greater the ceramic/metal interacti on nd the greater the tendency for the ceramic substrate to degrade. However when ceramic joints are m d with compatible filler materials do not show degradation. Introduction There has been an increasing concern universally in the past decade ove r global warming, thought by some policy makers to be caused primarily by increases in carbon dioxide (CO2) emissions through the use of fossil fuels for the generation of electric power. Th U.S. Department of Energy (DOE) projects that from 1995 to 2015, worldwide use of electricity w ll double to approach 20 trillion kilowatt hours. Government policies and regulations currently be ing negotiated in international accords may compel electric utilities to either reduce CO2 emissions or buy credits from nations producing less CO 2 per capita. In order to reduce such emissions, coalfired power plants ought to be made more efficient, or electricity producers will be forced to turn to more expensive fuels to avoid buying the credits. The DOE in an initiative to stimulate the development of more eff ici nt coal fired power systems began the Combustion 2000 Program in the early 1990’s. Through this program, DOE began to work with industry in the development of an ambitious high-effici ency coal-fired power plant technology called the “high-performance power system”. The goals for this system are 47% efficiency, with only one-tenth of the particulate SO x and NOx while reducing the cost of electricity by 10% [1]. The main feature of the system is a high temperature dvanced furnace that will use heat exchangers to produce clean air at up to 1400oC and 2 MPa to turn an aero derivative turbine . In order to reach the highest planned temperature of 1400oC, advanced structur al ceramics such as silicon carbide (SiC) must be used for construction of the heat e xchanger. However, it is difficult to join SiC by welding because it does not melt, but instead sinters under pressure at temperatures of over 1950oC [2], conditions very difficult to achieve in the case of a field repair. Reduction of automotive emissions can be attained by improving the the rmal fficiency of their engines. This effort demands higher operating temperatures, which in turn require materials with high temperature strength and resistance to corrosion and wear. A gain, engineering ceramics may be the materials of choice based, but their brittle nature, poor m achining properties, and cost severely limit their widespread utilization as monolithic component s. Their use can be expanded if ceramics can be joined to metals or used as ceramic-metal c omposite components. For example, Materials Science Forum Online: 2003-11-15 ISSN: 1662-9752, Vol. 439, pp 23-29 d i:10.4028/www.scientific.net/MSF.439.23