Using Thermal Spray and Laser Micromachining to Fabricate Sensors

The use of thermal spray to fabricate sensors directly onto engineering components is an emerging technology. The capabilities for sensor fabrication are considerably enhanced with the use of laser micromachining, in which feature sizes as small as 15-20 μm can be achieved. Such feature sizes are required for a variety of sensors, including strain and heat flux sensors, thermopiles and microheaters. Ultrafast lasers—lasers with pulse durations ≲1 ps—are particularly well suited for the multimaterial/multilayer processing required to fabricate sensors from materials deposited using thermal spray. In this work, the key issues associated with laser micromachining of thermal spray coatings for sensor applications are presented. Both resistive strain gages and microheaters are discussed in detail as representative sensor designs that require the fine feature and linewidth capability that laser micromachining provides, including details of their fabrication and practical design restrictions. This article summarizes with recommendations for future work.     

Low‐Temperature Control of Twins and Abnormal Grain Growth in BaTiO3

The microstructure of polycrystalline barium titanate (BaTiO₃) thin films processed with a liquid‐phase can be controlled by the crystallographic orientation of the underlying sapphire substrate. During postdeposition crystallization, the tendency for {111} twin nucleation, which drives subsequent abnormal grain growth, depends upon the specific sapphire facet. Specifically, tilting away from the close‐packed c‐plane modifies the orientation, morphology, and relative amount of an interfacial BaAl₂O₄ second phase. These factors control the density of twin formation, and thus overall grain size of the crystallized BaTiO₃. As the substrate orientation transitions from c‐plane, to r‐plane, to a‐plane, the twin density is reduced, the average grain size decreases systematically from 270 to 130 nm, and the grain structure becomes overall more homogeneous. This twinning mechanism and abnormal grain growth occur by 900°C, several hundred degrees lower than reported previously.     

Dynamic modeling and validation of a biomass hydrothermal pretreatment process—a demonstration scale study

Hydrothermal pretreatment of lignocellulosic biomass is a cost effective technology for second generation biorefineries. The process occurs in large horizontal and pressurized thermal reactors where the biomatrix is opened under the action of steam pressure and temperature to expose cellulose for the enzymatic hydrolysis process. Several by‐products are also formed, which disturb and act as inhibitors downstream. The objective of this study is to formulate and validate a large scale hydrothermal pretreatment dynamic model based on mass and energy balances, together with a complex conversion mechanism and kinetics. The study includes a comprehensive sensitivity and uncertainty analysis, with parameter estimation from real‐data in the 178–185°C range. To highlight the application utility of the model, a state estimator for biomass composition is developed. The predictions capture well the dynamic trends of the process, outlining the value of the model for simulation, control design, and optimization for full‐scale applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4235–4250, 2015     

Microscale fracture mechanisms of HfO2-Si environmental barrier coatings

Environmental barrier coatings (EBCs) play a vital role in protecting advanced turbine components subjected to extreme service environments, where mechanical, thermal and chemical behaviors typically dominate the design criteria. This study focuses on investigating the mechanical properties of individual phases within a HfO₂-Si ceramic matrix composite (CMC) structure through implementation of notched microcantilevers and micropillar splitting experiments. The microcantilever experiments resulted in fracture toughnesses ranging between 1.38–1.52 MPa-m^1/2 for the Si-rich phase and 2.26–2.38 MPa-m^1/2 for the HfO₂-rich phase depending on the method of analysis. From our micropillar splitting experiments, we found fracture toughnesses of 1.13 ± 0.39 MPa-m^1/2 for the Si-rich phase and 1.18 ± 0.26 MPa-m^1/2 for the HfO₂-rich phase. Comparisons with bulk single edge V-notched beams (SEVNBs) suggest the micropillar results are accurate whereas the microcantilever experiments may overestimate K_IC of the Si-rich and HfO₂-rich phases by ?0.2–1.2 MPa-m^1/2, most likely, due to dimensional errors that affect specimen and model compliances.     

Kinetics of PdO combustion catalysis

The kinetics of the catalytic combustion of methane by supported palladium oxide catalysts (2 wt.-% Pd/La₂O₃·11A1₂O₃ and 5 wt.-%Pd/ γ-A1₂0₃ were examined for several oxygen partial pressure levels over the temperature range from 40–900°C using temperature-programmed reaction and slow ramp and hold temperature-time transient techniques. Combustion rates were measured by differential reaction in a fixed bed of powdered catalyst at lower temperatures (200–500°C). Also, by preparing the catalysts as thin (ca. 10 μm) coatings on an alumina tube and conducting the experiments with very high flows of dilute methane and oxygen in helium, the rate measurements were extended up to 900°C without significant contribution from gas phase reactions. The specific combustion activity of supported PdO shows a persistent hysteresis between 450 and 750°C, i.e., the rate of combustion between these temperature limits depends strongly on whether the catalyst is cooling from above 750°C or heating from below 450°C. This region is also notable for negative apparent activation energy in the rate of methane oxidation, i.e., the rate increases with decreasing temperature during reoxidation of the Pd metal and decreases with increasing temperature (especially with low oxygen partial pressure) prior to decomposition of the bulk oxide. Detailed time-temperature transient kinetic analyses were performed for supported PdO catalysts within the 450–750°C temperature range. The hysteresis in methane combustion rate is caused by a higher activation energy for reduction of oxygen chemisorbed on metallic Pd and by suppressed reoxidation of Pd metal relative to PdO decomposition.     

Sensitive ultrasonic delineation of steroid treatment in living dystrophic mice with energy-based and entropy-based radio frequency signal processing

Duchenne muscular dystrophy is a severe wasting disease, involving replacement of necrotic muscle tissue by fibrous material and fatty infiltrates. One primary animal model of this human disease is the X chromosome-linked mdx strain of mice. The goals of the present work were to validate and quantify the capability of both energy and entropy metrics of radio-frequency ultrasonic backscatter to differentiate among normal, dystrophic, and steroid-treated skeletal muscle in the mdx model. Thirteen 12-month-old mice were blocked into three groups: 4 treated mdx-dystrophic that received daily subcutaneous steroid (prednisolone) treatment for 14 days, 4 positive-control mdx-dystrophic that received saline injections for 14 days, and 5 negative-control animals. Biceps muscle of each animal was imaged in vivo using a 40-MHz center frequency transducer in conjunction with a Vevo-660 ultrasound system. Radio-frequency data were acquired (1 GHz, 8 bits) corresponding to a sequence of transverse images, advancing the transducer from "shoulder" to "elbow" in 100-micron steps. Data were processed to generate both "integrated backscatter" (log energy), and "entropy" (information theoretic receiver, H_f) representations. Analyses of the integrated-backscatter values delineated both treated-and untreated-mdx biceps from normal controls (p<0.01). Complementary analyses of the entropy images differentiated the steroid-treated and positive-control mdx groups (p<0.01). To our knowledge, this study represents the first reported use of quantitative ultrasonic characterization of skeletal muscle in mdx mice. Successful differentiation among dystrophic, steroid-treated, and normal tissues suggests the potential for local noninvasive monitoring of disease severity and therapeutic effects.     

Industrial management for sustaining the environment

This paper discusses five concepts that industrial managers or advocates can adopt that will contribute to sustaining the environment through focused and knowledgeable industrial management. These are (1) develop a sensitivity to the constantly changing environment; (2) work without complaining or blaming; (3) organize a system of environmental diligence; (4) implement a strategy of environmental protection and development; and (5) recognize and develop a relationship between trade and the environment. Successful development and implementation of these concepts will greatly enhance industry's commitment to and sustainability of the environment.     

Microwave Power Absorption in Low-Reflectance,Complex, Lossy Transmission Lines

Simple sets of equations have been derived to describe the absorption of microwave power in three-region, lossy transmission lines in terms of S-parameter reflection and transmission amplitudes. Each region was assumed to be homogeneous with discontinuities at the region boundaries. Different sets of equations were derived to describe different assumptions about the amplitudes of the reflection coefficients at the different boundaries. These equations, which are useful when interference effects due to multiple reflections are small, were used to analyze S-parameter measurements on a transmission line that had a microfluidic channel in its middle region. The channel was empty for one set of measurements and filled with water for a second set of measurements. Most of the reflection assumptions considered here produced similar results for the fraction of the applied microwave power that was absorbed by a water-filled microchannel. This shows that the absorbed power is relatively insensitive to the reflection details as long as energy is conserved in the analysis. Another important result of this work is that the difference between the power absorbed in a water-filled channel and the power absorbed in the same empty channel can be a poor predictor of the power absorbed in the water in the presence of competing absorption processes such as absorption by the transmission-line metal.     

Stabilization of high-resistance seals in patch-clamp recordings by laminar flow

The formation of a high-resistance electrical seal between a cell membrane and a glass micropipet tip is essential in patch-clamp experiments. We have studied the electrical properties and the mechanical stability of the seal using a microfluidic chip generating laminar flow in open volumes. We show that, by using fluid flow (1-10 mm/s) acting along the symmetry axis of the cell-pipet, seals of a higher mechanical stability with increased resistances can be achieved, allowing up to 100% longer recording times and over 40% decreased noise levels (Irms). These improved properties are beneficial for high-sensitivity patch-clamp recordings, in particular, in longtime studies of ion channel receptor systems that are relevant in biosensor applications of the technique. Furthermore, these observations support the combination of patch-clamp with microfluidic devices, for example, for rapid solution exchange around a single cell sensor for high-throughput electrophysiology and for highly resolved kinetic studies.     

Microwave leakage-induced frequency shifts in the primary frequency standards NIST-F1 and IEN-CSF1

In atomic fountain primary frequency standards, the atoms ideally are subjected to microwave fields resonant with the ground-state, hyperfine splitting only during the two pulses of Ramsey's separated oscillatory field measurement scheme. As a practical matter, however, stray microwave fields can be present that shift the frequency of the central Ramsey fringe and, therefore, adversely affect the accuracy of the standard. We investigate these uncontrolled stray fields here and show that the frequency errors can be measured, and indeed even the location within the standard determined by the behavior of the measured frequency with respect to microwave power in the Ramsey cavity. Experimental results that agree with the theory are presented as well.