Using highly acidic phosphating solutions that dissolve rust, brush-on phosphating for large-scale steel structures can reduce the cost of rust removal, without the need of a post-treatment rinse. In very low pH medium, the presence of thiourea helps the formation of high-quality conversion films. A hydrogen sulfide acceleration mechanism is proposed, based on cathodic polarization data and previous studies. The formed films are amorphous and contain high water content, therefore a rather long post-treatment desiccation period is required and supported by analyzing the linear polarization resistance values in a desiccation model.

Two ultra-thin TiO(2) films with platinum electrodes were prepared on a porous anodic aluminium oxide thick layer and a ceramic plate, respectively. It was found that in both TiO(2) films the conductance was almost proportional to the fourth root of the H(2) concentration in N(2) ambient at 500 °C. A quantitative model based on the spill-over mechanism is established to describe this novel correlation.

We report a novel hydrogen-sensitive Schottky-diode device based on an SnO2 film consisting of nanoscale particles and with platinum electrodes on top, which has a very high response. SnO2 films were prepared through thermal oxidation of metallic Sn films, which were deposited using electron-beam evaporation with thicknesses ranging from 5 nm to 100 nm. The average size of the nano-particles shrinks as the thickness of the original Sn films decreases. Interdigital platinum (Pt) electrodes were fabricated on the SnO2 films for hydrogen sensing studies. Very high relative response (current change of 168 times) to low concentration H2 (100 ppm) was found for the device based on SnO2 film converted from 20 nm-thick as-deposited Sn film. Its response speed is also very fast, which is less than 10 s to reach half of the maximum response. It has excellent selectivity with low response to CO and null response to CH4. We propose that the sensing mechanism is the reduction of the Schottky barrier height (SBH) at the Pt/SnO2 interface. A pinch-off model and a circuit model are presented to reveal the relationship between the relative response and the film thickness or particle size.

An MOS capacitor type hydrogen gas sensor was fabricated with the structure of Ni/SiO2/Si by using conventional silicon wafer technologies Grown by dry oxidation at 900 C the thickness of the SiO2 film was only 24 A At 150 degrees C comparing to another MOS capacitor with 148 A thick oxide and otherwise identical configurations this sensor showed much faster response speed (the time interval to reach half of the magnitude of the steady state signal or t(50%) was only 4 s in response to 1% H-2 without deduction of the delay from the gas delivery system) as well as enhanced signal magnitude (about two times of the former for 1% H-2) Based on the hydrogen binding to the traps in the bulk SiO2 a mechanism was proposed to explain the very short response time on the device with the ultra thin SiO2 The gate leakage in the device is also discussed The presented sensor demonstrates a promising step in designing low cost H-2 detectors with very fast responses (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved

SummaryMixed chimerism has been shown to lead to prolonged major histocompatibility complex (MHC) disparate allograft survival and immune‐specific tolerance; however, traditional conditioning regimes often involve myeloablation, which may pose a significant safety risk. In this study we examined the use of donor C57BL/6 (H‐2b) immature dendritic cells (imDCs) to tolerize the BALB/c (H‐2d) recipient to bone marrow transplantation (BMT), allowing the induction of mixed chimerism without immunosuppression or myeloablation. We showed that successful mismatched bone marrow engraftment can be achieved using imDCs given up to 3 days prior to BMT and that mixed chimerism can be established and detected in excess of 100 days post‐BMT without evidence of graft‐versus‐host disease. Furthermore, we showed that imDCs can suppress lymphocyte proliferation in response to mismatched MHC stimulation, leading to increased expression of interleukin (IL)‐4 and IL‐10 and decreased expression of IL‐2 and interferon‐γ (IFN‐γ). The induction of stable chimeras through pre‐conditioning of mice with donor imDCs followed by BMT led to tolerance, allowing the long‐term survival (> 110 days) of mismatched cardiac allografts and the prolonged survival of mismatched skin allografts without the need for immunosuppression or myeloablation. Transplantation with third‐party C3H allografts were rapidly rejected in this model, suggesting that immune‐specific tolerance was achieved. The induction of immune‐specific tolerance without the need for immunosuppression or myeloablation represents a significant advance in transplant immunology and may provide clinicians with a plausible alternative in combating organ rejection following transplantation.

Thin titanium oxide (TiO2) films were prepared through electron-beam evaporation of titanium metal on substrates followed by oxidizing and sintering at 600°C in flowing oxygen. The thicknesses of the as-deposit metal films were 25nm, 50nm and 100nm. The phase of the TiO2 converted from the thermal oxidation was detected to be rutile. Nanoporous anodized aluminum oxide (AAO) and plain thermal silicon oxide on top of a commercial silicon wafer were used as substrates to support the TiO2 thin layer. A pair of interdigit platinum electrodes with a spacing of 5μm was fabricated on the TiO2 thin films by photolithography. At 500°C, the samples showed different sensing behaviors to hydrogen concentration levels ranging from 5ppm to 500ppm, with nitrogen as the background gas. It was found that the sensitivity was significantly enhanced by the increased specific surface area of the TiO2 thin film due to the shaping of the porous AAO substrate. The performance of the sensor based on the TiO2 film converted from 25-nm-thick Ti on the porous AAO substrate, which has the largest specific surface area among all the other samples, was featured by a conductance change of 25–90 times and considerable resolution for 5ppm to 500ppm H2, as well as very fast response and recovery (the time delay to reach or retreat to half of the maximum stable signal, t50%, was always no more than 10s). The rutile-phased thin TiO2 film on AAO is proven to be a promising high-temperature hydrogen sensor with satisfactory performance, excellent durability, and ideal compatibility to micro-miniaturization.

A novel hydrogen sensor based on Ni/SiO2/Si MOS capacitors were fabricated and characterized at hydrogen concentrations ranging from 50 to 1000ppm at an operating temperature of 140°C. The highest response occurs at the same bias voltage (−0.4V) for all the concentration levels measured and is about 18% at 50ppm. The response/recovery transients of the Ni-based sensors are similar to those of the Pd-based hydrogen sensors. A Langmuir isotherm model is adapted to explain the observed phenomena, which is in agreement with our experimental results.

Nanoporous Pd films supported by porous anodic aluminum oxides (AAOs) were investigated regarding their performance in detecting hydrogen gas with concentrations up to 1% in nitrogen at room temperature. Compared with dense Pd films that usually have very slow responses, nanoporous Pd films based on AAOs were found to have a quick and reversible response due to their enhanced absorption and disorption of hydrogen. Using thinner nanoporous films, concentrations of hydrogen as low as 250 ppm can be detected and a much higher sensitivity, up to 12% resistance variation, was obtained. Two competing hydrogen-sensing processes, the phase-induced increase of film resistance and the break-junction-induced decrease of film resistance, were found in the nanoporous Pd films upon absorption of hydrogen.

We have reviewed humidity sensors based on various materials for both relative and absolute humidity, including ceramic, semiconducting, and polymer materials. In the majority of publications, there are few papers dealing with absolute humidity sensors, which have extensive applications in industry. We reviewed extensively absolute humidity sensors in this article, which is unique comparing with other reviews of humidity sensors. The electrical properties of humidity sensors such as sensitivity, response time, and stability have been described in details for various materials and a considerable part of the review is focused on the sensing mechanisms. In addition, preparation and characterization of sensing materials are also described. For absolute humidity sensors, mirrorbased dew-point sensors and solid-state Al2O3 moisture sensors have been described. As the major problem in Al2O3 moisture sensors, long-term instability, has been solved, � -Al2O3 moisture sensors may have promising future in industry.