High-performance solid-electrolyte SOx sensor using MgO-stabilized zirconia tube and Li2SO4---CaSO4---SiO2 auxiliary phase

Solid-electrolyte-based electrochemical SO_x sensors fabricated with MgO-stabilized zirconia and Li₂SO₄---CaSO₄---SiO₂ (4:4:2 in molar ratio) exhibit fairly good sensing characteristics for 2–200 ppm SO₂ in air at 600–750 °C, with the e.m.f. responses following the Nernst equation for the two-electron reduction of SO₂. The 90% response and 90% recovery times to 20 ppm SO₂ are 10 s and 7 min at 650 °C, and 10 s and 3 min at 700 °C, respectively. It is further found that the sensor exhibits excellent selectivity to SO_x in the coexistence of CO₂ and NO_x, and good long-term stability. The sensor is simple in structure, easy to prepare, and quite tough chemically and mechanically. These features should ensure practical use for this SO_x sensor.     

Electrochemical measurement of SO3-SO2 in process gas streams

The two major industrial sources of sulphur dioxide emissions are electrical generation and non-ferrous smelting. While flue-gas scrubbing and acid-plant technology are well established, continuous methods for the determination of SO₂ in these process streams are based on expensive conventional UV or IR spectroscopic instrumentation in which the gases must be conditioned prior to analysis. Additionally, there appears to be no reliable continuous low-maintenance method of analysis for SO₃ in gases. Solid-state sensors for the continuous real-time measurement of concentrations of SO₃ and SO₂ in process gas streams offer the possibility of monitoring the efficiency of flue-gas scrubbing, determining the concentrations of SO₃ in corrosion-susceptible ducting or in acid-plant conversion towers and guarding against excessive releases of SO₃ from acid-plant tail gas. The measurement of SO₂ and SO₃ in gases by solid-state electrochemistry is reviewed. The electrochemical cells are described, and wherever possible, the temperature and concentration ranges of the various solid-state devices reported in the literature are given. We conclude with a summary of the further requirements for a successful inexpensive commercial solid-state sensor for SO₃ and SO₂ measurement in process gas streams.     

Production of singlet oxygen by Ru(dpp(SO3)2)3 incorporated in polyacrylamide PEBBLES

Polyacrylamide (PAA) and amine-functionalized PAA (AFPAA) nanoparticles with disulfonated 4,7-diphenyl-1,10-phenantroline ruthenium (Ru(dpp(SO₃)₂)₃) have been prepared. The nanoparticles produced have a hydrodynamic radius of 20–25 nm.

The amount of singlet oxygen (¹O₂) produced by Ru(dpp(SO₃)₂)₃ as been measured using anthracene-9,10-dipropionic acid (ADPA). A kinetic model for the disappearance of ADPA, by steady state irradiation of Ru(dpp(SO₃)₂)₃ at 465 nm, has been developed taking also into account a consumption not mediated by ¹O₂. This direct consumption of ADPA is evaluated by irradiating in the presence of NaN₃ and is about 30% of the total. All the experimental results are very well described by the model developed, both for free Ru(dpp(SO₃)₂)₃ and with this dye incorporated in the nanoparticles.

It is found that the polyacrylamide matrix does not quench the ¹O₂ produced, allowing it to reach the external solution of the nanoparticles and react with ADPA. When the matrix possesses amine groups, AFPAA, the amount of ¹O₂ that reacts with ADPA is slightly reduced, 60%, but most of the ¹O₂ produced can still leave the particles and react with external molecules. The particles produced may therefore be used as sources of ¹O₂ in photodynamic therapy (PTD) of cancers. The fact that those nanoparticles do not quench significantly the ¹O₂ makes possible the future development of ¹O₂ sensors based on PAA nanoparticles with the appropriate sensor molecule enclosed.     

Study on CuO–BaTiO3 semiconductor CO2 sensor

The prototype of a CO₂ sensor made of CuO–BaTiO₃, which has capacitance sensitive effect, is designed based on the pn heterojunctions of CuO and BaTiO₃ semiconductors. The preparation of BaTiO₃ semiconductor powders is pointed out, using the coprecipitation and semiconducting techniques. The characteristic quantities relating to the capacitance sensitive effect of the sensor are studied systematically with the aid of a gas tester. A reasonable mechanism of the sensor is proposed.     

An optical IR-source and CO2-chamber system for CO2 measurements

A new silicon IR source and CO₂-chamber system for measurement of CO₂ concentration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended across a KOH-etched cavity, is used to generate two switched “sample” and “reference” beams. The electrically modulated sources present a modulation time of 10 ms and a power consumption of 1 W. The CO₂ chambers, placed beneath the reference sources, are used to produce a reference beam for long term stability and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO₂ is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antireflective coating to optimize the filter's optical characteristics. Numerical simulations of the filters are presented and show good agreement with the measurements. The IR sources and the CO₂ filters are both fabricated at wafer level. Using the presented IR-sensor system, measurements with a 9-mm-wide test channel show high CO₂-sensitivity for CO₂ concentrations between 0 and 10% confirming that the stringent requirements for this respirator application can be fulfilled     

Potentiometric CO2 gas sensor with lithium phosphorous oxynitride electrolyte

Potentiometric cell, Au/LiCoO₂ 5 m/o Co₃O₄/Li_2.88PO_3.73N_0.14/Li₂CO₃/Au, has been fabricated and investigated for monitoring CO₂ gas. A LiCoO₂–Co₃O₄ mixture was used as the solid-state reference electrode instead of a reference gas. The idea is to keep the lithium activity constant on the reference side using thermodynamic equilibrium at a given temperature. The thermodynamic stability of the reference electrode was studied from the phase stability diagram of Li–Co–C–O system. The Gibb’s free energy of formation of LiCoO₂ was estimated at 500°C from the measured value of the cell emf. The sensors showed good reversibility and fast response toward changing CO₂ concentrations from 200 to 3000 ppm. The emf values were found to follow a logarithmic Nernstian behavior in the 400–500°C temperature range. CH₄ gas did not show any interference effect. Humidity and CO gas decreased the emf values of the sensor slightly. NO and NO₂ gases affect this sensor significantly at low temperatures. However, increased operating temperature seems to reduce the interference.     

基于OMI/OMPS中国季风区大气边界层SO2时空格局分析

为研究季风对大气边界层 SO₂变化的影响,利用2005~2014年OMI SO₂、2015~2017年OMPS NMSO₂遥感数据,选取中国季风区为研究对象,分析大气边界层SO₂时空分布特征,并选取4座典型城市,通过相关性分析和HYSPLIT后向轨迹模拟。结果表明：中国季风区PBL SO₂空间上呈现异质性,冬、夏季风变迁对于季风区大气边界层 SO₂柱浓度变化影响明显;温度和气压是影响大气边界层 SO₂柱浓度的主要气象因子,其次是地域性气象条件;冬季气流对日SO₂柱浓度升高影响较大,四川盆地及来自印度半岛、孟加拉湾的西南气流对重庆市SO₂柱浓度升高效果显著,银川市SO₂受蒙古高原偏北气流及天山北部西北气流影响,天津市和杭州市受华北平原及蒙古高原地区气流的作用。     

Coupled phase diagram and thermodynamic analysis of the 18 binary systems formed among Li2Co3, K2Co3,Na2Co3, Lioh, Koh, Naoh, Li2So4, K2So4 and Na2So4

Available phase diagram and thermodynamic data on the eighteen binary systems containing Li⁺ , Na⁺, K⁺, S0₄⁼, CO₃⁼, and OH⁻ have been collected and critically assessed. A set of self-consistent thermodynamic parameters describing the free energies of the compounds, solid solutions, and liquid solutions in the binary systems has been formulated. The phase diagrams have been calculated, and estimated error limits of all diagrams are given.     

Thermodynamic optimization and calculation of the ErCl3–MCl (M=Li,Na,K,Rb,Cs ) systems

In this paper, the binary phase diagrams of the ErCl₃–MCl (M = Li, Na, K, Rb, Cs) systems were studied by the CALPHAD (CALculation of PHAse Diagram) approach. The modified quasi-chemical model in the pair-approximation for short-range ordering was used to describe the Gibbs energies of the liquid phase in the systems. From measured phase diagram data and experimental thermochemical properties, a series of thermodynamic functions has been optimized based on computer-assisted analysis. A discussion of thermodynamic functions for strong interaction binary systems was undertaken. The results showed that the calculated phase diagrams and optimized thermodynamic parameters are self-consistent.     

Water activities, osmotic and activity coefficients of the system (NH4)2SO4–K2SO4–H2O at the temperature 298.15 K

The mixed aqueous electrolyte system consisting of ammonium and potassium sulfates has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total ionic strength values ranging from 0.60 to 8.25 mol kg⁻¹ for different ionic strength fractions (y) of (NH₄)₂SO₄ with y=0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LS II), Reilly–Wood and Robinson (RWR) and Pitzer models. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture.     

A comparative study of the physical properties of CdS, Bi2S3 and composite CdS–Bi2S3 thin films for photosensor application

Thin films of CdS, Bi₂S₃ and composite CdS–Bi₂S₃ have been deposited using modified chemical bath deposition (M-CBD) technique. The various preparative parameters were optimized to obtain good quality thin films. The as-deposited films of CdS, Bi₂S₃ and composite were annealed in Ar gas at 573 K for 1 h. A comparative study was made for as-deposited and annealed CdS, Bi₂S₃ and composite thin films. Annealing showed no change in crystal structure of these as-deposited films. However, an enhancement in grain size was observed by AFM studies. In addition change in band gap with annealing was seen. A study of spectral response, photosensitivity showed that the films can be used as a photosensor.     

Impedancemetric gas sensor based on Pt and WO3 co-loaded TiO2 and ZrO2 as total NOx sensing materials

Pt-loaded metal oxides [WO₃/ZrO₂, MO_x/TiO₂ (MO_x = WO₃, MoO₃, V₂O₅), WO₃ and TiO₂] equipped with interdigital Au electrodes have been tested as a NO_x (NO and NO₂) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO₃/TiO₂ showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO₂ in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO_x (NO or NO₂) concentration from 10 to 570 ppm. Pt-WO₃/TiO₂ showed responses to NO and NO₂ of the same algebraic sign and nearly the same magnitude, while Pt/WO₃ and WO₃/TiO₂ showed higher response to NO than NO₂. The impedance at 4 Hz in the presence of NO for Pt-WO₃/TiO₂ was almost equal at any O₂ concentration examined (1–99%), while in the case of Pt/WO₃ and WO₃/TiO₂ the impedance increased with the oxygen concentration. The features of Pt-WO₃/TiO₂ are favorable as a NO_x sensor that can monitor and control the NO_x concentration in automotive exhaust. The effect of WO₃ loading of Pt-WO₃/ZrO₂-based sensor is studied to discuss the role of surface W-OH sites on the NO_x sensing.     

Partial phase diagram of the ternary reciprocal system KF-AlF3-Al2O3-K2O

A K₂ZrF₆ treatment improves the wettability of SiC (or C) fibers by aluminum alloys. A possible mechanism involves the formation of K₃AlF₆ followed by the dissolution of the alumina film. DTA analyses of K₃AlF₆--Al₂O₃ mixtures show that a temperature invariant transition occurs at 1132K, the solid containing trace amounts of KAlF₄ and β-alumina at room temperature. Part of the ternary reciprocal system KF-AlF₃-Al₂O₃-K₂O is calculated, the Gibbs free energy of the liquid being described according to the CIS theory. The K₃AlF₆-Al₂O₃ isopteth section is given. It is characterized by a liquidus with a deep minimum at 1132K and 11.6 wt % alumina.     

Theoretical calculation of the phase diagram between one-dimensional long-period structures in the quasi binary sections: Pd3xRh3(1−x)V, Pt3xRh3(1−x)V, and Pt3VxTi(1−x)

The relative stabilities of L1₂, D0₂₂, D0₂₃, 21, and 3 structures in the Pd₃V, Pt₃V, Rh₃V, and Pt₃Ti compounds are investigated employing the Vienna ab initio simulation package. In the pseudobinary Pd_3xRh_3(1−x)V, Pt_3xRh_3(1−x)V, and Pt₃V_xTi_(1−x) alloys, the energy differences from L1₂ of D0₂₂, D0₂₃, 21, and 3 structures are assumed to be linear as function of the number of electrons per atom. At T=0K, the resulting energy diagram shows that the equilibrium between the limiting binary phases is the most stable state. At high temperature, the Gibbs energy curves are computed assuming a Bragg and Williams entropy of mixing in the pseudobinary sections. The D0₂₃ and 21 structures are stabilized in the pseudobinary Pd_3xRh_3(1−x)V, Pt_3xRh_3(1−x)V, and Pt₃V_xTi_(1−x) alloys. The phase diagram between the various structures is calculated in each pseudobinary section and compared with the experimental one.     

Liquid–solid equilibria in quinary system Na,Mg/Cl,SO4,NO3–H2O at 298.15 K

In order to develop the nitrate deposits found close to Lop Nur in the Xinjiang region in China, the solubilities of the system Na⁺,Mg²⁺/Cl⁻,SO₄²⁻, NO₃⁻–H₂O and its subsystems, the quaternary systems Na⁺,Mg²⁺/SO₄²⁻,NO₃⁻–H₂O and Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O, were studied at 298.15 K. The phase diagrams were plotted according to the solubilities achieved. In the equilibrium phase diagram of Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O, there are two invariant points, five univariant curves and four regions of crystallization: Mg(NO₃)₂6H₂O,MgCl₂6H₂O,MgSO₄7H₂O and MgSO₄(1–6)H₂O. In the equilibrium phase diagram of Na⁺,Mg²⁺/SO₄²⁻, NO₃⁻–H₂O, there are five invariant points, eleven univariant curves and seven regions of crystallization: Na₂SO₄,Na₂SO₄10H₂O,NaNO₃,MgSO₄Na₂SO₄4H₂O,NaNO₃Na₂SO₄2H₂O,Mg(NO₃)₂6H₂O and MgSO₄7H₂O. In the equilibrium phase diagram of the Na⁺, Mg²⁺/Cl⁻,SO₄²⁻,NO₃⁻–H₂O system, there are six invariant points, and ten regions of crystallization: NaCl, NaNO₃,Na₂SO₄,Na₂SO₄10H₂O,MgSO₄Na₂SO₄4H₂O, NaNO₃Na₂SO₄2H₂O,MgCl₂6H₂O,Mg(NO₃)₂6H₂O, MgSO₄(1–6)H₂O and MgSO₄7H₂O.     

H2 sensors using Fe2O3-based thin film

This paper describes the fabrication procedure as well as the sensing properties of new hydrogen sensors using Fe₂O₃-based thin film. The film is deposited by the r.f. sputtering technique; its composition is Fe₂O₃, TiO₂(5 mol%) and MgO(0–12 mol%). The conductance change of the film is examined in various test gases. The sensitivity to hydrogen gas is enhanced by treating the film in vacuum at 550 °C for 4 h and then in air at 700 °C for 2 h. The sputtered film is identified to be polycrystalline -Fe₂O₃ based on X-ray diffraction patterns. However, the surface layer is considered to be changed to Fe₃O₄ after heating in vacuum and then to γ-Fe₂O₃ after heating in air. The film is thus a multilayer one with a thin γ-Fe₂O₃ layer on a -Fe₂O₃ layer. The sensing mechanism is discussed based on measurements of the physical properties of the film, such as the temperature dependence of the sensor conductance, X-ray diffraction pattern, surface morphology, RBS (Rutherford back-scattering) spectrum and optical absorption spectrum.     

Pyroelectric and dielectric properties of sol–gel derived barium–strontium–titanate (Ba0.64Sr0.36TiO3) thin films

The barium–strontium–titanate (BST, Ba_0.64Sr_0.36TiO₃) thin films have been prepared by the sol–gel method on a platinum-coated silicon substrate. The resulting thin films show very good dielectric and pyroelectric properties. The dielectric constant and dissipation factor for Ba_0.64Sr_0.36TiO₃ thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The dependence of the capacitance as a function of the voltage shows a strongly non-linear character, and two peaks characterizing spontaneous polarization switching can be clearly seen in this curve, indicating that the films have a ferroelectric nature. The capacitance changed from 495 to 1108 pF with the applied voltage in the −5 to +5 V range at a frequency of 100 kHz. The peak pyroelectric coefficient at 30 °C is 1080 μC/m² K. The pyroelectric coefficient at room temperature (25 °C) is 1860 μC/m² K, and the figure-of-merit of this film is 37.4 μC/m³ K. The high pyroelectric coefficients and the greater figures-of-merit of Ba_0.64Sr_0.36TiO₃ thin films make it possible to be used for thermal infrared detection and imaging.     

MgO sacrificial layer for micromachining uncooled Y-Ba-Cu-O IRmicrobolometers on Si3N4 bridges

This paper describes a new micromachining technique for fabrication of semiconducting yttrium barium copper oxide (YBCO) microbolometers using magnesium oxide (MgO) as the sacrificial layer. This type of bolometer can be operated at room temperature, providing a low-cost alternative for more expensive cryogenically cooled thermal detectors used for infrared (IR) imaging. The new micromachining techniques described here would enable the fabrication of YBCO IR focal plane array (FPA) with CMOS signal processing circuitry. Devices were fabricated by growing YBCO films on 4000-Å-thick suspended Si₃N₄ membranes measuring 40×40 μm² in area and extended over micromachined air gaps, which provide the low thermal conductivity that is required for high responsivity. The gap was created by etching an MgO sacrificial layer. This is the first example of using MgO in this type of application. The MgO sacrificial layer technique is fully CMOS compatible and presents no major fabrication challenges. Thermal conductivities achieved in vacuum with the Si₃N₄ suspended structures were on the order of 10^-7 W/K, yielding an effective thermal isolation for bolometer operation. Optical characterization has shown responsivity up to 60 kV/W and detectivity over 10⁸ cm.Hz^1/2/W to black-body IR radiation, indicating that this technology is a suitable candidate for low-cost thermal imaging