Gas sensing properties of nanocrystalline metal oxide powders produced by thermal decomposition and mechanochemical processing

The objective of this research, was the synthesis of LaFeO3 and SnO2 fine powders for the subsequent preparation of thick film gas sensors. On producing fine metal oxide powders, often it is not possible to ensure separation of the particles during the synthesis, resulting in the formation of highly agglomerated material. In addition, there are often high synthetic costs associated with the powders obtained by these methods. Thermal decomposition and mechanochemical processing methods were selected to produce fine metal oxide powders. Thermal decomposition of a heteronuclear complex is a simple and relatively cheap method. Heat treatment of La[Fe(CN)6] · 4H2O leads to single-phase perovskite-type LaFeO3 fine powders. Heating in the temperature range 600-750 °C causes fast crystallite growth of slightly agglomerated particles and X-ray diffraction analysis showed only the pattern of orthorhombic transition phase of LaFeO3 particles. A paste for the preparation of the LaFeO3 thick film coating was obtained by mixing of polyvinyl alcohol solution and decomposed powder in a ball mill for 1 h. It was determined that there are two factors important for gas sensing, concentration of surface metal ions [Fe3+], and the concentration of oxygen adsorptive sites [Vo(..)]. LaFeO3−δ thick film with small crystallites, promotes a more rapid NO2 gas reaction at the surface and allows an equilibrium state to be obtained at 350 °C. Mechanochemical processing (MCP) is selected as the second, low cost method of manufacturing of fine powders in a conventional ball mill. During milling, deformation, fracture, and welding of powder particles continuously occur. The chemical reactions are activated by the repeated ball-powder collisions. Most of the reports on MCP that have appeared to date, concern the use of high-energy mills. It is shown that it may be possible to produce fine powder particles using a centrifugal mill of the conventional type instead of high-energy one. Nanocrystalline SnO2 powder was produced by two different chemical reactions. The first reaction, initiated by ball milling, produces water and the second reaction does not produce water. It should be noted that water, produced by the chemical reaction during milling, has a considerable influence on the reactivity of surface. Milling of predetermined stoichiometric amounts of SnCl2 with Ca(OH)2 and K2CO3 in an excess of CaCl2 and KCl respectively, resulted in the formation of the desired mass of SnO. After heat treatment and removal of the salt, slightly agglomerated SnO2 particles were produced with a tetragonal phase, confirmed by X-ray diffraction pattern. A very narrow particle size distribution of the powder is observed. The response of the LaFeO3 thick film to NO2 gas is investigated in the temperature range 250-350 °C, where the surface reactions are moderately fast. On exposure to low concentrations of H2S gas in air in the range 20-50 ppm the SnO2 film, prepared from anhydrous powder has higher gas response than the film prepared from hydrated powder.reviewe

Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors

This paper reports the improvement in the sensing performance of nanocrystalline SnO2-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO2 films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO2 with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO2:F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO2 was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO2:F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection

MultimediaN E-Culture demonstrator

The main objective of the MultimediaN E-Culture project is to demonstrate how novel semantic-web and presentation technologies can be deployed to provide better indexing and search support within large virtual collections of cultural-heritage resources. The architecture is fully based on open web standards, in particular XML, SVG, RDF/OWL and SPARQL. One basic hypothesis underlying this work is that the use of explicit background knowledge in the form of ontologies/vocabularies/thesauri is in particular useful in information retrieval in knowledge-rich domains

Ethanol oxidation activity and structure of carbon-supported Pt-modified PdSn-SnO2 influenced by different stabilizers

PdSn-SnO2 nanoparticles supported on Vulcan XC-72 carbon were synthesized by chemical reduction in the presence of three different stabilizing agents: ethylene diamine tetra-acetic acid (EDTA), sodium citrate (Nacitrate) and hexamethylenetetramine (HMTA). TEM analysis showed that PdSn-SnO2 /C catalyst made using the HMTA stabilizer produced the smallest particle size. XRD analysis detected the presence of PdSn alloy and the SnO2 phase in all three PdSn-SnO2 /C samples, and showed that PdSn-SnO2 (HMTA) had the smallest lattice parameter. After PdSn-SnO2 samples were modified by Pt, the particle size distribution and average size of nanoparticles of Pt-PdSn-SnO2 did not obviously change, and the fcc structure of PdSn in all three samples was retained. XPS measurement showed a higher upshift of Pt 4f binding energy occurred for Pt/PdSn-SnO2 /C (HMTA) compared to those of Pt/PdSn-SnO2 /C (EDTA) and Pt/PdSn-SnO2 /C (Nacitrate). Pt/PdSn-SnO2 /C (HMTA) was also found to have the highest CO and ethanol oxidation activity among the three catalysts.Web of Scienc

Lessons learned from the Alberta Border Testing Pilot Program

BackgroundDuring the Coronavirus disease (COVID-19) pandemic, countries implemented border control and quarantine measures to reduce transmission. The Alberta Border Testing Pilot Program (ABTPP) allowed international travellers entering Alberta to reduce their quarantine period following two negative COVID-19 tests. We evaluated participant experiences with the ABTPP and implementation.MethodWe used a parallel convergent mixed-methods design to explore participant experiences through electronic web-based questionnaires (n = 21,089; n = 13,839) and semi-structured telephone interviews (n = 30). We evaluated implementation through three staff focus groups (n = 11). We analysed questionnaires using descriptive statistics and analysed interviews using inductive and deductive thematic analysis. We deductively coded focus group data using the 2009 Consolidated Framework for Implementation Research (CFIR).ResultsQuestionnaires indicated minimal issues with registration forms (91.7%), symptom reports (95.5%), and COVID-19 testing (95.7%). Most respondents (95.1%) expressed willingness to participate in the ABTPP again. Interviews revealed three themes related to participant experience: program efficiency, clarity of information, and requisite effort. Focus groups identified key implementation facilitators including the single health information system, strong stakeholder partnerships, and good communication across partnerships. Barriers included program complexity, implementation timeline, and evolving external context.DiscussionParticipants reported high satisfaction with the ABTPP. Border testing programs should have high efficiency, require low effort, and use messaging that is clear and consistent. The effective implementation of border testing programs may be facilitated by strong leadership, adaptability, automated components, good communication, and simple technology. Learnings from participants and staff may help improve the implementation of border control programs for future pandemics or other emergencies.ConclusionsThe ABTTP was a novel border control measure during the COVID-19 pandemic. Our evaluation of both participant and staff experiences demonstrated high levels of traveller satisfaction and identified areas for improvement that can inform the development of future border control measures

Synthesis of carbon-supported PdSn–SnO2 nanoparticles with different degrees of interfacial contact and enhanced catalytic activities for formic acid oxidation

The conjunction of the PdSn alloy and SnO2 is of interest for improving catalytic activity in formic acid oxidation (FAO). Here, we report the synthesis of PdSn–SnO2 nanoparticles and a study of their catalytic FAO activity. Different degrees of interfacial contact between SnO2 and PdSn were obtained using two different stabilizers (sodium citrate and EDTA) during the reduction process in catalyst preparation. Compared to the PdSn alloy, PdSn–SnO2 supported on carbon black showed enhanced FAO catalytic activity due to the presence of SnO2 species. It was also found that interfacial contact between the PdSn alloy and the SnO2 phase has an impact on the activity towards CO oxidation and FAO.Web of Scienc