Sensors

58 KiB

Open AccessArticle

Reticulation of Aqueous Polyurethane Systems Controlled by DSC Method

by Suzana Cakic, Caslav Lacnjevac, Milos B. Rajkovic, Ljiljana Raskovic and Jakov Stamenkovic

Sensors 2006, 6(5), 536-545; https://doi.org/10.3390/s6050536 - 2 Jun 2006

Cited by 10 | Viewed by 8866

The DSC method has been employed to monitor the kinetics of reticulation ofaqueous polyurethane systems without catalysts, and with the commercial catalyst of zirconium(CAT^®XC-6212) and the highly selective manganese catalyst, the complex Mn(III)-diacetylacetonemaleinate (MAM). Among the polyol components, the acrylic emulsions [...] Read more.

The DSC method has been employed to monitor the kinetics of reticulation ofaqueous polyurethane systems without catalysts, and with the commercial catalyst of zirconium(CAT^®XC-6212) and the highly selective manganese catalyst, the complex Mn(III)-diacetylacetonemaleinate (MAM). Among the polyol components, the acrylic emulsions wereused for reticulation in this research, and as suitable reticulation agents the water emulsiblealiphatic polyisocyanates based on hexamethylendoisocyanate with the different contents ofNCO-groups were employed. On the basis of DSC analysis, applying the methods of Kissinger,Freeman-Carroll and Crane-Ellerstein the pseudo kinetic parameters of the reticulation reactionof aqueous systems were determined. The temperature of the examination ranged from 50oC to450oC with the heat rate of 0.5oC/min. The reduction of the activation energy and the increaseof the standard deviation indicate the catalytic action of the selective catalysts of zirconium andmanganese. The impact of the catalysts on the reduction of the activation energy is thestrongest when using the catalysts of manganese and applying all the three afore-said methods.The least aberrations among the stated methods in defining the kinetic parameters wereobtained by using the manganese catalyst. Full article

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436 KiB

Open AccessArticle

Micro Semiconductor CO Sensors Based on Indium-Doped Tin Dioxide Nanocrystalline Powders

by Il Jin Kim, Sang Do Han, Chi Hwan Han, Jihye Gwak, Hi Doek Lee and Jin Suk Wang

Sensors 2006, 6(5), 526-535; https://doi.org/10.3390/s6050526 - 10 May 2006

Cited by 15 | Viewed by 11064

Abstract

The precursors of SnO₂ or In₂O₃/SnO₂ nanocrystlline powders have been prepared bythe sol-precipitation method. The precursors were calcined at different temperatures to prepareSnO₂ or In₂O₃/SnO₂ nanocrystalline powders with different particle sizes. [...] Read more.

The precursors of SnO₂ or In₂O₃/SnO₂ nanocrystlline powders have been prepared bythe sol-precipitation method. The precursors were calcined at different temperatures to prepareSnO₂ or In₂O₃/SnO₂ nanocrystalline powders with different particle sizes. The nanocrystalliteswere examined by differential thermal analysis (DTA), X-ray diffraction (XRD) andtransmission electron microscopy (TEM). And then thick film CO sensors were fabricated usingprepared SnO₂ or In₂O₃/SnO₂ nanocrystlline powders loaded with PdO_x. The composition thatgave the highest sensitivity for CO was in the weight% ratio of 5 wt.% In₂O₃/SnO₂:PdO_x as99:1(wt %). The composite material was found sensitive against CO at the working temperature200 °C. It was found that the sensors based on In₂O₃/SnO₂ nanocrystalline system exhibitedvery short response time to CO at ppm level. These characteristics make the sensor to be apromising candidate for detecting low concentrations of CO. Full article

(This article belongs to the Special Issue Gas Sensors)

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263 KiB

Open AccessArticle

Light Dependent Resistance as a Sensor in Spectroscopy Setups Using Pulsed Light and Compared with Electret Microphones

by Derci Felix Da Silva and Daniel Acosta-Avalos

Sensors 2006, 6(5), 514-525; https://doi.org/10.3390/s6050514 - 9 May 2006

Cited by 16 | Viewed by 17173

Abstract

Light-dependent resistances (LDR) are cheap light sensors. A less known lightdetector is the electret microphone, whose electret membrane functions as a perfectabsorber, but only detects pulsed light. The aim of this study was to analyze the use of aLDR and an electret microphone [...] Read more.

Light-dependent resistances (LDR) are cheap light sensors. A less known lightdetector is the electret microphone, whose electret membrane functions as a perfectabsorber, but only detects pulsed light. The aim of this study was to analyze the use of aLDR and an electret microphone as a light sensor in an optical spectroscopy system usingpulsed light. A photoacoustic spectroscopy setup was used, substituting the photoacousticchamber by the light sensor proposed. The absorption spectra of two different liquids wereanalyzed. The results obtained allow the recommendation of the LDR as the first choice inthe construction of cheap homemade pulsed light spectroscopy systems. Full article

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153 KiB

Open AccessArticle

Enhancement of H₂-sensing Properties of F-doped SnO₂ Sensorby Surface Modification with SiO₂

by Chi-Hwan Han, Sang-Do Han and S. P. Khatkar

Sensors 2006, 6(5), 492-502; https://doi.org/10.3390/s6050492 - 9 May 2006

Cited by 34 | Viewed by 11306

Abstract

Effects of surface chemical modification with sodium silicate on the gas-sensingproperties of F-doped SnO₂ gas sensor designed and fabricated employing micro-electromechanical system (MEMS) technology were investigated. Gas sensing properties of thesensor were checked against combustible gases like H₂, CO, CH [...] Read more.

Effects of surface chemical modification with sodium silicate on the gas-sensingproperties of F-doped SnO₂ gas sensor designed and fabricated employing micro-electromechanical system (MEMS) technology were investigated. Gas sensing properties of thesensor were checked against combustible gases like H₂, CO, CH₄ and C₃H₈ at a heatervoltage of 0.7 V. The H₂ sensitivity of the surface modified F-doped SnO₂ micro sensormarkedly increased and reached S = 175 which was found to be about 40 times more thanthat of unmodified sensor (S = ~ 4.2). The increase in the sensitivity is discussed in terms ofincreased resistivity and reduced permeation of gaseous oxygen into the underlying sensinglayer due to the surface modification of the sensor. The present micro-hydrogen sensor withenhanced sensitivity due to SiO₂ incorporation is a low energy consuming portable sensormodule that can be mass-produced using MEMS technology at low cost. Full article

(This article belongs to the Special Issue Gas Sensors)

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119 KiB

Open AccessArticle

CNT Sensors for Detecting Gases with Low Adsorption Energy by Ionization

by Seongjeen Kim

Sensors 2006, 6(5), 503-513; https://doi.org/10.3390/s6050503 - 5 May 2006

Cited by 64 | Viewed by 11645

Abstract

In case of typical chemical gas sensors reacted by gas adsorption on surface of anactive layer, it is difficult to detect some gases which have low chemical adsorption energylike inert gases. In this paper, we report a gas sensor using carbon nanotube(CNT) array [...] Read more.

In case of typical chemical gas sensors reacted by gas adsorption on surface of anactive layer, it is difficult to detect some gases which have low chemical adsorption energylike inert gases. In this paper, we report a gas sensor using carbon nanotube(CNT) array aselectron emitters for the purpose of detecting these gases. Specifically, sensors werefabricated with applications of glass patterning by a sand-blast process and of anodicbonding between glass and silicon to improve the compactness of the structure and thereliability in process. The proposed sensor, based on an electrical discharge theory known asPaschen's law, worked by figuring the changes of dark discharge current and initialbreakdown voltage depending on the concentration and the identity of gases. In this work,air and Ar gases were examined and discussed. Full article

(This article belongs to the Special Issue Gas Sensors)

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118 KiB

Open AccessArticle

An Ion-selective Electrode for Anion Perchlorate in Thick-film Technology

by María Jesús Segui, Josefa Lizondo-Sabater, Ramón Martínez-Máñez, Félix Sancenón, Juan Soto, Eduardo García-Breijo and Luís Gil

Sensors 2006, 6(5), 480-491; https://doi.org/10.3390/s6050480 - 7 Apr 2006

Cited by 15 | Viewed by 11920

Abstract

The ionophore 1,4,7,10,13-penta(n-octyl)-1,4,7,10,13-pentaazacyclopentadecane(L¹) was used for the development of miniaturised perchlorate-selective electrodes in thick-film technology. Different PVC membranes containing L¹ and the plasticizers o-nitrophenyloctyl ether (NPOE), dibutyl phthalate (DBP), bis(2-ethylhexyl)sebacate (DOS) and dibutylsebacate (DBS) were prepared and placed on a [...] Read more.

The ionophore 1,4,7,10,13-penta(n-octyl)-1,4,7,10,13-pentaazacyclopentadecane(L¹) was used for the development of miniaturised perchlorate-selective electrodes in thick-film technology. Different PVC membranes containing L¹ and the plasticizers o-nitrophenyloctyl ether (NPOE), dibutyl phthalate (DBP), bis(2-ethylhexyl)sebacate (DOS) and dibutylsebacate (DBS) were prepared and placed on a graphite working electrode manufactured byusing thick film serigraphic technology. The perchlorate selective electrode containing DBSas plasticizer showed a potentiometric Nernstian response of -57 mV per decade in a rangeof perchlorate concentration from 1 x 10^-4 to 1 x 10^-1 M with a detection limit of 5 x 10^-5 M.The ion selective electrodes containing DBP and NPOE as plasticizers exhibit a workingrange from 6.3 x 10^-5 to 1 x 10^-1 M and 7.4 x 10^-5 to 1 x 10^-1 M for perchlorate, respectively,with a detection limit of ca. 2.2 x 10^-5 M. For all three electrodes a response time of ca. 5 s was found. The prepared electrodes do not show appreciable decay of the slope for at least 25 days. Potentiometric selectivity coefficients (log K^pot_ClO4-,_X-) with respect to the primaryanion perchlorate were evaluated using the fixed interference method. These coefficients areof the order of 10^-1.7 or smaller, indicating the relatively poor interference of the differentanions studied. Full article

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70 KiB

Open AccessArticle

Simulation Study of Nano Aqueous Flow Sensor Based on Amperometric Measurement

by Jian Wu, Qingli Zhou, Jun Liu and Zhengguo Lou

Sensors 2006, 6(5), 473-479; https://doi.org/10.3390/s6050473 - 6 Apr 2006

Cited by 3 | Viewed by 8707

Abstract

In this paper, a novel nano aqueous flow sensor which consists of two closelyspaced amperometric sensors is investigated by digital simulation. The simulation resultsindicate that the ratio of the responses of two closely spaced amperometric sensors is onlyrelated to flow rates in the [...] Read more.

In this paper, a novel nano aqueous flow sensor which consists of two closelyspaced amperometric sensors is investigated by digital simulation. The simulation resultsindicate that the ratio of the responses of two closely spaced amperometric sensors is onlyrelated to flow rates in the channel, insensitive to the analyte concentration in the solution.By comparing the output of two amperometric sensors, the flow rate in the channel can bededuced. It is not necessary to determine the analyte concentration in advance. Thesimulation results show it is able to detect flow rate by in the range of several nano-liters perminute when the distance between the working electrodes of two amperometric sensors is200 nm and the cross-section of the channel is 1 μm x 1 μm. Full article

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Sensors, Volume 6, Issue 5 (May 2006) – 7 articles , Pages 473-545

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