Logarithm Of CO Research Articles

Investigation of porous counter electrode for the CO 2 sensing properties of NASICON based gas sensor

In general, solid electrolyte based potentiometric CO 2 sensors respond well to changes in CO 2 concentration, following Nernst equation when dry CO 2 is used. Unfortunately, the sensing capability will be fatally disturbed when these sensors are exposed to humid conditions. To overcome this problem, a sensor using a porous BaCO 3 film as counter electrode (p-Sensor) was fabricated. For the purpose of comparison, sensor without this porous structure (o-Sensor, i.e. an opened counter electrode) and sensor with a dense BaCO 3 film (d-Sensor) also have been fabricated. The electromotive force (EMF) of all sensors exhibited excellence Nernstian behavior with the logarithm of CO 2 concentration in the range 300–755 ppm at 400 °C under dry condition. However, the EMF values of each sensor tended to shift upward with increase of relative humidity. It was found that the relative humidity dependence of EMF originates from both of auxiliary and counter electrodes. Under the same humid conditions, the order of the EMF deviation of three types of sensors was shown as the following: d-sensor > p-sensor > o-sensor. Nevertheless, only p-sensor still remained the Nernstain behavior even under humid conditions. The electron transfer numbers are in good agreement with theoretical value of n = 2. Moreover, the transients were sufficiently sharp, taking less than 1 min for 90% response or recovery. The most important thing is EMF can rapidly recover the original value without any deterioration. The reason for the satisfactory performance of p-sensor under humid condition was suggested to be due to the amount of H 2O molecular adsorbed on the porous counter electrode is very close to that of auxiliary electrode.

Relationship between aging time and EMF change of potentiometric CO 2 device using Na 1+ xZr 2Si xP 3− xO 12 (0 < x < 3)

Four kinds of NASICON (Na 1+ x Zr 2Si x P 3− x O 12, x = 1, 1.5, 2 or 2.75)-based CO 2 devices were combined with a Li 2CO 3–BaCO 3 (1:2 in molar ratio) auxiliary phase to investigate their CO 2 sensing properties. The EMF values of NASICON devices were correlated linearly with the logarithm of CO 2 concentrations in the range of 250–2500 ppm at 450 °C. When exposed to 250 ppm CO 2 for 200 h under dry condition, the EMF of each NASICON device decreased with aging time. To research the cause of the EMF drift, a mixture that consists of NASICON and Li 2CO 3 was heated at 750 °C in air. From X-ray diffraction measurement, it was confirmed that alkali-rich crystal phases such as Li 2ZrO 3 and Na 5Zr(PO 4) 3 were formed instead of Na 3Zr 2Si 2PO 12 phase. This suggests that the EMF drift relates with the formation of alkali-rich crystal phase at the interface between NASICON and auxiliary phase.

A high temperature potentiometric CO 2 sensor mixed with binary carbonate and glassy ceramic oxide

A high temperature (700 °C) lithium ion-based CO 2 sensor was fabricated using Li 2CO 3–BaCO 3 binary carbonate and SiO 2:B 2O 3:P 2O 5 (1:2:1 mol%) amorphous glassy ceramic oxide as sensing electrode. The sensor works efficiently at 700 °C without any degradation of the sensing material. The electro motive force (EMF) of the sensor is very stable and follows perfect Nernstian behavior with the logarithm of CO 2 concentration in the range 500–5000 ppm. It is revealed that Li 2Si 2O 5, Ba 3(PO 4) 2 and quartz were formed at high temperatures (500–700 °C) due to the reaction of Li 2CO 3 and BaCO 3 with glassy ceramic oxide. The time taken by the sensor to reach a change in 90% CO 2 is 10 s. The sensor does not show significant cross-sensitivity to the interfering gases like NO 2 and SO 2 at 500 °C. TG-DTA, XRD, SEM and FT-IR studies were employed to characterize and suggest a probable mechanism. The increase in EMF of the sensor may be due to the easier movement of Lithium ion in to the glass in the sensing electrode.

Characteristics and performance of binary carbonate auxiliary phase CO 2 sensor based on Li 3PO 4 solid electrolyte

Bulk type solid state potentiometric CO 2 sensors were fabricated based on Li 2CO 3–BaCO 3 binary auxiliary phase as a sensing electrode, Li 3PO 4 mixed with 5 mol% SiO 2 as a solid electrolyte and Li 2TiO 3 mixed with 10 mol% TiO 2 two phase system as a reference electrode. The concentration of BaCO 3 was varied in the auxiliary phase (mol%). The electromotive force (emf) of the investigated cells was linearly dependent upon the logarithm of CO 2 partial pressure over a wide range of 500–5000 ppm. The sensors have shown good CO 2 sensing properties at low concentrations of Barium carbonate additive. 10 mol% BaCO 3 loaded Li 2CO 3 sensor has shown the highest absolute emf and a very close theoretical Δemf/dec value at 500 °C than the other counterparts. The slopes of emf as a function of log P CO2 were in good accordance with the Nernstian slopes based on a two electron electrode reaction between the temperatures 450–500 °C. During the heat treatment, the interface formed between the sensing electrode and electrolyte and revealed by SEM, EDAX and X-ray diffraction studies indicates a new glassy phase consisting of Barium silicate (Ba 4Si 6O 16) and Barium phosphate (Ba 3P 4O 13). The penetration or diffusion of the Barium components deep inside the interfacial layer along with rich Li 2O content was proposed to be responsible for the improved sensing characteristics of the sensor.

Electrical properties of (Na 2O) 35.7(RE 2O 3) 7.2(SiO 2) 57.1 (RE = Y, Sm, Gd, Dy, Ho, Er and Yb) glasses and ceramics

Fifteen kinds of sodium rare earth silicate glasses and ceramics with (Na 2O) 35.7(RE 2O 3) 7.2(SiO 2) 57.1 (RE = Y, Sm, Gd, Dy, Ho, Er and Yb) composition were synthesized from a mixture of Na 2CO 3, RE 2O 3 and SiO 2. The densities of the glasses were in fairly good agreement with the theoretical densities and were 0.2–0.41 g cm −3 larger than those of the polycrystalline ceramics. The conductivities of the glasses are 1–2 orders lower than those of the ceramics and the highest electrical conductivity was achieved for the Yb ceramic sample with the smallest ion radius of RE 3+. The electromotive force, EMF, of the potentiometric CO 2 gas sensors using (Na 2O) 35.7(Y 2O 3) 7.2(SiO 2) 57.1 glass and ceramic increased linearly with an increase in the logarithm of CO 2 partial pressure, in accordance with Nernst's law. It was suggested from the slope of Nernst's equation that the two electron-transfer reaction associated with the carbon dioxide molecule takes place at the detection electrode above 450 °C.

Development of FET-type CO 2 sensor operative at room temperature

An FET-type CO 2 sensor operative at room temperature was developed by stacking a powder mixture of metal carbonate (auxiliary phase)—indium tin oxide (ITO, sensing electrode) as well as Na +-exchanged cation exchange membrane (ionic conductor gate) on an FET chip. Both ITO and the cation exchange membrane were indispensable to obtain stable response to CO 2 at room temperature, while the auxiliary phase was optimized to be Li 2CO 3–BaCO 3 (1:3 in molar ratio) from the stability of response against the disturbance by humidity. The device, Li 2CO 3–BaCO 3–ITO (1:3:1)/Na +-exchanged cation exchange membrane/FET, exhibited excellent CO 2-sensing characteristics at 30 °C. The response in gate-source voltage ( V GS) was linear to the logarithm of CO 2 concentration, with its slopes indicating n=2.0 where n is the number of reaction electrons involved in the electrochemical reduction per CO 2. The Nernst’s correlation was fairly stable against a change in RH between 30 and 70%. The times for 90% response and 90% recovery to switching-on and -off 3000 ppm CO 2 were 1 and 2 min, respectively.

Performance and stability of potentiometric CO 2 gas sensor based on the Pt, Li 2CO 3/Na 2O–Al 2O 3–4SiO 2//YSZ/Pt electrochemical cell

CO 2 sensing characteristics were examined in dry condition for Pt, Li 2CO 3/Na 2O–Al 2O 3–4SiO 2 (NA4S)/YSZ/Pt structure. The electromotive force (emf) value was linearly increased with logarithm of CO 2 concentration in the range of 10–10,000 ppm and the electron number was closed to 2.0. The electron number was hardly changed and the activity of alkali metal oxide in NA4S increased with time. As a reason to increase in the activity, the reaction of Li 2CO 3 as an auxiliary electrode with SiO 2 in NA4S layer and the formation of lithium silicates are considered. The formation of Li 2SiO 3 was accelerated by using H 2O, methanol or ethanol instead of α-terpineol as an additive for the mixing of Li 2CO 3 and silica. It was concluded that to depress the reaction with Li 2CO 3 and silica, the use of Li 2CO 3 mixed with α-terpineol for an auxiliary electrode was preferable.

Thick film CO 2 sensors based on Nasicon solid electrolyte

A planar miniaturised CO 2 sensor based on thick films of Nasicon (Na + conductor, Na 3Zr 2Si 2PO 12) electrolyte has been developed. The thick film was fabricated by screen printing Nasicon paste on an alumina substrate and then firing at 1543 K. scanning electron microscopy (SEM) analysis shows that the films achieved good densification, although reactions occur between Nasicon and alumina substrate, so conductivity of the thick film is lower than that of bulk Nasicon. The sensors interfaced with a binary carbonate auxiliary phase (Na 2CO 3–BaCO 3) applied as a slurry at 373 K showed good CO 2 sensing properties at 673–873 K. The electromotive force (emf) values obtained were linearly dependent upon the logarithm of CO 2 concentration over a wide range (6 ppm–100%). The slopes of emf versus log P CO 2 agreed well with the Nernstian slopes based on two electrons electrode reactions.

The performance and long-time stability of potentiometric CO 2 gas sensors based on the (Li–Ba)CO 3∣NASICON∣(Na–Ti–O) electrochemical cells

Solid-state potentiometric CO 2 sensors were fabricated using Na + conductor (Na 3Zr 2Si 2PO 12) as a solid electrolyte, Li 2CO 3–BaCO 3 fused carbonate with different compositions as a sensing electrode and the Na 2Ti 6O 13–Na 2Ti 3O 7 or TiO 2–Na 2Ti 6O 13 two phase systems as a reference electrode. The measured electromotive force of the investigated cells was found to be linear with the logarithm of CO 2 partial pressure in the range 100–12 600 ppm of CO 2 and in the temperature range 300–500 °C. The response time was ca. 40–120 s. The sensors exhibited reproducible signal during short-time experiments (<24 h). However, the unstable behaviour was observed during long-time measurements (several weeks) in case of some sensors, and it was found to be sensor composition dependent. A sensing mechanism is proposed on the basis of the sensing characteristics obtained. The possible explanation of the observed long-time instability of investigated sensors is also given.

Potentiometric sensor based on NASICON and In 2O 3 for detection of CO 2 at room temperature — modification with foreign substances

In an attempt to improve the CO 2 sensing properties of NASICON (Na + conductor)-based potentiometric device attached with In 2O 3 at room temperature, Na 3PO 4, NaHCO 3 and Na 2CO 3 were introduced as single-components or combinations in the CO 2 sensing layer of the device. Although, the original device suffered disturbance by humidity seriously, the disturbance could be reduced effectively, in some case almost completely, in the resulting modified devices, while the sensitivity to CO 2 could be even promoted. The best device obtained, for which both of Na 3PO 4 and NaHCO 3 were introduced, showed fairly excellent sensing characteristics, i.e. high sensitivity to CO 2 and high resistance to disturbance by humidity at 30°C. The emf of the device was linear to the logarithm of CO 2 concentration in the range 300–3000 ppm following well the Nernst equation for a 1.2 electron-reduction of CO 2.

A carbon dioxide gas sensor based on solid electrolyte for air quality control

A practical CO 2 gas sensor for air quality control is developed by using a combination of a Na 3Zr 2Si 2PO 12 (NASICON) as a solid electrolyte and Li 2CO 3 as a carbonate phase. The sensor's electromotive force (emf) shows a linear relationship with the logarithm of CO 2 concentration. Zeolite is chosen as a filter material in order to minimize the effect of interfering gases on the sensor's emf and shows very little sensor response deterioration to CO 2. Under continuous energizing, both the emf and a change in the emf (defined as Δemf) are stable over a period of 2 years. However, after the sensor is exposed to a high humidity atmosphere in an unpowered state, the emf decreases, but Δemf stays constant. A new data selection method for renewing the standard of the emf is investigated in order to monitor CO 2 concentration using Δemf. The output of the CO 2 monitor corresponds to a conventional non-dispersive infrared (NDIR) analyzer.

Solid electrolyte CO 2 sensor using NASICON and perovskite-type oxide electrode

Solid-state electrochemical sensor devices combined with sodium super ionic conductor (NASICON: Na 1+ x Zr 2Si x P 3− x O 12) discs and perovskite-type oxide electrodes have been developed for the detection of CO 2 in the range of 100–2000 ppm. Among the various sensor devices tested, Co-based perovskite-type oxide electrodes were found to show excellent sensing properties to CO 2 at 200–300°C. Especially, NdCoO 3- and La 0.8Ba 0.2CoO 3-based elements showed the best CO 2 sensing properties, i.e., the sensor response (EMF) was almost linear to the logarithm of CO 2 concentration in the range between 100 and 2000 ppm, the response time to 500 ppm CO 2 was as short as 1–2 min. An open-reference electrode type sensor element, which fitted with NdCoO 3 and La 0.8Pb 0.2CoO 3 for sensing and reference electrodes, respectively, showed excellent CO 2 sensing properties and hardly affected with oxygen partial pressure.

Solid-state electrochemical CO 2 sensor by coupling lithium ion conductor (Li 2CO 3-Li 3PO 4-Asl 2O 3) with oxide ion-electron mixed conductor (La 0.9Sr 0.1MnO 3)

A solid-state electrochemical cell of the type O 2(air), PtLa 0.9Sr 0.1MnO 3 Li 2CO 3(+5 mol% Li 3PO 4 + 6 mol% Al 2O 3)/ Au, CO 2, O 2 was composed to determine CO 2 concentration, where Li 2CO 3, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide (La 0.9Sr 0.1MnO 3) O 2 -electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO 2 partial pressure in CO 2/O 2/N 2 gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO 2 partial pressure within 1 min at 400 °C. The sensitivity to CO 2 of this cell was not affected by coexistence of O 2, and the EMF remained constant after the first 15 days. The mechanism for sensing CO 2 is discussed.

Six-Figure Logarithms, Cologarithms and Antilogarithms

Six-Figure Logarithms, Cologarithms and Antilogarithms

Non-Interpolating Logarithms, Cologarithms and Antilogarithms. By F W Johnson. Pp. x + 117. $2.25. 1931. (Simplified Series Publishing Co., San Francisco)

Non-Interpolating Logarithms, Cologarithms and Antilogarithms. By F W Johnson. Pp. x + 117. $2.25. 1931. (Simplified Series Publishing Co., San Francisco)

Non-Interpolating Logarithms, Cologarithms, and Antilogarithms.

Non-Interpolating Logarithms, Cologarithms, and Antilogarithms.