Galvanic Sensor Research Articles

A Galvanic Sensor for Monitoring the Corrosion Damage of Buried Pipelines: Part 3—Correlation of Probe Current to Cathodic Protection and Stray Current

Abstract In order to develop a new corrosion sensor for monitoring the status of cathodic protection of buried pipelines, the correlation of sensor output to protection abilities (protection potential and current) was evaluated using two types of laboratory tests. The galvanic sensor uses the well-known principle of galvanic corrosion and consists of two dissimilar metals (acting as the anode and cathode) installed in the soil near the pipeline. In this paper, a copper-pipeline steel (Cu-CS) probe was used. The cathodic protection status of the pipeline was simulated by a galvanostatic test. The galvanic current density was measured using a zero-resistance ammeter for the Cu-CS probe with the anode (CS) either connected or disconnected to the pipeline. The results showed a good correlation between the protection potential/current of the pipeline and the sensor output. Especially when the protection current was induced to the pipeline, the measured sensor current was negative (−), whereas when the stray cu...

A Galvanic Sensor for Monitoring the Corrosion Damage of Buried Pipelines: Part 2—Correlation of Sensor Output to Actual Corrosion Damage of Pipeline in Soil and Tap Water Environments

Abstract To develop a new corrosion sensor for detecting and monitoring the external and internal corrosion damage of buried pipeline, the correlation of its output to the corrosion rate of steel p...

Technical Note:Measuring Corrosiveness with a Dual Galvanic/Surface Film Resistance Sensor

Abstract A galvanic sensor system designed to measure atmospheric corrosiveness within an aircraft was modified to also measure surface film resistance. Its response to four laboratory conditions was compared to the mass loss of an aircraft alloy, UNS A92024. The experimental factors were relative humidity (RH) and level of sodium chloride (NaCl). The amount of salt added was equivalent to the cumulative deposition of salt aerosols at a marine site for one week. The four conditions were (a) low RH with no salt added, (b) high RH with no salt added, (c) low RH with salt added, and (d) high RH with salt added. The mass loss of UNS A92024 plates was above that due to cleaning alone for conditions (b), (c), and (d), whereas the galvanic sensor only responded to the most severe condition (d). The galvanic current declined with time when exposed to the same environment in a manner consistent with the development of mass-transfer limitations of oxygen for the cathodic reaction. Implications for improving the des...

A Galvanic Sensor for Monitoring the Corrosion Damage of Buried Pipelines: Part 1—Electrochemical Tests to Determine the Correlation of Probe Current to Actual Corrosion Damage in Synthetic Groundwater

Abstract In order to develop a new corrosion sensor for detecting and monitoring the corrosion of buried pipelines, sensor element design and the correlation of its output to the corrosion rate of ...

Development of a galvanic sensor system for detecting the corrosion damage of the steel embedded in concrete structure: Part 2. Laboratory electrochemical testing of sensors in concrete

The correlation between sensor output and the corrosion rate of steel bar was confirmed in concrete environment. Open-circuit potential, linear polarization resistance (LPR) measurement and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of steel bar embedded in concrete. Also, galvanic current measurements of designed sensors were conducted to obtain the charge of sensor embedded in concrete. In this study, the results of corrosion behavior of reinforcing steel showed a consistence among the data obtained by open-circuit potential monitoring, LPR and EIS measurements. Steel/copper sensor showed a good correlation in concrete environment between sensor output and corrosion rate of steel bar. However, there was no relationship between steel/stainless steel sensor output and corrosion rate of steel bar due to the low galvanic current output. Through the relationship between the steel/copper sensor output and the corrosion rate of reinforcing steel, the real corrosion damage of the reinforcing steel can be detected. Consequently, this confirms that the galvanic sensor system is a good method for detection of corrosion in reinforced concrete.

Probing of Atmospheric Corrosion of Metals: Carbon Steel

The methods of scanning vibrating capacitor (SVC, Kelvinprobe), IR microscopy (IRM), and galvanic current sensor are used in studying the atmospheric corrosion of carbon steel with locally applied NaCl. The SVC method is shown to give insight to the electrochemical heterogeneity of the surface. The distribution of cathodic and anodic domains is found by the IRM analysis of corrosion products. The passive surface of steel around the applied chloride takes part in the cathodic reaction of the corrosion process. The currents of the corrosion macrocell constituted by a chloride-covered anode domains and surrounding it cathodic area are measured by the sensor in humid air. From the areas of cathodic and anodic domains, the partial current ratio and the limiting stage of corrosion are found. The mechanism of galvanic couple formation and inhibition is discussed.

GAS COMPOSITION AND OXYGEN SUPPLY IN THE ROOT ENVIRONMENT OF SUBSTRATES IN CLOSED HYDROPONIC SYSTEMS

The objective of this study was to get more information about the root zone, mainly the gas composition in substrates, which are used in closed hydroponic systems. For analyses of carbon dioxide (CO2), ethylene (C2H4) and oxygen (O2) different methods were proved and used. For analyses of carbon dioxide and ethylene, a gas sampling system was used to get gas samples from the root zone. CO2 gas samples of 20 ml were analyzed with an IR sensor by air diffusion into a measuring cuvette. C2H4 gas samples of 3 ml were analyzed using gas chromatography (GC). Gas sample cells were inserted into the substrates at 2 or 3 heights. Dissolved oxygen was determined with a membrane covered galvanic sensor, in the air, in the in the nutrient solution, and in the drain solution. To analyze the root zone, a hydroponic system with chrysanthemum cv. 'Snow' on 3 substrates was performed. The following substrates were used: Sawagrow (polyester fiber), polyester fleece (thin layer of fleece), and UC-mix (peat substrate). Gas sampling at 2 or 3 heights from root zone did function well, results ranged from 350 ppm to 7700 ppm CO2, and from 0.0088 ppm to 0.1147 ppm of C2H4. The organic substrates UC-mix contains more CO2, from top to the bottom the CO2 level increased. The CO2 level is influenced by microbial and root respiration. The determined CO2 concentration is no limiting growth factor. Results of C2H4 shown an influence by the substrates and a gradient from the top to the bottom. But highest level was determined in the middle and at the bottom of the substrates. The time course shows during the day pattern according the photoperiod. The trend of C2H4 level was almost constant during the experiment. The dissolved O2 level in solution was about 57-82% and in drain solution 78%-99%. O2 level of solution and drain can be an indicator for oxygen deficiency, but it is no direct measurement in root zone or roots. The O2 content in air between 10.5% to 20.4%. During the experiment the O2 concentration decreased; for CO2 the opposite trend was found. INTRODUCTION Plant growth in closed hydroponic systems, with restricted root environment, and consequently, low buffering capacity is more related to water, nutrient solution, and oxygen supply. Water and nutrients are supplied with the nutrient solution, which is regulated by the composition of the solution and irrigation control. Available oxygen is mainly determined by the layout of the hydroponic system and the physical substrate properties. The oxygen diffusion rates into the water depends directly on volumetric air content, the partial oxygen pressure, and temperature. Within the hydroponic systems there is an oxygen gradient for design flow techniques and flow rates (Vestergaard, 1984; Bunt, 1991; Baas et al. 2000; Wever et al., 2000). In addition, the substrate parameters change at the end of each crop, due to decomposition of organic substrates or root and increasing root mass (Wever and van Leeuwen, 1995). Oxygen deficiency may be a limiting factor for plant growth. Oxygen deficiency can be tolerated by roots for a short time, even for several days (Buwalda, 1991; Gislerod et al., 1997; Yosida et al., 1997). Proc. IS on Growing Media Eds.: Alsanius, Jensen & Asp Acta Hort 644, ISHS 2004

Galvanic CO2 sensor with Li2O: B2O3 glass ceramics based composite

In order to develop an electrolyte with better thermal-stability, a new composite is prepared by partially crystallizing the lithium borate glass along the grain boundaries of Li2CO3: BaCO3 binary system. Highly dense material is obtained on controlled partial crystallization. The structural and electrical characterization proved its composite nature with enhancement in conductivity. A few potentiometric CO2 gas sensors prepared by using optimized composite electrolyte with lithium titanate as the reference electrode. This configuration resulted in a device of high mechanical strength with ease of fabrication and free from interfacial failures. Reproducible and reversible response is obtained for these sensors over a long-term operation at lower temperatures (275 – 450 °C). The sensor response found to obey Nernst relation with sensitivity and emf approaching the theoretical value.

Development of a galvanic sensor system for detecting the corrosion damage of the steel embedded in concrete structures: Part 1. Laboratory tests to correlate galvanic current with actual damage

The correlation between sensor output and corrosion rate of reinforcing steel was evaluated by laboratory electrochemical tests in saturated Ca(OH) 2 with 3.5 wt.% NaCl. In this paper, two types of electrochemical probes were developed: galvanic cells containing of steel/copper and steel/stainless steel couples. The corrosion behavior in saturated Ca(OH) 2 solution with and without 3.5 wt.% NaCl addition for the different electrodes was investigated by potentiodynamic test. Weight loss measurement and galvanic corrosion test were conducted to obtain the corrosion rate of reinforcing steel and the charge of sensor in saturated Ca(OH) 2 solution with 3.5 wt.% NaCl addition, respectively. The results of the potentiodynamic test indicated the possibility of detecting an ingress point of chlorides by measuring the galvanic current. In galvanic corrosion tests, the galvanic current of steel/copper couple was higher than that of steel/stainless steel couple, i.e., the steel/copper sensor is more suitable for high resistance environment. The steel/stainless sensor showed a better linear correlation than the steel/copper sensor. Through the relationship between the sensor system output and the weight loss (mg/cm 2) of steel, real corrosion damage of the steel embedded in concrete can be detected.

Continuous monitoring for cyanide in waste water with a galvanic hydrogen cyanide sensor using a purge system

A continuous monitoring system for cyanide with a galvanic hydrogen cyanide sensor and an aeration pump for purging was developed. Hydrogen cyanide evolved from cyanide solution using a purging pump was measured with the hydrogen cyanide sensor. The system showed good performance in terms of stability and selectivity. A linear calibration curve was obtained in the concentrating range from 0 to 15 mg dm3 of cyanide ion with a slope of −0.24 μA mg−1 dm−3. The lower detection limit was 0.1 mg dm−3. The 90% response time of the sensor system was within 3.5 min for a 0.5 mg dm−3 cyanide solution, when the flow rate of the purging air was 1 dm3 min−1. The system maintained the initial performance for 6 months in the field test. The developed galvanic sensor system was not subject to interference from sulfide and residual chlorine, compared with a potentiometric sensor system developed previously. The analytical results obtained by the present system were in good agreement with those obtained by the pyridine pyrazolone method. The correlation factor and regression line between both methods were 0.979 and Y=2.30×10−4+1.12X, respectively. This system was successfully applied for a continuous monitoring of cyanide ion in waste water.

Humidity sensing characteristics of manganese oxide prepared by sol-gel method

Electrolytic manganese dioxide (EMD), which has been commonly used as a cathode material in drycell batteries, catalyst and water puri®cation material, is a typical example of a multifunctional material. Xu and Miyazaki [1, 2], found that EMD derivatives could be utilized for humidity sensor materials [1], and developed a resistance-type humidity sensor with a high sensitivity and selectivity [2]. Recently, a new potential-type humidity sensor consisting of EMD solid electrolyte with two electrodes of different metals, such as Pt=Cu or Pt=Al, was explored [3, 4]. The humidity sensing properties were strongly dependent on the features of manganese oxides such as crystalline structure and powder morphology, so further research was needed for the development of an ef®cient humidity sensing system. The sol±gel process based on inorganic polymerization reaction from molecular precursors has provided a new approach to the preparation of inorganic materials [5]. This process has allowed better control of the characteristics of oxide powders. Bach et al. [6] reported the synthesis of manganese oxides via a sol±gel route in detail. Le Goff et al. [7, 8] investigated the structural and electrochemical properties of sol±gel-derived manganese oxides and revealed that these oxides were promising rechargeable cathodic materials for lithium batteries. In this study, the potential-type humidity sensing characteristics of manganese oxide samples prepared by a sol±gel method were evaluated in comparison with an International Common EMD sample no. 14 (IC no. 14 EMD). The sol±gel-derived manganese oxide powder was prepared by the following method, as reported by Bach et al. [6]. A 0.25 M aqueous potassium permanganate solution was mixed with an organic reducing agent, such as fumaric acid solution. The molar ratio of potassium permanganate to fumaric acid was ®xed at 3. Under this condition, a darkbrown transparent gel of KMnO2 was rapidly formed at room temperature. The gel was ®ltered and dried in air at 90±100 8C, giving a black xerogel powder. This KMnO2 xerogel was treated with a 2.5 M sulphuric acid solution for 5 h at room temperature to remove potassium. After the sulphuric acid treatment, the resulting manganese oxide powder was washed by decanting, neutralized with an ammoniacal aqueous solution, ®ltered and dried in air at 90±100 8C. The potassium content of the sample was analysed using a ame spectrophotometer (Shimadzu AA6400F). The crystal structure was characterized by X-ray diffraction (XRD); Mac Science M03X-HF) using CuKa radiation, and the Brunauer±Emmet± Teller (BET) surface area was measured with an adsorption porosimeter (Micromeritics ASAP 2000). The potential-type humidity sensor constituting a galvanic-type cell system was used in this work. The electrochemical cell system is in the form of Pt=MnOx=Al, where Pt and Al act as the cathode and anode, respectively, and MnOx (manganese oxides) act as the solid electrolyte. To fabricate a sensor element, each of the manganese oxide samples under examination was ground in an agate mortar and wetted with ethanol, then the resulting paste was coated onto a mullite tube (1.0 mm in diameter) with Pt and Al ®lament electrodes (0.25 mm in diameter). The electrodes were embedded in the coated MnOx layer to ensure that an electrical contact was made. The thickness of the MnOx layer was approximately 0.3 mm. The sensor element was placed in a test chamber where the humidity was controllable, as shown in Fig. 1. The electromotive force (EMF) by the galvanic cell-type sensor was measured at room temperature by means of an ADVANTEST-TR2114 digital voltmeter (internal impedance . 10 U), and the impedance of the sensor element containing MnOx was of the order of 10 U [4], which is well within the meaningful range of measuring impedance in this case. A sample of sol±gel-derived manganese oxide produced an almost amorphous XRD pattern, as shown in Fig. 2. The potassium content within this

Solid electrolyte probes for strontium employing a [formula omitted] reference and thermodynamic evaluation of the SrCl 2-AgCl system

A high-temperature galvanic sensor for strontium has been developed consisting of a closed-end tube of Sr-β alumina or Sr-β″ alumina containing a reference electrode consisting of a molten SrCl 2-AgCl solution in contact with a Ag wire. Measurements of the following cell are reported: Ag; (AgCl-SrCl 2) ¦ Sr-β or Sr-β″ alumina ¦ (AgCl-SrCl 2); Ag with different compositions of the salt solutions in the two electrodes. The cells are reversible, respond rapidly to temperature changes, and give emfs stable over several hours. Absolute reproducibility of ±2 mV is obtained, and results agree with the theoretical emf calculated thermodynamically. In order to obtain the thermodynamic properties of the liquid AgCl-SrCl 2 solutions required for the calculation of the theoretical emf, a critical evaluation and optimization of the thermodynamic properties and phase diagram of the AgCl-SrCl 2 system was carried out.

Behm's T-piece for reducing anesthesia gas pollution at the anesthesia work site

The safety standards demanded for performing anaesthesia and the increasing burden of work to be handled by OP personnel entail continuous supervision and elimination of hazards and leaks. One example illustrates this necessity: Anaesthetic agents in the circular system of the induction are pollute the atmosphere after disconnection of one patient and transport into the OP suite and are a potential risk to personnel and next patient. C. Behm developed a T-piece which connects the Y-piece with the scavenging system leading to elimination of residual anaesthetics from the circular system. A useful byproduct is the longer life of the galvanic O2 sensor.

Electrochemical solid-state micro-sensor for hydrogen determination

An electrochemical galvanic sensor for hydrogen determination in air is reported. It is based on a solid-state electrolyte with high proton conductivity at an ambient temperature, regeneratable electrode materials and is fabricated with planar technology as a pellet with the dimensions 12 × 5 mm and mass ∼5 g. During the sensor function the gas molecules are oxidized on the sensitive electrode connected with the counter electrode which contains as a catalyst macrocyclic or macrobicyclic polyaza cobalt(III) complexes. The sensor shows good sensitivity, stability and repeatability of the output signal, sufficient response time − T 90 is less than 15 s, low humidity dependency and long operating life of up to several years.

Novel approaches to galvanic oxygen analysis

This communication describes two modifications of a remarkably inexpensive galvanic membrane-covered oxygen sensor, presented in a recent paper. An oxygen sensor and a corresponding simple device were developed for extending the measurement range to less than 1 µg l–1. In this sensor a tubular supporting cathode from Ni—Cu alloy was located under a tubular cathode. The current in the circuit supporting cathode-anode was opposed to the current in the circuit cathode-anode, so automatically eliminating the residual current caused by the reduction of impurities and traces of oxygen in the electrolyte solution. With the aim of developing an oxygen sensor for low temperatures an electrolyte solution, containing C2H5OH, KOH and H2O, was utilized for filling the interior of the sensor, so preventing the freezing of the electrolyte solution at low temperatures (up to –40 °C). The operating characteristics of the trial sensors were equal or even better than those of the basic construction.

An improved Clark-type galvanic sensor for dissolved oxygen

A novel Clark-type galvanic oxygen sensor has been fabricated, in which the indicator electrode is made from an industrially produced Ni Cu alloy containing ≃ 30% Ni. The exposed are of the tubular-shaped indicator electrode is about 10 cm 2. The anodeis prepared from cadmium. The sensor is filled with 6 M aqueous KOH solution. The 95% response time of the device is on average 50 s, its residual current at zero oxygen concentration is negligible, its lifetime is one to two years, its output-current variation is less than 5% in a one-year period and an excellent linear calibration curve for oxygen concentrations in the range 0–17 mg l −1 is observed.

Design of solid electrolytes for use with dissimilar gas electrodes

The design of a solid electrolyte that permits the use of dissimilar gas electrodes in an electrochemical cell is presented. It consists of a functionally gradient material with spatial variation in composition. The activity of the conducting ion is fixed at each electrode using different gas species. The system chosen for demonstrating the concept consists of a solid solution between K2CO3 and K2SO4. The composition of the solid solution varies from pure K2CO3 in contact with a CO2 + O2 gas mixture at one electrode to pure K2SO4 exposed to a mixture of SO3 + SO2 + O2 at the other. Two types of composition profiles are studied, one with monotonic variation in composition and the other with extrema. The e.m.f. of the cells is studied as a function of temperature and composition of the gas mixture at each electrode. The results indicate that the e.m.f. is determined primarily by the difference in the chemical potential of potassium at the two electrodes. The diffusion potential caused by ionic concentration gradients in the electrolyte appears to be negligible when the corresponding ionic transport numbers are insignificant. Studies on the response characteristics of the cell based on the gradient electrolyte indicate that the nature of the variation in composition of the electrolyte has only a minor effect on the time evolution of e.m.f. The gradient solid electrolytes have potential application in multielement galvanic sensors at high temperatures.

Theoretical Analysis of the Electromotive Force of a Cell Incorporating a Composition Gradient Solid Electrolyte

New composition gradient solid electrolytes have been designed for application in high temperature solid‐state galvanic sensors and in thermodynamic measurements. The functionally gradient electrolyte consists of a solid solution between two or more ionic conductors with a common ion and gradual variation in composition of the other ionic species. Unequal rates of migration of the ions, caused by the presence of the concentration gradient, may result in the development of space charge, manifesting as diffusion potential. Presented is a theoretical analysis of the EMF of cells incorporating gradient solid electrolytes. An analytical expression is derived for diffusion potential, using the thermodynamics of irreversible processes, for different types of concentration gradients and boundary conditions at the electrode/electrolyte interfaces. The diffusion potential of an isothermal cell incorporating these gradient electrolytes becomes negligible if there is only one mobile ion and the transport numbers of the relatively immobile polyionic species and electrons approach zero. The analysis of the EMF of a nonisothermal cell incorporating a composition gradient solid electrolyte indicates that the cell EMF can be expressed in terms of the thermodynamic parameters at the electrodes and the Seebeck coefficient of the gradient electrolyte under standard conditions when the transport number of one of the ions approaches unity.

Galvanic sensor for determination of hydrogen sulfide

AbstractA galvanic cell for trace determination of hydrogen sulfide in gases is presented. The cell covers the range from 30 ppb to some hundred ppm. It is characterized by simple construction. The use of ferricyanide/ferrocyanide ions as a redox mediator system ensures very low cross sensitivity. The sensor is well‐suited for mobile use.

Galvanic sensor for the determination of hydrogen sulphide/sulphide in aqueous media

A simple galvanic cell without any external voltage for the trace determination of hydrogen sulphide is described. The signal corresponds to the concentration of the dissolved molecular H2S. For the calculation of total sulphide, the pH has to be taken into consideration. The sensor was tested in the range of concentration from 3·10−6 mol/l H2S to 9·10−5 mol/l H2S for pH<5. For pH 7.8 it covers a range from 1·10−6 mol/l H2S to 1·10−5 mol/l H2S. The sensitivity of the sensor substantially depends on the pH of the aqueous medium.