Electrodeless Conductivity Research Articles

Validation of conductivity tensor imaging against diffusion tensor magnetic resonance electrical impedance tomography

Diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) and electrodeless conductivity tensor imaging (CTI) are two emerging modalities that can quantify low-frequency tissue anisotropic conductivity properties by assuming similar properties underlie ionic mobility and water diffusion. While both methods have potential applications to estimating neuro-modulation fields or formulating forward models used for electrical source imaging, a direct comparison of the two modalities has not yet been performed in-vitro or in-vivo. Therefore, the aim of this study was to test the equivalence of these two modalities. We scanned a tissue phantom and the head of human subject using DT-MREIT and CTI protocols and reconstructed conductivity tensor and effective low frequency conductivities. We found both gray and white matter conductivities recovered by each technique were equivalent within 0.05 S/m. Both DT-MREIT and CTI require multiple processing steps, and we further assess the effects of each factor on reconstructions and evaluate the extent to which different measurement mechanisms potentially cause discrepancies between the two methods. Finally, we discuss the implications for spectral models of measuring conductivity using these techniques. The study further establishes the credibility of CTI as an electrodeless non-invasive method of measuring low frequency conductivity properties.

Conductivity Tensor Imaging of In Vivo Human Brain and Experimental Validation Using Giant Vesicle Suspension.

Human brain mapping of low-frequency electrical conductivity tensors can realize patient-specific volume conductor models for neuroimaging and electrical stimulation. We report experimental validation and in vivo human experiments of a new electrodeless conductivity tensor imaging (CTI) method. From CTI imaging of a giant vesicle suspension using a 9.4-T MRI scanner, the relative error in the reconstructed conductivity tensor image was found to be less than 1.7% compared with the measured value using an impedance analyzer. In vivo human brain imaging experiments of five subjects were followed using a 3-T clinical MRI scanner. With the spatial resolution of 1.87 mm, the white matter conductivity showed considerably more position dependency compared with the gray matter and cerebrospinal fluid (CSF). The anisotropy ratio of the white matter was in the range of 1.96-3.25 with a mean value of 2.43, whereas that of the gray matter was in the range of 1.12-1.19 with a mean value of 1.16. The three diagonal components of the reconstructed conductivity tensors were from 0.08 to 0.27 S/m for the white matter, from 0.20 to 0.30 S/m for the gray matter, and from 1.55 to 1.82 S/m for the CSF. The reconstructed conductivity tensor images exhibited significant inter-subject variabilities in terms of frequency and position dependencies. The high-frequency and low-frequency conductivity values can quantify the total and extracellular water contents, respectively, at every pixel. Their difference can quantify the intracellular water content at every pixel. The CTI method can separately quantify the contributions of ion concentrations and mobility to the conductivity tensor.

Electrodeless conductivity tensor imaging (CTI) using MRI: basic theory and animal experiments.

The electrical conductivity is a passive material property primarily determined by concentrations of charge carriers and their mobility. The macroscopic conductivity of a biological tissue at low frequency may exhibit anisotropy related with its structural directionality. When expressed as a tensor and properly quantified, the conductivity tensor can provide diagnostic information of numerous diseases. Imaging conductivity distributions inside the human body requires probing it by externally injecting conduction currents or inducing eddy currents. At low frequency, the Faraday induction is negligible and it has been necessary in most practical cases to inject currents through surface electrodes. Here we report a novel method to reconstruct conductivity tensor images using an MRI scanner without current injection. This electrodeless method of conductivity tensor imaging (CTI) utilizes B1 mapping to recover a high-frequency isotropic conductivity image which is influenced by contents in both extracellular and intracellular spaces. Multi-b diffusion weighted imaging is then utilized to extract the effects of the extracellular space and incorporate its directional structural property. Implementing the novel CTI method in a clinical MRI scanner, we reconstructed in vivo conductivity tensor images of canine brains. Depending on the details of the implementation, it may produce conductivity contrast images for conductivity weighted imaging (CWI). Clinical applications of CTI and CWI may include imaging of tumor, ischemia, inflammation, cirrhosis, and other diseases. CTI can provide patient-specific models for source imaging, transcranial dc stimulation, deep brain stimulation, and electroporation.

Co-treatment of converter slag and pyrrhotite tailings via high pressure oxidative leaching

High pressure oxidative acid leaching (HPOXAL) was successfully applied to slow-cooled converter slags from Vale's operations in Sudbury (Ontario, Canada). Extractions of Ni, Co and Cu exceeded 90% within 15–20 min and levelled at 95–97% after 45 min at 250 °C, 90 psi O 2 overpressure and 70 g/L initial H 2SO 4. Pyrrhotite tailings with ∼0.6% Ni content were also tested as a source of sulphuric acid in high pressure oxidation. Co-leaching of pyrrhotite tailings with converter slags at the same temperature, oxygen partial pressure and equivalent stoichiometric H 2SO 4 was found to have kinetics similar to that of leaching with sulphuric acid. Lowering the addition of pyrrhotite tailings (and hence, the acidity) was found to have a detrimental effect on the kinetics of leaching and final extractions (especially at 250 °C), and cause precipitation of metal sulphates. Continuous on-line acidity measurements were facilitated in experiments with an electrodeless conductivity sensor. It was shown that acid plays a major role in the conversion of fayalite to hematite and silica, and the dissolution of the base metals, while oxygen overpressure (or dispersion efficiency) determines the rate of acid generation and re-generation.

High-Temperature Conductivity Measurements of Concentrated NaCl−H2SO4−H2O Solutions up to 250 °C

An electrodeless conductivity cell was employed to investigate the electrical conductivity of concentrated NaCl−H2SO4−H2O solutions particularly at high temperatures. All solutions were measured from 25 to 250 °C at the equilibrium vapor pressures. The maximum measured concentrations of NaCl and H2SO4 were 0.40 and 0.45 m, respectively. At 250 °C and a fixed concentration of H2SO4, the conductivity of NaCl−H2SO4−H2O solutions increases with the increasing concentration of NaCl. Similarly, at 250 °C and a fixed concentration of NaCl, the conductivity of NaCl−H2SO4−H2O solutions increases with the increasing concentration of H2SO4. It was found that the ionic equivalent conductivity of H3O+ is a function of ionic strength at 250 °C and is independent of the solution speciation.

Evaluation of a new approach for the estimation of the time of the LH surge in dairy cows using vaginal temperature and electrodeless conductivity measurements

The objective of the study was to test the effectiveness of a new type of conductivity sensor, along with vaginal temperature, at identifying the LH peak associated with estrus in dairy cows. Twelve mature non-lactating Holstein–Friesian cows had their estrous cycles synchronized on two occasions, and then data were collected for the following spontaneous cycles. An indwelling electrodeless plastic-coated toroidal conductivity sensor, which also recorded temperature, was placed in the vagina throughout the cycle. Blood samples were collected for LH measurement, and ultrasound scanning used to confirm ovulation. Although there was a relationship between vaginal mucus conductivity measured by the toroidal sensor and the timing of the LH surge, it was not sufficiently robust in individual cows to be able to identify the time of the LH surge. The mean increase in vaginal temperature at estrus was 0.48 °C. An algorithm was developed which used the detected individual cow temperature peak to test the relationship with the LH peak. In 16 out of 21 cases where ovulation was confirmed and data existed, the estimated individual peak was within 4 h of the LH surge, in three cases it was ±6 h, and in two instances it was early. In conclusion, the temperature algorithm was able to identify the time of the LH surge and thus predict time of ovulation in a way that would allow effective AI, although this result needs to be tested in lactating cows. However, the toroidal conductivity sensing method was not able to produce data of sufficient quality to develop a predictive relationship in individual cows.

ONLINE FREE ACIDITY MEASUREMENT OF SOLUTIONS CONTAINING BASE METALS

Electrodeless conductivity was employed to investigate the feasibility of continuous online monitoring of the free acidity of sulphate and/or chloride solutions of Cu and other base metals from various hydrometallurgical processes. These solutions were measured with both commercial and experimental electrodeless conductivity sensors from 15 to 250 °C. It was confirmed that hydrogen ion has the greatest impact on conductivity by carrying the bulk of the current because it is the most mobile ion. In combination with a solution speciation analysis the conductivity sensor can be calibrated to account for the contribution of Cu electrolytes as well as other dissolved salts allowing fast and accurate online measurement of free acid. The sensor was tested at both lab and pilot scale with very good performance. The average difference between the measured and the titrated acid concentration was less than 5%, which is excellent for industrial applications.On a employé la conductivité sans électrodes pour investiguer la faisabilité de surveillance continue en ligne de l’acidité libre de solutions de sulfate et/ou de chlorure de Cu et d’autres métaux de base de divers procédés d’hydrométallurgie. On a mesuré ces solutions avec des capteurs de conductivité sans électrodes tant commerciaux qu’expérimentaux dans la gamme de 15 à 250 °C. On a confirmé que l’ion hydrogène avait le plus grand impact sur la conductivité en transportant la majorité du courant parce que c’est l’ion le plus mobile. En combinaison avec une analyse de spéciation de solution, on peut calibrer le capteur de conductivité pour tenir compte de la contribution des électrolytes de Cu ainsi que d’autres sels dissous, permettant la mesure en ligne rapide et précise de l’acide libre. On a évalué le capteur tant au laboratoire qu’à l’échelle pilote avec un très bon rendement. La différence moyenne entre la concentration d’acide mesurée et titrée était de moins que 5%, ce qui est excellent pour les applications industrielles.

Electrical Conductivity of Concentrated H2TiF6 + HF + H2O Mixtures

The electrical conductivity of H2TiF6 (1) + HF (2) + H2O (3) mixtures was measured in a wide range of mass fractions (0% < w1 < 55% and 0% < w2 < 11%) and temperature (15 °C < t < 35 °C) by means of an automatic system based on the “electrodeless conductivity” technique. The results were fitted to a polynomial equation in w1, w2, and t using a Mathematica package (Tkondu). The resulting model is able to reproduce experimental data with an uncertainty below 5%.

Application of the electrical conductivity of concentrated electrolyte solutions to industrial process control and design: from experimental measurement towards prediction through modelling

Different aspects of the conductivity of concentrated electrolyte solutions and their application to design and control of chemical processes are discussed and reviewed, with particular focus on the work of our research group during the last few years. An automated system based on the electrodeless conductivity technique for the measurement of the electrical conductivity of solutions as the basis of a titration strategy is described. The inadequacy of classical calibration methods when high conductivities are to be measured is highlighted and an alternative methodology is proposed. Our measurements on specific concentrated systems of interest in industrial applications and the development of general methodologies to treat experimental conductivity data at constant or varying temperature in order to get comprehensive inter- and extrapolation mathematical models are summarised. Theoretical approaches to explain the variability of conductivity data of electrolyte solutions with the solute concentration as well as the deviations from ideality found at higher concentrations are reviewed and critically evaluated. Solutions of mixed electrolytes are treated in a similar fashion.

Electrical Conductivity of Concentrated Aqueous Mixtures of HCl and KCl in a Wide Range of Compositions and Temperatures

The electrical conductivity of the HCl + KCl + H2O ternary system has been measured in a wide range of compositions (0 mol·dm-3 < cHCl < 6 mol·dm-3 and 0 mol·dm-3 < cKCl < 1.2 mol·dm-3) and temperatures (15 °C < t < 45 °C) making use of an automated station for conductometric titration based on the “electrodeless conductivity” technique. The experimental data obtained have been fitted to a polynomial in the HCl molar concentration, the KCl molar concentration, and the temperature. As a result, an empirical model enabling the interpolation of the conductivity of the chemical system under study within the limits of the variables investigated has been proposed.

In-Situ Chemical Concentration Control for Wafer Wet Cleaning

This paper demonstrates the use of conductivity sensors to monitor and control the concentration of RCA cleaning and hydrofluoric acid (HF) etching solutions. Commercially available electrodeless conductivity sensors were used to monitor and control the concentration of these process solutions. A linear relationship between the conductivity of the solution and the chemical concentration was obtained within the range studied. A chemical injection scheme was developed to maintain the chemical concentration within specified limits. Different concentrations of RCA-based cleaning solutions and HF solutions were investigated. Results show that these techniques are suitable for monitoring and controlling the concentration of chemicals in the process tanks for better process control. These techniques provide low cost of ownership of the process by using dilute chemicals and longer bath life (i.e., a more environmentally sound process).

Conductivity of Concentrated Aqueous Solutions of Several Fluorine-Containing Electrolytes in a Wide Range of Concentrations and Temperatures

Specific conductivities (κ) of concentrated aqueous solutions of several fluorine containing electrolytes, fluoroboric acid (HBF4), fluorosilicic acid (H2SiF6), and fluorotitanic acid (H2TiF6), at mass percents (100wAc) from 10 to 50 at 15, 25, 35, and 45 °C have been measured by making use of an automatic system based on the “electrodeless conductivity” technique. The results have been analyzed in terms of the well-established Casteel−Amis equation and by polynomial equations in the concentration. As a result, empirical models of the type κ = f(100wAc)t have been proposed, which reproduce the results of each chemical system with an overall precision of about ±0.3% and enable the interpolation of conductivity at each temperature in the whole range of concentration studied.

Effect of Additional Hydrofluoric Acid on the Conductivity of Concentrated Fluorosilicic Acid Aqueous Solutions

The specific conductivities (κ) of the H2SiF6 + HF + H2O ternary system have been measured in a wide range of compositions, 8 < 100wH2SiF6 < 45 and 0 < 100wHF < 12, at 25 and 35 °C by an automated system for conductimetric titration based on the “electrodeless conductivity” technique. An empirical model of the type κ = f(100wH2SiF6, 100wHF), which correctly fits the results at the two temperatures studied, is also presented.

In-Situ Chemical Concentration control cor Wafer Wet Cleaning

ABSTRACTThe continuously increasing integration of today's advanced semiconductors requires increasingly tight process control in the IC manufacturing steps. This paper demonstrates the use of conductivity sensors to monitor and control the chemical concentrations of RCA cleaning and HF etching solutions. Electrodeless conductivity sensors were used to monitor and regulate the concentration of these process chemicals. A linear relationship between the conductivity of the solution and the chemical concentration was obtained within the range studied. A chemical monitoring and concentration scheme (ICE-1™) was developed. Different concentrations of RCA and HF solutions were investigated. Results show that these techniques are suitable for monitoring and controlling the concentration of chemicals in the process tanks for better process control. These techniques provide a lower cost of ownership of the process due to longer bath lives and the use of dilute chemicals.

Investigation of electrodeless conductivity as a technique for monitoring sulfate levels during production of wet-process phosphoric acid

In the production of wet-process phosphoric acid (WPA), sulfate concentrations influence both the crystal form and growth rate of calcium sulfate and hence the filtration rate for separating calcium sulfate from the product WPA. The filtration rate must be rapid to maintain high rates for the production of WPA. One approach for continuously monitoring sulfate concentrations during production of WPA is to measure the electrical conductivity, temperature, and specific gravity of WPA, and then relate these data to the sulfate concentration using regression equations. An electrodeless conductivity probe was used to provide reproducible conductivity measurements in return acids (12–32% P2O5) used for the production of WPA (24–36% P2O5). The effect of iron, aluminum, and magnesium impurities on the conductivity measurements was also evaluated. Regression equations were developed from the data which can be used to accurately calculate P2O5 and sulfate concentrations in return acids within a specified temperature range.

Electrodeless conductivity

Electrodeless conductivity is a technique for measuring the concentration of electrolytes in solution and utilizes a probe consisting of two toroids in close proximity, both of which are immersed in the solution. In special cases, the toroids may be mounted externally on insulated pipes carrying the solution. One toroid radiates an alternating electric field in the audiofrequency range and the other acts as a receiver to pick up the small current induced by the ions moving in a conducting loop of solution. Coatings which would foul contacting electrodes, such as suspensions, precipitates or oil, have little or no effect. Applications are chiefly to continuous measurement in the chemical processing industries, including pulp and paper, mining and heavy chemical production. The principles and practical details of the method are reviewed and cell-diameter, wall, and temperature effects are discussed.

Frequency effects in the inductive measurement of electrical conductivity

The electrical theory and equivalent circuit of an inductive and electrodeless conductivity device are described. Predictions based on theory are compared with measurements using fluid samples of known conductivity. The general trend of the device response as the frequency is varied is shown to agree with theory. A simple model of the induced current flow in the fluid sample is proposed which relates the electrical properties of the device to the conductivity of the fluid in which it is immersed.

Design and construction of a high temperature and pressure electrodeless conductivity probe

An electrodeless conductivity probe has been designed and tested at temperatures up to 250 degrees C and pressures of 4.13 MPa (600 psi). A unique pressure seal permits temperature cycling. Design of the electronics permits accurate measurement of conductivities at various elevated temperatures in spite of the change of magnetic properties of the toroids with temperature. The design of the probe can be adapted for insertion, in-line, or bypass operation.

ChemInform Abstract: FURTHER STUDIES ON THE SOLID‐STATE CHEMISTRY OF IRRADIATED CHOLINE CHLORIDE

The remarkable radiation sensitivity of crystalline choline chloride has been investigated by studies of infrared and ESR spectra, photochemical transformation of radicals, microwave electrodeless conductivity, and exposure to hydrogen atoms, vacuum ultraviolet, and thermal electrons. These studies lend support to the involvement of both ethanol radicals and electrons in the chain decomposition. They also show that hydrogen atoms can induce the decomposition. These observations indicate that during subsequent thermal treatment of γ‐irradiated choline chloride, the detrapped electrons interact with ethanol radicals to form hydrogen atoms, which propagate the chain decomposition.

Further studies on the solid-state chemistry of irradiated choline chloride

The remarkable radiation sensitivity of crystalline choline chloride has been investigated by studies of infrared and ESR spectra, photochemical transformation of radicals, microwave electrodeless conductivity, and exposure to hydrogen atoms, vacuum ultraviolet, and thermal electrons. These studies lend support to the involvement of both ethanol radicals and electrons in the chain decomposition. They also show that hydrogen atoms can induce the decomposition. These observations indicate that during subsequent thermal treatment of γ-irradiated choline chloride, the detrapped electrons interact with ethanol radicals to form hydrogen atoms, which propagate the chain decomposition.