Hydrogen Ions In Solution Research Articles

(Invited) CMOS-Based Multimodal Sensing

In the coming Society 5.0, information will be collected, aggregated, and utilized in a wide range of areas through the IoT, and as the concept of "Trillion Sensors" states, the importance of "sensors" as an interface between physical space and cyberspace is increasing. In the development of sensor devices to meet this demand attempts to realize the sensing of multiple items by integrating single-function sensors with high detection selectivity have been the main focus in the past. On the other hand, our research group has proposed the measurement concept of multimodal sensing, in which sensors with broad detection characteristics are used to realize the sensing of multiple items, and has developed semiconductor CMOS-based sensors to realize this concept. In this talk, we introduce ion image sensors and odor sensors as examples of CMOS-based sensors suitable for multimodal sensing, and data analysis using machine learning, which is important for this measurement concept will be mentioned and introduce an example of machine learning-based sensing. The application of these sensors to smart agriculture and other fields will also be discussed, as well as the current status and issues for the practical application of sensor systems.An ion-sensitive transistor (ISFET) can be fabricated by changing the MOSFET's gate to an ion-sensitive membrane. An ion image sensor can be constructed by arraying ion-sensitive elements that operate based on the same principle using CMOS image sensor technology. This sensor visualizes the solution's hydrogen ion concentration (pH) and enables real-time observation of ion dynamics in the solution. By changing the ion-sensitive membrane of the sensor, it is possible to image specific ions such as potassium and calcium, and by adding an enzyme-immobilized membrane, it is also possible to capture chemical substances such as lactic acid. By combining these methods, the development of a multimodal sensor that can simultaneously image multiple ions and chemical substances is in progress as an approach from the hardware side. The future approach from the software side is expected to include measurement data processing by machine learning, thereby expanding the range of substances to be measured. In addition, making this sensor extremely thin makes it possible to perform ion imaging by inserting it into the object to be measured. Functional demonstration of visualization of ion distribution in a plant stem has been performed successfully, and we are currently studying its application in the field of smart agriculture.Since the ion image sensor mentioned above captures minute changes in electric potential generated by ion-sensitive membranes, it can be operated as a gas sensor by forming a membrane on the sensor whose electric properties change depending on gas adsorption. Certain polymer membranes respond to a wide range of gases, they can be used as odor-sensitive membranes. When multiple gas- and odor-sensitive membranes with different response characteristics are formed on a CMOS sensor, gas- and odor-specific response patterns can be obtained. Machine learning is effective in analyzing these patterns, and this presentation will introduce an example of gas-type discrimination.

Improved Sensitivity and Stability for SnO Ion-Sensitive Field-Effect Transistor-Based pH Sensor by Electrical Double Layer Gate and AlO Sensitive Film

Hydrogen ion sensor (pH sensor) with high sensitivity and good stability has great potential in modern life, medicine, industry, and other fields. As a core of the pH sensor, an ion-sensitive field-effect transistor (ISFET) based on SnO2 is paired with a high selectivity Al2O3 inorganic insulating film, which enhances its pH sensitivity. In the presence of a voltage applied to the extended gate, the gate and channel act as capacitance plates, and the sensor is equivalent to an electrical double layer (EDL). The hydrogen ions in solution alter the solution capacitance, which changes the capacitance of the solid dielectric layer, regulating the source–drain current. As a result of this work, the sensitivity of the ISFET-based pH sensor with extended gate increased <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.8\times $ </tex-math></inline-formula> to 25.33 nA/pH <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{V}$ </tex-math></inline-formula> when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{{\mathrm {GS}}}$ </tex-math></inline-formula> is 300 mV, compared to a SnO2-based sensor without the extended gate. Also, the stability of the sensor has been greatly improved, as well as the response time of 0.2 s. Our research provides an effective strategy for high-performance ISFET-based pH sensor, and the concept of using the pH-ISFET with an extended gate for direct quantification of pH values in solutions provides a dependable method for industrial applications.

Highly sensitive pH sensor based on flexible polyaniline matrix for synchronal sweat monitoring

The design of a flexible pH sensor with high sensitivity, excellent stability, and low cost has great potential in the applications of the medical care and health fields. In this study, a high-performance flexible pH sensor with a two-electrode configuration was fabricated. This flexible pH sensor integrated the three-dimensional polyaniline (3D PANI) working electrode and Ag/AgCl reference electrode for monitoring the pH value of sweat in real-time. Polyaniline with phytic acid as dopant and crosslinker with a three-dimensional porous matrix structure provided a larger contact area for hydrogen ions in solution and a wider transmission path for charges, which improves the pH response performance of the 3D PANI sensor. The results demonstrated that the 3D PANI sensor exhibited linear super-Nernstian behavior (69.33 mV/pH) in the physiological range (pH 4.00 ∼ 9.00) of sweat, excellent performances in terms of response time (7.75 s), reversibility (3.80 mV), repeatability (0.44 % RSD), drift rate (0.10 mV/h), and temperature drift (0.06 mV/pH/oC). Particularly, the 3D PANI sensor in the bending state showed identical performances to the unbent condition, which makes it a promising candidate in the field of in-situ real-time sweat pH sensors for wearable electronics.

Enhanced straw fermentation process based on microbial electrolysis cell coupled anaerobic digestion

The low quality and yield of methane severely hinder the industrial application of straw biogas fermentation, and no effective solution has been found so far. In this study, a novel method was developed when a microbial electrolysis cell (MEC) was coupled with normal anaerobic fermentation to enhance methane yield and purity. The fermentation process achieved a methane purity of more than 85%, which is considerably higher than that of previously published reports. With microbial stimulation and an electric current, the degradation of fibers has been greatly enhanced. The MEC system substantially improved the yield and purity of biogas, bringing a new path to the synthesis of methane by carbon dioxide and hydrogen ions in solution under electron irradiation. Electrochemical index analysis showed extra methane synthesis, due to the external circuit electron transfer. The results of the gas chromatography and solid degradation rate showed that the carbon source of extra methane was CO 2 produced during normal fermentation and additional volatile solid degradation. These results show that the MEC considerably enhanced the quality and yield of methane in the straw fermentation process, providing insights into normal anaerobic fermentation.

(Invited) Plasmon Resonant Amplification of Hot Electron-Driven Photocatalysis

We report measurements of photocatalytic water splitting using Au films with and without TiO2 coatings. In these structures, a thin (3–10 nm) film of TiO2 is deposited using atomic layer deposition (ALD) on top of a 100 nm thick Au film. We utilize an AC lock-in technique, which enables us to detect the relatively small photocurrents (~mA) produced by the short-lived hot electrons that are photoexcited in the metal. Under illumination, the bare Au film produces a small AC photocurrent (<1µA) for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) due to hot electrons and hot holes, respectively, that are photoexcited in the Au film. The samples with TiO2 produce a larger AC photocurrent indicating that hot electrons are being injected from the metal into the TiO2 semiconductor where they then reduce hydrogen ions in solution forming H2 (i.e., 2H+ + 2e- → H2). The AC photocurrent exhibits a narrow peak when plotted as a function of reference potential, which is a signature of hot electrons. Here, we photoexcite a monoenergetic source of hot electrons, which produces a peak in the photocurrent, as the electrode potential is swept through the resonance with the redox potential of the desired half-reaction. This stands in contrast to conventional bulk semiconductor photocatalysts, whose AC photocurrent saturates beyond a certain potential (i.e., light limited photocurrent). The photocurrents produced at the metal–liquid interface are smaller than those of the metal–semiconductor system, mainly because, in the metal–semiconductor system, there is a continuum of energy and momentum states that each hot electron can be injected into, while for an ion in solution, the number of energy and momentum states are very small.1 2, 3 We also report plasmon resonant excitation of hot electrons in a metal-based photocatalyst in contact with ferrocene redox couple in acetonitrile solution. Here the photocatalyst consists of a 50nm thick Au film and a top thin (5nm) film of Al2O3 deposited using atomic layer deposition. In this configuration, hot electrons, photo-excited in the metal, jump over the oxide barrier ultimately reducing ferrocenium in solution (i.e., Fe(C5H5)2 + + e- → Fe(C5H5)2) producing a photocurrent. In order to amplify this process, the bottom gold electrode is patterned into a plasmon resonant grating structure with a pitch of 500nm. The photocurrent (i.e., charge transfer rate) is measured as a function of incident angle using 633nm wavelength light. We observe peaks in the photocurrent at incident angles of ±10o from normal when the light is polarized parallel to the incident plane (p-polarization) and perpendicular to the lines on the grating. Based on these peaks, we estimate an overall plasmonic gain (or amplification) factor of 2.3X in the charge transfer rate. At these same angles, we also observe sharp dips in the photo-reflectance, corresponding to the condition when there is wavevector matching between the incident light and the plasmon mode in the grating. No angle dependence is observed in the photocurrent or photoreflectance when the incident light is polarized perpendicular to the incident plane (s-polarization) and parallel to the lines on the grating. Finite difference time domain (FDTD) simulations also predict sharp dips in the photoreflectance at ±10o, and the electric field intensity profiles show clear excitation of a plasmon-resonant mode when illuminated at those angles with p-polarized light.

Inhibitory effect of hydrogen ion on the copper ions separation from acid solution across graphene oxide membranes

Graphene-based materials have many unique features including atomic thickness and well-defined nanochannels, making their great properties for filtration and separation. The removal of low-level heavy-metal ions (e.g. Cu2+) by graphene oxide sheets has been discussed to ascertain their adsorption capacity, but separation and recovery of massive copper ions with graphene oxide (GO) membranes remain to be further studied. Besides, the permeation across GO membranes involving different ions in the very same solution is rarely investigated. Hence, the permeation properties of GO membranes concerning single and mixed solutions of acid and salt were examined in this study, and inhibitory effect of hydrogen ion on the copper ions transport was observed. Expectedly, GO membranes perform obvious permeation rate differences to acid (i.e. H2SO4, HCl) and copper salts (i.e. CuSO4, CuCl2) when they are tested individually. The diffusion coefficient of H+ is 16 times larger than that of Cu2+ when the anion is SO42−, and twice in the case of Cl−. The differences are mainly determined by physical screening of the capillary channels in the film for ions with different hydration radii and the rapid migration of hydrogen ions in solution. Furthermore, Experiments were carried out using mixed solution of acid and copper salt with the same anion and concentration. It was shown that the existence of H+, whose own transmission decreased by only 1.6 times, reduced the penetration of Cu2+ by an order of magnitude in the same time interval. We supposed this remarkable inhibitory effect is associated with shrink of interlayer spacing and competitive adsorption of H+ against Cu2+ on the surface of GO membranes in mixed solution. The properties of GO membranes show great application prospects in separation and wastewater reuse.

Influence of pH and temperature on alunite dissolution: Rates, products and insights on mechanisms from atomistic simulation

The processes, rates, controlling factors and products of alunite (KAl3(SO4)2(OH)6) dissolution were assessed using batch dissolution experiments at pHs of c. 3, 4, 4.6, 7 and 8, and temperatures of c. 280, 293 and 313K. Alunite dissolution is roughly congruent at pH3, while at pH≥3.9 the process is incongruent, giving a lower Al/K ratio in solution than in the pristine alunite sample. The decrease in the Al/K ratio appears to be caused by precipitation of secondary aluminium sulfate/hydroxysulfate minerals coating the surface of the dissolving alunite, as inferred from SEM images and XPS determinations, but these minerals do not passivate the alunite surface for the time frame of the experiments (up to 400h). The lowest dissolution rates are obtained for pH4.6 and 280K. Both the temperature increase and any pH variation from that point lead to faster dissolution rates.Based on the potassium release to solution, the influence of pH and temperature on the alunite dissolution rate for pH of 4.8 and below can be expressed as;rateK=10-4.4±0.5aH+0.10±0.02e-32±3/RTwhere rateK is the alunite dissolution rate (in mol·m−2·s−1); aH+ is the activity of hydrogen ions in solution; R is the Universal gas constant (in kJ·mol−1·K−1) and T is temperature (in K).For pH of 4.6 and above, the alunite dissolution rate can instead be expressed as;rateK=10-2.5±0.8aOH-0.14±0.02e-39±4/RTwhere aOH- is the activity of hydroxyl ions in solution.In light of the calculated values for the activation energy under the two sets of pH conditions (32±3 and 39±4kJ·mol−1), alunite dissolution appears to be surface-controlled. Examination of the most stable solvated alunite surfaces obtained by atomistic computer simulations suggests that the least energetically favourable steps during alunite dissolution are the detachment of either Al atoms or SO4 tetrahedra from exposed surfaces. Thus, these processes are most probably the rate-determining steps in alunite dissolution.

Traceability of pH to the Mole

Free acidity of aqueous solutions was initially defined in 1909 by Søren Peter Lauritz Sørensen as pH = −lgcH+ (c/mol·dm−3 or m/mol·kg−1 of the free hydrogen ions in solution, H+) soon (1910) was changed to pH = paH+ = −lgaH+, integrating the new concepts of activity, ai and activity coefficient γi, for the ionic species i under concern, H+ in this case; it is ai = −lg(miγi). Since individual ions do not exist alone in solution, primary pH values cannot be assigned solely by experimental measurements, requiring extra thermodynamic model assumptions for the activity coefficient, γH+, which has put pH in a unique situation of not being fully traceable to the International System of Units (SI). Also the concept of activity is often not felt to be as perceptible as that of concentration which may present difficulties, namely with the interpretation of data. pH measurements on unknown samples rely on calibration of the measuring setup with adequate reference pH buffers. In this work, the assignment of pH values to buffers closely matching the samples, e.g., seawater, is revisited. An approach is presented to assess the quantity pmH+ = −lgmH+ profiting from the fact that, contrary to single ion activity coefficients, mean activity coefficients, can be assessed based on experimentally assessed quantities alone, γExp ±, thus ensuring traceability to the mole, the SI base unit for amount of substance. Compatibility between γExp ± and mean activity coefficient calculated by means of Pitzer model equations, γPtz ±, validates the model for its intended use.

Tunable Photonic Band Gap of PS-b-P2VP Lamellar Film Using Metal Ions and pH Gradation.

Optical properties of photonic crystal film were investigated by tuning photonic band gap (PBG). The lamellar-forming photonic films were prepared by nearly symmetric poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) block copolymers. Molecular weight of PS block and P2VP block is 52 kg/mol, and 57 kg/mol, respectively. When submerged in water, the lamellar films were swollen and show Bragg reflection in visible light region. We observed that the reflection color can be tuned by ion concentration (e.g., hydrogen or metal ion) in water. The higher concentration of hydrogen ion in solution, the longer reflectance wavelength shifted (from 537 nm to 743 nm). In addition, max-reflectance wavelength is dependent on both metal ion and the concentration. The max-reflectance wavelength is shifted from 653 nm (i.e., in water without ion) to 430 nm, 465 nm, and 505 nm for 120 mM of Ca2+, Fe2+, and Cu2+, respectively. Therefore, we can control the photonic band gap of photonic devices by changing the condition of swelling solution.

Absorption Behavior and Removal of Gaseous Elemental Mercury by Sodium Chlorite Solutions

AbstractThe absorption behavior of Hg0 was studied experimentally by using sodium chlorite (NaClO2) as the absorbent in a bubble reactor. Primary influencing factors on the removal of Hg0 such as NaClO2 solution concentration, solution hydrogenion concentration (pH), reaction temperature, the concentration of Hg0, and other components in the flue gas, such as O2, SO2, and NO, were investigated. Approximately 65% removal of elemental mercury can be achieved under optimal experimental conditions. The removal mechanism of Hg0 was proposed by analyzing Hg2+ concentration in the spent absorption solution and comparing the electrode potentials between NaClO2 species and Hg2+/Hg0.

Biocompatibility and corrosion behavior of the shape memory NiTi alloy in the physiological environments simulated with body fluids for medical applications

Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO 2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids.

Comment on “The electrochemical Peltier heat of the standard hydrogen electrode reaction” by Zheng Fang et al.

Fang et al. recently performed electrochemical Peltier measurements, proposed an absolute entropy scale for the standard hydrogen electrode, and gave a value for the partial molar entropy of hydrogen ions in solution. That paper contains several ambiguities and omissions that should be resolved in order to make the information in the paper more useful. The thermodynamic state of the electron in their treatment is not fully specified, and the method used to calculate the partial molar entropy of solution phase hydrogen ions is not given. Furthermore, the calculation of partial molar entropy of solution phase hydrogen ions apparently omits the partial molar entropy of metal-phase electrons, a term that is necessary for such determinations if the starting point is electrochemical Peltier heat measurements. As a smaller matter, the paper overlooks specifying the units used for fugacity. The paper also overlooks previous work on absolute half-cell entropy.

Chalcopyrite dissolution rate law from pH 1 to 3

Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term flow-through experiments to obtain a dissolution rate law which can be coupled with reactive transport models to forecast Acid Rock Drainage. In the range of conditions under study, the rate of chalcopyrite dissolution is only slightly dependent on hydrogen ion activity, increasing with decreasing pH. The steady-state dissolution rates obtained in the present study were combined with earlier results presented by Acero et al. (2007a) to obtain the following expression for chalcopyrite dissolution rate law: where Rchalcopyrite is the chalcopyrite dissolution rate (mol m-2 s-1), aH+ is the activity of hydrogen ion in solution, R is the gas constant (kJ mol-1 K-1) and T is the temperature (K). This expression can applied through a wide range of environmental conditions similar to the ones found in systems affected by acid drainage. In agreement with earlier chalcopyrite kinetic studies, iron was released to solution preferentially over copper and sulfur, compared with the stoichiometry of the pristine mineral. Consistently, XPS examination of the samples showed that reacted surfaces were enriched in sulfur and copper (relative to iron) compared with the initial, pristine chalcopyrite surface. However, this surface layer does not exert any passivating effect on chalcolpyrite dissolution and the kinetics of the overall process in the long term seems to be surface-controlled.

A Chemical Basis for Sour Taste Perception of Acid Solutions and Fresh‐Pack Dill Pickles

Sour taste is influenced by pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity in foods containing organic acids. The objective of this study was to investigate the roles of protonated (undissociated) organic acid species and hydrogen ions in evoking sour taste. Sour taste intensity increased linearly with hydrogen ion concentration (R(2)= 0.995), and with the concentration of protonated organic acid species at pH 3.5 (R(2)= 0.884), 4.0 (R(2)= 0.929), and 4.5 (R(2)= 0.975). The structures of organic acid molecules did not affect sour taste after adjusting for the effects of protonated organic acid species and hydrogen ions. Sour taste intensity was also linearly related to the total concentration of protonated organic acid species in fresh-pack dill pickles (R(2)= 0.957). This study showed that the sour taste of organic acids was directly related to the number of molecules with at least 1 protonated carboxyl group plus the hydrogen ions in solution. Conclusions from these results are that all protonated organic acids are equally sour on a molar basis, that all protonated species of a given organic acid are equally sour, and that hydrogen ions and protonated organic acids are approximately equal in sour taste on a molar basis. This study provides a new understanding of the chemical species that are able to elicit sour taste and reveals a basis for predicting sour taste intensity in the formulation of acidified foods.

Effect of pH on cadmium biosorption by coconut copra meal

Biosorption of cadmium ion by coconut copra meal, an agricultural waste product was investigated as a function of initial solution pH and initial cadmium concentration. Pseudo-second-order kinetic analyses were performed to determine the rate constant of biosorption, the equilibrium capacity, and initial biosorption rate. Cadmium biosorption by copra meal was found to be dependent on the initial solution pH and initial cadmium concentration. Ion exchange occurred in the initial biosorption period. In addition, mathematical relationships were drawn to relate the change in the solution hydrogen ion concentration with equilibrium biosorption capacity, initial cadmium concentration, and equilibrium biosorption capacity.

Electrochemical noise study on 2024-T3 Aluminum alloy corrosion in simulated acid rain under cyclic wet–dry condition

Potential noise records have been collected for 2024-T3 aluminum alloy, which was exposed to simulated acid rain with different pH value for 15 wet–dry cycles. Meanwhile, Potentiodynamic polarization and SEM techniques were also used as assistant measurements. Three mathematic methods including average, standard deviation and wavelet transformation have been employed to analyze the records. The results showed that each single wet–dry cycle can be divided into three regions with respect to the change of the cathodic reaction rate, and with the increase of pH value the main cathodic reaction changes from the reduction of protons to that of oxygen molecules. The analysis of the EDP versus time evolution clearly indicates that the whole corrosion process can be divided into three segments for the case of pH 3.5 and only one for the cases of pH 4.5 and 6.0, which have been theoretically interpreted according to the corrosion theory and experimentally proved by SEM. The results also showed that the corrosion in the case of pH 3.5 was much more rigorous than that in the cases of pH 4.5 and 6.0. It may due to synergistic effects of that, the characteristic of hydrogen ions which is much more active than that of oxygen molecules, the high diffusion/migration rate of hydrogen ions in solution or through surface films and the lower stability of surface passive film at low pH value system.

Effect of nitrogen on corrosion behavior of 28Cr–7Ni duplex and microduplex stainless steels in air-saturated 3.5 wt% NaCl solution

The corrosion behavior of 28Cr–7Ni–O–0.34N duplex stainless steels in air-saturated 3.5-wt% NaCl solution at pH 2, 7, 10 and 27 °C was studied by the potentiodynamic method. Two types of microstructures were investigated: the as-forged duplex and microduplex (average austenite grain size 5–16 μm) structures. The austenite volume fractions of the tested steels were between 0.35 and 0.64. The nitrogen effect on corrosion behaviors of both duplex and microduplex stainless steels were the same. At pH 2, the corrosion potential increased when the nitrogen content increased, however, corrosion current density as well as corrosion rate decreased. At pH 7 and 10, the effect of nitrogen on corrosion potential and corrosion rate could not be observed. Corrosion potential at pH 10 was lower than at pH 7. Pitting potential increased when the nitrogen content in the tested steels increased at all tested pH. For the nitrogen effect on the passive current density, it seemed that only at pH 2, the average passive current densities reduced when the nitrogen content increased. Nitrogen may have participated in the passive film or has been involved in the reaction to build up passive film. The ammonium formation and nitrogen enrichment at the interface metal/passive film with adsorption mechanism were discussed. The dissolute nitrogen might have combined with the hydrogen ions in solution to form ammonium ions, resulting in increasing solution pH. The steel could then easily repassivate, hence the corrosion potential and pitting potential would increase. However, the ammonium formation mechanism could not explain the decrease of corrosion potential in basic solution. Nitrogen enrichment at the metal/passive film interface with adsorption mechanism seemed to be an applicable consideration in increasing pitting potential. However, this mechanism did not involve the ammonium ion formation. In general, for the duplex and microduplex stainless steels tested, nitrogen increased the general corrosion resistances in acid solution and pitting corrosion resistance at all solution pH. Metallographic observation in both tested duplex and microduplex steels after pitting corrosion at all tested pH revealed that, the corroded structure in the tested steels without nitrogen alloying was austenite, but those with nitrogen alloying was ferrite. Even though ferrite had a higher chromium content than austenite but higher dissolved nitrogen in austenite than in ferrite may have increased the pitting resistance equivalent number (PRE) of austenite to be higher than that of ferrite.

Effect of pH on lead removal from water using tree fern as the sorbent

The sorption of lead from water onto an agricultural by-product, tree fern, was examined as a function of pH. The sorption processes were carried out using an agitated and baffled system. Pseudo-second-order kinetic analyses were performed to determine the rate constant of sorption, the equilibrium sorption capacity, and the initial sorption rate. Application of the pseudo-second-order kinetics model produced very high coefficients of determination. Results showed the efficiency of tree fern as a sorbent for lead. The optimum pH for lead removal was between 4 and 7, with pH 4.9 resulting in better lead removal. Ion exchange occurred in the initial reaction period. In addition, a relation between the change in the solution hydrogen ion concentration and equilibrium capacity was developed and is presented.

Heavy metal removal by olive pomace: biosorbent characterisation and equilibrium modelling

This paper concerns with metal biosorption onto an agricultural waste, olive pomace. Experimental tests of adsorbent characterisation (potentiometric titration, IR analyses, selective extractions) and titration modelling (accounting for adsorbent heterogeneity by the introduction of a two-peak proton affinity distribution function) evidence that carboxylic and phenolic groups are the main active sites involved in metal removal. Potentiometric titration and single metal system biosorption tests (Pb, Cu, Cd) onto native and treated olive pomace samples are represented by an equilibrium model describing the competition among heavy metals and hydrogen ions in solution.

Crack growth threshold in soda lime silicate glass: role of hold-time

Atomic force microscopy was used to examine the shapes of cracks and residual features left behind on the fracture surface after holding cracks at a stress–intensity factor below the fatigue threshold for soda lime silicate glass. After propagating a crack at a stress–intensity factor of K I=0.37 MPa m 1/2, the crack was held either at K I=0.24 MPa m 1/2, or K I=0.1 MPa m 1/2 for periods ranging from 1 h to approximately 200 h. Cracks held at the higher K I left featureless lines on the fracture surface. Becoming more pronounced as the hold-time increased, these lines marked the position of a corrosive notch that formed during the hold period. At about 30 nm from the crack tip, the crack surface displacement decreased reaching zero at the crack tip. The crack tip shape was that of an ogee arch. At the lower hold valued of K I, crack bifurcation occurred during which the crack became wavy, part of the crack propagating into the crack plane, part out of the crack plane when the crack was repropagated. A smaller crack tip displacement was observed for these cracks. Results of this study are believed to be a consequence of corrosion of the fracture surface caused by a basic solution formed when alkali ions (Na + and K +) at the crack tip exchange with hydrogen ions in solution.