Deionized Water System Research Articles

Effect of Ion Size on Pressure-Induced Infiltration of a Zeolite-Based Nanofluidic System.

A nanofluidic system consists of a nano-porous medium and functional liquid, which demonstrates a higher energy absorption density compared to conventional systems for energy absorption. Alterations in the composition of the functional liquid can significantly impact the properties of a nanofluidic system. In this paper, the widely used zeolite ZSM-5 was chosen as the porous medium to establish a nanofluidic system. Three distinct electrolyte solutions, namely KCl aqueous solutions, NaCl aqueous solutions and MgCl2 aqueous solutions were employed as functional liquids while pure water served as the reference condition for configuring four kinds of nanofluidic systems. Pressure-induced percolation experiments were performed on the four zeolite-based systems. The difference in the infiltration process between the electrolyte solution systems and the deionized water system has been ascertained. The effect of the ion size on the infiltration and defiltration process has been determined. The results show that the introduction of ions induces a hydration effect, resulting in a higher critical infiltration pressure of the electrolyte solution system compared to an aqueous solution system. The magnitude of cation charge directly correlates with the strength of the hydration effect and the corresponding increase in critical infiltration pressure. Upon entering the nanochannel, the liquid infiltrates primarily in the form of ions rather than a cation hydration form. The larger the ion size, the shallower the penetration depth after entering the nanopore channel and the larger the corresponding relative outflow rate. The present work will provide valuable theoretical complementary and experimental data support for nanofluidic system applications.

Effect of Acidified Sodium Silicate on the Flotation Separation of Microfine Apatite from Chlorite in Seawater

In this work, selective flotation separation of microfine apatite and chlorite was achieved by using sodium oleate (NaOL) as a collector with a low dosage of acidified sodium silicate (ASS) as a depressant. The optimum ratio of sodium silicate to sulfuric acid for ASS was 5:3, and a good separation effect was also achieved in the mixed ore system. Compared to the deionized water system, the ions of Na+, Ca2+ and Mg2+ in seawater adsorbed on the surfaces of apatite and chlorite, which made the zeta potential of the two minerals shift positively. This presented a challenge to the selection of reagents for mineral separation. The addition of ASS changed the pH value of the pulp from weak alkalinity caused by seawater to weak acidity, which allowed the metal ions adsorbed on the mineral surface to desorb. Meanwhile, ASS can selectively adsorb on the desorbed chlorite surface in the form of Si(OH)4, which hindered the action of NaOL, leading to the depression of chlorite. NaOL adsorbed well on the desorbed surface of apatite and increased the apatite particle size from 27 μm to 229 μm, with a hydrophobic agglomeration effect, thus enhancing the flotation of microfine apatite.

Influence of the memory effect during CO2/CH4 mixed gas hydrate reformation process

The study of the memory effect can help to clarify the mechanisms of synthesis and decomposition of the CO2/CH4 mixed gas hydrate for mixed gas separation, CO2 sequestration, and CH4 recovery from unconventional natural gas reservoirs. To examine the impact of the memory effect on the CO2/CH4 mixed gas hydrate synthesis in terms of induction time, gas consumption rate, change of gas components, and separation factor, we conducted initial and second CO2/CH4 mixed gas hydrate synthesis experiments in a porous medium and deionized water system. The influence characteristics of the memory effect on CO2/CH4 hydrate synthesis under the predesigned decomposition temperatures (5 ∼ 25 °C) and pressures (0.5, 1.0, and 1.5 MPa) were investigated under decomposition times of 0.5 and 1.0 h. Compared to the induction time of the initial synthesis, the induction time of the second synthesis was greatly shortened, reaching a maximum of 87.42%. The induction time decreased with decreasing decomposition temperature and pressure in the same decomposition period. The decomposition time had a large effect on the peak value of the induction time during the second synthesis process. Besides, the memory effect was greatly affected by the decomposition time in depressurization cases, and the 0.5 h decomposition time was significantly better than that of 1.0 h. The memory effect had the strongest promotion effect on the second synthesis when the decomposition pressure and time were 1.0 MPa and 0.5 h, respectively. Furthermore, the memory effect improved the nucleation rate of the CO2/CH4 mixed gas hydrate and increased the amount of CO2 hydrate synthesis to 1.3 times that of the initial synthesis. Also, the memory effect influenced the hydrate to exhibit stronger CO2 selectivity, which provides a novel approach for the separation of mixed gases via the hydrate method.

Desalination of produced water via CO2 + C3H8 hydrate formation

Recent years have seen increased interest in gas hydrate production as a viable saline water desalination technique. Produced water is the liquid that is extracted from oil and gas fields and is typically salty. The management of produced water is a significant aspect of the petroleum industry because of its potential to serve as a source of fresh water for oil-producing nations with limited access to clean water, growing environmental concerns, and the strict laws governing the discharge of produced water into the environment. In this study, the effect of mixed gas (CO2 + C3H8 (70:30)) hydrate formation in treating produced water and kinetic studies on induction time, moles of gas consumed, rate, water recovery, and water-to-hydrate conversion were experimentally investigated. An aqueous solution with the same ion concentrations was prepared and experiments were performed at 275.15 K/277.15 K, 2.0 MPa, and 450 rpm. The findings unveiled that with an increase in salinity, the water recovery decreased showing the hindering effect of salts on mixed hydrate formation by reducing the solubility of mixed gas due to the strong electrostatic force of attraction between salt ions and water. A maximum of 67.3% water recovery was observed in 2.8 wt% produced water solution at 275.15 K, 2.0 MPa, and 450 rpm. Furthermore, the induction time increased by 52.64% in treating 2.8 wt% and a decrease in moles of gas consumed, water recovery, and water-to-hydrate conversion by 6.99%, 2.08%, and 9.69% compared to the deionized water system at 275.15 K. A removal efficiency of 47%-63% is achieved by using CO2 + C3H8 and the sequence of metal cation removal is in the order K+ > Na+ > Mg2+ > Ca2+ and anions SO42− > Cl− at 275.15 K. The results also showed that with a rise in the experimental temperature to 277.15 K the removal efficiency increased though the amount of hydrate formed is less. This study illustrates that the formation of mixed gas (CO2 + C3H8) hydrate can be used for treating produced water based on the water recovery, removal efficiency, electrical conductivity, and total dissolved solids results with lower energy consumption.

Enhanced hydrophilicity and antifouling performance of PES-C/emodin ultrafiltration membrane

In this article, an ultrafiltration membrane was fabricated from phenolphthalein polyethersulfone (PES-C) modified with emodin using a phase-inversion method. ATR-FTIR and UV-vis analysis showed that emodin had good compatibility with the PES-C ultrafiltration membrane. SEM showed that the prepared ultrafiltration membranes consisted of a porous skin layer and a macroporous support sublayer. The contact angle value of the pure PES-C ultrafiltration membrane was 77.71° and that of the PES-C ultrafiltration membrane blended with 0.105 wt.% emodin decreased to 65.71°, which explained the fact why its pure water flux significantly increased from 190 L/m2·h to 387 L/m2·h. The antifouling properties of the obtained ultrafiltration membranes were assessed by static protein adsorption, bacterial adhesion, antibacterial tests, and filtration experiments with BSA. The PES-C (13.895 wt.%)/emodin (0.105 wt.%) ultrafiltration membrane presented the lowest protein adsorption rate (1.44%), the highest flux recovery ratio (57%), and the largest inhibition zone diameter (3.0 ± 0.06 mm). Compared with that of the pure PES-C ultrafiltration membrane, the bacterial adhesion effect of the PES-C/emodin (0.105 wt.%) ultrafiltration membrane was significantly reduced. In addition, PES-C incorporated into the emodin ultrafiltration membrane had excellent stability in a deionized water system.

Evaluating the Effect of Residual Lignin Contents and Fermentation Systems on Bioethanol Production

Peroxide-acetic acid (Peroxide-HAc) pretreatment is a simplified and cost-effective technology due to its mild conditions without the catalysis of strong acids, which was introduced to treat sugarcane bagasse (SCB) in this paper. Then pretreated SCB was used to produce bioethanol using thermophilic Saccharomyces cerevisiae in deionized water (DW) and sodium citrate buffer solution (SCS) fermentation systems, respectively. Results: showed that peroxide-HAc pretreatment can selectively remove lignin and change morphological structures, thus positively increasing saccharification and fermentation efficiency downstream. SCB pretreated at 100 °C obtained the lowest residual lignin content of 2.88% and achieved the highest ethanol yield of 92.10% (0.45 g/g-biomass) in DW system. In particular, SCS can decrease the residual sugars content of pretreated SCB during simultaneous saccharification and co-fermentation (SSCF) process. The addition of Tween 80 improved SSCF of SCB pretreated at 80 °C likely because Tween 80 can block residual lignin adsorption with enzymes. The concentration of acetic acid and glycerol byproducts from SCB pretreated at 80 °C can be decreased by SCS and DW systems, respectively, comparing to SCS and DW systems with additing Tween 80. This study provided a systematic process route for the bioethanol production by mild pretreatment method.

Experiment and model investigation of D-sorbitol as a thermodynamic hydrate inhibitor for methane and carbon dioxide hydrates

Pipe plugging and cracking caused by gas hydrate blockage is the major problem in oil/gas flow assurance, especially in deep subsea pipelines. Thermodynamic inhibitors(THIs) are one of the effective methods to inhibit the formation of gas hydrate. This work evaluates the thermodynamic inhibition effect of D-sorbitol, a polyhydroxy compound, for both methane (CH4) and carbon dioxide (CO2) hydrates. The gas-liquid-hydrate equilibrium (GLHE) conditions for CH4 and CO2 were measured by the isothermal pressure search method in the presence of aqueous D-sorbitol solutions (1.00, 2.00, 3.00 mol%). The equilibrium pressure change (ΔP) and hydrate dissociation enthalpies (ΔHdiss) were used to reflect the thermodynamic effects of D-sorbitol on CH4 and CO2 hydrates. The ΔP data show that D-sorbitol has an obvious inhibition impact on CH4 and CO2 hydrates formation. Compared with deionized water system, CH4 hydrate GLHE pressure increased by 11.6, 25.0, 41.4%, while CO2 hydrate GLHE pressure increased by 10.1, 18.6, 32.7% in 1.00, 2.00, 3.00 mol% D-sorbitol solutions, respectively. The ΔHdiss data demonstrate that D-sorbitol does not participate in the formation of the hydrate crystal structure. Chen-Guo hydrate thermodynamic model and Wilson activity model were applied to predict the GLHE conditions of both CH4 and CO2 hydrates in the presence of D-sorbitol. The calculated results can well match the experimental values. The average relative deviations (ARD) between calculated and experimental data for CH4 and CO2 hydrate are less than 2.39% and 3.76%, respectively. D-sorbitol is a non-toxic and environment-friendly compound. The results in this work indicate that D-sorbitol can be applied to flow assurance strategies for hydrate blockage prevention.

First-principles calculations and experiments for Ce4+ effects on structure and chemical stabilities of Zr1-xCexSiO4

Using Ce atom as the surrogate for tetravalence actinides, the structure stability, chemical bonding and solubility of Zr1-xCexSiO4 have been investigated by combing first principles calculations and static leach test (MCC-1) experimentally to understand the effect of actinides on stability of ZrSiO4. The structural analysis indicates that the high symmetry of [CeO8] polyhedron could well maintain the structural stability of Zr1-xCexSiO4. However, due to the longer and weaker CeO bond than ZrO bond, LRCe is slightly higher than LRZr. Besides, the LRZr and LRCe are highest in acid leaching solution, followed in alkaline leaching solution and deionized water system. Worth noted, the negative solution energy of −22.254 eV indicates the pre-existing Zr vacancy is energetically favorite to accommodate actinides surrogate Ce impurities or quadrivalent actinides with slight structural deformation, showing the strong structural and chemical stabilities of ZrSiO4.

Trimethoprim degradation by Fenton and Fe(II)-activated persulfate processes

Trimethoprim is a pollutant ubiquitous in the environment due to its extensive application, and it cannot be effectively removed by conventional wastewater treatment processes. In this study, the Fenton and the Fe(II)-activated persulfate processes were employed to degrade trimethoprim in an aqueous solution. The results showed that the concentration of persulfate, H2O2 and Fe(II) a had significant influence on the degradation of trimethoprim in both processes. De-ionized water spiked with trimethoprim resulted in the complete degradation of trimethoprim (0.05 mM) by the mineralization of 54.9% of Fenton's reagent when the concentrations of H2O2 and Fe(II) were 1 mM and 0.05 mM, respectively. In contrast, 73.4% of trimethoprim was degraded by the mineralization of 40.5% of the Fe(II)-activated persulfate process when the concentration of persulfate and Fe(II) were each 4 mM. Intermediate compounds with different m/z were detected for the Fenton and the Fe(II)-activated persulfate processes, indicating alternative degradation pathways. In the actual wastewater spiked with trimethoprim, the removal efficiency of trimethoprim decreased to 35.8% and 43.6%, respectively, for the Fenton and the Fe(II)-activated persulfate processes. In addition, the decomposition efficiencies for hydrogen peroxide and persulfate were 43.8% and 92.5%, respectively, which was lower than those in the de-ionized water system. These results demonstrated that wastewater components had a negative influence on trimethoprim degradation and the decomposition of the oxidants (persulfate and H2O2). In summary, the Fe(II)-activated persulfate process could be used as an alternative technology for treating trimethoprim-containing wastewater.

The Effect of Chloride Ions on the Activity of Cerussite Surfaces

Chloride ions were found to potentially increase activity of cerussite surfaces. Dissolution experiments, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) studies, and density functional theory (DFT) computation were conducted in this study. Dissolution experiments showed that the lead ion concentrations in the NaCl solution system were lower than those in the deionized water system and that the lead ion concentrations in NaCl + Na2S aqueous systems decreased by approximately one order of magnitude compared with that in the Na2S system alone. Results of zeta potential measurements revealed that the pretreatment with chloride ions of cerussite caused a more positive zeta potential than that without chloride ions. XPS analysis results indicated that the number of lead ions on the mineral surface increased after cerussite was treated with chloride ions. Results of DFT computation implied that the number of lead atoms on the mineral surface increased and that the activity improved after PbCl+ was adsorbed onto the cerussite surface. The contribution of chloride ions to the activity on the mineral surface is attributed to the increase in the number of active sites and enhancement in the activity of these sites, resulting in improved sulfidization and flotation performance.

Morphology analysis of magnesium hydroxide prepared by magnesium oxide hydration within seawater

In order to investigate the microstructure of magnesium oxide hydration product within seawater, two reaction conditions (liquid‐solid and gas‐liquid‐solid) and two solutions (seawater and deionized water) were adopted for magnesium oxide hydration. The characterization of the hydration product using X‐Ray diffraction and scanning electron microscope was performed. Experimental results indicate that cations and anions in seawater promote the hydration. Most of the hydration products within seawater system display flower‐like morphology, but the agglomeration phenomenon is not obvious within deionized water system, especially for the supernatant layer products within deionized water system under gas‐liquid‐solid reaction condition. There was no stratification phenomenon occurred when MgO hydrated with seawater under three‐phase reaction condition.

Development of a self-cleaning dispersion and exposure chamber: Application to the monitoring of simulated accidents involving the generation of airborne nanoparticles

The release of hazardous nanoparticulate matter in accidental situations was simulated in a specially designed 13-m3 stainless steel airtight chamber, which allowed the dispersion analysis of airborne matter in a practically particle-free environment (less than 2 #/cm3) and in presence of background atmospheric aerosols. A fast recovering of the initial situation was achieved by means of a tandem HEPA-filtered air and deionized water system. Both unintended spilling of silica-based nanoparticulate powders and continuous emission of 100-nm SiO2 nanoparticles were used as aerosol generation events. The emission of airborne nanoparticles was analyzed in terms of particle number concentrations (PNC), size distributions and source strengths. The emission of nanoparticulate aerosols reached peak PNC for particles in the range from 5nm to 1μm with source strengths about 108 #/h in a background-filled environment and 1010 #/h in a practically particle-free atmosphere. No agglomeration was noticed for the released nanoparticles, suggesting that PNC was low enough to prevent coagulation and that particle diameters were over 80nm. Results indicate that emitted matter was within the range of the most penetrating particle sizes and with source strengths similar to accidental scenarios.

Preparation of spherical silica particles in reverse micro emulsions using silicon tetrachloride as precursor

Silica powders with spherical shape have been prepared by precipitation reaction of silicon tetrachloride with de-ionized water in the micro emulsion system. Two kinds of micro emulsion systems were used. One was cyclohexane/polyoxyethylene nonyl phenyl ether (NP-5)/de-ionized water system, and the other was heptane e/NP-5/de-ionized water. Transmission electron microscope (TEM), thermo gravimetric analysis (TG), X-ray diffraction (XRD) patterns, infrared spectrum (IR) were employed to characterize the micro structure, shape, thermal properties, phase, and molecular structure of the obtained silica. The results show that silica featuring spherical shapes and uniform characteristics was yielded by the precipitation method using silicon tetrachloride with de-ionized water in the micro emulsion system. A decreased tendency for silica particles agglomeration could be achieved by using lower mole ratio of water and SiCl4, and the particle size was 5.74nm when mole ratio of water and SiCl4 was 4 in NP-5/cyclohexane/deionized water micro emulsion system. The silica prepared by these two systems was amorphous silica and thermally stable after 600°C treatment. The structures of silica prepared from the different micro emulsion systems were similar; organic molecules can be removed completely from the silica through 600°C treatment.

AN INVITRO COMPARATIVE EVALUATION OF FLUORIDE RELEASE FROM DIFFERENT FLUORIDE CONTAINING RESTORATIVE MATERIALS IN VARIOUS STUDY SOLUTIONS

The aim of this study was to determine the level of fluoride released from four different tooth colored restorative materials; Vitremer, Fuji II LC, Dyract and Tetric ceram in three different storage solutions; artificial saliva, De-ionized water and pH cycling system and also to compare the amount of fluoride released. Fifteen discs of each material were prepared in a Teflon mould, varnish applied, polished, then stored at 37°C and 100% relative humidity for a day. Each storage solution of 2 ml was pipetted into five polypropylene tubes and five samples of each material were suspended individually and the fluoride released was measured using an Orion fluoride Specific Electrode and Digital Ion Analyzer. All the results were statistically analyzed and was concluded that vitremer showed the highest fluoride release followed by Fuji II LC, Dyract and Tetric Ceram in the pH cycling system followed by De-ionized water and least in Artificial saliva.

Determination of Low-ppt Levels of Acetate, Propionate, and Formate in Semiconductor-Grade Deionized Water via Ion Chromatography

The goals of this research were the development of a method to determine acetate, propionate, and formate at low part-per-trillion (ppt; w/w) levels in deionized water, and the assessment of sources of variability and contamination associated with the method; both objectives were met. A calibration study involving six replicates of each of four standards (blank, 20, 50, and 80 ppt) resulted in straight-line (with ordinary-least-squares fitting) curves for all analytes. At 95% confidence, the half-widths of the prediction intervals were +/- 30, 14, and 14 ppt for the three analytes, respectively. Much of the acetate and formate seen in blanks was found to originate in the deionized water system itself. For formate, peak heights increased with water temperature.

Measurements of Hydrate Equilibrium Conditions for CH 4, CO 2, and CH 4 + C 2H 6 + C 3H 8 in Various Systems by Step-heating Method

Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device. The experimental data for pure CH 4 or CO 2 + deionized water systems showed good agreement with those in the literatures. This kind of method was then applied to CH 4/CO 2 + sodium dodecyl sulfate (SDS) aqueous solution, CH 4/CO 2 + SDS aqueous solution + silica sand, and (CH 4 + C 2H 6 + C 3H 8) gas mixture + SDS aqueous solution systems, where SDS was added to increase the hydrate formation rate without evident influence on the equilibrium conditions. The feasibility and reliability of the step-heating method, especially for porous media systems and gas mixtures systems were determined. The experimental data for CO 2 + silica sand data shows that the equilibrium pressure will change significantly when the particle size of silica sand is less than 96 μm. The formation equilibrium pressure was also measured by the reformation of hydrate.

Nitrosamine, Dimethylnitramine, and Chloropicrin Formation during Strong Base Anion-Exchange Treatment

Strong base anion-exchange resins represent an important option for water utilities and homeowners to address growing concerns with nitrate, arsenate, and perchlorate contamination of source waters. Most commercially available anion-exchange resins employ quaternary amine functional groups. Previous research has provided contradictory evidence regarding whether these resins serve as sources of nitrosamines, considered as highly carcinogenic nitrogenous disinfection byproducts (N-DBPs), even without disinfectants. For three common varieties of commercial anion-exchange resins, we evaluated the importance of releases of nitrosamines, and two other N-DBPs (dimethylnitramine and chloropicrin), when the resins were subjected to typical column flow conditions with and without free chlorine or chloramine application upstream or downstream of the columns. In the absence of disinfectants, fresh trimethylamine- and tributylamine-based type 1 and dimethylethanolamine-based type 2 anion-exchange resins usually released 2-10 ng/L nitrosamines, likely due to shedding of manufacturing impurities, with excursions of up to 20 ng/L following regeneration. However, the lack of significant nitrosamine release in a full-scale anion-exchange treatment system after multiple regeneration cycles indicates that releases may eventually subside. Resins also shed organic precursors that might contribute to nitrosamine formation within distribution systems when chloramines are applied downstream. With free chlorine or chloramine application upstream, nitrosamine concentrations were more significant, at 20-100 ng/L for the type 1 resins and approximately 400 ng/L for the type 2 resin. However, chloropicrin formation was lowest for the type 2 resin. Dimethylnitramine formation was significant with free chlorine application upstream but negligible with chloramines. Although no N-DBPs were detected in cation-exchange-based consumer point-of-use devices exposed to chlorinated or chloraminated waters, our results indicate that inclusion of anion-exchange resins in these devices, as in laboratory deionized water systems, would likely be problematic.

Preparation of Ultrafine Beclomethasone Dipropionate Drug Powder by Antisolvent Precipitation

The purpose of this study was to prepare ultrafine beclomethasone dipropionate (BDP) powder via antisolvent precipitation without any surfactants. Various solvents were screened to determine the suitable system for optimum processing while deionized water was kept as the antisolvent. Methanol was selected as the solvent, because a higher degree of supersaturation could be achieved. Several experimental parameters, such as the volume ratio of solution to antisolvent, the concentration of BDP−methanol solution, the temperature, and the stirring speed and time, were investigated in the methanol−deionized water system. The results showed that the yielded powder had a mean particle length of 850 nm and 85% of the particles were distributed in the range of 0.2−1.2 μm, whereas the raw particle size was 2.13 μm, ranging in size from 0.2 μm to 12 μm. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis indicated no change in chemical group structure and crystal structure during the ...

Solid-state13C-NMR analysis of size components in handsheets prepared by fatty acid soap size-alum systems

The mechanism of paper sizing in fatty acid soap size-alum systems was studied by structural analyses of the size components in handsheets prepared with13C-labeled fatty acid soap size. Patterns of sizing performance and aluminum content of the handsheets were similar to those for the rosin soap size-alum sizing systems, although the patterns of calcium content were different. Solid-state13C-nuclear magnetic resonance analysis of the handsheets revealed that fatty acid calcium salt was the predominant size component in the handsheets prepared using tap water. This calcium salt is formed from the fatty acid soap size (fatty acid potassium salt) by ion exchange with calcium ion in pulp suspensions and retained on pulp fibers through aluminum compounds originating from alum added. On the other hand, when deionized water was used, free fatty acid was the major component in the handsheets. Fatty acid aluminum salt was present as a minor component in the handsheets prepared in both tap water and deionized water systems. Therefore, all size components (i.e., fatty acid calcium salt, free fatty acid, fatty acid aluminum salt) seem to contribute to the appearance of sizing features.

The potential for unanticipated biodegradation during EIS analysis of polymer-coated metallic substrates

During a recent long-term electrochemical test in aqueous NaCl produced from deionized water, microscopic inspection revealed that the surface of the polymer was heavily colonized by micro-organisms, which had developed naturally. The deionized water was considered as a possible source and, to establish the extent of contamination, samples were procured from universities in Italy, the U.S.A. and England. In all cases, when aliquots were cultured to test for the presence of biological contaminants, both bacterial and fungal growth ensued, thus reflecting the widespread contamination of deionized water systems. Many electrochemical experiments currently employ electrolytes produced from deionized water, and there is a body of evidence suggesting both that biodegradation may be partially responsible for early failure of inoculated samples and that the technique of EIS is sensitive enough to reveal such failures when they occur. There is, however, no conclusive evidence showing that EIS is capable of distinguishing between classical and biologically induced degradation. Thus, unanticipated biological contamination of long-term electrochemical tests may seriously affect the integrity of an experiment and subsequent interpretation of results. However, even if a source of non-contaminated water is available, a problem may still exist due to the ubiquitous nature of contaminants. Thus, assuming the absence of extraordinary measures to destroy biological contaminants, samples associated with longer term electrochemical experiments may suffer from inadvertent inoculation and subsequent growth. In addition, it seems likely that where this is followed by undetected and unanticipated biodegradation of a coating, a metal or the combined system, subsequent EIS analysis may produce spurious data.