H2C2O4 Solution Research Articles

Synthesis and Investigation of New Vitreous Materials with Two Magnetic Subsystems (Fe3O4 and MnxOy)

New vitreous composite materials (CMs) with two magnetic subsystems are synthesized by impregnation magnetite-containing matrices from iron-containing nanoporous glasses in aqueous MnCl2 and H2C2O4 solutions and the subsequent formation of manganese oxides MnxOy (x = 1, 2, 3; y = 1, 2, 3, 4) inside the pore space of the matrices as a result of thermolysis of the reaction product of the dopants (MnC2O4). The chemical (elemental) and phase compositions, the valence-coordination state of iron and manganese, and the characteristics of the magnetic state of the synthesized CMs are studied and compared with the characteristics of nanoporous matrices.

Obtaining Porous Structures in the Form of Parallel Plates on Aluminum Substrates

We report how to obtain self-organized porous microstructures of Anodized Aluminum, using high purity Aluminum substrates of 1 cm2 and 0.5 mm, 0.13 mm thick. Microstructures were obtained by electrochemical attack, using a solution of NaOH and H2C2O4 at a temperature of 55 °C, 20V and attack times of 10, 20, 30, 60, 120, 180, 240 minutes. As a result, micrographs showed pores in the form of parallel sheets of aluminum oxides and hydroxides said according to the characterization tests

Biotite reactivity in nitric and oxalic acid at low temperature and acid pH from surface and bulk dissolution measurements

The dissolution of biotite, a trioctahedral mica, was investigated for a temperature range of 25–70 °C and a pH range of 1–3 in the presence of HNO3 (nitric acid) and H2C2O4 (oxalic acid) solutions. Single millimetric, cleaved flakes of biotite were reacted in batch and flow-through experiments to obtain kinetic information and elucidate the mechanisms that control the overall dissolution reaction under these conditions. The reacting basal surface was explored using in-situ laser confocal microscopy (LCM-DIM) and ex-situ scanning and phase shifting interferometry (VSI-PSI), while the release of tetrahedral (Al and Si), octahedral (Mg and Fe) and exchange (K) cations in solution was monitored over time. This experimental approach allowed us to calculate far-from-equilibrium dissolution rates associated with changes in topography of the (001) surface (horizontal retreat (Rstep) and vertical retreat (Rvertical)), etch pit formation and growth (Rpit) and the release of Si in solution, i.e., bulk dissolution (Rbulk,Si). In HNO3 solutions, a proton promoted reaction mechanism (PPRM), through proton adsorption on the biotite surface, was dominant. The variation of Rstep, Rvertical and Rbulk,Si accounting for the dissolution of (hk0) surfaces at different temperature and pH was used to calculate the apparent activation energy (Ea) and the proton reaction order (nH+). The respective values decreased from 63 kJ mol−1 at pH 1 to 31 kJ mol−1 at pH 3 and increased from 0.46 at 25 °C to 0.77 at 70 °C. This variability was related to the variation of proton consumption with temperature. In H2C2O4 solutions, formation and growth of etch pits on the (001) surface occurred, yielding an increase in surface roughening. Rpit accounted for the rate of etch pit development which was observed to increase, as temperature increased. Based on Rpit, relatively high Ea values (121 kJ mol−1 and 162 kJ mol−1) were associated with an early evolution of the basal etch pits, whereas lower values (36 kJ mol−1 and 56 kJ mol−1) were calculated using Rbulk,Si. The present study contributes to the interpretation of the mechanisms involved in the biotite dissolution process at highly acidic pH, in the presence of inorganic and organic acid, and low temperature (T ≤ 80 °C). Furthermore, our results highlight the importance of combining surface and bulk analyses to assess the balance between the different reactions involving proton consumption during the dissolution and its dependency on temperature, pH and organic acids concentration.

Influence of dealloying solution on the microstructure of nanoporous copper through chemical dealloying of Al75Cu25ribbons

Abstract

The effect of 2D-MoS2 doped polypyrrole coatings on brass corrosion

Abstract Conductive polymers have an important potential against the corrosion applications because they are highly resistant to chemicals besides they have homogeneous coating properties and transport metals to more noble regions. However, the major disadvantage of conductive polymers such as polypyrrole (PPy) is their low mechanical strength. In this study, the doping effect of MoS2 into the PPy coatings by the electropolymerization of polypyrrole (PPy) and exfoliated MoS2 on the corrosion of brass was investigated. The corrosion protection of these coatings were determined by measuring the corrosion rates with Tafel polarization method in 0.1 M H2SO4 media. PPy and MoS2 doped PPy (MoS2@PPy) coatings were successfully obtained by the use of chronoamperometry technique in 0.2 M H2C2O4 solutions with 0.2 M pyrrole and various concentrations of MoS2. It was observed that MoS2@PPy coatings were homogeneously coated without and with all MoS2 concentrations on the metal surface and well adhered to the brass surface, but MoS2@PPy coating with 25 ppm MoS2 showed the best corrosion protection. The surface and chemical characterizations of the coatings were performed by SEM-EDS.

Solubility of Ozone in Aqueous Solutions of Oxalic Acid and Potassium and Sodium Nitrates: Determination of the Anion-Specific Parameter for the Oxalate Ion in a Model for the Solubility of Gases in Electrolyte Solutions

The solubility of ozone in solutions of oxalic acid H2C2O4 and potassium nitrate at concentrations up to 1 and 2 M, respectively, is studied at 25°C. The Sechenov constants for these electrolyte solutions are found: 0.081 ± 0.010 and 0.082 ± 0.004 M–1, respectively. The anion-specific parameter in the Weisenberger–Schumpe gas solubility model for oxalate ion is determined: $${{h}_{{{{{\text{C}}}_{2}}{\text{O}}_{4}^{{2 - }}}}}$$ = 0.1266 M–1. A set of coefficients is determined using the experimental data from various sources to calculate the density of H2C2O4 solutions as a function of temperature in the range of 5–100°C at solution concentrations up to the saturated concentration at a given temperature.

In Situ Preparation and Corrosion Resistance of a ZrO2 Film on a ZrB2 Ceramic

ZrO2 films were in situ prepared using the anodic passivation of a ZrB2 ceramic in alkaline solutions. The composition and structure of the films were characterized using field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The corrosion resistances were evaluated in 0.1 M oxalate solution using the potentiodynamic polarization method (PDP) and the electrochemical impedance spectroscopy (EIS) technique. The results show that ZrO2 films can be prepared using anodization from −0.8 to 0.8 V standard hydrogen electrode (SHE) in 2–16 M NaOH solutions. During the anodization, the dehydration reaction of Zr(OH)4 to ZrO2 caused the volume shrinkage and tensile stress of the films. When the thickness of the films exceeded a critical value, the mud-cracking morphology occurred. The films without cracks exhibited the inhibition effect and provided effective corrosion protection in a 0.1 M H2C2O4 solution, which had a positive correlation with the film thickness. The film obtained when put in an 8 M NaOH solution (near the critical thickness) was found to significantly improve its corrosion resistance when put in a 0.1 M H2C2O4 solution by almost one order of magnitude compared with the bare ceramic.

172Hf → 172Lu Radionuclide Generator Based on a Reverse-Tandem Separation Scheme

The distribution coefficients of Hf(IV) and Lu(III) between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and mixed HCl–H2C2O4 solutions and between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and citric acid solutions were determined. A number of modifications of the 172Hf → 172Lu generator, based on reverse separation schemes, were examined. Systems consisting of an anion-exchange resin and a solution of appropriate organic acid were taken as a chemical basis of the generator. Irreversible sorption of 172Lu in generator columns was studied. The optimum operation mode of the 172Hf → 172Lu generator based on the reverse-tandem scheme with periodic transfer of the parent radionuclide into the liquid phase was determined.

Activation of the nickel foam as a current collector for application in supercapacitors

Nickel foam is widely used as a current collector and as a major component of the faradic electrode in supercapacitors. Activation of nickel foam would allow increasing the capacity of the nickel hydroxide electrode or preparing high-speed electrodes without additional active material. Multiple (1 – 20 times) short-term (5 min) treatment in a 1 М solution of HCl, H3BO3 or H2C2O4 has been proposed. The possibilities of activation of commercial nickel foam samples manufactured by “Novoment-Perm” (Russian Federation) and “Linyi Gelon LIB Co Ltd” (China) have been studied. Activated and non-activated nickel foam samples have been studied by means of X-ray diffraction analysis and scanning electron microscopy, electrochemical characteristics were determined by means of cyclic voltamperometry and galvanostatic charge-discharge cycling in the supercapacitor regime. The comparative analysis of nickel foam samples from Chinese and Russain manufacturers has revealed very low reactivity and low susceptibility to activation of nickel foam from Chinese manufacturer. An assumption has been made that low reactivity is because the sample is composed of Ni-P or Ni-B alloy. The maximum specific capacity of 0.084 F/cm2 has been obtained after 20 treatments in HCl solutions. The activation mechanism is the increase in the specific surface area of nickel. However, this value is significantly lower than that of non-activated nickel foam from Russian manufacturer (0.333 F/cm2). It has been discovered that the nickel foam sample from Russian manufacturer can be easily activated. The maximum activation effect is achieved when treated with oxalic acid: specific capacities are 1.213 F/cm2 (one treatment), 6.578 F/cm2 (five treatments) and 20.003 F/cm2 (twenty treatments). The activation mechanism is the formation of nickel oxalate on the surface of nickel foam. The results of the comparative analysis have revealed the effectiveness of activation of the nickel foam sample from Russian manufacturer by multiple short-term treatment with oxalic acid. It has been concluded that activation of the nickel foam sample from Chinese manufacturer by multiple short-term treatment in solutions of hydrochloric, boric and oxalic acids is ineffective. Activation of nickel foam from Chinese manufacturer requires the development of a different method.

Corrosion protection of new composite polymer coating for carbon steel in sulfuric acid medium by electrochemical methods

In this paper, electropolymerization technique has been used for the obtained of new composite: polypyrrole – dioctyl sulfosuccinate sodium/poly N-ethylaniline (PPY-AOT/PNEA) coatings over carbon steel of type OLC 45 electrode for anticorrosion protection. The PPY-AOT/PNEA coatings were successfully synthesized onto OLC 45 electrode by galvanostatic deposition from aqueous solutions 0.1 M NEA, 0.1 M PY, 0.01 M AOT and 0.3 M H2C2O4 solution at different current densities (5, 3 and 1 mA/cm2) in different molar ratio. The anionic surfactant (AOT) as a dopant ion used during electropolymerization can have a significant result on the anticorrosion protection of the composite film by hindering the penetration of aggressive ions. The polymeric composite coatings have been analyzed by cyclic voltammetry (CV), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) methods. The corrosion resistance of PPY-AOT/PNEA coated carbon steel has been examined by potentiodynamic polarization techniques and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H2SO4 solutions. The data of the corrosion samples demonstrated that PPY-AOT/PNEA coatings assure a great anticorrosion protection of OLC 45 electrode in corrosive media. The corrosion rate of PPY-AOT/PNEA coated OLC 45 has been indicated to be ~9 times lower than of uncoated electrode. The corrosion protection effectiveness of the composite coating is more than 89%. The best efficiency is accomplished of PPY-AOT/PNEA obtained by electrodeposition at 5 mA/cm2 current densities applied in molar ratio 5:1.

Conditions for a nearly perfect match between pulse voltammetry and linear scan voltammetry

It is formally shown that linear scan voltammetry for a reversible charge-transfer on redox and metal/metal-ion electrodes can be approximated with great precision using the forward individual current in differential pulse voltammetry implemented with a ratio of 0.4 between the pulse duration and the period of the waveform. For redox electrodes the same is also possible using the forward current in square wave voltammetry. In each case, there is coincidence with the linear scan voltammogram for a constant pulse-to-step height ratio. The relevance of this new approach is discussed and an experimental application with the Ti(IV)/Ti(III) couple in 0.25 M H2C2O4 solution at the mercury drop electrode is presented.

Pore Embryos in Porous/Compact/Porous Anodic Alumina by Three-Step Anodization

In order to study the formation process of the pore embryos in porous anodic alumina (PAA) and compact aluminum oxide (CAO), a new three-tier structure (PAA-CAO-PAA) was designed and fabricated in 3 wt% H2C2O4 and 8 wt% ammonium sebacate aqueous solutions. By exactly controlling the time of the third anodization in 3 wt% H2C2O4 solution, the formation process of the pore embryos is explicitly seen for the first time. The hemispherical pore bottom and hemispherical barrier-oxide base generated in the first anodization. After the second anodization, two hemispherical structures disappear and two interfaces become flat. When the third anodization finished under given voltage and anodizing time, the hemispherical structures reappear. A bigger hemispherical barrier-oxide base and spiny oxide formed in the third anodization. Besides, the newly formed pore embryos are not connected with the above pores and the channels cannot be observed in the compact oxide layer. All these facts cannot be explained by the traditional field-assisted dissolution model. Based on the oxide flow model and the electronic current theory, the formation process of pore embryos under the compact layer can be elucidated by the oxygen bubble mould effect.

Determination of conversion reaction mechanism of celestite to acidic strontium oxalate hydrate in aqueous solution of H2C2O4

One of the most important steps to obtain high-temperature superconductive and self-activated luminescence strontium compounds is the production of strontium oxalate as precursor. The aim of this study is to determine the conversion reaction mechanism of celestite to acidic strontium oxalate hydrate in solutions obtained by dissolving H2C2O4 in distilled water. The effect of temperature on the conversion reaction mechanism using excess amounts of H2C2O4 with respect to the conversion reaction stoichiometry was determined.The conversion of celestite to acidic strontium oxalate in H2C2O4 solutions proceeds in two consecutive reaction steps. In the first step, SrC2O4·H2O is formed and in the second, H[Sr(C2O4)1.5(H2O)] is formed. The conversion reaction ends by the formation of SrC2O4·H2O on the surfaces of the celestite particles. The saturation concentration of H[Sr(C2O4)1.5(H2O)] chelate compound decreases during cooling of the solution and the excess amount of Sr(HC2O4)(C2O4)0.5·H2O crystallizes. XRD, ICP - OES and simultaneous TG/DTA – MS analytical techniques were used to explain the conversion reaction mechanism.

Extraction of Ga and Ge from zinc refinery residues in H2C2O4 solutions containing H2O2

A new oxalic acid (H2C2O4) and hydrogen peroxide (H2O2) based extraction process was developed to recover valuable metals - in particular Ga and Ge - from the zinc refinery residues. H2C2O4 and H2O2 leaching studies indicated that the selective leaching of metals in the residues, that primarily contain Zn, Cu, Fe, SiO2, Ga and Ge, can be achieved. Under the optimal leaching conditions ([H2C2O4]=110g/L, [H2O2]=0.12mol/L, L/S ratio=8, T=40°C and t=30min), 99.32% of the Ga, 98.86% of the Ge and 30.25% of the Fe were leached out, whereas the leaching of Zn, Cu and Si only reached 0.30%, 0.82% and 0.43%, respectively. Concerning leachate purification, 98.31% of the iron could be removed in the form of FeC2O4·2H2O with minor losses of Ga and Ge (1.08% and 0.68%) using an ultrasound-assisted iron powder replacement method under optimal conditions. The Ga (99.36%) and Ge (99.89%) were subsequently extracted by tri(octyl-decyl)amine (N235). After extraction, the loaded organic phase was stripped of Ga (98.91%) and Ge (99.21%) into separate solutions using sequential treatments of 2mol/L H2SO4 and 4mol/L NaOH respectively. Based on these results, a process flow sheet of efficient separation and recovery of Ga and Ge is presented.

Coatings of Conducting Polymers for Corrosion Protection of Mild Steel

The investigation of electrochemical behavior of different conducting polymers, polythiophene (PTh), polypyrrole (PPy) and polyterthiophene (PTTh) on a mild steel (MS) electrode were done. Moreover, the combinations of the conducting polymers PTh and PPy was investigated. The synthesis of all polymeric coatings was done by the cyclic voltammetry technique. The electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion performance of coated mild steel by different polymers in 0.5 M of different acid solutions (HCl, HClO4, H2 C 2 O 4, H3PO4 and HNO3). The protection of all polymeric coatings against corrosion of the substrate was promising and the bilayer coating PPy/PTh gave the best protection efficiency in all used acids. The order of efficiency for the different coatings in HCl and HNO3 solutions was MS/PPy/PTh > MS/PPy > MS/PTTh > MS/PTh but the order in HClO4, H3PO4 and H2 C 2 O 4 solutions was MS/PPy/PTh > MS/PTTh > MS/PPy > MS/PTh.

Corrosion behavior of sintered CeNdFeB magnets in different solutions

The capability of CeNdFeB as a substitute for NdFeB is of considerable interest due to its cost effectiveness and fascinating magnetic properties. In this paper, we have systematically investigated the corrosion behavior of the sintered CeNdFeB magnets in alkaline and acidic media in order to evaluate their commercial viability. Electrochemical and immersion tests have been conducted using sintered CeNdFeB magnets with different amounts of Ce (0.0 wt%, 29.6 wt%, 44.6 wt%, 54.8 wt%) as substitution of Nd in different concentrations of sodium hydroxide (NaOH), nitric acid (HNO3), hydrochloric acid (HCl), sulfuric acid (H2SO4), and oxalic acid (H2C2O4). We have found that the sintered CeNdFeB magnets exhibit passive behavior and the corrosion rate decreases in NaOH and H2C2O4 solutions by comparison with sintered NdFeB magnets. When exposed in strong acids, the sintered CeNdFeB has comparable corrosion properties with sintered NdFeB in HNO3 solution and lower anticorrosion properties in HCl and H2SO4 solutions.

Recovering Y and Eu from Waste Phosphors Using Chlorination Roasting—Water Leaching Process

Recovering Y and Eu from waste phosphors using chlorination roasting followed by a water leaching process was investigated in this study. Firstly, by chlorination roasting and water leaching, Y and Eu elements present in waste phosphors were efficiently extracted into a leach solution. Secondly, the majority of the impurities in the solution can be removed by adjusting the pH to 4.5 using a Na2S and NH3·H2O solution. Thirdly, the rare earths can be precipitated afterwards by adding a H2C2O4 solution and adjusting the pH to 2.0. Then rare earth oxides (REOs) can be obtained after calcining at 800 °C for 1 h. The characterization study of the waste phosphors and the rare earth oxide products was performed by XRD, XRF, and SEM-EDS analysis to determine the phase and morphological features. Influences of the factors, such as roasting temperatures and time, the addition of ammonium chloride on the roasting of waste phosphors, as well as the pH and the amount of oxalates on the precipitation of Y and Eu, were investigated. The maximum grade (99.84%) of mixed rare earth oxides and recovery rate (87.35%) of Y and Eu were obtained at the optimized conditions.

ChemInform Abstract: Tl2C2O4·H2C2 O4: A New Crystalline Form of Thallium(I) Oxalate.

AbstractThe title compound is synthesized by addition of solid Tl2CO3 to a boiling solution of H2C2O4 in H2O (10 min, 75% yield) and characterized by single crystal XRD, FTIR, and FT Raman spectroscopy.

High Performance Pure Sulfur Honeycomb-like Architectures Synthesized By Cooperative Self-Assembly Strategy for the Lithium/Sulfur Battery

In this study, pure sulfur particles with honeycomb morphology were prepared via a cooperative self-assembly process, in which sodium dodecyl benzene sulphonate (SDBS) was used as a soft template to form the porous structure. To the best of the authors’ knowledge, there has been no report on using the cooperative self-assembly method to prepare honeycomb-like sulfur particles. Moreover, the method proposed in this paper is simple, easily scaled up, and has low energy consumption. As shown in Figure 1a, the structure of SDBS in aqueous solution can easily take on different forms, responding to the concentration of SDBS (CSDBS) and the concentration of salt (Csalt) in the solution1. The mechanism of the pore formation is shown in Figure 1b and c. First, after dropping H2C2O4 solution into Na2S2O3 and SDBS solution, the SDBS lamellar micelles are transformed to spherical micelles as the concentrations of SDBS and salt decrease. At the same time, the sulfur starts to precipitate. Thus, cooperative self-assembly occurs between the sulfur and the SDBS spherical micelles. Then, many more sulfur particles are produced, resulting in further condensation. Secondly, after adding a large amount of H2O into the above solution, the SDBS spherical micelles break, and the SDBS is removed. The sulfur particles with porous honeycomb-like structure are then finally obtained, which is shown in Figure 1e. We believe that this method can provide useful information to a broad audience of readers working on the synthesis of porous sulfur for various applications, such as in chemical fertilizers, the pharmaceutical industry, the rubber and fibre industries, bioleaching processes, anti-microbial agents, insecticides, fumigants, etc. It will also be of interest to researchers working on Li/Sulfur batteries, which are now considered as an environmentally friendly and competitive alternative to classical Li-ion batteries. Due to their porous structure, the Li/S batteries fabricated from the as-prepared honeycomb-like sulfur cathode without any extra adsorption additives show significantly improved electrochemical performance compared with the batteries using commercial sulfur powder. As shown in Figure 1f, the cells with the honeycomb-like sulfur electrode retained a reversible discharge capacity higher than 650 mAh g−1 for 50 cycles, while the discharge capacity of the commercial sulfur (FESEM image in Figure 1d) is about 200 mAh g-1. And the honeycomb structure also gave much better rate capability than that of the commercial sulfur electrode.Figure captions:Figure 1. (a) Different types of SDBS structure in aqueous solution; (b) details of the synthesis; (c) mechanism of the synthesis of the honeycomb like sulfur particles; (d) FESEM image of commercial sulfur; (e) FESEM image of honeycomb-like sulfur; (f) cycling performance of honeycomb-like sulfur electrode and commercial sulfur electrode in lithium/sulfur batteries.Reference:N. Pal and A. Bhaumik, Adv.Colloid and Interface Sci., 2013, 189, 21-41

Kinetic investigation of dissolution of CaWO4 in oxalic acid solution

In this study, the effects of stirring speed, temperature, H2C2O4 concentration and particle size on the dissolution rate of CaWO4 in H2C2O4 solutions were investigated. CaWO4 was dissolved in H2C2O4 solutions as series parallel type reaction. In the first step which took place according to Langmuir-Hinshelwood Mechanism, H2C2O4 was adsorbed as a mobile adsorption layer on the surface of CaWO4, reacted to form adsorbed calcium aqua oxalato tungstate (Ca[WO3(C2O4)H2O]) intermediate product and the adsorbed Ca[WO3(C2O4)H2O] was desorbed into the solution. In the second step, Ca[WO3(C2O4)H2O] hydrolysed and formed H2WO4 which reacted with H2C2O4 to form hydrogen aqua oxalato tungstate (H2[WO3(C2O4)H2O]) as end product together with solid CaC2O4H2O. Model kinetic equations were derived which showed the relationships of the fractional conversion of CaWO4, the concentration of Ca[WO3(C2O4)H2O] and the concentration of H2[WO3(C2O4)H2O] with time. The diagrams drawn according to the model kinetic equations were in good agreement with the experimentally obtained diagrams (R2>0·99).Dans cette étude, on a examiné les effets de la vitesse d’agitation, de la température, de la concentration d’H2C2O4 et de la taille de particule sur la vitesse de dissolution de CaWO4 dans des solutions d’H2C2O4. On a dissous le CaWO4 dans des solutions d’H2C2O4 en une réaction de type série-parallèle. Dans la première étape, qui avait lieu d’après le Mécanisme de Langmuir-Hinshelwood, l’H2C2O4 était adsorbé en une couche mobile d’adsorption à la surface du CaWO4, réagissait pour former le produit intermédiaire adsorbé, aqua oxalato tungstate de calcium (Ca[WO3(C2O4)H2O]), et ce Ca[WO3(C2O4)H2O] adsorbé était désorbé dans la solution. Dans la seconde étape, le Ca[WO3(C2O4)H2O] était hydrolysé et formait l’H2WO4 qui réagissait avec l’H2C2O4 pour former de l’aqua oxalato tungstate d’hydrogène (H2[WO3(C2O4)H2O]) comme produit final avec le CaC2O4H2O solide. On a dérivé les équations cinétiques du modèle, lesquelles montraient les relations de la conversion fractionnelle du CaWO4, de la concentration de Ca[WO3(C2O4)H2O] et de la concentration d’H2[WO3(C2O4)H2O] en fonction du temps. Les diagrammes dessinés d’après les équations cinétiques du modèle étaient en bon accord avec les diagrammes obtenus expérimentalement (R2>0·99).