DIAGRAMAS DE POURBAIX PDF

  • June 15, 2019

Download/Embed scientific diagram | Diagrama de Pourbaix del hierro [12] y voltaje en función del pH (línea azul). from publication: Síntesis de nanopartículas. Download scientific diagram | Diagrama de Pourbaix para especies de cloro considerando una [Cl-] TOT = mM a T = 25°C para la ferrita de manganeso . ESPECIE. ΔG° (cal/mol). Pb. 0. PbO. , Pb3O4. , Pb2O3. , PbO2. , Pb2+. -5, Pb4+. 72, H2O. , REACCIONES DE.

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Pourbaix diagram – Wikipedia

While such diagrams can be drawn for any chemical system, it is important to note that the addition of a metal binding agent ligand will often modify the diagram. Vertical, horizontal, and sloped.

Using the Pourbaix diagram correctly will help shed light not only on the nature of the species present in the solution or sample but may also help to understand the reaction mechanism. Above this line, water will be oxidized to form oxygen gas, and it will usually not be possible to pass beyond this line as long as there is still water present to be oxidized.

Diagrama de Pourbaix – Wikipédia, a enciclopédia livre

This will vary with temperature. On either side of the line, one form of the species will instead be said to be predominant. Environmental Chemistry – a global perspective porbaix ed. United States Government Printing Office.

Archived from the original on The lines in the Pourbaix diagram show the equilibrium conditions, that is, where the activities are equal, for the species on each side of that line. In the Pourbaix diagram for uranium, the limits of stability of water are marked by the two dashed green lines, and the stability region for water falls between these lines.

In order to draw the position of the lines with the Nernst equation, the activity of the chemical species at equilibrium must be defined. Using the Nernst equation as above, but with an E 0 of 1. The reaction equation is found to be:.

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The vertical axis is labeled E H for the voltage potential with respect to the standard hydrogen electrode SHE as calculated by the Nernst equation. Views Read Edit View history. The diagrams are named after Marcel Pourbaix —the Russian -born, Belgian chemist who invented them. As a function of temperature. Wikimedia Commons has media related to Pourbaix diagrams. For instance, carbonate has a great effect upon the diagram for uranium.

The reaction equation is written:. As such a Pourbaix diagram can be read much like a standard phase diagram with a different set of axes. A simplified Pourbaix diagram indicates regions of “Immunity”, “Corrosion” and “Passivity”, instead of the stable species.

Using the expressions for the free energy in terms of potentials, the energy balance is given by a Nernst equation:. In other projects Wikimedia Commons. Pourbaix diagrams have several uses, for example in corrosion studies, geoscience and in environmental studies. In these cases, pE is used instead of E H. Predominant ion boundaries are represented by lines.

See diagrams at right. The same values should be used for all species present in the system. The reaction equation may be written:.

A base-balanced equation can be converted to an acid-balanced equation using the equilibrium constant for the self-ionization of waterand only acid-balanced equations are considered below. The “H” stands for hydrogen, although other standards may be used, and they are for room temperature only. In addition, changes in temperature and concentration of solvated ions in solution will shift the equilibrium lines in accordance with the Nernst equation. This page was last edited on 26 Decemberat Pourbaix diagrams are also known as E H -pH diagrams due to the labeling of the two axes.

Similarly to phase diagrams, they do not allow for reaction rate or kinetic effects. Retrieved from ” https: In many cases, the possible conditions in a system are limited by the stability region of water. Geological Survey water-Supply Paper They thus give a guide to the stability of a particular metal in a specific environment.

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The equation must be balanced for M, H, O and charge. The presence of trace amounts of certain species such as diagramss ions can also greatly affect the stability of certain species by destroying passivating layers. Usually, the activity of a species is approximated as equal to the concentration for soluble species or partial pressure for gases.

Passivation occurs when the metal forms a stable coating of an oxide or other salt on its surface, the best example being the relative stability of aluminium because of the alumina layer formed on its surface when exposed to air. There are three types of line boundaries in a Pourbaix diagram: Below this line, water will be reduced to hydrogen, and it will usually not be possible to pass beyond this line as long as there is still water present to be reduced.

The reaction equation is:. From Wikipedia, the free encyclopedia.

Diagrama de Pourbaix

The diagrams also do not take kinetic effects into account, meaning that species shown as unstable might not react to any significant degree in practice. Immunity means that the metal is not attacked, while corrosion shows that general attack will occur.

Archived copy as title Commons category link is on Wikidata. Sometimes additional lines are drawn for other concentrations. By using this site, you agree to the Terms of Use and Privacy Policy. Pourbaix diagrams are widely used to describe the chemical behaviour of chemical species in the hydrosphere.

For the simple ds of a thermodynamic system consisting of a metal M and water, various reaction equations may be written having the form:.