CONTRIBUTION A L'ETUDE DES ARSENIATES DOUBLES DE SODIUM ET D'UN METAL TRIVALENT (ALUMINIUM OU FER) PDF Download

Author: M.. SCREPEL
Publisher:
ISBN:
Category :
Languages : fr
Pages : 21

View

Book Description
PREPARATION D'ARSENIATES DOUBLES DE SODIUM ET D'UN METAL TRIVALENT (AL OU FE). COMPOSITION, PROPRIETES, PYROLYSE, STRUCTURE CRISTALLINE DE CES COMPOSES

Author: VALERIE.. TROMMETTER
Publisher:
ISBN:
Category :
Languages : fr
Pages : 253

View

Book Description
LA QUALITE DE LA RESSOURCE EAU PEUT ETRE DEGRADEE PAR LA PRESENCE D'ELEMENTS CHIMIQUES INDESIRABLES D'ORIGINE NATURELLE OU ANTHROPOGENIQUE. CETTE ETUDE AVAIT POUR OBJECTIF UNE MEILLEURE COMPREHENSION DES MECANISMES DE TRANSPORT D'UN COMPOSE TRES TOXIQUE, L'ARSENIATE AS(V), EN PRESENCE D'UN MILIEU POREUX SATURE EN EAU AFIN D'ESTIMER SON DEVENIR DANS UN AQUIFERE SOUTERRAIN. AFIN DE SE RAPPROCHER AU MIEUX DES CONDITIONS REELLES, LES EXPERIENCES ONT ETE MENEES A L'AIDE DE REACTEURS COLONNE PERMETTANT DE TENIR COMPTE DE LA DYNAMIQUE DES ECOULEMENTS. LES CONCENTRATIONS EN AS(V) UTILISEES SONT INFERIEURES A 14 MOL.L - 1 ET LE MILIEU POREUX EST UN SABLE DE QUARTZ D'ORIGINE NATURELLE. LES ETUDES ONT PERMIS DE METTRE EN EVIDENCE QUELQUES PROPRIETES DE TRANSPORT D'AS(V) A TRAVERS LE MILIEU POREUX. TOUT D'ABORD, IL EXISTE UN EFFET CINETIQUE, PROBABLEMENT D'ORIGINE DIFFUSIONNELLE, AINSI QU'UNE ABSENCE DE RELATION LINEAIRE ENTRE LA CONCENTRATION EN SOLUTION ET CELLE SORBEE DANS LE DOMAINE DE CONCENTRATIONS ETUDIEES. LA FORCE IONIQUE INFLUENCE PEU LA SORPTION, CE QUI CONFIRMERAIT QU'AS(V) S'ADSORBE PAR FORMATION DE COMPLEXES DE SPHERE INTERNE. EN PRESENCE DE PHOSPHATES, LA RETENTION D'AS(V) DIMINUE FORTEMENT, CE QUI INDIQUE QU'IL EXISTE UNE COMPETITION POUR LES SITES DE SURFACE. LE PH EST EGALEMENT UN PARAMETRE IMPORTANT DE LA SORPTION D'AS(V) PUISQUE LA RETENTION EST MAXIMALE DANS UN DOMAINE DE PH COMPRIS ENTRE 4 ET 6. AUX PH 6 ET 7, UNE FRACTION D'AS(V) EST REDUITE EN AS(III). EN OUTRE, A PH 4, UNE DISSOLUTION DES MINERAUX A BASE DE FER A ETE MISE EN EVIDENCE. LA NATURE DES SITES RESPONSABLES DE LA SORPTION D'AS(V) PAR CE MILIEU POREUX COMPOSE DE DIFFERENTES PHASES MINERALOGIQUES A EGALEMENT ETE RECHERCHEE. LES ETUDES ONT MONTRE QUE LES GROUPEMENTS SILANOLS ONT PEU D'AFFINITE POUR AS(V) ALORS QUE LES (HYDR)OXYDES DE FER, D'ALUMINIUM ET DE MANGANESE ET EVENTUELLEMENT LES ARGILES, PRESENTS EN FAIBLE TENEUR, SONT LES PRINCIPAUX RESPONSABLES DE LA RETENTION D'AS(V).

Author: Louis Cot
Publisher:
ISBN:
Category :
Languages : fr
Pages : 57

View

Book Description

Author: Michel Ronis
Publisher:
ISBN:
Category :
Languages : fr
Pages : 244

View

Book Description

Author: Robert Mas (chimiste).)
Publisher:
ISBN:
Category : Arsenates
Languages : fr
Pages : 50

View

Book Description
Nos connaissances sur les arséniates de cuivre sont d'ailleurs limitées : aucune étude d'ensemble n'a été effectuée et les essais opérés par les quelques auteurs qui se sont intéressés à cette question sont le plus souvent difficilement reproductibles, faute des précisions nécessaires. Il nous est donc apparu utile de reprendre l'étude systématique des arséniates de cuivre et, notamment, d'établir le diagramme d'équilibre [...] afin de déterminer avec certitude quels étaient les arséniates susceptibles d'exister ainsi que leurs conditions de stabilité. Ce premier travail, rendu délicat par l'existence d'équilibres métastables, nous a permis de caractériser des sels qui n'avaient pas été signalés. En présence d'espèces chimiques définies, nous avons pu aborder l'examen des propriétés physiques et chimiques des divers arséniates de cuivre ; en particulier l'étude de l'action de la chaleur et des réducteurs, non abordée jusqu'ici, nous a conduits à des résultats assez différents de ceux obtenus avec d'autres arséniates. La possibilité d'utiliser les réactions de double décomposition pour préparer ces sels nous a amenés à étudier l'action exercée sur ceux-ci par les solutions salines ; ceci nous a permis d'interpréter certains des résultats obtenus précedemment et de donner au problème général de la préparation des arséniates de cuivre, résolu jusqu'ici d'une façon assez empirique, une base rationnelle. Il convenait enfin, étant donné les applications éventuelles de ces produits en phytopharmacie, d'examiner les propriétés de ces sels en relation avec leur emploi comme insecticides.

Author: National Research Council
Publisher: National Academies Press
ISBN: 0309170435
Category : Nature
Languages : en
Pages : 241

View

Book Description
Having safe drinking water is important to all Americans. The Environmental Protection Agency's decision in the summer of 2001 to delay implementing a new, more stringent standard for the maximum allowable level for arsenic in drinking water generated a great deal of criticism and controversy. Ultimately at issue were newer data on arsenic beyond those that had been examined in a 1999 National Research Council report. EPA asked the National Research Council for an evaluation of the new data available. The committee's analyses and conclusions are presented in Arsenic in Drinking Water: 2001 Update. New epidemiological studies are critically evaluated, as are new experimental data that provide information on how and at what level arsenic in drinking water can lead to cancer. The report's findings are consistent with those of the 1999 report that found high risks of cancer at the previous federal standard of 50 parts per billion. In fact, the new report concludes that men and women who consume water containing 3 parts per billion of arsenic daily have about a 1 in 1,000 increased risk of developing bladder or lung cancer during their lifetime.

Author: Agnes Buka
Publisher: World Scientific
ISBN: 1848167997
Category : Science
Languages : en
Pages : 299

View

Book Description
The book intends to give a state-of-the-art overview of flexoelectricity, a linear physical coupling between mechanical (orientational) deformations and electric polarization, which is specific to systems with orientational order, such as liquid crystals. Chapters written by experts in the field shed light on theoretical as well as experimental aspects of research carried out since the discovery of flexoelectricity. Besides a common macroscopic (continuum) description the microscopic theory of flexoelectricity is also addressed. Electro-optic effects due to or modified by flexoelectricity as well as various (direct and indirect) measurement methods are discussed. Special emphasis is given to the role of flexoelectricity in pattern-forming instabilities. While the main focus of the book lies in flexoelectricity in nematic liquid crystals, peculiarities of other mesophases (bent-core systems, cholesterics, and smectics) are also reviewed. Flexoelectricity has relevance to biological (living) systems and can also offer possibilities for technical applications. The basics of these two interdisciplinary fields are also summarized.

Author: Gerald G. Moy
Publisher: Springer
ISBN: 9781493939091
Category : Technology & Engineering
Languages : en
Pages : 0

View

Book Description
Unless a food is grossly contaminated, consumers are unable to detect through sight or smell the presence of low levels of toxic chemicals in their foods. Furthermore, the toxic effects of exposure to low levels of chemicals are often manifested slowly, sometimes for decades, as in the case of cancer or organ failure. As a result, safeguarding food from such hazards requires the constant monitoring of the food supply using sophisticated laboratory analysis. While the food industry bears the primary responsibility for assuring the safety of its products, the overall protection of people’s diets from chemical hazards must be considered one of the most important public health functions of any government. Unfortunately, many countries do not have sufficient capability and capacity to monitor the exposure of their populations to many potentially toxic chemicals that could be present in food and drinking water. Without such monitoring, public health authorities in many countries are not able to identify and respond to problems posed by toxic chemicals, which may harm their population and undermine consumer confidence in the safety of the food supply. From a trade perspective, those countries that cannot demonstrate that the food they produce is free of potentially hazardous chemicals will be greatly disadvantaged or even subject to sanctions in the international marketplace. The goal of a total diet study (TDS) is to provide basic information on the levels and trends of exposure to chemicals in foods as consumed by the population. In other words, foods are processed and prepared as typical for a country before they are analyzed in order to better represent actual dietary intakes. Total diet studies have been used to assess the safe use of agricultural chemicals (e.g., pesticides, antibiotics), food additives (e.g., preservatives, sweetening agents), environmental contaminants (e.g., lead, mercury, arsenic, cadmium, PCBs, dioxins), processing contaminants (e.g., acrylamide, polycyclic aromatic hydrocarbons, chloropropanols), and natural contaminants (e.g., aflatoxin, patulin, other mycotoxins) by determining whether dietary exposure to these chemicals are within acceptable limits. Total diet studies can also be applied to certain nutrients where the goal is to assure intakes are not only below safe upper limits, but also above levels deemed necessary to maintain good health. International and national organizations, such as the World Health Organization, the European Food Safety Agency and the US Food and Drug Administration recognize the TDS approach as one of the most cost-effective means of protecting consumers from chemicals in food, for providing essential information for managing food safety, including food standards, and for setting priorities for further investment and study. Total Diet Studies introduces the TDS concept to a wider audience and presents the various steps in the planning and implementation of a TDS. It illustrates how TDSs are being used to protect public health from chemicals in the food supply in many developed and developing countries. The book also examines some of the applications of TDSs to specific chemicals, including contaminants and nutrients.

Author: Oswald Kubaschewski
Publisher: Pergamon
ISBN:
Category : Science
Languages : en
Pages : 386

View

Book Description
Materials Thermochemistry, the 6th Edition of Metallurgical Thermochemistry, aims to demonstrate the central role of thermochemistry in the understanding and designing of materials and materials processes. Extensively revised and up-dated, the 6th Edition of this classic work includes all the latest developments in experimental methods, new methods for estimating thermochemical data for both pure and alloy substances, new practical applications of thermochemical calculations, and up-dated tables of critically evaluated thermochemical data for inorganic substances and binary alloy systems. The basic principles of chemical thermodynamics are presented in a straightforward way with many examples of the use of thermochemical calculations in solving a variety of materials' problems. Although thermodynamics is an established field, this 6th Edition presents the newest experimental methods and calculations of complex equilibria associated with the most recent materials and environmental considerations (e.g. environmental pollution). This text is suitable for graduates and undergraduates alike and provides basic information necessary for researchers to apply thermochemical principles and data to the optimization of materials and materials processes.

Author: I. Barin
Publisher: Springer Science & Business Media
ISBN: 3662022931
Category : Science
Languages : en
Pages : 950

View

Book Description
For the practical application of thermochemistry to the development and control of tech nical processes, the data for as many substances as possible are needed in conjunction with rapid and simple methods of calculating equilibrium constants, heat balances and the EMF of galvanic cells. For these three types of calculation the following three ther modynamic functions are suitable: The Planck function, the enthalpy and the Gibbs free energy, which are here defined and tabulated as unambigous functions of temperature for pure substances. The first edition of the tables was published in 1973 under the title "Thermochemical Properties of Inorganic Substances". The present supplementary volume contains the data and functions for a further 800 inorganic substances. In addition, the data for about 250 substances from the first volume have been up-dated. These usually small corrections produce better consistency with the data from more recent publications. The comments of users and reviewers of the first volume have largely been concerned with the difference between the present thermodynamic functions and the system used in the JANAF tables, the somewhat unconventional handling of heat balances adopted here, the notation of cell reactions, the description of non-stoichiometric phases and the accuracy of the tabulated data. To answer these questions and criticims the theore tical concepts and the practical use of the tables are dealt with in more detail in the introduction, following the recommendation of some reviewers.