Frenkel defects are most common in salts that have a large anion and a relatively small cation. To preserve electrical neutrality, one of the normal cation sites, usually octahedral, must be vacant.
Since most ionic compounds do not conduct electricity in the solid state, however they do conduct electricity when molten or dissolved in a solvent that separates the ions, allowing them to migrate in response to an applied electric field. In response to an applied voltage, the cations in solid electrolytes can diffuse rapidly through the lattice via octahedral holes, creating Frenkel defects as the cations migrate. Sodium—sulfur batteries use a solid Al 2 O 3 electrolyte with small amounts of solid Na 2 O.
Because the electrolyte cannot leak, it cannot cause corrosion, which gives a battery that uses a solid electrolyte a significant advantage over one with a liquid electrolyte. This results in a positive charge of 0. Because the overall charge is greater than 0, this stoichiometry must be incorrect. The stoichiometry of the solid is thus Na 0. In a sample of MgO that has the sodium chloride structure, 0.
Assuming that all of the cation sites are fully occupied, what is the stoichiometry of the sample? Answer : If the formula of the compound is Mg 0. The formula is thus Mg 0. The law of multiple proportions , states that chemical compounds contain fixed integral ratios of atoms. In fact, nonstoichiometric compounds contain large numbers of defects, usually vacancies, which give rise to stoichiometries that can depart significantly from simple integral ratios without affecting the fundamental structure of the crystal.
These compounds are nonstoichiometric because their constituent metals can exist in multiple oxidation states in the solid, which in combination preserve electrical neutrality. One example is iron II oxide ferrous oxide , which produces the black color in clays and is used as an abrasive.
Its stoichiometry is not FeO because it always contains less than 1. The crystal lattice is able to accommodate this relatively high fraction of substitutions and vacancies with no significant change in structure. Because a crystal must be electrically neutral, any defect that affects the number or charge of the cations must be compensated by a corresponding defect in the number or charge of the anions.
Real crystals contain large numbers of defects. Defects may affect only a single point in the lattice a point defect , a row of lattice points a line defect , or a plane of atoms a plane defect. A point defect can be an atom missing from a site in the crystal a vacancy or an impurity atom that occupies either a normal lattice site a substitutional impurity or a hole in the lattice between atoms an interstitial impurity. In an edge dislocation, an extra plane of atoms is inserted into part of the crystal lattice.
Multiple defects can be introduced into materials so that the presence of one defect prevents the motion of another, in a process called pinning. Because defect motion tends to stop at grain boundaries, controlling the size of the grains in a material controls its mechanical properties. In addition, a process called work hardening introduces defects to toughen metals. Schottky defects are a coupled pair of vacancies—one cation and one anion—that maintains electrical neutrality. A Frenkel defect is an ion that occupies an incorrect site in the lattice.
Cations in such compounds are often able to move rapidly from one site in the crystal to another, resulting in high electrical conductivity in the solid material. Such compounds are called solid electrolytes. Nonstoichiometric compounds have variable stoichiometries over a given range with no dramatic change in crystal structure. This behavior is due to a large number of vacancies or substitutions of one ion by another ion with a different charge.pt.uvelomyfyh.ga
Crystal defect | crystallography | myofetomanut.gq
How are defects and impurities in a solid related? Can a pure, crystalline compound be free of defects? How can a substitutional impurity produce a vacancy? Why does applying a mechanical stress to a covalent solid cause it to fracture? Use an atomic level description to explain why a metal is ductile under conditions that cause a covalent solid to fracture.
How does work hardening increase the strength of a metal? How does work hardening affect the physical properties of a metal? Work-hardened metals and covalent solids such as diamonds are both susceptible to cracking when stressed. Explain how such different materials can both exhibit this property. Suppose you want to produce a ductile material with improved properties. Would impurity atoms of similar or dissimilar atomic size be better at maintaining the ductility of a metal?
TMT4130 - Inorganic Chemistry
How would introducing an impurity that forms polar covalent bonds with the metal atoms affect the ductility of the metal? Explain your reasoning. Substitutional impurities are often used to tune the properties of material. Why are substitutional impurities generally more effective at high concentrations, whereas interstitial impurities are usually effective at low concentrations? How will the introduction of a metal ion with a different charge as an impurity induce the formation of oxygen vacancies in an ionic metal-oxide crystal?
Many nonstoichiometric compounds are transition metal compounds. If you wanted to induce the formation of oxygen vacancies in an ionic crystal, which would you introduce as substitutional impurities—cations with a higher positive charge or a lower positive charge than the cations in the parent structure? Impurity atoms of similar size and with similar chemical properties would be most likely to maintain the ductility of the metal, because they are unlikely to have a large effect on the ease with which one layer of atoms can move past another under mechanical stress.
- Slow River.
- Inorganic Chemistry- Special Topics Flashcards by Evan Kelly | Brainscape.
- Defects in Metals.
- The Old Vengeful (David Audley, Book 12);
- Journal of Solid State Chemistry.
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Most transition metals form at least two cations that differ by only one electron. Laboratory studies of the properties of chemicals of biological origin and the influence of chemical and physical factors on these properties. Laboratory techniques used for the isolation and identification of biochemicals.
Techniques include: free radical and condensation polymerization; molecular weight distribution by gel chromatography; crystallinity and order by differential scanning calorimetry; pyrolysis and gas chromatography; dynamic mechanical and dielectric behavior; morphology and microscopy; surface properties. Physical chemistry of everyday phenomena. Intermolecular forces and electrostatic phenomena at interfaces, boundary tensions and films at interfaces, mass and charge transport in colloidal suspensions, electrostatic and London forces in disperse systems, gas adsorption and heterogeneous catalysis.
Structural and physical aspects of polymers organic, inorganic, natural.
Molecular and atomic basis for polymer properties and behavior. Characteristics of glassy, crystalline, and paracrystal-line states including viscoelastic and relaxation behavior for single-and multi-component systems. Thermodynamics and kinetics of transition phenomena. Structure, morphology, and behavior. Organic chemistry of synthetic high polymers. Polymer nomenclature, properties, and applications. Functionality and reactivity or monomers and polymers. Mechanism and kinetics of step-growth and chain-growth polymerization in homogenous and heterogenous media. Brief description of emulsion polymerization, ionic polymerization, and copolymerization.
Must have completed one year of physical chemistry and one year of organic chemistry.
First year graduate student seminar course and introduction to research. Topics include: research opportunities in the department, introduction to instrumentation facilities, ethics in science, use of library facilities, effective teaching methods. A description of common ligands and their bonding is covered, as well as applications of organnometallic chemistry in organic synthesis and catalysis.
Introduction to transition metal complexes; theories of bonding; kinetics and mechanisms of transition metal complex reactions; selected aspects of organometallic chemistry; bio-inorganic chemistry. Must have completed one semester of physical chemistry and have CAS graduate student status. Research in one of the following fields of chemistry: analytical, inorganic, organic, physical, polymer, biochemistry. Principles of drug design, structureactivity relationships in antibacterial, antimalarial, antiinflammatory and psychoactive drugs; synthesis and modes of action of pharmacologically active agents radioactive pharmaceuticals.
Coverage includes the stages of the drug approval process and how these relate to the laboratory activities that provide the scientific basis of the New Drug Application NDA. Lectures treat drug discovery, chemical process development of the active pharmaceutical ingredient API , and pharmaceutical process development of the drug product.
Regulatory issues in screening and testing, the management of the preclinical trials, and the management of clinical trials will be covered. Principles and applications of statistical mechanics to chemical problems. A study of the techniques for evaluating the properties of matter in bulk from the properties of molecules and their interactions. Development of the principles of classical and statistical thermodynamics and their applications to chemical systems. In classical thermodynamics, emphasis will be on systems in which composition is of major concern: solutions, chemical and phase equilibria.
Kinetic theory of gases; chemical reaction kinetics.
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Must have CAS graduate student status. For decades diagnostic products and technologies have been used to monitor or detect a variety of indicators for disease and infection. Each year, over 4, devices are reviewed by the U. Today, regulations have set in motion the use of Biomarkers as a key element for new pharmaceutical development. Biomarkers in a way similar to Diagnostic markers will become a method to demonstrate safety and efficacy of experimental drugs during human trials. This course will review the history of Biomarker and medical device law and regulations in the United States.
It will also define the current scientific requirements for Biomarkers to meet the new regulations. Case studies will be used to educate participants on the use of Biomarkers in pharmaceutical development as well as Design Controls, Quality System Regulations, Manufacturing Requirements for diagnostic testing technologies. Students will also use knowledge gained to prepare class presentations to address current issues within the field. This course is one of four courses required to fulfill the requirements for a Certificate in Regulatory Affairs. It may be applied as a level credit in the Masters of Chemistry degree program.
Theory and applications of equilibrium and nonequilibrium separation techniques at both the analytical and preparative levels. Solvent and buffer extractions, chromatographic separations e. Examples will focus on biological applications. Discussion of the current literature in analytical chemistry, including spectroscopy, separations, and electrochemistry.