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Материалы IV студенческой конференции «химия. Экология. Медицина» направления работы - страница №16/19

MOLYBDENUM AS AN EARTH TREASURE

Nongo Tersoo, group 7. Scientific adviser is Nataliya Tkachuk.


Molybdenum is a Group 6 chemical element with the symbol Mo and atomic number 42. The metal was first isolated in 1781 by Peter Jacob Hjelm. Molybdenum does not occur naturally as a free metal on Earth, but rather in various oxidation states in minerals. The free element, which is a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is in making many types of steel alloys, including high strength alloys and superalloys.

Alloys


About 86% of molybdenum produced is used in metallurgical applications such as alloys, with the rest of molybdenum used as compounds in chemical applications. Estimated fractional global industrial use of molybdenum is structural steel 35%, stainless steel 25%, chemicals 14%, tool & high-speed steels 9%, cast iron 6%, molybdenum elemental metal 6%, and superalloys, 5%.

The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of armor, aircraft parts, electrical contacts, industrial motors and filaments.

Most high-strength steel alloys (example 41xx steels) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.

Molybdenum is also used in steel alloys for its high corrosion resistance and weldability. Molybdenum contributes further corrosion resistance to "chrome-moly" type-300 stainless steels (high-chromium steels that are corrosion-resistant already due to their chromium content, but in reality "chrome-moly" is not a type-300 stainless, but instead a 41xx series that is not stainless) and especially so in the so-called superaustenitic stainless steels (such as alloy AL-6XN). Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.



TZM (Mo (~99%), Ti (~0.5%), Zr (~0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe) and salt vapors used in molten salt reactors for 1100 hours with so little corrosion that it was difficult to measure. Other molybdenum-based alloys which do not contain iron, have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.

Langmuir

Amritpal Singh Khangura, group 8. Scientific adviser is Svetlana Kozub.


Langmuir contributed to atomic theory and the understanding of atomic structure by defining the modern concept of valence shells and isotopes. Langmuir was president of the Institute of Radio Engineers in 1923. He joined Katharine B. Blodgett to study thin films and surface adsorption. In 1932 he received the Nobel Prize in Chemistry "for his discoveries and investigations in surface chemistry." In 1938, Langmuir's scientific interests began to turn to atmospheric science and meteorology. In 1953 Langmuir coined the term "pathological science", describing research conducted with accordance to the scientific method, but tainted by unconscious bias or subjective effects. He introduced the concept of electron temperature and in 1924 invented the diagnostic method for measuring both temperature and density with an electrostatic probe, now called a Langmuir probe and commonly used in plasma physics. The Langmuir equation (also known as the Langmuir isotherm, Langmuir adsorption equation or Hill-Langmuir equation) relates the coverage or adsorption of molecules on a solid surface to gas pressure or concentration of a medium above the solid surface at a fixed temperature. The equation was developed by Irving Langmuir in 1916. The equation is stated as: θ =α.P/1+α.P

θ is the fractional coverage of the surface, P is the gas pressure or concentration, α is a constant. The constant α is the Langmuir adsorption constant and increases with an increase in the binding energy of adsorption and with a decrease in temperature.

Langmuir

Pooja Praharaj, group 11. Scientific adviser is Nataliya Tkachuk.


Irving Langmuir (31 January 1881 – 16 August 1957) was an American chemist and physicist. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his "concentric theory of atomic structure”. He was the first industrial chemist to become a Nobel laureate. He awarded the 1932 Nobel Prize in Chemistry for his work in surface chemistry. Langmuir was president of the Institute of Radio Engineers in 1923. He joined Katharine B. Blodgett to study thin films and surface adsorption.

His initial contributions to science came from his study of light bulbs (a continuation of his Ph.D. work). His first major development was the improvement of the diffusion pump, which ultimately led to the invention of the high-vacuum tube. A year later, he and colleague Lewi tonks discovered that the lifetime of a tungsten filament was greatly lengthened by filling the bulb with an inert gas, such as argon. He also discovered that twisting the filament into a tight coil improved its efficiency. These were important developments in the history of the incandescent light bulb. His work in surface chemistry began at this point, when he discovered that molecular hydrogen introduced into a tungsten-filament bulb dissociated into atomic hydrogen and formed a layer one atom thick on the surface of the bulb.

In 1917, he published a paper on the chemistry of oil films that later became the basis for the award of the 1932 Nobel Prize in chemistry. He was one of the first scientists to work with plasmas and was the first to call these ionized gases by that name, because they reminded him of blood plasma.

Langmuir contributed to atomic theory and the understanding of atomic structure by defining the modern concept of valence shells and isotopes. Langmuir was president of the Institute of Radio Engineers in 1923. He joined Katharine B. Blodgett to study thin films and surface adsorption. In 1932 he received the Nobel Prize in Chemistry "for his discoveries and investigations in surface chemistry." In 1938, Langmuir's scientific interests began to turn to atmospheric science and meteorology. In 1953 Langmuir coined the term "pathological science", describing research conducted with accordance to the scientific method, but tainted by unconscious bias or subjective effects. He introduced the concept of electron temperature and in 1924 invented the diagnostic method for measuring both temperature and density with an electrostatic probe, now called a Langmuir probe and commonly used in plasma physics.



THE CONTRIBUTION OF GREAT CHEMISTS TO THE DEVELOPMENT OF MODERN CHEMISTRY, MEDICINE AND PHARMACEUTICAL SCIENCES.NAMED REACTION IN CHEMISTRY

Boateng Isaac, group 12. Scientific adviser is Svetlana Kozub.


The contributions of chemistry to society are vast and almost numberless. An in-exhaustive list would include:Vaccines,Food safety practices,Treatment programs for diseases,Diagnostic tools in healthcare,Plastics,Synthetic fibers,An understanding of oil,Cosmetics and cleaners.
Vaccines and immunization were first popularized in the 1770s by Edward Jenner, who took pus from the hand of a victim of cowpox, and used it to protect people from the much more serious smallpox. Jenner was hailed as having stumbled onto something amazing, and the era of modern vaccines began. Without exactly understanding the chemistry - or indeed the biology - behind his discovery, Jenner had helped launch a revolution in chemistry that continues today with the development of vaccines for the dread diseases of our age, like Swine Flu.
An understanding of chemistry was also key to the development of modern food health and hygiene practices. By understanding the actions of microbes on the human body, these practices have helped eliminate other dread diseases in the Western world, such as dysentery and cholera, as well as many types of food poisoning.
Similarly, to Jenner's vaccines, understanding the chemistry of modern diseases is the key to the ongoing battle against conditions like cancer, AIDS and the common cold. By understanding the chemistry of how, say, cancer cells do what they do inside a human body, we have been able to devise treatments that can in some cases kill the disease, or at least provide an effective treatment regime. Diagnostic tools like dyes, that show up only certain times of tissue on ultrasound readers are also the result of chemical marking processes.
From oil comes plastics - but only if you understand how to make them, which means, altering the chemical structure of the oil and processing it to synthesize the plastic out of which half of our modern world appears to be made. Likewise, synthetic fibers are called synthetic because they've been developed by chemists to behave in certain ways - without chemistry, there would be no lycra.
Also, in the modern age, as we have become more fastidious about cleanliness and our appearance, we have developed huge industries dedicated to the development of cosmetics and cleansers - all of which are mixtures of chemicals (either naturally or synthetically produced), that have been blended to give us the effects we want without causing us any harm. Likewise, our quest for cleanliness has led us to develop surface cleaners, which are mixtures of entirely different chemicals that will destroy bacteria - and again, our knowledge of chemistry has both advised us of the threat, and helped us master it.This list is by no means complete - chemistry has had a part in practically every facet of the modern world - but without chemistry, it should be clear that the world we live in, would look very different.

Linus Carl Pauling

Ayanfe Adeleke, group 12. Scientific adviser is Svetlana Kozub.


Linus Carl Pauling (February 28, 1901 – August 19, 1994) was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century. Pauling was one of the founders of the fields of quantum chemistry, and molecular biology.

In the summer of 1930, Pauling made a European trip, during which he learned about the use of electrons in diffraction studies similar to the ones he had performed with X-rays. After returning, he built an electron diffraction instrument at Caltech with a student of his, L. O. Brockway, and used it to study the molecular structure of a large number of chemical substances.

Pauling introduced the concept of electronegativity in 1932. Using the various properties of molecules, such as the energy required to break bonds and the dipole moments of molecules, he established a scale and an associated numerical value for most of the elements – the Pauling Electronegativity Scale – which is useful in predicting the nature of bonds between atoms in molecules.

In the late 1920s Pauling began publishing papers on the nature of the chemical bond, leading to his famous textbook on the subject published in 1939. It is based primarily on his work in this area that he received the Nobel Prize In Chemistry in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances". Pauling summarized his work on the chemical bond in The Nature of the Chemical Bond, one of the most influential chemistry books ever published.




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