...BAND THEORY OF SOLIDS According to quantum free electron theory of metals, a electron in a metal experiences constant(or zero) potential and free to move inside the crystal but will not come out of the metal because an infinite potential exists at the surface. Bloch Theorem: According to this theorem, the periodic potentials due to the positive ions in metal have been considered. (i.e. the electrons moves in a periodic potential provided by lattice). If the electron moves through these ions, it experiences varying potentials. The potential of an electron at the positive ion site zero and is maximum in between two ions. i.e. the potential experienced by an electron varies periodically with the same period as the lattice. The potential is negative because of attractive force between electrons and positive ions. Along X- direction in the crystal, the potential function V(x) has the periodicity of lattice given by V(x) = V(x + a ) where, ‘x’ is distance of the electron from the core and ‘ a’ is the periodicity of the lattice. The energies of electron can be known by solving Schreodinger’s time independent wave equation for motion of an electron along x-direction is given by Bloch showed a type of solution for the above equation, given by ψ(x) = uk (x) eikx where uk(x) represents periodic function given by uk (x) = uk(x+a) Here, K = 2π/λ = propagation vector and λ = wavelength of debroglie’s wave associated with the moving...
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...Ceramics is one of the most ancient industries on the planet. Once humans discovered that clay could be dug up and formed into objects by first mixing with water and then firing, the industry was born. As early as 24,000 BC, animal and human figurines were made from clay and other materials, then fired in kilns partially dug into the ground. Almost 10,000 years later, as settled communities were established, tiles were manufactured in Mesopotamia and India. The first use of functional pottery vessels for storing water and food is thought to be around 9000 or 10,000 BC. Clay bricks were also made around the same time. Glass was believed to be discovered in Egypt around 8000 BC, when overheating of kilns produced a colored glaze on the pottery. Experts estimate that it was not until 1500 BC that glass was produced independently of ceramics and fashioned into separate items. Fast forward to the Middle Ages, when the metal industry was in its infancy. Furnaces at that time for melting the metal were constructed of natural materials. When synthetic materials with better resistance to high temperatures (called refractories) were developed in the 16th century, the industrial revolution was born. These refractories created the necessary conditions for melting metals and glass on an industrial scale, as well as for the manufacture of coke, cement, chemicals, and ceramics. Another major development occurred in the second half of the 19th century, when ceramic materials for electrical...
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...ABSTRACT The mechanical properties of composite materials are strongly dependent on micro structural parameters of the system. The evolution of microstructure depends largely on the cooling rate during phase change. Though the microstructure evolution depends on many process parameters, the final structure is decided by cooling conditions during solidifications. The mould material has a decided effect on the structure formation. The use of end chills during casting not only favours directional solidification but also accelrates solidification. Faster cooling rates give rise to finer structures and improved mechanical properties. In this work an attempt is made to prepare Al-B4C composites cast using stainless steel and cast iron chills in a colplete adiabatic system. The microstrucutre and micro-hardness of the chill cast specimens are analyzed and reported. It is observed that the chill material has a significant influence on the microstructure and properties of the cast specimens. Finner structure and better mechanical properties were observed with the specimen cast using stainless-steel chill whereas cast iron chill gave rise to coarse structure with reduces mechanical properties. INTRODUCTION Engineering Materials There are more than 50,000 materials available to engineers for the design and manufacturing of products for various applications. These materials range from copper, cast iron, brass, which have been available for so many years, to the more recently...
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...Sean Davis GE 254 8/12/13 The Rock Cycle The rock cycle is the natural transformation of rock over a period of time. Rocks are created and destroyed in cycles. The rock cycle is a model that describes the formation, breakdown, and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes. Rocks are made of minerals; which are naturally occurring, crystalline solid of definite chemical composition and a characteristic crystal structure. Rocks are any naturally formed, nonliving, firm, and clear aggregate mass of solid matter that constitutes part of a planet. Igneous rocks are formed from magma cooling underground, or lava above ground are formed from prior igneous, metamorphic, or sedimentary rocks which have become melted, usually as a result of plate collision and seduction. When these igneous rocks are exposed to weathering and corrosion, they break down into smaller particles that are moved by wind and water to a place of deposition, where they can form into sedimentary rock strata, through a process where excess water is squeezed out by overburden pressures and the particles are cemented together by various minerals precipitating out of solution. Igneous and metamorphic rocks can both be turned into sedimentary rocks in this way. Igneous and sedimentary rocks can also be changed by heat and/or pressure into metamorphic rocks, by transforming their existing mineral structures into new minerals or realigning the existing minerals. There are...
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...in a uniform distribution of the molecules throughout the system. This process is called diffusion (Everett and Everett, n.d.). Diffusion is defined as the movement of molecules away from the area of their highest concentration to an area of low concentration. Net diffusion can be restated as the movement of particles along the concentration gradient. According to Meyertholen (n.d.), there are several factors which may affect the rate of diffusion of a substance. These factors include the following: (1) Temperature: higher the temp-higher the rate of diffusion, (2) Size of particle: bigger the particle-higher the energy to diffuse , (3) State of matter: solid takes more time to diffuse compared to liquids, liquids take more time to diffuse compared to gases and gases take less time to diffuse compared to liquids and solids, (4) Nature of matter: denser the matter-slower the rate of diffusion. My objective was to determine the properties of ammonia (NH3) and of hydrochloric acid (HCl) that are related to diffusion. I hypothesized that ammonia diffuse faster than hydrochloric acid. For more support we conduct also an experiment that would detect the diffusing substances in an agar plate using colored compounds; potassium permanganate, methylene blue and potassium...
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...physical means. For example salt dissolved in water can be recovered by allowing the water to evaporate. A physical change involves a change in physical properties. Examples of physical properties include melting, transition to a gas, change of strength, change of durability, changes to crystal form, textural change, shape, size, colour, volume and density. An example of a physical change is the process of tempering steel to form a knife blade. A steel blank is repeatedly heated and hammered which changes the hardness of the steel, its flexibility and its ability to maintain a sharp edge. Methods Heating and cooling Many elements and some compounds change from solids to liquids and from liquids to gases when heated and the reverse when cooled. Some substances such as iodine and carbon dioxide go directly from solid to gas in a process called sublimation. Magnetism Ferro-magnetic materials can become magnetic. The process is reversible and does not affect the chemical composition. Crystallisation Many elements and compounds form crystals. Some such as carbon can form several different forms including diamond, graphite, graphene and fullerenes includingbuckminsterfullerene. Crystals in metals have a major effect of the physical...
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...Criteria P4 Metallic materials Copper: A ductile, malleable, reddishbrown metallic element that is an excellent conductor of heat and electricity and is widelyused for electrical wiring, water piping, and corrosion-resistant parts, either pure or in alloys such as brass and bronze. Recrystallisation: The process of recrystallisation usually begins when the cold worked metal is heated to a temperature of about half of it's melting temperature on the absolute kelvin scale. for example the melting point of copper is (1083 +273)K=1356K so it will anneal and recrystallises at temperatures of about 678K(about 600 C).Mild steel is mainly iron and a similar calculation indicates annealing can replace a sequence of forming and annealing operations. Alloying: Copper and its alloys are widely used in deep draw and flat stamped products because they have excellent electrical and thermal performance, good resistance to corrosion, high ductility and relatively low cost. Thermoplastic polymeric materials Polymer processing temperature: The effect of temperature change on polymers * When substances made of small molecules are heated, they simply melt and form a free-flowing liquid; however with polymers the process is more complex. * When polymers are cooled, they will often become very brittle. When heated, the polymers will first become flexible before melting. * This is due to their structure. In some polymers, there are areas of crystalline and amorphous regions...
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...Study of the different flow patterns in the melting section of a co-rotating twin-screw extruder. Polymer Engineering and Science - February 1, 2003 Guo Yichong Word count: 5666. citation details [pic] INTRODUCTION Twin-screw extrusion (TSE) Involves solid conveying, melting, mixing, venting and homogenizing, and the extrusion process affects the quality of polymer products considerably. Co-rotating twin-screw extruders are mainly used for compounding, and they are commonly of modular design, which means the screw elements can be configured to reach optimal conditions. Conveying elements and kneading blocks are the two common types of screw elements, which are designed based on conjugation or kinematics principles. Investigations of co-rotating TSE have covered many aspects. Recent literature shows that some investigations first obtained data from experiments, and then obtained the regularity about the TSE process according to the experimental results (1-3). Such studies usually had some practicality, for instance, to clarify the temperature profiles, pressure drop, etc. Other investigations simulated the process with physical and mathematical methods, and then verified the simulation results with experimental data (4-9). They often emphasized the theoretical significance. Several experimental methods have been used in TSE melting studies. Todd (10) conducted his experiments using a clam-shell barrel. Bawiskar and White (11) and Potente and Melish (12) adopted the screw extraction...
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...In the article As the West Goes Dry, Service uses melting snow on the West and Northwest mountains to exemplify the effects of global warming. The western side of the country uses snow packs from the mountains for its reservoirs during the spring and summer months. 75% of water in Western streams is attributed to melted snow. Even with only a slight increase in temperature overtime (0.8’C), the snow packs have decreased significantly and the summertime flow of water from the melted snowpack is expected to be 20-50% less this year. Some climatologists believe these increases in temperature can be explained by the warming and cooling trends in the 1900s, where temperature increased during 1920s-1940s and decreased during 1950s-1960s, however that trend theory does not explain the largest loses of snowpack are at the lowest elevations. Even if we are currently in a warming trend, temperatures are only predicted to increase further and faster, leaving us with the same issues. The decrease in snow packs will impact where the limited water will be dispersed in the warmer months. This will especially affect farmers and agriculture. It will also increase the risk for natural disasters such as forest fires. The author offers unbiased information for the reader on the current melting snow in the West, why it is increasing, and what the potential outcomes could be. Service uses multiple academic sources, including reputable climatologists who oppose Service's explanation to further delve...
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...The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Nanomaterials may provide solu- tions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water treatment [1,2]. This increasing demand must be accompanied by “green” synthesis methods. In the global efforts to reduce generated hazardous waste, “green” chemistry and chemical processes are progressively integrating with modern developments in science and industry. Implementation of these sustainable processes should adopt the 12 fundamental principles of green chemistry [3–7]. These principles are geared to guide in minimizing the use of unsafe products and maximizing the efficiency of chemical processes. Hence, any synthetic route or chemical process should address these principles by using environmentally benign solvents and nontoxic chemicals [3]. Nanomaterials often show unique and considerably changed physical, chemical and biological properties compared to their macro scaled counterparts [8]. Synthesis of noble metal nanoparticles for applications such as catalysis, electronics, optics, environmental, and biotechnology is an area of constant interest [9–15]. Gold, silver, and copper have been used mostly for the synthesis of stable dispersions of nanoparticles, which are useful in areas such as photography, catalysis, biological labeling...
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...The purpose of this experiment was for the student to be able to perform the dehydrobromination of meso-stilbene dibromide in order to produce an alkyne, diphenylacetalyene. The dehydrobromination of meso-stilbene dibromide requires removal of two hydrogen bromides—in other words, a double elimination. In order for the elimination of the halogen to happen, the hydrogen being attacked and the leaving group need to be on the same plane. More specifically, the molecule has to be in an anti-periplanar orientation in order to have the elimination reaction happen more efficiently. Even though a molecule in a syn-periplanar orientation also has the hydrogen and leaving group in the same plane, the fact that both groups are on the same side makes the molecule sterically hindered. The staggered conformation of the meso-stilbene dibromide is orbitally more favorable than the eclipsed conformation making the anti-periplanar orientation the more favorable orientation for an elimination reaction. Fortunately, the fact that meso-stilbene dibromide had a single bond allowed for this molecule to develop the anti-periplanar orientation by having rotated the bond until the hydrogen and the leaving group were on opposite sides of the molecule. When producing alkynes, there are two steps involved in the reaction: the formation of an intermediate alkene with a vinyl halide followed by the elimination of the halide to result in an alkyne. For the creation of the intermediate vicinal bromide in this...
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...Contaminated water contains biological microorganisms such as bacteria, fungi, and viruses. Silver nanoparticles are used conventionally as an antimicrobial compound to exhibit multi-interactional activity to fight bacteria. Inevitably, low concentration of silver compounds will remain in the environment. For example values of accumulated silver nanoparticles for surface water, American soil, sludge, , Sewage Treatment Plant (STP) effluent, STP sludge, and sediment were reported 0.088 µg/L/year, 6.6 µg/kg/year, 526 µg/kg/year, , 16.40 µg/L/year, 1.29 mg/kg/year, and 153 µg/kg/year respectively. The residue of silver nanoparticles could cause the evolution in the bacteria in order to adapt to novel environments. The consequence of exposing bacteria...
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...Questions relating to Sanders and Hunter Chapt 7 1. The 31P spectrum of phosphate changes as the pH of the solution is changed, because it changes what is in the solution. It can make the phosphate change from its anionic form to its cationic form which changes the spectra because it reflects the molecular structure. 2. The time scale of the instrument is what determines whether the signals are averaged or separate, if it is in slow exchange the signals are spate and if they are in fast exchange the signals are averaged. 3. A molecular complex with 2 conformations gives a pair of peaks on a 13C 200MHz spectrometer. a. When the temperature of the sample was increased from 20 to 50 the pair of peaks changed to a single peak because the time scale changed. It changed from slow exchange (separate signals) to fast exchange that gave an averaged single peak instead. b. When repeated on a 80MHz spectrometer the pair of peaks stayed at 50, it is due to the change in the frequency between the exchange site, at 50 using a 800MHz spectrometer may give the same frequency for the exchange sites as 20 using a 200MHz spectrometer. This makes the spectra look the same of the pair of peaks didn’t collapse. 4. In an NMR: a. Slow exchange is when the two conformations of a molecule can be seen in the spectra. b. Fast exchange is when the two conformations of a molecule are exchanging too fast for the two separate signals to be read that an averaged signal of the molecule is seen on the spectra...
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...Step-By-Step Procedure * 1. Fill the jar with your ice cubes. There should be enough ice cubes so that they reach the top, but leave enough room so you can securely tighten the cap. * 2. Add to heaping tablespoons of salt into the jar, covering the ice. Screw on the lid of the jar tightly. * 3. Shake the jar vigorously for about 30 seconds. * 4. Place the jar on a solid surface, such as a table. Leave the jar for a short while (about 10 minutes). * 5. When you return to your jar, observe if your jar has water droplets on the outside. If it does not, leave the jar undisturbed for a while longer. When the jar does finally have visible water droplets on the outside, proceed to step 6. * 6. Wrap your tissue around the outside of the jar, then take it off and observe how wet it is! Note The rate at which the droplets (known as condensation) begin to form on the outside of the jar will vary depending on the environmental conditions where the experiment is taking place. Observation At what point did you start to see water droplets? Can you explain what's happening? How could the water droplets be forming on the OUTSIDE of the jar when the ice is on the INSIDE of the jar, and the cap is screwed on tight? Where have you seen other natural occurrences of condensation? (here's a hint... think of what's on the ground on a cold morning). Result The salted ice quickly makes the sides of the glass jar very cold. As the water that exists in the air as a gas...
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...metal embrittlement (LME) is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when tested in the presence of specific liquid metals. Generally, a tensile stress or a residual stress is needed to induce embrittlement. Many mechanisms were proposed to explain the phenomenological characteristics of LME. The significance of liquid metal embrittlement is revealed by the practical observation of several structures experiencing ductility losses and cracking during hot dip galvanizing or during subsequent fabrication. Liquid metal embrittlement effects can be observed even in solid state, when one of the metals is brought close to its melting point (e.g. cadmium-coated parts operating at high temperature). This phenomenon is known as solid metal embrittlement. OBSERVATIONS OF LME Mechanical structures are typically a space frame fabricated from parallel large diameter tubes, called chords, cross braced by smaller diameter perpendicular and diagonal tubes(e.g. sign bridge structures over freeway) .After welding, the structure is hot dip galvanized. The hot dip galvanizing process consists of submerging the structure in a bath of molten zinc. This leaves a relatively uniform zinc coating over the entire structure upon removal from the bath. This coating provides corrosion protection for the underlying steel tubes and welds. Their inspection, after a while, revealed numerous cracks in the welds...
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