Lecture 09

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Information about Lecture 09

Published on January 11, 2008

Author: Petronilla

Source: authorstream.com

Today’s objectives-Advanced processing and Optical Fibers:  Today’s objectives-Advanced processing and Optical Fibers Optical Fiber Processing Initial tube CVD of core Sintering and annealing coating Applications Upcoming Test 1 Fiber Optic Concept:  Fiber Optic Concept Cu wires are great for transmitting current. They aren’t so good for transmitting multiple independent data streams (voice, video, etc). Adjacent wires interact and degrade each other’s signal. They are expensive to maintain. The signal must be detected, cleaned up, amplified, and sent again often. Fiber optics may be the solution. Multiple signals can be transmitted on a signal cable simultaneously. Light does not interfere with itself in the same way that electrons do. But, how do we make an optical fiber? Ultra pure core glass, surrounded by Flaw free cladding glass, surrounded by Continuous protective polymer coating (or coatings), bundled with Tens or hundreds of other fibers, protected by Corrosion resistant outer jacket for structural integrity and handling protection. Purifying Silica:  Purifying Silica Purify Si Mine sand (raw silica) React with chlorine to produce SiCl4 and other metals from the impurities in the sand (FeCl3, etc.) Heat this mixture (essentially distilling) Collect SiCl4 vapors only Condense the pure SiCl4 vapors CVD of optical fibers:  CVD of optical fibers Prepare a silica tube (glass extrusion). Heat the tube Inject SiCl4 and O2 into the tube At the heated portion, the SiCl4 is oxidized UItra pure SiO2 is deposited on the inner walls of the tube Draw the tube through the furnace, continuously coating the inner walls. SiO2 particles deposit and sinter along the tube, leaving a hollow core [for now]. Fiber drawing and protecting:  Fiber drawing and protecting Anneal the multiwalled tube to the glass softening temperature. The tube and inner coating collapse to a solid, multilayered rod. Fire the rod at an even higher temperature softening it further. Draw the fiber through a nozzle, thinning the fiber dramatically. Core diameters from <5 to 500 um are used. Polymer coatings must also be applied. Fibers are finally bundled. Continuous production:  Continuous production Fibers are drawn at 30 to 60 feet per second. Multiple polymer coatings may be applied Thermoplastic (buffer) Aramid (strength) PVC of fluoride co-polymer Spools of up to several kilometers are wound. 2000 °C Fiber optic diameter:  Fiber optic diameter Plastic fiber has a core diameter of up to 900 um. 20-30 feet max length. Easy to work with. Cheap. Glass fibers have cores from 8 to 62.5 um across. Connecting two fibers end-to-end is the hardest par—requires a microscope or an automatic connection of some kind. Fiber testing:  Fiber testing Fibers must generally pass the following tests Tensile strength greater than 100,000 lb/in2 Dimensional tolerance Temperature dependence Optical properties Importance of Fiber Purity:  Importance of Fiber Purity This complicated procedure is necessary due to the incredible sensitivity of optical fiber communications to impurities and flaws. Fiber optics only became a reality in 1970, when Corning figured out how to make fiber optics with less than 99% loss/km. Light transmission through 1 km of fiber drops to 1% of the input intensity if there are only: 2 Co atoms per billion 20 Fe atoms per billion 50 Cu atoms per billion Transmission in modern fibers is still limited to: 60 to 75 percent/km for light with a wavelength of 850 nm. Transmission losses <1% have been achieved over >3000 miles. “if seawater were as clear as this type of fiber optic cable then you would be able to see to the bottom of the deepest trench in the Pacific Ocean.” -http://www.telebyteusa.com/foprimer/foch2.htm Repeating Stations:  Repeating Stations Repeating stations are generally placed at regular distances along a fiber network to detect and amplify the signals since loss will occur over km, or hundreds of km, of fiber. When light drops to 95% of transmission, a repeating station is required. Since the cost of the repeaters is high compared to fiber, tremendous effort goes into making pure, flaw free optical fibers. Repeating stations today are generally 100 km apart for major fiber bundles (trans-oceanic, etc). http://www.telebyteusa.com/foprimer/foch2.htm Future fiber optic manufacturing?:  Future fiber optic manufacturing? Why bother purifying Si and the trouble of making pure and flaw-free fiber optics when a spider does it naturally? http://www.newscientist.com/article.ns?id=dn3522 Review Material:  Review Material Lecture 1 Electronegativity Ionic bonding Covalent bonding Lecture 2 Unit cells of CsCl, rocksalt, zincblende, fluorite, perovskite Unit cell density. How to derive, and the table of, radius ratio rules/CN/structure type. Site filling depending on cation:anion ratio Structure, and lattice and basis of CsCl, NaCl, and perovskites Name, structure, and basic properties of 3 types of SiOx and 4 forms of carbon. Lecture 3 Identify and draw directions and planes. Defect types to satisfy charge balance, including cation interstitial, anion interstitial, cation and/or anion vacancies, schottky (paired vacancies), frenkel (cation out of place), multivalent self, interstitial, substitutional, and multivalent defects. Defects that form in a crystal to compensate for the addition of an impurity or dopant ion. Slide13:  Lecture 4 Use of phase diagrams Use of the lever rule Partial stabilization of zirconia Lecture 5 Compressive versus tensile stresses How to measure mechanical properties of ceramics (why different from metals/polymers?) Measure/Calculate Elastic Modulus Measure/Calculate flexural strength. Is this higher or lower than tensile strength? Why are ceramic components are not as strong as expected from theory? Options to strengthen a polycrystalline/single crystal ceramic. Calculate fracture toughness Draw a Weibull curve and explain its significance; method to guarantee a part from failing. Mechanism for delayed fracture Slide14:  Lecture 6 Name 2 additives in glass Viscosity vs. Temperature for glass; roughly where is the annealing range and where is the working range How to, and why does one, temper glass? Glass ceramics--how to prepare, and what advantage does a glass ceramic offer over a normal glass? Describe how porcelain and other ceramics are manufactured (slip, form/cast/press, dry, sinter, vitrification). What is vitrification? How is it used to strengthen a ceramic part? Lecture 7 Describe how ceramics are manufactured from powders (powder, press, sinter, diffusion) Describe how concrete is manufactured (cement, water, particles, chemical reaction) For cement, sketch and explain both the heat evolution vs. time, and strength vs. time. How do you select a composition from a phase diagram for a refractory (highest temperature possible, least liquid possible!) Slide15:  Lecture 8 Know processing, applications, and advantages/disadvantages of 3 of the following ceramic fabrication techniques: single crystal, MEMS, sol-gel, biomimetic, thermal evaporation, sputtering, CVD, and PLD. Lecture 9 Describe the manufacture of optical fibers (purify silica, prepare tube, cvd of pure silica into tube, anneal at softening temp to make solid rods, fire and draw to fibers, protect with polymer layers, bundle). SUMMARY:  SUMMARY Optical Fiber Processing Initial tube CVD of core Sintering and annealing coating applications Preparation for Test 1 and reading for next class: Exam Prep (this presentation and web site) Optical Fibers (this presentation, download from web site) Environmental Effect of Materials Processing (download from the web site)

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