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LECTURE 10.1. LECTURE OUTLINE. Weekly Deadlines CRRA #5 Processing of Sulfur Concept Map Self-Review Questions Electronic Properties I. CRRA #5. Processing Concept Map. CRRA #5. Processing: Self-Review Questions. General Comment.
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LECTURE OUTLINE • Weekly Deadlines • CRRA #5 Processing of Sulfur • Concept Map • Self-Review Questions • Electronic Properties I
CRRA #5 Processing Concept Map
CRRA #5 Processing: Self-Review Questions
General Comment • Overkill! The essay contains far more content than I would ever expect in a student essay. However, it is as complete an essay as I could write on the subject. Even so, it only scores ten out of twenty!
Are the geological/geochemical processes, through which the raw material(s) is/are created described? • Yes (1).It is a qualified yes. Beginning at the bottom of the first page, the formation of native sulfur, via volcanic activity is mentioned: • “According to Davis and Detro (1992), early civilizations obtained what little sulfur they required by either: • (i) harvesting the native element formed from volcanic activity. This native sulfur was formed through the reaction between the gasses SO2 and H2S as: SO2 + 2H2S 2H2O + 3S.” • However, the formation of sulfur deposits as part of the cap-rock on oil deposits is not described. So I will give myself one point!
Are the biological/biogenic processes through which the raw material(s) is/are created described? • No (0).There is nothing on the biogenic formation of sulfur in this essay component, although it is mentioned in the structures component.
Are the geographical locations of the raw materials presented? Are political implications addressed? • Yes (1).The text does describe the sulfur deposits in Sicily, Texas, and Louisiana. See Section 5.3 • “Vast deposits of sulfur had been found in, e.g., Louisiana and Texas, but were buried below layers of, e.g., clay, rock and quicksand (Partington 1937).” • However, political implications are not addressed—hence, one point.
Are mining methods, including “beneficiation”/concentration described? • Yes (2).The Frasch process is presented in some detail, both in the text (Section 5.3) and in Figure 3.
Is the primary processing/extraction of the material from the raw material presented? • Yes (2).The extraction of the elemental sulfur from pyrite (FeS2) is described in the text and with respect to Figure 1a.
Figure 1. Scanned images of woodcuts from De Re Metallica (from Agricola, 1556). Figure 1a) depicts the formation of elemental sulfur from fool’s gold (FeS2) and/or chalcopyrite (CuFeS2). Relatively large lumps of the ore are loaded into an earthenware pot (see far left of figure), which contains several perforations in its base (see center foreground). The ore-containing pots are placed over circular holes in iron plates and heated with wood. The liquid sulfur drips through the perforations in the base of the pots and then into a second series of pots, the latter containing water. • Figure 1b) shows the distillation of elemental sulfur from a “sulfur/earth” mixture. The mixture of sulfur (perhaps 15-25%) and materials such as gypsum and limestone is put in a flat-bottomed pot, which sits atop a furnace. The pots are covered with lids, which are sealed with “lute” (which was probably a mixture of clay and powdered charcoal). A spout from the flat-bottomed pot feeds into a second pot (B). The impure sulfur boils in the first pot and is transported to the second pot via the spout where it condenses to a liquid, which is tapped into a wooden trough.
Are the methods for purifying originally impure materials (i.e. secondary processing) discussed? • Yes (2).The purification of sulfur, through the process of distillation, is discussed (also see Figures 1b and 2b).
Figure 2a)is aschematic diagram of an environmental disaster—a calcaroni, or sulfur kiln (from Partington, 1937). The kiln is loaded with lumps of the sulfur/rock mixture and covered with a layer of powdered sulfur. When the latter is ignited, a fraction of the sulfur is melted and collected in a reservoir at the bottom. The vertical channels are air vents. • Figure 2b) shows a sulfur refinery (from Partington, 1937). Sulfur is boiled in an iron retort and the sulfur vapors are condensed in a brickwork chamber. Note the similarity between this process and that described by Agricola in 1556 (Figure 1b).
Are tertiary processing methods introduced (e.g., casting, extrusion, rolling, and cutting)? • No (0).
Are the processing methods related to the physical properties of the material? • No (0).Although it is implicit in the description of the Frasch process that sulfur has a low melting point, it is not explicitly stated.
Are environmental issues related to primary, secondary, or tertiary processing addressed? • Yes (2).Section 5.4, “Non-Discretionary Sulfur,” relates to environmental concerns: • “The increasing environmental concerns of the latter half of the twentieth century saw a quickening in the amount of sulfur recovered from the waste gasses of various industrial processes and a concomitant decrease in the amount of discretionary sulfur needed.”
Is the final assembly, which might involve a joining process (gluing, welding, soldering) described? • No (0). • SCORE: 10/20.
ELECTRONIC PROPERTIES I • Metallic Conduction • Ohm’s Law • Number of Free Electrons/Atom • Drift Velocity • Free Electron/Electron Hole Pairs • The Group IV Elements
CONDUCTIVITY AND OHM’S LAW • The current that flows through a material is proportional to the voltage (or electrical pressure difference). • Or: • I a V • Or: • I = sV Wheresis called the conductivity
CONDUCTIVITY AND OHM’S LAW The current that flows along the wire is equal to the number of charge carriers (electrons) multiplied by their “drift velocity” multiplied by the charge on the electron. Or: I = qnv
CONDUCTIVITIES OF MATERIALS • For metals: n/atom ~ 1 • For non-metals: n/atom ~ 0 • For semiconductors: n is small, but finite • For metals, the conductivity (s) depends on how the drift velocity varies with with something such as temperature.
THE DRIFT VELOCITY AND THE CONDUCTIVITY OF METALS • In metals, the variation in conductivity is related to the variation in the drift velocity of the electrons. • The drift velocity decreases as the frequency of atomic collisions increases. • The drift velocity decreases as temperature increases. • The drift velocity decreases as the solute level increases.
EFFECT OF “PURITY” AND TEMPERATURE ON METALLIC CONDUCTIVITIES
HOW ARE FREE ELECTRONS CREATED IN A COVALENTLY BONDED SEMICONDUCTOR? • Free electron/electron hole pairs may be created by: • light √√ • heat √√ • electric field xx
IONIZATION ENERGIES OF THE GROUP IV ELEMENTS I • For diamond-C, the outer-shell electrons are in the L-shell. They are so closely bound that the ionization energy is prohibitively high. Diamond-C is a prototypical electrical insulator. • n/atom ~ 0
IONIZATION ENERGIES OF THE GROUP IV ELEMENTS II • For lead, the outer-shell electrons are in the P-shell. They are so loosely bound that lead’s outer-shell electrons are free at room temperatures. Lead is a prototypical electrical conductor. • n/atom ~ 1
IONIZATION ENERGIES OF THE GROUP IV ELEMENTS III • For silicon and germanium, the ionization energies are such that their electrical properties are midway between those of a “typical” insulator and a “typical” conductor. They are elemental semiconductors!
