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As the popularity of photovoltaic (PV) cells and integrated circuits (IC) increases, the need for silicon also increases. Silicon is one of the most used materials in these two industries. It is an inexpensive and abundant semiconductor. However, the process of producing pure silicon adds cost, and it is generally unknown to the public. One of the first steps in producing silicon is a process called carbon-thermic reduction. Silicon dioxide (SiO2) that is found in beach sand and quartz is melted down in a caldron at a temperature of 1450 degrees Celsius.
Coke and other forms of carbon are then added to the mixture, because at this high temperature, the oxygen has more of an affinity to carbon instead of the silicon. A current is then run through the solution. As the impurities float to the top of the mixture, carbon monoxide (CO) vaporizes out of the solution and the metallurgical grade silicon (MGS) is siphoned off the bottom. Although there are more steps needed to produce silicon for the IC and PV industries, this initial step may be modeled in a high school laboratory, through a single displacement redox reaction.
Environmental Science, Chemistry, Physics
1-2 class periods.
Handouts included. Reagents: copper sulfate (solid), aluminum (foil or wire), and 1.0 molar HCl (if using the specific chemistry lesson). Apparatus: 250 ml-beaker, drying oven, graduated cylinder, wash bottle, stirring rod, tongs, ring stand, goggles, lab apron, steel wool, balance, funnel, and filter paper.
National Standards: 9-12
- SEC-A: 1.a. Identify questions and concepts that guide scientific investigation.
- SEC-A: 1.b. Design and conduct scientific investigations.
- SEC-A: 1.d. Formulate and revise scientific explanations and models using logic and evidence.
- SEC-A: 1.e. Recognize and analyze alternative explanations and models.
- SEC-B: 6.a. Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter.
- SEC-B: 6.b. Electromagnetic waves––including radio waves, microwaves, infrared radiation, ultraviolet radiation, x-rays, and gamma rays––result when a charged object is accelerated or decelerated.
- SEC-B: 6.c. Each kind of atom or molecule can gain or lose energy only in particular discrete amounts and, thus, can absorb and emit light only at wavelengths corresponding to these amounts.
- SEC-B: 6.d. In some materials, such as metal, electrons flow easily, whereas in insulating materials such as glass, they can hardly flow at all.
- SEC-F: 3.a. Human populations use resources in the environment to maintain and improve their existence.
- SEC-F: 3.b. The earth does not have infinite resources; increasing human consumption places severe stress on the natural processes that renew some resources, and depletes those resources that cannot be renewed.
- SEC-F: 3.c. Humans use many natural systems as resources. Natural systems have the capacity to reuse waste but that capacity is limited. Natural systems can change to an extent that exceeds the limits of organisms to adapt naturally or humans to adapt technologically.
- SEC-F: 4.a. Natural ecosystems provide an array of basic processes that affect humans. Those processes include maintenance of the quality of the atmosphere, generation of soils, control of the hydrologic cycle, disposal of wastes, and recycling of nutrients. Humans are changing many of these basic processes, and the changes may be detrimental to humans.
- SEC-F: 5.d. Natural and human-induced hazards present the need for humans to assess potential danger and risk. Many changes in the environment designed by humans bring benefits to society, as well as cause risks. Students should understand the costs and trade-offs of various hazards––ranging from those with minor risk to a few people to major catastrophes with major risk to many people.
- SEC-F: 6.b. Understanding basic concepts and principles of science and technology should precede active debate about the economics, policies, politics, and ethics of various science and technology related challenges. However, understanding science alone will not resolve local, national, and global challenges.