Device for Measuring Electrical Potential during High Temperatures - Lab Report Example

DEVICE FOR MEASURING ELECTRICAL POTENTIAL DURING HIGH TEMPERATURES Name: Subject: Name of instructor Institution: Date: Summary Principally, electrochemical reactions are chemical reactions which are caused by presence of applied electrical voltage from an external supply. For example, in battery cell, which involves electrochemical reaction and this, creates a change in voltage due to these chemical reactions. Electrochemical reactions are based on the oxidation and reduction reactions of the electrodes. The oxidation - reduction reaction involves the transfer of the electrons from one element to another which chemically linked. The reduction reaction involves any process that involves addition of the electron to another atom or silicon, that is, the process of adding oxygen and/or removing hydrogen in a chemical reaction. This process involves basically oxidation of the reducing agent. The oxidation process is a reverse of the reduction since it involves the removal of the oxygen from the reacting reagent. This process involves removal of oxygen or addition of hydrogen in the reaction. Measurement of electric potential when the reaction occurs at high temperatures has proven to be a major problem. There is need to develop a high accuracy calibration machine that can be used to measure the molten oxides electrical conductivity potential during reactions. The electrochemical process would always take place when there is an electrolyte and the material reacting. An example may be the reaction of iron oxide which is in the slag and the carbon found in liquid iron. An electrochemical reaction is the one in which there is the transfer of electrons and the electrons transfer have to take place at a certain distance which is greater than the dimension of the atom. Basically when mixing the water and acid it’s important to follow the appropriate steps to prevent explosion of the acid which may cause harm to the operator. This procedure should be of the order that, the acid should be added to the water and not the opposite. If the water is added to the concentrated acid it can explode violently causing injuries to the operator. Also it is important to note that if you want to dilute sulphate of zinc and copper, the sulphate should be added to water and not vice versa. The inter-phase change of silicon to slag from a metal usually undergoes an electrochemical reaction. Additional electrical current to this system should thus fasten the process of slag removal from metal. This project will base its study on the design and development of experimental apparatus that measures electrical potential during reactions at high temperature of above 1000 C. Study on a selected high temperature will also be a part of the project. Table of contents 1. Introduction............................................................................................................5 1.1 problem statement...........................................................................7 1.2 objective..........................................................................................7 2. Literature review.....................................................................................................8 2.1 Review of available technologies................................................9 2.2 The new trends...........................................................................10 3. Methodology..........................................................................................................11 3.1 Experimental apparatus..............................................................11 3.2 procedure of experiment..............................................................16 3.3 Results and discussion..................................................................18 4. Conclusion...............................................................................................................21 5. Recommendation.....................................................................................................22 6. Risk assessment.........................................................................................................26 1. Introduction It’s evident from the current work that the acceleration of reaction processes is possible by the application of external currents and voltages. If a current density of 2.33A/cm2 at 4V is used, it accelerates the transfer rate of silicon from silica to a silicon reduced slag. Without the application of electric current the rate of transfer from metal to slag is 0.000297moles %/S at the same base ratio. At 90A, there is about 98.95% efficiency towards formation of the silicon slag. The higher the rate of current flow the higher the rate at which the slag sulphates thus forming a resistive layer at the cathode and hence potential conduction stops. Transfer of silicon from metal to slag happens through an electrochemical process. This process happens through the exchange of electrons between the metal phase and slag phase. Silicon is produced from an electric furnace using carbon electrodes at temperature of about 1900 0C where the carbon reduces the silica to silicon and carbon monoxide (De Mattei & Robbert, 1981). The process equation occurs in two stage equation as shown below. SiO2 + C → Si + CO2 SiO2 + 2 C → Si + 2 CO This results in the formation of the liquid silicon which collects at the bottom of the reaction furnace. The liquid silicon is removed from the electric furnace which is at 1000 0C and then cooled. This type of silicon produced through this process is called metallurgical silicon and it is 98% pure with few impurities of carbon. When this method is applied in the extraction of the silicon from silica it is evident that, there is formation of silicon carbide (SiC) (Monier, R et al., 1965). To avoid this formation of silicon carbide it’s therefore important to use silicon oxide (SiO2), which eliminates the silicon carbon from the reaction thus forming the required silicon. This reaction is as shown below. 2 SiC + SiO2 → 3 Si + 2 CO The above equation is the overall ionic equation for the silicon formation process when silicon carbide forms in a reaction of silicon extraction. As the silicon reaction forms the electrical potential difference is measured through the voltmeter. The voltmeter is used to determine the amount voltage that can be transferred through a given conduit within a given time. This potential is recorded in volts. The reaction continues as long as the compound is maintained at the molten state, and so working with 1000 0C is the ideal temperature to use when using silicon compound as the electrolyte. Slag transfer from silicon is cathodic and, in order to maintain electro - neutrality of the system the anodic reactions must precede simultaneously in the process. The above equations, suggests that electric current might have an impact on these process. Therefore a laboratory scale electrochemical set-up has been designed and developed to study the effect of electric current. For the process of electrolysis to take place producing pure silicon metal, a melt must: 1. Possess character of an ionic conductor. 2. Its value of conductivity should be acceptable 3. Should not have elements more noble than silicon since they will co-deposit with silicon contaminating it. 4. It should also have low vapour pressure. 5. Be less dense than liquid silicon 6. Have high solubility for silicon oxide 7. Should be conducive to environment benign 8. Be of low cost A high-accuracy, calibration-free technique for measuring the electrical conductivity if molten oxides 1.1 Problem statement To design a device that can be used to determine the electrical potential of an electrochemical during the high temperatures in a chemical reaction. Also, to conduct experiments relating to the electrochemical measurements to determine the chemical properties of the electrochemical and elevated temperatures of 1000 0C. 1.2 Objectives The main objective of the project is to design a device that can be used to determine the electrical potential of an electrochemical at elevated temperatures of 1000 0C. Some of the key objectives include: To compare the past designs regarding the electrical potential determination using electrochemical processes. To design a new and more efficient electrochemical design for determining electrical potential at elevated temperature of the chemicals. To help the students learn on the purpose for determining the electric potential at an elevated temperature. To help the chemical operators dealing with determination about the risk assessment procedures associated with the handling of the chemicals that are used in the electrical potential determination without causing accidents or careless mistake which otherwise be detrimental to whole operation. To the chemical reaction of silicon at temperature below 1900 0C, replacing it with 1000 0C. 2. Literature review Basically, silicon form double compounds when it mixes with other metallic elements, and these compounds are called silicides, e.g. silicon carbide (SiC). The silicon carbide compound is hard and has a high melting point and it is also abrasive. Silicon majorly forms these compounds to attain different chemical and physical properties for its reaction at different environments. Most of these silicon compounds of silicon cannot be separated at temperatures of 1000 0C hence they require higher temperatures to separate them. But, this research focuses mainly on the operating temperature of 1000 0c thus meaning that it defines the type of the silicon compound for this experiment (Bard and Larry, 2001). Currently, the purification of silicon is done by the process that involves conversion of the silicon compound which, can be simplified by use of the distillation process of compound to the original state of the compound. The compound is then changed to the original pure silicon compound. The type of the silicon compound that is mostly used is the Trichlorosilane compound. There are also other silicon compounds that can be used which include silicon tetrachloride and silane. These gases can be blown over the silicon at high temperature of about 1000 0C thus decomposing it to highly pure silicon. This reaction can involve the use of zinc vapors to produce silicon at due point. This reaction takes the following equation. SiCl4 + 2 Zn → Si + 2 ZnCl2 The silicon formation according to the above equation the by - products of this reaction are capable of clocking and blocking the lines that pass the molten silicon compound (Greenwood & Earnshaw, 1997). In addition, silicon and boron have certain unique characteristics. Silicon is found in the fourth group in the chemical periodical table; whereas boron is found in the third group. Silicon possesses a specific gravity of about 2.4 whereas its melting point is 1420 o C. Its dielectric constant is known to be 13. On the other hand boron has, boron has a p-type conductivity and posses a density of 2.35g/ml. They are bad conductors of current butt exhibit a semi-conductivity property. 2.1 Review of available techniques The Coaxial Cylinders technique is a high accuracy, calibration free technique, which has been often in contact with a metal and not any dielectric, this method provides for the measurement of the electric properties of the molten which cannot be accessed by classical high-accuracy techniques. The coaxial cylindrical electrodes are immersed in the molten over a range of frequency and measurements taken (Bryan, 1995). The same process is then repeated with the electrodes immersed deeper and measurements taken again over the same range of frequencies. There are 11 techniques that have been designed based on the design of the electrodes. Among these are high accuracy techniques and low accuracy techniques. For the high accuracy techniques they have well defined current paths. The functionality of current path may depend upon the electrical properties for example: liquid being investigated, electrodes and the container being characterized. Five electrodes designs gave low accuracy techniques: 2 wires, 4 wires, 4 wires with 2 immersions, crucible, different crucible, ring and 2 toroid. There four high accuracy techniques based on three electrode design i.e. interdigitated, capillary, differential capillary and meandering winding. The relationship between the range limits of the impedance measuring instrument and the ability to conduct electricity of the liquid being investigated. 2.2 The new methods The conductivity of electricity of a material is usually difficult to be determined directly. Therefore most of the time they are derived from resultant values measured e.g. resistance. R=ρ () =  Where: R=resistance ρ =electric resistivity K=electric conductivity L=length of current path A=cross-sectional area The conductivity of a liquid metal in electrochemical impedance spectroscopy is derived from the impedance, Z. The total impedance may be derived from other sources of the parts of measuring device. Therefore Z used is the total of impedance in the circuit. The steps for finding k from the impedances, Z when co-axial cylinder electrodes are employed: Measurements of Z are taken over a wide range of frequencies at different depths Correcting the short circuits at different depths The values of the short circuit correction are taken by taking the values at which Zz, is minimal. A graph of Z against the relative depths is plotted The gradient is a straight line. 3. Methodology MEASUREMENTS OF MOLTEN OXIDES ELECTRICAL CONDUCTIVITY Two molten oxides N and L are measured as a function of temperature to investigate there conductivity. N is a metal richer in silica content and L is the melt richer in metal-oxide. The two oxides show that with increase in temperature conductivity also increases. 3.1 Apparatus used in the experiment 1. Furnace The figure below shows the cross section of a furnace. A layer of water surrounding the furnace chamber provides a gas tight seal from the closed one end alumina reaction tube. In the reaction tube the gas in it is separate from the temperature in the furnace and the atmosphere of the room and therefore the temperatures can be varied separately. The furnace temperatures can rise up to 1800 C. It’s usually has to be oxygen tight to prevent oxidation of the heaters made of graphite. This was attained through the use of a rotary mechanical pump which would help in lowering the process temperature to prevent oxidation of the cathode. 2. Motion apparatus The device above was made of metal bellows. The electrodes are made to be upright by the bellows without changing the orientation of the inert atmosphere in the chamber. Turning the nuts causes the nuts to be engaged. The length moved by the threaded aluminium tube is accurately measured by the digital micrometer. The figure below illustrates the bellows device mounted on the apparatus using specifically designed water cooled fixture. Vacuum tight feed-through were used for alignment and separation of the leads and thermocouples. 3. Electrodes They should be able to withstand high temperatures and the hash surrounding of the liquid metal oxides. Since molybdenum is chemically inert and its machinability properties are excellent it was preferred where contact with the molten metal was to occur. The high electrode build up is shown in the figure below. A solid rod was used to produce the outer electrode of 1.25cm diameter. Electrodes and the inner diameter were made from molybdenum rods. To prevent the heat loss above the electrodes section the system was designed such that it disks placed at the top of the electrodes, connected to the leads. Placing of these disks would also help in acquiring the whole electrode assembly. 4. Certification For the certification, the high temperature apparatus the properties used to measure conductivity properties of 0.1 D KCl (aq) at standard temperatures. All the other parts of the apparatus were used also to measure this. The oxide elements Ca0-Mg0-Si0 was used in the study since it’s a least complex system that has all the components required for direct oxide electrolysis. It also permits for high changes of the composition at varied temperatures of below 1600 C. The two melts had a composition of: (M) 50.95% CaO, 12.51 % MgO, 36.54 % SiO, and (S) 24.59 % CaO, 26.15% MgO, 48.25 % SiO. The above can be explained using each of their melt structures. The electrical conductivity is widely known to depend on the liquid melt structure. When basic oxides are slowly added it leads to the separation of the oxygen bonds and bridging oxygen are made. Finally there is formation of ions of oxygen which are free. Liquid metal rich in silica has silica network which does not contain any free oxygen since the oxygen bond with 1 or 2 silica. In the Nernst equation, Ecell=cell-(2.303RTlnf)log Q S (Fe sln+ 2e-= S2-. Cu 2+ +Zn Cus+Zn2+ cell=Ecell-(0.05912)log[ 3.2 The procedure of the experiment 1. Preliminaries The apparatus made of molybdenum parts were keenly cleaned and dried. Heat treatment was given to the BN parts. Leads and the electrodes were then appropriately put in place. Hand protections, preferably cotton gloves, were used to eliminate natural oil contaminating the electrodes. The top fitting lead was then put in place after placing well the electrodes. This placement was confirmed using an aluminium foil impression. Molybdenum sheaths were put in the top fitting. After the proper set up of the electrodes, molybdenum crucible was added with 300g of melted oxide. It was then put in the middle of the COE alumina reaction tube. Motion apparatus was then connected with the furnace. Lastly the electrode set up is put in via the motion set up and the top fitting closed tightly using the O-ring seal. After evacuating the chamber where the reactions will take place, it was then filled with UHP argon severally. It was then left for one day. Furnace temperatures were then elevated to 400 C for two to five days owing to the state of the charge. 2. Measurements Impedance measurements were made when the electrodes were being put slowly to fill the melt surface. A drop of impedance was recorded when the electrodes initially came into contact with the surface. The electrodes were then dipped into the melt deep and then retracted slowly to a shallow depth where it was left for approximately ten minutes. Again the electrodes were dipped back to the initial depth and after two minutes the thermal readings were taken and the impedance recorded for the frequencies between 350 to 1 kHz. The electrodes are then put deeper for the next measurements. The process is then repeated. The impedance for the next 6 immersions is recorded. At the end of this process, the electrodes are carefully removed from the melt. The temperature of the furnace was then increased to the next temperature that is desired for study. The process was done for six different temperature of interest and then many measurements were done repetitively to ensure consistency. A sample of melt was then taken using the sampling rods. All molybdenum parts viability was assured by the bright silvery appearance of these parts which were open to the elevated temperatures. 3.3 Results and discussions The values recorded for the electrical conductivity of the liquid melt of liquid N and L were by least square regression fitted to an Arrhenius type equation. For melt N  k=7.1779 (±0.357) -, For 17331903 For melt L,  k = 7.1779 (± 0.553) – , For 1763 < T < 1903 As al linear, polynomial fits were be better  k = -38.873 + 1.5329 × 105 (1/T) - 1.5529 × 108(1/T)2 Where: K is in S cm-I and T is in Kelvin. The results are plotted below Temperature dependence of the electrical conductivity of melts N and L The comparison of linear and polynomial fits of data for the melt of N Risk assessment and the Safety procedures Precautions When working with the electro- chemicals care should be taken to avoid direct contact of the chemicals with the hands, since they are corrosive and they itchy effect on the hands and body they come into contact. These chemicals should never be injected to the mouth or they should be taken through the mouth for safety reasons. The vapors from the chemicals are considerably dangerous and therefore should never be inhaled in case, and if inhaled by accident the patient should be treated with immediate effect to avoid complications. It is important to note that the children at the place work or anybody can confuse food bottles and the chemical bottles; therefore, it is important to see to it that the chemicals are kept away from the areas where they can be confused with food containers or bottles. Lastly, the chemical containments should be properly labeled as a precautionary measure to avoid confusion when working the chemicals to avoid accidents. Cost Item price Furnace Electrodes Motion apparatus 4 Conclusion From the figures above, melt L and no increase by the polynomial fit of the data. Melt L is acidic and that means it has a silicate network structure. Melt N is neutral since it’s neither acidic nor basic. The small curve in the L data may have been caused by the alteration of the liquid structure. The level of polymerization will have an effect on the electric conductivity of a melt. Bigger chain network in the system, the more the barrier of the movement of cautions hence the less the conductivity of the melt. The use of silicon compounds for extraction of pure silicon from the molten state compound is ideal to acquire silicon free from contaminants that affect the chemical and physical properties of silicon obtained. The need to use the carbon as the main electrode in the silicon electrolysis is based on the fact that carbon reduces metals in the reactivity series. Hence, the electric potential measurement is possible as long as the reaction is stable and the electrolyte is in its aqueous from. 5 Recommendations When using boron nitride in the in the electrical potential determination it is important to ensure that, it is first heat treated to eliminate the moisture and binders. This is necessary because if otherwise it would shatter at the start of the reaction. This Boron Nitride compound has to be stored under a desiccant to prevent repeating the whole process of heat treatment since exposure to air allows the Boron Nitride to absorb air from the ambient. When planning to use molybdenum electrodes it is necessary to clean them before using to remove the oxide coating. The oxide coating would otherwise prevent conduction at the start of the reaction and hence it cannot conduct the voltage which should be determined. References Alyousif, M., 2002, Corrosion and Corrosion Fatigue of Aluminium Alloys. Manchester: Wiley. Bard, J., and Larry, F., 2001, Electrochemical Methods: Fundamentals and Applications. New York: Wiley. Blewer, S., 1986, Tungsten and Other Refractory Metals for VLSI Applications: Proceedings of the 1985 Workshop Held October 7, 1985, Albuquerque, New Mexico, U.S.A. and the 1984 Workshop Held November 12-13, 1984, Albuquerque, New Mexico, U.S.A. Pittsburgh, PA: Materials Research Society. Bryan, A., 1995, Electrochemical Reactions. London: Queen's University of Belfast. De Mattei, C. 1981. Electrodeposition of Silicon at Temperatures above its Melting Point. Journal of the Electrochemical Society, 128: 1712. GreenwN, A. 1997.chemistry of the elements (2nd ed.). Oxford: Butterworth- Heimann. Fifield, W., and Haines, P., 2000, Environmental Analytical Chemistry. Malden, MA: Blackwell Science. Hein, M, and Susan, A., 2004, Foundations of College Chemistry. Hoboken, NJ: J. Wiley & Sons. Kobayashi, A., 2008, Smart Processing Technology. Ibaraki: High Temperature Society of Japan. Kroposki, D., 2006, Electrolysis: Information and Opportunities for Electric Power Utilities. Golden, CO: National Renewable Energy Laboratory Larminie, J., and Andrew, D., 2003, Fuel Cell Systems Explained. Chichester, West Sussex: J. Wiley. McDonald, O., Soboroff, D.and. Cochran, G. 1980 Electrolytic Reduction of Chromium (VI) Copper Using Coke Electrodes. [Washington, D.C.]: U.S. Dept. of the Interior, Bureau of Mines. Monier, R et al. 1965. Dual Cell Refining of Silicon and Germanium. Us Patent 31219, 561. Perepezko, H. 2009. The Analysis and Modelling of Phase Stability and Multiphase Designs in High Temperature Refractory Metal-Silicon-Boron Alloys. Ft. Belvoir: Defense Technical Information Center, Rasband, B. 1996. Formation and Transport Properties of Defects in Boron-doped Silicon Studied through Tight Binding Bond Models. New York: McGraw-Hill. Rosario, R. 2006. Electrochemical Preparation and Physicochemical Characterization of Porous Silicon and Anodic Films of Porous Si02. New York: Houghton Mifflin. Stansfield, A. 2009. The Electric Furnace: Its Construction, Operation and Uses. New York [u.a.: McGraw-Hill Yasuda, K., Nohira, T., Hagiwara, R. and Ogata. Y . 2007."Direct Electrolytic Reduction of Solid SiO2 in Molten CaCl2 for the Production of Solar Grade Silicon." Electrochimica Acta 53.1 (2007): 106-10. Yasuda, K. and Yukio, O. 2006."Direct Electrolytic Reduction of Solid Silicon Dioxide in Molten LiCl—KCl—CaCl2 at 773 K." ChemInform 37(7)69-74. Zumdahl, S., and Susan A. 2003. Chemistry. Boston: Houghton Mifflin. Risk assessment Experimental risk Risk Description Probability Consequence Level of risk Solution Holding objects with bare hands Burning of hands possible critical high Should put on gloves Inhalation of poisonous gases Respiratory diseases possible critical high Put on nose guards Fire Much heat is produced to the environment possible critical High Keep flammable things away Read More

This project will base its study on the design and development of experimental apparatus that measures electrical potential during reactions at high temperature of above 1000 C. Study on a selected high temperature will also be a part of the project. Table of contents 1. Introduction............................................................................................................5 1.1 problem statement...........................................................................7 1.2 objective..........................................................................................7 2. Literature review.....................................................................................................8 2.1 Review of available technologies................................................9 2.2 The new trends...........................................................................10 3. Methodology..........................................................................................................11 3.1 Experimental apparatus..............................................................11 3.2 procedure of experiment..............................................................16 3.3 Results and discussion..................................................................18 4. Conclusion...............................................................................................................21 5. Recommendation.....................................................................................................22 6. Risk assessment.........................................................................................................26 1. Introduction It’s evident from the current work that the acceleration of reaction processes is possible by the application of external currents and voltages. If a current density of 2.33A/cm2 at 4V is used, it accelerates the transfer rate of silicon from silica to a silicon reduced slag. Without the application of electric current the rate of transfer from metal to slag is 0.000297moles %/S at the same base ratio. At 90A, there is about 98.95% efficiency towards formation of the silicon slag. The higher the rate of current flow the higher the rate at which the slag sulphates thus forming a resistive layer at the cathode and hence potential conduction stops. Transfer of silicon from metal to slag happens through an electrochemical process. This process happens through the exchange of electrons between the metal phase and slag phase. Silicon is produced from an electric furnace using carbon electrodes at temperature of about 1900 0C where the carbon reduces the silica to silicon and carbon monoxide (De Mattei & Robbert, 1981). The process equation occurs in two stage equation as shown below. SiO2 + C → Si + CO2 SiO2 + 2 C → Si + 2 CO This results in the formation of the liquid silicon which collects at the bottom of the reaction furnace. The liquid silicon is removed from the electric furnace which is at 1000 0C and then cooled. This type of silicon produced through this process is called metallurgical silicon and it is 98% pure with few impurities of carbon. When this method is applied in the extraction of the silicon from silica it is evident that, there is formation of silicon carbide (SiC) (Monier, R et al., 1965). To avoid this formation of silicon carbide it’s therefore important to use silicon oxide (SiO2), which eliminates the silicon carbon from the reaction thus forming the required silicon. This reaction is as shown below. 2 SiC + SiO2 → 3 Si + 2 CO The above equation is the overall ionic equation for the silicon formation process when silicon carbide forms in a reaction of silicon extraction. As the silicon reaction forms the electrical potential difference is measured through the voltmeter. The voltmeter is used to determine the amount voltage that can be transferred through a given conduit within a given time. Read More