Analysis of Composition Corrosion Cells - Assignment Example

EXPERIMENT ANSWERS By Student’s name Course code and name Professor’s name University name City, State Date of submission Table of Contents Table of Contents 2 EXPERIMENT 2: PROPERTIES OF BRICK AND BLOCK MATERIALS 5 Question 1: Specimen graphs of cumulative mass of water absorbed (g) against square root of time. 5 Question 2: Initial rate of absorption 8 Question 3: Capillarity action 8 Question 4: Important Properties of a Brick 9 Question 5: Negative effects of Water absorption by bricks 10 EXPERIMENT 3: THE STUDY OF COMPOSITION CORROSION CELLS 10 Question 1: Corrosion 10 Question 2: Conditions Favouring Corrosion 11 Question 3: Electrode Potential 11 Question 4: Galvanization 12 Question 5: Reactivity series for the experimental electrolytes used 13 EXPERIMENT 4: STRUCTURE AND PERFORMANCE OF TIMBERS FOR USE IN CONSTRUCTION 14 Question 1: Cellular structures and load versus deflection graphs of samples 14 Question 2: Modulus of Elasticity 17 Question 3: Coefficient of thermal expansion 17 Question 4: Modulus of elasticity and Rupture 18 Question 5: Functions of various cells 18 EXPERIMENT 5: THE EFFECT OF WATER CEMENT RATIO UPON THE COMPRESSIVE STRENGTH OF CONCRETE 20 Question 1: Graph of strength against water: cement ratio 20 Question 2: Effects of water cement ratio on density and compressive strength 20 Question 3: Effects of water cement ratio on hydration of cement 21 Question 4: Effects of water cement ratio on porosity of the mix 21 Question 5: Effects of porosity on durability on concrete 22 EXPERIMENT 6: THERMAL CONDUCTION AND HEAT TRANSFER IN METALS 23 Question 1: Analysis of experimental data on sieve analysis 23 Question 2: Well graded Aggregate 24 Question 3: Characteristics of aggregate and their influence on properties of fresh concrete 24 Question 4: Effects of Chloride Salts on rebar 25 Question 5: Why aggregate is used in concrete 25 EXPERIMENT 7: THERMAL CONDUCTION AND HEAT TRANSFER IN METALS 26 Question 1: Graph of temperature against time for part 1 26 Question 2: Stabilization temperature 26 Question 3: Thermal Conduction in various conductors 27 Question 4: Graph of extension against time 27 Question 5: Best thermal conductor and insulator 28 EXPERIMENT 8: DETERMINATION OF THE EFFECTS OF A SMALL SOURCE IGNITION ON TEXTILE COVERINGS (HOT METAL NUT METHOD) 29 Question 1: The level of effects 29 Question 2: Orientation of sample with respect to flame spread 30 Question 3: Graph of temperature against diameter 30 Question 4: Diagrams 31 Question 5: Discuss the importance of this test 31 List of References 32 EXPERIMENT 2: PROPERTIES OF BRICK AND BLOCK MATERIALS Question 1: Specimen graphs of cumulative mass of water absorbed (g) against square root of time. Table 2.1: Absorption of water by capillarity for a thermalite block. Time (Minutes) Mass of water absorbed per minute (g) 1 564 1 2 146 1.41 3 102 1.73 4 73 2 5 10 2.23 6 0 2.45 7 0 2.65 8 0 2.83 9 2 3 10 2 3.16 Table 2.2: Absorption of water by capillarity for an engineering brick. Time (Minutes) Mass of water absorbed per minute (g) 1 0 1 2 1 1.41 3 0 1.73 4 0 2 5 0 2.23 6 0 2.45 7 0 2.65 8 0 2.83 9 0 3 10 0 3.16 Table 2.3: Absorption of water by capillarity for a facing brick. Time (Minutes) Mass of water absorbed per minute (g) 1 32 1 2 7 1.41 3 6 1.73 4 8 2 5 5 2.23 6 6 2.45 7 3 2.65 8 4 2.83 9 3 3 10 4 3.16 Question 2: Initial rate of absorption The initial rate of absorption (IRA) is the quantifiable amount of water absorbed through a bed face of a brick within one minute. This factor can be used to define the hardness of a brick because it is closely related to cohesion. Cohesion is the bonding capability which affects the bond between the bricks and mortars. Brick layers have been observed to adjust the mortar in order to comply with the wall height due to suction force with mortar. IRA affects the bonding capability of the unit due to its capability to absorb water in order to hydrate the cement material. There are acceptable levels of water that should be maintained by a brick since the too quick absorption of means that the next course shall not be bedded properly. In cases where mortar retains a lot of water, the mortar floats on the bed posing as a difficulty to lay the next layers. This leads to poor bonding between one layer of brick and the other (Boral, 2013). Question 3: Capillarity action Capillarity action is the ability of water to flow through small pores of soil without any assistance from physical phenomenon. This occurs since water molecules are characterised by cohesion and adhesion forces. Water adhesion in soil is affected by the interconnecting pore spaces as exhibited by water pipe experiments which are analogous to the same. Water flow by capillarity through small pores of soil has been found to be faster than huge pores because of higher adhesive and cohesion forces with water. This translates to hygroscopic properties – ability of bricks to attract water due to high cohesion forces. Better brick and motor binding occurs when the pores are of smaller size, a factor that determines the rate at which capillarity occurs (Melander & Lauersdorf, 1993). Question 4: Important Properties of a Brick Some of the most important properties of a brick include: i. Strength: A brick should possess high compressive strength. The raw materials used, manufacturing process, shape and size should be chosen carefully. ii. Aesthetic appeal: Bricks should possess natural attractive colour so as to avoid the extra costs of beautification. iii. Porosity: Bricks must be able to release and absorb moisture in order to maintain a good strength balance. This is also a desirable trait during construction process as it enhances capillarity. iv. Fire resistance: Bricks are preferred due to their incombustibility. This factor should therefore be adhered to in order to promote safety of building in cases of fire outbreaks. v. Thermal insulation: This property aids in maintaining the external and internal environment in terms of temperature. vi. Sound insulation: Bricks should offer a good insulation to sound from external sources. vii. Wear resistance: Durability is a mandatory property in all construction materials (Clay Bricks, 2007). Question 5: Negative effects of Water absorption by bricks The compressive strength of bricks is adversely lowered thereby posing as a danger to the inhabitants. Secondly drying up during the construction period may be problematic thereby extending a project period. EXPERIMENT 3: THE STUDY OF COMPOSITION CORROSION CELLS Question 1: Corrosion This is a chemical or electrochemical reaction between a metal and environmentally present elements such as oxygen that leads to deterioration in original physical and mechanical properties. Prevention or minimization of corrosion can be done by any of the following methods depending on mode of corrosion. i. Applying coatings: These can be paints or coats of from the low reactive series with anti-corrosive properties. Placing a barrier against the main structure prevents direct contact or reaction with the environmental elements thereby protecting them from destruction. ii. Anodization: This is usually done by electrochemical reactions in bath that coat the structure with several nanometres of the low reaction element. This film acts like a coating although the mode of application differs from that of paint coatings. iii. Reactive Coatings: Reaction coatings are also known as corrosion inhibitors. These chemicals insulate the structure chemically and electrically rendering it less sensitive to reaction with environmentally available materials. Question 2: Conditions Favouring Corrosion The experimental setup consisted of water with cleaning agent (electrochemical corrosion) and fresh water with oxygen (chemical). In such circumstances as these, water with cleaning agent catalysed the corrosion process of the metal while conditions with oxygenated water occurred naturally and slowly as compared to its counterpart. Enclosed jar did not allow for corrosion because the vital element required for corrosion i.e. oxygen was eliminated thereby inhibiting this process. Question 3: Electrode Potential The table below shows the reactivity order of selected materials namely aluminium, lead, iron, magnesium, zinc and nickel from the most reactive to the least reactive. This table is generated based on the electrode potential – it has been established that the greater the negative electrode potential in a given element the higher the chances that corrosion shall occur. Table 3.1: Reactivity series for aluminium, lead, iron, magnesium, zinc and nickel. Metal Electrode Potential (Volts) Magnesium -2.37 Aluminium -1.66 Zinc -0.76 Iron -0.44 Nickel -0.25 Lead -0.13 Question 4: Galvanization Galvanic cells are formed by using a composition of either dissimilar metals or a multiphase of alloys. In application of two dissimilar metals, the metals in contact such as nickel and gold or zinc and nickel are joined in a single phase. The metal that is higher in terms of reactivity becomes the cathode while the one with lower reactivity becomes the anode. The metal that is exposed to the anodic reactions corrodes thereby coating the cathode – a similar technology is used in construction of batteries. On the other side, multiphase alloying is formed from metal alloys that are found in stainless steel aluminium alloys etc. Each phase consists of its own alloy that is exposed to anodic reactions in order to coat the subject accordingly (Materials Home, 2014). Cathodic protection is a corrosion protection technique that involves making the susceptible metal surface the cathode while the sacrificial metal is made the anode. As explained in the introductory section above, anodic reactions are more corrosive thus rendering the structure safe from destruction. On the other side, sacrificial anodes are manufactured from metals of higher reactivity than the metals they are intended to protect from anodic reactions or corrosion. These anodes are then buried in the medium perceived as the electrolyte as seen in mild steel ships which are protected by zinc anodes. When a metal is placed in an electrolyte, galvanic corrosion is prone to occur. Galvanic corrosion has been exploited in such applications as primary batteries in order to generate voltage. The metal place in an electrolyte acts as the anode by reacting to produce voltage. This occurs as a corrosion process that renders the material’s ions migrating top the solution. Question 5: Reactivity series for the experimental electrolytes used The following table represents the findings from the experiment to determine the most reactive electrolyte in a series of water, acidic and alkaline electrolytes used. For a start, the electrode with most negative electrode potentials was observed to be the most reactive. The lower the pH the higher the corrosive levels. Table 3.2: Reaction series of metals in various types of electrolyte. Experimental Data Anodic (More Reactive) WATER ELECTROLYTE ACIDIC ELECTROLYTE ALKALINE ELECTROLYTE Aluminium Zinc Aluminium Zinc Aluminium Zinc Lead Lead Mild Steel Mild Steel Mild Steel Stainless Steel Stainless Steel Stainless Steel Lead Brass Brass Brass Copper Copper Copper Cathodic (Less Reactive) EXPERIMENT 4: STRUCTURE AND PERFORMANCE OF TIMBERS FOR USE IN CONSTRUCTION Question 1: Cellular structures and load versus deflection graphs of samples The following cellular structures were obtained under x10 and x40 microscopic magnifications. Figure 4.1: Cellular structure of soft wood. Table 4.1: Deflection data obtained for hardwood and softwood samples. Load Deflection(Soft Wood) Deflection (Hardwood) 50 0.08 0.85 150 0.34 1.09 250 0.58 1.31 350 0.81 1.55 450 1.05 1.81 700 1.63 2.42 950 2.22 3.23 1200 2.83 4.31 1450 3.48 6.78 1700 4.26 _ 1950 5.16 _ Question 2: Modulus of Elasticity Modulus of elasticity of the given timber samples is obtainable through equation (4.1) shown below; (4.1) Where: is the deflection at a point in the elastic segment of the curve. = the load (N) of corresponding to deflection point under consideration in = the length between supports = the elasticity modulus. 190,857,875/17711 = the moment of area Question 3: Coefficient of thermal expansion Thermal expansion is the trend observed in materials such that when they are exposed to various temperatures they either shrink (negative expansion) or expand. The coefficient of thermal expansion is the factor used to express the expansion capability of a material when exposed to heat. The relationship between expansion and temperature has been found to be linear for most materials. Question 4: Modulus of elasticity and Rupture Modulus of elasticity is the factor that determines a material’s tendency to deform elastically. It is a ration between stress and strain in the elastic deformation zone i.e. (4.2) Modulus of rupture is the standard of measure for a timber material sample prior to rupture. This is the overall strength of a timber sample but not an indicator of ultimate strength or modulus of elasticity (Meier, 2014). (4.3) For hardwood: For softwood: Question 5: Functions of various cells Table 4.2: Functions of various special cells in trees. CELL TYPE FUNCTION Vessels (hardwoods) These are cells stacked on top of each other to form the vessels are responsible of the difference between softwood and hardwood. They are meant to offer support to the tree by shaping the tree trunk. Fibres (Hardwoods) They are solely meant for support. They are shorter than tracheid and about 10 times longer than vessels. Tracheid (Softwoods) They offer both mechanical and conductive properties in softwoods i.e. support and plant nutrient or water transfer. Rays These are rings that enable the transport of dissolved food nutrients and water across the stem in a radial manner. EXPERIMENT 5: THE EFFECT OF WATER CEMENT RATIO UPON THE COMPRESSIVE STRENGTH OF CONCRETE Question 1: Graph of strength against water: cement ratio Figure 5.1: A graph of compressive strength against water cement ratio. Question 2: Effects of water cement ratio on density and compressive strength Various researchers have set up experiments to study this important concrete phenomenon. Considering that cement is the finest material among those used in mixing concrete; it has the greatest effect on density as it takes a higher pore space as compared to sand. Moderating water to low levels means that there shall be a lighter cement mix that poses as a control over the trapped macroscopic capillary voids thus manipulating the density. The higher the amount of water used, the higher the density of the resulting concrete. Less water usage in concrete poses reverse properties due to difficulty in expelling the air voids due lower lubrication. Among 60 samples of concrete tested for compressive properties by Ling et al. (2006) those with an optimum water to cement ratio in concrete possessed the best compressive strength. Mixtures containing a low water cement ration were observed to have lower compressive strength due to lack of proper hydration or lubrication of pores to expel air and other foreign impurities (Ling, et al., 2006). Question 3: Effects of water cement ratio on hydration of cement As highlighted in the section above in conjunction with experimental data, the higher the amount of water in the constituting ratio, the higher the hydration of cement. This is based on Ling’s argument that the void is expelled creating a better lubrication among the cement particles thereby creating a better seepage or capillarity for water molecules through cement making it more hydrated. Question 4: Effects of water cement ratio on porosity of the mix In order to answer this question better, a reverse approach is used to expound on the formation of porous concrete pavements. In order to create a porous concrete system, the fine aggregates are limited from sand and coarse aggregate mix. The reason behind this is to leave large pores that water can seep through. While manufacturing concrete, keeping water cement ration at a minimum translates to large pores due to lack of lubrication to allow for complete expulsion of macro pores. This thus increases the porosity of concrete, The vice versa occurs when a large amount of water is used in concrete mix or plainly a high water cement ratio allows for higher strength higher density results due to close packaging materials. This reduced the chance of water passing through (Ling, et al., 2006). Question 5: Effects of porosity on durability on concrete Highly porous concrete materials are less durable than those which possess less pores. Depending on application, the strength of concrete is made to be porous to an acceptable percentage by varying the water cement ratios. The porous concrete is susceptible to higher water accumulation due to capillarity which may weaken a structure due to added or extraneous weight. EXPERIMENT 6: THERMAL CONDUCTION AND HEAT TRANSFER IN METALS Question 1: Analysis of experimental data on sieve analysis The results obtained in accordance to the 5mm sieve indicated that the aggregate was fine. According to the experiment manual coarseness index in BS EN 12620:2002 Table B1, it is indicated that when the mass passing through a sieve is from 55-100%, then the aggregate is considered as fine. The data collected exhibited that 98.05% of aggregate passed through the sieve which qualifies them as fine. The allowable coarse and fine aggregate contents should be 40% and 60% in concrete respectively by absolute mass. The lower and upper limit for coarse materials are however placed at 38% and 42% respectively. In terms of ratio this translates to 1.38 and 1.68 for coarse and fine aggregate respectively (Popovics, 1992). The benefits of grading go a long way to giving a balanced nature in concrete for a balance of numerous important factors. Good grading is achieved when the maximum size of aggregate is reduced since the particle shape becomes less favorable towards increasing the cement ratio and eventually fine aggregate plays a great role in determining the compressive strength of resulting concrete. As shown in experiment 5 the size of the aggregate plays important role in determining the porosity of concrete. When the particle sizes are smaller and well cured, the results achieved are tremendous in terms of strength and durability. Question 2: Well graded Aggregate Aggregate is said to be well graded when maximum and minimum aggregate sizes are combined in a desirable ration to achieve a mixture that does not contain voids. When dense and well graded aggregates are mixed, the void between the particles becomes compacted leaving a well packed structure that is responsible of a good quality of concrete products. Question 3: Characteristics of aggregate and their influence on properties of fresh concrete Aggregate possesses the following characteristics which are influential on the properties of fresh concrete: i. Particle shape and surface texture: this property affects concrete in the perspective of hardness. Rough textured and elongated aggregate further requires more water to produce workable concrete than round or cubic aggregate. ii. Chemical Stability: The chemical property is important in terms of the reactivity with cement and the other constituting components which may render the concrete stronger or weaker depending on the influence. iii. Resistance to freezing and thawing: This property determines the ability of aggregate to absorb water to an extent of leaving the concrete with insufficient pore space to accommodate the expansion activity when it comes to freezing (Aggregate & Sand Producers Association of Southern Africa, 2006). Question 4: Effects of Chloride Salts on rebar Corrosion due to chloride salts has continue to be a problem in reinforced concrete. Corrosion caused by chloride salts inside reinforced concrete is unpreventable to some extent exposing buildings to dangers of collapse due to loss in strength. This happens when chloride ions due to endosmosis lead to complete corrosion of reinforcing steel. On the other hand water absorption levels of silt affect the strength of concrete thereby interfering with bonding capability. In cases where the concrete is hardened, silt comes into contact with air voids causing wall internals to swell thereby weakening concrete. Question 5: Why aggregate is used in concrete i. For grading purposes. ii. To influence concrete strength. iii. To act as filler material due to cost. iv. Readily and largely available. EXPERIMENT 7: THERMAL CONDUCTION AND HEAT TRANSFER IN METALS Question 1: Graph of temperature against time for part 1 Question 2: Stabilization temperature Original temperature of hot water - temperature decrease = temperature at which stabilization is achieved. Temperature decrease of warm water = 24.9ºC Temperature at which warm water stabilizes = 53.2 ºC Question 3: Thermal Conduction in various conductors The following data was obtained from the experiment with regard to various metal strips being investigated. Table 7.1: Order of conductivity Sequence that the paraffin wax melts (metal wax) Aluminum Copper Brass Lead The paraffin wax melts in the order shown above which at the same time couples as the sequence of thermal conductivity. The best conductor from the above information is aluminum with the best thermal insulator being copper. This also follows the rate at which the paraffin wax melted. Question 4: Graph of extension against time Table 7.2: Thermal expansion From the graph above, the best insulator was found to be aluminum with the best thermal conductor being iron. This was dependent on the highest achievable amount of heat and the manner in which they dissipated the heat to their surrounding environment. Question 5: Best thermal conductor and insulator The thermal conductivity of the materials in the 4th part of the experiment entirely depended on the ability to dissipate energy. The distance covered was also an important property to look at as the best thermal conductor would conduct heat energy faster to cover the greatest distance. In this case, the highest distance was travelled by copper which is the best thermal conductor followed by brass, aluminum then steel. Looking at the time taken by the sample to cool down would determine which the best insulator was. Steel was found to cool down quickly – this is one of the best insulation characteristics. Therefore steel was the best insulator in this case followed by its aluminum and brass counterparts. EXPERIMENT 8: DETERMINATION OF THE EFFECTS OF A SMALL SOURCE IGNITION ON TEXTILE COVERINGS (HOT METAL NUT METHOD) Question 1: The level of effects The table below sums up all the findings made by this study: Table 8.1: A summation of all the experimental findings. TYPE OF SAMPLE AND SAMPLE MEASUREMENTS INCLUDING THICKNESS SIDE TESTED DIMENSION OF IGNITION (RADIUS) OBSERVATIONS ON UNDERSIDE OF SAMPLE EFFECTS OF IGNITION Carpet 5mm thick Top 20mm Melted Flames and some smoke Sample 2 Top 25mm Melted Flames and some smoke Sample 3 Top 22mm Melted Flames and some smoke Sample 4 Top 28mm Melted Flames and some smoke Sample 5 Underside 23mm Circular burn marks Flames and some smoke Sample 6 Underside 18mm Circular burn marks Flames and some smoke Question 2: Orientation of sample with respect to flame spread The orientation of the sample affected the flame spread in that increasing the angle of inclination slightly led to quicker glow and even eruption of fire. This according to Atreya et al. (1986) is attributed to dominant re-radiative losses due to induced ambient of oxygen concentrations. Question 3: Graph of temperature against diameter Figure 8.1: Graph of temperature against the diameter of flame spread (University of California, 2009). Question 4: Diagrams Figure 8.2: Sample of carpet before and after the experiment. Question 5: Discuss the importance of this test The objectives of this experiment were to understand flame spread and smoke development including the contribution made from the floor coverings and the potential they have towards the hazardous conditions. This shall help in safeguarding the occupants from injuries and illnesses related to the catastrophic nature of fire during the evacuation process. Further, this shall aid in facilitating fire emergency services so as to aid in curbing the spread of fire between buildings. Property can be easily protected if fire engineers learn on structural failure with respect to this kind of experiment. List of References Aggregate & Sand Producers Association of Southern Africa, 2006. Aggregates for concerete. [Online] Available at: http://www.aspasa.co.za/Aggragates/AggragatesForConcrete.html [Accessed 4 May 2014]. Atreya, A., Carpentier, C. & Herkleroad, M., 1986. Effect Of Sample Orientation On Piloted Ignition And Flame Spread. Fire Safety Science, Volume 1, pp. 97-109. Boral, 2013. Brick Properties. [Online] Available at: http://www.boral.com.au/images/common/clay_bricks_pavers/pdfs/brick_properties.pdf [Accessed 1 May 2014]. Clay Bricks, 2007. About Bricks. [Online] Available at: http://www.claybricks.com/more_info/basic-of-bricks.html [Accessed 2 May 2014]. Ling, T.-C., Nor, H. & Mudiyono, R., 2006. The Effect of Cement and Water Cement Ratio on Concrete Paving Block. Johore, Universiti Teknologi Malaysia. Materials Home, 2014. Composition Cells. [Online] Available at: http://www.efunda.com/materials/corrosion/corrosion_types.cfm [Accessed 1 May 2014]. Meier, E., 2014. Modulus of Rupture. [Online] Available at: http://www.wood-database.com/wood-articles/modulus-of-rupture/ [Accessed 1 May 2014]. Melander, J. M. & Lauersdorf, L. R., 1993. Masonry: Design and Construction, Problems and Repair, Issue 1180. New York: ASTM International. Popovics, S., 1992. Concrete Materials: Properties, Specifications, and Testing. New Jersey: William Andrew. University of California, 2009. Methane Catalytic Combustion Modeling. [Online] Available at: http://firebrand.me.berkeley.edu/cpchou/catalysis/catalysis.html [Accessed 2 May 2014]. Read More

iv. Fire resistance: Bricks are preferred due to their incombustibility. This factor should therefore be adhered to in order to promote safety of building in cases of fire outbreaks. v. Thermal insulation: This property aids in maintaining the external and internal environment in terms of temperature. vi. Sound insulation: Bricks should offer a good insulation to sound from external sources. vii. Wear resistance: Durability is a mandatory property in all construction materials (Clay Bricks, 2007).

Question 5: Negative effects of Water absorption by bricks The compressive strength of bricks is adversely lowered thereby posing as a danger to the inhabitants. Secondly drying up during the construction period may be problematic thereby extending a project period. EXPERIMENT 3: THE STUDY OF COMPOSITION CORROSION CELLS Question 1: Corrosion This is a chemical or electrochemical reaction between a metal and environmentally present elements such as oxygen that leads to deterioration in original physical and mechanical properties.

Prevention or minimization of corrosion can be done by any of the following methods depending on mode of corrosion. i. Applying coatings: These can be paints or coats of from the low reactive series with anti-corrosive properties. Placing a barrier against the main structure prevents direct contact or reaction with the environmental elements thereby protecting them from destruction. ii. Anodization: This is usually done by electrochemical reactions in bath that coat the structure with several nanometres of the low reaction element.

This film acts like a coating although the mode of application differs from that of paint coatings. iii. Reactive Coatings: Reaction coatings are also known as corrosion inhibitors. These chemicals insulate the structure chemically and electrically rendering it less sensitive to reaction with environmentally available materials. Question 2: Conditions Favouring Corrosion The experimental setup consisted of water with cleaning agent (electrochemical corrosion) and fresh water with oxygen (chemical).

In such circumstances as these, water with cleaning agent catalysed the corrosion process of the metal while conditions with oxygenated water occurred naturally and slowly as compared to its counterpart. Enclosed jar did not allow for corrosion because the vital element required for corrosion i.e. oxygen was eliminated thereby inhibiting this process. Question 3: Electrode Potential The table below shows the reactivity order of selected materials namely aluminium, lead, iron, magnesium, zinc and nickel from the most reactive to the least reactive.

This table is generated based on the electrode potential – it has been established that the greater the negative electrode potential in a given element the higher the chances that corrosion shall occur. Table 3.1: Reactivity series for aluminium, lead, iron, magnesium, zinc and nickel. Metal Electrode Potential (Volts) Magnesium -2.37 Aluminium -1.66 Zinc -0.76 Iron -0.44 Nickel -0.25 Lead -0.13 Question 4: Galvanization Galvanic cells are formed by using a composition of either dissimilar metals or a multiphase of alloys.

In application of two dissimilar metals, the metals in contact such as nickel and gold or zinc and nickel are joined in a single phase. The metal that is higher in terms of reactivity becomes the cathode while the one with lower reactivity becomes the anode. The metal that is exposed to the anodic reactions corrodes thereby coating the cathode – a similar technology is used in construction of batteries. On the other side, multiphase alloying is formed from metal alloys that are found in stainless steel aluminium alloys etc.

Each phase consists of its own alloy that is exposed to anodic reactions in order to coat the subject accordingly (Materials Home, 2014). Cathodic protection is a corrosion protection technique that involves making the susceptible metal surface the cathode while the sacrificial metal is made the anode.

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