Nobel metals are types of metals that are resistant to both oxidation and corrosion in that they are not like all the other base metals. These metals do not undergo corrosion or oxidation even in the best of condition (Uhlig, 2008). In addition to that, these metals are considered to be very rare because they are not easily found in the crust of the earth and when found they tend to be very expensive. Nobel metals include platinum, gold, silver, rhodium among others. On the other hand, there are some metals that are also resistant to corrosion and oxidation but are not considered as Nobel metals. A very good example of these types of metals is titanium which is resistant to both corrosion and oxidation even under the best of conditions but is not considered a Nobel metal (Uhlig, 2008).
Corrosion is regarded a gradual process by which base metals are destroyed. This gradual process often takes place as a chemical reaction or an electrochemical reaction. For an electrochemical corrosion reaction to take place in any given condition there must be four very important parts of the reaction which include anode, cathode, electrolyte and a source of external connection. The Nobel metals are often considered as cathode but do not take place in this kind of reaction mainly because they are mainly not reactive in their normal state which makes it difficult for them to take place in any give reaction (Uhlig, 2008).
Research analysts have been able to establish that any base metal that is coated with these Nobel metals will reduce the rate of corrosion and oxidation and such these metals have been used in coating other metals to reduce corrosion and oxidation. This process of Nobel metals being used to coat other metals to prevent or reduce cases of corrosion and oxidation is called galvanization. Some of these Nobel metals have been used in the manufacture of expensive jewelry. Other uses of these Nobel metals are the making of coins because they are very un-reactive (Baboian, 2009).
Corrosion of Nobel Metals
Nobel metals which have been known to have a high tendency of not taking part in any form in a chemical or electrochemical reaction are very rare to find on the crust of the earth and when found they tend to be very expensive. These kind of chemical and electrochemical reactions that take place in other base metals that do not take place in the case of Nobel metals include rusting among others (Uhlig, 2008). In these chemicals reactions a base metal reacts with the different factors in the atmosphere which includes moisture to complete a chemical reaction thereby forming another form of the base metal that was involved in the chemical reaction.
As opposed to other base metals, Nobel metals tend not to take part in the chemical and electrochemical reaction because of their low reactivity in term of being able to react to form any other substance. Research analysts have been able to establish that these Nobel metals are stable in the presence of any kind of reducing agent which is the main reason why they are considered to be very resistant to corrosion and oxidation in any state (Baboian, 2009). These Nobel metals are considered as cathodes in that when negatively polarized in special condition they are able to undergo bulk corrosion. These kinds of chemical and electrochemical reactions that take place in special conditions are very rare which make it difficult for the Nobel metal to react by themselves naturally (Baboian, 2009).
A very good example of these Nobel metals is gold which the second most non reactive metal after platinum. Gold which is a rare metal to find on the crust of the earth is very expensive when found and remains in a single state that is it does not tend to react with other reducing agents in its normal state unless undertaken in a series of special conditions. In addition to that, Gold may become reactive when exposed to very high temperatures in that it may be able to take part in a chemical and electrochemical reaction which may in turn lead to corrosion. Research analysts have seen that Nobel metals can corrode when exposed to very high temperatures in that they are now able to take part in chemical and electrochemical reactions (McCafferty, 2010).
The type of corrosion that takes place in Nobel metals is known as galvanic corrosion where two base metals make electrical contact. The electrical contact must be in the presence of electrolytes and the metals that are involved in the corrosion process are not similar in any way. In this type of corrosion, the rate by which the corrosion takes place depends on the environment that the reaction is taking place in. A very good example of this kind of reaction is when magnesium would react with gold much faster when exposed to a humid environment as opposed to the reaction between aluminum and platinum which will be much slower when exposed to an environment with less humidity (Garverick, 2008).
Many theories have been used by research analysts to explain the root cause of these Nobel metals not being able to react with other metals or bases to form other forms of the metals. Research analysts have been able to come up with two different theories that explain the reasons as to why Nobel metals do not corrode even in the best of conditions as opposed to the other base metals which easily react with other metals and alkalis to form other metals (Garverick, 2008).
The two theories that are used to explain the non reactivity of the Nobel metals include the acid theory and chemical theory. These two theories have been brought up by different scientists in a bid to understanding the main reason as to why Nobel metals are so un-reactive even in the presence of other metals and the best of conditions. Though there has been many theories related to why the Nobel metals do not react, these two theories are the universally accepted theories that can be used to explain the reasons why the Nobel metals are not able to react with other metals (Garverick, 2008).
In the acid theory, research analysts have said that the corrosion that takes place has been attributed to the presence of an acid in the reaction. This has been the case in the corrosion of most base metals in that when the corrosion of these base metals takes place, there is always the presence of an acid which slows down the speed of the reaction. A very good example that has been used by research analysts in being able to understand more clearly the effect of the acid in the reaction is rust which tests positive for Carbon Monoxide ions and reacts with lime or caustic soda which are considered acidic to form Carbon Dioxide which in turn reduces the speed of the corrosion.
In the chemical theory, corrosion which takes place on the surface of a base metal is caused by a reaction between the base metals and the atmospheric gases. These atmospheric gases include oxygen, hydrogen sulphide, halogens among others in the atmosphere (Garverick, 2008). The most responsible gas for causing corrosion in the atmosphere is oxygen which accounts for over 60% of the total. In this theory, oxidation takes place and base metal forms a metal oxide which forms a thin layer that protects the metals from further corrosion (Bardal, 2004).
These theories have been used to explain why Nobel metals do not react in their normal states. In the acid theory, scientists have said that these Nobel metals react in the presence of acid thus the reduction in the speed of reaction by the Nobel metals to 0%. On the other hand, other scientists have used the chemical theory in explaining why the Nobel metals do not react and have said that the Nobel metals have already reacted with the atmospheric gases thus forming a thin layer on the surface that protects them from further reaction when exposed to the environment (Bardal, 2004).
A formula that can be used to explain the resistance of the Nobel metals towards corrosion is R (t) =1/ (1/R1+1/R2+1/R3). In this formula R (t) represents the total resistance that is offered by the Nobel metals towards corrosion. R1 is the resistance of the base material that is involved the corrosion of the base metal. R2 is the resistance of the base metal in which this base metal is not resistant to corrosion. R3 represents the Nobel metal that has been used in the process of coating the base metal to prevent the process of corrosion (Craig, 2011).
In this stage, this paper will tend to analyze the result of the graph and the formula that is used to explain the resistance that is being offered by the Nobel metals towards corrosion.
Analysis of the Graph
The graph above represents the rate of corrosion of Nobel metals in that at the beginning of the graph the rate of corrosion is low and after the Nobel metals have been exposed to special conditions, the rate of reaction rapidly increases as one can be able to see in the graph. At this point in time, the rate of corrosion is the highest in which the Nobel metals are able to react with other substances to form metal oxides. After corrosion has taken place a thin layer of the oxide that is formed that protects the Nobel metal from corrosion in that the rate of corrosion reduces drastically. This explains the reason as to why Nobel metal tends to be non reactive in the presence of another substance (Warne, 2003).
Analysis of the Formula
The formula has been used by research analysts in trying to explain the reason as to why the Nobel metals tend to be very non reactive in the presence of other substances. The formula is used to calculate the total resistance that is offered by the Nobel metals in which research analysts have been able understand which Nobel metals are the most non reactive even when exposed to special conditions. In the formula, the total resistance of the Nobel metals is calculated by taking the resistance of the base material that is involved in the corrosion process. This base material that is being used in the corrosion process is not a metal. One also takes into consideration the resistance of the base metal that is involved in the corrosion process. Lastly, one has to also take into consideration the resistance of the Nobel metal that is used to coat the base metal in a bid to preventing corrosion (Davis, 2001).
In conclusion, Nobel metals tend to be very non reactive when exposed to the environment which has made it suitable for them to be used in the manufacture of coins and jewelry. In addition to that, the Nobel metals are very rare to find on the crust of the earth and when found they tend to be very expensive. Different theories have been used to explain why the Nobel metals tend to be very un-reactive but none of the theories has been fully proven by research analysts.
Baboian, R. (2009). Corrosion Tests and Standards: Application and Interpretation. London, UK: Oxford University Press.
Bardal, E. (2004). Corrosion and Protection. London, UK: Harvard University Press.
Craig, B. (2011). Handbook of Corrosion Data. London, UK: John Wiley and Sons.
Davis, J. (2001). Surface Engineering for Corrosion and Wear Resistance. Oklahoma, OK: Cengage Learning.
Garverick, L. (2008). Galvanic Corrosion. Chicago, CH: Chicago University Press.
McCafferty, E. (2010). Introduction to Corrosion Science. Oklahoma, OK: Cengage Learning.
Uhlig, H. (2008). Corrosion and Corrosion Control. London, UK: John Wiley and Sons.
Warne, F. (2003). Electrical Engineer’s Reference Book. New York, NY: Sage.