The pattern in the data is such due to the nature of gold’s atoms; the atoms are packed very closely, which increases its density. The reason why the density decreases alongside its carat number is a result of the presence of other metal atoms, which interfere in its atomic structure. I will illustrate these results below:
Table 2:
The table above displays the hardness of different gold alloys, according to two different methods of alloying: casting and annealing. Casting is the method by which liquefied metals are poured into a mold and then allowed to solidify. Annealing consists of heating metals above its re-crystallisation temperature then mixing them before maintaining a suitable temperature and then allowing the mixture to cool.
Looking at the above chart, I have seen two patterns:
- The hardness of the alloys are inversely proportional to its purity i.e. as the purity increases, the hardness decreases. The hardness of the alloys increases from 9 carat to 14 carat, then steadily decreases. The least hardest is 9 carat and the hardest is 24.
As mentioned previously, the reasons for this trend is due to the nature of the atoms in the alloy. In 24 carat gold, the atoms are able to side over each-other because of the attraction between the metal ions and the electrons. As the purity of gold decreases, the presence of foreign atoms disrupts the usual ability of gold atoms sliding over each-other by settling between them. The more foreign atoms there are, the more difficult it is for the gold atoms to slide over each other, thus making the alloy harder and its malleability as well as its ductility lower.
2) I have also seen that annealing produces harder alloys than casting.
This could be because annealing mixes the two materials together more effectively than casting, which means that the extra atoms are embedded between the gold atoms more firmly. This means that the atoms in alloys made by annealing find it much harder to glide over eachother, thus making the alloy harder than cast.
Table 3:
Looking at the above data, it is obvious that the percentage of gold increases as the carat number increases. This is because the purity of gold increases as its carat number increases.
Also, some alloys have the same carat number, but are different in colour; this could be due to the constitution of the elements found in the alloy. For example, the only chemical difference between 9 carat (yellow) and 9 carat (white) is that the latter contains nickel. The same is the case with 14 carat (yellow) and 14 carat (white). Effectively, the nickel could be the primary factor in the appearance of the alloys.
I have also realised that the only chemical difference between 18 carat (yellow) and 18 carat (white) is that the latter contains palladium; like nickel, it may be the cause for the difference in colour between the alloys. Also, after reviewing the density of the both alloys in Table 1, it is clear that 18 carat (white) is significantly denser than that of 18 carat (yellow). Again, this could be because 18 carat (white) contains an extra element, palladium, so the reason for the difference in density could be linked with the fact that one contains palladium whereas the other does not.
These differences suggest that nickel and palladium are the substances added to gold in order to whiten it.
Another trend which I have found is that the alloys which appear yellow in colour contain a greater amount of copper than their white counterparts; for example, 9 carat (yellow) contains 5% more copper than 9 carat (white) and 14 carat (yellow) contains 4.2% more than 14 carat (white). So the factor for the difference between the colours could be due to the amount of copper.
Validity and Reliability
For my investigation I extracted data from the source . In order to make the data valid, I made sure I used data only from this source and not any other source. This meant that my comparison between the data which I had collated would be more accurate and valid than if I were to take data from a variety of sources and then compared them.
However, the reliability of the source which I collected my data from could be questioned; 24 carat gold.co.uk is a leading British gold supplier, so they could alter the information they provide on alloys and pure gold; for example, they could exaggerate regarding the chemical properties of gold alloys to make them seem more disadvantageous than they are in reality, in order to make people buy pure 24 carat gold.
To make my investigation more valid, I could have taken data from a gold manufacturing company, rather than a gold selling company, or even from a government website; there is less chance that they would be bias towards 24 carat gold, which would make my data more accurate, reliable and valid.
Furthermore, I could have also analysed a few other factors of alloys, such as their electrical conductivity, thermal conductivity, or I could even have looked at which alloy is more popular. This would have showed me a broader range of similarities and differences between different gold alloys.
Also, in my investigation I did not take into account all the possible alloys of gold; I simply relied on a certain number, for example, in Table 1 I only displayed the results of 9 carat, 14 carat etc. Instead, I could have increased the range of alloys I analysed and seen whether the patterns I have found carry on; this would have made my investigation even more accurate and reliable.
Pros and Cons of Alloying Gold
Alloying gold has a number of advantages; firstly, pure gold is very expensive, whereas alloyed gold proves to be much cheaper. This means a lot of people have the ability to purchase gold, not just the rich. Also, pure gold occurs naturally as a very soft, malleable metal; therefore, alloying gold with a metal such as copper, silver, nickel, palladium and zinc enhances the strength of gold, making it more useful for jewellery whilst reducing its malleability and ductility. Silver atoms are slightly larger than gold atoms, so alloying gold with silver will generally improve its hardness and strength; alloying gold with copper is even more effective than silver, as it is significantly smaller than the gold atom, and has the ability to distort the gold crystal lattice.
Pure gold also occurs naturally with a very high density; alloying enables it to lower its density, making it much lighter. Alloying gold also means that it can adjust its colour, giving it a range of colours to choose from; for example, alloying gold with silver will make the gold green in colour; these factors make gold a more ideal material for jewellery than pure gold.
The chemical specialities of gold, such as its conductivity both in terms of electrical and thermal, means that there is a high demand for using it in the production of computer chips, visors for spacesuits etc. therefore, alloying gold means that less gold is wasted on jewellery, which also means that there is enough gold to meet the demands for it.
Another benefit for alloying gold is that it can act as a substitute for other precious metals, such as platinum. Platinum is very expensive, but white gold is almost an exact replica of it, and is much cheaper. Also, gold alloys are nearly completely resistant to chemical attack: 18 or 22 carat gold hardly reacts with chemicals and 9 carat gold is even less reactive.
Alloying gold with copper can also be used in dentistry; they are mainly used to create crowns or inlays, and sometimes tooth fillings which are extremely strong yet allow a soft bite with opposing teeth.
However, alloying gold also has its drawbacks. Gold alloys are poor conductors of electricity due to the existence of foreign atoms, which disrupt the free electrons, making it harder to conduct electricity; this means gold alloys are not ideal for the manufacture of computer chips.
Many people are unaware of the fact that the gold they buy is not actually pure gold; therefore, it is easy for traders to deceive their customers, selling the gold alloy at an extortionate price whilst insisting that the gold is 100% pure.
Pure gold is almost completely unreactive with oxygen, which means that it does not tarnish or rust; however, when gold is alloyed, the presence of other reactive metals subjects the alloy to reacting with oxygen, tarnishing the gold. This is a major drawback for the manufacture of jewellery.
A further disadvantage of alloying gold, and one which is often discussed is the usage of nickel in alloys. Nickel is occasionally used to “bleach” gold; naturally, this means there is a small but significant amount of nickel present in the alloy; evidence has suggested that nickel is poisonous, and has found links with dermatitis through allergic reactions with the skin. A recent E.U. appeal has called for the ban of using nickel in jewellery, allowing only a certain amount of ppm. In some countries, even palladium is banned as it is considered to be a toxic substance.
The methods used to alloy gold (casting and annealing) consume huge amounts of energy; annealing involves subjecting the metal to just above re-crystallisation temperature, which emits large amounts of greenhouse gases as a result of burning fossil fuels. Manufacturing pure gold does not release as much atmospheric pollution as manufacturing gold alloys.
Gold alloys are sometimes used in tooth fillings; the problem with these is that it gives an unnatural tooth colour, so a lot of dental patients prefer to have them removed and do not like having these fillings.
Finally, alloying is not entirely cost effective; for example, palladium is a very expensive and also heavy metal, thus jewellery made in palladium white metals tend to be more expensive than nickel whites. Also, elements which are used to whiten gold, such as chromium and iron, are usually hard and very hard to process and purify before they can successfully be alloyed with gold. Gold alloys also tend to be more brittle, so a sharp blow would most probably cause it to disintegrate.
Conclusion
Gold alloys have a number of advantages along with disadvantages; the way to decide whether it is more advantageous than pure gold is to see whether the benefits outweighs its drawbacks; gold alloys are stronger, lighter, cheaper and more effective, as they offer a wider range of usage than pure gold, which is naturally too soft and weak to meet the demands for gold in modern times.
