Metals and alloys have entered our lives so closely that sometimes we don't even think about them. As early as 4-3 millennia BC, the first acquaintance of man with nuggets took place. A lot of time has passed since then, and every year metal processing has only improved.
Zinc played a big role in this. Alloys based on it are used in many industries. In this article, we will look at zinc alloys and their role in our lives.
Transition metal
Zinc is known to be a bluish-white brittle transition metal. It is mined from semi-metallic ores. The process of obtaining pure zinc is quite complex and time-consuming. First of all, ore containing from 1-4% zinc is enriched by selective flotation. Through this process concentrates (55% Zn) are obtained. Next, you need to get zinc oxide. For this, the resulting concentrates are calcined in furnaces in a fluidized bed. Only fromzinc oxide, you can get this metal in its pure form, and there are two ways to do this.
Obtaining zinc
The first is electrolytic, based on the treatment of zinc oxide with sulfuric acid. As a result of this reaction, a sulfate solution is formed, which is purified from impurities and subjected to electrolysis. Zinc is deposited on aluminum cathodes, which is then melted in induction furnaces. The purity of zinc thus obtained is about 99.95%.
The second method, the oldest one, is distillation. The concentrates are heated to a very high temperature (about 1000 ° C), zinc vapors are released, which, by condensation, settle on clay vessels. But this method does not give such purity as the first. The resulting vapor contains about 3% of various impurities, including such a valuable element as cadmium. Therefore, Zn is further purified by segregation. At a temperature of 500°C it is defended for some time and a purity of 98% is obtained. For further production of alloys, this is enough, because then zinc is still alloyed with the same elements. If this is not enough, rectification is used and zinc is obtained with a purity of 99.995%. Thus, both methods allow obtaining high-purity zinc.
An inseparable pair of metals
Typically, lead is present in zinc alloys as an impurity. In nature, this inseparable pair of metals is found quite often. But in fact, a high lead content in a zinc alloy degrades its physical properties, creating a tendency to intergranular corrosion if it iscontent exceeds 0.007%. Lead and zinc are most commonly found together in tin bronzes and brass.
If we talk about the eutectic of these two elements, it is important to note that up to a temperature of 800°C they do not mix with each other and represent two different liquids. During rapid cooling, a uniform distribution of Pb occurs in the form of rounded inclusions along the grain boundaries. Zinc-lead alloy is used to make printing plates due to the fact that it dissolves very quickly in acid. Most often, lead impurities are removed from zinc using a distillation method.
Copper zinc alloy
Brass is an alloy known even before our era. At that time, zinc had not yet been discovered, but the ore was widely used. Previously, brass was obtained by alloying smithsonite (zinc ore) and copper. It was only in the 18th century that this alloy was first made using metallic zinc.
In our time, there are several varieties of brass: single-phase and two-phase. The former contain about 35% zinc, while the latter contain 50% and 4% lead. Single-phase brass is very ductile, while the second variety is characterized by brittleness and hardness. Having considered the state diagram of these two elements, we can conclude that they form a series of electronic phases: β, γ, ε. An interesting variety of brass is tompak. It contains only up to 10% zinc and due to this it has a very high ductility. Tompak is successfully used for steel cladding and bimetal production. before himused to make coins and imitation gold.
Zinc and steel
Almost in every home you can find galvanized things: buckets, pots, boiling water, etc. All of them are reliably protected from rust thanks to zinc. Figuratively speaking, of course, steel is coated with this metal, and logically, we are not talking about an alloy. On the other hand, knowing how galvanizing occurs, the opposite can be argued. The fact is that zinc melts at a very low temperature (about 400 ° C), and when it enters the steel surface in a liquid state, it diffuses into it.
The atoms of both substances are very tightly bound together, forming an iron-zinc alloy. For this reason, we can safely say that Zn is not "laid" on the product, but "embedded" in it. This can be observed in a normal household situation. For example, a scratch appears on a galvanized bucket. Is it starting to rust here? The answer is unequivocal - no. This is because when moisture enters, zinc compounds begin to break down, but at the same time they form some kind of protection for steel. So, in most cases, such zinc alloys are designed to protect products from corrosion. Of course, other substances, such as chromium or nickel, can also be used for these purposes, but the cost of these products will be many times higher.
Tin and zinc
This alloy is no less popular than the others we have already reviewed. In 1917-1918 in Bulgaria, it was widely used to make special vessels that held warm liquid for a long time.(analogues of modern thermoses). Nowadays, zinc-tin alloy is very widely used in the radio and electrical industries. This is due to the fact that the composition with a Zn content of 20% is soldered very well, and the deposit polishing is maintained for a long time.
Of course, as an anti-corrosion coating, this alloy can also be used. Its characteristics are very similar to cadmium coating, but at the same time less expensive.
Properties of zinc alloys
Of course, all compositions with this metal differ from each other in its percentage. In general, zinc alloys have good casting and mechanical properties. First and foremost is corrosion resistance. Most of all, it manifests itself in an atmosphere of dry clean air. Possible manifestations of corrosion can be seen in industrial cities. This is due to the presence of hydrochloric acid vapors, chlorine and sulfur oxides in the air, which, condensing with moisture, make it difficult to form a protective film. Copper-tin-zinc is an alloy that is characterized by high protective properties. It is this composition that is least susceptible to corrosion, especially in an industrial atmosphere. If we talk about the casting properties of zinc, then, of course, they depend on the alloying elements in its alloys.
So, for example, aluminum makes their structure homogeneous, fine-grained, ennobles it, reduces the negative effect of iron. Another important alloying element is copper. It increases strength and reducesintercrystalline corrosion. The copper-zinc alloy has high impact strength, but at the same time partially loses its casting properties.
Fields of application of zinc and its alloys
In fact, parts made of zinc alloys are quite common in our time. Despite the fact that plastic is replacing metal products, in some cases they cannot be dispensed with. For example, the automotive industry is an industry that cannot do without zinc alloys. Filters, sumps, carburetor and fuel pump housings, wheel covers, mufflers - all this and much more is made using compounds of this chemical element.
Due to the fact that zinc alloys have good casting properties, complex parts of various shapes are cast from them with a minimum wall thickness. Construction is another area in which these alloys are indispensable. Rolled zinc is used for roofing, pipes and gutters. Despite the fact that there is a tendency to reduce the production of zinc alloys, it is not possible to abandon their production due to the relative cheapness and mechanical properties of the material.
