1. Introduction

The element Zirconium is one of the most abundant metal that exist in earth and has a lot of applications but it is not widely popular. It was commonly known as one of the rarest elements but the recent advancements on its extraction it was discovered that it is actually more abundant than nickel, copper, lead, zinc, and other familiar metals. Due to it’s impressive physical and chemical properties, Zirconium has taken a lot of applications in the metal works which we will discuss in full detail later. This paper will discuss all the important information regarding Zirconium and it’s application to the Chemical Engineering industry.

Zirconium was first discovered by Martin Heinrich Klaproth in 1789, but it was not in it’s pure form. According to How Products are Made it was just 130 years later that Van Arkel and De Boer in 1923 was the pure metallic form was produced. The difficulties in extracting Zirconium from ores are really evident. There exist a lot of processes but there are only 7 processes that are officially used up to date. Out of that 7, only three are important, namely: Reduction of the halides with sodium or magnesium, decomposition of the halides on hot filaments, and fusion electrolysis of the double fluorides. In this paper, however, only the first one will be discussed in detail. Before we proceed with it’s fabrication and process, let us see first the physical and chemical composition of Zirconium.

  1. Properties

Zirconium the 40th element in the periodic table, it is a hard, grayish-white, and shiny metal. Its has a flaky-like appearance(as described from peridictable.com). It also occurs in the form of a black or bluish-black powder. It has a melting point of 1,857°C and a boiling point of 3,577°C. With a density of 6.5 grams per cubic centimeter.

Zirconium has one physical property of special importance, it is transparent to neutrons. According to Chemistry Explained, neutrons are tiny particles with no charge in the nucleus of almost all atoms. Industrially, they are used to make nuclear fission reactions occur. Nuclear fission is the process in which large atoms break apart. Large amounts of energy and smaller atoms are produced during fission. Fission reactions are used to provide the power behind nuclear weapons just like in the atomic bomb. They are also used to produce energy in a nuclear power plant.

One of the difficult problems in building a nuclear power plant is selecting the right materials. Many metals capture neutrons that pass through them. The neutrons become part of the metal atoms and are no longer available to make fission reactions.

Zirconium is a fairly inactive element. When exposed to air, it reacts with oxygen to form a thin film of zirconium oxide. This film protects the metal from further corrosion. Zirconium does not react with most cold acids or with water. However, it does react with some acids that are very hot.

Here are the important properties of Zirconium. It is considered to be an incompressible metal. It is ductile, malleable and solid at room temperature. In powder form, it is highly flammable but the metal form is not.

The tensile strength of Zirconium is high, and it increases even more in cold temperatures and decreases with hot temperatures. In the early production of it, where purity is still low, it has a low tensile strength but with the present purity of production the tensile strength is increased largely.

The present hardness of Zirconium is Rb 77-80, compared to most metals it has a relatively higher hardness. It was observed that Nitrogen and Oxygen impurities in Zirconium ingots have made the hardness of Zirconium higher. In the same way, temperature has huge effects on its hardness, at low temperatures the hardness increases and at high temperatures it decreases.

Another property of Zirconium is its creeping strength. It is defined as the permanent change of shape from prolonged stress or exposure to high temperatures. According to Bureau of mines, they found out that pure Zirconium metal has a rapid loss of creep strength, thus it is not useful for structural material that requires high temperature even if it has a high melting point.

The two most important properties of Zirconium is its corrosion resistance and nuclear reaction uses. It basically is corrosion resistant to every liquid and gas substances. It is also very feasible to produce in large quantities that’s why it is used, or an alloy of it is usually used, compared to Tungsten and Molybdenum, which are known to be much more corrosion resistant than Zirconium.

Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply. For this purpose, it is mainly used in the form of zircaloys. The benefits of Zirconium alloys is their low neutron-capture cross-section and good resistance to corrosion under normal service conditions. Metals that captures neutron cannot be used again for nuclear reactions that’s why Zirconium is used  often. Now, let’s look at how Zirconium are fabricated.

  • Considerations

In the introduction it was discussed that there were actually many processes in fabrication of Zirconium and only 7 are still used today. But only one of those seven will be discussed here, the process that is commonly used by the companies because of its high purity output.

Magnesium reduction process is developed by the Bureau of Mines laboratory and it produces zirconium metal that are free from most of the naturally occurring contaminants. According to their laboratory this process requires this 7 steps:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

According to In the first step, Zircon, an ore that contains large amount of Zirconium, is reacted with Carbon in an electric arc furnace to form zirconium carbide or carbonitride. During the reaction to form the carbide most of silica is reduced to silicon monoxide, which volatilizes and is removed as a fume. The resulting carbide higher zirconium concentration than zircon. Because of a pyrophoric tendency the carbide must be protected from the atmosphere during cooling.

Secondly, Chlorination of the carbide to form zirconium tetrachloride. Chlorination of the carbide in an internally heated shaft furnace proceeds exothermally. Zirconium tetrachloride is collected in a condenser, while the tetrachlorides of silicon and titanium pass through a scrubbing tower to waste.

Next, tetrachloride is purified. It is dissolved in water and by a security-classified process is converted to high-purity oxide by removal of hafnium and other remaining contaminants.

Then, high-purity zirconium chloride is formed from the oxide. Oxide is mixed with carbon,briquetted, and heated in an atmosphere of chlorine to form zirconium tetrachloride essentially free from contaminants.

Further purification of the zirconium tetrachloride by heating. The more volatile impurities are removed by heating the charge just below its sublimation temperature and holding it at that temperature for about 8 hours. Zirconium tetrachloride has a strong tendency to form the oxychloride when exposed to the moist atmosphere.

Then, zirconium tetrachloride reduced with molten magnesium.. Gaseous zirconium tetrachloride reacts with the molten magnesium to form zirconium sponge and magnesium chloride. Less volatile constituents remain as a residue and do not contaminate the metal.

Lastly, this is the final step in preparing ductile zirconium sponge. The excess magnesium and magnesium chloride are removed by heating in an evacuated iron retort. It is important to keep the temperature of this operation below 934 C, the temperature of formation of the zirconium-iron eutectic. Iron does not seem to affect the ductility of zirconium, but since its general effects are not know completely, therefore contamination by it is avoided.

The resultant product then are melted and the results are Zirconium Ingots. Then, these Ingots are used to fabricate zirconium products. The abnormal loss of strength of zirconium at elevated temperatures has helped a lot on the hot working of the metal. This has helped both in hammer and press forging of ingots where center burst are rarity, and in cold forming techniques. Zirconium has only half I’s original hardness at 300 C, and therefore the speed and amount of work in any cold – forming operations, with a subsequent temperature rise, affect working of the metal.Here are some of the fabrication processes that zirconium undergo.

First issheath working. It is the covering a material with an exterior layer of metal or other materials. The procedure consisted  of sheathing the zirconium ingot in heavy – wall seamless mechanical tubing, welding end plugs to the sheath to form a complete seal, and then working the assembly in the same manner as a normal ingot. After forging the rolling, the iron sheath is stripped and the zirconium metal worked to finished size.

Next is forging. It is usually employed on ingots that have 3-10 inches in diameter and weighs up to 500 pounds. Forging is shaping metal using localized compressive forces, power hammers are usually used.

Then, swaging and wire drawing. Swaging is transforming a piece of metal into a desired shape through pressure or hammering, it usually employs bending and shaping. Wire drawing is the reduction of size of cross-section wires by pulling the wire through a drawing dies.

Lastly, machining is also used in zirconium to cut it into a final shape and size using a controlled material-removal process. Zirconium can also be shaped by other operations such as turning, boring, planning, and milling. But overheating must be avoided because of its tendency to be weakened after heating. Producing zirconium is not as hard as it looks like but it is expensive. On the next paragraphs we will see the availability and cost of zirconium.

The raw materials required for producing zirconium are plentiful, it is more abundant than most of the other widely metals. There are two requirements for producing ductile zirconium, first is presence of hafnium is prohibited especially in the nuclear applications. Secondly is the allowed use of hafnium because it is not detrimental to the process. But mostly, zirconium are produced with no presence of hafnium in it. Thereby causing the price to spike up, because hafnium is nearly similar to zirconium and they are hard to separate.

The average present price of a 99.6% zirconium as gathered from the manufacturers is 150$/kg (~7,000Php/kg). Unfortunately there are no companies manufacturing zirconium here in the Philippines. Even though the price is high, industries are using it often because of its numerous applications which will be discussed next. (chemistry.pormona.edu., 2015)

  1. Applications to Chemical Engineering

Zirconium promises o become one of the most versatile metals. This good properties comes from its, physical, chemical, and nuclear properties. Most metals, does not match to the capacity of zirconium especially on its nuclear properties. It’s application ranges from chemical, medical, and nuclear field.

In the nuclear reactors, it is still the best container for the reactions because of its failure to absorb neutrons, which is really favored in nuclear reactions.

In the chemical equipment, zirconium is usually picked because of its high non-corrosive property that most liquids and gases does not react with it.Here are some chemical equipment that utilizes the non corrosive property of zirconium. Zirconium-lined tanks, basket strainer, high – speed agitator, pH electrode assembly, thermowell, saddles, agitator hub, exhaust fan, needle valve, globe valve, pipe fittings, spray nozzles, water aspirator, surge bottle, hydraulic valve, shaft sleeve, pump parts. Other chemical equipment are: immersion heaters, heat exchangers, reactors and tank linings, evacuators, agitators and mixers, filter decks, drainage grids, rotary valves, vacuum, pressure filter parts, pump and pump parts, valves, and pipe fittings.

Another application of zirconium is its alloys. Many of the metals that needs non-corrosive properties are mixed with zirconium.

The studies completed in zirconium indicates that zirconium has all of the attributes of tantalum and even more it has less weight and lower cost. Tantalum has been used repeatedly in medical equipment and zirconium are now also being employed. Some of the medical or surgical adaptations of zirconium are: pyrophorics, such as flashlight powder, photoflash bulb, explosive primers, and pyrotechnics and fireworks, hydrogen reservoir, metal-to-glass seals, welding flux, and thermocouples.

Zirconium has a lot of applications and its processes are still being studied until now to lessen the cost and to maximize the effectivity of procedures.

  1. References

Zirconium. (n.d.). Retrieved October 7, 2015, from http://www.madehow.com/Volume-1/Zirconium.html

Zirconium. (n.d.). Retrieved October 7, 2015, from http://www.chemistry.pomona.edu/chemistry/periodic_table/elements/zirconium/zirconium.htm

Technical data for Zirconium. (n.d.). Retrieved October 7, 2015, from http://periodictable.com/Elements/040/data.html

Chemistry Explained. (n.d.). Retrieved October 7, 2015, from http://www.chemistryexplained.com/elements/T-Z/Zirconium.html

Miller, T. (1956). Zirconium: Its Production and Properties (1st ed.). Washington: United States Department of the Interior, Bureau of Mines.