What is Platinum Wire ? Its Definition
The platinum name is derived from the Spanish «platina», which means «small silver». Platinum is a ductile, bright silvery white metal, malleable and a member of group 10 of the periodic table of elements. It has the third highest density, behind osmium and iridium.
Platinum wire is not affected by air and water, but will dissolve in regia hot water, in hot concentrated phosphoric and sulphuric acids, and in molten alkali. It is as resistant as gold to corrosion and tarnish. In fact, platinum wire will not oxidize in the air, no matter how strongly it is heated.
Characteristics of Platinum Wire
Platinum wire can come in many varieties of thicknesses and styles, in addition to being coated with ceramic or other insulators. Platinum wire can be pure or an alloy, and alloys typically use iridium or rhodium as a hardener for durability. Platinum wire may also include palladium or gold as an alloy or veneer.
Platinum is a shiny silver-grey metal that is malleable and ductile. Malleable means capable of being hammered into thin sheets. Platinum can be hammered into a thin sheet of no more than 100 atoms thick, thinner than aluminum foil. Ductile means that the metal can be stretched into thin wires.
Platinum has a melting point of approximately 1.773°C (3.223°F) and a boiling point of approximately 3.827°C (6.921°F). Its density is 21.45 grams per cubic centimeter, making it one of the densest elements.
- Platinum is a relatively inactive metal. When exposed to air, it does not fog or corrode.
- It is not attacked by most acids, but will dissolve in royal water.
- Agua regia is a mixture of hydrochloric and nitric acids.
- It often reacts with materials that do not react with any of the acids separately.
Platinum also dissolves in very hot alkalis. An alkali is a chemical substance with properties opposite to those of an acid. Sodium hydroxide («common bleach») and lime water are examples of alkalis. An unusual property of platinum is that it will absorb large amounts of hydrogen gas at high temperatures.
Platinum absorbs hydrogen like a sponge absorbs water. Platinum metals are often found together in nature. In fact, one of the problems in producing platinum is finding a way to separate it from other platinum metals. However, unlike gold, these metals are not produced in masses large enough to mine. Instead, they are generally obtained as by-products of mining other metals, such as copper and nickel.
Platinum is one of the rarest elements. Its abundance is estimated to be approximately 0.01 parts per million in the earth’s crust. The world’s largest supplier of platinum is by far South Africa. In 1996, that nation produced 117,000 kilograms of platinum. The next largest producer was Canada, which produced only 8,260 kilograms in 1996. The only other major platinum producer is the United States.
Most of the platinum in the United States comes from the Stillwater mine in Montana.
There are six natural platinum isotopes: platinum-190, platinum-192, platinum-194, platinum-195, platinum-196 and platinum-198. Of these, only 190 platinum is radioactive. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element name is the mass number.
The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any element can vary. Each variation is an isotope.
Artificially radioactive platinum isotopes have also been produced. These isotopes are produced when very small particles are fired at the atoms. These particles adhere to the atoms and make them radioactive.
No radioactive platinum isotope has any commercial application. The main challenge in obtaining pure platinum is to separate it from other platinum metals. The first step in this process is to dissolve the mixture in royal water. Platinum dissolves in water regia, and other platinum metals do not. Platinum metal can be removed from the water regia in a form known as platinum sponge. Platinum sponge is a spongy black platinum powder material. Finally, the powder is heated to very high temperatures and melted to produce pure metal.
Utility of Platinum Wire
Platinum wire is useful for making an electrical connection in a sealed glass system, as it has approximately the same rate of thermal expansion as glass and will seal well with molten glass. It was widely used in early electric bulbs and radio tubes for this purpose, but was quickly abandoned when lower cost materials such as Dumet were developed.
Their wear and tarnish characteristics are well suited for making fine jewelry. Platinum and its alloys are used in surgical tools, laboratory utensils, electrical resistance wires and electrical contact points. It is used (30%) as a catalyst in the catalytic converter, an optional component of the exhaust system of gasoline-powered cars.
The largest use (50%) of platinum is for jewelry, another 20% is used in industry: platinum is used in the chemical, electrical, glass, and airplane industries, and each represents about 10 tons of metal per year. The glass industry uses platinum for fiber optics and liquid crystal display glass, especially for laptops.
Function of Platinum Wire in the Laboratory
- Platinum wire is used for flame testing and especially for testing beads of minerals and other unidentified inorganic compounds.
- Platinum is virtually inert, being resistant to attack by most chemicals. Unlike nickel-chromium, iron or other wire materials, platinum will not contaminate bead tests with any color of its own.
- Platinum wire can be used as a microelectrode indicator electrode in voltammetry.
- As a transvascular embolic agent.
- To study the chronopotentiometry of hydrogen peroxide with a platinum wire electrode.
- In gas detection instruments.
History and Origin of Platinum Wire
The first known reference to platinum can be found in the writings of the Italian physician, scholar and poet Julius Caesar Scaliger (1484-1558). Apparently, Scaliger saw platinum while visiting Central America in 1557.
He referred to a hard metal that the natives had learned to work with, but the Spaniards had not. The metal had been called platinum («small silver») by the natives. The name was given to the material because it interfered with the extraction of silver and gold. As the natives did not know that the plate was useless, they considered it a nuisance.
The first complete description of the platinum was given by the Spanish military leader Don Antonio de Ulloa (1716-95). While serving in South America from 1735 to 1746, de Ulloa collected samples of platinum. He later wrote a report on the metal, describing how it was extracted and used. Ulloa is often credited for discovering platinum on the basis of the report he wrote.
Reports of the new element were disseminated throughout Europe. Scientists were fascinated by its physical properties. Not only was it beautiful to look at, but it was also resistant to corrosion (oxidation). Many people saw that it could be used in jewellery and art objects, such as gold and silver. The demand for metal began to grow, which led to what was then called the «Platinum Age in Spain».
Platinum was discovered by South American peoples who produced artifacts from an alloy of white gold and platinum. In 1783, French chemist Francois Chabaneaus discovered and patented a method to produce viable platinum.
However, the quality of the metal remained very inconsistent from batch to batch; unknown to him, there were impurities of, as then, undiscovered metals. The English chemist William H Wollaston developed a commercial process to produce pure platinum in the early 19th century.
In the course of his platinum mineral studies he also discovered the metals osmium, iridium, rhodium and palladium, the elements that had made Chabaneaus’ work so frustrating.
What is the use of platinum wire ?
It is used for flame testing.
Why is Platinum Wire Used in Flame Testing ?
There are 3 points:
1) Platinum does not impart any color to the flame.
2) It does not oxidize under the high flame temperature of a Bunsen burner.
3) It is almost chemically inert. Even at high temperatures, it remains free of free radicals / acid radicals.
Therefore, platinum wire is crucial for a flame test. In addition, a platinum wire must be thoroughly cleaned before using it for a new flame test.
It is also used for transfer of bacteria.
Clinical samples (biological samples obtained from a patient) are often obtained using a sterile swab which is then scratched in a sterile growing medium (a plate).
Bacterial growth media provide nutrients, water, and a surface where bacteria can multiply.
Sometimes bacteria are transferred from one plate to another, such as when a microbiologist is trying to isolate a specific type of bacteria or when preparing multiple plates of a specific type of bacteria for use by microbiology students.
When transferring bacteria, it is important that the bacterial sample is not contaminated with bacteria from the surrounding environment.
This is why media plates are sterile before being inoculated with a sample.
The instrument used to transfer bacteria must also be initially sterile, before the bacterial sample is obtained. The whole process of trying to reduce contamination of materials used in microbiology is called practicing the sterile or aseptic technique.
Advantage of Using an Inoculation Circuit
An inoculation circuit is a thin metal device with a handle at one end and a looped wire at the other end.
The looped end is useful for obtaining bacterial samples from colonies that grow on media or liquid media plates, as the handle may contain a drop of liquid, something like a bubble wand contains liquid soap.
Disposable devices are available for transferring bacterial samples, such as sterile swabs and even sterile toothpicks. The advantage of an inoculation cycle is that the instrument can be used and sterilized repeatedly, reducing the amount of contaminated laboratory waste generated.
The 1 microliter loops are made of 26 ga platinum wire with 15% iridium. The 10 microliter loops are calibrated and made of 19 ga B and S platinum wire with 5% rhodium.
Platinum loops and needles are used to transfer bacterial cultures.
These loops and needles are made of platinum wire with 15% added iridium for added rigidity, allowing thinner wire for delicate work.
Use of Platinum Wire
When the flame test is done the mode of use is:
Clean a platinum or nicrome wire (a nickel-chrome alloy) by dipping it in concentrated hydrochloric acid and then keeping it in a hot (not luminous) Bunsen flame.
Repeat this until the wire does not produce any color in the flame.
Note: In fact, there will always be a trace of orange in the flame if you use nicrome. You soon learn to ignore this. Platinum is much better to use, but it is much, much more expensive.
If you have a particularly dirty piece of nicrome wire, you can cut the end. You don’t do that with platinum!
Dilute hydrochloric acid can be used instead of concentrated acid for safety reasons, but it doesn’t always provide such intense flame colors.
When the cable is clean, moisten it again with a little acid and then dip it in a small amount of the solid you are testing so that it adheres to the cable. Replace the wire in the flame.
If the color of the flame is weak, it is often worthwhile to dip the wire back into the acid and put it back into the flame as if you were cleaning it. You often get a very short but intense flash of color when you do this.
A platinum wire is cleaned by immersing it in concentrated HNO3 and then placing it in the non-luminous part of the bunsen flame. Otherwise, the previously tested radicals will impart colour to the flame, which can cause confusion.
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