The Chemistry of Vacuum Tubes

Introduction

YouTube Video


 

I chose vacuum tubes because I find how they work very enticing, and society would be without many things if they had never existed.

They have made a difference in my life via music.  Though I enjoy all aspects of music, my one true favorite type of music is Metal (you could say I'm a heavy metal scientist).  Without vacuum tubes, I would not be able to produce sound from any electrical instrument.  I also wouldn't be a to use a microwave to heat food!



Composition of ...


    1. Cathodes (heated electrode): Thoriated Tungsten- 2% Thorium (IV) Oxide, ThO2. 98% Tungsten, W. (Sometimes just Tungsten)

    2. Anode (electron receiver plate): Molybdenum, Mo

    3. Grids: Lead, Pb

    4. Glass casing: fused quartz or pure silica glass- SiO2


Main Chemicals, Compounds, Components

  • Thoriated Tungsten/ or just Tungsten (W) or (W+ThO2)

    • An alloy of oxidized Thorium and 98% pure Tungsten

    • This accounts for almost everything inside of Tubes, for it has an absurdly high melting point, 6,191°F (3,422°C), and great conductivity.

    • Tungsten is retrieved from the ore minerals scheelite (CaWO4, calcium tungstate) and wolframite ((Fe,Mn)WO4, iron-manganese tungstate).

    • Mostly mined in China, but also in Russia and Canada.

    • This allows the Cathode to be heated to temperatures that allow for thermionic emission at high levels.


  • Fused quartz (SiO2)

    • Naturally occurring and pure in form. Not to be confused with the man made "Fused Silica".

    • Quartz is the most common solid mineral on Earth, it can be mined from almost anything.

    • This holds the structure of Tubes, not accounting for massive output tubes which are made of lead from time to time.  It is quite strong, and has a very high melting point for glass. 1715°C


Both materials are extremely hard to work with, due to their high melting point, but produce hardy vacuum tubes that can last lifetimes if used with care.  Both are found naturally,  but Fusing Tungsten with Oxidized Thorium is a man made process.


Chemistry's Role

How it works: In the most simple form of a vacuum tube, the diode, there are two powered electrodes held inside of a fused quartz casing containing no air in order to not hinder the electromagnetic event that occurs (hence the name "vacuum tube").  One electrode is negatively charged (cathode) and the other is positively charged (anode), this allows the free movement of electrons between the two.  The cathode is heated (Sometimes directly, but also can be heated by a filament) to very high temperatures to allow it to emit electrons (thermionic emission), this is why it is made of materials with very high melting points and high conductivity, and more than not, coated in an oxidized metal such as Thorium.  These electrons bounce around inside the tube, naturally, most of these electrons absorb into the positively charged anode, and are carried through and electrical current that flows in one direction (this is called rectifying).


What they are used for:  Through recent history, vacuum tubes have played a very important role in the technology we use today.  They power things ranging from microwaves to revolutionizing communication devices, or the LEDS in your alarm clock.  These also paved the way for solid state transistors, which are more commonly used after the second half of the 20th century do to their cheap efficiency compared to tubes.


When? The original theory for thermionic emission was heard back around the 1870's, but Thomas Edison made use of it and paved way for technology as we know it.  This theory was then cultivated in the early 20th century by British scientist John Ambrose Fleming.


Resources

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm 

A brief history lesson, and a basic description of how the parts of Tubes work together.


.http://www.radio-electronics.com/info/data/thermionic-valves/vacuum-tube-theory/tube-electrodes.php 

The structure of a vacuum tube and how the parts work.


http://en.wikipedia.org/wiki/Hot_cathode#Thoriated_filaments 

Thermionic emission and how filaments work with cathodes.


.http://en.wikipedia.org/wiki/Vacuum_tube#Transmitting_tubes 

More on how tubes work, different types of tubes and their uses, powering tubes.


http://link.springer.com/article/10.1007%2FBF01441991 

An example of the melting points of Tungsten.


https://www.youtube.com/watch?v=8n4WVRKkmww 

The process in which tubes are made.


http://proguitarshop.com/andyscorner/amp-bias-explained  

Yet another explanation of how the process of Tubes works, also includes info on biasing.


http://m.mineralseducationcoalition.org/minerals/tungsten 
Everything you want to know about Tungsten!


About the Author


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Wyatt is a Junior at Billings Senior High School who happens to be a musician at heart.  Devoting his life to this passion, and his fondness of metal music, it only makes sense for him to deeply love the chemistry of Vacuum Tubes.  He plans on pursuing a career in music education until the day he passes from this mortal dimension and will hopefully achieve a doctorate in said field.
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