• Blog Stats

    • 77,682 hits
  • Archives

  • Enter your email address to subscribe to this blog and receive notifications of new posts by email.

    Join 157 other followers

  • Copyright notice

    This blog entry and all other text on this blog is copyrighted, you are free to read it, discuss it with friends, co-workers and anyone else who will pay attention.

    If you want to cite this blog article or quote from it in a not for profit website or blog then please feel free to do so as long as you provide a link back to this blog article.

    If as a school teacher or university teacher you wish to use content from my blog for the education of students then you may do so as long as the teaching materials produced from my blogged writings are not distributed for profit to others. Also at University level I ask that you provide a link to my blog to the students.

    If you want to quote from this blog in an academic paper published in an academic journal then please contact me before you submit your paper to enable us to discuss the matter.

    If you wish to reuse my text in a way where you will be making a profit (however small) please contact me before you do so, and we can discuss the licensing of the content.

    If you want to contact me then please do so by e-mailing me at Chalmers University of Technology, I am quite easy to find there as I am the only person with the surname “foreman” working at Chalmers. An alternative method of contacting me is to leave a comment on a blog article. If you do not know which one to comment on then just pick one at random, please include your email in the comment so I can contact you.

This should have been in Camera

Dear Reader,

The recklessness of some people drives me to a new level of distraction, I have chosen to not name the case or the newspaper in this blog article but I will tell you the story. Some irksome pest tries to build a homemade bomb, this homemade special fails. Then the news paper reports the court case explaining how and why it failed to detonate.

What I think is that any public discussion of a failed bomb is an educational moment which we are better off without. The problem I see is that building any complex gadget is hard when you have to make everything yourself. Having had an interest in electronics I can tell you that many gadgets have taken a lot of development work to get to the level which the public now considers “normal”.

Also having been in the business of developing chemical processes, I can tell you that the creation of a process (or even just the implementation of an existing process)  can take a lot of work. One of the things which always makes it more easy is a knowledge of how someone else did it successfully and an understanding of what went wrong the last time.

The knowledge that a particular method or material is unsuitable for a task is a great help, it saves a lot of time and effort. The reason is that a person will not go chasing after something which does not work. By publishing a truthful discussion of how a bomber failed the newspapers are helping the next generation of bombers by improving their knowledge.

Some years ago I was told something interesting at the ITU in Germany, they commented that a large fraction of illicit plutonium samples which have been intercepted contain red materials. They believe that the Soviet intelligence services leaked some misinformation about “red mercury”. The story is that “red mercury” greatly increases the ease of building a working nuclear weapon.

By releasing this crazy story about a spoof material, the Soviets were attempting to  waste the time and efforts of would-be nuclear terrorists. By encouraging them to chase a false lead it would have helped world peace. The reason is that every hour and dollar a terrorist spends looking for ways to obtain and use this material is a hour or dollar which they could not use one something which is more likely to provide them with a weapon. Very clever I think !

I have to ask why the facts of this type of case be discussed in public, and why the newspaper staff did not have the sense not to self censor what they published.

Advertisements

Reference electrodes

OK yesterday was an interesting day the electric power went off during a thunderstorm at about 13:15 which brings me onto the topic of electrochemistry; I tried to write as long as the electrochemical cells in my laptop allow me to.

I was recently at a nuclear research centre where fuel is placed inside a research reactor to allow a range of different reactors to be simulated both under their normal conditions and under accident conditions. One of the things which I saw was the mention of a Fe/Fe3O4 reference electrode.

Before we go any further you need to know what a reference electrode is, it can be thought of as a stake driven into the ground and a landmark. This allows to locations of other things to be measured relative to the stake.

The classic reference electrode is the normal hydrogen electrode, this is the primary standard but it is a real dinosaur.

H2 → 2H+ + 2e

It requires a supply of good clean hydrogen (fire risk) and it is not easy to use. The potential is controlled by the proton concentration in the half cell and the partial pressure of the hydrogen. Much of the time people want to use electrodes which are more simple to use.

A classic which is an old friend of mine is the saturated calomel electrode; please note it is not a caramel electrode! Calomel is mercury(I) chloride (Hg2Cl2) which is a white solid with a low solubility. The electrode operates using the following equation.

2Hg + 2Cl→ Hg2Cl2 + 2e

The electrode consists of some mercury metal covered with some calomel which is then immersed in saturated potassium chloride solution. Hence as a result it is banned in Sweden, I can recall as a first year undergraduate at Imperial College making my own SCE in a teaching lab.

The potential of this electrode is largely controlled by the solubility product of calomel and the potassium chloride concentration.

Needless to say chemists have come up with some alternative electrodes which do not contain mercury and are suitable for aqueous media. One of these is the silver / silver chloride electrode which is used by many electrochemists.

A typical Ag/AgCl electrode consists of a silver wire with a coating of silver chloride which is immersed in a chloride solution. It operates by the following equation.

Ag + Cl→  AgCl + e-

Some other reference electrodes exist such as the copper / copper sulphate electrode which is quite popular for corrosion studies. This one is a copper wire which is immersed in copper sulphate solution. This forms part of the classic Daniel cell. I will let you write out the mechanism for this electrode.

When I saw description of a iron/iron oxide reference electrode which is designed for use under BWR conditions. This reference electrode is intended for use under the rather extreme conditions found in a boiling water reactor. It will be hot and unlike a PWR it will not be possible to maintain a constant concentration of hydrogen. The lack of hydrogen rules out the use of a platinum reference electrode.

I have not been able to find details of the construction of the iron/iron oxide electrode but I have found from the literature details of a copper/cuprous oxide electrode. This electrode is a mixture of copper powder and copper(I) oxide inside a yttrium stabilised zirconia (YSZ) tube.

The half cell will be Cu | Cu2O | ZrO2 | H2O

The reaction in the reference electrode will be

2 Cu + O2-→ Cu2O + 2e-

The YSZ is an oxide conductor, oxide anions are mobile in this solid. So the overall set of equations for the electrode will be

2 Cu + O2-→  Cu2O + 2e- on the central wire

H2O → 2H+ + O2- and HO → H+ + O2- on the surface of the YSZ tube

If we combine the equations we can get a single equation.

2 Cu + H2O + O2- → Cu2O + 2e + 2H+ + O2-

Remove the items which appear on both sides of the arrow.

2 Cu + H2O → Cu2O + 2e + 2H+

As the overall electrode equation has protons in it then the electrode potential will change as a function of pH, this is a disadvantage over electrodes such as the SCE. But on the other hand the SCE is dependant on the chloride concentration inside it.

PS. The power came back on about 1 hour and 15 minutes after it went off.

%d bloggers like this: