8/18/2019 Electrode Manufacturing

1/2

- when you need to be sure...

The making of a combined pH electrode –the inside stor y

Radiometer Analytical’s experiencein electrochemistry dates back nearly seventy years to when thecompany pioneered its very first pHmeter in Copenhagen, Denmark.

Today, it develops and manufac-

tures a comprehensive range of instruments, software, sensors andcalibration standards, extending itsexpertise across the entire measur-ing chain.

The company is particularly proudof its range of more than 300 elec-trodes - combined pH, glass or ref-erence electrodes, metal electrodes,ion-selective electrodes and con-

ductivity cells - for every applica-tion and budget.

Electrodes are manufactured onits premises in Villeurbanne,France using a blend of traditionalknow-how and state-of-the-art tech-nology.

It takes between 2 and 11 days to manu-facture a combined pH electrode,

depending on the type. The electrodedescribed below features Red Rod tech-nology - a unique concept developed by 

Radiometer Analytical which ensures fast response time across a wide temperaturerange.

First of all, 2 m long crystal tubes withdiameters of between 2 mm and 12 mmare used to manufacture the internal andexternal bodies of a combined pH elec-trode.

These crystal tubes are subjected to cold

 working with a wet or dry saw thendrilled. The blades and bit are diamondtipped for maximum cutting efficiency.The parts obtained are then subjected toheat treatment.

The cutting process leaves sharp edgesthat need to be smoothed off using firepolishing (photos 1 and 2).

The following stage, called annealing,allows any stresses introduced into theglassware to be removed. The electrode

is then separated into two compartmentsby a double welding operation (photo 3)

Next, the ceramic porous junction(Ø 1 mm) is fitted (photos 4 and 5).

This is an extremely delicate process as,if the temperature is too high, the ceram-ic porous junction becomes blocked andthe ions will not be correctly exchangedand, if it is too low, there is a risk of leakage.

Now comes the most spectacular andmost skilful stage of the process - the

blowing of the glass bulb. A steady handand a trained eye are the essential toolshere as the diameter of the glass bulb

Photo 1: burning process

Photo 2: filling hole before (left) and after burning (right) 

Photo 3: right: before double welding 

left: after double welding 

Photo 4: porous junctions

Photo 5: fitting the porous pin

8/18/2019 Electrode Manufacturing

2/2

(sensitive membrane) must measure10.5 mm with a tolerance of only 1 mm.It has to be right first time.

The glass used to form the pH-sensitivepart of the electrode is made using astrictly confidential formula - and deter-mines the performance of the electrode.

Firstly, the base of the electrode is pre-pared to form an adherent surface. Thisbase is created using a blob of moltenglass, which is blown into a bubble thenbroken off (photos 6 and 7).

The base of the electrode is dipped intoan oven of molten glass at a temperatureof 1200°C (see top photo overleaf).

 At the next stage, the glass is blown(photo 8) to form the sensitive glassmembrane. The glass parts are thencarefully cleaned and checked beforebeing sent to the assembly line.

On the assembly line the electrode isfilled with KCl crystals and an inner fill-

ing solution. Next, the internal and exter-

nal Red Rod reference elements contain-ing AgCl powder are inserted (photo 9)and the electrode is glued to seal it.

 A copper shield is fitted to provide theelectrical connection of the referenceelectrode and the shielding of the elec-trode head. The cable is attached.

Each electrode is tagged to ensure com-plete traceability.

 A second gluing phase takes place toinsulate the electrode correctly. It is then

left to dry for 24 hours.

The electrodes are virtually finished at this stage. All that remains is to glue onthe head already attached to the cable,as can be seen from photo 10.

The assembled electrode is soaked in ahydrating solution for 12 hours to condi-tion it. Once this is done, the specifica-tions of each electrode are checked onan automated control bench (photo 11).

 A certificate is then issued stating the

individual electrode specifications suchas slope, response time etc.

Now the electrodes can be boxed ready to be sent out to the customer (photo 12).Few people realise how many delicateoperations are required to manufacturethe electrodes they use every day.

Thanks to our unparalleled experience inelectrochemistry, you can be sure of obtaining accurate and reproducibleresults every time when you choose aRadiometer Analytical electrode

.

Photo 8: blowing the glass bulb

Photo 9: Red Rod reference elements

Photo 10: electrodes during manufacturing 

Photo 11: control bench

Photo 12: packed electrodewith certificate of conformity 

   D   1   1

   A   0   1   2   ©    R

  a    d   i  o  m  e   t  e  r   A  n  a

    l  y   t   i  c  a

    l   S   A   S .

   2   0   0   5  -

   0   6   A .

   A    l    l  r   i  g

    h   t  s  r  e  s  e  r  v  e

    d .

   D  a   t  a  s  u

    b   j   e  c   t   t  o  c    h  a  n  g  e  w   i   t    h  o  u   t  n  o   t   i  c  e .

Photos 6 and 7:preparing the blank for dipping