Antares Analytical Technical Bulletin for

February 2003

Subject: Argon Systems for Baird Spectrometers, Part 2

Relevant Models: All DV series, FSQ,  Foundrymate, ICP, MAX II, HA10 /12 used for metals analysis. This Bulletin does not apply to MOA / FAS spectrometers

Relevant Matrix: Not Applicable

Background Information: January’s Technical Bulletin dealt with basic argon systems, how they were put together (depending on the unit), and their principle and operation. This Bulletin will deal with the more common problems associated with argon systems. While these will deal with Baird units, the principles will be the same to other manufacturer’s (Labtest, GNR, Angstrom, Spectro etc).

Things to Remember:

  1. The HR / KH can burn in the source but not in the stand. Gas flow / purity has no affect on the burning in the source …. but can cause no burning in the stand. By burning in the source we refer to jumping the auxiliary gap inside the source (you will hear it) but not jumping the analytical gap in the stand. An exception will be the later model DV6E & Foundrymate using the TR300 / 400 (a variation of the HR400) which uses a solid state igniter board, in place of the traditional auxiliary gap.
  2. Assuming all other spectrometer functions are normal, the purity of your argon has more affect on analytical performance than probably anything the operator has control over.
  3. Argon Purifiers do, eventually, become saturated and will need servicing. (See Argon Purifiers below)
  4. Under normal use, except for changing argon exhaust filters or maintaining oil levels in the exhaust bottles, the argon system needs little periodic maintenance.
  5. Very few parts which can “fail” and these are limited to the solenoids on the gas panels and, for HR400 equipped spectrometers, the hold down clamp on the sample stand & the mirror solenoid in the DV6 entrance optics. These are both argon pressure activated solenoids.

Problems & Solutions: All problems & solutions below assume the gas pressures for the spectrometer are set correctly as outlined in our Tech Bulletin last month. Before troubleshooting any problem below, please be sure the gas pressures are set accordingly.

Poor burns: Poor burns will usually be milky white or a small dark center burn on the sample. There will be little or no burn “penetration” of the sample surface. In either case analytical results will be bad. This type burn can be caused by several different causes, but the most common is bad argon or problems with the argon system.

Solution:

  1. Argon leak at the tank or inlet lines: Many times a leak will develop, especially after changing argon tanks. Check for leaks, etc using soapy water or a commercial leak detection fluid.
  2. Argon leak at the sample stand: Many times after cleaning the ceramic counter electrode holder a poor burns will be the end result. This almost always a result of not seating the counter electrode holder back into the sample block correctly or forgetting to reseat the O ring (OmniSeal) within the ceramic electrode holder correctly.
  3. Contaminated argon: This is a very common problem in areas of the world where the quality of gas can’t always be guaranteed. Changing the argon tank with a new tank of known purity will test for this problem.   
  4. NOTE:  We’ve always found it a good practice that if you suspect a bad tank of argon, the old tank you are replacing will usually have enough supply left to check. Hook the old tank back up and if, after a few minutes flushing the spectrometer, the burns become good with the old tank …. Your new tank of argon is probably bad.
  5. Inadequate Gas Flow: Check your gas pressures as outlines in January 2003 Bulletin.
  6. For the KH5 equipped spectrometers (DV & FSQ only): Rarely the sample block will develop a leak and cooling water from the water pump will creep into the burn  chamber …. Contaminating argon in the burn chamber. The only solution to this problem is replacement of the sample block assembly. Not a problem with the HR equipped spectrometers as the HR400 has no water cooling.
  7. Possible Source problem: Please contact Antares for advice.

Poor Burns / analytical results after changing argon tanks. Tanks should be changed when argon volume drops to about 100 – 125 PSI on the supply indicator of the argon regulator. Letting run any lower and you run the risk of possible contaminants on the bottom of tank interior. Changing tanks when your supply volume is more than 100 – 125 PSI and you’re just wasting money. Baird spectrometers will easily run with a tank volume down to 125 PSI assuming you still have 40 PSI (KH equipped spectrometers) or 30 (HR400 equipped spectrometers) supply pressure.

Solution:  This is one of the more common problems and can be dealt with quite easily.

  1. Normally the burns will be poor for the 1st 20 or so burns. As you have opened the argon system, oxygen (atmosphere) has entered the argon lines and need time to flush. Usually taking 20 or 30 burns should clear this up.
  2. If poor analytical results still persist, check the argon regulator for a loose connection or argon leak. Use soapy water or a gas leak fluid if necessary.
  3. Assuming there is no argon leak the next logical step would be to suspect bad argon, even if using an argon purifier (see below about problems associated with argon purifiers). Experience has shown that argon suppliers do not test each batch of argon as it’s supplied so a Certificate of Purity is no guarantee you have good argon from the vendor.
  4. If the poor analytical results are limited to P, S, C, B … please see October 2001 Antares Technical Bulletin … poor argon flow is only one cause of this particular problem.

Source Burning but no Stand Burning: This problem can be caused by several conditions. Most common are a very dirty burn chamber, no argon flow, low argon pressure or a leak around the counter electrode O ring. In all cases check for correct gas flow, sufficient gas flow and that the counter electrode holder and O ring are mounted correctly and tightly. WARNING: The screws which hold in the ceramic counter electrode holder to the sample block should be finger tight ONLY. Do not use a wrench or any tool to tighten these screws.

Poor UV  Light Transmission (DV, FSQ, F’Mate with the ½ meter option & ICP) : This problem can be caused by lack of argon flow through the entrance optics. Purity of argon will not have any affect of the UV light transmission. Please see Technical Bulletin, October 2001, for more details.

Sample Clamp / Entrance Shutter Solenoid (HR 400 equipped FSQ, FoundryMate and DV6): The FSQ / HR400 only has a gas powered hold down clamp. Entrance optics solenoid is still electrically powered. Since these 2 parts are powered by argon pressure a lack of pressure can cause both to either not operate / open correctly and can cause problems with the analytical results. Consult your Baird supplied manuals, or contact Antares Analytical, for help in setting this pressure. This pressure is set by a needle valve located on the rear of the gas panel.

Argon Purifiers: The standard argon purifier supplied with Baird spectrometers is manufactured by Sircal UK.

Purifier Basics:

  1. An argon purifier is suggested where are a consent supply of 99.996% pure argon is not guaranteed readily available, is suspect or is to expensive in the local market. The argon purifier allows a lower quality (more readily available and / or less expensive) to be used and the purifier will then filter (absorb) the oxygen, moisture and hydrocarbons so a clean pure supply of argon is delivered to the spectrometer.
  2. The minimum argon purity for effective purification is 99.9% argon. Welder Grade argon, in most cases shouldn’t be used.
  3. The lower purity argon used, the more quickly the argon purifier will need servicing. Please see the Sircal manual for approximate time frames for Servicing. The Sircal manual provides a very good table illustrating the estimated time frame vs. the purity of argon used. 
  4. An argon purifier filters these impurities using a series of tubes, all of which eventually will need servicing, depending on the quality of the argon being used. These tubes, all easily replaceable, are the A)  Titanium Oxide Tube which filters out the various hydrocarbons, B) The Copper Oxide tube which filters out the oxygen in the argon and C) Molecular Sieve which filters the water vapor and other impurities.
  5. The Titanium and Copper tubes work are heated to about 700 degrees F which causes a “catalytic” affect similar to the catalytic converter on an automobile. Another way to illustrate the action is that these tubes are like sponges. The more impurities these tubes need to absorb, the sooner they become saturated. Once saturated they lose their ability to absorb impurities and these impurities are passed through.
  6. Note: These tubes can’t be “regenerated” and once absorbed can only be replaced. Replacement is not difficult and can be performed by plant maintenance personnel.
  7. The molecular sieve, eventually, will become saturated but this absorbed moisture can be released using the REGEN button on the purifier. Please follow the instructions provided in the Sircal manual for this procedure.

Purifier Problems: Normally there is very little which will go wrong with the purifier from a hardware / repair standpoint.

  1. The Sircal manual gives a good troubleshooting guide for various problems.
  2. The main Maintenance items, listed above, will eventually need replacing and there is no “shortcut” to avoid this eventual expense.
  3. The surest way to tell if your argon purifier Ti & Cu tubes needs replacing is looking at the quality of the burns. As burns become more “milky” or dark   one of possibly 3 things is happening
    1. The molecular sieve is getting saturated with and will need regeneration. Please follow the procedure in the Sircal manual for this.
    2. It is possible the heater in the purifier is heating the tubes to a lower temperature than required, so the Ti & Cu tubes can’t generate the full “catalytic affect” so isn’t able to absorb as much impurity as it would, if the heater were generating sufficient heat. Consult your Sircal manual for more information.
    3. Your argon purifier wil need these tubes replaced. As stated, there is no tell tale way to decide which tubes should be replaced, thus the best idea is to replace them in pairs.

For any other suspected problems with your argon system, please contact our Tech Dept at Antares Analytical for more help.

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This Technical Bulletin is written by Gerry Smith, Technical Services Manager of Antares Analytical. Having spent 22 years with Baird in various capacities, including many years as Final Test / Calibration Manager and Senior Service Engineer, International Operations, he or any of our Technical Support Staff, are well qualified to answer any Technical or Applications problems you may have.

This bulletin is meant for informational purposes only and it not meant as a substitute for Service performed by a qualified Service Engineer. Any use of this information is done strictly at the discretion of the user. Antares Analytical is not responsible for any misfortune which results as the result of use of these Technical Bulletins, in place of service by a Qualified Service Engineer.