Use of Platinum Equipments

ATTENTION!
Do not forget to take occupational health and safety precautions while performing all these procedures.

MATERIAL SELECTION IN LABORATORY EQUIPMENT

Platinum and Platinum group metals are excellent materials for chemical laboratories due to their high chemical corrosion resistance and high melting applications.

Below is the information about platinum and its alloys:

PURE PLATINUM: Melting Point is 1772 C. It is soft and easy to form. It has excellent corrosion resistance to most acid and molten salts. However, since it loses its hardness and deformation resistance at 700 C - 1000 C, its mechanical strength is increased by alloying with Iridium, Gold or or Rhodium.

95% PLATINUM - 5% GOLD: Melting Degree is 1710 C. Maintains deformation resistance and hardness at higher temperatures than pure platinum. Its most important feature is its high wetting resistance when in contact with molten glassy structures. After the sample is frozen, it is easily removed from the mold. Therefore, it is the best Platinum alloy to be selected for Crucibles and Molds used in sample preparation in XRF Analysis. Therefore, more XRF Analysis can be made.

PLATINUM - RHODIUM (3.5% - 10%): Melting Point is 1789 - 1850 ° C. Rhodium is the element that provides the highest increase in hardness and strength among the alloys that platinum makes with other metals. As the rhodium content increases, the crucible retains its shape at higher temperatures. The wetting resistance to the mold is much weaker than the gold alloy. It is not recommended for use in molds.

85% PLATINUM - 10% RHODIUM - 5% GOLD: 5% Gold Platinum alloy has similar properties. However, the wetting property is weaker but the mechanical strength is higher.

HOW TO EXTEND THE WORKING TIME OF LABORATORY EQUIPMENT

Most metals have a lower melting temperature than pure platinum when alloying with platinum in certain proportions.

These alloys, which will occur unintentionally during the use of crucibles, cause cracking, point melting or complete deformation.

These elements are Boron, Silicon, Phosphorus, Arsenic, Tin, Antimony, Lead, Bismuth, and Sulfur.

THE EUTECTIC POINTS OF ALLOYS WITH HARMFULL ELEMENTS

When oxygen is insufficient, platinum-damaging elements are released due to chemical reduction. For this reason, even in mass loss and ash determination experiments, it should be worked in oxidizing atmospere.

When heating with Bunsen Burner, the flame must always be rich in oxygen. If carbon or organic substances are present in the sample, platinum harmful substances are released by the reduction reaction.

Excessive attention should be paid to the samples containing silicon, phosphorus, boron or sulphur. These elements which are reduced during melting in the crucible cause fragility in the crucible. Particular attention should be paid to the Determination of Ash of Flours and the effect of Phosphorus in other organic compounds.

Platinum equipment is not only damaged by the samples to be analyzed. External factors such as contact with Silicon-Carbide resistances that allow the heating of melting furnaces or contact with resistance residues poured into the furnace base should also be considered.

All surfaces on which platinum equipment will be placed in laboratories should always be kept clean and there should be no residues that may react with hot platinum.

The platinum-contacting surfaces of tongs and similar equipment used in the reception of crucibles from the melting furnace must be coated with platinum.

Platinum equipment should not be contacted with iron containing equipment. For example, for heating with Bunsen burner, the feet where the crucibles are placed should be covered with ceramic or platinum.

EFFECT OF ACID AND MELTED SALT

Halogen Compounds, Aqua Regia and concentrated acidic mixtures cause platinum corrosion when wet chemical analyzes are performed.

High temperature molten alkali metal hydroxide or cyanide salts are very corrosive. However, by comparison, potassium compounds are more corrosive than sodium salts.

In soda or soda-potash meltings, the top of the crucible is covered with a platinum lid to form an atmosphere of CO2 and oxidation of the crucible is prevented.

 

HEATING

Unnecessary prolonged heating of platinum equipment results in an increased tendency for brittleness and cracking due to the growth of the crystal structure.

It should not be contacted with non-platinum metals in hot state (especially at incandescent temperature), nor should platinum remain in contact with equipment for a long time. Otherwise, they welded together due to the self-diffusion mechanism.

WHAT TO DO FOR LONG-TERM USE

  • It is better to use the used crucibles in the analysis of unknown contents of the crucible, at least as if the new crucible is contaminated.
  • Never place crucibles on Silicon-Carbide heaters.
  • There should be no elements that will damage the platinum in the furnace surface coatings.
  • Some organic materials form suitable oxidizing media. (For example, adding a small amount of ammonium nitrate before heating)
  • When the platinum equipment is hot, it should only be carried with Platinum Coated Tongs.
  • Bunsen burner must be burned with strong oxidizing flame. (Blue / Colorless = Oxidizer) (Avoid yellow flame.)
  • Since pure platinum is very soft, alternative platinum alloys can be used. (Like alloying with rhodium.)

CLEANING OF PLATINUM EQUIPMENTS

  • Cleaning platinum equipment immediately after use increases the service life.
  • Basically, Crucibles and molds should be cleaned with a suitable solvent. For example boiling with Nitric Acid (diluted with Hydrogen Peroxide if needed) or Hydrochloric acid.
  • If adequate cleaning cannot be achieved; Potassium Bisulfate or Potassium Diphosphate can be alternative. Sodium Carbonate or Borax may also be used for the same purpose.
  • Never clean or test with Aqua Regia or Peroxide Hydroclock Acid. Because free chlorine in the reaction dissolves platinum.
  • Contaminated surface of platinum equipment can be cleaned by polishing with corundum (Al2O3) based abrasive. Never use metal carbide based abrasives.
  • Corundum residues on the surface should be cleaned with Hydrofluoric Acid.
  • Platinum equipment should not be cleaned by annealing. In this case, harmful elements penetrate the internal structure, causing more pollution.
  • After cleaning, it should be washed with pure water, dried with pressurized water and immersed in alcohol.

If you cannot clean your Platinum crucibles according to the above information, you can inspect your crucibles by sending them to Aktive Platin. 
 

EXAMPLES

 

1-CLEANING OF IRON AND MANGANESE CONTAMINATED CRUCIBLES

Chemicals to be used:

  • Sodium Metasilicate (Na2SiO3; Melting Point: 1088 ° C) or
  • Lithium Tetraborate (Li2B4O7; Melting Point: 920 ° C)
  • Tap Water and diluted HCl 

 

Procedure:

1.Make sure that the crucible is dry and fill 2/3 with Sodium Metasilicate,

2. Put it in the oven at 1100-1125  ° C and wait until the metasilicate melts. This period is usually 15-20 minutes.

3. Prepare a sufficiently deep and wide metal container on a ceramic block near the oven.

4. Remove the crucible from the oven with Platinum Tip Tongs and quickly pour as much of the liquid as possible into the metal bowl.

5. Allow the crucible to cool. During this time, the breaking sound of the residual glassy structure remaining in the crucible is heard.

6. To accelerate cooling, hot crucible can be immersed in a container of water.

7. After the crucible has cooled sufficiently, clean the glassy parts. If it is not completely cleaned, it will not be a problem, because they are soluble in water.

8. If the process is not cleaned enough, the above process is repeated once more.

9. Final cleaning is done with dilute HCL containing water.

10. Almost all glassy structures have been cleaned. Place the crucible in a beaker filled with water and end the process by changing the water several times.

11. Dry the crucible.

*** DO NOT FORGET TO TAKE OCCUPATIONAL HEALTH AND SAFETY MEASURES WHEN DOING ALL THESE PROCEDURES***

2-CLEANING OF SILICUM OXIDE, SILICATE, METAL AND METAL OXIDE 

Chemicals to be used:

  • Potassium Bisulphate (KHSO4; Melting Point: 197 ° C) FOR STRONG CLEANING or
  • Sodium Carbonate (Na2CO3; Melting Point: 854 ° C) FOR NORMAL CLEANING or
  • Sodium Tetraborate (B4H2ONa2O17); Melting Point: 75 ° C) ROUGH FOR CLEANING
  • Water and diluted HCl 

 

Procedure:

  1. Fill the crucible with 1/3 of the capacity Potassium Bisulfate.
  2. Heat the crucible over the bunsen burner and allow the Potassium Bisulfate to melt.
  3. Hold the crucible with Tip Platinum-coated Tongs and mix by circling over the open flame and see Potassium salt reaching red temperature.
  4. Pour the molten salt into the appropriate container (Ceramic or metal).
  5. Boil in 20% (v / v) HCl to remove residues in crucible.
  6. Then de-ionized water in the wash repeatedly and dry. 

 

3- CLEANING SAMPLES USING ACID

CITRIC ACID: Fill 10% Citric acid solution into the Ultrasonic Cleaning device and heat to 50 ° C and leave the crucible inside.

To accelerate the cleaning time, fill 20% w / v citric acid solution into a beaker and soak in crucible at 80 ° C.

  • HYDROCHLORIC ACID: Soak the crucible in 10% HCL for faster cleaning.
  • NITRIC ACID: Boil the crucible in chlorine-free HNO3 for much more efficient and quick cleaning.
  • NEVER USE AQUA REGIA !!!