In general, we recommend:
- The following maximum temperatures are not exceeded:
1400°C for platinum
1500°C for ZGS platinum
1550°C for 10% rhodium platinum
1600°C for ZGS 10% rhodium platinum
1300°C for 5% gold platinum
1400°C for ZGS 5% gold platinum.
1450°C for 3% gold 10% rhodium platinum
2200°C for iridium
- Heat is only applied as necessary; excessive heating promotes crystal growth which can produce cracks.
- Heat is used under oxidising conditions; reducing conditions can make the apparatus brittle. Ensure only the outer cone of a gas burner heater is used, and avoid a smoky flame as the carbon or carbon monoxide will make the metal brittle.
- Crucibles are not used to melt metals, which will dissolve platinum.
- Avoiding contact between hot labware and base metals:
- Use clean triangles of platinum-iridium or silica to support crucibles when making fusions.
- Use clean platinum tipped tongs to handle hot platinum vessels; if only base metal tongs are available allow the vessel to cool before handling.
- Place hot vessels on a clean refractory material, not on a metallic tray or dirty surface.
When high temperatures are involved, avoid unknown substances as well as the following to prevent platinum being attacked:
- Chlorine and volatile chlorides
- Highly carburet gasses and vapours
- Sulphur dioxide
- Aqua-regia, which should be avoided at all temperatures
- Hydrochloric and hydrobromic acid, which should be avoided at all temperatures
- Concentrated sulphuric and phosphoric acid with prolonged heating
- Antimony, arsenic, phosphorus, selenium, tellurium and their compounds
- Fused cyanides and nitrates
- Fused alkali oxides, hydroxides, peroxides and sulphides
- Fused alkali chlorides and alkali earth chlorides in the presence of air or above 1000°C
- Magnesium pyrophosphate over 900°C
- Iron oxide above 1200°C
- Lead and bismuth oxides above 1250°C
- Silica and borax
- Sulphur with prolonged heating
- Phosphorus pentoxide
Platinum vessels should always be cleaned after use.
- To remove stains use fused potassium hydrogen sulphate, which will remove adherent silica, silicates, metals and metal oxides. After fusion carefully run the melt over the inner surface, allow to cool and then dissolve in boiling water and rinse thoroughly. Boiling in diluted hydrochloric acid can supplement this.
- More persistent stains may need fusion with sodium carbonate and hydrofluoric acid.
- Remove tungsten and molybdenum residues by dissolving them in a strong sodium hydroxide solution.
- Remove iron stains by covering the apparatus with 1g of ammonium chloride and applying full heat for about two minutes.
- Over time a dull surface will develop, which can be re-polished with a mild metal polish.
Platinum tipped tongs are unsuitable for removing platinum vessels from acid leach solutions; the acid will attack the frames causing the shoes to loosen and detach.
The labware shape and surface should be preserved for maximum life and inadvertent handling can cause distortions. Minor crucible distortions can be reshaped on a reshaping block with a plug inside, which is rotated slowly with a moderate pressure. The block and plug can then be used to store the crucible.