About Zirconium

Zirconium

Zirconium will withstand a range of caustics and acids to a greater degree than any other commonly used metal.

It is immune to sterilising solutions, most of the organic chemicals, dyestuffs and a wide variety of inorganic chemicals.

Heating/Cooling Information

Excellent low cost replacement to platinum virtually eliminates sample contamination.

Zirconium has good corrosion resistance to most organic and inorganic acids, salt solutions, strong alkalis and a few molten salts. An effective all round crucible for fusions using sodium carbonate and sodium peroxide.

Heating zirconium produces a creamy white passive oxide film which is a corrosion barrier and is stable in both reducing and oxidising conditions.

Under vacuum zirconium crucibles can be heated to 1450°C. The temperature limit for use in air is 450˚C to 500˚C.

A slow heating ramp rate and cooling rate is recommended to minimise the thermal shock on crucibles.

Zirconium crucibles should not be taken out of the furnace at high temperature otherwise they may crack. Remove from heat when the temperature is under 100°C.

Features and Benefits

The average number of fusions that can be made in a zirconium crucible, as opposed to those of nickel, the ratio of longevity stands at 20 to 1. The investment of a zirconium crucible is recovered many times over.

In addition to cost effectiveness, zirconium crucibles hold several advantages over other materials in the laboratory. When compared to platinum there are several distinct advantages.

– Ideal for most fusions done in full heat, resulting in little or no attack or oxidation of the crucible regardless material or flux mixture.

– Resistant to melts of alkali (Na, K, Li) carbonates, hydroxides, peroxides, borates, nitrates, chlorides and some fluorides, or combinations of above.

– Completely resistant to most solvents of all concentrations except hydrofluoric acid.

– Offers virtual elimination of sample contamination.

– Resistance to molten sodium peroxide.

– Will not alloy with more easily reducible metals.

– Unlike platinum no smoothing and reshaping is necessary.

High Temperatures

Normal temperature range -196°C to +550°C.

Notes

Cleaning Zirconium Crucibles

Hydrofluoric acid should not be used for cleaning.

Applications for Zirconium Crucibles

Zirconium crucibles are suitable for several applications in analytical chemistry.

Sodium Peroxide Fusions – used with refractory or high-silica materials such as chromate, magnetite, ilmenite, retile, silicon, silicon carbide, and certain alloys and steels. An excellent general flux for almost any material.
Sodium Carbonate Fusions – decomposes most silicates of aluminium, calcium, chromium, nickel; also halides of silver; and sulphates of barium and lead.
Lithium Salt Fusions – flux for oxide and silicate materials when sodium and potassium need to be determined or when large amounts of sodium would interfere with x-ray fluorescence or atomic absorption procedures.

Fusions in Zirconium Crucibles

Fusions are best where there is little or no attack or oxidation of the crucible – regardless of the sample material or flux mixture.

In making fusions, the sample is mixed with 4 to 10 times its weight of flux and placed over a bed of flux in the crucible and heated.

When molten it either becomes clear/homogeneous, or a very bright red, the fusion is now complete. The fused mass can be allowed to solidify in the crucible. The crucible and contents can then be placed in a beaker covered with water and the suitable solvent added to remove the fused mass from the crucible. Any material adhered to crucible can be dissolved out with more solvent.

Under these conditions only a few milligrams of zirconium will be introduced into the sample. If this trace needs removing it can be accomplished by using strong acid solutions (HCl, H2SO4).

Fluxes which can be used in Zirconium Crucibles

Listed below are fluxes that can be used to reduce melting points.

Sodium Peroxide – use with refractory materials such as chromite, magnetite, ilmenite, rutile, silicon, silicon carbide, certain alloys and steels, etc., an excellent general flux for most materials. Two precautions to be taken when fusing chromite or other material high in chrome. When these materials are fused with peroxide, the chrome is oxidized to chromate which will tend to leave a yellow film on the inside of the crucible which will be unnoticed until the crucible has been removed from the subsequent dissolving operation, rinsed and dried.

This can be prevented by adding a few millilitres of hydrogen peroxide to the acid solvent (H2S04) while the crucible is still immersed. The peroxide in acid reduces chromate to chromic chrome which goes readily into solution. The excess peroxide can be eliminated by boiling. Chrome can then be determined by the usual persulfate oxidation followed by a reduction titration.

Peroxide fusions of silicon carbide and other finely pulverized metals tend to react violently at very low temperatures with oxidizing fluxes and will often damage iron or nickel crucibles on their first use.

Sodium Carbonate: melting point approximately 850°C. Decomposes most silicates of aluminium, calcium, chromium nickel, etc.; also halides of silver, and sulphates of barium and lead.

Potassium Carbonate: melting point approximately 910°C. Acts the same as sodium carbonate and can be mixed with it.

Sodium and Potassium Carbonate: mixture acts as either one alone but melts at a lower temperature than either one alone.

(Na, K) Carbonates plus oxidizing agent: (KNO3, KC103, Na202, Mg0, Zn0): Used on sulphide ores of arsenic, antimony, iron, nickel, molybdenum, etc.

Sodium Hydroxide: melting point approximately 320°C. Basic flux for oxidized ores of tin, zinc, antimony, etc.

Potassium Hydroxide: melting point approximately 360°C.

Sodium Chloride: melting point approximately 800°C. Neutral flux. Can be used as a cover for fusion mixtures.

Potassium Nitrate: melting point approximately 340°C. Powerful oxidizing agent and basic flux. Used as a mixture with carbonates.

Sodium Nitrate: melting point approximately 320°C. Acts same as potassium nitrate.

Lithium metaborate: melting point approximately 840°C. Flux for various oxide and silicate materials when sodium and potassium need to be determined.

Lithium Carbonate: melting point approximately 620°C.

Lithium Hydroxide: melting point approximately 450°C. Can be added to other fluxes to help lower melting points.

Lithium Fluoride: melting point approximately 870°C. Added to (Na, K) carbonates.

Calcium Carbonate – Ammonium Chloride: A sintering flux used to make soluble alkalis for analysis of sodium and potassium.

Sodium Borate (Borax glass): melting point approximately 740°C. Used with (Na, K) carbonates to give a lower melting flux for refractory silicates and oxides of aluminium, iron, nickel, etc.

This list of fluxes can be used in any combination in zirconium crucibles so long as the fusions are made in the reducing flame of the gas burner or in a furnace equipped to provide an inert atmosphere such as argon or helium.

An additional benefit can be obtained by combining two or more sodium or potassium salts (carbonates, peroxides, hydroxides); or two or more lithium salts (borates, peroxides, carbonates, hydroxides). Using this procedure, the melting temperature of the fusion can often be lowered to a temperature below that at which any of the fluxes alone would melt. This lower melting point also results in a faster fusion process and an increase to the useful life of the zirconium crucible.

Zirconium crucibles and covers and other laboratory ware, are an excellent alternative to platinum, porcelain and glass for making peroxide and similar fusions in preparing samples for chemical analysis.

While prolonged exposure to air at temperatures of more than 750°C can have a negative effect on zirconium, this can be reduced by either: using cooler reduced portion of the flame, or use of a vacuum oven.