Zirconium Crucibles - Extremely Corrosion Resistant Metal
The remarkable corrosion resistant qualities of Zirconium are used extensively in the Chemical Processing Industry. Zirconium can withstand a wider range of caustics and acids than any other commonly used fabricating material.
Zirconium Crucible Sizes
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Zirconium Crucibles Information – Facts and Advantages
It is no secret that zirconium crucibles cost more than porcelain, steel or nickel. Quite a bit more. But, based on an average number of fusions which can be made in a zirconium crucible, as opposed to those of nickel, the ratio of longevity stands at 20 to 1. Therefore, the higher cost of zirconium crucibles is recovered three times over. In addition to cost effectiveness, zirconium crucibles hold several advantages over other materials.
If compared to platinum crucibles, several distinct advantages are readily apparent.
- Improper procedure in heating over a Bunsen burner can cause the reducible contents to be converted into harmful, low-fusing metals which may react with the platinum crucibles.
- No platinum tipped tongs or special triangles are required for handling hot zirconium crucibles.
- Sudden contact with cold, metallic surfaces will have no deleterious effects on a zirconium crucible.
- Hydrofluoric acid is the only cleaning agent which should not be used to clean zirconium crucibles.
- Smoothing and shaping after use is not a special consideration. Zirconium crucibles require a minimum of specialized care.
- The inherent strength of zirconium precludes the necessity of reinforced rims and thicker bottoms as is the case of platinum crucibles in certain instances.
Zirconium crucibles are especially adaptable to the needs of the analytical chemistry laboratory, such as in strong alkaline fusions employed to reduce refractory samples to a soluble form, and for high temperature ignition ashing purposes.
Zirconium metal is a most effective all-round crucible for fusions using sodium carbonate or sodium peroxide and is an excellent low-cost replacement for platinum crucibles. Based on an average of 100 fusions per crucible, zirconium is more cost-effective than less expensive crucibles of porcelain or steel.
- Excellent low cost replacement to platinum.
- Does not require handling with platinum tipped tongs.
- Virtually eliminates sample contamination.
- Effective all round crucible for fusions employing sodium carbonate and sodium peroxide.
- Under vacuum can be heated to 1450°C.
Tariff Code : 8109 90 00
Many regard Zirconium as a rare metal yet it is not uncommon but an exotic material. Zirconium, however, has many rare, even unique, qualities such as its remarkable corrosion resistance, being used extensively in the chemical processing industry. Zirconium will withstand a range of caustics and acids to a greater degree than any other commonly used metal and stands in a class by itself.
Cleaning Zirconium crucibles
Hydrofluoric acid is the only cleaning agent that should not be used to clean zirconium crucibles.
Applications for Zirconium Crucibles
Zirconium crucibles are suitable for several applications in the analytical chemistry.
- Sodium Peroxide Fusions – used with refractory or high-silica materials such as chromate, magnetite, illmenite, retile, silicon, silicon carbide, and certain alloys and steels. An excellent general flux for almost any material.
- Sodium Carbonate Fusions – decomposes most silicates of aluminum, 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 made in the reducing flame of the burner 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. The burner set-up should be under a fume-hood and positioned under a Tripod Initially, the crucible and contents should be gently introduced over the flame, moving it in and out as melting commences. When molten, the heat can be raised and the contents ‘swirled’ to keep the sample off the bottom – use any Stainless Steel tongs to handle the crucible and accomplish the swirling action, which should be continued throughout the fusion process.
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 solution.
Fluxes which can be used in Zirconium Crucibles
Listed below are fluxes that can be used to reduce melting points along with some applications that are normally troublesome.
- Sodium Peroxide – use with refractory materials such as chromite, magnetite, illmenite, rutile, silicon, silicon carbide, certain alloys and steels, etc., an excellent general flux for almost any material. 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 milliliters of hydrogen peroxide to the acid solvent 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 and alloys are another matter. These materials tend to react violently at very low temperatures with oxidizing fluxes and will often burn right through iron or nickel crucibles on their first use. However, these can be safely fused in zirconium if the sample is first mixed with about 4 to 6 times its weight of powdered anhydrous sodium carbonate; (0.25gram sample is usually more than enough) then add about twice the sample weight of sodium peroxide and mix. The crucible and contents are then gently moved toward a fairly cool flame and moved cautiously in and out of the flame until melting around the edges begins. It must not be put in the flame and held there unless all spattering, if any, has ceased. When the mixture appears to be melted and quiet, the temperature can be increased and fusion continued as usual. The fusion should be kept swirling and finished at a red heat.
- Sodium Carbonate: Melting Point approximately 850°C. Decomposes most silicates of aluminum, calcium, chromium nickel, etc.; also halides of silver, and sulfates 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 aluminum, 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 maybe helium. Nitrogen might be used if the fusion time at high temperature was relatively short, but not recommended and will embrittle zirconium after exposure for long periods of time that may shorten the useful life of the crucible.
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 an easier-to-pour melt, 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 the very expensive noble metals e.g platinum and fragile glass, porcelain and quartz ware 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 enveloping the crucible in an inert atmosphere.
Should however your requirements demand Platinum Crucibles, Winward offer an extensive range, please contact us for more details.