The analytical laboratory is a vital part of all industrial plants and research facilities. The techniques employed therein have developed rapidly in recent years, however the fundamentals upon which many of these techniques are based on have remained constant and the vast majority demand the use of high purity inert materials. In this category Platinum has properties that make it an ideal choice. It has a high degree of chemical inertness even at the most extreme conditions and yet can be Re-Fabricated into a wide variety of products utilized for sample preparation throughout many different industries.
Metals used for laboratory apparatus must have the following properties:
High temperature strength
High melting point
Ductility
Corrosion resistance
Oxidation resistance
Platinum and its alloys possess these qualities and is therefore the most widely used metal for analytical laboratory apparatus. Properties of platinum and some common platinum alloys are briefly discussed here.
Platinum (Pt)
Platinum is best known and least rare of the platinum group metals. Its high melting point, 1773 degrees Celsius, ductility and excellent resistance to chemical attack by acids and fusion mixtures makes it very suitable for laboratory ware.
Platinum 5% Gold (Pt/Au)
Universally accepted material of choice for crucible and casting molds for spectro-graphic analysis by x-ray fluorescence (XRF). The alloy has higher temperature strength than pure platinum and has a "non-wetting" property, which results in easy removal of the sample after fusion and allows for many reproducible assays.
Platinum 3.5% Rhodium (Pt/Rh)
The rhodium alloys have higher hardness and high temperature strength making it suitable for more aggressive conditions.
Platinum 10% Rhodium (Pt/Rh)
This alloy has melting point of 1850 degrees Celsius, it has greater hardness and higher strength than other platinum alloy. It is capable of maintaining its shape under the hottest furnace conditions.
Platinum Gold Rhodium (87/3/10) (Pt/Au/Rh)
This alloy combines the "non-wetting" property of the Pt/Au alloy and the extra strength and durability of Pt/Rh alloys.
Other Metals
Gold (Au)
Gold can be used in labware. Its most common application is for hydrofluoric acid treatment of siliceous materials.
Silver (Ag)
Pure silver can be used for fusion with alkali hydroxides.
| Comparison of Properties |
Pt |
Pt-10Rh |
Pt-5AU |
AU |
| Density gcm-3 |
21.45 |
19.99 |
21.33 |
19.32 |
| Melting Point Celsius |
1770 |
1850 |
1660 |
1064 |
Electrical Resistivity
(0° C) W cm |
9.85 |
18.40 |
18.50 |
2.06 |
Temp Coefficiant of
resistance (0-100º C) º C-1 |
0.0039 |
0.0017 |
0.0021 |
0.004 |
| Annealed Hardness Hv |
40 |
90 |
90 |
26 |
Ultimate Tensile Strength
(20ºC) Nmm-2 |
125 |
300 |
345 |
120 |
| Tensile Elongallon (20º C) % |
40 |
35 |
24 |
42 |
Glass wetting Resistance
(Equilibrium Contact
Angle of E Glass at 1200º C) |
26 |
45 |
83 |
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