Helpers of all sizes for analysts

Geologists analyze soil samples, the oil industry studies crude oil, and the steel industry wants to know the composition of slag. These are completely different fields, but all begin the analysis process with a high-temperature fusion treatment of the samples. But what equipment should be used for the fusion process? Platinum crucibles are ideally suited for the job, and are used in industrial and scientific laboratories around the world. Heraeus is a leading global manufacturer of platinum crucibles. It is remarkable that after over 130 years, we are still finding ways to improve this product.

Crucibles, casting dishes and boats made of precious metals are standard laboratory equipment for preparing samples for X-ray fluorescence analysis (XRF), for microanalysis, for fusions and for ashing. Larger iridium crucibles are used for growing single crystals from high-melting oxides (e.g., sapphire) for the optical and laser industries. Good chemical resistance to aggressive media, the high melting point and stability at high temperatures are key properties that have characterized platinum and platinum alloys in laboratory equipment for decades. Since 1870, Heraeus has been producing standard and customized laboratory equipment at its facilities in Hanau with a high degree of vertical integration and in a vast range of sizes.

Indispensable material for chemical laboratory equipment
Selecting the right material and treating it properly in everyday use are crucial for the successful application of laboratory equipment. Laboratory staff and analysts have a broad spectrum of materials and sizes to choose from for their equipment. “We produce crucibles in sizes ranging from ‘micro-thimbles’ to ‘rain barrels’ – whatever the customer wants,” explains Stefan Lang, Sales Manager at W. C. Heraeus. Heraeus manufactures several thousand standard crucibles the size of a shot glass annually – but can make them much larger, too. A custom crucible the size of a rain barrel was recently manufactured – using about 20 kilograms of platinum. “That makes this giant not only one of the largest, but also one of the most expensive crucibles Heraeus has ever produced. How much this crucible actually cost is just as much a trade secret as its purpose and application,” says Lang with a grin. However, the traditional fields of application for crucibles are no secret. These precious metal aids are indispensable for performing analyses. Many industries – including the iron and steel, cement production and waste incineration industries – regularly perform XRF analyses during production for quality assurance purposes. In environmental and foodstuff analyses, it is essential to analyze the heavy metal content in soil or grain samples, for example. To perform a reproducible analysis of the samples, scientists first homogenize them in crucibles by the fusion process. This creates a fused tablet that displays a uniform composition throughout and can be studied using spectroscopic methods.

The demands on crucible materials are growing steadily, which is why we still continue to optimize platinum crucibles  after more than 130 years, particularly regarding their durability. By alloying platinum with 5% gold, the stability can be improved in the 1100 to 1200°C temperature range. But there are even better ways.

Dispersion hardened platinum as a new class of materials
Heraeus has established dispersion hardened platinum (DPH) as a new class of materials for laboratory equipment-materials that have been developed in close cooperation with clients from both analytical laboratories and the business world. “Compared to pure platinum and solid solution platinum alloys, DPH materials are more resistant to corrosion, as well as thermal loadings and mechanical stress,” explains Prof. David Lupton, Head of Development at W. C. Heraeus.

The innovative material is in particularly high demand where crucibles need to be especially long lasting, stable at high temperatures, corrosion resistant and dimensionally stable. Dispersion hardened platinum is also used in the glass industry, for example, for stirrers and glass fiber bushings. DPH platinum is also suited for growing single crystals in oxidizing atmospheres. “The addition of finely distributed zirconia prevents grain growth until just below the melting point. The finer microstructure makes DPH far less sensitive to corrosion at the grain boundaries than comparable materials. That ensures the improved durability,” as platinum specialist Lupton explains its exceptional properties. DPH platinum crucibles have opened up opportunities for new applications. While traditional crucibles allow sample fusion up to around 1100°C, these innovative new crucibles have boosted that temperature to over 1600°C.

The experts at Heraeus all agree: Platinum crucibles will continue to play an essential role in quality assurance for decades to come. Our close collaboration with different users guarantees it. “We advise our customers in detail. The purpose and location of use, pre-treatment of sample materials, selecting the specific fusion process and temperature: These are just a few of the criteria that determine the correct choice of crucible,” comments Stefan Lang. The experts at Heraeus use the whole range of alloys and shapes and provide just-in-time manufacturing of custom crucibles. “We make everything we deliver – our vertical integration is our seal of quality for our customers.” Dr. Jörg Wetterau

Source: technology report 02 – Heraeus Technology Magazine (March 2009)