It is important to select the correct crucible for your analytic process to ensure accurate results and avoid costly damage to machines and labware. There are many factors to take into consideration, some quite general and others very specific. These include:
Almost every user and application has quite a unique combination of furnaces, processes, treatments and end products. As such choosing a crucible that will ensure optimal performance is highly individualized. The IAM Drijfhout team of experts are here to help you choosing the right crucible.
A crucible needs to be able to withstand high operating temperatures, as well as be chemically compatible with the sample material (inert and unreactive). At IAM Drijfhout we offer a wide range of platinum and platinum alloy crucibles. Platinum is an industry standard for crucibles, this is because of the following properties:
Adding alloying elements to pure platinum provides specific crucible characteristics which can be favourable for particular analyses. For example rhodium (Rh) elevates the melting point of platinum.
Using pure platinum and its alloys ensures high-performance analytical crucibles known for their extended lifespan and chemical resistance. IAM Drijfhout can supply you with the following platinum crucibles:
|Pure platinum (Pt)||Pure platinum crucibles have excellent resistance to chemical deterioration and a melting point above 1770 °C.|
|Platinum-gold crucibles||These 95% Pt / 5% Au crucibles are considered the industry benchmark for the preparation of fusion samples. |
They were specifically developed for XRF analysis, with a structure that maintains flatness, thus ensuring excellent mixing performance and accurate analysis results.
The addition of gold brings extra benefits:
– The melting point of 1780 – 1850 °C is extremely high
– Crucible strength is increased
– Reduces premature wrinkling effect
– Recrystallization tendencies are reduced
– Samples are easier to remove
– Thermodynamic stability is improved
– Non-wetting to molten glass
– Easier to clean and maintain
– These crucibles are also very suitable for the oil & petrochemical industry.
|An alloy composed of 10%, or 3% rhodium with a melting point of 1780-1850°C.|
Platinum-rhodium alloys offer better hardness and strength compared to other platinum alloys.
This makes them suited to harsh conditions and the more rhodium the crucible contains the longer it will hold its shape in the hottest conditions.
However, rhodium is particularly sensitive to a number of elements (e.g. sulfur (S), lead (Pb) and tin (Sn).
So, as always it is essential to know the composition of a sample in order to select the correct crucible.
|The more iridium that is added to the platinum the stronger the crucible and the more resistant it is to thermal corrosion. |
Platinum crucibles with 10 percent iridium have a melting point of nearly 1790 degrees Celsius.
|Stabilized platinum||Stabilized crucibles and casting dishes have zirconium dioxide (ZrO2) added, indicated by the abbreviation XRS (X-Ray Stabilized). |
The platinum (or platinum-gold alloy) is effectively hardened and as such these crucibles have a higher base strength with improved resistance to contamination or deformation.
They are especially suited to fusion processes.
IAM Drijfhout can provide the following general recommendations. However it is important that you take your specific process, limitations and sample compositions into consideration.
During the fusion processes of x-ray fluorescence (XRF) and inductively-coupled plasma (ICP) analysis, temperatures can reach up to 1250 °C. The material of the crucible needs to be able to withstand the maximum temperature as well as the ramp rate. Precision crucibles with high thermodynamic stability need to be made of a material that will prevent cross-reactivity with the samples. This is because contaminants will be detected at the sub parts per million (ppm) level.
Platinum and platinum alloys are an industry standard for crucibles in sample fusion, ensuring that high-purity, homogenous samples can be prepared for XRF and ICP analysis. In almost all cases, a platinum-gold alloy is the most suited (PtAu5%). In certain exceptional situations platinum-iridium may be the better choice.
In fusions at higher temperatures, PtAu5% is also the industry standard, and occasionally the stabilized version is chosen: PtAu5%XRS. There are, however, high temperature fusions where crucibles made of platinum-rhodium alloys (PtRh10% or 20%) may also be an option. An example is the glass industry where there are no highly contaminated samples. In the petrochemical industry PtRh10% or PtIr3% might sometimes be chosen for high temperature fusions.
During ashing, organic substances are incinerated. The most suitable crucible for this process is a gold-platinum alloy. The reason is that ashing takes place at a lower temperature and this alloy has the best resistance to organic matter. Alternatives, depending on the sample composition, could be platinum, platinum-iridium and platinum-rhodium crucibles.
Platinum and platinum-iridium dishes (or low-profile crucibles) are used for evaporation and concentrating processes. The dishes are wider than they are high, allowing a large surface area for the uniform heating and evaporation of the sample. A practical example would be to evaporate hydrogen fluid (HF) and carbon compounds at approximately 800 °C.
Platinum-iridium is a unique low temperature alloy in that it is completely resistant to all acids and alkalis. However, at temperatures above 1100 °C it will start evaporating and thus losing weight and stability. Platinum-iridium crucibles are useful in the chemical industry.
In electroanalysis, either platinum or platinum-iridium crucibles are the most suited.
For thermal analytical measurements the most suitable crucibles are platinum or platinum-rhodium (PtRh10% and 20%).
The GCS series of crucibles (mostly platinum and PtAu5%) are widely known and used, starting at a volume of 2.5ml. Specific types that are commonly chosen include:
|Crucibles product code|
|Platinum||GCS25, GCS30, GCS50, GCS100 and GCS120|
|PtAu5%||GCS30, GCS35, GCS40 and GCS60|
For each of these particular types, IAM Drijfhout can supply a range of sizes to ensure that our clients have the correct volume for their application.
The GD-series of evaporation dishes are popular in pure platinum, PtAu5% and PtRh10%. The following types are popular:
|Dishes product code|
|Platinum||GD50, GD60, GD75 and GD100|
|PtAu5%||GD40, GD60, GD75, GD100, GD125 and GD150|
|PtRh10%||GD125 is mainly used|
Evaporating dishes can be ordered in a variety of sizes to meet the volume requirements of our customers.
IAM Drijfhout has more than 100 different standard crucibles with a wide range of options in shape and volume. Our team of experts are on hand to answer any question you might have and to advise you on the best crucible or dish for your analysis.