There are increasing demands on engineering materials to operate at higher temperatures, with improved corrosion resistance and greater strength. Such demands have been a driving force behind the Research & Development work throughout Johnson Matthey, leading to a range of products that seek to impart the properties of precious metals to non-precious substrates.
In 1993 Johnson Matthey launched ACT™, The Advanced Coatings Technology, a novel technique for depositing a thin layer of platinum onto a range of ceramic substrates.
ACT™ coatings are used primarily in the glass industry. They provide unparalleled corrosion resistance, extending the service life of glass-contact ceramics and enhancing process control.
ACT™ users do not fall into one category of glass manufacture. Coatings are supplied to all spheres of the industry, including lead crystal, borosilicate, container and float glass.
More established products include ACT™ coated thermocouples and feeder consumables such as orifice rings, plungers, spout bowls and tubes.
Johnson Matthey also offers coatings on large ceramic components such as danner mandrels, tweels and furnace blocks. It is expensive and time-consuming to change these parts, so any extension in service life can bring considerable technical and financial benefits.
Coatings on AZS/ fusion cast ceramics for areas such as the throat or glass/metal line are of particular interest to many glass manufacturers as they offer an opportunity to extend furnace campaigns by a number of years. Increasing numbers of furnaces are now being protected in this manner and the benefits of the ACT™ coated throat and channel blocks have been, and continue to be, successfully demonstrated.
Ceramic Specification
Surface finish and cleanliness of ceramic substrates have been identified as key parameters affecting the success of the ACT™ coating process.
All ceramic parts are inspected upon receipt. Where possible we ask that the following criteria be met:
1. Surface completely clean over area to be coated
2. No finger prints over area to be coated
3. No greasy marks over area to be coated
4. No pencil/pen/ink/crayon marks over area to be coated
5. No sellotape/masking tape marks over area to be coated
6. No stains over area to be coated
7. No metallic spots over area to be coated
8. No surface cracks in the area to be coated, with a crack width greater than 0.25mm
We prefer to coat ceramic articles with a minimal amount of surface porosity, but we recognise that this is difficult to achieve with slip-cast or bonded ceramics.
If the item to be coated is taken from stock, we recommend that all of the available parts are evaluated against the above criteria so that the optimum part is sent for coating. If possible we prefer to receive two parts so that there is one spare.
Failure to fulfil these requirements will result in further preparation work being carried out by Johnson Matthey prior to ACT™ coating, which may lead to a subsequent delay in the delivery of a coated item.
In order to coat fusion cast AZS ceramics at least 4mm should be machined from the as-cast surface. All areas to be coated undergo a form of surface preparation, which guarantees perfect adhesion if the surfaces have been machined. We are currently unable to guarantee this level of adhesion on as-cast surfaces, although this situation may change in the future.
Please ensure that all ceramic parts are adequately packed prior to their dispatch. Approximately 25% of the ceramics sent to Johnson Matthey for coating arrives broken due to poor packing. We recommend that the ceramic is packed in double-thick cardboard or wooden boxes and protected from physical damage through the use of plenty of bubble wrap or alternative packing materials.
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