CTE Measurement - How To
03-15-2021, 04:37 PM,
#1
Question  CTE Measurement - How To
Hi,

We are currently trying to evaluate CTE for different ceramic top coats with various spraying parameter.

How is it normal to measure CTE for coatings?

Best Regards,
EmilAV
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05-02-2021, 11:32 AM,
#2
RE: CTE Measurement - How To
Hi EmilAV
Behavior of metal oxides as sprayed are different about full ceramics pieces. In which is possible to have CTE, but the Coefficient of Thermal Expansion on metallic oxides sprayed, changes with systems, parameters, gun in use, this because porosity of the coating has different porosities, so it isn’t standard, you could do a valuation piece by piece, measuring it directly while change the temperature
Best regards
Luigi
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05-05-2021, 10:12 AM,
#3
RE: CTE Measurement - How To
Thank for the reply Luigi,

I have some problems understanding the numbers supplied by powder manufacturers. For myself, I have done some powder pellets and done dilatometry analysis (DIL). Intuitively, I am perfectly clear that these values probably doesn't represent the actual coatings. CTE in a coatings should also be an anisotropic in thermal spray coatings. Normally and parallel to the surface should be different due to the nature of the build up. Therefore, I seek methods of measuring the relevant behaviour. It would also be interesting to understand numbers presented by the powder suppliers.
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05-05-2021, 10:46 AM, (This post was last modified: 05-05-2021, 10:48 AM by Vadim Verlotski.)
#4
RE: CTE Measurement - How To
(05-05-2021, 10:12 AM)EmilAV Wrote: Thank for the reply Luigi,

I have some problems understanding the numbers supplied by powder manufacturers. For myself, I have done some powder pellets and done dilatometry analysis (DIL). Intuitively, I am perfectly clear that these values probably doesn't represent the actual coatings. CTE in a coatings should also be an anisotropic in thermal spray coatings. Normally and parallel to the surface should be different due to the nature of the build up. Therefore, I seek methods of measuring the relevant behaviour. It would also be interesting to understand numbers presented by the powder suppliers.

Hi Emil,
Dense ceramic made from YSZ has a coefficient of thermal expansion of approx. 10.8x10-6K-1. Theoretically, the plasma-sprayed coating has a similar value, but because of the crack network, the term "thermal expansion coefficient" loses its meaning. Since the coating is connected to a certain solid substrate, it moves together with the substrate and shows a coefficient of thermal expansion of the substrate to the outside.
In short: ceramic layers with a network of cracks adapt to the deformation of the substrate, provided that the substrate has a higher theoretical coefficient of thermal expansion.
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05-05-2021, 03:25 PM, (This post was last modified: 05-05-2021, 03:26 PM by EmilAV.)
#5
RE: CTE Measurement - How To
Thank you Dr. Verlotski for your reply.

I understand your point regarding networks of cracks. The substrate being key to the key driver for the global deformation/expansion is for me quite clear. As you mention, as long as it is not the other way around. However, my interest in these numbers is based on the urge to understand and quantify the mismatch between different substrate and dense ceramic HVOF coatings where cracking would be a limitation to the actual application. The best approach I can come up with today would be spraying extremely thick coatings and isolate them from the substrate to perfrom DIL on small pieces of pure coating.
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05-05-2021, 04:33 PM, (This post was last modified: 05-05-2021, 05:03 PM by Vadim Verlotski.)
#6
RE: CTE Measurement - How To
(05-05-2021, 03:25 PM)EmilAV Wrote: Thank you Dr. Verlotski for your reply.

I understand your point regarding networks of cracks. The substrate being key to the key driver for the global deformation/expansion is for me quite clear. As you mention, as long as it is not the other way around. However, my interest in these numbers is based on the urge to understand and quantify the mismatch between different substrate and dense ceramic HVOF coatings where cracking would be a limitation to the actual application. The best approach I can come up with today would be spraying extremely thick coatings and isolate them from the substrate to perfrom DIL on small pieces of pure coating.

Your reasoning is absolutely correct. To determine the CTE of the coating, it must be sprayed with a thick layer (more than 2 mm) on a soft metal substrate, and then saw off the substrate from the coating. A standard beam must be cut out of the sawn-off coating, which is suitable for measuring with a dilatometer. I myself made such polished beams, 30x2x2 mm in size, cut from thick coatings sprayed onto an aluminum substrate.
By the way, by cutting out beams from the coating, you can determine not only the CTE, but also the modulus of elasticity of the coating, as well as its bending strength.


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10-20-2022, 05:00 AM,
#7
RE: CTE Measurement - How To
Coatings are materials applied to surfaces to improve their appearance or protect them from the elements. Accordingly, it's essential to measure CTE (carbon concentration) regularly to ensure that the coatings perform as expected.
CTE is an important metric because it helps you determine if your coatings are degrading over time and whether they need to be replaced sooner rather than later. By knowing the carbon concentration of your coating materials, you can make informed decisions about how best to maintain them and what changes may be necessary over time.
Another reason why measuring CTE is essential is that it can help identify potential health risks associated with using these materials. For instance, high levels of CTE might indicate exposure to harmful substances such as lead or other toxic metals.
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10-20-2022, 01:08 PM,
#8
RE: CTE Measurement - How To
CTE means Coefficient of Thermal Expansion.
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10-28-2022, 09:36 AM,
#9
RE: CTE Measurement - How To
There are many potential reasons to measure CTE for coatings, including risk assessment, regulatory compliance, and improving quality control. Many companies use CTE to assess the long-term health risks posed by their products. This is done by measuring how much CTE was present in the brain of test subjects who died from causes related or unrelated to coatings exposure.
CTE can be measured using various methods, but typically it involves injecting epoxy resin into rats' brains and then taking tissue samples for analysis years later. The amount of CTE in these samples can help calculate the exposure level that these test subjects experienced over their lifetime.
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