Hello to all
I am investigating about metallic rod coating with glass. The thermal expansion of metal and glass are equal approximately. What's your idea about a tight and sticky coating?
Thanks for your assistance
You assume that the thermal expansion of metal and glass are approximately equal - is that for the metal and glass you are investigating or a general assumption? Normally the CTEs are very different and this causes cracking during cooling.
Hi Saad,
That sounds cool. My PhD focus was on bulk glass, not coatings, but I find the topic of glass coatings interesting enough to do some side reading on. A common approach to applying glass coatings seems to be suspending a frit in a low-viscosity medium, air spraying it onto the substrate, dehydrating and then baking it. I'm not sure if you are familiar with this approach and I can share some of what I found if you aren't.
A few general concerns with applying a glass coating seem to involve the melting temperature of the glass and (especially for high temperature applications) the coating's reactive or crystallization tendencies with the substrate. Even if you know that the CTE of substrate matches the glass prior to coating, that might not be the case for the composite material, especially after prolonged use.[1] While thinking about structure from a glass chemistry perspective might help somewhat in selecting compositions and thinking about this issue, predicting melting temperatures and crystallization in these complex multi-component systems appears challenging since you aren't going to get a phase diagram for a 6+ component system.
That said, here's a cool coating success [2]. Note that the glass coatings academic research seem concentrated in thermal barrier coatings for high temperature applications- correct me if I'm wrong as I may be only seeming the most visible research; I recommend checking out patent literature for other applications.
[1] Wang, Xin, et al. "Effect of YSZ-incorporated glass-based composite coating on oxidation behavior of K438G superalloy at 1000° C." Journal of the European Ceramic Society 37.3 (2017): 1013-1022.
[2] Liu, Peng, et al. "Protecting stainless steel by glass coating during slab reheating." Surface and Coatings Technology 205.12 (2011): 3582-3587.
Technology of enamelling has been known since ancient times. For various metals and alloys there are already finished enamels (glasses with suitable thermal expansion) and parameters of the firing. Look in old books about enameling or ask an enamel company for your metal matching enamel.
You could try using Sol-Gel methods to get the coating. There is a lot of literature available on the technique.
Hi to all
Thank you very much for your contributions. My goal of this coating is to protect the metal rod against chemical corrosion in high temperature (about 1300 degree of centigrade) raised from molten glass.
So I should use borosilicate glass which has high temperature melting point.
It will be very useful if you share your idea about this matter.
Thanks a lot
There are no layers that protect against glass melting in air at 1300°C. In the protective gas molybdenum rod would be suitable, but in air such a rod can only be produced from platinum.
Just as Vadim stated, this is to the best of my understanding an area of active research. Look up environmental barrier coatings or thermal barrier coatings. A lot of that work is being done to create better coatings for turbine blades.
Also, glasses aren't the only protective option, as illustrated in the following article:
Zhu, Ming, Meishuan Li, and Yanchun Zhou. "Oxidation resistance of Cr 1− x Al x N (0.18≤ x≤ 0.47) coatings on K38G superalloy at 1000–1100 C in air." Surface and Coatings Technology 201, no. 6 (2006): 2878-2886.
Edited to add one additional review reference: Clarke, D. R., and C. G. Levi. "Materials design for the next generation thermal barrier coatings." Annual Review of Materials Research 33, no. 1 (2003): 383-417.
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