For different purposes, molten metals will be in contact with a ceramic material. For example a furnace nozzle guides the melt flow to the mold is usually made from a thermo-chemical resistant ceramic.
- However, in the case of Mg metal, chemical reactions and temperature drop are very fast.
- Beside, mechanical strength and elongation must be high enough to suffer mechanical shocks.
- Moreover, machinability and density of a ceramic material must be good enough to form in the desired shape.
I will highly appreciate if you let me know your answers and reasons in this regard.
#Magnesium
#Oxidation
#Flamability
#
Best regards,
Aluminum titanate ceramic can be very useful for the application:
https://www.ceramtec-industrial.com/en/materials/aluminum-titanate
I think highly dense Yttria stabilized zirconia ceramic nozzle can do the job, but you should know the art and technology for preparing a fine noozzle
Many thanks every one? How about CaO? Actually Mg+CaO=Ca+MgO is a thermodynamically not favorable reaction. Therefor CaO must be inactive facing Mg melt.
In a purely chemical sense, you are right, ceramics from calcium oxide do not react with metallic magnesium. However, in addition to the chemical aspect, there is also an engineering one, in which calcium oxide ceramics look not so good at all. The fact is that ceramics for metal melting and pouring must be a subject to high thermal shock resistance, mechanical strength, stability in a humid atmosphere, and realistic product manufacturing technology. In all these parameters, ceramics from calcium oxide are catastrophically inferior to ceramics from aluminum titanate. Suffice it to say that products made of calcium oxide crumble already during storage, simply from prolonged contact with a humid atmosphere (water from the air contributes to the formation of loose calcium hydroxide from dense calcium oxide). In addition, calcium oxide refractories are very sensitive to rapid heat changes, which limits their use to the lining of continuous metallurgical furnaces.
In conclusion, I want to note that you need not worry so much about a possible chemical reaction between the magnesium melt and ceramics. The fact is that the melting point of magnesium is only 650 ° C, and this is not enough for the reduction reaction of such oxides as aluminum oxide and titanium oxide. Most likely, even compact silicon oxide will not significantly react with magnesium melt at these temperatures. For this reason, by the way, quartz glass is a very interesting material for pouring magnesium melt.
CaO can be more stable than MgO in the Mg melt. It depends on the composition and the temperature whether CaO or MgO is thermodynamically more stable. Therefore, it is not advisable to use CaO as a Cruise, in addition to Vadim Verlotski explanations.
CALPHAD
https://www.researchgate.net/publication/322233671_The_Mg-Ca-O_system_Thermodynamic_analysis_of_oxide_data_and_meltingsolidification_of_Mg_alloys_with_added_CaO?_sg%5B0%5D=xoWNujAtzQLb-hMT3dAZY1A7Dzo71eEZDnFqRKQGbgMGfCX-FaI08YGwCE5BrGb2jWipGViYU1xtAwg.-so8SreOWH6S4APPadrP9iPZvLT3sNjL5qWu7C8YE5bgm63BLjZI3vt40ApMXN7unXzc0Knz03QcewT8WKWIfA&_sg%5B1%5D=J5oY9roSDB1UAEhTM0We3diK0-dL_XUCr3Rc4Uk4JzcRzUsM-ZMPYvWyrFAmpGYuYLklYSQs9YIeA6wVZ1gCwK_TYaQ.-so8SreOWH6S4APPadrP9iPZvLT3sNjL5qWu7C8YE5bgm63BLjZI3vt40ApMXN7unXzc0Knz03QcewT8WKWIfA&_sg%5B2%5D=sh9VWsALtmIJgWS7Iz9TiCOkcNN318CSNOzhJ7ALwSWSEEMPbvAYfBqZb5eq7zL0jemswxdlLs4FD61MSQ.-so8SreOWH6S4APPadrP9iPZvLT3sNjL5qWu7C8YE5bgm63BLjZI3vt40ApMXN7unXzc0Knz03QcewT8WKWIfA&_sgd%5Bpc%5D=1
EXPERIMENT
https://www.researchgate.net/publication/316488230_The_Effect_of_CaO_on_Magnesium_and_Magnesium_Calcium_Alloys?_sg%5B0%5D=tZe0yYGMFDcAK3nSY5lR7KuBn1ZhtH58UuAJXTOj3509FOPczfBHgI5sU2yjcHH0uaFNt4tbp2f5UZcimuU_lGNTwfZWK-nAS3ZSTYmA.ODHr515-mvsm4rBvW0kBjs9vsPyR_79uJB_hFbyhDesw3ewszrmtT9VtqP223HFqG-XYfuY-02R4oJTbgIHzZQ
https://www.researchgate.net/publication/265853895_CaO_dissolution_during_melting_and_solidification_of_a_Mg-10_wt_CaO_alloy_detected_with_in_situ_synchrotron_radiation_diffraction?_sg%5B0%5D=tZe0yYGMFDcAK3nSY5lR7KuBn1ZhtH58UuAJXTOj3509FOPczfBHgI5sU2yjcHH0uaFNt4tbp2f5UZcimuU_lGNTwfZWK-nAS3ZSTYmA.ODHr515-mvsm4rBvW0kBjs9vsPyR_79uJB_hFbyhDesw3ewszrmtT9VtqP223HFqG-XYfuY-02R4oJTbgIHzZQ
Dear Björn Wiese
Many thanks for the informative articles,
You are right CaO is stable. I think, in order to make a nozzle, I must look for stable and passive material. Definitely it is not reactive exposing to the hot (melt) Mg. So it seems it must be a good option.
I have seen some refractory board of CaO+SiO2. I thought they must be useful. Isn't it?
Dear Ahmad Bahmani
I agree with Björn Wiese.
But beware that Shae Kwang Kim strongly believes that the dissolution of some oxides, including what you have mentioned, occurs in molten Mg. You can have a look at his papers and patents, and also followings:
Article Non-ignitable dilute Mg-0.36Al-1CaO (wt.%) alloy with high c...
Article Mg-Ca Alloys Produced by Reduction of CaO: Understanding of ...
However, I'm not sure about the kinetics of the reaction and whether it can affect your alloy whithin a short casting period. It is just a clue to stimulate you to further research on this. I hope it can help.
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