Dear Shahin Khademinia , what you are looking for is so-called "Deoxidation" and is widely employed in melting and purification of copper metal. More explicitly, deoxidation involves addition of a solid or gaseous material to the cruicible in order to avoid oxide formation during the annealing process. In particular, you can purge the crucible either with an inert gas like Argon or Nitrogen, or with a reducing gas like carbon monoxide, hydrocarbons (methane, ethane, etc.), ammonia, nitrogen/hydrogen mixture to eliminate oxygen molecules from the environment. Besides, as I said, you can also deoxidize copper using some solid reducing agents comprising phosphorous, boron, lithium, aluminium, magnesium, calcium boride and even zinc. However, it must be noted that an optimized amount of these reducing agents must be exploited, otherwise the excess reagent will affect the quality of copper. Despite all this, when it comes to me, I prefer to melt the copper powder in a vacuum furnace or a controlled-atmosphere furnace purged with N2 or Ar. Another point worth mentioning is that you can melt copper in the air atmosphere and then, take advantage of electropolishing to remove the oxide layer and get a shiny copper surface. Attached you can find a few articles concerning deoxidation and electropolishing of copper metal. Below you may also find the link of Industrial Electrochemistry book from Prof. Derek Pletcher which is a quite well-known and useful resource for such electrochemical processes.

Article Surface State of Sacrificial Copper Electrode by Electropoli...

https://www.springer.com/gp/book/9780751401486 Best,

There are several ways, depending on your hardware budget:

از خلا استفاده کن تا از اکسید شدن جلوگیری بشه

یا نهایتا میتونی ذرات اکسید شده رو توی کوره تحت گاز هیدروژن احیا کنی

I agree with what Vadim Verlotski and Mahdi Ghamsari,

Methods to avoid oxidation of Cu during melting are by creating a protective medium. One approach is through a vacuum medium of Ar or N2 in a vacuum furnace. Mesh can be with electric resistance heaters or through a high frequency and current inductor. Another approach is to create a protective cloud of Ar or N2. This approach for melting powder particles is more inappropriate due to the loss of metal dust.

As far as my knowledge allows me to, in actual industrial application like what I have faced in copper tube manufacturing process, for a molten copper and continous casting machine line, regard to economical terms, nitrogen is commonly used.

Dear Shahin Khademinia;

you can sinter copper powder at a temperature above the melting point of copper (​1083°C), details in the reference ;

https://www.hoganas.com/globalassets/download-media/sharepoint/handbooks---all-documents/handbook-2_production_of_sintered_components_december_2013_0675hog_interactive.pdf