Start heating sodium metal in a ceramic crucible until it ignites, start a slow stream of oxygen and place lid on top of the crucible. Care must be taken care to not overheat the mixture, sodium peroxide will decompose if heated above 600°C. When the burning stops cool the product down and seal in an airtight container.
4Na + O2 = 2Na2O
2Na2O + O2 = 2Na2O2
The sodium ignited, start slow oxygen flow
Addition of oxygen with lid on the reaction should look like this
When the peroxide mixture is still hot some gray oxides are present
After cooling down there is crude sodium peroxide in the beaker