Minor nitpick: diamond is only metastable, especially at high temperatures. It will slowly turn to graphite. After sufficient space travel, all diamond parts will be graphite parts.
Actually, no! The activation energy for the conversion of diamond to graphite is about 540 kJ/mol, and using the Arrhenius equation to get the rate constant for diamond-graphite conversion, with a radiator temperature of 1900 K, we get that after 10,000 years of continuous operation, 99.95% of the diamond will still be diamond. At room temperature, the diamond-to-carbon conversion rate is slow enough that protons will decay before any appreciable amount of graphite is made.
Even for a 100,000 year burn, 99.5% of the diamond will still be intact at 1900 K.
There isn’t much room to ramp up the temperature, though. We can stick to around 99%+ of the diamond being intact up to around 2100 K, but 2200 K has 5% of the diamond converting, 2300 K has 15% converting, 2400K has 45%, and it’s 80 and 99% conversion of diamond into graphite over 10,000 years for 2500 K and 2600 K respectively.
Minor nitpick: diamond is only metastable, especially at high temperatures. It will slowly turn to graphite. After sufficient space travel, all diamond parts will be graphite parts.
Actually, no! The activation energy for the conversion of diamond to graphite is about 540 kJ/mol, and using the Arrhenius equation to get the rate constant for diamond-graphite conversion, with a radiator temperature of 1900 K, we get that after 10,000 years of continuous operation, 99.95% of the diamond will still be diamond. At room temperature, the diamond-to-carbon conversion rate is slow enough that protons will decay before any appreciable amount of graphite is made.
Even for a 100,000 year burn, 99.5% of the diamond will still be intact at 1900 K.
There isn’t much room to ramp up the temperature, though. We can stick to around 99%+ of the diamond being intact up to around 2100 K, but 2200 K has 5% of the diamond converting, 2300 K has 15% converting, 2400K has 45%, and it’s 80 and 99% conversion of diamond into graphite over 10,000 years for 2500 K and 2600 K respectively.