sinter烧结的意思是?

文章中合成磷酸钒钠，煅烧步骤描述为A was first sintered at 350 °C for 4 h and then annealed at 700 °C for 4 h in Ar/H2 (95%:5%) with the heating rate of 5 °C min-1. 请问sintered at 350 °C for 4 h这一步也是在氩氢混合气中还是在空气中进行？