Turbine rotor units and method of producing the same

A turbine rotor unit comprising:

• a bearing housing;
• a ceramic rotor comprising a front surface and back surface;
• a ceramic shaft integral with said back surface of said ceramic rotor, said ceramic shaft having an outer peripheral surface;
• a metal shaft having a first longitudinal end, a hollow cylindrical portion with a first inside peripheral surface and second inside peripheral surface, said first inside peripheral surface having a diameter which is larger than an inside diameter of said second inside peripheral surface, said first inside peripheral surface being located closer to said back surface of said ceramic rotor than said second inside peripheral surface, a second portion of said outer peripheral surface of said ceramic shaft being fixed to said metal shaft at said second inner peripheral surface, thereby forming a contact surface area between said metal shaft and said ceramic shaft, such that a longitudinally extending radial gap exists between a first portion of said outer peripheral surface of said ceramic shaft and said first inside peripheral surface, wherein a portion of said longitudinal extending radial gap is located between two bearing members within said bearing housing, and said contact surface area is located completely within said bearing housing.