The BZX79C18 from Micro Commercial Components is a Zener Diode with Zener Voltage 16.8 to 19.1 V, Zener Current 1 mA, Voltage Forward 0.9 V, Current 5 mA, Current Reverse Reverse Leakage Current:- 0.05 uA. More details for BZX79C18 can be seen below.