The thermophysical properties of arc plasma are essential for setting up physical model of a gas sealed relay. In order to obtain the thermophysical data of N

2

-Ag arc plasmas in the condition that temperature ranges from 300 to 20 000 K

pressure is 0.1

0.4

0.8 and 1.0 MPa

and proportion of Ag vapor is 1%

10% and 50%

respec-tively

the thermodynamic properties of N

2

-Ag arc plasmas are calculated using Gibbs free energy minimization. New potential model is adopted to calculate collision integrals of N

2

-Ag arc plasmas

thus the trans-port properties are determined. Emphasis is put o

n the evolution of thermophysical properties under different pres-sures and silver vapor proportions. The results indicate that increasing pressure can suppress the decomposition re-action and ion-ization reaction in arc plasmas. When the proportion of Ag vapor reaches 50%

it has a significant impact on the thermophysical properties. The data obtained in this study are validated by literatures

so they can be applied to modelling and simulation of arc plasma in gas sealed relay with silver contacts.