Cold spray (CS) deposition of a durable silver coating with high infrared reflectivity for radiation energy saving in the polysilicon CVD reactor

The radiative energy loss accounts for roughly 70% of the energy loss in the polysilicon chemical vapor deposition (CVD) reactors and therefore takes up to about 25% cost in the production of polysilicon used for solar cells. In this work, cold spray (CS) process was used to deposit Ag coating with ultra-high infrared reflectance on inner wall of the CVD reactor to minimize the radiative losses. To solve the bond strength problem of depositing soft coatings on hard substrate by CS, a Ni buffer layer with medium hardness was introduced. Results show that Ag coating can be successfully deposited with a porosity lower than 0.1%. Even the as-sprayed Ag coating has a high near-infrared reflectivity of 92% which was much higher than that of a well-polished substrate surface (65%) suggesting an excellent radiation energy saving capacity. The bond strength of the Ag coating is significantly increased from 3.7 MPa to 35.4 MPa and the thermal shock resistance is improved from 22 ± 3 to over 150 cycles by the Ni buffer layer. The scientific methodology demonstrated here can be a cost effective approach to reduce the radiation energy losses in the polysilicon-CVD industry.