Patent ID: 8864908

Claim:
A crucible protection sheet comprising expanded graphite and being arranged between an inner crucible containing silicon and an outer crucible containing graphite, the crucible protection sheet being characterized in that: the gas permeability represented by the following equation (1) is 1.0×10 −4 cm 2 /s or less, and the compression ratio represented by the following equation (2) is 20% or higher and 74% or lower: Gas permeability = Q·L /(Δ P·A ) (1) where Q is the gas flow rate (Pa·cm 3 /s), ΔP is the pressure difference (Pa) between two chambers, A is the gas transmission area (cm 2 ) of the crucible protection sheet, which is the area of a passage that allows the two chambers to communicate with each other, and L is the thickness (cm) of the crucible protection sheet, and Compression ratio (%)=[( t 1 −t 2 )/ t 1 ]×100 (2) where t 1 is the thickness (mm) after applying a pre-load (0.686 MPa±1%) for 15 seconds, and t 2 is the thickness (mm) after applying a total pressure (34.3 MPa±1%) for 60 seconds, wherein the thickness is from 0.2 mm to 0.6 mm, wherein the bulk density is from 0.5 Mg/m 3 to 1.5 Mg/m 3 , wherein the planar thermal conductivity is 120 W/(m·K) or higher, and wherein, when the sheet in a square shape having a side of 200 mm is divided into square-shaped test regions each having a side of 25 mm and the thermal conductivity of each test region is measured, the quotient obtained by dividing the difference between the thermal conductivity of the test region having the greatest thermal conductivity and the thermal conductivity of the test region having the least thermal conductivity by the mean value of the thermal conductivities of all the test regions is restricted to be 0.1 or less.