| 摘要 |
<PICT:1087205/C6-C7/1> In the vacuum deposition of aluminium on a surface such as an electric lamp reflector, the aluminium is located in an inert refractory crucible comprising at least 25% boron nitride which is bonded to a refractory metal strip such as Ta, W or Mo and the aluminium is flash evaporated by rapid resistance heating of the metal strip. The evaporator comprises a Ta, W or Mo strip 22 bonded to a refractory crucible 20 comprising 50% boron nitride and 50% titanium diboride by an aluminium strip (24), the assembly being clamped together and heated to 1200 DEG -1600 DEG C. under vacuum or argon. The crucible has a central depression (38) and outer grooves (40) Figs. 2-7 (not shown). In a modified form the metal strip is bonded to slots on either side of the crucible Figs. 8 and 9 (not shown). A further embodiment Fig. 10 (not shown) comprises a stack of boron nitride annular shaped members on a boron nitride disc with a Mo spacer between each member and aluminium spacers between the Mo and the ceramic. The evaporating apparatus shown in Fig. 11 comprises an annular member 57 with the rim of the lamp reflectors abutting the sealing gaskets 58 positioned about the periphery. The evaporator 36 is held between a fixed member 64 and a spring-loaded member 66 and is held under tension by spring 68. The aluminium source is placed in the crucible 20 in strip form and after evacuation the Mo strip 22 is resistance heated to 1500 DEG C. to flash evaporate the aluminium. The Mo strip is held under tension during heating and cooling. In an alternative arrangement the aluminium is first melted in the crucible to wet and impregnate the crucible prior to its insertion in the evaporating apparatus 57. |
