GASES IN METALS 



193 



Vacuum Melting 



Apparatus and Method 



In order simply to prepare metals as gas-free as possible, at Bell 

 Telephone Laboratories a special vacuum furnace was devised and 

 constructed which has been extremely satisfactory and helpful in 

 studying the effects of gases on the properties of metals. A schematic 

 diagram of this furneice is shown in Fig. 4. The metal to be melted 



ALUNOUM BOAT 

 NORTON CO. N0.11889 ALUNDUM THIMBLE 



NORTON CO. N0.6945 



MC LEGO 

 GAUGE 



LEADS TO 



HIGH 



FREOUENCY 



CONVERTER 



Fig. 4 — Furnace for melting metals in high vacuum. 



is contained in an alundum boat which is placed horizontally in an 

 alundum thimble. The alundum thimble acts as a radiation shield 

 and is supported concentrically on alundum cradles in a horizontal 

 pyrex glass tube. The metal is heated inductively by high frequency 

 currents supplied by a 35 KVA Ajax Northrup converter. 



After the furnace is charged, the pyrex tube is sealed off with an 

 oxygen hand torch, and is baked out at 450° C. by a nichrome wound 

 furnace, the position of which is interchangeable with that of the high 

 frequency induction coil. The pyrex tube is baked out for several 

 hours so that subsequent heating by radiation from the melted metal 

 causes no appreciable evolution of gas. 



The gases given up by the liquid metal are pumped out of the 

 system by a four stage Gaede mercury diffusion pump backed by an 

 oil pump. A liquid air trap prevents mercury vapor from entering 



