238 



UNITED STATES MINERAL RESOURCES 



ents. The varied concentration of these byproduct 

 materials in their primary ores is significant, al- 

 though it is secondary in importance to the tech- 

 nology employed in processing the primary materi- 

 als, inasmuch as the technology is what determines 

 whether the initial gallium, germanium, and indium 

 contents are concentrated or dissipated. 



The principal physical and chemical properties of 

 the three elements are listed in table 45. Gallium is 

 notable for its low melting point and long liquid 

 range and its expansion upon solidifying. Germanium 

 also expands upon solidifying but is more notable for 

 its high electrical resistivity in ultrapure form. In- 

 dium also melts at a low temperature but is notable 

 for its softness and malleability. 



Table 45. — Selected properties of gallium, germanium, and 

 indium. 



PRINCIPAL USES 



The principal uses for gallium, germanium, and 

 indium are as ingredients in transistors, diodes, and 

 rectifiers, which are basic electronic components 

 used in a wide variety of communications and con- 

 trol systems. The importance of these tiny devices 

 in modern technology is difficult to overestimate — 

 they perform the functions that formerly required 

 vacuum tubes, but they do so with greater reliabil- 

 ity, very small power consumption, negligible heat 

 loss, extended durability, ruggedness, and compact- 

 ness. Without these so-called solid state devices, the 

 present generation of large computers would not 

 have been feasible, because of the space, power re- 

 quirements, and heat generated by an equivalent 

 number of vacuum tubes. The amount of gallium, 

 germanium, or indium used in each individual tran- 

 sistor or diode is quite small, but the very large 

 number of such devices now being manufactured 



provides a significant market for these little-known 

 materials. 



Gallium, in addition to being used in these semi- 

 conductor devices, is used to modify other semi- 

 conductor materials, to form leads for transistor 

 connections, and to provide a device that emits visi- 

 ble light as an indicator in various instruments. As 

 an alloying ingredient, gallium forms a number of 

 low-melting alloys of potential use. It also has 

 potential application as a catalyst and in fluorescent 

 materials. 



Germanium is used dominantly in single-crystal 

 high-purity form in the manufacture of transistors, 

 diodes, and rectifiers. A typical transistor contains 

 a wafer of germanium alloy 4 square millimeters in 

 area and about 0.2 millimeters thick, whereas a 

 diode is only about one-fourth as large, and rectifier 

 crystals may be much larger. The weight of a tran- 

 sistor wafer is a few thousandths of a gram. In addi- 

 tion to major applications in communications and 

 computers, germanium semiconductor devices have 

 considerable use in nuclear radiation detection in- 

 struments. Germanium also is used in infrared equip- 

 ment and in special optical glass. As an alloying 

 ingredient, it increases hardness and improves roll- 

 ing properties in alloys with copper, aluminum, and 

 magnesium. It is used in gold solders and in jewelry 

 manufacture. It is a constituent in several phos- 

 phors and has been used as a catalyst in polyester 

 textile manufacturing. 



Indium is used as a desired impurity in german- 

 ium and silicon transistors, as a solder for tran- 

 sistor leads, and in the fabrication of transistors, 

 thermistors, and optical devices. It has been used 

 in low-melting alloys and as a bearing alloy. It is 

 used as a gasket material in aerospace hardware, 

 as a sealant for glass-to-metal and glass-to-glass 

 joints, in dental alloys, and in jewelry and silver- 

 ware alloys to keep metals bright. Proposed uses 

 include colorants for glass and as catalysts in 

 petroleum refining. 



ALTERNATE MATERIALS 



Silicon in high-purity form is an alternate and 

 less expensive material that competes extensively 

 with germanium in the fabrication of transistors 

 and diodes, and selenium and tellurium are used in 

 rectifiers. Gallium, germanium, and indium can be 

 used to some extent in substitution each for the 

 other material. The specific characteristics of each, 

 however, are unique in some applications, and there- 

 fore, complete substitution is not likely. 



