Rhenium is number 75 on the periodic table with a density of 21.02 gm/cc and a melting point of 3180°C. It is second only to tungsten in melting temperature and to Osmium in density.

Rhenium is rare, expensive, and extremely difficult to machine. Availability in size and shape is very limited. It is most commonly used as an alloying agent to improve the properties of other metals (mostly refractory metals).

Rhenium has several unique properties that are also imparted to its alloys. One of the most important of these is its high melting point of 3180°C. This is second only to tungsten. The high melting point, coupled with its ability to maintain ductility even after recrystallization, offers many advantages.

Rhenium also offers high electrical resistivity over a wide temperature range. The resistivity is higher than tungsten. This characteristic, plus having a low vapor pressure, make it a good choice for filaments. This is especially true when considering ductility and the fact that it is not affected by the oxidation/reduction cycle as is tungsten.

Rhenium has several unique properties that are highly desirable:

• a very high melting temperature
• extreme resistance to chemical reactivity
• ability to maintain ductility after recrystallization
• high electrical resistivity over a wide temperature range
• low vapor pressure
• resistance to oxidation at very high temperatures
• good shock resistance
• low friction

These properties can be transferred to other metals with which it is alloyed. As a result, it is used to alloy with molybdenum and tungsten to improve on their properties.

One of rhenium's major uses is as a catalyst in the crack distillation of petroleum products. Another common use is as filaments in mass spectrometers. Rhenium is available in 99.97 (commercial) purity and 99.995 (zone refined) purity. These purity levels become most important in the mass spectrometer industry. Use for mass spectrometer filaments is a high demand area. These are normally stocked for quick delivery in purities of both commercial (99.97%) and zone-refined (99.995%) grades.

As an alloying agent, it is used to produce 50/50 Mo/Re for use primarily in power tube parts. Its ductility (especially after recrystallization), weldability, formability, and strength all contribute to making it an ideal candidate for heat chokes, cathode stem supports, and similar parts.

Rhenium makes tungsten more ductile and machineable. Alloyed with tungsten in 3 %, 5 % and 26% content, rhenium gives stable electrical properties enabling it to be used for thermocouple wire for very high temperature thermocouples.

Rembar supplies rhenium in powder, wire, sheet and rod form. Rhenium is available only in a very limited size range: about 3" wide for foil and sheet and only up to about 1/2" diameter in rod.

In addition, rhenium is not machinable by conventional methods such as turning, milling, etc. It can be ground and EDM machined. It can also be formed and welded. Rembar will advise you on the practicality of making a part out of rhenium and, if it can be made, Rembar can make it.

When rhenium is alloyed with molybdenum or tungsten, it imparts its properties to these materials and permits a cost-effective solution. This allows the advantage of these properties at a considerably lower cost than that of pure rhenium. The alloys are available in several ratios:

• Tungsten/26 Rhenium
• Tungsten/5 Rhenium
• Tungsten/3 Rhenium
• 50/50 Molybdenum/Rhenium

Note that, although this alloy is nominally 47% rhenium, the reference to this alloy is as above.

In addition, molybdenum / rhenium sheet is available in two standard alloys with 47.5 % and 41 % rhenium. The Mo 41 % Re alloy becomes even more ductile after exposure to high temperatures because it does not develop a sigma phase.

When formed as tubing, thin-walled Mo 47.5% Re provide the advantages of high ductility and a high melting point. This alloy is used for electronics, nuclear, and space applications. Rembar specializes in seamless tubing made to specifications less than .375" O.D.. Mo 47.5% Re tubing is produced as small as.020" O.D.

These choices allow the selection of the proper alloy for a particular application while optimizing cost-effectiveness.

Molybdenum/rhenium wire remains very ductile even after high temperature exposure. Tungsten/rhenium wire is used for heating elements in high temperature furnaces, thermocouples, and in the electronics industry. This alloy's advantage is its ability to maintain greater ductility compared to tungsten after exposure to extremely high temperatures.

Physical Properties of Rhenium
PROPERTY
Atomic Weight	186.2
Density	21.02 g/CC
Melting Point	3180°C
Boiling Point	5900°C
Coefficient of Thermal Expansion (20°C)	6.5 x 10-6/°C
Electrical Resistivity (20°C)	13.5 microhms-cm
Electrical Conductivity	13.9% IACS
Specific Heat	.032 cal/g/°C
Thermal Conductivity	.39 cal/cm2/cm°C/sec