Doped tungsten doubles the lifetime.

We use creep-resistant WVM to manufacture heaters for sapphire growth. These have more than twice the service life of conventional tungsten heaters.

WVM for sapphire growing Sapphire growth takes place at high temperatures of approximately 2100 °C. In the Kyropoulos process, rod heaters made from pure tungsten are generally used. These often have to be replaced after just a few cycles. This is due to the high level of embrittlement and deformation. This can sometimes be so extreme that the heater rods touch the shielding and cause short-circuits.

To meet the needs of single crystal growth applications, we have further developed a material that has already earned the plaudits of the lighting industry for its behavior at high temperatures. WVM: The material consists of pure tungsten with very low quantities (30-70 ppm) of potassium. The creep resistance of this material is several times better than that of pure tungsten. This capability was recently confirmed by the material's impressive performance in a sag test performed by PLANSEE's materials engineers.

Putting WVM to the test.


We simulated the use of our material at high temperatures and under various mechanical loads. The sag test proves it: WVM sags four times less than pure tungsten. The reason: The potassium leads to a more stable and coarser crystalline structure than pure tungsten. This property also has a positive influence on the material's creep resistance.


Testing conditions:
Temperature: 2100 °C, duration: 6 hours, stress in outer fiber : 22 MPa

WVM key facts
Melting point3420 °C / 3693 K
Purity99.97 %
Coefficient of thermal expansion at 20 °C4,2 · 10-6m/(m·K)
Thermal conductivity164 W/(m·K)
Electrical conductivity at 20 °C18 · 106[1/Ω·m)]


WVM in comparison with pure tungsten:

Recrystallization temperature
2000 °C at 99.99 % deformation level
Stability at high temperatures, creep resistance
Fineness of grain
Thermal conductivity
Electron work function


= similar to pure tungsten + better than pure tungsten ++ a lot better than pure tungsten

WVM heaters for sapphire growing.


Rod heaters, mesh heaters, and sheet heaters made from WVM provide excellent dimensional stability, in particular when it comes to high-temperature processes such as sapphire growth. While conventional tungsten heaters have to be replaced after just a few cycles, WVM heaters easily last for 2 to 3 times as long.

What's more, at 99.97%, the purity of WVM is the same as that of pure Plansee tungsten. And there's nothing to worry about: The potassium content in WVM is nonvolatile. As a result, the material is suitable for use in extremely sensitive high-vacuum processes in the same way as pure tungsten.


Mesh heater Sheet heater WVMW heater for sapphire growth processes


When it comes to sapphire growth, Plansee is able to offer more than just hot zones with particularly durable heaters. The company also produces the corresponding pressed-sintered tungsten crucibles. These have an ultra-smooth surface. The sapphire can be extracted without difficulty from the crucible without any damage to the crucible surface. For sapphire manufacturers, this reduces the need for the costly, time-intensive reconditioning of the crucible surface. The smooth crucible surface is less susceptible to corrosion in contact with the sapphire melt.

Another impressive characteristic of Plansee tungsten crucibles is their excellent homogeneity of high density of over 93 %. This means that they are nondeformable even at high and rapidly changing temperatures. Plansee insists on an exceptionally contaminant-free production process to ensure that only perfectly pure sapphire leaves the crucible. Every manufacturing step, from the metal powder through to the finished crucible, is performed in-house.

Precision manufacturing.


Plansee offers more than just outstanding material quality. We have more than 90 years of experience in the processing of refractory metals. Whether WVM heaters or crucibles for sapphire growth: We will manufacture your product to your precise specifications.

More products for high-temperature processes.


Heaters are not the only WVM products in our range. Why not ask us about our nondeformable shielding layers for high-temperature furnaces? Do you want an energy-efficient hot zone for your furnace? We are the specialists you need. Our engineers will work with you from the very first drawings of your furnace components through to the completion of the product. Contact us:

Discover more about our products and find your local contact person:
Heaters for high temperature furnaces
Tungsten crucibles for sapphire growing