Resistivity of tungsten down to -40degC

[cupoftea]

Hi,
All web pages only give tungsten resistivity down to 20degC.
Do you know it down to -40degC?

Also, is this tungsten IR lamp have a filament made of tungsten?

Infra Red 118mm 500 watt Slim Ruby R7s Patio Heater Light Bulb

www.lamps2udirect.com

..its "datasheet" doesnt say.

 

[wwfeldman]

according to
Lide, D. CRC Handbook of Chemistry and Physics, 75 edition. CRC Press, 1995: 12.
at

Resistivity of Tungsten - The Physics Factbook

hypertextbook.com

"electrical resistivity of tungsten RW in n-ohm·m are given in
RW = 48.0 (1 + 4.8297 × 10−3 T + 1.663 × 10−6 T2)"

i added the last parenthesis
interesting unit - looks like nano ohm meters to me


this website talks about the temperature coefficient of resistivity

20.3 Resistance and Resistivity – College Physics

pressbooks.online.ucf.edu

as does this one:

Resistivity and Conductivity - Temperature Coefficients Common Materials

Resistivity, conductivity and temperature coefficients for common materials like silver, gold, platinum, iron and more..

www.engineeringtoolbox.com

 

[FvM]

In a first order estimation, resistance of pure metals is proportional to absolute temperature, surely sufficient accurate for your problem.

 

[crutschow]

All web pages only give tungsten resistivity down to 20degC.
Do you know it down to -40degC?

According to my extrapolation of the tungsten resistance curve, at -40°C it should be about 73% of the value at 20°C.

Also, is this tungsten IR lamp have a filament made of tungsten?

I would expect so, but it could also be an alloy like NiChrome, used in may heating elements such as toasters and stove tops.

 

[D.A.(Tony)Stewart]

Using @wwfeldman's link to the Physics Factbook, I plotted the data and an adequate trend using a 6th order Polynomial.

It has both the absolute Resistivity and the relative value referenced to R300K ( 27 °C)

You can use the ratio At -40 °C = 233 °K relative to your known value or the R/R300K .

Here is the equation for the R/R300K with x= °K and f(x) = R/R300K

Now the reduction in resistance with a constant voltage will raise the power dissipation and thus reduce the thermal colour temperature difference expected. But then I do not know the reason for your temperature.

It appears to have a resistivity ratio of 80% for R233/R273K or R-40C/R0C if you were wondering about the initial cold surge current for this PTC or positive tempco metal.

I suspect the reference IR lamp has a dominant visible temperature around 900 'K @ 500W if it is "ruby red" with most of the power in the IR spectrum.

I wonder what the spectral bandwidth is?