What is it?

Looking up Google, the top ten hits give eight different values.
Even if the web is wrong, you’d at least expect them to copy from one another.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

The Handbook of Chemistry and Physics (1996) gives sublimes at 3,642 °C, with a triple point of 4,492 °C.

Help!

mollwollfumble said:

What is it?

Looking up Google, the top ten hits give eight different values.
Even if the web is wrong, you’d at least expect them to copy from one another.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

The Handbook of Chemistry and Physics (1996) gives sublimes at 3,642 °C, with a triple point of 4,492 °C.

Help!

Scholar Google isn’t a huge amount of help so far.

From 1915, “For this reason the use of the formula by Forcrand for extrapolation to still higher temperatures, to get the boiling point of carbon, cannot be regarded as very significant.”

From 1935, “the maximum brightness temperature of the carbon crater is 3,810° K, the probable true crater temperature lies between 3,925° and 3,970° K” for sublimation of carbon under electric arc.

From 1942, “The boiling point of carbon is given by International Critical Tables as 42000K (Volume 3, p. 205)”. I assume that to mean 4,200 °K.

From 1951, “sublimation point of carbon 3810°K”.

From 1974, “3700 , the sublimation point of carbon”. The paper uses both celsius and kelvin so not sure which.

From 1994, “sublimation point of carbon (4000°C)”

From 2004, “The boiling point of carbon (4200 °C)”

From 2006, “sublimation point of carbon (≅ 4000 °C)”

From 2006, “The sublimation point of carbon was evaluated as 4099 K by Massalski “

Following up on that last reference, “ M. Massalski, ASM Handbook, vol 2., Metals Park, OH, USA, 1986, p. 2175.” so it’s neither new nor a direct measurement.

mollwollfumble said:

What is it?

Looking up Google, the top ten hits give eight different values.
Even if the web is wrong, you’d at least expect them to copy from one another.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

The Handbook of Chemistry and Physics (1996) gives sublimes at 3,642 °C, with a triple point of 4,492 °C.

Help!

Nobody knows.

The Rev Dodgson said:

mollwollfumble said:

What is it?

Looking up Google, the top ten hits give eight different values.
Even if the web is wrong, you’d at least expect them to copy from one another.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

The Handbook of Chemistry and Physics (1996) gives sublimes at 3,642 °C, with a triple point of 4,492 °C.

Help!

Nobody knows.

If nobody knows, why does everyone claim to know?

This link may or may not be a help.

https://link.springer.com/chapter/10.1007/978-3-319-21350-7_3

Carbon Triple Point (Graphite/Liquid/Vapor) from 2015.

Determination of parameters (P, T) for the triple point of carbon (solid–liquid–gaseous) began in 1939 (Basset), and continued in 1959 (Noda). But the impressive result was obtained only in 1976 (Gokcen) for the pressure at the triple point of carbon (∼120 bar). Study of Shoessov at pressures up to 1000 bar, however, had no progress in temperature measurement. The study only by Haaland (1976) gave a truthful value for the melting temperature (close to 5000 K). In addition, Haaland gave a brief analysis of the main results on different high-temperature carbon investigations, noting that the vapor (more precisely, carbon sublimate) affect the quality of the temperature measurements. Later researchers have taken a number of measures to avoid that of the steam jet (sublimate) has appeared in the optical path under temperature measurements. The determination of specific input energy under beginning of melting, enabled investigators to interpret the accuracy of the temperature measurements near the melting point of graphite. Millisecond heating current (M. Sheindlin) allowed us to obtain reliable dependence of enthalpy (input energy) against temperature of the graphite in the solid state up to 4500 K. This experiment is discussed in this chapter. Experiments of different duration (from seconds to nanoseconds) showed no dependence of the melting temperature on the heating rate (Table 3.3). The results of the various experiments performed as under heating by current or by laser heating give the matching results on the melting temperature of graphite (4800–4900 K), provided that the pressure is maintained above 110 bar.

But that’s too high a pressure.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

What is it?

Looking up Google, the top ten hits give eight different values.
Even if the web is wrong, you’d at least expect them to copy from one another.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

The Handbook of Chemistry and Physics (1996) gives sublimes at 3,642 °C, with a triple point of 4,492 °C.

Help!

Nobody knows.

If nobody knows, why does everyone claim to know?

This link may or may not be a help.

https://link.springer.com/chapter/10.1007/978-3-319-21350-7_3

Carbon Triple Point (Graphite/Liquid/Vapor) from 2015.

Determination of parameters (P, T) for the triple point of carbon (solid–liquid–gaseous) began in 1939 (Basset), and continued in 1959 (Noda). But the impressive result was obtained only in 1976 (Gokcen) for the pressure at the triple point of carbon (∼120 bar). Study of Shoessov at pressures up to 1000 bar, however, had no progress in temperature measurement. The study only by Haaland (1976) gave a truthful value for the melting temperature (close to 5000 K). In addition, Haaland gave a brief analysis of the main results on different high-temperature carbon investigations, noting that the vapor (more precisely, carbon sublimate) affect the quality of the temperature measurements. Later researchers have taken a number of measures to avoid that of the steam jet (sublimate) has appeared in the optical path under temperature measurements. The determination of specific input energy under beginning of melting, enabled investigators to interpret the accuracy of the temperature measurements near the melting point of graphite. Millisecond heating current (M. Sheindlin) allowed us to obtain reliable dependence of enthalpy (input energy) against temperature of the graphite in the solid state up to 4500 K. This experiment is discussed in this chapter. Experiments of different duration (from seconds to nanoseconds) showed no dependence of the melting temperature on the heating rate (Table 3.3). The results of the various experiments performed as under heating by current or by laser heating give the matching results on the melting temperature of graphite (4800–4900 K), provided that the pressure is maintained above 110 bar.

But that’s too high a pressure.

Too high for what?

> Too high for what?

When we talk about boiling sublimation point, we mean at standard pressure, 1 bar. 110 bar is too high a pressure to be the same temperatures as 1 bar.

> https://link.springer.com/chapter/10.1007/978-3-319-21350-7_3

Following on to reference 33 from that.

“E.I. Asinovsky, A.V. Kirillin, A.V. Kostanovskii, Experimental investigation of the thermal properties of carbon at high temperatures and moderate pressures. Phys. Uspekhi 45, 869–882 (2002)” via Google scholar and SciHub.

That article clears things up enormously. Particularly Figure 1 and Figure 3.

“At present, the number of papers in which the results of original studies into carbon melting, the phase equilibrium coexistence curves, and the triple point parameters (pressure pt and temperature Tt) are presented is several dozen .Nevertheless, the carbon Tt can only be specified with an error of about 1000 K, which differs dramatically from the situation with metals, where this error does not exceed several kelvins.”

“to make the understanding of the results depicted in Fig.1 easier, we note that they were obtained by three different experimental methods.

• An electric current is passed through a graphite rod in a high pressure chamber (HPC), with a characteristic heating time of about 1 s. The vapour pressure is measured.
• The graphite sample is heated in the HPC by irradiating the sample with high-power laser radiation, with a characteristic heating time of about 1 s. The radiation spectrum gives the temperature.
• A thin wire specimen is heated by sending avery short (10^-3 to 10^-6 s), high-density current pulse through the wire (electric explosion).

Figure 1. Literature search of phase transition points (melt, boil or sublime) at lowish pressures. A pressure of 0 on the log scale is 1 bar. If you ignore the solid line with vertical bars, the experimental results from the literature are just about random, anywhere between 4000 and 5000 Kelvin.

Figure 3 helps to make sense of this by looking at higher pressures. Results of literature search together with author’s measurements. The near vertical line is melting point, the line to the right is boiling point. The lowest points are at 1 bar. The scatter in temperature is nearly independent of pressure.

This allows me to say that the boiling point of carbon at 1 bar is 4,000 +- 250 Kelvin. The melting point of graphite (but see below) at 1 bar, extrapolated down from 80 bar, is 4,050 +- 100 Kelvin.

This helps to explain why some researchers say that carbon sublimes, and why others say that carbon melts and then boils.

But why is it so difficult to measure, when compared to metals?

mollwollfumble said:

> Too high for what?

When we talk about boiling sublimation point, we mean at standard pressure, 1 bar. 110 bar is too high a pressure to be the same temperatures as 1 bar.

> https://link.springer.com/chapter/10.1007/978-3-319-21350-7_3

Following on to reference 33 from that.

“E.I. Asinovsky, A.V. Kirillin, A.V. Kostanovskii, Experimental investigation of the thermal properties of carbon at high temperatures and moderate pressures. Phys. Uspekhi 45, 869–882 (2002)” via Google scholar and SciHub.

That article clears things up enormously. Particularly Figure 1 and Figure 3.

“At present, the number of papers in which the results of original studies into carbon melting, the phase equilibrium coexistence curves, and the triple point parameters (pressure pt and temperature Tt) are presented is several dozen .Nevertheless, the carbon Tt can only be specified with an error of about 1000 K, which differs dramatically from the situation with metals, where this error does not exceed several kelvins.”

“to make the understanding of the results depicted in Fig.1 easier, we note that they were obtained by three different experimental methods.

• An electric current is passed through a graphite rod in a high pressure chamber (HPC), with a characteristic heating time of about 1 s. The vapour pressure is measured.
• The graphite sample is heated in the HPC by irradiating the sample with high-power laser radiation, with a characteristic heating time of about 1 s. The radiation spectrum gives the temperature.
• A thin wire specimen is heated by sending avery short (10^-3 to 10^-6 s), high-density current pulse through the wire (electric explosion).

Figure 1. Literature search of phase transition points (melt, boil or sublime) at lowish pressures. A pressure of 0 on the log scale is 1 bar. If you ignore the solid line with vertical bars, the experimental results from the literature are just about random, anywhere between 4000 and 5000 Kelvin.

Figure 3 helps to make sense of this by looking at higher pressures. Results of literature search together with author’s measurements. The near vertical line is melting point, the line to the right is boiling point. The lowest points are at 1 bar. The scatter in temperature is nearly independent of pressure.

This allows me to say that the boiling point of carbon at 1 bar is 4,000 +- 250 Kelvin. The melting point of graphite (but see below) at 1 bar, extrapolated down from 80 bar, is 4,050 +- 100 Kelvin.

This helps to explain why some researchers say that carbon sublimes, and why others say that carbon melts and then boils.

But why is it so difficult to measure, when compared to metals?

There are several reasons why it is so difficult to measure.

The main one is that it’s practically impossible to ensure uniform temperature. A carbon rod heated by electricity for instance heats up faster along the centreline than at the edges. For the other methods, the temperature is even less uniform.

The second one is that there’s low latent heat (compared to metals). So liquid evaporates rapidly from the melt pool at temperatures below the boiling point and, conversely, superheats easily. Ditto solid below and above the melting point.

The third one is phase changes in the solid state. At high temperatures, graphite transitions into a mixture of carbyne and diamond-like carbon. The solid-solid phase transition has a latent heat release that can (at least in theory) lead to a thermal runaway type explosion. The details of this phase transition are very unclear at present.

Time to edit wikipedia?

mollwollfumble said:

Time to edit wikipedia?

Posted the edit to talk on the wikipedia page rather than the main page. See if it gets a response.

mollwollfumble said:

mollwollfumble said:

Time to edit wikipedia?

Posted the edit to talk on the wikipedia page rather than the main page. See if it gets a response.

No response so far. Good.

“E.I. Asinovsky, A.V. Kirillin, A.V. Kostanovskii, Experimental investigation of the thermal properties of carbon at high temperatures and moderate pressures. Phys. Uspekhi 45, 869–882 (2002)” via Google scholar and SciHub.

Figure 3 helps to make sense of this by looking at higher pressures. Results of literature search together with author’s measurements. The near vertical line is melting point, the line to the right is boiling point. The lowest points are at 1 bar. The scatter in temperature is nearly independent of pressure.

This allows me to say that the boiling point of carbon at 1 bar is 4,000 +- 250 Kelvin. The melting point of graphite (but see below) at 1 bar, extrapolated down from 80 bar, is 4,050 +- 100 Kelvin.

This helps to explain why some researchers say that carbon sublimes, and why others say that carbon melts and then boils.

But why is it so difficult to measure, when compared to metals?

Redrawn Fig. 3 in a form suitable for Wikipedia.

Does that match up with what i found before, ie.

4,827 °C boiling point, melting point 3,500 °C
3,642 °C, sublimes
3,825 °C boiling point, melting point 3,550 °C
3,825 °C, sublimes
4,832 °C boiling point, melting point 3,367 °C
3,630 °C, sublimes, triple point 4,330 ± 300 °C
4,027 °C boiling point, melting point 3,550 °C for diamond
4,830 °C boiling point, melting point 3,500 °C for graphite

Not really, the range from Fig. 3 is 3,800 to 4,760 K.
As against 3.900 to 5,105 K from the web. That top temperature is a lot hotter.

There’s also a disagreement for melting point, 4,050 +- 100 K from Fig. 3.
As against 3,640 to 3,915 K from the web, with an outlier of 4,100 K.

What a mess. All the researchers are missing something here. I wonder what it is?