Naohiko Sasajima

Metal carbide-carbon peritectic systems as high-temperature fixed points in thermometry

WC?C, Cr3C2?C and Mn7C3?C peritectic systems were investigated for their potential of serving as high-temperature reference points in thermometry. Mixtures of high-purity graphite powder with W, Cr and Mn powder of 99.99%, 99.9% and 99.95% purity by mass, respectively, were placed in graphite blackbody crucibles and melting/freezing plateaus were observed by means of a radiation thermometer. The observed melting temperatures were 2749??C (WC?C), 1826??C (Cr3C2?C) and 1331??C (Mn7C3?C), with a repeatability?in each case?of 0.02?K. The melting range for WC?C and Cr3C2?C peritectics was roughly 0.1?K. WC?C showed a flat freezing plateau that agreed with the melting plateau within the repeatability. The three fixed points are possible candidates, like the metal (carbide)?carbon eutectic fixed points, in the realization of an improved high-temperature scale above the copper point.

Investigation of Fixed Points Exceeding 2500 °C Using Metal Carbide‐Carbon Eutectics

The melting and freezing plateaus of four metal carbide‐carbon (MC‐C) eutectics, B4C‐C, δ(Mo carbide)‐C, TiC‐C and ZrC‐C eutectics were investigated by radiation thermometry for the first time. The observed melting temperatures were 2386 °C, 2583 °C, 2761 °C and 2883 °C, respectively. The plateau shapes of δ(Mo carbide)‐C, TiC‐C and ZrC‐C eutectics are relatively flat compared to the quite rounded plateau shape of the B4C‐C eutectic. The results indicate that MC‐C eutectics can establish a new series of high‐temperature fixed points above 2500 °C.

Investigation of WC-C peritectic high-temperature fixed point

WC-C peritectic (2749degC) fixed point was investigated to evaluate their potential of serving as high-temperature reference points in thermometry. Three WC-C fixed-point cells were constructed and the melting and freezing plateaus were evaluated by means of radiation thermometer. The repeatability of the melting temperature of WC-C peritectic in one day was 17 mK with the melting range of approximately 70 mK. The repeatability of the freezing temperature of WC-C peritectic was 21 mK with the freezing range of less than 20 mK. The WC-C cells were easily constructed, like metal-carbon eutectic cells, without any reaction with crucible. From these results, it is concluded that WC-C peritectic has more potential as high-temperature standards than TiC-C eutectic (2761degC).

Dual-wavelength reflectance-ratio (DWR) method applied to high-temperature metals

Applicability of the dual-wavelength reflectance-ratio (DWR) method to high-temperature spherical metals was investigated. Solid nickel, copper and platinum spheres were used as samples for establishing the experimental setup and procedure. The samples were heated inductively and their temperatures were monitored with a thermocouple attached to the sample. Their radiances were measured using a pyrometer at two different wavelengths, 900 and 1350 nm. Their temperatures were calculated by analyzing the sample radiances with and without reflection of an auxiliary light source. The obtained temperatures by the DWR method agreed with the temperatures measured by a thermocouple within 50 K in the temperature range from 850 to 1600 K.

Metal Carbide-Carbon Eutectic and Peritectic Fixed Points as High-Temperature Standards

TiC-C eutectic and WC-C peritectic systems were investigated for their potential of serving as high-temperature reference points in thermometry. Mixtures of high-purity graphite powder with Ti and W were filled in graphite crucibles and melting/freezing plateaus were observed by means of a radiation thermometer. The observed melting range of WC-C peritectic was roughly 0.1 K with repeatability of 0.02 K. The melting range of TiC-C eutectic was roughly 0.5 K with repeatability of 0.09 K. The freezing curve of TiC-C showed a sharp peak after recovery from supercool, followed by a gently-sloped curve, probably due to composition of eutectic ingot or impurities. WC-C peritectic seems to have more potential as high-temperature standards, although it is still at a preliminary stage of investigation

Metal-carbon and metal carbide-carbon eutectic fixed points as high-temperature standards

Results of scale uncertainty simulations using metal-carbon (M-C) and metal carbide-carbon (MC-C) eutectic fixed points showed that extension of the fixed-point temperature range to above 2500/spl deg/C is the key to the improvement of the scale. From this viewpoint /spl delta/(Mo carbide)-C, TiC-C and ZrC-C eutectics were investigated by radiation thermometry. The observed melting temperatures were 2583/spl deg/C, 2761/spl deg/C and 2882/spl deg/C, respectively. The results indicate that MC-C eutectics can establish a new series of high-temperature fixed points above 2500/spl deg/C.