The combination of inaccuracies in the temperature measurements, taking into account likely common errors in both blackbody and radiance temperature measurements, indicates that the inaccuracy in the normal spectral emittance is approximately 3 percent. The inaccuracy 3 of the melting points is estimated to be approximately 10 K for the alloys 99 Nb–1 Zr and 80 Nb–10 Ta–10 W, and 15 K for 90 Ta–10 W. A somewhat higher imprecision in the case of the blackbody temperature measurements may be attributed to the movements of the sighting hole in the specimen during melting. Specific items in the error analysis were recomputed whenever the present conditions differed from those in the earlier publications.Īs it may be seen from table 2, the imprecision 2 of true (blackbody) and radiance temperature measurements was 0.3–1.9 K and 0.2–0.8 K, respectively. Sources and estimates of errors in experiments similar to the ones conducted in this study are given in earlier publications. In all cases, the standard deviation of an individual point from the smooth function was less than 0.06 percent. Below the melting point electrical resistivity for each alloy was fitted, using the least squares method, to a linear function in temperature. However, in the case of the alloy 80 Nb–10 Ta–10 W ( figure 6) the change in the electrical resistivity was gradual, starting approximately 15 K below the melting point. The results indicate that electrical resistivity of the alloys 90 Ta–10 W ( figure 4) and 99 Nb–1 Zr ( figure 5) changed almost abruptly at the start of melting. The values for the 100 K range below the melting points are given in table 4. The results for the electrical resistivity of the alloys near and at their respective melting points are shown in figures 4, ,5, 5, and and6. The dimensions were based on their room temperature values the cross-sectional area was determined from the measurement of weight and density. The results of radiance temperature at the melting point of the alloys and corresponding values for the normal spectral emittance are given in table 3.Įlectrical resistivity of the tubular specimens was calculated using the relation ρ = RA/L, where R is the resistance, A the cross-sectional area, and L the length of the specimen between the potential probes. However, 80 Nb–10 Ta–10 W results ( figure 3) do not indicate the existence of any well-defined plateau, with the exception of a short segment immediately after reaching the melting point. It may be seen ( figure 2) that both 90 Ta–10 W and 99 Nb–1 Zr samples behaved normally, that is, radiance temperature increased and exhibited a plateau upon melting. Similar results for the alloy 80 Nb–10 Ta–10 W are shown in figure 3. The experimental results of the radiance temperature of 90 Ta–10 W and 99 Nb–1 Zr alloys near and at the respective melting points are shown in figure 2. The circular area viewed by the pyrometer was 0.2 mm in diameter. The measurements were performed at 650 nm which corresponds to the effective wavelength of the pyrometer’s interference filter. Sample sizes are small, being just enough powdered material to fill a small capillary tube, and the output reading is accurate to within 0.3 – 0.5C with good reproducibility.Where ϵ is the normal spectral emittance, T m the melting point, T s the radiance temperature, c 2 the second radiation constant (1.4388 × 10 −2 m K), and λ the effective wavelength of the optical system. Digital control means that the sample is heated, the melting point recorded, and the apparatus cooled ready for the next sample is just a few minutes, without operator intervention. The modern melting point meter is faster and more accurate, providing reproducible results which do not rely on the skill of the individual operator and which can be printed for a permanent record. Why then, should one invest in an automated melting point meter? While it is possible to manually heat a sample and observe it, perhaps through a microscope, to determine melting point, this is a cumbersome and unreliable approach. It is also a technique which it is possible to complete, without specialist equipment. The determination of melting point is a fundamental technique in sample analysis, yielding essential information on material composition and purity.

Melting point measure