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. If the two samples are different, the melting point will be depressed.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. If the unknown sample is identical to the known sample, the melting point will remain unchanged. Determine the melting point of the mixture.Grind them together using a mortar and pestle or a fire polished glass stirring rod and then fill a capillary tube with the mixture. Make a homogeneous mixture of equal amounts of the unknown and the known substances. When a satisfactory melting point range has been determined, choose a known substance that has a melting point within 5☌ of the observed value.Record the temperature at which the solid in the capillary tube melts.Use the bunsen burner to heat the mineral oil slowly.The thermometer with a capillary tube attached using rubber tubing Insert the thermometer through a hole in a cork, and clamp the cork to the ring stand as shown.įigure 5.Place a sample of the compound into a capillary tube and use a thin piece of rubber tubing as a rubber band to attach the capillary tube to a thermometer (see Figure 5).Place a beaker of mineral oil on the wire gauze.Set up a ring stand with a bunsen burner (which should be attached to a gas valve using rubber tubing), a ring above it, and wire gauze on the ring (see Figure 4).This time, make sure that the increase in temperature is no more than 2oC per minute. Once a melting point range is determined, prepare another capillary tube (tubes should only be used once and then discarded) and set the MEL-TEMP to the appropriate power level, based on the power level/temperature chart.Observe the melting process though the magnifying lens. Set the MEL-TEMP at a high enough level to make a rapid determination of melting point. Place the capillary tube in the MEL-TEMP melting point apparatus.Force the crystals to slide to the bottom of the tube using one of the following methods: tap the tube (open end up) on the lab bench drop the capillary tube through a 2-3 foot piece of glass tubing or rub the capillary tube along a piece of wire gauze. Put the capillary tube (open end down) into the crystals and tap it on the bottom of the crystallization dish to get the crystals into the tube. Fill a capillary tube with crystals about 3 mm high.
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