Graphite temperature measurement

Findlay, W. J., Zdrojewskl, A., and Qulckert, N. "Temperature Measurements of a Graphite Furnace Used In Flameless Atomic Absorption". Spectrosc. Lett. (1974), 7, 63-72. 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

Calorimeters Temperature measurements Graphite, water, polystyrene lOi-lO i... 

The methods of temperature measurement of graphite filaments are also subject to criticism. Temperature must be measured by an optical pyrometer. Duval (19) admits a possible error of 50° C. due to uncertainty in the calculated emissive power of a dull graphite surface (60). Furthermore, the temperature range of investigation cannot be extended far below 1000° C. without making arbitrary extrapolations of temperature vs. voltage curves. 

The employed technique for this purpose was the so-called colloidal-probe AFM (Atomic Force Microscopy). A carbon microparticle with high degree of carbonization was attached to the top of the cantilever tip, forming the colloidal probe, and its interaction force with cleaved graphite was measured within a liquid cell filled with organic liquid, controlled at a desired temperature above the bulk freezing point of the liquid. The two surfaces will form a slit-shaped nanospace because the radius of the particle is far larger than the separation distance concerned here. 

Calorimeters temperature measurement graphite, water, polystyrene... 

The selected A H"(298.15 K) was calculated by the 3rd law method using vapor pressures reported by Pollock (i). Pressures for the reaction BOgCCcr) 2Be(g) + C(graphite) were measured by Pollock in the temperature range 1430-1669 K by Knudsen technique. Vapor pressure data for this decomposition reaction have also been reported by Baboin ( ), Quirk (3 ) and Muratov and Novoselova (4). The calculated AjH"(298.15 K) values are summarized as follows ... 

According to a laboratory manual published by the National Distillers Chemical Co. a well-dried three-necked Pyrex flask, capacity 1-3 liters, may be used as the reactor (see Fig. 267). A stirrer with a graphite-packed gland is inserted through the middle neck. The other two necks serve for filling and temperature measurement. 

Any Ca, Mg or Zn which may be dissolved in the Ce is removed by placing the product in a crucible made of MgO, CaO, BeO or Ta, wdiich in turn is placed in a second crucible made of graphite. This assembly is placed in a quartz tube with one end closed and the other connected to a high-vacuum pump via a water-cooled brass coupling. The coupling is provided with a glass window to facilitate optical temperature measurement. The well-insulated quartz tube is placed for 30 minutes in an induction furnace heated to 1250 °C. The melt is held at this temperature for 10-15 minutes, until cessation of bubbling. 

Instrumentation Laboratories has recently modified their tantalum boat unit to also accommodate a graphite cuvette. The cell is enclosed so atomization of the sample can occur in an inert atmosphere. A temperature-sensing device is included to permit accurate temperature measurements and temperature control. 

Figure 2 Temperature distribution as a function of time in the end-heated (a) and side-heated (b) atomizers shown in Figure 1. The graphite tubes are 28 and 17.5 mm long in (a) and (b), respectively, and zis the distance from the tube center (mm) where the temperature measurements were made.

Semi-adiabatic calorimeters have been designed for dosimetry at high-energy electron accelerators (1-10 MeV) both for calibration and for routine process control (Humphreys and McLaughlin 1989 Miller and Kovacs 1985 Burns and Morris 1988) and also for low energies between 100 keV and 500 keV (Janovsky and Miller 1987). The disc-shape absorber is either water or graphite containing thermistors for temperature measurement placed in the center of the absorber. The absorber is placed in polystyrene foam insulation. 

The laboratory type 270 kVA DC arc furnace used in this work was graphite lined and 250 kg charge capacity. The diameter of the fiimaee was 36 cm and 90 cm depth. The voltage and current readings were measured by manually. During the taping of the alloy, temperature measurements were done by using of an optical pyrometer. 

Zhou et al [163] also measured the tensile properties of carbonized PAN yarns. The 1000°C carbonized bundle had a tensile strength of 325 15 MPa and a modulus of 40 4 GPa. These values increased to 542 45 and 58 6 GPa, respectively, with the increase of the final graphitization temperature to 2200°C. The values are measured for the bundle which can differ from the properties of single fibers to a great extent. 

In order to keep the graphite temperature from exceeding the chosen limits a separate cooling system has been provided. Flow, pressure and temperature of the circulating coolant are measured and controlled by reliable Instrumentation. 

Since molded graphite does not deform plastically, at least at low temperatures, measurement of its tensile strength is difficult and unreliable. Instead, it is preferable to measure flexural (transverse) strength, which is a more reproducible property. Tensile strength is generally 50 to 60% of the flexural strength and compressive strength is approximately twice as much. 

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