Tungsten crucibles

Ion guns or cavity sources have also been developed for improving elemental ionization for TIMS measurement (Duan et al. 1997 Wayne et al. 2002). As shown in Figure 4, one ion source is based on a tungsten crucible with a cavity (0.02 cm diameter, 1 cm depth) into which sample is loaded. The crucible is heated by electron... 

For very high temperatures up to 2400 °C a different Micro TG/DTA sample holder (Fig. 13 f) must be used which usually is equipped with tungsten crucibles. The thermocouple in this case is a combination of W — W 26% Re. This type can be applied for thermoanalytical measurements in high vacuum and in inert atmosphere (noble gases). 

Lanthanum in purified metallic state may be obtained from its purified oxide or other salts. One such process involves heating the oxide with ammonium chloride or ammonium fluoride and hydrofluoric acid at 300° to 400° C in a tantalum or tungsten crucible. This is followed by reduction with alkali or alkaline earth metals at 1,000°C under argon or in vacuum. 

Neodymium, along with lanthanum, cerium and praseodymium, has low melting points and high boiling points. The fluorides of these and other rare earth metals are placed under highly purified helium or argon atmosphere in a platinum, tantalum or tungsten crucible in a furnace. They are heated under this inert atmosphere or under vacuum at 1000 to 1500°C with an alkali or alkaline earth metal. The halides are reduced to their metals ... 

The primary process operations are conducted sequentially in the same tungsten crucible. These primary operations are conducted in a circular processing assembly with operating stations dedicated for each operation. Decladding is conducted at the first station, oxide reduction is conducted at the second station, FP-3 donor is conducted at the third station, and U-Pu donor is conducted at the fourth station. Each station has the necessary apparatus to conduct the desired operations (introduction of fuel assembly, stirring, and transfer of molten salt and metal phases into and out of the crucible). Figure 4 gives a cross section view of the turntable. 

At each of the operating stations a tungsten crucible is located on the turntable. After each operation is completed, the turntable is rotated for the next operation. Prior to rotation, the turntable (and crucibles) must be lowered so that the stirrers and transfer tubes will not obstruct the rotation of the crucibles. After rotation, the crucibles are raised back to the operating level at the new operating position. The mechanisms and seals for raising, lowering, and rotating the turntable are located below the heated zone of the furnace. 

The studies of amorphous RAl alloy thin films are recent ones. Two modes of evaporation have been used to obtain such samples. They consist either of utilizing a rf sputtering apparatus, or of evaporating from a tungsten crucible an agglomerate such as RAU. 

Thin film La-Sm samples are prepared from two distinct evaporation sources such as tungsten crucibles. This procedure yields two different sorts of sandwich films Sm-La and Sm-La-Sm (Gasgnier, 1981). These samples are deposited at room temperature. Upon heating with the electron beam of the electron microscope the thinner lanthanum films of the two sequences show the formation of C- and B-Sm203 and A-La203. The thicker lanthanum films of the Sm-La-Sm... 

For deposition of copper onto polyaniline, the dispersion was dried on a stainless steel foil. Copper was evaporated from a tungsten crucible. For the TEM measurements, thin polyaniline films were prepared on glass slides. To transfer the polyaniline films onto Ni meshes, the glass slides were dipped... 

For metals with high vapor pressures, the alloys are best prepared by melting in sealed tantalum or tungsten crucibles heated inductively or in a resistance furnace. Fortunately these high vapor pressure non-rare earth metals do not react with the crucible materials. 

Polymer samples were placed in a tungsten crucible in a Knudsen cell inlet system of a time-of-flight MS. The system was evacuated. Samples were then heated at a linear rate. Spectra were determined at 1 minute intervals. The thermocouple was welded to a support rod 3 mm below the crucible and had been calibrated against a thermocouple in the bottom of the crucible at each heating rate. Details are summarised in Tables 9.4 and 9.5 for three polymers. 

Preparation of ThN by reaction of 2 atm N2 with Th melted in an induction-heated tungsten crucible has been reported by Olson, Mulford [9]. This technique is only suited for small preparations if the expensive crucible is not to be sacrificed. The crucible should be heated slowly so as to avoid direct contact of liquid Th metal with the W which alloys rapidly. 

Preparation. Th2N2Sb has been synthesized in two different ways 1) the cold-pressed powder mixture ThSb + ThN is heated in a tungsten crucible and lid assembly under 1 atm N2 for 2 h at 1200°C and 2) the powder mixture 2ThN + Sb is sealed in an evacuated quartz capsule and heated for 30 d at 1000°C [5]. 

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