Boron Nitride Crucibles

Boron nitride is one of the most outstanding corrosion-resistant materials. It is inert to gasoline, benzene, alcohol, acetone, chlorinated hydrocarbons and other organic solvents. It is not wetted by molten aluminum, copper, cadmium, iron, antimony, bismuth, silicon, germanium, nor by many molten salts and glasses. It is used extensively as crucible material, particularly for molten metals, glasses and ceramic processing. 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

Fig. 9. Boron nitride ceramics. BN ceramics with SiC addition for break rings in continuous ferrous metals casting. Hot-pressed and HIPed BN crucibles and electrical insulators. (Courtesy of ESK-Kempten, a company of WACKER-Chemie)...

Boron nitride X-ray lithography masks, high-temperature crucibles. 

The molecules were deposited with OMBE, NaCl was sublimed from a boron-nitride crucible. 

Figure 8.9. Schematic representaion of the boron nitride (BN) capillary conductivity cell. 1 - steel tube, 2 - molybdenum contact rod, 3 - thermocouple, 4 - pressed BN cell holder, 5 - tungsten electrode, 6 - melt, 7 - pyrolytic BN tube, 8 - graphite crucible.

Samples of about 60 mg were placed in the glove box under dried argon atmosphere into high purity boron nitride crucibles and tightly closed by a BN lid with a screw. 

Measurement below 7.5 mole % Nb20s was impossible, since at high concentration of K2NbF7 interaction between boron nitride crucible and potassium fluoroniobate takes place according to the reaction... 

DCNDBQT was physically vapour deposited (PVD) under ultra high vacuum conditions (UHV) with a pressure of 5 x 10 mbar. The substrates (TiOj/Si) were annealed to 180 °C for 20 minutes in order to remove any water layer from the surface. The molecules were evaporated from homebuilt boron nitride crucibles at an evaporation rate of 1.0-1.5 ml min with the substrates kept at room temperature. The deposition rate was monitored with a quartz microbalance and a frequency counter. 

A critical point in the work presented in this communication was the generation of a steady stream of silicon atoms which have to be condensed together with the substrate molecule and an excess of matrix material onto the cooled window. In our early experiments, silicon was vaporized from a tantalum Knudsen cell (Figure 1.2, Type A) or a boron nitride crucible which was surrounded by an aluminum oxide tube. The oven was resistively heated to temperatures of 1490-1550 °C by means of a tungsten wire wound around the alumina tube (Figure 1.2, Type B). In later runs, a rod of dimensions 0.7-2-22... 

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