Metal crucible materials attacked

Good resistance to melts, espec-cially acidic ones Resistant to attack by ash components and flue dust Compatible with all other materials containing alumina and silica Vessels for metallic and alloy melts (Tamman crucible), protective tubes for pyrometers. External protective tubes for pyrometers sheathing tubes for electrlc-oven heating colls... 

Highly resistant attacked only by oxidizing agents, e.g., air above 550 C, steam and CO2 above 900°C stable to metals, if bese do not form carbides. More suitable for melting experiments than carbon crucibles because less reactive If the other material contains SIO2, silicon carbide is formed above about 1300 C. Stable AljO, BeO, and MgO up to about 1800-1900 C Same as carbon... 

Impurities in the rare metals produced by the iodide process can generally be reduced to a few tens of parts per million or less, for each element, provided care is taken in the selection of materials of construction. This initial advantage over other processes arises from the fact that the rare metals are produced without direct contact with a crucible or other container. Elements with volatile iodides should clearly be avoided in locations where the temperature is appropriate for attack by iodine vapour. Similarly, the crude feed should be as free from such elements as possible. For example, the whole of the zirconium impurity in a crude titanium feed would be carried over into the product, and vice versa, since the iodide process is equally suitable for the impurity as for the rare metal being purified. A large fraction of the iron and aluminium would be transferred, but decontamination factors from other elements such as nickel, chromium, carbon silicon and nitrogen are usually of the order of 10 to 100. 

HM 7—7.5) White, translucent, hard caramic material. Readily soluble in HF Titanium and in concentrated H2SO4, and reacts rapidly with molten alkali dioxide hydroxides and fused alkali carbonates. Owing to its good corrosion (rutile, resistance to liquid metals such as Ni and Mo, it is used in crucibles titania) for melting these metals. Titania is readily attacked unds an inert atmosphere by molten metals such as Be, Si, Ti, Zr, Nb, and Ta,... 

White and translucent hard material used as abrasive for grinding. Excellent electric insulator and also wear resistant. Insoluble in water and in strong mineral acids, readily soluble in strong alkali hydroxides, attacked by HE or NH HEj. Owing to its corrosion resistance, in inert atmosphere, in molten metals such as Mg, Ca, Sr, Ba, Mn, Sn, Pb, Ga, Bi, As, Sb, Hg, Mo, W, Co, Ni, Pd, Pt, and U it is used as crucible container for these liquid metals. Alumina is readily attacked in an inert atmosphere by molten metals such as Li, Na, Be, Al, Si, Ti, Zr, Nb, Ta, and Cu. Maximum service temperature 1950°C... 

Colorless amorphous (i.e., fused silica) or crystalline (i.e., quartz) material having a low thermal expansion coefficient and excellent optical transmittance in far UV. Silica is insoluble in strong mineral acids and alkalis except HE, concentrated HjPO, NH HE, concentrated alkali metal hydroxides. Owing to its good corrosion resistance to liquid metals such as Si, Ge, Sn, Pb, Ga, In, Tl, Rb, Bi, and Cd, it is used as crucible container for melting these metals, while silica is readily attacked in an inert atmosphere by molten metals such as Li, Na, K Mg, and Al. Quartz crystals are piezoelectric and pyroelectric. Maximum service temperature 1090°C... 

Short-term tests indicated that the practical upper limit for tantalum as a container for uranium is about 1450°C. However, attack below this temperature is significant. A tantalum crucible with a wall thickness of 0.06 in. was completely corroded after 50 h at 1275°C. Other investigations have shown that tantalum is not attacked by uranium-magnesium and plutonium-magnesium alloys at 1150°C. Extensive tests on components for molten metal fuel reactors have demonstrated that tantalum is a satisfactory material for several thousand hours of service in liquid-metal... 

Polycrystalline rare-earth sesquisulfides have been prepared by this method for La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. Europium sesquisulfide does not exist. For the more reactive rare-earth metals (La to Sm), the silica ampule will be severely attacked unless protected. This may also be a problem for other rare earths if high temperatures and long heating times are employed. Carbon is the most suitable material for protecting the silica in these syntheses. A graphite crucible may be used, but it is generally satisfactory simply to coat the inside of the silica tube with carbon by the pyrolysis of benzene. Benzene is poured into the silica tube, which is closed at one end it is then poured back out with the residue left clinging to the tube. The tube is placed in a furnace at 800° for a few minutes. 

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