Article No : a05_061
Carbides
HELMUT TULHOFF, Hermann C. Starck Berlin, Werk Goslar, Goslar, Federal Republic of Germany
1. Survey ...... 565 2.6. Hafnium Carbide...... 576 1.1. Saltlike Carbides ...... 565 2.7. Vanadium Carbide ...... 576 1.2. Metal-like Carbides ...... 567 2.8. Chromium Carbide ...... 577 1.3. Diamond-like Carbides ...... 567 2.9. Molybdenum Carbide ...... 578 1.4. Carbides of Nonmetallic Elements...... 567 3. Mixed Carbides ...... 579 1.5. Crystal Structure...... 567 3.1. Tungsten – Titanium Carbide ...... 580 1.6. General Production Processes ...... 568 3.2. Other Mixed Carbides...... 580 1.7. Uses ...... 569 3.3. Carbonitrides...... 581 2. Metal-like Carbides of Industrial Importance 569 3.4. Mixed Carbonitrides ...... 581 2.1. Tungsten Carbide ...... 569 4. Carbides of the Iron Group and Manganese 581 2.2. Titanium Carbide ...... 573 5. Complex Carbides ...... 581 2.3. Tantalum Carbide ...... 574 References ...... 582 2.4. Niobium Carbide ...... 575 2.5. Zirconium Carbide ...... 576
1. Survey viewed as a diamond-like carbide because of its hardness and other properties resembling those Most of the elements form binary compounds of SiC. with carbon, all of which can be called carbides. Figure 1 surveys the four types of carbides in The properties of these carbides are very differ- the form of a periodic table. Elements that do not ent; therefore, like binary hydrides and nitrides, form binary compounds with carbon, or are not the carbides should be classified into groups. To known to form carbides, are not shown. The avoid too many subdivisions, the following four carbides of the iron group and manganese are types of carbides may be defined: a subgroup of the metal-like carbides.
1. saltlike carbides of metallic elements, e.g., CaC2 1.1. Saltlike Carbides 2. metal-like carbides of metallic elements, e.g., WC Saltlike carbides of metallic elements are the 3. diamond-like carbides, e.g., B4C carbides of the elements of groups 1 – 3 and 4. carbides of nonmetallic elements, e.g., CO 11 – 13 (I – III, both A’s and B’s) of the periodic table, the lanthanides and actinides included. This classification suggests another group: the Exceptions are Ga, In, and Tl, which do not form elements that do not react with carbon, e.g., Sn. carbides, and B4C, which is a typical diamond- Generally, the four groups of carbides can not like carbide. be strictly separated from each other. Numerous The saltlike carbides – also called ionic carbides carbides are in intermediate positions between – are attacked by water to form hydrocarbons. these groups. One example is BeC2 [57788-94- Most of these carbides form acetylene, e.g.: 0]. It is a typical saltlike carbide and is decom- posed by water. On the other hand, it may be CaC2þ2H2O ! CaðOHÞ2þC2H2