Thixotropic changes occurring on reheating a coal tar pitch containing mesophase
✍ Scribed by G.W. Collett; B. Rand
- Publisher
- Elsevier Science
- Year
- 1978
- Tongue
- English
- Weight
- 472 KB
- Volume
- 16
- Category
- Article
- ISSN
- 0008-6223
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✦ Synopsis
Ahstraet-A coal tar impregnation pitch has been heated to 420°C under shear conditions and cooled. Microstructural investigation of the material showed ellipsoidal mesophase particles produced by shear deformation. On reheating in quiescent conditions, these particles were observed to revert to the spherical shape after a 3.5 hr treatment at 300°C. Material which experienced the same initial heat& cycle but no shear was also reheated, with isothermal intervals, up to 300°C. Plow curves measured isothermally at temperatures between 250 and 300°C showed marked thixotropic behaviour. The thixotropic loop widened with increasing ageing time at each temperature, but the effects were reversible indicating a physical phenomenon. It is suggested that this behaviour is probably the result of a slow coagulation of the "solid-like" mesophase particles to form a weak structure which can be broken down at low rates of shear.