SINTERING OF POWDERS FROM ALKALINE BASALTIC TUFFS IN AIR AND INERT ATMOSPHERES

10th International Multidisciplinary Scientific GeoConference - SGEM2010, www.sgem.org, SGEM2010 Conference Proceedings/ ISBN 10: 954-91818-1-2, June 20-26, 2010, Vol. 1, 149-156 pp

ABSTRACT
The possibility to obtain a low cost petrurgical material by direct sintering of alkaline
basaltic tuffs is demonstrated. The parent rock was milled for 10-15 min and the
resulting powder was pressed at 100 MPa. The sintering and the phase formation in air
and inert atmospheres were studied by dilatometry and DTA, respectively. The phase
composition of obtained samples was evaluated by XRD whereas the stricture was
highlighted in details by SEM. Some mechanical and thermal properties of the new
materials were measured.

The final samples, obtained by sintering in air at 1100°C, are characterized by zero
water absorption, 5-6 vol% closed porosity, 2-3 % crystallization induced porosity and
structure similar to a glass-ceramic. Due to the high crystallization trend of parent tuffs
phase formation takes place during the sintering and cooling steps; this leads to
formation of different crystal phases (pyroxene, anorthite, spinel, olivine and hematite)
and total crystallinity of about 60%.

It was also elucidated that in inert atmospheres, because of absence of Fe2+ oxidation
and resulting lower viscosity, the densification occurs at a temperature lower with 50-60
°C. At the same time the crystallinity is higher and reaches 65-70%.

Notwithstanding of the simple and inexpensive production cycle the obtained materials
are characterized by very attractive properties: bending strength of 105 MPa, Young
modulus of 90 GPa, and coefficient of thermal expansion of 85. 10 -7 * deg -1.

Keywords: igneous rocks, sintering, crystallization, mechanical properties