Effect of mullite whiskers on the microstructure and mechanical properties of oil well cement

Abstract

This study addresses the issues of excessive brittleness and susceptibility to cracking in cementite by creating mullite whiskers, which enhance its mechanical characteristics, by the molten salt process utilizing Na₂SO₄, metakaolin, and Al₂(SO₄)₃·18 H₂O as raw ingredients. Multiple analytical methodologies, such as thermogravimetric analysis (TG), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), were utilized to investigate the phase, microstructure, and pore attributes of the whisker-modified cement slurry, along with the mechanism through which mullite whiskers enhance the cement slurry. The test findings indicate that the needle-shaped mullite whiskers exhibit excellent dispersion and a consistent aspect ratio. They accelerate the cement hydration process without altering the types of hydration products produced. The addition of mullite whiskers markedly improves the initial compressive and tensile strength of the cement slurry. The incorporation of 0.7 % whiskers resulted in a rise in compressive and tensile strengths of the cement slurry by 55.26 % and 41.86 % at 3 days, and by 45.27 % and 43.52 % at 7 days, respectively. The percentage of detrimental pores in the cement slurry was diminished by 19 %, and the porosity was reduced by 8.11 %. Mullite whiskers can act as nucleation sites for cement hydration, expediting the development of hydration products. Furthermore, it can fill the micropores inside the cement matrix and enhance the microstructure. The bridging effect and pull-out energy dissipation mechanism of the whiskers augment the strength and hardness of the cement slurry, thus reducing its propensity to break.