Key Takeaways & Executive Findings
- •• Acidic SiO2 nanofluids significantly enhance coal wettability, reducing the contact angle by up to 43.86% at pH 2. • SiO2 nanoparticles act as bridging agents, increasing the adsorption layer thickness from 15.44 Å to 20.51 Å in high-mass fraction systems. • Mild acidity (pH 5) improves coal nanomechanical properties, with elastic modulus and hardness increasing by ~18%. • Strong acidity causes corrosion that outweighs nanoparticle support, leading to mechanical degradation.
Abstract
Conventional hydraulic fracturing is widely used for underground gas control in coal mines; however, in deep, soft coal seams, poor wettability and low mechanical strength can cause rapid energy release under gas pressure and mining-induced disturbances. These conditions increase the risk of coal and gas outbursts, complicate rapid outburst elimination, and pose serious threats to safe mine operations. In this study, SiO2 nanofluid solutions with varying acidity were prepared, and molecular dynamics simulations, contact angle measurements, fourier transform infrared spectroscopy, nanoindentation tests, and three-dimensional super-depth microscopy were employed to systematically investigate the mechanisms by which acidic SiO2 nanofluids enhance the wettability and nanomechanical strength of soft coal seams. The results show that SiO2 nanoparticles act as bridging agents between water molecules and the coal matrix. In the high-mass fraction H2O/SiO2/coal system, the adsorption layer thickness increases from 15.44 Å in the pure water system to 20.51 Å. Acidic SiO2 nanofluids substantially reduce the coal-water contact angle; at pH 2, the contact angle decreases to 47.9°, representing a 43.86% reduction relative to raw coal. The total absorption peak area of oxygen-containing functional groups increased accordingly, promoting a transition of the coal surface from hydrophobic to hydrophilic. SiO2 nanofluids with varying acidity also induce pronounced changes in the mechanical properties of coal samples. Under mildly acidic conditions (pH 5), the elastic modulus and hardness increase by 17.880% and 18.794%, respectively, while the peak displacement and contact displacement decrease by 8.056% and 8.117%. Mild acidity promotes the formation of local micropores and facilitates the embedding of SiO2 nanoparticles, enhancing structural support and improving nanomechanical performance. In contrast, under strong acidic conditions, the corrosion effect outweighs the supporting role of the nanoparticles, resulting in mechanical degradation. Overall, the synergistic effects of acidic environments and SiO2 nanofluids significantly influence the wettability and mechanical behavior of coal. By elucidating their combined modification mechanisms, this study provides theoretical support and new perspectives for fluid-injection enhancement and dynamic disaster prevention in deep, soft coal seams.
1. Introduction
With the rapid development of the global economy, shallow mineral resources are gradually being depleted, and coal exploitation is increasingly shifting to deeper layers. Deep mining is thus facing pronounced 'three highs and one strong disturbance' issues [1]. Soft coal seams typically exhibit low strength, loose structure, well-developed porosity, and are strongly influenced by geological structures. Under the combined effects of gas pressure and mining disturbances, these originally soft coal seams are prone to failure, allowing accumulated gas to be rapidly released through fractures, which increases the risk of coal and gas outburst accidents and poses a serious threat to underground operational safety [2–6].
Currently, gas extraction technologies primarily rely on hydraulic outburst prevention measures, but the effectiveness of these methods is often limited by the poor wettability and low mechanical strength of deep soft coal seams. Therefore, there is a critical need to develop novel approaches that can simultaneously enhance the wettability and mechanical integrity of coal to improve gas extraction efficiency and mitigate dynamic disasters.
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Linfan Qi, Xianfeng Liu, Baisheng Nie, Jialiang Li, Peng Chen, Han Han, Zhongbei Li, Shanyang Wei, Bozhi Deng (2026). Mechanisms of enhanced wettability and nanomechanical strength in soft coal seams modified by acidic SiO2 nanofluids. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2026.03.001
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Frequently Asked Questions
What is the main objective of this study?
The study aims to investigate the mechanisms by which acidic SiO2 nanofluids enhance the wettability and nanomechanical strength of soft coal seams, providing theoretical support for fluid-injection enhancement and dynamic disaster prevention in deep mining.
How do acidic SiO2 nanofluids improve coal wettability?
SiO2 nanoparticles act as bridging agents between water molecules and the coal matrix, increasing the adsorption layer thickness and reducing the contact angle. At pH 2, the contact angle decreases by 43.86% compared to raw coal, promoting a transition from hydrophobic to hydrophilic surface.
What effect do acidic SiO2 nanofluids have on coal mechanical properties?
Under mildly acidic conditions (pH 5), the elastic modulus and hardness increase by 17.880% and 18.794%, respectively, while peak and contact displacements decrease. However, strong acidity causes corrosion that outweighs nanoparticle support, leading to mechanical degradation.
What experimental methods were used in this study?
The study employed molecular dynamics simulations, contact angle measurements, Fourier transform infrared spectroscopy, nanoindentation tests, and three-dimensional super-depth microscopy to systematically analyze the effects of acidic SiO2 nanofluids on coal.
What are the practical implications of this research?
The findings provide theoretical support for enhancing gas extraction efficiency and preventing coal and gas outbursts in deep soft coal seams by using acidic SiO2 nanofluids as a modification agent.
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