CO₂相变致裂是一种高效增渗、增抽和消突的新型煤矿瓦斯治理技术，应用效果显著。该技术的核心是高压动力载荷作用于煤层的强化造缝及其卸压增渗效应。然而，新生裂缝的形貌特征以及破坏成因机制研究薄弱。目前井下厘米—米级尺度裂缝的观察和描述，主要用于揭示煤层的造缝增透机理。更小尺度的微米级显微裂隙研究，可更系统和全面描述裂缝的形貌和发育规律，揭示CO₂相变致裂作用下煤的破坏机理。应用自行研制的高压CO₂冲击大型物模试验装置系统，对无烟煤试件进行了120 MPa高压CO₂冲击，基于场发射扫描电镜(FESEM)的观察，研究了微米级裂隙特征、发育规律及其形成机理。结果表明：(1) 致裂后煤样的割理系统充分沟通，形成多尺度的复杂微裂隙网络。(2) 煤基质破碎并发育大量微米尺度的新生显微构造，发现了3种典型显微构造是“损伤坑” “三翼型”裂隙和“页理状构造”。(3) CO₂的超临界相、气相、或者二者的混合相态冲击破碎近喷孔端煤样，冲击波可能是试件远端破坏造缝的主要力学机制。(4) 显微构造的形成和损伤演化机制为：在煤基质表面形成损伤坑，并以损伤坑为中心形成 “三翼型”张性锯齿状分支裂隙，多个“三翼型”裂隙组合形成复杂的微裂隙网络系统。强化造缝形成的复杂网状裂隙系统，是煤层卸压、增渗、增抽和高效消突的内在原因。

CO₂ phase transition fracturing (CPTF) is a newly developed technique for coal mine gas control and is characterized by high efficiency, high coal seam permeability, a high gas drainage rate, and outburst elimination. The core of CPTF is reinforced fracturing and the pressure-relief and permeability-enhancement effects of coal seams under high-pressure dynamic loading. Nevertheless, there is a lack of studies on the morphological characteristics and formation mechanisms of newly formed fractures. Current observation and description of the underground fractures on a centimeter-meter scale primarily aim to reveal the fracturing and permeability-enhancement mechanisms of low-permeability coal seams. However, the study of microfractures on a nanometer-micron scale formed by CO₂ fracturing can describe the morphology and occurrence patterns of fractures more systematically and comprehensively and reveal the failure mechanisms of coal seams under the action of CPTF. In this study, anthracite samples were subjected to high-pressure CO₂ impact (120 MPa) using an independently developed large-scale physical test facility. Based on the observations obtained using a field emission scanning electron microscope (FE-SEM), this study investigated the characteristics, occurrence patterns, and formation mechanisms of micron-scale fractures. The results are as follows: (1) The cleat systems in the fractured coal samples were fully interconnected and formed a multi-scale, complex microfracture network; (2) The coal matrix in the samples was fractured and developed numerous new nanometer-scale microstructures, of which three types of typical microstructures were discovered, namely damage marks, Y-shaped fractures, and foliation structures; (3) The CO₂ in the supercritical phase and in the gas phase or in the supercritical phase mixed with the gas phase impacted and fractured the coal samples near the nozzles, and the remote fracturing of the samples was supposed to be primarily induced by shock wave; (4) The microstructures formed and evolved in three steps. First, damage marks formed on the surface of the coal matrix. Then, Y-shaped tensile, dentate branch fractures formed centering around the damage marks. Finally, multiple Y-shaped fractures combined to form a complex microfracture network. The complex reticular fracture system formed by the enhanced fracturing is the underlying reason for the pressure relief, high permeability, high gas drainage rate, and outburst elimination of coal seams.