硅酸盐学报

氮化硅(Si_3N₄)陶瓷材料具有优良的综合性能，因耐高温、抗腐蚀等优势在众多行业中应用前景广泛。本工作使用纯Si粉做原料，不添加任何烧结助剂，采用氮化反应烧结制备Si_3N₄陶瓷，并对该种方式下制备的孔隙率达30%的Si_3N₄陶瓷材料的抗酸腐蚀能力进行研究，探索HF浓度、腐蚀时间对Si_3N₄陶瓷样品的腐蚀行为、腐蚀规律。结果表明，纯Si粉氮化反应烧结制备的Si_3N₄陶瓷材料经HF腐蚀200 h后，随着HF浓度增大、腐蚀时间增加，陶瓷样品质量、密度、抗弯强度逐渐降低，气孔率增大。Si_3N₄陶瓷样品浸泡在HF中与之发生反应，生成(NH₄)_2Si F₆相，并在样品表面形成疏松腐蚀层，陶瓷内部Si和N的损耗导致样品气孔增多、致密度降低，从而使得陶瓷样品性能降低。通过对反应烧结获得的多孔Si_3N₄陶瓷的抗酸腐蚀性能进行探索，为Si_3N₄陶瓷极端环境应用下的性能研究提供了参考。

Introduction Silicon nitride(Si_3N₄) ceramic materials are widely used in industries due to their excellent high temperature resistance and corrosion resistance. With the increasing application of Si_3N₄ ceramic materials, the research on the service in various extreme environments has attracted recent attention, especially the corrosion resistance of Si_3N₄ ceramics in corrosive liquids(i.e., the corrosion behavior of HF on Si_3N₄ ceramics). Si_3N₄ ceramics have a superior acid corrosion resistance. A prolonged contact with HF solution leads to a decrease in the stability of Si_3N₄ ceramics, thus damaging the overall function. For porous Si_3N₄ ceramics, its unique structure aggravates the corrosion of acid solution. In some special applications, porous Si_3N₄ ceramics are required to have sufficient strength and acid resistance to ensure application stability and life. However, the existing reports mostly focus on Si_3N₄ composite ceramics or dense Si_3N₄ ceramics with sintering aids. Little work on the preparation of Si_3N₄ ceramics using pure Si powder as a raw material for nitridation sintering, specifically the corrosion behavior of porous Si_3N₄ ceramics in HF, has not been reported yet. In this work, Si_3N₄ ceramics were prepared via nitridation reaction sintering using a pure Si powder as a raw material without any sintering additives. The acid corrosion resistance of Si_3N₄ ceramic materials with a porosity of up to 30% prepared was investigated to explore the corrosion behaviors of and time on Si_3N₄ ceramic samples at different HF concentrations. Methods High-purity porous Si_3N₄ ceramics with a porosity of 30% were prepared via nitridation reaction sintering using Si powder with a purity of 99.99%(in mass fraction) as a raw material. After cold isostatic pressing at 200 MPa, the ceramics were processed into the samples with appropriate sizes, and their density, flexural strength, and phase composition were analyzed. The HF solutions with different mass fractions of 20%, 30%, and 40% were prepared, respectively. In the first group, the same amount of HF solution with different mass fractions was taken, put into plastic containers with the ceramic samples, and corroded at room temperature for 200 h. In the second group, the HF solution with a mass fraction of 40% was used as an etching solution, and the samples were placed for corrosion. The corrosion time was 100, 200, 300 h, and 400 h, respectively. Each group of samples was sealed and placed in dark. Afterwards, the samples were cleaned, dried and tested, and the changes of mass, density phase composition and other properties before and after the corrosion were analyzed. Results and discussion As the mass fraction of HF solution increases from 20% to 40%, the ceramic sample reacts with HF to form a corrosion product(NH₄)_2SiF₆ phase, which attaches to the surface of the sample to form a loose corrosion layer, and gradually fells off and dissolves in the acid solution, resulting in an increase in the mass loss rate. Simultaneously, the increase of pores caused by corrosion reaction also results in a higher porosity, lower density, and reduced flexural strength of the ceramic samples as the HF concentration increases. The change in the microstructures of the samples before and after the corrosion indicates that the Si_3N₄ ceramic sample is immersed in HF solution to produce(NH₄)_2SiF₆, which causes the loss of Si and N, leading to an increased porosity and a reduced density within the sample, and thereby degrading the performance of the ceramic sample. The mass loss rate and porosity of ceramic samples increase, while density and flexural strength decrease as the corrosion time increases from 100 h to 400 h. From the perspective of corrosion rate, the corrosion rate decreases after 200-h corrosion. This is because the corrosion products of(NH₄)_2SiF₆ formed on the sample surface can block a direct contact between HF and the ceramic sample at a constant HF solution concentration. The extension of the corrosion time does not lead to an increase in the corrosion rate, indicating that the corrosion layer plays a significant role in maintaining the stability of Si_3N₄ ceramics in a corrosive environment. Conclusions Si_3N₄ ceramic materials prepared by nitridation reaction sintering with pure Si powder were corroded in HF solution for 200 h. The results showed that the mass, density and bending strength of ceramic samples decreased gradually, and the porosity increased with the increase of HF concentration and corrosion time. The Si_3N₄ ceramic sample was immersed in HF solution and reacted with HF to form a phase of(NH₄)_2SiF₆, leading to a loose corrosion layer on the surface of the sample. The mass loss and density of Si_3N₄ ceramic samples were reduced due to the corrosion reaction, and the presence of the corrosion layer reduced the corrosion rate, indicating that the high-purity porous Si_3N₄ ceramics were more stable in HF solution, and could maintain a better corrosion-resistant performance.