Abstract In this study, the crack behaviour of porous kaolin based ceramics was experimentally investigated. The samples (ceramic bodies) were fabricated with the inclusion of pore formers in determined proportions and subjected to heat treatment. Next, the apparent porosity of the samples was measured using the water immersion method. The values confirmed the increased porosity (up to 47%) for the samples with embedded pores. We speculated that the open pores on the surface of the samples which were quite evident, especially with styrofoam as pore formers, may also have penetrated through, hence the enhanced porosity values for the samples. Acoustic emission (AE) activity which reveals the formation of microcracks in the ceramics due to the different thermal expansion coefficients in the cooling stage was recorded for the samples. The first signals of AE counts appeared at 800 °C, where the compressive stresses between the different phases (particles with different coefficients of thermal expansion) led to an appearance of microcracks. By introducing porosity to the samples, the AE signals were less pronounced. This was evident for the samples with sawdust as pore formers, and it was inferred that in this sample, microcracking was suppressed. As a validation protocol for AE measurements, mechanical measurements on the produced samples were conducted through the indentation technique to obtain the fracture toughness of the samples. The results conformed to the observation made during AE measurements. The samples embedded with sawdust as porogens produced the highest fracture toughness of 4.77 MPa.m1/2 by reason of the suppression of microcracking after heat treatment.

中文翻译：

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热处理高岭土基陶瓷的裂纹行为和力学性能：造孔剂的影响

摘要 本研究对多孔高岭土基陶瓷的裂纹行为进行了实验研究。样品（陶瓷体）在制造时包含确定比例的成孔剂并进行热处理。接下来，使用水浸法测量样品的表观孔隙率。这些值证实了具有嵌入孔的样品的孔隙率增加（高达 47%）。我们推测样品表面上非常明显的开孔，尤其是泡沫聚苯乙烯作为成孔剂，也可能已经渗透，因此样品的孔隙率值增加。记录样品的声发射 (AE) 活动，该活动表明由于冷却阶段中不同的热膨胀系数在陶瓷中形成微裂纹。AE 计数的第一个信号出现在 800 °C，其中不同相（具有不同热膨胀系数的颗粒）之间的压应力导致出现微裂纹。通过将孔隙率引入样品，AE 信号不太明显。这对于以锯末作为造孔剂的样品来说是明显的，并且推断在该样品中，微裂纹被抑制了。作为 AE 测量的验证协议，通过压痕技术对生产的样品进行机械测量，以获得样品的断裂韧性。结果与在 AE 测量期间进行的观察一致。由于热处理后的微裂纹得到抑制，嵌入木屑作为致孔剂的样品产生了最高的断裂韧性，为 4.77 MPa.m1/2。