## 3 Results
### Microstructure of DKM
#### 3.1.2 Pore Characteristics of DKM  
The pore size distribution curve of pure kaolin is characterized by a single prominent peak at diameter of 0.2-0.6 \(\upmu\)m (Figure 5a), which represents the inter-aggregate pores according to Figure 3. The domain of intra-aggregate pores was not found in the kaolin sample because this type of pore is not abundant, resulting from the dominant face-to-face contact between kaolinites (Figures 3 and 4). For diatom, the dominant domain corresponding to diameters of 0.06-0.2 \(\upmu\)m and the subdomain at diameter of 10 \(\upmu\)represent the skeletal and intra-skeletal pores, respectively. Skeletal pores are small in volume but numerous, which is opposite to the case of intra-skeletal pores. The pore size distribution curve of diatoms in the range of \(d\) = 0.2-0.6 \(\upmu\)m is more like a plateau than a peak. This plateau, as well as the second-highest peak (\(d\) = 0.6-2 \(\upmu\)m), correspond to the pores in the open fabric of the diatom skeletons (Figure 3b). The pore size distribution of DKM is trimodal and located between those of kaolin and diatoms. For DKM, the domain for \(d\) = 0.2-2 \(\upmu\)m corresponds to the intra-aggregate pores, inter-aggregate pores, and the pores in the diatom skeletons. The skeletal and intra-skeletal pores in the DKM are reflected by the peaks at diameters of 0.06-0.2 \(\upmu\)m and 10 \(\upmu\)m, respectively, which is consistent with the case for the diatoms. With increasing diatom content, the pore size distribution curve of the DKM approaches that of the diatoms in shape.  
Figure 3: Scanning electron microscopy images of (**a**) kaolin (0D-100K) (**b**,**c**) diatoms (100D-0K), (**d**–**f**) a DKM (60D-40K), and (**g**–i**) crushed diatoms.  
Figure 5b shows the cumulative pore distribution of DKM, which is intermediate to that of diatom and kaolin. The \(CV\)-\(d\) curve of kaolin falls rapidly as \(d\) increases from 0.2 \(\upmu\)m to 0.6 \(\upmu\)m, while that of diatom falls in a stepwise manner as \(d\) increases from 0.06 \(\upmu\)m to 2 \(\upmu\)m; the \(CV\)-\(d\) curves of both kaolin and diatom for other pore ranges are approximately unchanged. As the diatom proportion increases, the pore volume considerably increases, and the pattern of the \(CV\)-\(d\) curve progressively changes from the kaolin to the diatom.  
Based on the \(IV\)-\(d\) curves, the DKM pores are classified as tiny (\(d<0.2\)\(\upmu\)m), small (0.2 \(<d<0.6\)\(\upmu\)m), medium (0.6 \(<d<2\)\(\upmu\)m), and large (\(d>2\)\(\upmu\)m) following the study of [PERSON] et al. [30]. The diatoms have more medium and tiny pores, but far fewer small pores compared to the kaolin (Figure 5c). When increasing the diatom content in DKM, the number of medium pores and small pores increases, which corresponds to the rightward shift of the second dominant peak (Figure 5a). By contrast, the proportion of tiny pores is scarcely affected by the diatom content and is higher than that of the kaolin. From a micro-level perspective (Figure 3a,f), the difference between the pore volume distribution curves of kaolin and DKMs in Figure 5c is due mainly to the skeletal and intra-skeletal  
Figure 4: Transmission electron microscopy images of (**a**) kaolin (15,000\(\times\) magnification); (**b**) kaolin (40,000\(\times\)); (**c**) diatoms (8000\(\times\)); and (**d**) diatoms (80,000\(\times\)).  
Figure 5: Results of mercury intrusion porosimetry tests on DKM samples: (**a**) \(IV\)–\(d\) curves; (**b**) \(CV\)–\(d\) curves; (**c**) volume proportion of pores with different diameters.  
pores from the diatom frustules and the varying sizes and shapes of inter-aggregate and intra-aggregate pores in diatom-kaolin aggregates.