Le Fu,Bohan Wang,Junjie Song,Chenglong Xu,Guofu Xu,Qiuan Sun,Jiwu Huang,Håkan Engqvist,Wei Xia
The content of crystalline phase plays a significant role in manipulating the microstructure and mechanical properties of glass-ceramics. This study aims at exploring the optimum content of crystalline phase in ZrO 2 –SiO 2 nanocrystalline glass-ceramics (NCGCs) in terms of obtaining the highest mechanical properties. To this end, the mechanical properties of ZrO 2 –SiO 2 NCGCs with 70 mol%, 75 mol%, 80 mol% ZrO 2 were tested and compared with those of the previously prepared NCGCs with ZrO 2 content ranging from 35 mol% to 65 mol%. Results showed that 65 mol% was the optimum content of ZrO 2 in terms of obtaining the highest flexural strength . The flexural strength of NCGCs with ZrO 2 content over 65 mol% was lower than that of the NCGCs with 65 mol% ZrO 2 . This was because the NCGC with 65 mol% ZrO 2 had a homogenous microstructure, with ZrO 2 nanocrystallites homogeneously distributed in an amorphous SiO 2 matrix. Whereas, when ZrO 2 content was increased to 75 mol%, ZrO 2 nanocrystallites were not homogeneously distributed in the SiO 2 matrix anymore. The formation of SiO 2 “holes/canyon” due to ZrO 2 grain coalescence resulted in the decrease of flexural strength. The fracture mechanism and wear properties of the NCGCs were also investigated.
The damage modes of Al 2 TiO 5 flexible ceramics (AT) with microcracks strengthened were studied by machine leaning for damage mode identification. Results show that the optimal number of clusters increases from 3 to 4 with the increase of ZrO 2 content. Meanwhile, the concentrated region of cluster with the same label gradually shifts to the direction of low amplitude with increase of ZrO 2 . In addition, the quantity of cluster is easy saturated since the AT grain boundary microcracks are strengthened by the formation of ZrTiO 4 . For achieving the automatic identification of different damage modes, support vector machine based on Kennard-stone training set selection was used to distinguish the damage modes of other samples in the same sample set. Almost the same evolution trend of corresponding clusters in new samples and training samples proves high efficiencies of this method.
A microwave hydrothermal (MWH) method was used to deposit WO 3 onto ZrO 2 –Al 2 O 3 with various ZrO 2 contents to prepare hydrodesulfurization (HDS) catalysts with high WO 3 loading (23 wt%) close to industrial hydrotreating, for achieving high W dispersion and weak W-support interaction. The catalysts with the same WO 3 and ZrO 2 contents were prepared by a conventional impregnation (IM) method as reference. The effects of catalyst preparation methods and ZrO 2 contents on the catalyst property and dibenzothiophene HDS activity were investigated. The results show that the MWH method leads to highly dispersed octahedrally coordinated W species which are weakly linked on ZrO 2 –Al 2 O 3 and easy to be reduced; no bulk WO 3 crystallites are observed even at high ZrO 2 content (50 wt%). Therefore, it causes better sulfidation and shorter WS 2 slabs. Contrarily, the IM method induces W species to agglomerate into bulk WO 3 crystallites which are poorly dispersed and hard to be reduced, which is further aggravated by ZrO 2 . The HDS activity of the MWH-prepared catalysts significantly increases with ZrO 2 up to 40 wt% ZrO 2 . This catalyst shows 2 times higher rate constant and 1.64 times higher efficiency of HDS than the IM-prepared catalyst with the same ZrO 2 content. For the IM-prepared catalysts, the HDS activity slightly increases at small amount of ZrO 2 (10 wt%) and then decreases drastically.
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