Preperation, Structure and Performance of Mullite Whisker Reinforced Ceramics-based Composites

Author:Chen Xu Dong

Supervisor:li tie hu

Database:Doctor

Degree Year:2018

Download:21

Pages:119

Size:5127K

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Mullite whiskers have excellent mechanical,electrical,optical,high temperature and corrosion resistance,and are widely used as toughening materials for ceramic matrix composites.However,it is still a major challenge in the field of material engineering to develop a kind of mullite whisker reinforced ceramic composite with excellent mechanical and chemical stability,low density and simple preparation process and low cost.In this paper,mullite whisker was prepared by traditional sintering method.Using fly ash,coal gangue,bauxite and other minerals as raw materials,feldspar,manganese ore and talcum as sintering aids,mullite whisker reinforced corundum ceramic composites,mullite whisker network structure reinforced ceramic composites,bird’s nest-like mullite whisker 3-D Network were prepared,the low density high strength ceramsite proppant based on the mullite whisker network structure reinforced ceramic composite,and the influence of the complex sintering agent on the phase composition,microstructure and properties of the above materials were also studied.By direct sintering,mullite whisker reinforced corundum ceramic composites were prepared with fly ash,illite and bauxite as raw materials,adding talcum and aluminum fluoride as a complex catalyst.The morphology and distribution of mullite whiskers were controlled by adjusting the amount of composite sintering aids and firing temperature.When the addition of composite sintering aids is 6w.t.%,the performance of mullite whisker reinforced corundum ceramic composites can be obtained at 1400 firing temperature.The apparent density is 2.94 g·cm-3,the bending strength is 144.46 MPa,and the acid solubility is 6.89%.When the burning temperature rises above 1500℃,a ceramic composite made up of mullite whiskers can be obtained,but the prepared mullite whisker will grow over,increase the porosity and decrease the performance.With 70% fly ash as raw material,the structure of mullite whisker network structure was obtained by introducing feldspar-talcum-BaCO3-pyrolusite complex catalyst,and the content and length to diameter ratio of mullite whisker could be controlled by adjusting the amount of pyrolusite.When the content of manganese ore is 6w.t.%,a low density and high strength mullite whisker network structure reinforced ceramic composite material can be prepared at 1390℃.Its bulk density is 1.48 g·cm-3,and its flexural strength is 190.10 MPa.In addition,the composite has excellent chemical stability and its acid solubility is 2.55 wt%.With 60% fly ash as raw material,low density and high intensity mullite whisker network structure can be controlled under the compound burning system of feldspar-BaCO3-pyrolusite complex catalyst.The growth rate,length to diameter ratio and distribution form of mullite whisker can be controlled effectively by regulating the content of feldspar.When the addition of feldspar is 4w.t.%,the mullite whisker diameter at 1350℃ is 200 nm and the length is about 5 μm.The network structure formed by this whisker is the best to enhance the mechanical properties of mullite based ceramic composites.The bending strength is 199.89 MPa,the bulk density is 1.51 g·cm-3.The effects of sintering additives on the growth,development,morphology and distribution of mullite whisker were studied by SEM,and the formation mechanism of mullite whisker network structure was revealed.Using the CO2 soft template method,using 70% coal gangue and 21% bauxite as raw material,the bird’s nest like 3-D mullite whisker network structure was successfully prepared in lithium chinastone-MnO2-CaCO3 complex catalyst.When the addition of lithium chinastone is 4w.t.%,the mullite whisker diameter at 1400℃ is 200 nm and the length is about3 5μm.The flexural strength of the bird’s nest like 3-D mullite whisker network structure reinforced ceramic composite is 165.61 MPa,the volume density is 1.55 g·cm-3,and the acid solubility is 3.15 wt%.With low density and high strength mullite whisker network structure reinforced ceramic composite as raw material,the low density and high strength mullite based ceramic proppant was prepared by the process of sugar coating machine.In accordance with the China Petroleum and natural gas industry standard "SY/T 5108-2014 Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations",the properties of the prepared ceramic support were tested.The results show that the bulk density is 1.46 g·cm-3,the apparent density is 2.70 g·cm-3,the crushing rate is 2.40%,the best acid resistance at 1350℃ is 2.63%,which is far below the standard requirement 7%.The main phase of the ceramic proppant is mullite phase,and the good mullite whisker network structure provides excellent strength and acid resistance.