The development of additive manufacturing technique provides possibility to prepare SiC ceramics with complex shapes. However, defect control in the debinding and sintering stages is still a great challenge for the vat photopolymerized components. Here, SiC ceramics were manufactured by vat photopolymerization followed by liquid silicon infiltration, using SiC whiskers as the reinforcement. In the debinding stage, the SiC whiskers prevented the propagation of micro-cracks that induced by the formation and emission of gaseous substance. Also, the SiC whiskers provided channels for the infiltration of liquid silicon during sintering, thus the bulk density of the as-sintered SiCw/RBSC composite reached 2.95 g/cm3 at the whiskers fraction of 8 wt.%. Because of the various toughening mechanisms introduced by SiC whisker, the flexural strength and Vickers hardness of the composite increased up to 352.2 MPa and 17.54 GPa, respectively. Thus, this work provides a new strategy to control micro-defects in vat photopolymerized SiC ceramics.
In this study, glass cenospheres are coated with resorcinol/formaldehyde resin in an alkaline solution, and the polymer layer is subsequently transformed into carbon shell by pyrolysis. Because carbon is a strong and lightweight material, the resulting aluminum matrix syntactic foam reinforced with carbon coated glass cenospheres shows low density of 1.35 g cm-3, and high energy absorption capacity of 80.3 MJ m- 3. The excellent energy absorption properties are ascribed to the conformal carbon shell that can disperse stress, leading to high compressive strength of the foam. The improved wettability of filler surfaces by liquid metals during pressure infiltration casting is verified using both optical and electron microscopy. In addition, XRD results suggest that no obvious interfacial reactions happen during the preparation of foam.
The industrial application of ceramic membrane in wastewater treatment is usually inhibited by the high manufacturing cost. Here, a low-cost ceramic membrane with whisker-constructed microstructure was prepared using fly ash as the major material and AlF3 as the catalyst. The influence of AlF3 contents and sintering temperatures on the synthesis of mullite whiskers and consequently the permeance-selectivity of the whiskerconstructed ceramic membrane, was investigated. With the increase of AlF3 content, the pore-forming mechanism of the ceramic membrane transformed from particles-packing to mullite whiskers-interlocking. The formation and growth mechanism of mullite whiskers were clarified. The formation of silicate liquid-phase during sintering accelerated the shrinkage of the ceramic membrane and merged the short and fine whiskers. For the ceramic membrane with 10 wt% catalyst sintered at 1100 degrees C, the porosity and average pore size corresponded to 62.3% and 0.41 & mu;m, respectively. Thus, this work provided a strategy for the preparation of mullite whiskersconstructed ceramic membrane with high porosity at low sintering temperature, which facilitated the highvaluable utilization of fly ash spontaneously.
Ceramic membranes with high porosity and excellent separation efficiency are necessary for the efficient treatment of large-scale wastewaters. However, the conventional ceramic membranes are usually prepared by particles-packing, which inhibits the advances of separation efficiency because of the low porosity and connectivity. Here, a fibrous ceramic membrane with mullite whiskers-interlocked structure was prepared by gas-solid reaction. The effects of aluminum fluoride (AlF3) on the formation and growth of mullite whiskers, and then the permeability and selectivity of the ceramic membranes were investigated. With the increase of AlF3 contents, the mullite phase evolved from needle-like, rod-like to flake-like structure, thus the catalyst accelerated the growth of mullite whiskers in the diameter direction. For the ceramic membrane sintered at 1400 & DEG;C, the porosity increased from 58% to 76% while the average pore sizes increased from 0.65 to 3.93 & mu;m because of the whisker-constructed structures. For the ceramic membrane sintered at 1450 & DEG;C, the emulsion flux increased stably from 295 L/(m(2)& BULL;h) to 992 L/(m(2)& BULL;h) with the increase of trans-membrane pressure, and the oil rejection exceeded 98%. Thus, this study provides a feasible strategy for the preparation of ceramic membranes with high porosity and excellent separation performances.
Asbestos fiber cement boards are still widely used domestically,despite that asbestos can leads to serious and fatal illness such as lung cancer.Nowadays,people concern more about environmental protection and health problem,asbestos-free fiber cement siding boards become more popular.The mechanical properties and durability of the paper pulp fiber reinforeced cement board are studied and the influences of Ca/Si ratio and wollastonite microfiber content are also investigated.The results show that with the Ca/Si molar ratio of raw materials between 0.5～0.6 can produce boards with higher flexural strength.Wollastonite microfiber about 5wt%can also improve the water saturated flexural strength and decrease the water sorptivity.The properties of commonly used boards with and without asbestos are analyzed,and the results indicate that the latter has higher tensile strength perpendicular to face and higher water saturated flexural strength,meanwhile,its freeing-thawing resistance,hot-shower resistance,hot-water resistance,and dry-wet resistance can also meet the requirements of relevant Chinese standards.
