In the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ...ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina‐calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore‐forming agent process by adjusting the amount of CaCO3 and polymethyl methacrylate (PMMA) microspheres added. Al2O3 and CaCO3 were used as raw materials, PMMA microspheres were used as pore‐forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO3 and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina‐calcium aluminate ceramics were investigated. The results show that as the CaCO3 addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina‐calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO3 during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al2O3. The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.
In this study, poly (ether ether ketone) (PEEK)/polytetrafluoroethylene (PTFE) composites reinforced with carbon fibers (CFs) and graphite (Gr) were fabricated by compressive molding technology. The ...friction and wear properties of the PEEK/PTFE composites sliding against Si3N4 balls were investigated using ball-on-disk configuration under dry sliding conditions, and the morphologies of the worn surfaces were also observed with a scanning electron microscope (SEM) and a three-dimensional morphometer. The results indicated that the introduction of CFs significantly improved the tribological properties of the composites, but the friction coefficient of the PEEK/PTFE/CFs composites were higher than the pure PEEK/PTFE composites. However, it was found that a combinative addition of CFs and Gr creates an obvious synergetic effect of improving the friction-reducing and anti-wear abilities of the composites. The mechanisms of the improved tribological properties of the PEEK/PTFE/CFs/Gr composites were discussed based on the analysis of the worn surfaces and tribofilms.
In order to obtain a high material removal rate and good surface quality, the effect of Cu
2+
ions and glycine complex as a catalyst on the chemical mechanical polishing (CMP) performance of Si-face ...6H-SiC substrates was investigated. The results indicated that the slurry with Cu
2+
-glycine complex had a higher material removal rate (MRR) and better surface quality than that without Cu
2+
-glycine complex. The maximum MRR of the Si-face 6H-SiC substrate was 83 nm/h with an average roughness (Ra) of 0.336 nm using the slurry containing 6wt% silica (SiO
2
) and 4wt% hydrogen peroxide (H
2
O
2
) at pH 10. In contrast, when Cu
2+
-glycine complex were added as a catalyst, the maximum MRR was increased to 118 nm/h with Ra of 0.155 nm. The ultraviolet–visible (UV–vis) spectroscopy analysis indicated that the Cu
2+
-glycine complex was an effective catalyst for the decomposition of H
2
O
2
to generate more hydroxyl (
·
OH) radicals. Meanwhile, due to the fact that more softened layer was formed and the SiO
2
abrasive nanoparticles were deeply pressed into the softened layer to produce a plowing action under the polishing pressure, coefficient of friction (COF) was increased by adding the Cu
2+
-glycine complex. Finally, the polishing mechanism of the Si-face 6H-SiC substrates using the Cu
2+
-glycine complex was discussed.
Tribological and corrosion properties of chemically bonded ceramic coating (CBC) is limited due to the porous structure. To overcome the limitation, polytetrafluoroethylene (PTFE) is infiltrated into ...CBC by vacuum impregnation, and the related tribological and corrosion properties are investigated. CBC with the infiltration of PTFE (CBC/PTFE) shows a lower coefficient of friction than CBC because a transfer lubricant film is formed due to PTFE. In addition, the wear resistance is also improved with the infiltration of PTFE. Besides, CBC/PTFE possesses a better corrosion resistance attributing to the excellent hydrophobicity of PTFE and the compact layer caused by the filling of PTFE into the pores of CBC.
To enhance the tribocorrosion properties of chemically bonded phosphate ceramic coating (CBPCC), GO-ZnO was prepared and added into CBPCC. And the tribocorrosion behaviour of CBPCC was investigated. ...Results show that, with the introduction of GO-ZnO, the open circuit potential of CBPCC shifts in a positive direction and corrosion current density decreases. In addition, the total material loss, the total mechanical wear loss and the total electrochemical corrosion loss of CBPCC all decrease with the increase of GO-ZnO. The wear track of CBPCC after tribocorrosion without GO-ZnO is rough and porous, while the wear track becomes smooth and dense with the incorporation of GO-ZnO. The material in wear track is anchored by GO-ZnO due to the strong bond between GO-ZnO and CBPCC, which decreases the wear loss. Because of the extra force from the tribocorrosion experiment, the material anchored by GO-ZnO forms to a dense structure which prevents electrolyte diffusion into CBPCC. Moreover, GO-ZnO can block the electrolyte diffusion pathway and make it more tortuous. The resistance to the electrolyte diffusion decreases the corrosion current density and the increased wear loss due to electrochemical corrosion.
To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. ...Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.
Phytic acid (PA) benzotriazole composite conversion films with different concentrations of BTA were prepared by an impregnation method, and their wettability, microstructure, and corrosion resistance ...were studied. The results showed that when the BTA content was 1.6 wt %, the maximum water contact angle of the conversion film reached 137.5°, and the corrosion current density reached a minimum of 1.610 × 10
–7
A/cm
2
. The salt spray and corrosive liquid environments experimental results also showed that the synergistic effect of PA and BTA was the best when the BTA concentration was 1.6 wt %. Hydrogen bonds are formed between PA chelates and BTA chelates enhancing the density of the conversion film leading to the improvement of corrosion resistance of conversion film on a copper surface with the introduction of BTA.
Hybridization of nitric oxide (NO) donors with known anti-cancer agents have been emerged as a strategy to achieve improved therapeutic effect and to overcome chemo-resistance in cancer therapy. In ...this study, furoxan moiety as an efficient NO donor was introduced to phenstatin, a microtubule-interfering agent (MIA), leading to the design and synthesis of a series of furoxan-based NO-releasing arylphenones derivatives. In biological evaluation, the synthesized compounds showed moderate to potent anti-tumor activities against several human cancer cell lines. Among them, compound 15h showed the most potent activities against both chemo-sensitive and resistant cancer cell lines with IC50 values ranging from 0.008 to 0.021 μM. Further mechanistic studies revealed that 15h worked as a bifunctional agent exhibiting both tubulin polymerized inhibition and NO-releasing activities, resulting in potent anti-angiogenesis, colony formation inhibition, cell cycle arrest and apoptosis induction effects. In the nude mice xenograft model, 15h significantly inhibited the paclitaxel-resistant tumor growth with low toxicity, demonstrating the promising potential for further preclinical evaluation as a therapeutic agent, particularly for the treatment of chemo-resistant cancers.
Display omitted
•A series of furoxan-based NO-releasing arylphenones derivatives were synthesized and evaluated for anti-tumor activities.•Compound 15h showed enhanced anti-tumor activities on both chemo-sensitive and resistance cells in vitro and in vivo.•Compound 15h exhibited bifunctional effects on both tubulin polymerization and NO-releasing.
Zinc oxide (ZnO) decorated multi-walled carbon nanotubes (MWCNTs) hybrid material was prepared to improve the tribological performance of chemically bonded ceramic coatings. TEM results reveal that ...ZnO has been successfully fabricated on the surface of MWCNTs. The tribological performance of the ceramic coatings with MWCNTs–ZnO hybrid material was investigated using a ball-on-disc method. The results show that the friction coefficient and wear rate of the ceramic coatings decrease with the increase of MWCNTs–ZnO hybrid material. The ceramic coatings with MWCNTs-ZnO hybrid material shows a smooth worn surface with less cracks and delamination. In addition, the worn surface of the counterpart ball shows a smaller worn area and a smooth surface. The excellent wear resistance of the ceramic coatings is attributed to the good bonding strength between MWCNTs–ZnO hybrid material and ceramic matrix.
