This paper presents a novel ultrasonic vibration-assisted machining method for ceramic gels(wet green bodies),aiming to overcome the limitations of conventional ceramic machining methods,which often cause defects such...This paper presents a novel ultrasonic vibration-assisted machining method for ceramic gels(wet green bodies),aiming to overcome the limitations of conventional ceramic machining methods,which often cause defects such as chipping and cracking owing to the low strength of dried green bodies and the brittleness of pre-sintered and sintered ceramics.Additionally,they struggle to produce ceramics with special shapes,non-communicating slots and holes.The proposed method leverages the shear-stress-induced reflow property of ceramic gel by applying high-frequency ultrasonic vibration in the vertical direction to selectively remove the undesired part of the ceramic gel.This approach enables precise,nondestructive processing for surface modification,slotting,and drilling achieving feature sizes on the order of microns.The experimental results further demonstrate its effectiveness in bonding ceramic components.This method offers a promising alternative to conventional ceramic machining methods for advanced ceramic manufacturing.展开更多
Slurries with high solid loading and low apparent viscosity are critical for spontaneous coagulation casting(SCC)and other in situ slurry solidification techniques.This work evaluated polyacrylic acid(PA)with a low mo...Slurries with high solid loading and low apparent viscosity are critical for spontaneous coagulation casting(SCC)and other in situ slurry solidification techniques.This work evaluated polyacrylic acid(PA)with a low molecular weight modified as a superior dispersant(M-PA)to increase the versatility and applicability of SCC,which traditionally employs Isobam 600AF as a dispersant in combination with Isobam 104.Varying the ratio of M-PA to Isobam 104 increased the solid loading of the alumina slurry—formulated with a commercial powder(D_(50)=0.45μm)—from 56 to 58 vol%.The relative density of the alumina green body increased from 62.0%to 67.0%.The ceramics derived from a 56 vol%solid loading slurry,when sintered at 1550℃,exhibited a relative density of 98.7%,a Vickers hardness of 17.3 GPa,and a flexural strength of 583 MPa,surpassing those of ceramics prepared with other dispersants.The ceramics derived from a 58 vol%solid loading slurry,when sintered at 1500℃,exhibited a relative density of 98.9%and a Vickers hardness of 17.8 GPa.These findings demonstrate the potential of M-PA to broaden the applicability of SCC and suggest that the strategy of using a low-molecular-weight dispersant may enable the fabrication of high-density green bodies through SCC,resulting in high mechanical properties of ceramics under low sintering temperatures.展开更多
Porous ceramics have been widely used in heat insulation,filtration,and as a catalyst carrier.Ceramics with high porosity and high strength are desired;however,this high porosity commonly results in low strength mater...Porous ceramics have been widely used in heat insulation,filtration,and as a catalyst carrier.Ceramics with high porosity and high strength are desired;however,this high porosity commonly results in low strength materials.In this study,porous alumina with high porosity and high strength was prepared by a popular direct foaming method based on particle-stabilized wet foam that used ammonium polyacrylate(PAA)and dodecyl trimethyl ammonium chloride(DTAC)as the dispersant and hydrophobic modifier,respectively.The effects of the dispersant and surfactant contents on the rheological properties of alumina slurries,stability of wet foams,and microstructure and mechanical properties of sintered ceramics were investigated.The microstructure of porous ceramics was regulated using wet foams to achieve high strength.For a given PAA content,the wet foams exhibited increasing stability with increasing DTAC content.The most stable wet foam was successfully obtained with 0.40 wt%PAA and 0.02 wt%DTAC.The corresponding porous alumina ceramics had a porosity of 82%,an average grain size of 0.7μm,and a compressive strength of 39 MPa.However,for a given DTAC content,the wet foams had decreasing stability with increasing PAA content.A possible mechanism to explain these results is analyzed.展开更多
Transparent Al_(2)O_(3) ceramics with grains aligned to the c-axis were prepared by adding platelets with a low aspect ratio into fine equiaxed particles.The mixed powders were formed into green bodies using spontaneo...Transparent Al_(2)O_(3) ceramics with grains aligned to the c-axis were prepared by adding platelets with a low aspect ratio into fine equiaxed particles.The mixed powders were formed into green bodies using spontaneous coagulation casting and sintered by pressureless sintering and hot-isostatic pressure sintering.Zeta potentials and rheological behavior of the slurries,relative densities of green bodies,and orientation and optical properties of sintered bodies were investigated and discussed.The platelet with a high aspect ratio suppressed densification more seriously during sintering than the one with a low aspect ratio.An excellent oriented structure was obtained when 5 wt%platelets with a low aspect ratio were added,and transparent Al_(2)O_(3) ceramics with grains aligned to c-axis were successfully prepared;the in-line transmittance was 78.4%at 600 nm,which is the highest one in the currently reported literature.展开更多
A green body with a density as high as possible is critical to diminish the crisis of deformation or cracking when large-size parts are sintered.Here,a new method,i.e.,re-fluidising the aged ceramic gel is developed t...A green body with a density as high as possible is critical to diminish the crisis of deformation or cracking when large-size parts are sintered.Here,a new method,i.e.,re-fluidising the aged ceramic gel is developed to prepare the high-density green body.Alumina slurry with 56 vol%solid loading and copolymers of isobutylene and maleic anhydride were aged without vaporisation and re-fluidised by non-intrusive shearing after removing the exuded water.The re-fluidised slurry was re-casted.The resultant wet gel was dried and deboned at a low temperature.The relative density of the obtained green body was 64.6%,1.5%higher than that without aging and re-fluidising.The linear sintering shrinkage of the body decreased by 0.7%.The enhanced green density is explained from the viewpoint of the solid loading and the structure of the slurry.展开更多
基金supported by the National Natural Science Foundation of China(No.52130207).
文摘This paper presents a novel ultrasonic vibration-assisted machining method for ceramic gels(wet green bodies),aiming to overcome the limitations of conventional ceramic machining methods,which often cause defects such as chipping and cracking owing to the low strength of dried green bodies and the brittleness of pre-sintered and sintered ceramics.Additionally,they struggle to produce ceramics with special shapes,non-communicating slots and holes.The proposed method leverages the shear-stress-induced reflow property of ceramic gel by applying high-frequency ultrasonic vibration in the vertical direction to selectively remove the undesired part of the ceramic gel.This approach enables precise,nondestructive processing for surface modification,slotting,and drilling achieving feature sizes on the order of microns.The experimental results further demonstrate its effectiveness in bonding ceramic components.This method offers a promising alternative to conventional ceramic machining methods for advanced ceramic manufacturing.
基金supported by the National Natural Science Foundation of China(Nos.52130207 and U23A6014)。
文摘Slurries with high solid loading and low apparent viscosity are critical for spontaneous coagulation casting(SCC)and other in situ slurry solidification techniques.This work evaluated polyacrylic acid(PA)with a low molecular weight modified as a superior dispersant(M-PA)to increase the versatility and applicability of SCC,which traditionally employs Isobam 600AF as a dispersant in combination with Isobam 104.Varying the ratio of M-PA to Isobam 104 increased the solid loading of the alumina slurry—formulated with a commercial powder(D_(50)=0.45μm)—from 56 to 58 vol%.The relative density of the alumina green body increased from 62.0%to 67.0%.The ceramics derived from a 56 vol%solid loading slurry,when sintered at 1550℃,exhibited a relative density of 98.7%,a Vickers hardness of 17.3 GPa,and a flexural strength of 583 MPa,surpassing those of ceramics prepared with other dispersants.The ceramics derived from a 58 vol%solid loading slurry,when sintered at 1500℃,exhibited a relative density of 98.9%and a Vickers hardness of 17.8 GPa.These findings demonstrate the potential of M-PA to broaden the applicability of SCC and suggest that the strategy of using a low-molecular-weight dispersant may enable the fabrication of high-density green bodies through SCC,resulting in high mechanical properties of ceramics under low sintering temperatures.
基金supported by the National Natural Science Foundation of China(51602194 and 51772309)Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures(SKL201901).
文摘Porous ceramics have been widely used in heat insulation,filtration,and as a catalyst carrier.Ceramics with high porosity and high strength are desired;however,this high porosity commonly results in low strength materials.In this study,porous alumina with high porosity and high strength was prepared by a popular direct foaming method based on particle-stabilized wet foam that used ammonium polyacrylate(PAA)and dodecyl trimethyl ammonium chloride(DTAC)as the dispersant and hydrophobic modifier,respectively.The effects of the dispersant and surfactant contents on the rheological properties of alumina slurries,stability of wet foams,and microstructure and mechanical properties of sintered ceramics were investigated.The microstructure of porous ceramics was regulated using wet foams to achieve high strength.For a given PAA content,the wet foams exhibited increasing stability with increasing DTAC content.The most stable wet foam was successfully obtained with 0.40 wt%PAA and 0.02 wt%DTAC.The corresponding porous alumina ceramics had a porosity of 82%,an average grain size of 0.7μm,and a compressive strength of 39 MPa.However,for a given DTAC content,the wet foams had decreasing stability with increasing PAA content.A possible mechanism to explain these results is analyzed.
基金This work was supported by the National Natural Science Foundation of China(Nos.51772309 and 52130207).The authors thank Prof.Jing WANG(Dalian University of Technology)for the synthesis of Al2O3 platelets.
文摘Transparent Al_(2)O_(3) ceramics with grains aligned to the c-axis were prepared by adding platelets with a low aspect ratio into fine equiaxed particles.The mixed powders were formed into green bodies using spontaneous coagulation casting and sintered by pressureless sintering and hot-isostatic pressure sintering.Zeta potentials and rheological behavior of the slurries,relative densities of green bodies,and orientation and optical properties of sintered bodies were investigated and discussed.The platelet with a high aspect ratio suppressed densification more seriously during sintering than the one with a low aspect ratio.An excellent oriented structure was obtained when 5 wt%platelets with a low aspect ratio were added,and transparent Al_(2)O_(3) ceramics with grains aligned to c-axis were successfully prepared;the in-line transmittance was 78.4%at 600 nm,which is the highest one in the currently reported literature.
基金This work was supported by the National Natural Science Foundation of China(No.52130207).
文摘A green body with a density as high as possible is critical to diminish the crisis of deformation or cracking when large-size parts are sintered.Here,a new method,i.e.,re-fluidising the aged ceramic gel is developed to prepare the high-density green body.Alumina slurry with 56 vol%solid loading and copolymers of isobutylene and maleic anhydride were aged without vaporisation and re-fluidised by non-intrusive shearing after removing the exuded water.The re-fluidised slurry was re-casted.The resultant wet gel was dried and deboned at a low temperature.The relative density of the obtained green body was 64.6%,1.5%higher than that without aging and re-fluidising.The linear sintering shrinkage of the body decreased by 0.7%.The enhanced green density is explained from the viewpoint of the solid loading and the structure of the slurry.
