A preceramic polymer, polyzirconosaal （PZSA）, was synthesized by the ligand-exchange reaction between polyzirconoxane （PZO） and salicyl alcohol （SA）. The precursor was air-stable and exhibited excellent solubili...A preceramic polymer, polyzirconosaal （PZSA）, was synthesized by the ligand-exchange reaction between polyzirconoxane （PZO） and salicyl alcohol （SA）. The precursor was air-stable and exhibited excellent solubility and rheology. These properties are useful for the processing of C/C-ZrC composites v/a precursor infiltration and pyrolysis （PIP） process. The polymer to ceramic conversion was investigated by TG, XRD and TEM. Nanosized ZrC was formed by pyrolysis of this precursor at 1300 ℃ in argon with ceramic yield of 57.8%.展开更多
A new polymer,polyzirconoxanesal（PZS）,is synthesized from the reaction of zirconium oxychloride octahydrate （ZrOCl;-8H;O） with acetylacetone（Hacac） and salicyl alcohol（SA） by one-pot protocol.The polymer is so...A new polymer,polyzirconoxanesal（PZS）,is synthesized from the reaction of zirconium oxychloride octahydrate （ZrOCl;-8H;O） with acetylacetone（Hacac） and salicyl alcohol（SA） by one-pot protocol.The polymer is soluble in common organic solvents,such as ethanol,methanol,acetone,tetrahydrofuran and chloroform,and exhibits rheology with viscosity of 100- 300 mpa s at 25℃.These properties are suitable for uses in fabrication of ceramic matrix fiber composites.Pyrolysis of this polymer at 1300℃in argon provides nanosized ZrC with spherical morphology and size of 20-100 nm.展开更多
Ceramic materials able to heal manufacture or damage induced microstructure defects might trigger a change in paradigm for design and application of load bearing ceramics.This work reviews thermodynamic and kinetic as...Ceramic materials able to heal manufacture or damage induced microstructure defects might trigger a change in paradigm for design and application of load bearing ceramics.This work reviews thermodynamic and kinetic aspects governing the regeneration of solid contact able to transfer stress between disrupted crack surfaces in ceramics.Major crack healing processes include perturbation of crack-like pores followed by sintering of isolated pores,as well as reaction with an environmental atmosphere and filling of the crack space with an oxidation product.Since thermally activated solid state reactions require elevated temperatures which may exceed 1000℃,processes able to trigger crack healing at lower temperatures are of particular interest for transferring into engineering applications.Generic principles of microstructure modifications able to facilitate crack repair at lower temperatures will be considered:(i)acceleration of material transport by grain boundary decoration and grain size reduction,and(ii)reduction of thermal activation barrier by repair filler activation.Examples demonstrating crack healing capability include oxidation reaction of low energy bonded intercalation metal from nano-laminate MAX phases and catalyzed surface nitridation of polymer derived ceramics containing repair fillers.展开更多
Perhydropolysilazane,a low viscosity preceramic polymer with good wettability and high char yield,was used to fabricate three-dimensional silica fiber reinforced silicon nitride matrix composites through the repeated ...Perhydropolysilazane,a low viscosity preceramic polymer with good wettability and high char yield,was used to fabricate three-dimensional silica fiber reinforced silicon nitride matrix composites through the repeated infiltration-curing-pyrolysis cycles.With the increase of the pyrolysis temperature from T_(1),T_(2)to T_(3),the density of the composites increased all through,but the flexural strength showed a maximum value at T_(2)followed by a sharp decrease.The composite prepared at T_(2)exhibited a good ceramization of the preceramic polymer,a high flexural strength of 144.9 MPa and excellent dielectric property.The high performance of the composite resulted from the good state of the silica fibers,controlled fiber/matrix interfacial microstructures and high-purity dense silicon nitride matrix.展开更多
A systematic research on the pyrolysis process of polymethysilicone (SAR-2) and the thermostability of the pyrolysis residue was made by the thermogravimetric analysis, DTA and infrared spectroscopy.The experimental r...A systematic research on the pyrolysis process of polymethysilicone (SAR-2) and the thermostability of the pyrolysis residue was made by the thermogravimetric analysis, DTA and infrared spectroscopy.The experimental results indicate that the pyrolysis residue of SAR-2 converted into the amorphous SiC_xO_(4-x) phase above 900 ℃,the residue at 1200 ℃ is the most thermostable and antioxidant.It is suitable to be used as polysilicone preceramic.展开更多
Three-dimensionally (3D) long range ordered macroporous SiC ceramics were prepared through infiltrating polymethylsilane (PMS) into the 3D ordered sacrificial silica template, pyrolysis and the template removal. It wa...Three-dimensionally (3D) long range ordered macroporous SiC ceramics were prepared through infiltrating polymethylsilane (PMS) into the 3D ordered sacrificial silica template, pyrolysis and the template removal. It was found that the pore size (84―658 nm), BET surface area (299.44―584.64 m2/g) and micropore volume (0.25―0.64 cm3/g) of the achieved porous SiC can be tailored by utilizing different sizes silica sphere templates. There exist three kinds of pores in the porous ceramics: sphere inversed pores, windows and mesopores (2―5 nm). The sphere inversed pores were packed as hcp structure and three dimensionally penetrated through the windows, and the mesopores endowed the porous ceramics surprising high BET surface areas and micropore volumes.展开更多
Soluble Hf-containing polymers are significant processable precursors for the fabrication of ultra-high temperature ceramics.In this work,cyclic Hf-Schiff base polymers were synthesized via direct polymerization of ha...Soluble Hf-containing polymers are significant processable precursors for the fabrication of ultra-high temperature ceramics.In this work,cyclic Hf-Schiff base polymers were synthesized via direct polymerization of hafnium alkoxide and bis-salen monomers.The defined structure and molecular weight of the polymers were characterized by NMR spectroscopy,gel permeation chromatography and MALDI-TOF mass spectroscopy.The feed ratio of monomers regulated the molecular weight and solubility of the polymers.This synthetic strategy features simple operation under ambient conditions,efficient reaction with high yield and cyclic polymers as the main products.The Hf-Schiff base polymers were converted to HfC/C materials after pyrolysis under argon at 1600°C,which was identified by XRD measurements,elemental analyses and Raman spectroscopy.This work will inspire more precise and efficient synthesis and applications of metallopolymers.展开更多
In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of pr...In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of preceramic polymers,geopolymers,and sol-gel solutions.We mainly focus on processing with liquid feedstocks because they have some advantages with respect to slurry-based feedstocks in which powders are present.Particularly,lower viscosity,enhanced transparency,and lack of scattering and sedimentation are advantageous features for vat photopolymerization processes,whereas the absence of particulates reduces clogging problems at the nozzle for extrusion-based processes.Simultaneously,preceramic polymers and geopolymers have some limitations in terms of the range of ceramic compositions that can be obtained;sol-gel solutions are intrinsically unstable,whereas printed objects suffer from drying issues.Nevertheless,we successfully produced high-quality parts using a variety of additive manufacturing techniques,some of which(e.g.,volumetric additive manufacturing)have been proposed for the fabrication of ceramic components for the first time.展开更多
The joining of graphite, ceramic SiC and C_f/SiC composites via preceramic silicone resin(SR) at high temperature (8001400℃) was studied. The curing and pyrolysis process of SR, pyrolysis temperature, inert and a...The joining of graphite, ceramic SiC and C_f/SiC composites via preceramic silicone resin(SR) at high temperature (8001400℃) was studied. The curing and pyrolysis process of SR, pyrolysis temperature, inert and active fillers were especially discussed. The results show that the curing process of SR was accomplished by consuming Si—OH. The temperature of 1200℃ is the appropriate treating temperature for graphite and SiC ceramic, and the temperature of 1400℃ is suitable for C_f/SiC composites. Inert filler SiC powder(5%, mass fraction) has much positive influence on the shear strength of the joints. Active filler nano Ai, Si powder can greatly improve the properties of the joints treated at high temperature. The improvement is over 700%.展开更多
基金supported by"the Fundamental Research Funds for the Central Universities"(No. 2011QNA20)
文摘A preceramic polymer, polyzirconosaal （PZSA）, was synthesized by the ligand-exchange reaction between polyzirconoxane （PZO） and salicyl alcohol （SA）. The precursor was air-stable and exhibited excellent solubility and rheology. These properties are useful for the processing of C/C-ZrC composites v/a precursor infiltration and pyrolysis （PIP） process. The polymer to ceramic conversion was investigated by TG, XRD and TEM. Nanosized ZrC was formed by pyrolysis of this precursor at 1300 ℃ in argon with ceramic yield of 57.8%.
文摘A new polymer,polyzirconoxanesal（PZS）,is synthesized from the reaction of zirconium oxychloride octahydrate （ZrOCl;-8H;O） with acetylacetone（Hacac） and salicyl alcohol（SA） by one-pot protocol.The polymer is soluble in common organic solvents,such as ethanol,methanol,acetone,tetrahydrofuran and chloroform,and exhibits rheology with viscosity of 100- 300 mpa s at 25℃.These properties are suitable for uses in fabrication of ceramic matrix fiber composites.Pyrolysis of this polymer at 1300℃in argon provides nanosized ZrC with spherical morphology and size of 20-100 nm.
基金Financial support from DFG projects GR 961/34 and GR 961/32(Reinhart Kosselleck)is gratefully acknowledged。
文摘Ceramic materials able to heal manufacture or damage induced microstructure defects might trigger a change in paradigm for design and application of load bearing ceramics.This work reviews thermodynamic and kinetic aspects governing the regeneration of solid contact able to transfer stress between disrupted crack surfaces in ceramics.Major crack healing processes include perturbation of crack-like pores followed by sintering of isolated pores,as well as reaction with an environmental atmosphere and filling of the crack space with an oxidation product.Since thermally activated solid state reactions require elevated temperatures which may exceed 1000℃,processes able to trigger crack healing at lower temperatures are of particular interest for transferring into engineering applications.Generic principles of microstructure modifications able to facilitate crack repair at lower temperatures will be considered:(i)acceleration of material transport by grain boundary decoration and grain size reduction,and(ii)reduction of thermal activation barrier by repair filler activation.Examples demonstrating crack healing capability include oxidation reaction of low energy bonded intercalation metal from nano-laminate MAX phases and catalyzed surface nitridation of polymer derived ceramics containing repair fillers.
文摘Perhydropolysilazane,a low viscosity preceramic polymer with good wettability and high char yield,was used to fabricate three-dimensional silica fiber reinforced silicon nitride matrix composites through the repeated infiltration-curing-pyrolysis cycles.With the increase of the pyrolysis temperature from T_(1),T_(2)to T_(3),the density of the composites increased all through,but the flexural strength showed a maximum value at T_(2)followed by a sharp decrease.The composite prepared at T_(2)exhibited a good ceramization of the preceramic polymer,a high flexural strength of 144.9 MPa and excellent dielectric property.The high performance of the composite resulted from the good state of the silica fibers,controlled fiber/matrix interfacial microstructures and high-purity dense silicon nitride matrix.
文摘A systematic research on the pyrolysis process of polymethysilicone (SAR-2) and the thermostability of the pyrolysis residue was made by the thermogravimetric analysis, DTA and infrared spectroscopy.The experimental results indicate that the pyrolysis residue of SAR-2 converted into the amorphous SiC_xO_(4-x) phase above 900 ℃,the residue at 1200 ℃ is the most thermostable and antioxidant.It is suitable to be used as polysilicone preceramic.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59972042)the Korea National Research Laboratory Program (Grant No. M10400000061-04J0000-06110) the Doctor Innovation Fund of National University of Defense Technology in China (2001-2004).
文摘Three-dimensionally (3D) long range ordered macroporous SiC ceramics were prepared through infiltrating polymethylsilane (PMS) into the 3D ordered sacrificial silica template, pyrolysis and the template removal. It was found that the pore size (84―658 nm), BET surface area (299.44―584.64 m2/g) and micropore volume (0.25―0.64 cm3/g) of the achieved porous SiC can be tailored by utilizing different sizes silica sphere templates. There exist three kinds of pores in the porous ceramics: sphere inversed pores, windows and mesopores (2―5 nm). The sphere inversed pores were packed as hcp structure and three dimensionally penetrated through the windows, and the mesopores endowed the porous ceramics surprising high BET surface areas and micropore volumes.
基金by the National Natural Science Foundation of China(No.21604090)。
文摘Soluble Hf-containing polymers are significant processable precursors for the fabrication of ultra-high temperature ceramics.In this work,cyclic Hf-Schiff base polymers were synthesized via direct polymerization of hafnium alkoxide and bis-salen monomers.The defined structure and molecular weight of the polymers were characterized by NMR spectroscopy,gel permeation chromatography and MALDI-TOF mass spectroscopy.The feed ratio of monomers regulated the molecular weight and solubility of the polymers.This synthetic strategy features simple operation under ambient conditions,efficient reaction with high yield and cyclic polymers as the main products.The Hf-Schiff base polymers were converted to HfC/C materials after pyrolysis under argon at 1600°C,which was identified by XRD measurements,elemental analyses and Raman spectroscopy.This work will inspire more precise and efficient synthesis and applications of metallopolymers.
基金support from the China Scholarship Council(Grant No.201804910741).Y.Feng acknowledges the support from the China Scholarship Council(Grant No.201806220175).
文摘In this review,we summarize the research activities carried out by our research group at the University of Padova on the additive manufacturing of ceramics from liquid feedstocks.Particularly,we evaluate the use of preceramic polymers,geopolymers,and sol-gel solutions.We mainly focus on processing with liquid feedstocks because they have some advantages with respect to slurry-based feedstocks in which powders are present.Particularly,lower viscosity,enhanced transparency,and lack of scattering and sedimentation are advantageous features for vat photopolymerization processes,whereas the absence of particulates reduces clogging problems at the nozzle for extrusion-based processes.Simultaneously,preceramic polymers and geopolymers have some limitations in terms of the range of ceramic compositions that can be obtained;sol-gel solutions are intrinsically unstable,whereas printed objects suffer from drying issues.Nevertheless,we successfully produced high-quality parts using a variety of additive manufacturing techniques,some of which(e.g.,volumetric additive manufacturing)have been proposed for the fabrication of ceramic components for the first time.
文摘The joining of graphite, ceramic SiC and C_f/SiC composites via preceramic silicone resin(SR) at high temperature (8001400℃) was studied. The curing and pyrolysis process of SR, pyrolysis temperature, inert and active fillers were especially discussed. The results show that the curing process of SR was accomplished by consuming Si—OH. The temperature of 1200℃ is the appropriate treating temperature for graphite and SiC ceramic, and the temperature of 1400℃ is suitable for C_f/SiC composites. Inert filler SiC powder(5%, mass fraction) has much positive influence on the shear strength of the joints. Active filler nano Ai, Si powder can greatly improve the properties of the joints treated at high temperature. The improvement is over 700%.
