The properties of SiC kiln furniture bonded with fine silicon powderare related to the bonder’s crystal structure. At high temperature, it will crystallize ina-cristobalite with great bulk effect. MnO2 mineralizer ca...The properties of SiC kiln furniture bonded with fine silicon powderare related to the bonder’s crystal structure. At high temperature, it will crystallize ina-cristobalite with great bulk effect. MnO2 mineralizer can make a-cristobalite convertto a-tridymite whose bulk effect is small. The crystal structure and its amount were investigated with XRD technique. The influence of different amounts of MnO2 on thecrystal structure and polycrystal transformation, and that of crystal structure on theproperties of kiln furniture were studied. The best proportion of MnO2 added was determined to be 2.0%.展开更多
Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effec...Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effects (including binder type and binder addition quantity) on the crystal structure and catalysis properties of photocatalyst. In this work, the catalysis activity was defined as the degradation rate of methyl orange solution upon ultraviolet lamp irradiation, and the specific areas were determined with nitrogen desorption method. TiO2 crystal form was measured with X-ray powder diffraction and their micro-morphology was observed with SEM. Experimental results indicate that these two binders do not affect the crystal form transformation of TiO2, but silica gol can increase the specific surface area of TiO2 photocatalyst obviously and the addition of sodium silicate can decrease it. In all, silica gol is a better candidate than sodium silicate for higher catalysis property. In conclusion, 6% silica gol is the optimal addition concentration. Under this condition, the ratio of anatase to rutile TiO2 is 64:36, the specific area is 29.67 m^2/g, and as expected, the degradation rate of methyl orange could be as high as 90% after irradiation for 5 days.展开更多
TiO2 photocatalyst was supported with tetrabutyl titanate sol as precursor and fine silicon powder obtained from ferroalloys factory as carder to discuss the influence of pH value of gel precursor on microstructure an...TiO2 photocatalyst was supported with tetrabutyl titanate sol as precursor and fine silicon powder obtained from ferroalloys factory as carder to discuss the influence of pH value of gel precursor on microstructure and activity of photocatalyst in the process of synthesizing nano-TiO2 by using sol-gel method, the purpose of which is to provide fundamental data for the recycle of photocatalytic material. Under the irradiation of ultraviolet light, the photocatalytic degradation rate of methyl orange solution was used to characterize the photocatalytic activity of the sample. The specific surface area of the sample was tested by N2 desorption method, crystal form of TiO2 was analyzed by X-ray powder diffraction, and the microtopography of the sample was observed by scanning electron microscopy. The experimental results showed that the acidity of gel precursor could greatly affect the specific surface area and photocatalytic activity of the photocatalyst, and the optimum pH value of the precursor was determined as 2.0, and at this time the specific surface area of photocatalyst could reach 34.0 m^2/g. In the sample, the proporticn of anatase to rutile is 7:3, which makes l0 mg·L^-1 methyl orange solution fade after irradiation by 15W ultraviolet light for 24 h, and the degradation rate might be up to 98.1%.展开更多
The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ra...The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.展开更多
Effects of particle size (A:d50 = 336. 9 μm, B:d50 =123.5μm, C: d50=19.5 μm, D: dso=2.21μm) and content (1 wt% , 3 wt% , 5 wt% , 7 wt% ) of silicon powder on cold crushing strength (CCS) , pore size dis...Effects of particle size (A:d50 = 336. 9 μm, B:d50 =123.5μm, C: d50=19.5 μm, D: dso=2.21μm) and content (1 wt% , 3 wt% , 5 wt% , 7 wt% ) of silicon powder on cold crushing strength (CCS) , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens' pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.展开更多
In order to reduce the hydrolysis rate of Si powder and inhibit the swelling and cracking of cast samples,Si powder was treated at different temperatures for 5 h,and then slurries and SiC-Si3N4 materials were prepared...In order to reduce the hydrolysis rate of Si powder and inhibit the swelling and cracking of cast samples,Si powder was treated at different temperatures for 5 h,and then slurries and SiC-Si3N4 materials were prepared.The effect of the preheating temperature on the composition of the Si powder,the hydrolysis rate as well as the nitridation of the SiC-Si3N4 materials was studied.The results show that with the increase of the pretreatment temperature of Si powder,the oxidation degree of Si powders increases,the viscosity of the slurry with PAAS dispersant decreases gradually,and the hydrolysis reaction of Si powder decreases gradually;the Si powder pretreated at 700℃ or lower has little effect on the nitriding process,while the Si powder pretreated at 800 t has a great effect on the nitriding process,which is not conducive to the nitriding sintering of the samples.Therefore,the Si powder pretreated at 700 t for 5 h has the best properties,which not only has lower hydrolysis rate and good slurry fluidity,but also has mild effect on the nitriding reaction.展开更多
Silicon nitride (Si3N4) powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The...Silicon nitride (Si3N4) powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor (2.27 cm.s^-1) in the Arrhenius equation, activation energy (114 kJ·mol^-1), and effective diffusion coefficient (6.2×10-s cm2.s^-1). A formula was also derived to calculate the reaction rate constant.展开更多
In this study, the electrorheological (ER) behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil (SO) medium was investigated. Sedimentation stabilities of suspensio...In this study, the electrorheological (ER) behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil (SO) medium was investigated. Sedimentation stabilities of suspensions (c = 5 wt%) prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated.展开更多
The XRPD (X-ray powder diffxactometry) patterns of silicon powder with a unit cell structure of diamond were determined from 298 to 1473 K. Lattice parameters of Si linearly increase with temperature. The thermal shif...The XRPD (X-ray powder diffxactometry) patterns of silicon powder with a unit cell structure of diamond were determined from 298 to 1473 K. Lattice parameters of Si linearly increase with temperature. The thermal shifts of the positions of all reflection peaks are linearly correlated with the temperature. The coefficients of the intrinsic linear thermal expansion and volumetric thermal expansion were determined as 3.87×10-6/K and 1.16×10-5/K respectively. It indicates that Si is still a suitable standard in the XRPD method at high temperatures.展开更多
This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of m...This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.展开更多
The basic formulation of Al2O3- C slide plates was65%( in mass,the same hereinafter) white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, a...The basic formulation of Al2O3- C slide plates was65%( in mass,the same hereinafter) white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al + 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al + 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides: AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.展开更多
Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(whe...Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.展开更多
A reaction bonding technique and a method of layer coating were developed to fabricate porous SiC.The green body was prepared using 250.0μm SiC particles as the raw material,fineα-Al2O3 and SiC powders with mass rat...A reaction bonding technique and a method of layer coating were developed to fabricate porous SiC.The green body was prepared using 250.0μm SiC particles as the raw material,fineα-Al2O3 and SiC powders with mass ratio of 2.5:1as sintering additives,65.2μm graphite as the pore-forming agent and polyvinyl alcohol(PVA)as the binder.The micro powders were coated on the surface of coarse SiC particles.After sintering,fine SiC particles were oxidized to silica(SiO2)then transforming into cristobalite,which finally reacted withα-Al2O3 to produce mullite(3Al2O3·2SiO2).The results show that SiC particles are bonded by the mullite and oxidation-derived SiO2.The apparent porosity of the specimens decreases from 31.3%to 20.5%with the amount of micro powders increasing from 5 mass%to 20 mass%.The bending strength increases at the first stage and then decreases with the increase of fine powders,and the specimen with 10 mass%of fine powders shows relatively high bending strength of 23.5 MPa.展开更多
Poly-crystalline silicon thin film has big potential of reducing the cost of solar cells. In this paper the preparation of thin film is introduced, and then the morphology of poly-crystalline thin film, is discussed. ...Poly-crystalline silicon thin film has big potential of reducing the cost of solar cells. In this paper the preparation of thin film is introduced, and then the morphology of poly-crystalline thin film, is discussed. On the film we developed poly-crystalline silicon thin film solar cells with efficiency up to 6.05% without anti-reflection coating.展开更多
The oxidation behavior of different SiAlON phases(β-SiAlON,X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry(TG) and field-emission ...The oxidation behavior of different SiAlON phases(β-SiAlON,X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry(TG) and field-emission scanning electron microscopy(FE-SEM).The effect of ferric oxide impurities in coal gangue was studied.The results show that ferric oxide contributes to the growth of SiAlON crystalline during the synthesis process.In the oxidation experiment,the existence of ferric oxide decreases the oxidation resistance of SiAlON.The reason is that the impurity causes the formation of a liquid phase at a higher temperature.At 1423-1623 K,the oxidation of SiAlON powders is diffusion controlled and it can be described by Chou's model.A fair agreement is found between theoretical calculations and the experimental data.展开更多
Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive),...Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to -20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550℃ for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiQ into Si3N4 was found at 1550℃. The Si3N4 powders, synthesized at 1550℃, exhibit a mixture phase of α- and -Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.展开更多
The nanocomposite of MoSi2-SiaN4 (molybdenum disilicide-silicon nitride) was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different prod...The nanocomposite of MoSi2-SiaN4 (molybdenum disilicide-silicon nitride) was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different products such as a- and B-MoSi2, SiaN4, Mo2N, and M05Si3 at various milling times. A thermodynamic appraisal showed that the milling of Moa2Siss powder mixture was associated with highly exothermic mechanically induced self-sustaining reaction (MSR) between Mo and Si. The MSR took place around 5 h of milling led to the formation of a-MoSi2 and the reaction between Si and N2 to produce Si3N4 under a nitrogen pressure of 1 MPa. By increasing the nitrogen pressure to 5 MPa, more heat is released, resulting in the dissociation of Si3N4 and the transformation of a-MoSi2 to β-MoSi2. Heat treatment was also performed on the milled samples and led to the formation of Mo2N and the transformation of a-MoSi2 to β-MoSi2 at the milling times of 10 and 40 h, respectively.展开更多
Silicon powders possess good thermal stability and rub resistance and can be used as the filler of high temperature wear-resistant coating;it can possess good wettability and dispersibility in the organic polymer by s...Silicon powders possess good thermal stability and rub resistance and can be used as the filler of high temperature wear-resistant coating;it can possess good wettability and dispersibility in the organic polymer by surface modification of silane coupling agent. Organic silicon has good thermal stability, which can modify the frangibility and thermal stability of epoxy resin. A certain proportion of modified silica powder, curing agent and additives were dispersed to modified epoxy resin can compound wear-resistant coating. The results show that: the modification effect can be the best if the dosage of silane coupling agent is 1.5% of silicon powder. If the methyl triethoxy silane is 50 phr and modified silica powder is 200 phr, then various performances of coating tend to be the best.展开更多
In order to improve oxidation resistance and ther- mal shock resistance of Al2O3-C refractories, two groups of specimens were prepared with phenolic resin as binder, adding 0, 2 wt% , 4 wt% and 6 wt% commercial SiC or...In order to improve oxidation resistance and ther- mal shock resistance of Al2O3-C refractories, two groups of specimens were prepared with phenolic resin as binder, adding 0, 2 wt% , 4 wt% and 6 wt% commercial SiC or ZrO2-SiC composite powder synthesized from zircon respectively to Al2O3- C refractories, pressing at 200 MPa, drying fully at 250℃, and then carbon embedded firing at 1400℃ for 2 h. Oxidation resistance and thermal shock resistance were researched, phase composition was analyzed by XRD. The results showed that the oxidation of SiC in additives could protect carbon in specimens effectively and thus decreased the mass loss ratio and oxidation area, and improved the oxidation resistance of the specimen. Thermal shock resistance was improved owing to the micro crack toughening of ZrO2 and grain toughening of SiC. In this experiment, the specimens with 6 wt% ZrO2 -SiC composite powder or 6 wt% SiC powder had the best oxidation resistance and thermal shock resistance.展开更多
文摘The properties of SiC kiln furniture bonded with fine silicon powderare related to the bonder’s crystal structure. At high temperature, it will crystallize ina-cristobalite with great bulk effect. MnO2 mineralizer can make a-cristobalite convertto a-tridymite whose bulk effect is small. The crystal structure and its amount were investigated with XRD technique. The influence of different amounts of MnO2 on thecrystal structure and polycrystal transformation, and that of crystal structure on theproperties of kiln furniture were studied. The best proportion of MnO2 added was determined to be 2.0%.
基金the Natural Science Foundation of Fujian Province(No.T08J0129)the Science and Technology Developing Foundation of Fuzhou University(No. 2008-XQ-001)Research Project of the Education Department of Fujian Province(JA05185)
文摘Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effects (including binder type and binder addition quantity) on the crystal structure and catalysis properties of photocatalyst. In this work, the catalysis activity was defined as the degradation rate of methyl orange solution upon ultraviolet lamp irradiation, and the specific areas were determined with nitrogen desorption method. TiO2 crystal form was measured with X-ray powder diffraction and their micro-morphology was observed with SEM. Experimental results indicate that these two binders do not affect the crystal form transformation of TiO2, but silica gol can increase the specific surface area of TiO2 photocatalyst obviously and the addition of sodium silicate can decrease it. In all, silica gol is a better candidate than sodium silicate for higher catalysis property. In conclusion, 6% silica gol is the optimal addition concentration. Under this condition, the ratio of anatase to rutile TiO2 is 64:36, the specific area is 29.67 m^2/g, and as expected, the degradation rate of methyl orange could be as high as 90% after irradiation for 5 days.
基金Fujian Science and Technology Administration (2004I003 and 2006N0037)
文摘TiO2 photocatalyst was supported with tetrabutyl titanate sol as precursor and fine silicon powder obtained from ferroalloys factory as carder to discuss the influence of pH value of gel precursor on microstructure and activity of photocatalyst in the process of synthesizing nano-TiO2 by using sol-gel method, the purpose of which is to provide fundamental data for the recycle of photocatalytic material. Under the irradiation of ultraviolet light, the photocatalytic degradation rate of methyl orange solution was used to characterize the photocatalytic activity of the sample. The specific surface area of the sample was tested by N2 desorption method, crystal form of TiO2 was analyzed by X-ray powder diffraction, and the microtopography of the sample was observed by scanning electron microscopy. The experimental results showed that the acidity of gel precursor could greatly affect the specific surface area and photocatalytic activity of the photocatalyst, and the optimum pH value of the precursor was determined as 2.0, and at this time the specific surface area of photocatalyst could reach 34.0 m^2/g. In the sample, the proporticn of anatase to rutile is 7:3, which makes l0 mg·L^-1 methyl orange solution fade after irradiation by 15W ultraviolet light for 24 h, and the degradation rate might be up to 98.1%.
基金Supported by the National Natural Science Foundation of China(No.51202171)the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20120143120004)the"111"Project(No.B13035)
文摘The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.
文摘Effects of particle size (A:d50 = 336. 9 μm, B:d50 =123.5μm, C: d50=19.5 μm, D: dso=2.21μm) and content (1 wt% , 3 wt% , 5 wt% , 7 wt% ) of silicon powder on cold crushing strength (CCS) , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens' pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.
文摘In order to reduce the hydrolysis rate of Si powder and inhibit the swelling and cracking of cast samples,Si powder was treated at different temperatures for 5 h,and then slurries and SiC-Si3N4 materials were prepared.The effect of the preheating temperature on the composition of the Si powder,the hydrolysis rate as well as the nitridation of the SiC-Si3N4 materials was studied.The results show that with the increase of the pretreatment temperature of Si powder,the oxidation degree of Si powders increases,the viscosity of the slurry with PAAS dispersant decreases gradually,and the hydrolysis reaction of Si powder decreases gradually;the Si powder pretreated at 700℃ or lower has little effect on the nitriding process,while the Si powder pretreated at 800 t has a great effect on the nitriding process,which is not conducive to the nitriding sintering of the samples.Therefore,the Si powder pretreated at 700 t for 5 h has the best properties,which not only has lower hydrolysis rate and good slurry fluidity,but also has mild effect on the nitriding reaction.
基金supported by the Natural Science Foundation of China(No.51106008)the Major State Basic Research and Development Program of China(No.2012CB720406)
文摘Silicon nitride (Si3N4) powders were prepared by the direct nitridation of silicon powders diluted with a- Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor (2.27 cm.s^-1) in the Arrhenius equation, activation energy (114 kJ·mol^-1), and effective diffusion coefficient (6.2×10-s cm2.s^-1). A formula was also derived to calculate the reaction rate constant.
基金This work was supported by the Omya Mining Co of Istanbul and Harran University.
文摘In this study, the electrorheological (ER) behavior of suspensions prepared from d50 = 2.4 lam talc powder, dispersed in insulating silicone oil (SO) medium was investigated. Sedimentation stabilities of suspensions (c = 5 wt%) prepared using these talc powder powders were determined to be 78 days. The ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. The shear stress of talc powder suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and showed a typical shear thinning non-Newtonian visco-elastic behavior. Effects of frequency on the ER activity of talc powder/SO system were also investigated.
文摘The XRPD (X-ray powder diffxactometry) patterns of silicon powder with a unit cell structure of diamond were determined from 298 to 1473 K. Lattice parameters of Si linearly increase with temperature. The thermal shifts of the positions of all reflection peaks are linearly correlated with the temperature. The coefficients of the intrinsic linear thermal expansion and volumetric thermal expansion were determined as 3.87×10-6/K and 1.16×10-5/K respectively. It indicates that Si is still a suitable standard in the XRPD method at high temperatures.
基金financially supported by Guangdong Innovative and Entrepreneurial Research Team Program ( No. 2013G061)the National Natural Science Foundation of China ( No. 51402055)
文摘This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.
文摘The basic formulation of Al2O3- C slide plates was65%( in mass,the same hereinafter) white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al + 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al + 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides: AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.
文摘Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.
基金financially supported by National Key R&D Program of China (Grant No.: 2016YFB0601100)State Key Laboratory of Multi-phase Complex Systems (MPCS-2017- A-06)
文摘A reaction bonding technique and a method of layer coating were developed to fabricate porous SiC.The green body was prepared using 250.0μm SiC particles as the raw material,fineα-Al2O3 and SiC powders with mass ratio of 2.5:1as sintering additives,65.2μm graphite as the pore-forming agent and polyvinyl alcohol(PVA)as the binder.The micro powders were coated on the surface of coarse SiC particles.After sintering,fine SiC particles were oxidized to silica(SiO2)then transforming into cristobalite,which finally reacted withα-Al2O3 to produce mullite(3Al2O3·2SiO2).The results show that SiC particles are bonded by the mullite and oxidation-derived SiO2.The apparent porosity of the specimens decreases from 31.3%to 20.5%with the amount of micro powders increasing from 5 mass%to 20 mass%.The bending strength increases at the first stage and then decreases with the increase of fine powders,and the specimen with 10 mass%of fine powders shows relatively high bending strength of 23.5 MPa.
基金This work was supported by the Chinese Academy of Sciences within the Hundred Talent Project(No.99-019-422288)National High Technical Research and Development Programme of China(No.2001AA513060).
文摘Poly-crystalline silicon thin film has big potential of reducing the cost of solar cells. In this paper the preparation of thin film is introduced, and then the morphology of poly-crystalline thin film, is discussed. On the film we developed poly-crystalline silicon thin film solar cells with efficiency up to 6.05% without anti-reflection coating.
基金supported by the National Natural Science Foundation of China(No.50874013)the support from the Key Lab. of the Ministry of Education of China for Ecologic & Recycle Metallurgy,University of Science and Technology Beijing
文摘The oxidation behavior of different SiAlON phases(β-SiAlON,X-phase SiAlON and 12H powders) synthesized from coal gangue in air atmosphere was investigated using isothermal thermogravimetry(TG) and field-emission scanning electron microscopy(FE-SEM).The effect of ferric oxide impurities in coal gangue was studied.The results show that ferric oxide contributes to the growth of SiAlON crystalline during the synthesis process.In the oxidation experiment,the existence of ferric oxide decreases the oxidation resistance of SiAlON.The reason is that the impurity causes the formation of a liquid phase at a higher temperature.At 1423-1623 K,the oxidation of SiAlON powders is diffusion controlled and it can be described by Chou's model.A fair agreement is found between theoretical calculations and the experimental data.
基金supported by the National Natural Science Foundation of China (Nos. 50802006 and 51172017)the Natural Science Foundation of Beijing (No. 2102028)+2 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-11-004A)the Fok Ying Tung Education Foundation Fund for Young College Teachers (No. 122016)the Public Foundation of Beijing Key Lab for Advanced Powder Metallurgy and Particulate Materials (USTB)
文摘Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to -20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550℃ for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300℃, and the complete transition of SiQ into Si3N4 was found at 1550℃. The Si3N4 powders, synthesized at 1550℃, exhibit a mixture phase of α- and -Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.
文摘The nanocomposite of MoSi2-SiaN4 (molybdenum disilicide-silicon nitride) was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different products such as a- and B-MoSi2, SiaN4, Mo2N, and M05Si3 at various milling times. A thermodynamic appraisal showed that the milling of Moa2Siss powder mixture was associated with highly exothermic mechanically induced self-sustaining reaction (MSR) between Mo and Si. The MSR took place around 5 h of milling led to the formation of a-MoSi2 and the reaction between Si and N2 to produce Si3N4 under a nitrogen pressure of 1 MPa. By increasing the nitrogen pressure to 5 MPa, more heat is released, resulting in the dissociation of Si3N4 and the transformation of a-MoSi2 to β-MoSi2. Heat treatment was also performed on the milled samples and led to the formation of Mo2N and the transformation of a-MoSi2 to β-MoSi2 at the milling times of 10 and 40 h, respectively.
文摘Silicon powders possess good thermal stability and rub resistance and can be used as the filler of high temperature wear-resistant coating;it can possess good wettability and dispersibility in the organic polymer by surface modification of silane coupling agent. Organic silicon has good thermal stability, which can modify the frangibility and thermal stability of epoxy resin. A certain proportion of modified silica powder, curing agent and additives were dispersed to modified epoxy resin can compound wear-resistant coating. The results show that: the modification effect can be the best if the dosage of silane coupling agent is 1.5% of silicon powder. If the methyl triethoxy silane is 50 phr and modified silica powder is 200 phr, then various performances of coating tend to be the best.
文摘In order to improve oxidation resistance and ther- mal shock resistance of Al2O3-C refractories, two groups of specimens were prepared with phenolic resin as binder, adding 0, 2 wt% , 4 wt% and 6 wt% commercial SiC or ZrO2-SiC composite powder synthesized from zircon respectively to Al2O3- C refractories, pressing at 200 MPa, drying fully at 250℃, and then carbon embedded firing at 1400℃ for 2 h. Oxidation resistance and thermal shock resistance were researched, phase composition was analyzed by XRD. The results showed that the oxidation of SiC in additives could protect carbon in specimens effectively and thus decreased the mass loss ratio and oxidation area, and improved the oxidation resistance of the specimen. Thermal shock resistance was improved owing to the micro crack toughening of ZrO2 and grain toughening of SiC. In this experiment, the specimens with 6 wt% ZrO2 -SiC composite powder or 6 wt% SiC powder had the best oxidation resistance and thermal shock resistance.