New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,al...New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,along with the growth of Sn whiskers on the whitened Cr-Al-B MAB phase,Al whiskers also formed,mainly attributed to the thermal activation of whisker cultivation at 400℃and promotion effect of Sn in the Cr-(Al,Sn)-B MAB phase solid solution.Partial Al whiskers,interspersed with small amounts of Sn,exhibited transparency under the scanning electron microscopy image.These whiskers underwent random growth and sucking back into the matrix simultaneously.The temperature during whisker cultivation had a significant effect on the whisker growth.展开更多
Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining...Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.展开更多
In the current study the wear behavior of the ZK60/SiC composites reinforced by particles and whiskers in both as-cast and extruded conditions was examined.Furthermore,the wear behavior of the extruded samples along t...In the current study the wear behavior of the ZK60/SiC composites reinforced by particles and whiskers in both as-cast and extruded conditions was examined.Furthermore,the wear behavior of the extruded samples along the extrusion direction and perpendicular to the extrusion direction was studied.The wear tests were performed at temperatures of 100,200,and 300℃under loads of 10,20,and 30 N.The results showed that the whisker-reinforced sample(5.8×10^(–4)g/[N.m])had higher wear resistance than the particle-reinforced sample(1.3×10^(–3)g/[N.m]).The lowest wear rate was observed for the extruded sample in the extrusion direction(3.53×10^(–4)g/[N.m]).It was also found that the wear rate increased by∼20%with increasing temperature,but in the ZK60/SiC_(w)sample,dynamic precipitation increased the wear resistance.The coefficient of friction was also found to increase with rising temperature,showing an increase of approximately 12.5%at a 10 N load and 20%at a 30 N load.Examination of the worn surfaces by scanning electron microscopy showed that the as-cast ZK60 alloy at 100℃had the oxidative-abrasive as the dominant mechanism.It was found that by extruding the sample,the strength of the sample increased and the mechanism changed to adhesive wear.In the ZK60/SiC_(p)composite,the viscoplastic wear mechanism was dominant.Although in the extruded sample the dominant mechanism changed to plastic deformation.As temperature increases,the viscoplastic wear mechanism became dominant again.In the as-cast ZK60/SiC_(w)composite,the abrasive wear mechanism changed to delamination with increasing temperature.By extruding the sample,the dominant mechanism changed to adhesive wear.Finally,dynamic precipitation induced by temperature caused an increase in the wear resistance.展开更多
A highly thermally conductive magnesium borate/boron nitride(A-MBN)composite whisker was developed which was surface functionalized by(3-Aminopropyl)triethoxysilane.Its growth mechanism was proposed.Then,A-MBN/epoxy c...A highly thermally conductive magnesium borate/boron nitride(A-MBN)composite whisker was developed which was surface functionalized by(3-Aminopropyl)triethoxysilane.Its growth mechanism was proposed.Then,A-MBN/epoxy composites were prepared.When the A-MBN content is 8wt%,the thermal conductivity of the A-MBN/EP composite is 0.61 W·m^(-1)·K^(-1),which is 230%higher than that of pure EP.At the same time,the tensile strength of the composite material is 85.4%higher than that of the pure EP,and it also maintains excellent electrical insulation property.Finally,the infrared imaging test verifies the excellent heat dissipation performance of the composite material,indicating that the composite material has broad application prospects in the field of thermal conductive materials.展开更多
The zinc oxide whiskers were synthesized by the equilibrium gas expanding method at the temperature of 700 C with metallic zinc as the main raw material without any catalysts. The effects of the growth time on microst...The zinc oxide whiskers were synthesized by the equilibrium gas expanding method at the temperature of 700 C with metallic zinc as the main raw material without any catalysts. The effects of the growth time on microstructure and photoluminescence properties were investigated. The results show that the as-grown samples are composed of uniform tetrapod-like ZnO whiskers. The length and diameter of the arms of the tetrapod-like ZnO whiskers increase obviously with the increase of the growth time. The strong single ultraviolet （UV） emission centering 385-391 nm without any accompanying deep-level emission is observed in the room temperature photoluminescence （PL） spectra of the whiskers. The intensity of UV emission increases markedly with the increase of growth time.展开更多
In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural stren...In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.展开更多
A new approach to the massive production of TiC whiskers with high purity and low cost was presented. It is a modified carbothermal reduction method （MCTR） characterized by argon stream flowing vertically and passin...A new approach to the massive production of TiC whiskers with high purity and low cost was presented. It is a modified carbothermal reduction method （MCTR） characterized by argon stream flowing vertically and passing through the interior of the mixture of raw materials. It is found for the first time that there is an optimum flow of the upward flowing argon stream, at which large quantity of high quality TiC can be obtained. This paper described the new method, analyzed the mechanism and conditions for the formation of high purity TiC whiskers on a large scale, and compared MCTR with the traditional carbothermal reduction method （TCTR）. Based on the analysis and comparison, it is concluded that in order to produce high quality transition metal carbides, nitrides and carbonitrides with low cost TCTR must be replaced by MCTR.展开更多
Based on study of strain distribution in whisker reinforced metal matrix composites, an explicit precise stiffness tensor is derived. In the present theory, the effect of whisker orientation on the macro property of c...Based on study of strain distribution in whisker reinforced metal matrix composites, an explicit precise stiffness tensor is derived. In the present theory, the effect of whisker orientation on the macro property of composites is considered, but the effect of random whisker position and the complicated strain field at whisker ends are averaged. The derived formula is able to predict the stiffness modulus of composites with arbitrary whisker orientation under any loading condition. Compared with the models of micro mechanics, the present theory is competent for modulus prediction of actual engineering composites. The verification and application of the present theory are given in a subsequent paper published in the same issue展开更多
The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in th...The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in the as-cast 20%SiCw/Mg composite (SiCw content in volume fraction) were investigated, and the elastic modulus of the composite was measured with an ultrasonic velocity analyzer. Results show that there is an evident difference between the plane-orientation function and the space-orientation function of whiskers and the space-orientation function can represent the actual condition of the composite. Only by using the space-orientation function of whiskers, the difference of elastic modulus of the as-cast composite in different directions can be explained reasonably.展开更多
The AlN whiskers were composed by the Al_2O_3-C system with someCaF_2 and NH_4Cl addition un- Der the condition of the carbothermalreduction treatment Of 1450 deg.c and 2h as well as nitrogenousatmosphere. The Compose...The AlN whiskers were composed by the Al_2O_3-C system with someCaF_2 and NH_4Cl addition un- Der the condition of the carbothermalreduction treatment Of 1450 deg.c and 2h as well as nitrogenousatmosphere. The Composed AlN whiskers were analysed and the resultsshow That some whiskers morphology such as plate curved, Brachedcorrugated were observed and the rations of length To diameter changegreatly. The composed whiskers are not Even, some surface quality isnot high, TEM analyse show That the fiber axes are normal to [0112]and [1101]. The Mechanism of the growth of the whiskers is supposedto be VLS(Vapor-Liquid-Solid)展开更多
The effect of interface reaction on the fractal dimensions of fracture surface in aluminum borate whisker-reinforced aluminum alloy 6061 composite was investigated. The composite was fabricated by squeeze-casting tech...The effect of interface reaction on the fractal dimensions of fracture surface in aluminum borate whisker-reinforced aluminum alloy 6061 composite was investigated. The composite was fabricated by squeeze-casting technique. The fracture surfaces created in tensile test were measured by vertical sectioning method. Fractal phenomena were found in two plots, in which the measuring units were from 3 to 15 μm and 1 to 5 μm, respectively. The relation was established between the tensile properties and fractal dimension with measuring units of 3-15 μm. The results show that the ultimate tensile strength increases while the fracture surface roughness increases with fractal dimension increasing due to the change in fracture mode depending on the degree of interface reaction status induced by heat treatment. But when the measuring units are 1-5 μm, fractal dimension does not change with heat treatment.展开更多
In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of S...In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.展开更多
Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from a...Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from aqueous solutions by calcium sulfate whisker(CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of p H, reaction time, whisker dosage, and initial As concentration. X-ray diffraction(XRD) and scanning electron microscopy(SEM) were used to characterize the samples prepared. The results showed that p H of the aqueous solution was an important parameter for As(Ⅲ)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker(CSDW) and calcium sulfate anhydrous whisker(CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)-1and 39.18 mg As(V)·(g CSAW)-1were obtained. Some calcium arsenate solids products,such as Ca As O3(OH)(weilite, syn), Ca3(As O4)2(calcium arsenate), Ca O–As2O5, Ca–As–O, Ca5(As O4)3OH·x H2O(calcium arsenate hydroxide hydrate), and Ca H(As O4)·2H2O(hydrogen calcium arsenic oxide hydrate), were detected at p H = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.展开更多
Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, mor...Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H20 and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H20, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of A1F3·3H20. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.展开更多
Composite Portland cement （PC） played an important role in various kinds of construction engineering owing to low hydration heat,low-cost,and application of solid industrial waste,but its brittleness and low strengt...Composite Portland cement （PC） played an important role in various kinds of construction engineering owing to low hydration heat,low-cost,and application of solid industrial waste,but its brittleness and low strength limited its use in stress-bearing locations.The aim of this study is to improve the toughness and fracture resistance by incorporating CaCO3 whisker in cement matrix.Effect of different content of calcium carbonate whiskers on the mechanical properties of PC was investigated.The results showed that the flexural strength,impact strength and split tensile strength were increased by 39.7%,39.25% and 36.34% at maximum,respectively.Microstructure and elements of the whiskers in hardened cement were observed and analyzed by SEM/EDS.The mechanisms of the reinforcement of CaCO3 whisker on cement were also discussed,and the conclusion was that the improvement could be correlated to energy-dissipating processes owing to crack bridging,crack deflection,and whisker pull-out at the crack tips.展开更多
High-quality LDH-SO4-CO3 whiskers were synthesized via liquid precipitation method using MgSO4·7 H2 O and Al2(SO4)3·18 H2O as precursors and Na2CO3-NaHCO3 buffer solution as precipitant. The influence of buf...High-quality LDH-SO4-CO3 whiskers were synthesized via liquid precipitation method using MgSO4·7 H2 O and Al2(SO4)3·18 H2O as precursors and Na2CO3-NaHCO3 buffer solution as precipitant. The influence of buffer solution concentration on the characteristics of the samples was investigated. The asgrown whiskers were characterized by X-ray diffraction, transmission electron microscopy, and BrunauerEmmett-Teller N2 specific surface area measurements. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. The LDH-SO4-CO3 whiskers with well-defined geometry, distinct intercalated structure, decent quality, and excellent dispersing capability can be obtained under the following conditions: buffer solution volume ratio of 45%, reaction temperature of 83°C, and reaction time of 182 h. The obtained whiskers are well-crystallized and exhibit homogeneous morphology consisting of fiber bars.展开更多
In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanic...In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.展开更多
Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The p...Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.展开更多
The mechanical and tribological properties of polyetheretherketone （PEEK） composites filled with CaCO3 whisker in various content of 0～45% （wt pct） were investigated. The composite specimens were prepared by comp...The mechanical and tribological properties of polyetheretherketone （PEEK） composites filled with CaCO3 whisker in various content of 0～45% （wt pct） were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10^-6 mm^3/Nm for 25% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.展开更多
基金financial support from the National Natural Science Foundation of China(Grant Nos.42066003 and 51701053)Hainan Province Science and Technology Special Fund(Grant No.ZDYF2023GXJS148)+1 种基金General Program of Natural Science Foundation of Hainan Province(Grant Nos.420RC522 and 517076)Evaluation Project of Guangdong Provincial Key Laboratory(Grant No.2023B1212060043).
文摘New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,along with the growth of Sn whiskers on the whitened Cr-Al-B MAB phase,Al whiskers also formed,mainly attributed to the thermal activation of whisker cultivation at 400℃and promotion effect of Sn in the Cr-(Al,Sn)-B MAB phase solid solution.Partial Al whiskers,interspersed with small amounts of Sn,exhibited transparency under the scanning electron microscopy image.These whiskers underwent random growth and sucking back into the matrix simultaneously.The temperature during whisker cultivation had a significant effect on the whisker growth.
基金Projects(50874130,50974034)supported by the National Natural Science Foundation of ChinaProject(FMRU2008K01)supported by the Open Research Fund of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education,Wuhan University of Science and Technology,China
文摘Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.
文摘In the current study the wear behavior of the ZK60/SiC composites reinforced by particles and whiskers in both as-cast and extruded conditions was examined.Furthermore,the wear behavior of the extruded samples along the extrusion direction and perpendicular to the extrusion direction was studied.The wear tests were performed at temperatures of 100,200,and 300℃under loads of 10,20,and 30 N.The results showed that the whisker-reinforced sample(5.8×10^(–4)g/[N.m])had higher wear resistance than the particle-reinforced sample(1.3×10^(–3)g/[N.m]).The lowest wear rate was observed for the extruded sample in the extrusion direction(3.53×10^(–4)g/[N.m]).It was also found that the wear rate increased by∼20%with increasing temperature,but in the ZK60/SiC_(w)sample,dynamic precipitation increased the wear resistance.The coefficient of friction was also found to increase with rising temperature,showing an increase of approximately 12.5%at a 10 N load and 20%at a 30 N load.Examination of the worn surfaces by scanning electron microscopy showed that the as-cast ZK60 alloy at 100℃had the oxidative-abrasive as the dominant mechanism.It was found that by extruding the sample,the strength of the sample increased and the mechanism changed to adhesive wear.In the ZK60/SiC_(p)composite,the viscoplastic wear mechanism was dominant.Although in the extruded sample the dominant mechanism changed to plastic deformation.As temperature increases,the viscoplastic wear mechanism became dominant again.In the as-cast ZK60/SiC_(w)composite,the abrasive wear mechanism changed to delamination with increasing temperature.By extruding the sample,the dominant mechanism changed to adhesive wear.Finally,dynamic precipitation induced by temperature caused an increase in the wear resistance.
基金Funded by the Guangxi Natural Science Foundation(No.2024GXNSFBA010338)。
文摘A highly thermally conductive magnesium borate/boron nitride(A-MBN)composite whisker was developed which was surface functionalized by(3-Aminopropyl)triethoxysilane.Its growth mechanism was proposed.Then,A-MBN/epoxy composites were prepared.When the A-MBN content is 8wt%,the thermal conductivity of the A-MBN/EP composite is 0.61 W·m^(-1)·K^(-1),which is 230%higher than that of pure EP.At the same time,the tensile strength of the composite material is 85.4%higher than that of the pure EP,and it also maintains excellent electrical insulation property.Finally,the infrared imaging test verifies the excellent heat dissipation performance of the composite material,indicating that the composite material has broad application prospects in the field of thermal conductive materials.
基金Project(2009AA03Z427)supported by the National High-tech Research and Development Program of ChinaProject(2006z02-006-3)supported by the Science Foundation of Sichuan Province,China
文摘The zinc oxide whiskers were synthesized by the equilibrium gas expanding method at the temperature of 700 C with metallic zinc as the main raw material without any catalysts. The effects of the growth time on microstructure and photoluminescence properties were investigated. The results show that the as-grown samples are composed of uniform tetrapod-like ZnO whiskers. The length and diameter of the arms of the tetrapod-like ZnO whiskers increase obviously with the increase of the growth time. The strong single ultraviolet （UV） emission centering 385-391 nm without any accompanying deep-level emission is observed in the room temperature photoluminescence （PL） spectra of the whiskers. The intensity of UV emission increases markedly with the increase of growth time.
基金The National Natural Science Foundation of China (No.51102035)
文摘In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.
文摘A new approach to the massive production of TiC whiskers with high purity and low cost was presented. It is a modified carbothermal reduction method （MCTR） characterized by argon stream flowing vertically and passing through the interior of the mixture of raw materials. It is found for the first time that there is an optimum flow of the upward flowing argon stream, at which large quantity of high quality TiC can be obtained. This paper described the new method, analyzed the mechanism and conditions for the formation of high purity TiC whiskers on a large scale, and compared MCTR with the traditional carbothermal reduction method （TCTR）. Based on the analysis and comparison, it is concluded that in order to produce high quality transition metal carbides, nitrides and carbonitrides with low cost TCTR must be replaced by MCTR.
基金National Natural Science Foundation of China !( 19870 2 65 ,1973 2 0 60 ) Chinese Academ y of Sciences Foundation
文摘Based on study of strain distribution in whisker reinforced metal matrix composites, an explicit precise stiffness tensor is derived. In the present theory, the effect of whisker orientation on the macro property of composites is considered, but the effect of random whisker position and the complicated strain field at whisker ends are averaged. The derived formula is able to predict the stiffness modulus of composites with arbitrary whisker orientation under any loading condition. Compared with the models of micro mechanics, the present theory is competent for modulus prediction of actual engineering composites. The verification and application of the present theory are given in a subsequent paper published in the same issue
文摘The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in the as-cast 20%SiCw/Mg composite (SiCw content in volume fraction) were investigated, and the elastic modulus of the composite was measured with an ultrasonic velocity analyzer. Results show that there is an evident difference between the plane-orientation function and the space-orientation function of whiskers and the space-orientation function can represent the actual condition of the composite. Only by using the space-orientation function of whiskers, the difference of elastic modulus of the as-cast composite in different directions can be explained reasonably.
文摘The AlN whiskers were composed by the Al_2O_3-C system with someCaF_2 and NH_4Cl addition un- Der the condition of the carbothermalreduction treatment Of 1450 deg.c and 2h as well as nitrogenousatmosphere. The Composed AlN whiskers were analysed and the resultsshow That some whiskers morphology such as plate curved, Brachedcorrugated were observed and the rations of length To diameter changegreatly. The composed whiskers are not Even, some surface quality isnot high, TEM analyse show That the fiber axes are normal to [0112]and [1101]. The Mechanism of the growth of the whiskers is supposedto be VLS(Vapor-Liquid-Solid)
基金Project (20070213042) supported by Specialized Research Fund for the Doctoral Program of Higher Education, China
文摘The effect of interface reaction on the fractal dimensions of fracture surface in aluminum borate whisker-reinforced aluminum alloy 6061 composite was investigated. The composite was fabricated by squeeze-casting technique. The fracture surfaces created in tensile test were measured by vertical sectioning method. Fractal phenomena were found in two plots, in which the measuring units were from 3 to 15 μm and 1 to 5 μm, respectively. The relation was established between the tensile properties and fractal dimension with measuring units of 3-15 μm. The results show that the ultimate tensile strength increases while the fracture surface roughness increases with fractal dimension increasing due to the change in fracture mode depending on the degree of interface reaction status induced by heat treatment. But when the measuring units are 1-5 μm, fractal dimension does not change with heat treatment.
基金This work was financially supported by the National Natural Science Foundation of China for Distinguished Young Scholars (No. 50225210) the Foundation of Aeronautic Science of China (No. 03H53044).
文摘In order to effectively employ the unique high temperature mechanical properties of carbon/carbon composite substrates, SiC coatings reinforced by SiC whiskers were prepared by pack cementation method. The effect of SiC whiskers on the oxidation resistance properties of the single-layer coating and double-layer coating was investigated. SiC whiskers in the single-layer SiC coating have little effect on the anti-oxidation property but obviously improve the thermal shock property. The double-layer coating with inner-layer reinforced coating exhibits more perfect anti-oxidation ability than the double-layer coating with SiC inner-layer coating.
基金Supported by the Science and Technology Plan Project of Hunan Province(2013FJ3034)the Open Foundation of the Innovation Platform in Higher Education of Hunan Province(12K051)the programs of Xiangtan University(2011XZX12,2010QDZ37)
文摘Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(Ⅲ)/As(V) from aqueous solutions by calcium sulfate whisker(CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of p H, reaction time, whisker dosage, and initial As concentration. X-ray diffraction(XRD) and scanning electron microscopy(SEM) were used to characterize the samples prepared. The results showed that p H of the aqueous solution was an important parameter for As(Ⅲ)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker(CSDW) and calcium sulfate anhydrous whisker(CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)-1and 39.18 mg As(V)·(g CSAW)-1were obtained. Some calcium arsenate solids products,such as Ca As O3(OH)(weilite, syn), Ca3(As O4)2(calcium arsenate), Ca O–As2O5, Ca–As–O, Ca5(As O4)3OH·x H2O(calcium arsenate hydroxide hydrate), and Ca H(As O4)·2H2O(hydrogen calcium arsenic oxide hydrate), were detected at p H = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.
文摘Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H20 and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H20, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of A1F3·3H20. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.
文摘Composite Portland cement （PC） played an important role in various kinds of construction engineering owing to low hydration heat,low-cost,and application of solid industrial waste,but its brittleness and low strength limited its use in stress-bearing locations.The aim of this study is to improve the toughness and fracture resistance by incorporating CaCO3 whisker in cement matrix.Effect of different content of calcium carbonate whiskers on the mechanical properties of PC was investigated.The results showed that the flexural strength,impact strength and split tensile strength were increased by 39.7%,39.25% and 36.34% at maximum,respectively.Microstructure and elements of the whiskers in hardened cement were observed and analyzed by SEM/EDS.The mechanisms of the reinforcement of CaCO3 whisker on cement were also discussed,and the conclusion was that the improvement could be correlated to energy-dissipating processes owing to crack bridging,crack deflection,and whisker pull-out at the crack tips.
基金Funded by National Natural Science Foundation of China(No.51272207)Science and Technology Plan of Guangdong Province((No.2013B021100019)
文摘High-quality LDH-SO4-CO3 whiskers were synthesized via liquid precipitation method using MgSO4·7 H2 O and Al2(SO4)3·18 H2O as precursors and Na2CO3-NaHCO3 buffer solution as precipitant. The influence of buffer solution concentration on the characteristics of the samples was investigated. The asgrown whiskers were characterized by X-ray diffraction, transmission electron microscopy, and BrunauerEmmett-Teller N2 specific surface area measurements. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. The LDH-SO4-CO3 whiskers with well-defined geometry, distinct intercalated structure, decent quality, and excellent dispersing capability can be obtained under the following conditions: buffer solution volume ratio of 45%, reaction temperature of 83°C, and reaction time of 182 h. The obtained whiskers are well-crystallized and exhibit homogeneous morphology consisting of fiber bars.
文摘In order to explore the serviceability and reinforcement of CaCO3 whisker in portland cement matrix, the durability of CaCO3 whisker and effect of low whisker content（0%-4.0%） on the working performance and mechanical properties of portland cement were investigated. The experimental results show that CaCO3 whiskers have a good stability and serviceability in cement, and should not significantly alter the rheological properties of the cement paste. The flexural and compressive strength of portland cement reinforced by CaCO3 whiskers was increased by 33.3% and 12.83%, respectively.
基金Funded by the National High-tech Research and Development Program of China(2011AA06A106)
文摘Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.
文摘The mechanical and tribological properties of polyetheretherketone （PEEK） composites filled with CaCO3 whisker in various content of 0～45% （wt pct） were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10^-6 mm^3/Nm for 25% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.
