The variations of Debye temperature and lattice parameter of Ti-30Mo alloy with different hydrogen contents were measured by means of X-ray diffraction.It was found that as the hydrogen content increases,the Debye tem...The variations of Debye temperature and lattice parameter of Ti-30Mo alloy with different hydrogen contents were measured by means of X-ray diffraction.It was found that as the hydrogen content increases,the Debye temperature decreases,but the lattice parameter of the aUoy increases.The above results experimentally support the decohesion theory that the in- crease of hydrogen in metals will weaken the cohesive force between the atoms and make met- als brittle.展开更多
The lattice parameter change of Nd∶GGG crystal was studied by X-ray powder diffraction and the least square fitting method.The results indicate that the lattice parameters of Nd∶GGG increase along the crystal growth...The lattice parameter change of Nd∶GGG crystal was studied by X-ray powder diffraction and the least square fitting method.The results indicate that the lattice parameters of Nd∶GGG increase along the crystal growth direction.By analyzing the Nd∶GGG crystal structure and ions occupying site,the reason of lattice parameter change is mainly attributed to the volatilization of gallium ingredient and lead to the Ga vacancy sites(Oxygen octahedral center)were occupied by Gd^(3+)with large ionic radii,and that the substitute increases with the crystal growth direction.In addition,the Gd sites(oxygen dodecahedron center)were occupied by dopant Nd^(3+)with large ionic radii and the Nd3+distribution coefficient in GGG crystal is smaller than 1,therefore,the substitute also increased with the crystal growth direction,which is another reason led to the lattice parameter increase along the crystal growth direction.In order to decrease the lattice parameter change and improve the crystal quality,some methods were adopted to restrain effectively the Ga_(2)O_(3)volatilization and decrease the Nd^(3+)concentration change along the crystal growth direction.展开更多
Hydroxyapatite whiskers are used as reinforcement for biomaterials because of their needlelike morphology and strong strength of single crystal. HAP nanoparitcles are used in drug delivery system, protein separation a...Hydroxyapatite whiskers are used as reinforcement for biomaterials because of their needlelike morphology and strong strength of single crystal. HAP nanoparitcles are used in drug delivery system, protein separation and anticancer drug besides their implant applications. Many new properties arise from nanoeffects while nanoeffects come from specialty of nanostructure. The Ca（NO3）2·4H2O and （NH4）2HPO4 were used as starting reagents for preparation of HAP whiskers and nanoparticles. The whiskers are 100-200 μm long while nanoparticles are 30-80 nm in size. XRD is applied to characterize the lattice parameter difference of whisker and nanoparticle. Compared with those of HAP whiskers, the a-axis and b-axis of HAP nanocrystals are shortened while the c-axis is elongated. That makes nanoparticles capable of their non-needle-like morphology, higher reaction activity and special bioeffects.展开更多
The lattice parameters a and the molar volumes Km of Pb-based a-phase solid solutions in the Pb-Sn-Cd ternary system were determined by means of X-ray diffraction. The lattice parameters a vary linearly with the molar...The lattice parameters a and the molar volumes Km of Pb-based a-phase solid solutions in the Pb-Sn-Cd ternary system were determined by means of X-ray diffraction. The lattice parameters a vary linearly with the molar fractions, the molar volumes show a positive deviation from the ideal solution behaviour, and the contribution of the solute Cd to the excess molar volumes V is much larger than that of the solute Sn. According to Vegard' s law orsub-regular solution model, the relationship between the experimental data of a or Vm andthe compositions of alloy is obtained by the mathematic regressive method, the prediction precisions of the both formulae are within the limits of experiment error.展开更多
During the crystal growth of Nd,Cr∶GSGG by Czochralski method,in some cases eutectic reaction occurred in the nether region of the crystal,and the boule was divided into two obvious different parts,which is upper Nd...During the crystal growth of Nd,Cr∶GSGG by Czochralski method,in some cases eutectic reaction occurred in the nether region of the crystal,and the boule was divided into two obvious different parts,which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO_(3).By X-ray powder diffraction,the structure change of NdCr∶GSGG crystal ofΦ27 mm×120 mm with eutectic along its grown direction<111>was studied.By the least square method and extrapolation function f=sinθ-sinθ^(1-t)(t is an adjustable parameter),the lattice parameters of Nd,Cr∶GSGG and additional GdScO_(3)phase were computed.The results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction,which changes from a=(1.25650±0.00007)nm of the top to(1.25798±0.00010)nm of the bottom.In the process of Nd,Cr∶GSGG growth,Gd^(3+)in Nd,Cr∶GSGG is partly replaced by Nd^(3+)with larger ionic radii,and the volatilization of Ga component results in its composition variance,which cause the lattice parameters increase along growth direction.In the eutectic section,there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO_(3).The lattice parameters of GdScO_(3)are a=0.5443±0.0007,b=0.5699±0.0005 and c=(0.7865±0.0009)nm,and that of Nd,Cr∶GSGG is(1.25798±0.00010)nm.In the final growth stage,excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously,and results in the eutectic reaction,and the outgrowth of Nd,Cr∶GSGG and GdScO_(3).So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.展开更多
Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-...Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg17Al12 from the supersaturated α-Mg solid solution. The pre- cipitate exhibited granular and lath-shaped morphologies in Mg matrix and ftocculent precipitation around AlN particles.展开更多
Two ternary Al-2.2Zn-0.95Mg and Al-5.SZn-2.1Mg （in wt pct） alloys, with Zn：Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500℃ for 0.5 h and...Two ternary Al-2.2Zn-0.95Mg and Al-5.SZn-2.1Mg （in wt pct） alloys, with Zn：Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500℃ for 0.5 h and aged at 180℃ for times between 0.5 and 80 h. The structural characterization was carried out by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, selected area electron diffraction （SAED） and Vickers mierohardness measurements （HV）. The study was focused on the investigation of the precipitates formation and the relationship between hardness and lattice parameter for α-Al. The results showed that there was an inverse correlation for all the experimental conditions, and the aged peaks coincided with lattice parameter minima. Significant precipitates formation only occurred for the alloy containing 5.5 wt pct Zn and 2.1 wt pct Mg, provoking an important strengthening and variations in the lattice parameter, however, this was not observed for the alloy containing 2.2 wt pct Zn and 0.95 wt pct Mg. A plausible explanation of the increment of hardness values could be the presence of a well distributed η phase （MgZn2）. At initial stages of the precipitation process, η′ was the most abundant precipitate while the phase τ- was observed at overaged conditions. These results showed that the aging response of the conventionally cast Al-Zn-Mg alloys could be obtained using the lattice parameter of the α-Al matrix, even for alloy systems with low precipitates formation.展开更多
In this study, the effect of thermal oxidation on the lattice parameters of Ti-4Al-2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1-7 h in electric furnace under air atmosphere. The lattice...In this study, the effect of thermal oxidation on the lattice parameters of Ti-4Al-2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1-7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures（600 and 700 °C）. The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.展开更多
Crystals of CdSxSe1-x alloys have been grown from the vapour phase. Some of the physical properties, such as lattice parameters, crystal structure and x-rays data of CdSxSe1-x alloys were determined using x-ray diffra...Crystals of CdSxSe1-x alloys have been grown from the vapour phase. Some of the physical properties, such as lattice parameters, crystal structure and x-rays data of CdSxSe1-x alloys were determined using x-ray diffractometry. X-ray diffractometry has shown that CdS-CdSe mixed crystals had the wurtzite structure for all compositions between CdS and CdSe. The lattice parameters （both a and c） were found to show a linear dependence with composition. The dependence of the lattice parameters of a and c on composition can be expressed as： a（x） = 4.165 ＋ 0.16x; c（x） = 6.713 ＋ 0.27x. The variation of band gap with composition was determined for these samples from optical absorption measurements, which showed that the band gap varied smoothly and monotonically, but not linearly over the composition range typical results were found between 2.42-1.74 eV at room temperature.展开更多
The electronic structures of pure V, Nb and Ta metals with bcc structure were determined by one atom (OA) theory. According to the electronic structures of these metals, their potential curves, cohesive energies, latt...The electronic structures of pure V, Nb and Ta metals with bcc structure were determined by one atom (OA) theory. According to the electronic structures of these metals, their potential curves, cohesive energies, lattice parameters, elasticity and the dependence of linear thermal expansion coefficients on temperature were calculated. The electronic structures and characteristic properties of these metals with fcc and hcp structures and liquid states were studied.展开更多
The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resu...The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resulting in enhanced deformation related heating and corresponding coarser grained microstructures.No substantial effect on the texture development is revealed.The mechanical properties simultaneously increase in stress and strain levels with increasing Ag content,especially in tension as a result of the changing impact of the slip modes which can be associated with a decrease of the lattice parameters as well as the c/a ratio of the hcp lattice structure.In compression tests with twin dominated flow,the impact is much smaller on the compressive yield stress but higher with respect to the twinning related strain hardening rate.Solid solution strength functions for Fleischer and Labusch were determined,also confirming the anisotropic behaviour of the extruded Mg alloys.展开更多
The phase transformation of chalcopyrite and the effect of its phase status on bacterial leaching were studied. Under the protection of high-purity argon, different temperatures(203, 382 and 552℃) were applied to nat...The phase transformation of chalcopyrite and the effect of its phase status on bacterial leaching were studied. Under the protection of high-purity argon, different temperatures(203, 382 and 552℃) were applied to natural chalcopyrite to complete the phase change. In addition, the chalcopyrite was bioleached before and after the phase change. The results show that the chalcopyrite heated at 203 and 382℃ remained in the α phase, whereas the chalcopyrite changed from α to β phase at 552℃. The leaching rates of chalcopyrite after the phase transitions at 203, 382 and 552℃ were 32.9%, 40.5% and 60.95%, respectively. Further, the crystal lattice parameters of chalcopyrite increased and lattice energy decreased, which were the fundamental reasons for the significant increase in leaching rate. Electrochemical experiments demonstrated that with increasing annealing temperature, the polarization resistance decreased and corrosion current density increased. The higher the oxidation rate was, the higher the leaching rate was.展开更多
The accurate phase boundary of MgAION/(AIN+MgAION) in MgO-AIN-Al2O3 ternary system, has not been determined precisely so far. In the present study, the lattice parameters of MgAION solid solution with various composit...The accurate phase boundary of MgAION/(AIN+MgAION) in MgO-AIN-Al2O3 ternary system, has not been determined precisely so far. In the present study, the lattice parameters of MgAION solid solution with various compositions were determined precisely with X-ray powder diffraction. According to the relationship between the lattice parameters of MgAION solid solution and the contents of AIN and MgO, the phase boundaries of MgAION/(AIN+MgAION) in MgO-AIN-AI2O3 ternary system at 1600℃ and 1700℃ were precisely determined.展开更多
The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact meas...The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact measure of lattice parameter.And,the precipitation of the second-phase in aging process was simulated after test the resistivity of the alloy in a continuous heating process and delayed time processing.The results show that when heating in the same rate,the alloy resistivity increases with temperature first,a mutation point appears at 110℃,and the resistivity reaches its peak at 120℃.Then,the resistivity decreases and achieves a minimum at about 170℃.Afterwards,it increases again.The change of resistivity results from a combined effect of the temperature and phase transformation.The volume precipitation of η' phase dominates at about 120℃,and the resistivity of forgings decreases accordingly.When the specimen cools in a furnace at 240℃,the phase transformation finishes basically and the alloy content of Al-matix keeps stable,thus,the alloy resistivity depends on the temperature only.It decreases with temperature and time since the end of precipitation.The higher the temperature is,the bigger it will be.With a big descending rate of the resistivity curve,the time to reach the stable value becomes shorter.展开更多
The effect of Cu addition on the spinodal decomposition of the Al-Zn alloy with symmetrical compositions has been investigated by X-ray diffraction analysis. It is found that the single fcc phase can be obtained in th...The effect of Cu addition on the spinodal decomposition of the Al-Zn alloy with symmetrical compositions has been investigated by X-ray diffraction analysis. It is found that the single fcc phase can be obtained in the AlZn alloy with the addition of 2 at. pct Cu after solution treatment at 400℃ and water quenching to room temperature. The modulation structure occurs in two types of alloys aged at room temperature for 30 min. The spinodal process remarkably slows down above or at the three phase equilibrium temperature, particularly at room temperature due to the addition of 2 at. pct Cu. The spinodal time increases by 20 times when aging at 300℃ and by more than 30 times when aging at room temperature.展开更多
The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-con...The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.展开更多
An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction （XRD） patterns of the film show strong c-axis ...An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction （XRD） patterns of the film show strong c-axis oriented crystal structure with preferred （002） orientation. The Phi-sca~ XRD pattern confirms that the epitaxiM ZnO exhibits a single- domain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and （002） peaks shift systematically toward lower 20 values due to the change of lattice parameters. The lattice parameters show linear increase in their values with increasing temperature.展开更多
The aims of the work were to study the effect of Ge (0-6wt. %) on the paramagnetic-antiferromagnetic transition and martensitic transformation of Fe-Mn alloy using the susceptibility, micro structure examination, X-ra...The aims of the work were to study the effect of Ge (0-6wt. %) on the paramagnetic-antiferromagnetic transition and martensitic transformation of Fe-Mn alloy using the susceptibility, micro structure examination, X-ray diffraction (XRD) and latticeparameter measurement. Ge lowers the Néel temperature, TN, and enhances the magnetic susceptibility x, changing the Pauli paramagnetism above TN to paramagnetismstate obeying the Curie Weiss law, which is essentially similar to that of γ-Fe-Mnalloys containing Al or Si; Ge depresses γ-ε martensitic transformation, whichattribute to Ge increasing the stacking fault energy; Moreover, Ge increases the lattice parameter of γ phase, and low content Ge increases the lattice parameter of γphase more than that of high Ge content. Comparing Ge(4s24p2) with Si(3s23p2) and Al(3s2 3p1), which have the same outer-shell of electron structures, we found that their effects on the martensitic transformation of Fe-Mn alloy are completely different. The result suggests the outer-shell of electron is not the main factor of governing the Ms temperature of Fe-Mn alloy although it is essential in the alloy's antiferromagnetic transition. The relation among the Ms temperature, stacking fault energy and lattice parameter of austenite, has been discussed in brief.展开更多
The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diff...The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.展开更多
Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated ...Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.展开更多
文摘The variations of Debye temperature and lattice parameter of Ti-30Mo alloy with different hydrogen contents were measured by means of X-ray diffraction.It was found that as the hydrogen content increases,the Debye temperature decreases,but the lattice parameter of the aUoy increases.The above results experimentally support the decohesion theory that the in- crease of hydrogen in metals will weaken the cohesive force between the atoms and make met- als brittle.
基金Project supported by the National Natural Science Foundation of China(50472104,60478025)
文摘The lattice parameter change of Nd∶GGG crystal was studied by X-ray powder diffraction and the least square fitting method.The results indicate that the lattice parameters of Nd∶GGG increase along the crystal growth direction.By analyzing the Nd∶GGG crystal structure and ions occupying site,the reason of lattice parameter change is mainly attributed to the volatilization of gallium ingredient and lead to the Ga vacancy sites(Oxygen octahedral center)were occupied by Gd^(3+)with large ionic radii,and that the substitute increases with the crystal growth direction.In addition,the Gd sites(oxygen dodecahedron center)were occupied by dopant Nd^(3+)with large ionic radii and the Nd3+distribution coefficient in GGG crystal is smaller than 1,therefore,the substitute also increased with the crystal growth direction,which is another reason led to the lattice parameter increase along the crystal growth direction.In order to decrease the lattice parameter change and improve the crystal quality,some methods were adopted to restrain effectively the Ga_(2)O_(3)volatilization and decrease the Nd^(3+)concentration change along the crystal growth direction.
基金Funded by the National Natural Science Foundation of China(No.50472040)Hubei Science and Technology Committee(No.2001AA306B02,No.2002AA105A06),China
文摘Hydroxyapatite whiskers are used as reinforcement for biomaterials because of their needlelike morphology and strong strength of single crystal. HAP nanoparitcles are used in drug delivery system, protein separation and anticancer drug besides their implant applications. Many new properties arise from nanoeffects while nanoeffects come from specialty of nanostructure. The Ca（NO3）2·4H2O and （NH4）2HPO4 were used as starting reagents for preparation of HAP whiskers and nanoparticles. The whiskers are 100-200 μm long while nanoparticles are 30-80 nm in size. XRD is applied to characterize the lattice parameter difference of whisker and nanoparticle. Compared with those of HAP whiskers, the a-axis and b-axis of HAP nanocrystals are shortened while the c-axis is elongated. That makes nanoparticles capable of their non-needle-like morphology, higher reaction activity and special bioeffects.
文摘The lattice parameters a and the molar volumes Km of Pb-based a-phase solid solutions in the Pb-Sn-Cd ternary system were determined by means of X-ray diffraction. The lattice parameters a vary linearly with the molar fractions, the molar volumes show a positive deviation from the ideal solution behaviour, and the contribution of the solute Cd to the excess molar volumes V is much larger than that of the solute Sn. According to Vegard' s law orsub-regular solution model, the relationship between the experimental data of a or Vm andthe compositions of alloy is obtained by the mathematic regressive method, the prediction precisions of the both formulae are within the limits of experiment error.
基金Project supported National Natural Science Foundation of China(60478025,50472104)
文摘During the crystal growth of Nd,Cr∶GSGG by Czochralski method,in some cases eutectic reaction occurred in the nether region of the crystal,and the boule was divided into two obvious different parts,which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO_(3).By X-ray powder diffraction,the structure change of NdCr∶GSGG crystal ofΦ27 mm×120 mm with eutectic along its grown direction<111>was studied.By the least square method and extrapolation function f=sinθ-sinθ^(1-t)(t is an adjustable parameter),the lattice parameters of Nd,Cr∶GSGG and additional GdScO_(3)phase were computed.The results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction,which changes from a=(1.25650±0.00007)nm of the top to(1.25798±0.00010)nm of the bottom.In the process of Nd,Cr∶GSGG growth,Gd^(3+)in Nd,Cr∶GSGG is partly replaced by Nd^(3+)with larger ionic radii,and the volatilization of Ga component results in its composition variance,which cause the lattice parameters increase along growth direction.In the eutectic section,there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO_(3).The lattice parameters of GdScO_(3)are a=0.5443±0.0007,b=0.5699±0.0005 and c=(0.7865±0.0009)nm,and that of Nd,Cr∶GSGG is(1.25798±0.00010)nm.In the final growth stage,excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously,and results in the eutectic reaction,and the outgrowth of Nd,Cr∶GSGG and GdScO_(3).So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.
文摘Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg17Al12 from the supersaturated α-Mg solid solution. The pre- cipitate exhibited granular and lath-shaped morphologies in Mg matrix and ftocculent precipitation around AlN particles.
文摘Two ternary Al-2.2Zn-0.95Mg and Al-5.SZn-2.1Mg （in wt pct） alloys, with Zn：Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500℃ for 0.5 h and aged at 180℃ for times between 0.5 and 80 h. The structural characterization was carried out by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, selected area electron diffraction （SAED） and Vickers mierohardness measurements （HV）. The study was focused on the investigation of the precipitates formation and the relationship between hardness and lattice parameter for α-Al. The results showed that there was an inverse correlation for all the experimental conditions, and the aged peaks coincided with lattice parameter minima. Significant precipitates formation only occurred for the alloy containing 5.5 wt pct Zn and 2.1 wt pct Mg, provoking an important strengthening and variations in the lattice parameter, however, this was not observed for the alloy containing 2.2 wt pct Zn and 0.95 wt pct Mg. A plausible explanation of the increment of hardness values could be the presence of a well distributed η phase （MgZn2）. At initial stages of the precipitation process, η′ was the most abundant precipitate while the phase τ- was observed at overaged conditions. These results showed that the aging response of the conventionally cast Al-Zn-Mg alloys could be obtained using the lattice parameter of the α-Al matrix, even for alloy systems with low precipitates formation.
基金the Sahand University of Technology,Tabriz,Iran,for the financial support and provision of laboratory facilities
文摘In this study, the effect of thermal oxidation on the lattice parameters of Ti-4Al-2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1-7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures（600 and 700 °C）. The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.
文摘Crystals of CdSxSe1-x alloys have been grown from the vapour phase. Some of the physical properties, such as lattice parameters, crystal structure and x-rays data of CdSxSe1-x alloys were determined using x-ray diffractometry. X-ray diffractometry has shown that CdS-CdSe mixed crystals had the wurtzite structure for all compositions between CdS and CdSe. The lattice parameters （both a and c） were found to show a linear dependence with composition. The dependence of the lattice parameters of a and c on composition can be expressed as： a（x） = 4.165 ＋ 0.16x; c（x） = 6.713 ＋ 0.27x. The variation of band gap with composition was determined for these samples from optical absorption measurements, which showed that the band gap varied smoothly and monotonically, but not linearly over the composition range typical results were found between 2.42-1.74 eV at room temperature.
文摘The electronic structures of pure V, Nb and Ta metals with bcc structure were determined by one atom (OA) theory. According to the electronic structures of these metals, their potential curves, cohesive energies, lattice parameters, elasticity and the dependence of linear thermal expansion coefficients on temperature were calculated. The electronic structures and characteristic properties of these metals with fcc and hcp structures and liquid states were studied.
基金This research was partly funded by Helmholtz Association in the frame of Helmholtz-Russian Science Foundation Joint Research Group grant num-ber HRSF-0025.
文摘The effect of Ag in solid solution on the microstructure,texture and the deformation behaviour of indirectly extruded Mg was investigated.Ag as a solid solution strengthener affects the behaviour during extrusion,resulting in enhanced deformation related heating and corresponding coarser grained microstructures.No substantial effect on the texture development is revealed.The mechanical properties simultaneously increase in stress and strain levels with increasing Ag content,especially in tension as a result of the changing impact of the slip modes which can be associated with a decrease of the lattice parameters as well as the c/a ratio of the hcp lattice structure.In compression tests with twin dominated flow,the impact is much smaller on the compressive yield stress but higher with respect to the twinning related strain hardening rate.Solid solution strength functions for Fleischer and Labusch were determined,also confirming the anisotropic behaviour of the extruded Mg alloys.
基金Project(2018zzts768) supported by the Fundamental Research Funds for the Central South University,ChinaProject(51204207) supported by the National Natural Science Foundation of China
文摘The phase transformation of chalcopyrite and the effect of its phase status on bacterial leaching were studied. Under the protection of high-purity argon, different temperatures(203, 382 and 552℃) were applied to natural chalcopyrite to complete the phase change. In addition, the chalcopyrite was bioleached before and after the phase change. The results show that the chalcopyrite heated at 203 and 382℃ remained in the α phase, whereas the chalcopyrite changed from α to β phase at 552℃. The leaching rates of chalcopyrite after the phase transitions at 203, 382 and 552℃ were 32.9%, 40.5% and 60.95%, respectively. Further, the crystal lattice parameters of chalcopyrite increased and lattice energy decreased, which were the fundamental reasons for the significant increase in leaching rate. Electrochemical experiments demonstrated that with increasing annealing temperature, the polarization resistance decreased and corrosion current density increased. The higher the oxidation rate was, the higher the leaching rate was.
文摘The accurate phase boundary of MgAION/(AIN+MgAION) in MgO-AIN-Al2O3 ternary system, has not been determined precisely so far. In the present study, the lattice parameters of MgAION solid solution with various compositions were determined precisely with X-ray powder diffraction. According to the relationship between the lattice parameters of MgAION solid solution and the contents of AIN and MgO, the phase boundaries of MgAION/(AIN+MgAION) in MgO-AIN-AI2O3 ternary system at 1600℃ and 1700℃ were precisely determined.
基金Sponsored by the Matching Project of Commission of Scientific and Technical Industry on National Defence(JPPT-×××-1)
文摘The precipitation of MgZn2 phase in aging process of Al-Zn-Mg-Cu alloy forging was characterized qualitatively after transmission electron microscope(TEM)observation,X-ray diffraction phase analysis and the exact measure of lattice parameter.And,the precipitation of the second-phase in aging process was simulated after test the resistivity of the alloy in a continuous heating process and delayed time processing.The results show that when heating in the same rate,the alloy resistivity increases with temperature first,a mutation point appears at 110℃,and the resistivity reaches its peak at 120℃.Then,the resistivity decreases and achieves a minimum at about 170℃.Afterwards,it increases again.The change of resistivity results from a combined effect of the temperature and phase transformation.The volume precipitation of η' phase dominates at about 120℃,and the resistivity of forgings decreases accordingly.When the specimen cools in a furnace at 240℃,the phase transformation finishes basically and the alloy content of Al-matix keeps stable,thus,the alloy resistivity depends on the temperature only.It decreases with temperature and time since the end of precipitation.The higher the temperature is,the bigger it will be.With a big descending rate of the resistivity curve,the time to reach the stable value becomes shorter.
基金supported by the National Natural Science Foundation of China under grant No.59971015supported by the Laboratory of Atom Imaging of Solids,Institute of Metal Research,the Chinese Academy of Sciences.
文摘The effect of Cu addition on the spinodal decomposition of the Al-Zn alloy with symmetrical compositions has been investigated by X-ray diffraction analysis. It is found that the single fcc phase can be obtained in the AlZn alloy with the addition of 2 at. pct Cu after solution treatment at 400℃ and water quenching to room temperature. The modulation structure occurs in two types of alloys aged at room temperature for 30 min. The spinodal process remarkably slows down above or at the three phase equilibrium temperature, particularly at room temperature due to the addition of 2 at. pct Cu. The spinodal time increases by 20 times when aging at 300℃ and by more than 30 times when aging at room temperature.
文摘The perovskite oxide La_ 1-xSr_xCoO_3 ( 0≤x≤0.5) series were prepared under different sintering conditions. Crystal structure was determined by powder X-ray diffraction and lattice parameters as a function of Sr-concentration x were obtained by using Rietveld method. The dc resistivity investigated in the temperature range of 80～300 K indicates that the electric properties exhibit a metallic-insulator (semiconducting) (M-I) transition for 0.2<x<0.3. The samples with x=0.2 is close to the M-I transition boundary. The influence of sintering conditions on the lattice parameters, resistivity and the ferromagnetic phase transition temperature T_C of La_ 1-xSr_xCoO_3 for the cases x=0.2 and 0.5 was discussed. The change of the electric properties of semiconductor-like sample (x=0.2) with sintering temperature and sintering period is just opposite to that of metallic sample (x=0.5). Annealing in flowing oxygen can decrease the resistivity of semiconductor-like sample.
基金Project supported by the National Natural Science Foundation of China (Grant No.10490192)
文摘An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction （XRD） patterns of the film show strong c-axis oriented crystal structure with preferred （002） orientation. The Phi-sca~ XRD pattern confirms that the epitaxiM ZnO exhibits a single- domain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and （002） peaks shift systematically toward lower 20 values due to the change of lattice parameters. The lattice parameters show linear increase in their values with increasing temperature.
基金The project was supported by the National Natural Science Foundation of China (Grant No.59601007).
文摘The aims of the work were to study the effect of Ge (0-6wt. %) on the paramagnetic-antiferromagnetic transition and martensitic transformation of Fe-Mn alloy using the susceptibility, micro structure examination, X-ray diffraction (XRD) and latticeparameter measurement. Ge lowers the Néel temperature, TN, and enhances the magnetic susceptibility x, changing the Pauli paramagnetism above TN to paramagnetismstate obeying the Curie Weiss law, which is essentially similar to that of γ-Fe-Mnalloys containing Al or Si; Ge depresses γ-ε martensitic transformation, whichattribute to Ge increasing the stacking fault energy; Moreover, Ge increases the lattice parameter of γ phase, and low content Ge increases the lattice parameter of γphase more than that of high Ge content. Comparing Ge(4s24p2) with Si(3s23p2) and Al(3s2 3p1), which have the same outer-shell of electron structures, we found that their effects on the martensitic transformation of Fe-Mn alloy are completely different. The result suggests the outer-shell of electron is not the main factor of governing the Ms temperature of Fe-Mn alloy although it is essential in the alloy's antiferromagnetic transition. The relation among the Ms temperature, stacking fault energy and lattice parameter of austenite, has been discussed in brief.
文摘The ZnAl<sub>x</sub>Fe<sub>2-x</sub>O<sub>4</sub> (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.
文摘Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.
