Gd99.75Fe0.25合金的大磁热效应及应用特性研究

采用X射线衍射、物理性能测试系统、显微硬度计及电化学工作站研究了经氩弧熔炼、1123K均匀化热处理168h的Gd99.75Fe0.25合金的磁热效应及应用特性。结果表明:Gd99.75Fe0.25合金仍保持纯Gd的六方晶体结构;Gd99.75Fe0.25合金的居里温度为294K,且在居里点附近发生铁磁到顺磁的二级相变,2和5T外场下的最大磁熵变分别为4.99和9.37J·kg-1·K-1,均大于纯Gd;Gd99.75Fe0.25合金的显微硬度(HV0.2)590MPa,与纯Gd相当,但少量Fe的掺杂提高了Gd的耐蚀性。含少量Fe的Gd99.75Fe0.25合金具有大的磁热效应及良好的应用特性,是一种有很大应用潜力的室温磁致冷材料。     

Nb掺杂Gd合金的大磁热效应和显微硬度增强

在氩气气氛中用熔炼法制备了Gd100-xNbx(x=0,1,2,3,5)系列合金,铸锭经1273K均匀化退火96h后水淬至室温。结果表明:Gd100-xNbx系列合金仍保持纯Gd的六方相结构;Nb掺杂合金的居里温度比纯Gd均低2K,在居里点附近发生的磁性转变为二级相变,5T外场下的最大磁熵变约为纯Gd的85%。通过少量Nb(≤5at%)掺杂后,Gd100-xNbx系列合金的显微硬度明显得到提高,与纯Gd相比,显微硬度最大提高幅度达～53%(x=5)。含少量Nb的Gd100-xNbx合金具有较大的磁熵变和较好的加工性能,是一类有很大应用潜力的室温磁致冷材料。     

Sn合金化对Gd5Si2Ge2磁致冷材料结构和性能的影响

以商业纯Gd为原料,采用非自耗电弧炉氩气保护下熔炼了Gd5Si2Ge2-xSnx(x=0.2,0.5,1)和Gd5Si2-yGe2Sny(y=0.1,0.2,0.5)系列合金,研究Sn合金化对Gd5Si2Ge2晶体结构和磁热性能的影响.粉末XRD结果表明Sn代Ge样品具有正交Gd5Si4型结构;Sn少量代Si(y=0.1,0.2)的样品具有单斜Gd5Si2Ge2型结构;Gd5Si1.5Ge2Sn0.5则为单斜和正交的混合结构.用超导量子磁强计(SQUID)测定了样品的M-T和不同温度的M-H曲线,结果表明Gd5Si2Ge2-xSnx(x=0.2,0.5,1)不具有巨磁热效应;Gd5Si1 9Ge2Sn01合金的最大磁熵变达15.3 J/kg·K(0 T～5 T),具有巨磁热效应.     

Gd0.95Nb0.05合金磁热效应的研究

采用X射线衍射技术、直接磁热效应测量仪和VSM振动样品磁强计研究电弧熔铸和400℃,1h热处理后低纯Gd0.95Nb0.05合金的磁热效应。结果表明:适量Nb的加入不改变商业Gd的居里温度,但明显提高了商业Gd的磁热效应,最大绝热温变由3.1K增加到3.5K,1.5T磁场下最大磁熵变为3.99J/(kg·K);Gd0.95Nb0.05合金经过400℃,1h热处理后,居里温度提高了2K,最大绝热温变和最大磁熵变有不同程度的增加。与高纯Gd相比,商业原料制备的Gd0.95Nb0.05合金成本低廉,是一种非常实用的磁制冷工质材料。     

Gd3+xAl2-x系合金磁热效应的直接测量

用真空高频磁悬浮炉制备了Gd3Al2,Gd3.1Al1.9,Gd3.2Al1.8,Gd3.33Al1.7四种合金。用直接测量法测量了在1.5T磁场下纯Gd和样品的磁热效应。结果表明,在1.5T磁场下,Gd3Al2,Gd3.1Al1.9,Gd3.2Al1.8,Gd3.33Al1.7和纯Gd的最大绝对温变分别为2.1K,2.0K,1.6K,1.5K和3.2K;Gd3.1Al1.9的居里温度最高,为286K。     

Gd1-xVx系列合金的磁热效应研究

采用真空电弧熔炼方法制备Gd1-xVx(x=0.01,0.03,0.05,0.07,0.09)系列合金.研究发现:Gd1-xVx合金完全保持了纯Gd的六方型晶体结构,其在居里温度附近的磁特性符合二级相变规律;合金居里温度比纯Gd低1～2 K,并且随x的增加变化很小;在低磁场下Gd1-xVx合金具有较大的磁熵变、绝热温变以及较宽的ΔSM-T 曲线峰,并且所有样品的相对制冷能力都明显优于纯Gd.     

室温磁致冷材料的研究进展

对室温磁致冷材料的最新进展作了综合报道,主要包括Gd、Gd-Si-Ge、La-Fe-(Si、Al)、Mn-As-Sb、Mn-Fe-P-As几个化合物系列。Gd,居里温度294K,其磁热性能在所有纯金属中最好;Gd5Si2Ge2,居里温度274K,在此温度处具有巨磁热效应;在La-Fe-Co-Si、La-Fe-Co-Al化合物中,改变Co的含量可以使化合物的居里温度得到调整,其磁热性能可以与Gd比拟甚至超过Gd;MnFeP0.45As0.55,居里温度308K,具有巨磁热效应,磁热性能远远超过Gd。在MnAs1-xSbx化合物中,随Sb(0相似文献   

钛设备制造业“推荐企业”标准

以高纯蒸馏Gd为原料制备了Gd5ShGe2合金，研究了不同热处理工艺对合金的显微组织结构及磁热效应的影响。利用扫描电子显微镜及电子能谱对合金的显微组织结构及成分进行了测试。利用振动样品磁强计测量了合金在250K～290K范围内的等温磁化曲线，并根据麦克斯韦方程对其磁熵变进行了计算。研究发现，通过适当的热处理，合金的显微组织得到充分地均匀化，合金中的杂质相得到有效去除。因此，磁熵值较铸态提高将近200％，磁有序温度下降约lOK。     

磁致冷材料研究进展

介绍了磁致冷材料磁热效应的表征方法，概述了国内外各温度区间磁致冷材料的研究进展。在20K以下温区，磁致冷材料研究主要集中在具有高导热率、低点阵热容和极低有序化温度的石榴石，如Gd3Ga5O12(GGG)，Dy3Al5O12(DAG)，Gd3Ga5-xFexO12(GGIG)及Er基磁致冷材料；20K～77K温度区间，磁致冷材料研究主要集中在重稀土金属间化合物中，如(Dy1-xErx)Al2复合材料等；在室温附近，具有大磁热效应的磁致冷材料以稀土Gd，Gd5(SixGe1-x)4(0≤x≤0．5)和MnFeP1-xAsx(0．15≤x≤0．66)合金为代表，特别是Gd5Si2Ge2(Tc=274K)和MnFeP0.45As0.55(Tc=300K)合金，在磁场5T下具有巨磁热效应，是Gd的2倍以上。总结了各温度区间磁致冷材料的选择依据。重点评述了室温磁致冷材料的最新研究成果，展望了室温磁致冷材料的发展前景。     

Gd的纯度对Gd52.5Co18.5Al29非晶合金的玻璃形成能力及磁热效应的影响

研究了稀土金属Gd的纯度对Gd52.5Co18.5Al29非晶合金的玻璃形成能力和磁热效应的影响。研究表明Gd的纯度从99.94%下降到99.2%,非晶合金的临界直径从4mm减小到3mm;磁热效应并未随纯度降低而下降,采用高纯和低纯金属Gd制备的Gd52.5Co18.5Al29非晶合金的最大磁熵变和相对制冷量分别为9.4J·kg-1·K-1,8.1×102J·kg-1和9.5J·kg-1·K-1,8.4×102J·kg-1。因此,采用商业低纯Gd制备的Gd-基非晶合金适合作为磁致冷候选工质。     

Y1.7Er0.3Fe17快淬带的结构和磁熵变

采用熔体快淬法(铜辊速度为20m/s)制备Y1.7Er0.3Fe17快淬带,通过X射线衍射仪、振动样品磁强计(VSM)和三维原子探针(3DAP)对样品的晶体结构、磁熵变和原子在三维空间中分布情况进行研究。结果表明,Y1.7Er0.3Fe17快淬带具有菱方Th2Zn17型结构,与标准PDF卡片(48-1454)相比较,Y2Fe17主相晶胞体积略减小;样品的居里温度在308K附近,磁场变化为1.5T,样品的最大磁熵变值为2.10J·kg-1·K-1;Fe在晶界处含量略有降低,其它区域内,Y、Er和Fe3种原子均匀分布在三维空间中。     

Y1.7Er0.3Fe17快淬带的结构和磁熵变

采用熔体快淬法（铜辊速度为20 m/s）制备Y1.7Er0.3Fe17快淬带,通过X射线衍射仪、振动样品磁强计（VSM）和三维原子探针（3DAP）对样品的晶体结构、磁熵变和原子在三维空间中分布情况进行研究。结果表明,Y1.7Er0.3Fe17快淬带具有菱方Th2Zn17型结构,与标准PDF卡片（48-1454）相比较,Y2Fe17主相晶胞体积略减小;样品的居里温度在308 K附近,磁场变化为1.5 T,样品的最大磁熵变值为2.10 J·kg-1·K-1;Fe在晶界处含量略有降低,其它区域内,Y、Er和Fe 3种原子均匀分布在三维空间中。     

Magnetocaloric effect of （Gd1-xNdx）Co2 alloys in low magnetic field

The phases and magnetocaloric effect in the alloys （Gd1-xNdx）Co2 with x = 0, 0.1, 0.2, 0.3, and 0.4 were investigated by X-ray diffraction analysis and magnetization measurement. The samples are single phase with a cubic MgCu2-type structure. The To decreases obviously with increasing Nd content from 404 K of the alloy with x = 0 to 272 K of the alloy with x = 0.4; forx = 0.3, the To is 296 K, which is near room temperature. In the samples （Gd1-xNdx）Co2 with x = 0.0, 0.1, 0.2, 0.3, and 0.4, the maximum magnetic entropy change is 1.471, 1.228, 1.280, 1.381 and 1.610 J·kg^-1·K^-1, respectively, in the applied field range of 0-2.0 T. The results of Arrott plots confirmed that the transition type were second order magnetic transition forx = 0, 0.3, and 0.4.     

Gd60Co26Al14大块非晶合金的磁熵变

利用铜模吸铸法制备了Gd60Co26Al14非晶合金.采用示差扫描量热法(DSC),X射线衍射(XRD)和超导量子磁强计(SQUID)研究了其结构与磁热性能.XRD分析表明:铸态Gd60Co26Al14合金是完全的非晶结构;DSC测试显示Gd60Co26Al14合金在加热过程中在571 K发生玻璃化转变,并且出现了两个结晶温度,分别是602 K和642 K.SQUID测试结果表明:Gd60Co26Al14合金出现两个居里温度,分别是82 K和128 K;合金在外磁场5 T下82 K处的磁熵变达到7 J·(kg·K-1).     

(Mn1-xFex)5Sn3合金晶体结构和居里温度

用粉末冶金法(磁场压制烧结)制备(Mn1-xFex)5Sn3(x=0.1～0.5)合金,对其晶体结构、居里温度进行研究。室温XRD分析表明,该系列合金均保持Mn5Sn3的InNi2型相结构,计算发现合金的晶格常数随着x量增大而减小。通过M-T曲线测量结果表明:居里温度TC在室温附近244～391K连续可调,且随着Fe含量的增加而提高,居里温度随成分近似呈线性变化;成分为(Mn0.70Fe0.30)5Sn3合金的居里温度为295K,在外加磁场为0～1.5T下,最大磁熵变约为0.87J·(kg·K)-1,是一种成本低廉的室温磁制冷候选材料。     

LaFe11.9-xCoxSi1.1B0.2(x=0.7,0.8,0.9)合金的磁热效应

使用电弧熔炼法制备了LaFe11.9-xCoxSi1.1B0.2(x=0.7,0.8,0.9)系列合金.XRD分析表明该系列合金除微量的α-Fe相外,均由NaZn13型立方结构单相组成.晶格常数随着Co含量的增加而增大,分别为1.1487,1.1496,1.1498nm;磁性测量表明该系列合金的Curie温度在室温附近,并且也随着Co含量的增加而分别增加到270,290,300 K.在外场变化△B=1.5 T时,该系列合金的最大磁熵变均为金属Gd的2倍左右,相对制冷能力与金属Gd基本相同.     

Phase Transformation and Magnetic Property of Ni-Mn-Ga Powders Prepared by Dry Ball Milling

This study investigated the phase transformations and magnetic properties of Ni-Mn-Ga alloy powders prepared by dry ball milling in argon atmosphere. The Fe and Cr elements were found to be introduced in the alloy after ball milling, which should result from the severe collision and friction among the particles, balls, and vial. The x-ray diffraction result indicated that the Fe and Cr elements should have alloyed with the Ni-Mn-Ga matrix. The martensitic transformation temperature and Curie temperature of the 800?°C annealed powders decreased by ~33?°C and increased by ~28?°C, respectively, as compared to that of the bulk alloy. The comprehensive effect of the changing of valence electron concentration of the alloy due to the introduction of Fe and Cr and the grain refinement of the alloy caused by ball milling should be responsible for the reduction of martensitic transformation temperature. The saturation magnetization of the 800?°C annealed powders became larger (~5?emu/g) than that of the bulk alloy. The enhancement of magnetic properties, such as the increase of Curie temperature and enhancement of saturation magnetization of the annealed Ni-Mn-Ga powders, should be attributed to the increase of magnetic exchange caused by introduction of Fe in the alloy. The contaminations of Fe and Cr elements emerging from the dry ball milling process changed the phase transformation and magnetic properties of the Ni-Mn-Ga alloy. Therefore, the dry ball milling process is difficult to control the contamination from the milling medium and not suitable to prepare Ni-Mn-Ga powders. On the contrary, the wet ball milling method under liquid medium should be a better method to prevent the contamination and fabricate pure Ni-Mn-Ga ferromagnetic shape memory alloy powders.     

Mn1.25Fe0.75P1-xSix系列合金物相形成与磁热效应

研究了Mn1.25Fe0.75P1-xSix(x=0.50,0.52,0.54,0.56,0.58,0.60)合金的物相、热滞及磁热效应。通过XRD分析表明,合金主相均为Fe2P六角结构(空间群为P 6 2m)。在不同Si含量时,合金中存在FeSi型或Fe3Si型第二相。通过调节Si和P含量的比率,合金的居里温度随Si含量的增加成线性增加,从240 K到313 K。而合金的热滞在逐渐减小。当Si含量为0.58时,在外磁场变化为0~1.5 T下合金的最大等温磁熵变为8.6 J/kg·K。     

Effect of heat treatment on structure and magnetic properties of Fe65.5Cr4Mo4Ga4P12C5B5.5 bulk amorphous alloy

This study deals with the Fe65.5Cr4Mo4Ga4P12C5B5.5 ferromagnetic bulk amorphous alloy. XRD analysis showed an amorphous structure of the as-cast sample. The same method revealed that, after annealing at 973 K for τ=10 min, the sample displayed a crystalline structure with crystalline phases formed. The crystallization process of the alloy was examined by DTA analysis. It was shown that crystallization took place in the temperature range between 810 K and 860 K with the exo-maximum peak temperature at 846 K with a heating rate of 20 K·min-1. The method also showed that, at temperatures ranging from 753 K to 810 K, the alloy exhibited the properties of supercooled liquids. A correlation between heat-induced structural changes and magnetic properties of the alloy was determined by thermomagnetic measurements. Maximum magnetization M=3.7 Am2·kg-1 of the alloy was reached after its annealing at 733 K for τ=10 min. Upon annealing, the alloy exhibited a relaxed amorphous structure. Annealing the alloy above the crystallization temperature led to a decrease in bulk magnetization. After annealing at 973 K for τ=10 min, the bulk magnetization of the alloy was M'=0.45 Am2·kg-1. Accordingly, after crystallization and formation of new compounds, the magnetization of the alloy was decreased by a factor of about 7.7. The strength of the magnetic field applied during the measurements was H=10 k A·m-1. The samples were tested for changes in the microstructure and hardness of both the amorphous phase and the resulting crystalline phase.