钒合金化对Gd5Si2Ge2巨磁热效应合金结构和性能的影响

Gd5Si2Ge2合金的发现为常温范围磁制冷实用化发展提供了可能,然而其居里温度有待进一步提高。本文就添加钒进行合金化对它的改性作用开展了初步研究。结果表明:Gd5(Si2-xGe2-xV2x)合金(x≤0.03)能保持母相Gd5Si2Ge2的晶体结构,但显微组织却随钒的加入而发生显著改变;钒合金化使合金居里温度由～3℃提高到～18℃,同时磁化强度水平升高,居里点附近磁化强度变化陡度增大。     

MnP_(1-x)M_x系列合金的磁热效应

研究了1∶1型MnP基系列合金MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)的结构及其磁热效应。室温X射线衍射表明该系列合金的主相结构均为正交MnP结构,空间群为Pnma。在用Ge,Sb,Zn,Sn作为替代元素的合金中存在少量第二相Mn5.64P3。磁性测量表明该系列合金MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)的存在由铁磁-顺磁的二级相变。其居里温度Tc分别为286,295,294,295,295K。通过磁化曲线计算了MnP1-xMx(M=Si,Sb,Ge,Zn,Sn)(x=0,0.1)合金的最大等温磁熵变-ΔSm,均在0.7～1.3J.kg-.1K-1之间。     

Gd4(BixSb1-x)3系列合金在低磁场下的磁热效应

用高频悬浮炉熔炼了Gd4(BixSb1-x)3系列合金,利用X光粉末衍射技术确定其结构。在1.3T的磁场下,利用自制的△Tad-T曲线测量仪直接测量了该系列合金的磁热效应。发现Gd4(BixSb1-x)3系列合金在低磁场下具有较大的磁热效应,通过改变Bi的含量,其居里温度在267K～332K温度之间增加,从而在一个较宽的温度范围内能获得较大的绝热温变。在对退火前后的样品进行△Tad-T测量后,发现其热稳定性很好。实验结果说明Gd4(BixSb1-x)3系列合金是一种性能良好的磁致冷材料。     

以低纯度钆研究Gd5Si2Ge2的磁热效应及制备工艺

以99%级的低纯度金属Gd为原料, 采用真空感应炉制备工艺, 辅以1470 K热处理工艺, 获得了与99.99%级高纯度Gd为原料制备的Gd5Si2Ge2合金相近的磁热效应, 5 T外场下最大磁熵变达17.5 J·kg^-1·K^-1, 对比电弧熔炼与感应熔炼两种制备方法, 感应熔炼条件下C, N, O杂质含量明显降低, 发现了Gd5Si2Ge2合金巨磁熵变与相结构的本质联系.     

Gd3-xMnxAl2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,Gd2.9Mn0.1Al2,Gd2.8Mn0.2Al2,Gd2.7Mn0.3Al2四种合金.用直接测量法测量了在1.5T磁场下这四种合金的磁热效应.结果表明,在1.5T磁场下,Gd3Al2,Gd2.9Mn0.1Al2,Gd2.8Mn0.2Al2的最大绝对温变分别为2K,1.5K和1.3K;随Mn含量的增加,居里温度Tc提高.     

Gd3-xZnxAl2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、Gd2.9Zn0.1Al2、Gd2.7Zn0.3Al2、Gd2.4Zn0.6Al2四种合金.用直接测量法测量了在1.5T磁场下这四种合金的磁热效应.结果表明,在1.5T磁场下,Gd3Al2、Gd2.9Zn0.1Al2、Gd2.7Zn0.3Al2、Gd2.4Zn0.6Al2的最大绝对温变分别为2.0K、1.4 K、1.1K和0.7K;当Zn含量为0.1时,居里温度为287K.     

Dy对Gd磁热效应的影响

通过对Gd及不同配比的Gd-Dy合金的X射线衍射分析和磁热效应T-ΔTad曲线测量结果的分析表明,Dy的添加没有改变Gd的晶体结构,而使其居里温度和磁热效应发生有规律的改变.     

La_(1.1)Fe_(11.4)Si_(1.55)Ge_(0.05)合金的磁热效应

使用电弧熔炼法制备了La1.1Fe11.4Si1.55Ge0.05合金。研究了用少量的Ge替代Si后,La1.1Fe11.4Si1.55Ge0.05合金的磁性和磁热效应。粉末X射线衍射结果表明:在1273K真空退火处理10d后,合金La1.1Fe11.4Si1.55Ge0.05主相为NaZn13型立方结构,存在微量的α-Fe相。热磁曲线M-T与Arrott曲线表明:在居里温度Tc=205K处发生由铁磁性(TTc)转变为顺磁性(TTc)的二级磁相变。在磁场变化0～1.5T下,根据等温磁化曲线通过Maxwell关系式计算得出最大磁熵变-ΔSmmax=9J.kg-.1K-1。Ge替代Si后该合金在其居里温度Tc处-ΔSm-T曲线半高宽增大,使合金的相对制冷能力RCP(S)有所提高。     

室温磁热效应直接测量仪的研制

简单介绍了室温磁热效应测量仪的工作原理及组成,并且测量了Gd样品的磁热效应T-△Tad曲线,该仪器具有操作简单方便、测量费用低廉等优点,它可以作为室温磁制冷材料研究的重要测量手段,同时也可以解决目前磁制冷材料普遍只研究等温磁熵变的不足的问题.     

用于室温磁制冷样机工质盘的Gd1-xCx合金

对Gd1-xCx(x=0、0.02、0.035、0.05)合金的磁热性能及显微硬度的分析测试表明,C的加入可大幅提高材料的维氏硬度;在一定成份范围内, C元素的加入对Gd的居里温度影响不大;2%(原子分数) C的加入几乎不降低Gd的绝热温变峰值, Gd0.95C0.05的最大磁熵变有所降低但降幅不大,综合比较,Gd0.98C0.02合金是制作工质盘理想的磁致冷材料.     

Gd含量对Gd5Si2Ge2晶体结构和磁性能的影响

用非自耗电弧炉熔炼了Gd5 xSi2Ge2系列样品。用X射线粉末衍射(XRD)和Rietveld方法研究了Gd5 xSi2Ge2系列样品的晶体结构。用自制的仪器测量了样品的居里温度,用振动样品磁强计研究了样品的磁卡效应。对样品的晶体结构分析结果表明:Gd的含量x的变化对Gd5Si2Ge2化合物的晶体结构有较大的影响,当x>0时,样品中含有Gd5(Si,Ge)4和Gd5(Si,Ge)3两个相,并且随着x的增加Gd5(Si,Ge)4相会减少,Gd5(Si,Ge)3相会增加;当x<0时,样品会形成Gd5(Si,Ge)4和Gd(Si,Ge)两相,并且随着x的减少Gd5(Si,Ge)4相会减少,Gd(Si,Ge)相会增多。对样品的磁性能分析结果表明:Gd的含量x>0和x<0时都会降低样品的磁卡效应,样品的居里温度会随着x的增加而增加。     

Magnetocaloric Effect of Alloys Gd（Al1-x Cox ）2

The magnetocaloric effect in alloys Gd（Al1-xCox）2 with x = 0, 0.05, and 0.10 were investigated using X-ray diffraction （XRD） and magnetization measurements. It was found that three alloys crystallized in a single phase with MgCu2-type structure. The lattice parameter and Curie temperature decreased with increasing Co content, whereas the magnetic-entropy change increased. With a magnetic-field change of 2 T, the maximum of the magnetic-entropy change reached 4.6 J·kg^-1·K^-1 near Curie temperature at approximately 95 K in the alloy GdAl1.8Co0.2, which appeared to be an alternative candidate for active magnetic refrigerants working in the temperature range centered at 100 K.     

Magnetic Entropy Change of （Gd1-xREx）5Si4（RE = Dy, Ho） Alloys

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys     

Influence of the Erbium Substitution for Gd in Gd5Si1.8Ge2.2Alloys on the Magnetocaloric Effect in Low-Field

The phases and magnetocaloric effect in the alloys (Gd1-xErx)5Si1.8Ge2.2 with x=0,0.1,0.2 and 0.3 were investigated by X-ray diffraction analysis and magnetization measurement. The samples were single phase with the monoclinic Gd5Si2Ge2-type structure. With the increase of Er content, the Curie temperature (Tc) decreased obviously from 253K of the alloy with x=0 to 114K with x=0.3. The maximum magnetic entropy changed in the samples of (Gd1-xErx)5Si1.8Ge2.2 with x=0.0,0.1,0.2 and 0.3 were 6.88,8.32,9.59 and 10.24 J·kg-1·K-1 respectively in the applied field change of 0~2.0T.     

(Sr1-xMx)Al2O4(M=Ca,Ba)∶Eu发光材料的研究

以SrAl2O4∶Eu发光材料为基础,通过对基质的部分修饰,合成了(Sr1-xMx)Al2O4(M=Ca,Ba)∶Eu磷光体,并利用XRD对其晶体结构进行了研究,结果表明:加入Ca后,原来在室温下稳定存在的属于单斜晶系的鳞石英结构SrAl2O4相逐渐变成六方晶系,证明Ca有稳定六方相的作用,而加入Ba晶形则不发生改变。同时研究了该发光粉的发射光谱,讨论了Ca和Ba的引入对发光性能的影响。     

Magnetocaloric effect of(Tb_(1-x)Ce_x)Co_2 alloys in low magnetic field

The phases in alloys(Tb1-xCex)Co2 with x=0,0.1,0.2,0.3,0.4 and 0.5 were investigated by X-ray diffraction analysis,and the magnetocaloric effect for x=0-0.4 was studied by magnetization measurement.The samples were almost single phase with MgCu2-type cubic structure.The magnetization decreased with the increase of Ce.The Curie temperatures(Tc) of Tb1-xCexCo2 alloys with x from 0.1 to 0.4 were 180,165,160 and 152 K,respectively.For x=0.5 in the range from 100 K to 230 K,the point of magnetic transition was n...     

Study on Gd-Si-Ge Alloys Using Domestic Gd

To evaluate the possibility of using Gd-Si-Ge alloys in magnetic refrigerators, samples of Gd-Si-Ge alloys were made of domestic Gd. The magnetocaloric effect of samples was estimated by magnetic entropy change (-△ASm) calculated from M-H curves according to Maxwell relation. The first order phase transformation was destroyed due to the impuritiesin the commercial Gd, so that no giant magnetocaloric effect was found. The samples made of purified Gd exhibit first order phase transformation, and the -△Sm is basically consistent with the published data of Ames laboratory, USA. This work proves that Gd-Si-Ge alloys made of domestic Gd can be utilized in magnetic refrigerators.