高能球磨对La2/3Ca1/3MnO3晶体结构和磁性的影响

通过在传统的烧结工艺上加上球磨工艺制备了单相La     

Large Magnetic Entropy Effect in La2／3Ca1／3MnO3

The magnetocaloric effect in the colossal magnetoresistance material La2/3Ca1/3MnO3 was studied. From the measurements of temperature dependence of magnetization in various magnetic fields, the large magnetic entropy change associated with the ferromagnetic-paramagnetie transition was discovered. This result suggests that perovskite manganites are suitable candidates as working substance in magnetie refrigeration technology.     

等离子喷涂La_(0.8)Ca_(0.2)CrO_3高发射率涂层研究

本文以氧化镧、氧化钙、氧化铬为原料,按分子式La0.8Ca0.2Cr O3进行配料,球磨后,采用固相合成法制备原始粉末,再经喷雾干燥处理,将其制备成团聚体粉末,并将粉末粒度分布范围控制在20~60μm,采用等离子喷涂法在高温合金基体表面制备高发射率涂层。采用IRE-2型红外辐射仪对其全波段发射率进行了测试,利用XRD对涂层的相结构进行了分析,并对涂层的金相、结合强度及抗热震性能进行了测试。结果表明,所制备的La0.8Ca0.2Cr O3涂层结合强度为21MPa,孔隙率为14.8%,在600~800℃高温范围内,其全波段发射率可达0.87~0.88,同时,该涂层试样经1100℃~室温水热震10次后没有发生剥落失效现象,涂层具有良好的抗热震性能。     

Pr_(0.4)Ca_(0.6)Mn_(1-x)Cr_xO_3的磁性质及电荷有序相

用固相反应法制备了Pr0.4Ca0.6Mn1-xCrxO3(x=0,0.04,0.06,0.08,0.10,0.12),通过X射线衍射(XRD)图谱,磁化强度-温度(M-T)曲线、电子自旋共振(ESR)图谱,并用ESR作出归—化强度-温度(I/I300—T)曲线、谱线宽度-温度(△Bpp-T)曲线,研究Cr3+替代Mn3+对Pr0.4Ca0.6MnO3的磁性质及电荷有序相的影响。结果表明,母体样品Pr0.4Ca0.6MnO3的电荷有序转变温度Tco=267 K,205K~62 K温区是长程反铁磁序,50 K以下在反铁磁背景下出现少量铁磁成分;Cr替代量x=0.06时,电荷有序相已基本被破坏,随温度降低材料从顺磁向反铁磁转变,同时在反铁磁背底下存在铁成分;Cr替代量达到x=0.10时,电荷有序相完全被破坏,250 K以下是反铁磁与铁磁混合相,铁磁成分增多。用有磁性的且与Mn4+有相同电子结构(t32ge0g)的Cr3+替代Mn3+破坏电荷有序相的机制是:Cr3+替代Mn3+引起自旋序的改变从而引起电荷序的破坏,说明在CE型反铁磁体系中,自旋序与电荷序之间存在强耦合相互作用。     

添加剂CeO_2对La_2Mg_(17)-50% Ni储氢性能的影响

研究了球磨添加CeO2对La2Mg17-50%(质量分数,下同)Ni复合合金的相结构和储氢性能的影响,并对合金的形貌和吸放氢性能进行了检测。XRD结果表明,球磨加入CeO2后,在La2Mg17-50%Ni合金中除了Mg2Ni和Ni相外,产生Ce Mg12相。SEM形貌图清晰地看见CeO2附在La2Mg17-50%Ni合金表面上呈白色小颗粒。吸氢动力学性能表明,加入CeO2后,使La2Mg17-50%Ni合金的最大吸氢量从3.298%增加到3.594%。添加CeO2后合金的最佳饱和吸氢温度降为200℃(3 MPa),且吸氢动力学性能提高至1 min内的吸氢量达到3.382%,是其最大吸氢量的94%。然而,CeO2在放氢过程中的积极作用并不明显。     

Anisotropic Magnetoresistance of Perovskite La_(2/3)Ca_(1/3)MnO_3/YBa_2Cu_4O_8/La_(2/3)Ca_(1/3)MnO_3 Trilayer Films

Magneticanisotropyhasbeenfoundinmanyex oticmaterials,suchasmetallicsuperlatticeswithgi antmagnetoresistanceeffectsandthehightempera turesuperconductingoxideYBa2Cu3O7 δ[1～4].The anisotropycouldfindnovelusesinnewdeviceappli cations.Agoodexampleisthehig…     

MnO_2/γ-Al_2O_3催化剂上3-戊酮的合成研究

采用γ-Al2O3为载体,金属氧化物为活性组分,以丙酸为原料,在固定床反应器上合成了3-戊酮。实验研究了γ-Al2O3上负载不同活性组分对反应收率的影响,确定了活性物质为MnO2时催化活性最高;研究了催化剂的负载量、浸渍时间、焙烧温度及实验反应温度对催化剂活性及反应产率的影响。结果表明,Mn的负载量为10%～13%,浸渍时间大于5 h,焙烧温度为450～600℃,焙烧时间为4～7 h制得的催化剂活性最优;较佳的反应温度范围为330～410℃。在此条件下,丙酸转化率大于95%,产物选择性大于90%。     

高能球磨法制备超细Al2O3粉末

采用高能球磨法制备超细Al2O3粉末,研究了球磨时间、球磨转速及工艺控制剂等工艺参数对Al2O3粉末粒度和形貌的影响。结果表明:在一定范围内,延长球磨时间,提高球磨转速均能有效地减小颗粒尺寸;在球磨过程中加入工艺控制剂,能有效地防止粉末粘附在磨球和磨罐上,并改善粉末颗粒的均匀性。在本文试验条件下,加入工艺控制剂乙醇,球磨转速为400r/min,球磨时间为30h等条件下,获得Al2O3粉末的D50为0.82μm,Al2O3粉末粒径分布在0.12～6.37μm范围内。     

烧结温度对SPS制备Ag/La2O3触点材料的影响

采用放电等离子烧结(SPS)技术制备了Ag/La2O3触点材料,研究了烧结温度对其致密度、显微结构及力学性能的影响.结果表明:采用SPS技术制备Ag/La2O3触点材料的工艺中,烧结温度对材料的致密度有着显著的影响,500℃烧结体的致密度最大,达到了97.2%,且试样的抗弯强度最高,约为450MPa;塑性断裂是其主要断裂方式,在不同烧结温度的烧结过程中没有新相出现,La2O3颗粒在银基体中均匀弥散分布.     

一维纳米LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2纤维的合成及性能研究

通过静电纺丝法制备出一维纳米Li Ni1/3Co1/3Mn1/3O2纤维,根据扫描电子显微镜(SEM)、X射线衍射(XRD)、充放电实验,循环伏安法和交流阻抗法对纳米纤维的形貌、晶体结构和电化学性能进行研究.结果表明,纳米纤维的直径在150~300 nm之间,且具有典型的α-Na Fe O2层状结构;所制备的Li Ni1/3Co1/3Mn1/3O2纳米纤维在0.5 C(85 m A/g)的倍率下循环30次容量保持率达到了94.1%;在倍率分别为0.1 C、0.2 C、0.5 C、1.0 C、2.0 C和0.2 C的充放电测试中,其比容量分别达到了157 m Ah/g、144 m Ah/g、134 m Ah/g、125 m Ah/g、115 m Ah/g和141 m Ah/g;在CV和EIS测试中,材料表现出优异的可逆性和循环稳定性.由于具有特殊的一维形貌,Li Ni1/3Co1/3Mn1/3O2纳米纤维表现出优异的电化学性能.     

Structure and Transport Properties in CMR Materials of La（1-x）2/3Ca1/3MnO3 with Rare Earth Vacancies

Samples of manganese oxides La（1-x）2/3Ca1/3MnO3（x 〈 0.10） with Lavacancy were prepared by standard solid-state reaction method. All the samples are single phase, with orthorhombic symmetry （Pnma ）, analyzed by XRD and with Rietveld Refinement. The effect of different La-site vacancies concentration on electronic transport of La（1-x）2/3Ca1/3MnO3 was investigated. The insulator-metal transition temperature （about 267 K） nearly remains unchanged with the increase of vacancy concentration, which indicates that small La-vacancy does not destroy the double exchange interaction. But the electronic resistance increases and MR value decreases with La-vacancy content x 〉 0.04. The maximum of the MR value （8 T） is about 220% at transition temperature （TMI）.     

(La1-xPrx) 2/3Sr1/3CoO3 的成相过程与电导性能研究

采用固相反应法合成了(La1-xPrx) 2/3Sr1/3CoO3 (x=0.2,0.4,0.6,0.8) 双稀土氧化物系列粉体,研究了(La0.6Pr0.4) 2/3Sr1/3CoO3的成相过程和电导性能.结果表明,在实验过程中首先出现了La2O(CO3)和La2SrOx相,而La2SrOx相在270℃～910℃的较大范围内一直存在,再经过两次吸热到910℃时出现了(La0.6Pr0.4) 2/3Sr1/3CoO3 晶相,当温度达到1000℃时,(La0.6Pr0.4) 2/3Sr1/3CoO3 成为主晶相,在1250℃下烧结2h后,样品已成单一钙钛矿结构(La0.6Pr0.4) 2/3Sr1/3CoO3相.(La1-xPrx)2/3Sr1/3CoO3(x=0.2,0.4,0.6,0.8)双稀土氧化物的电导率在700℃附近时出现最大值,其中(La0.8Pr0.2) 2/3Sr1/3CoO3的电导率在中温范围内最大,适合作为中温固体氧化物燃料电池阴极材料.     

铝与K2TiF6混合粉末的高能球磨反应

以Al粉和K2 TiF6 混合粉末为原料 ,利用高能球磨法制备Ti Al基金属间化合物。采用XRD ,SEM ,EPMA和DTA等方法对球磨 1,2 5 ,5 ,8h的粉末进行分析 ,在球磨时间超过 2 .5h的粉末中有TiAl3,TiAl出现 ,并伴有副产物KAlF4 和K3AlF6 生成。随着反应的进行 ,产物中TiAl相含量逐渐增加 ,产物粒度可达纳米级。     

Microstructure and Electrical Properties of Er2O3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.     

Transport Properties of Rare Earth Manganese Oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3

CompoundsofthetypeLn1-xAxMnO3(Ln =rareearth ,A =Ca ,Ba ,Sr ,etc .)havebeenthepopularsubjectsofextensiveresearchrecently ,mainlyduetotheexistenceofcolossalmagnetoresistance(CMR ) [1～ 3] .Atroomtemperature ,theperovskitecompoundLnMnO3isantiferromagneticinsulatorwhereMnistrivalent .ThepartialsubstitutionoftrivalentLnionswithdivalentionssuchasCa ,Ba ,Sr ,andPbetc .yieldsanewcompoundexhibitingstrongferro magnetismandhighmetallicconductivity .Thetrans portpropertyinthesecompoundscanbepartly…     

Microstructure and Electrical Properties of Er_2O_3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

Zinc oxide (ZnO) varistors exhibit highly nonlin-ear voltage-current (V-I) properties and it is ex-pressed bythe relationI=KVα,whereKis a constantandαis a nonlinear coefficient .They are extensivelyused as surge arresters in electric power lines ,such a…     

Structure and Transport Properties of La0.67Ca0.33Mn1-xAlxO3

The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La0.67Ca0.33MnO3. It is found that the volume of the crystal cell decreases monotonically when the population of Al3 increases across the entire doping range. As the Al3 population increases, the resistance of the material rises rapidly, while the insulator-metal transition temperature TIM decreases linearly. At small Al3 dosage, a thermal activation model properly describes the transport properties at T>TIM, while a metallic model is more suitable at T相似文献   

高能球磨金属铬、铝粉末的特征

利用金属铬及铝粉末进行高能机械球磨，分析、研究了这些粉要的组织与相结构的变化。随着球磨时间的延续，脆性铬粉末由于冷焊与破碎相互作用的结果而使其平均粒度不断减小，衍射峰发生宽化及峰高降低现象；而韧性铝粉末则表现出强烈的冷焊性，使绝大多数粉末都粘附于磨球表面及罐壁，同时在剧烈变形的铝粉末微观组织中发现有许多位错环，而无位错缠结。     

Nonlinear current-voltage characteristics originated from phase segregation and micro-cracks in polycrystalline La_（0.67）Ba_（0.33）MnO_3

Polycrystalline La0.67Ba0.33MnO3 bulk samples were annealed in flowing 95%Ar:5%H2 (AH) mixed gas at 973 K for different time respectively. The influence of the annealing time on the current-voltage properties was systematically investigated. Linear current-voltage characteristics were observed in the as-prepared and the 10 h annealed samples, and nonlinear current-voltage characteristics was found in the 100 h annealed sample. At the same time, segregation of impurity phase and micro-cracks were found on the surfaces of the 100 h annealed samples, which was testified to be Ba ion impurity. Analysis showed that the changes of electronic properties were caused by barium ion im-purities and micro-cracks in the 100 h annealed sample.