低温化学合成La2CuO4粉体及其表征

采用醛酸盐／硝酸盐自蔓延燃烧法低温合成了Ｌａ２ＣｕＯ４的前驱物粉体,然后在不同的温度进行焙烧处理,得到了单一相的Ｌａ２ＣｕＯ４粉体。研究了不同的Ｏ／Ｆ比率对前驱物和焙烧产物组成和显微形貌的影响。发现Ｏ／Ｆ比率不但对前驱体的组成有影响,而且对焙烧产物的显微形貌有很大影响。在Ｏ／Ｆ＝０．２０的前驱物粉体经７００．８００．９００℃处理６ｈ的焙烧产物颗粒上发现立体网络状结构。在前驱物焙烧过程中Ｈ２Ｏ和ＣＯ２的释放通道形成网络状结构,Ｈ２Ｏ在其中扮演了重要角色。ＸＲＤ用于物相鉴定,ＳＥＭ,ＴＥＭ用于显微形貌分析,ＥＤＳ用于化学成分分析。     

La/Cu比及分散剂对溶胶-凝胶法制备La2CuO4及光学性质的影响

采用溶胶-凝胶法,以硝酸镧和硝酸铜为原料,在不同La/Cu物质的量比条件下合成了La2CuO4粉体。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和紫外-可见-近红外光谱(UV-Vis-Nir)对样品的物相组成、显微形貌以及光学性能进行了分析。结果表明,n(La)/n(Cu)比为化学计量比2∶1时,可以制备出单一相的La2CuO4;n(La)/n(Cu)<2∶1时,产物含有CuO杂质相;n(La)/n(Cu)>2∶1时,含有La2O3杂质相。根据UV-Vis-Nir光谱分析,n(La)/n(Cu)为2∶1,所得La2CuO4的光学带隙为1.37eV,杂质相的产生使光学带隙减小。以抗坏血酸、葡萄糖为分散剂,有较好的分散效果,聚乙二醇作为分散剂时,出现团聚现象,相应的光学带隙分别为1.39、1.41和1.33eV。     

尿素低温燃烧法合成Ce_(0.8)Gd_(0.2)O_(1.9)电解质粉末及烧结性能

采用以尿素为燃料的低温燃烧法一步合成了电解质粉末Ce0.8Gd0.2O1.9(GDC),通过XRD、TGDSC、BET、FESEM等手段对合成粉体进行了物相测定、热分析、比表面积测定和形貌观察,并考察了粉体的烧结性能。结果表明,尿素-硝酸盐干凝胶自蔓延燃烧点火温度约为279.0℃。通过工艺参数的有效设计,经过低温燃烧过程即可直接得到立方萤石结构的纯相GDC粉体,该粉体为粒径在20~60nm的类球形颗粒,粒子间虽有微弱的软团聚,却具有较高的烧结活性,在1 300℃仅需烧结2h即可达到95.2%的相对密度。该温度比固相法制备该粉体的烧结温度至少降低300℃。     

溶胶凝胶-自燃烧法合成La 9.33Si 6O26超细粉体

用柠檬酸和乙二醇做络合剂和燃料,硝酸盐做氧化剂,用氨水调节溶胶pH值,通过溶胶凝胶-自燃烧法一步合成了可用于固体氧化物燃料电池(SOFC)的新型固体电解质La9.33Si6O26.用XRD、TEM等分析方法对合成粉体进行了物相测定与形貌观察,并初步考察了粉体的烧结性能.结果表明:通过工艺参数的有效设计,溶胶-凝胶和自燃烧过程可以在短时间内达到合成所需要的高温,一步合成粒径约为150～300 nm的单相La9.33Si6O26超细粉体,其烧结温度比固相法制备的粉体的烧结温度约低200℃.     

固体氧化物燃料电池阴极材料La_(0.8)Sr_(0.2)Cu_(1-x)Co_xO_(2.5-δ)的制备和性能研究

为探索适于中温条件下使用的固体氧化物燃料电池的阴极材料,采用柠檬酸-硝酸盐燃烧合成法制备了La0.8Sr0.2Cu1-xCoxO2.5-δ(x=0～0.4)粉体。利用X-射线衍射(XRD)技术对粉体的性能进行了表征,XRD结果表明,经800℃焙烧的粉体的对称性较高,已形成钙钛矿结构。采用直流四电极法测试La0.8Sr0.2Cu1-xCoxO2.5-δ试样的电导率,测试温度范围为100～800℃,试样的电导率ln(σT)与1/T之间呈很好的线性关系,说明La0.8Sr0.2Cu1-xCoxO2.5-δ在测试温度范围内服从小极化子导电机制。Co掺杂量对试样的电导率和电导活化能有着明显的影响,当Co掺杂量为0时,La0.8Sr0.2CuO2.5-δ的电导率最高,电导活化能最小。     

凝胶自蔓延燃烧法制备纳米La_2O_2CO_3粉体

研究一种以溶胶-凝胶作为前躯体制备纳米La2O2CO3粉体的新方法,以柠檬酸和硝酸镧为原料,采用凝胶自蔓延燃烧法制备纳米La2O2CO3粉体,并利用X射线衍射、差热分析、透射电镜等手段对合成产物进行表征,确定最佳的工艺条件。结果表明:在前驱溶液的pH值为2,烘干温度为400℃,煅烧温度为600℃时,可以制备出平均晶粒尺寸为30 nm的La2O2CO3颗粒,且粉体的粒径均匀,粒径分布狭窄。     

铜铁氧体纳米晶的溶胶-凝胶自蔓延燃烧法合成和表征

以硝酸铜、硝酸铁、硝酸钴和柠檬酸为原料,采用溶胶-凝胶自蔓延燃烧法一步直接合成了单相Co0.5Cu0.5Fe2O4纳米晶.借助TG/DTA、IR、XRD和SEM等手段分别对溶胶-凝胶自蔓延燃烧机理、粉体在不同退火温度下的结构演化过程以及燃烧粉体的表面形貌进行了研究.结果表明,自蔓延燃烧过程是在硝酸根离子和羧酸根离子之间进行的热诱导阴离子氧化还原反应,其中,硝酸根离子作氧化剂,羧酸根离子作还原剂.干凝胶燃烧后,产物已经初步晶化,晶粒尺寸约20nm.经600℃,2h退火即可得到晶化较好的Co0.5Cu0.5Fe2O4纳米粉体,燃烧粉末为多孔结构,密度为2.9g/cm3.     

溶胶-凝胶法合成纳米NiZn铁氧体研究

以金属硝酸盐为原料,柠檬酸为螯合剂,采用溶胶-凝胶法和自蔓延燃烧反应相结合制备纳米NiZn铁氧体粉体.用X射线衍射图谱研究了不同pH值干凝胶的均质化特性和自蔓延后NiZn铁氧体粉体,并用红外吸收光谱研究了干凝胶的自蔓延过程,用透射电镜对合成的纳米粉体进行了形貌表征.     

La1.9Sr0.1Ni0.9Cu0.1O4+δ混合导体的合成与导电性能研究

采用氨基多羧酸配合物法合成La1.9Sr0.1Ni0.9Cu0.1O4 δ超细粉料,对合成产物的结构和性能进行了表征.研究结果表明,配合物前驱体经900℃保温2h热处理即形成单一的K2NiF4结构,合成粉料的颗粒细小、均匀(约100nm).X射线衍射Rietveld分析结果显示,La1.9Sr0.1Ni0.9Cu0.1O4 δ为正交结构(空间群为Fmmm).与La1.9Sr0.1NiO4 δ相比,La1.9Sr0.1Ni0.9Cu0.1O4 δ表现出较好的烧结性能.与La2Ni0.9Cu0.1O4 δ相比,La1.9Sr0.1Ni0.9Cu0.1O4 δ具有较高的总电导率.在1400℃烧结的La1.9Sr0.1Ni0.9Cu0.1O4 δ的相对密度达到95.3%,在600～800℃的测试温度范围内陶瓷样品的总电导率为78～99S/cm,在800℃的测试温度下陶瓷样品的氧离子电导率为2.0×10-2S/cm.     

La2O3掺杂MoSi2的SHS合成及其性能研究

以Mo粉、Si粉和La2O3为原料,通过自蔓延高温燃烧合成(SHS)的方法制备了La2O3掺杂的MoSi2材料．研究表明,掺杂剂La2O3的加入对MoSi2燃烧合成过程的热力学和动力学具有明显的影响．并通过XRD和SEM对燃烧合成产物的物相组成和形貌进行了分析,发现La2O3的加入对合成产物的物相组成没有明显影响,但可以大大降低合成产物的晶粒尺寸．同时,力学性能研究结果表明,La2O3的加入可以提高MoSi2材料的室温断裂韧性．     

Low-temperature chemical synthesis of lanthanum copper oxide

Lanthanum copper oxide (La₂CuO₄) precursors for superconductors were synthesized by acetate/nitrate self-propagating combustion synthesis (SPCS) in the presence of urea at different ratio of O/F. Phase-pure La₂CuO₄ powder could be obtained by calcining the as-prepared precursors at temperature as low as 600 °C. It was demonstrated that the ratio of O/F strongly influenced the composition and morphology of the precursors as well as the samples calcined at various temperatures. We have studied the synthesis conditions, demonstrating the existence of a relationship between the calcination temperature and the calcination time needed to obtain the pure phase. An interesting stereoscopic network structure was observed on the samples synthesized at the ratio of O/F = 0.20, morphology evolution of the samples was also investigated. The emission of H₂O as well as CO₂ was responsible for the formation of the structure during the calcination process.     

甘氨酸-硝酸盐燃烧法制备Beta-Al_2O_3固体电解质研究

甘氨酸(GNP)为还原剂、硝酸盐为氧化剂,利用甘氨酸-硝酸盐燃烧法制备beta-Al_2O_3前驱粉料。利用热分析(TG/DSC)、X射线衍射分析(XRD)、扫描电镜(SEM)、核磁共振(NMR)和交流阻抗谱(EIS)等测试技术对beta-Al_2O_3的合成工艺进行研究。结果表明:该法合成beta-Al_2O_3前驱粉料的温度为1150℃,比固相反应法低了150℃,平均粒径约为42.0nm,具有较好的成型和烧结性能。将素坯在1620℃保温烧结,得到的烧结体的结构中Al(Ⅳ)和Al(Ⅵ)分别位于δ=45和δ=-6附近,相对密度为97.6%;350℃时的离子电导率为0.046S·cm~(-1)。     

Combustion synthesis of CuFe2O4

Metallic ferrites are investigated as prospective materials for different applications especially as anodes in extractive metallurgy. CuFe₂O₄, one of the important ferrites, is envisaged for substituting the carbon anode in Hall-Heroult cells. A single step combustion process has been used for the synthesis of CuFe₂O₄ powder from cupric nitrate, ferric nitrate and urea. The experimental conditions for maximum conversion efficiency of the precursor powders have been optimized. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) have confirmed the formation, structure and homogeneity of the as-prepared powders. The detailed physical, electrical and structural characterization of the materials have been carried out for the specimens obtained on sintering at different temperatures up to 1000 °C.     

A novel method for preparation of barium strontium titanate nanopowders

Ba_0.6Sr_0.4TiO₃ (BST) nanopowders have been prepared using the modified citrate method with ammonium nitrate as a combustion promoter, and the formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. It is found that the peaks of barium carbonate disappear when the precursor powders are calcined at 650 °C. The fine particles of the nanopowders calcined with the combustion promoter addition are homogeneous and well-dispersed and their narrow size distribution is about 60-90 nm. Comparatively, the particles of the powder calcined without the ammonium nitrate addition are inhomogeneous, with an evident agglomeration. The mechanism for the above results is attributed to that a reaction can generate soft and loose precursor powders by the adoption of ammonium nitrate, and hence a pure BST phase could occur at the low synthesis temperature of 650 °C.     

Effect of acidity on the glycine–nitrate combustion synthesis of nanocrystalline alumina powder

Nanocrystalline alumina powders were prepared by combustion synthesis using glycine as fuel and nitrate as an oxidizer. The effect of the pH values in the precursor solutions on crystallite sizes, surface areas and morphologies of the synthesized alumina powder has been investigated by X-ray diffractometry, thermal analysis, nitrogen adsorption–desorption, and transmission electron microscopy. With decreasing the pH values in the precursor solutions, the obtained materials could be modified from segregated nanoparticles (pH 10.5) to aggregates of nanoparticles (pH 6.0), and finally to a flaky morphology (pH 2.5). The rates of decomposition, the interaction of coordination as well as the hydrogen bonding of the glycine and the Al-hydroxides species at different pH values were found to be responsible for the generation of flake and/or segregated nanoparticles during auto-ignition reactions. The as-prepared combustion ashes were converted into pure nanocrystalline alumina after calcination at elevated temperatures. The specific surface areas of the products calcined at 800 °C ranged from 96 to 39 m²/g with the pH decreased from 10.5 to 2.5.     

沉淀剂对La_2Zr_2O_7制备过程的影响

分别采用氨水和草酸铵作沉淀剂,通过化学共沉淀法制备了单相La2Zr2O7粉末。利用DSC-TGA和XRD等方法对LZ前驱体的煅烧分解过程、产物物相进行了分析和表征。结果表明:氢氧化物前驱体在400~750°C分解得到无定型的复合氧化物,800℃保温2.5h即完成相转变形成单相组分的La2Zr2O7;而草酸盐前驱体在400~650°C草酸盐发生分解得到无定型氧化镧、氧化锆的混合物;700°C以后,La(OH)3的分解、无定型氧化物晶化得到六方结构氧化镧与单斜相氧化锆、Zr4+扩散到La2O3晶界生成La2Zr2O7等三个反应同时进行。获得单相组分La2Zr2O7的煅烧条件至少要1450℃,保温2.5h。草酸盐前驱体中镧和锆两种成分局部的分布不均匀是造成其处理温度比氨水法要高的直接原因。     

微波均相沉淀法制备Nd:YAG纳米粉体及其表征

以Al(NO3)3,Y(NO3)3为母盐,尿素为沉淀剂,添加占母盐质量为8%的(NH4)2SO4,以不同浓度的Nd3+取代Y3+,采用微波均相沉淀法制备了具有良好分散性和可烧结性、平均粒径为71nm的Nd:YAG纳米粉体。利用IR、DTA-TG、XRD、TEM、LD等技术对YAG前驱物及其煅烧粉体进行表征。结果表明:采用微波均相法,前驱体在1100℃下煅烧,可得到分散良好的纯YAG相,无YAP、YAM中间相出现,且YAG的单相程度不随Nd3+掺杂浓度的增加而变化。     

Powder synthesis and characterization of nanocrystalline CeO2 via the combustion processes

Nanocrystalline CeO₂ powders were synthesized by the combustion reactions using citric acid and glycol as fuels and nitrate as an oxidant. The adiabatic flame temperatures in the auto ignition processes of the precursors were calculated theoretically. XRD measurements indicated that the powders produced in the combustion processes were cubic fluorite CeO₂ phase. The size and morphology of the particles and extent of agglomeration in the powders were studied using transmission electron microscopy (TEM) and the particle size analyzer respectively. Blue shifts of the absorption peak of the as-prepared powders were observed.     

纳米FePO4的合成及其正极材料LiFePO4/C的电化学性能研究

以Fe3+为铁源,采用控制结晶技术合成了纳米FePO4.xH2O,将FePO4.xH2O于500℃热处理4 h后得到纳米FePO4前驱体,然后通过碳热还原在不同温度下煅烧合成橄榄石结构的纳米LiFePO4/C样品.采用差热/热重、X射线衍射、扫描电镜、比表面测试、电化学性能测试等分析测试方法对纳米FePO4.xH2O、FePO4前驱体及不同煅烧温度下制得的纳米LiFePO4/C样品进行表征.研究结果表明,700℃烧结10 h合成LiFePO4/C样品的粒径在40~100 nm左右,比表面积为79.8 m2/g;700℃煅烧合成样品在电压2.5~4.2 V,倍率为0.1C、1C、5C、10C、15C时的放电比容量分别达到156.5、134.9、105.8、90.3和80.9 mAh/g,具有较好的倍率性能;样品还表现出较好的容量保持率.     

Preparation of La1−xSrxMnO3 powders by combustion of poly(ethylene glycol)–metal nitrate gel precursors

La1–xSrxMnO3 powders were prepared by auto-ignited combustion of poly(ethylene glycol) (PEG)–metal–nitrate gel precursors. The thermal behaviour of the precursors strongly depends on the ratio of PEG to metal nitrate, which is closely related to the ratio of fuel to oxidizer. The burning behaviour in a furnace was successfully explained by valence concepts normally encountered in propellant chemistry. The formation of a pure perovskite phase was significantly influenced by the homogeneity of the gel precursor. Perovskite structured oxides were formed through two different paths, one of which was direct formation from the burning of a gel precursor and the other was a subsequent structural evolution by heat treatment after burning. The formation procedure of the perovskite and the morphology of powders could be explained in terms of the burning behaviour of the precursor and the role of organic residue.