ErFe_(11)Ti化合物在流动氮气氛中的差热-热重分析

通过X射线衍射(XRD)、差热-热重(DTA-TG)联用仪以及磁测量等手段研究了ErFe11Ti化合物在流动氮气氛从室温(~300 K)到1473 K升温过程中成分、结构及居里温度等变化行为。结果表明,温度为600 K左右时,ErFe11Ti化合物吸氮反应最剧烈,吸氮以后化合物的居里温度TC有明显提高。当温度较高时,ErFe11Ti可能部分分解为Er-N,α-Fe(Ti)。α-Fe和Ti分别在860和1300 K左右发生吸氮反应,生成FeNy和Ti2N2。在整个升温过程中,DTA曲线未因样品升温至某成分的居里点发生而出现明显放热峰,这可能是因为样品的相变潜热较小所引起的。     

LiNd(PO3)4晶体的热分析研究

对LiNd(PO₃)₄晶体分别在N₂气和空气下进行了TG和DTA热分析研究,给出TG和DTA曲线,讨论了LNP晶体在N₂气和空气下不同的热分解机理.得到分解产物分别为Nd₄(P₂O₇)₃和NdP₂O₇.     

TGA和Py-GC/MS研究不同氛围下烟草的热失重和热裂解行为

应用热重红外联用技术(TG-FTIR)和热裂解气相色谱-质谱联用技术(Py-GC/MS)对卷烟烟丝的热失重和热裂解行为及其裂解产物进行研究.采用热重分析法测定不同气氛下卷烟样品的热失重(TG)、微商热重(DTG)曲线,以及热裂解过程中H2O、CO2、CO、NH3和CH4等气体物质的释放量.结果表明,裂解气氛不同可以显著...     

激光打印机墨粉的热重分析

应用热重分析方法对21种激光打印机用墨粉样品作了热失重研究。在氮气气氛中,分别对21种样品用TA 2050型热重分析仪在静态恒温及动态升温条件下的热稳定性及热解曲线的差异作了比较。在整个静态恒温条件的分析过程中,21个样品的失重在0.60%～1.16%之间,多数在1%左右。从动态升温的热失重数据及其热解曲线可见,各种墨粉之间存在较明显的差异,例如在曲线上呈现单个或多个失重台阶,失重的温度和温度区间的不同以及趋于恒重状态的温度和残重的不同等。据此认为热重分析可以为鉴别不同牌号的墨粉提供依据,而且还可对墨粉的组分作出初步判别。     

用热分析方法研究WO3和MeCO3固相反应的化学行为

本文应用MOM型-Derivatograph热分析仪研究了WO₃与Me₂CO₃(Me=Li,Na,K,Rb,Cs)系列的固相反应.由TG和DTA二曲线指示了反应变化的全过程.对热分析的TG曲线,以Coats-Redfern计算方法处理,求取反应活化能(E),反应级数(n),频率因子(A)和速度常数(K)等动力学参数.此外,用Kissinger方法算得Na₂CO₃与WO₃系统的E值(372.0千焦/摩尔)与Coats-Redfern方法计算的E值(347.8千焦/摩尔)相接近.     

钕铁硼磁钢居里温度的测定

居里温度是影响钕铁硼磁钢应用的重要因素和反映磁性材料温度稳定性的基本参数。对于居里温度的测量,多数方法局限在小尺寸的样品测量,但在工程应用中,往往关注的是磁钢的整体特性,而小尺寸样品的测量不能很好反映磁钢的整体特性。通过钕铁硼磁钢的热膨胀实验发现:热膨胀系数α的最小值所对应的温度点不会因磁钢的取向改变而改变,此温度点就是钕铁硼磁钢的居里温度。由于不受几何尺寸与取向的限制,此方法能更好地反映钕铁硼磁钢整体的居里温度。同时还对比了M-T曲线测试法、差热(DSC)或热重(TG)分析测试法、 ARROTT图测试法,研究进一步证实了热膨胀测试居里温度具有很高的准确性;通过材料测试与分析进一步证明了所测居里温度的合理性。     

LCT-1型微量差热天平的性能

差热天平是一种DTA和TG联用的热分析仪,可同时获得DTA曲线和TG曲线。由于两种信息是在同一样品上同时获得,因此不仅升温速率、气氛、试样粒度和重量等各种条件完全相同,而且两者测定是完全同步进行的,便于实验结果的互相补充和验证。故一般研究工作中差热天平采用较多,过去此类仪器都靠进口,1979年北京光学仪器厂首先试制成功LCT—1型微量差热天平,填补了国内空白,仪器各项指标     

环戊烷和环己烷在silicalite-1分子筛上的热脱附行为

采用智能质量分析仪(IGA)及TG/DTG法研究了环戊烷和环己烷在硅沸石silicalite-1上的热脱附行为。当环戊烷在silicalite-1上吸附量小于4 m/uc时,TG/DTG曲线表明环戊烷在silicalite-1上存在一个脱附过程。吸附量大于4 m/uc,TG曲线显示热脱附过程明显分为两个阶段,DTG曲线中出现两个明显的脱附峰,彼此分离。环己烷在silicalite-1上只存在一种脱附过程,DTG曲线只出现一个脱附峰。从环戊烷和环己烷的热脱附曲线中也可看出,随着吸附量的增加脱附峰温逐渐向高温方向偏移。     

化学反应的热动力学研究进展

根据化学反应的放热速度研究反应动力学的分支学科称为热动力学。本文回顾了国内外学者在各种量热体系中研究热动力学的进展情况,特别偏重于评价热动力学的基础理论和研究方法及其应用前景的发展动向。但因限于篇幅,对于各种热分析仪器(DTA、DSC、TG等)中的动力学研究,本文未予涉及。     

QDTA/T/EGD/GC在线联同技术 Ⅵ.煤的热氧化、燃烧反应过程及其机理的研究

应用QDTA/T/EGD/GC在线联同技术及其装置,测定了四种不同变质程度的煤质之DTA/EGD/GC燃烧特性曲线,从中可提供如下三方面的信息和数据:(1)依据DTA测得的燃烧特性曲线,可取得在氧化、燃烧全过程中各项热特性的表征温度。(2)依据跟踪DTA逸出气成份的浓度变化所测得的EGD曲线,可了解不同煤质在热解、着火和燃烧特性等方面的差异。(3)依据DTA/EGD曲线的演变,可截取各个反应温度下之逸出气,进行在线的GC分析。在上述实验结果的基础上,应用过氧化物学说探讨煤的低温氧化反应机理。     

Magnetic Temperature Standards for TG

Magnetic transition temperatures, Tc, are measured by simultaneous TM/DTA for Alumel, cobalt, nickel, and three alloys of Ni and Co. The observed values of Tc are corrected using the values for the melting temperatures of pure metals used to define the International Temperature Scale. These corrections are based on the simultaneous melting of these pure metals alongside, but separate from, the magnetic sample. Nine investigators, using a wide variety of instrumentation, have made these measurements utilizing a standard protocol. The results are compared for several heating rates. It is planned to make these same magnetic materials ultimately available to the public for calibration of temperature of their TG instruments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study on the decomposition kinetics of FOX-7 and HNF

At TNO Prins Maurits Laboratory the characterisation and application of energetic materials is one of the main research topics. In this respect, the activities are focussed on using thermal analysis techniques such as TG/DTA and DSC. Standard DSC and TG/DTA techniques usually apply a linear temperature increase. During this gradual temperature change, the sample may pass certain phase changes related to different crystal structures, followed by a melting/decomposition of the material. In this way physicochemical properties like phase change temperatures, melting point, enthalpy of melting, decomposition temperature, etc. can be determined. By applying different heating rates, an analysis of the decomposition kinetics can be performed as well, which gives additional information on the decomposition process of the material. In this way the activation energy of the decomposition process and the 'shelf-life' of the material, when stored at a certain temperature, can be assessed. In a co-operation with the Technical University of Aachen, two relatively new and promising energetic materials were investigated: FOX-7 and HNF. FOX-7, or 1,1-diamino-2,2-dinitroethylene, is a less sensitive explosive, which could find application as a substitute of RDX (less sensitive but with preservation of performance). Hydrazinium nitroformate (HNF) is an oxidiser with potential use as a high-performance, chlorine-free ingredient in rocket propellants. The results of the TG/DTA and DSC tests, as well as the results of the analysis of the decomposition kinetics of these two materials, will be reported and discussed in this paper. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal evolution of ferromagnetic metallic glasses

A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic metallic glasses. Results obtained for the amorphous alloys Fe₄₀Ni₄₀P₁₄B₆ and Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value of 770°C measured as Curie temperature of crystallised Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing that the first crystallisation yields to a-Fe nanocrystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Cadmium Substitution on Structural and Magnetic Properties of Nano Sized Nickel Ferrite

The structure and crystal phase of the nanocrystalline powders of Ni_1-xCd_xFe₂O₄ (0≤x≤0.5) mixed ferrite, synthesized by wet chemical co-precipitation method, were characterized by X-ray diffraction. Results showed that the lattice parameter increased with increasing Cd concentration. Microstructure was studied by scanning electron microscopy. TG/DTA stud-ies were carried out on co-precipitated sulphate complexes. These studies revealed the low ferritization temperature (650 oC) of the ferrite system synthesized by presently adopted route of synthesis and occurrence of simultaneous decomposition and ferritization processes.Further studies by infrared spectroscopy were also conducted. Moreover, magnetic properties of the prepared nanoparticles were studied by magnetization and a.c. susceptibility mea-surements. The response of prepared Ni_1-xCd_xFe₂O₄ mixed ferrites to magnetic field was investigated. Results show that, magnetic susceptibility, Curie temperature, and effective magnetic moment decreased as the Cd content increases.     

Gd7Pd3-xFex合金磁性及磁热效应的研究

采用电弧熔炼和高温退火的方法制备了Gd7Pd3-xFex(x=0, 0.2, 0.5, 0.8和1)合金材料,并对该系列合金材料的磁特性及磁热效应进行了研究。X射线粉末衍射研究表明,所有的材料均形成Th7Fe3型结构。并且随着x的增大,晶格常数、居里温度、饱和磁化强度和最大磁熵变均有所降低。相比于Gd7Pd3,掺入Fe元素的材料可以获得更接近室温的居里温度和更宽的工作温区,从而导致了7 T磁场下高达1096 J·kg^-1的相对制冷能力(RCP), Gd7Pd3-xFex有望被用于室温附近的磁制冷。     

Effect of cerium, holmium and samarium ions on the thermal and structural properties of the HZSM-12 zeolite

The study of the incorporation of rare earth elements as additives in Y zeolites is a very interesting field of research, mainly by its potential application as additives in catalytic cracking process. In this work was studied the thermal and structural properties of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12. The acid properties were investigated by pyridine thermo desorption via TG. The results showed two events of mass loss attributed to elimination of pyridine adsorbed on the weak+medium acid sites and on the strong acid sites.     

A new method for studying crystallization of amorphous alloys

Experiments on the crystallization of amorphous Fe?Si?B alloys were carried out by thermogravimetric analysis (TG). This new method gives us some important information about the magnetic phase transformation of amorphous alloys, especially the magnetic volume change in crystallization beside the energy change obtained by the traditional DSC and DTA methods. Crystallization activation energies of Fe?Si?B amorphous alloy are calculated from both TG and DTA curves. The experiment also showed that the addition of Nb, Cu and Mo would influence the crystallization transition temperature of amorphous Fe?Si?B alloys greatly.     

Magnetic properties of lanthanide chalcogenide semiconducting nanoparticles

To understand the importance of the band gap to the magnetic ordering in magnetic semiconductors, we have studied the effect of particle size on the ferromagnetic Curie temperature in semiconducting EuS. We have synthesized capped approximately 20 nm EuS nanoparticles using a single-source precursor, [Eu(S(2)CN(i)()Bu(2))(3)Phen] decomposed in trioctylphosphine. The nanoparticles have been characterized by X-ray powder diffraction, TEM, and magnetic susceptibility measurements as a function of temperature and field. The Curie temperature, based on Arrott plots, is depressed by 1-2 K from the bulk value.     

Use of thermomagnetometry in the study of iron-containing pyrotechnic systems

Thermal analysis is routinely used to characterize pyrotechnic fuels, oxidants and fuel/oxidant mixtures [1]. Thermomagnetometry (TM) can provide additional information if the magnetic properties of the materials change during reaction. TG, TM and DTA results for the iron/potassium permanganate, iron/barium peroxide, and iron/strontium peroxide systems as loose powders or pressed pellets indicate predominantly solid-gas mechanisms for reactions in these systems.     

Thermoanalytical methods in the study of inorganic thin films

Thermoanalytical (TA) methods are relatively seldom applied for assessing the physical and chemical proeprties of thin films, but they can be used in studies of composition, phase transitions and film—substrate interactions. In the present paper the possibilities of TA methods in thin film studies are reviewed. The thermoanalytical methods considered are the classical TG and DTA/DSC methods but some complementary methods will also be briefly mentioned. The main emphasis is given to true thin films. Details of sample preparation are also given. An important application of TA methods is characterization of precursors for the CVD growth of thin films, and this is also discussed.