Mg-Al-CO_3与Zn-Al-CO_3水滑石热稳定性差异的研究

层状双金属氢氧化物（ Layered double hydroxides,简称 LDHs）是一类近年来发展迅速的阴离子型粘土,又称水滑石,其组成通式为： [M? 1-xM? x(OH)2]x＋ Ax/nn-mH2O,其中 M?是二价金属离子, M?是三价金属离子, An－是阴离子。这种材料是由相互平行的层板组成,层板带有永久正电荷;层间具有可交换的阴离子以维持电荷平衡。通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛用作催化剂、吸附剂及油田化学品等,已引起人们的关 注 [1～ 4]。有关 Mg-Al-CO3与 Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道 [1…     

Thermal decomposition of [Co(NH3)6][Fe(C2O4)3]•3H2O in inert and reductive atmospheres

Russian Chemical Bulletin - The thermal decomposition of [Co(NH3)6][Fe(C2O4)3]?3H2O in hydrogen and helium atmospheres was studied. The thermal decomposition of the complex proceeds via the...     

Substituent effects and stereochemical mechanisms for substitution reactions of 18F for halogen atoms in CF3X, (CH3)3−n CHnX,and CH3X

No thermal substitutions of ¹⁸F for X (X  halogen atom) are observed with CF₃X and (CH₃)_3?nCH_nX substrates in excess SF₆. The absence of thermal yield increasing with weaker CX bond energies, as found with CH₃X substrates, is attributed to the much larger mass versus H of F and CH₃ substituents. The thermal substitution of ¹⁸F/X in CH₃X molecules probably occurs by an inversion mechanism.     

Comparison of thermal properties and kinetics of decompositions of NaHCO3 and KHCO3

The thermodynamics and kinetics of the thermal decompositions of NaHCO₃ and KHCO₃ were studied by means of simultaneous TG-DSC. Analysis of the isothermal mass-change traces indicated that the thermal decompositions of NaHCO₃ and KHCO₃ follow an Avrami-Erofeyev A_1.5 law. The A_1.5 law was tentatively explained by assuming a combination of the A₁ and A₂ laws. It was illustrated that KHCO₃ is more stable than NaHCO₃ as concerns the thermodynamics and kinetics of the thermal decompositions. The apparent activation energies for the decompositions of the two hydrogencarbonates were a little larger than the corresponding enthalpy changes.     

Thermal analysis of the oxide–chloride systems GdCl3–Gd2O3 and GdCl3–KCl–Gd2O3

Journal of Thermal Analysis and Calorimetry - The thermal analysis of the oxide–chloride systems GdCl3–Gd2O3 and GdCl3–KCl–Gd2O3 with the Gd2O3 content up to...     

Thermal degradation of aged polytetrahydrofuran and its copolymers with 3-azidomethyl-3′-methyloxetane and 3-nitratomethyl-3′-methyloxetane by thermogravimetry

The thermal decomposition behavior of the aged tetrahydrofuran copolymers with 3-azidomethyl-3′-methyloxetane (AMMO) or 3-nitratomethyl-3′-methyloxetane (NMMO) were studied by thermogravimetry and evolved gas analysis, and compared with aged polytetrahydrofuran (poly-THF) The thermal stability decreased in the order poly-THF > poly-AMMO-THF-AMMO > poly-NMMO-THF-NMMO, whereas the range of temperature for decomposition increased in the order poly-THF < poly-AMMO-THF-AMMO < poly-NMMO-THF-NMMO. The apparent activation energies of the degradation for polymers with ageing, calculated by the Ozawa method, were smaller than that without ageing. © 1996 John Wiley & Sons, Inc.     

Thermal decomposition of lutetium nitrate trihydrate Lu(NO3)3·3H2O

Journal of Thermal Analysis and Calorimetry - The thermal decomposition of lutetium nitrate starts with essentially a process of dehydration of the initial monomer Lu(NO3)3·3H2O with further...     

Li_3TaO_4粉体的制备及表征

钽酸锂作为一种具有潜在应用价值的新型固体氚增殖剂,主要有三种化合物:LiTaO3,Li3TaO4和Li7TaO6,Li3TaO4具有较高的锂密度(0.46g/cm3),还具有高熔点(1400℃)、良好的热学稳定性和较高的热导率等特点。本文采用固相反应法制备出高相纯(99%)、小粒径(1.4μma.v)的β-Li3TaO4粉末。并从锂密度、相结构稳定性、热学稳定性和热导率方面讨论了Li3TaO4作为氚增殖剂备选材料的可能性。     

La(NO3)3和Pr(NO3)3对高岭石脱羟基动力学的影响

采用热重和微商热重(TG/DTA)综合热分析技术在不同升温速率下研究了掺入La(NO₃)₃和Pr(NO₃)₃的高岭石的热分解过程, 利用Coats-Redfern积分法和Achar微分法对热分析实验数据进行动力学计算, 得到了高岭石脱羟基反应过程中的控制机理函数、 活化能和指前因子等动力学参数; 分析了2种稀土掺入对高岭石脱羟基过程动力学参数的影响, 并用Ozawa法对活化能进行了验证. 结果表明, 未掺稀土和掺入Pr(NO₃)₃的高岭石的脱羟基反应过程均受化学反应模型F₃控制, 反应的活化能分别为307.94和282.86 kJ/mol, 指前因子lnA的值分别为47.8980和44.1718; 掺入La(NO₃)₃的高岭石脱羟基反应过程控制机理函数发生改变, 受化学反应模型F₂控制, 反应活化能为196.02 kJ/mol, 指前因子lnA的值为29.5551. 与未掺稀土的高岭石对比, 掺入Pr(NO₃)₃后活化能和指前因子略有降低; 而掺入La(NO₃)₃后则显著降低, 分别降低了36.34%和38.30%. 采用Ozawa法验证得到的活化能与Coats-Redfern积分法和Achar微分法结果一致.     

Thermal characterization of NaNO3/KNO3 with different concentrations of Al2O3 and TiO2 nanoparticles

Journal of Thermal Analysis and Calorimetry - The thermo-physical properties of NaNO3/KNO3 (solar salt) added with Al2O3 and TiO2 nanoparticles as phase change material in thermal energy storage...     

Thermal transformations in nanosized MoO3 layers

The degree of the transformation of MoO₃ films (d= 8–130 nm) increased as the duration (1–140 min) and temperature (373–573 K) of thermal treatment grew and as the film thickness decreased under atmospheric conditions. The thermal treatment of MoO₃ films decreased the optical density at λ = 350 nm and caused the appearance of an absorption maximum at λ = 870 nm. A mechanism of thermal transformations of MoO₃ was suggested. The mechanism included the formation of the [(V _a)⁺⁺e] center during the preparation and thermal treatment of MoO₃ films and thermal electron transition from the valence band to the [(V _a)⁺⁺e] center level with the formation of the [e(V_a)⁺⁺e] center.     

Thermal Analysis of the System Na3AlF6–NaVO3

Summary. The phase diagram of the system Na₃AlF₆–NaVO₃ was determined by means of thermal analysis. The system is a simple binary eutectic one. The eutectic point was estimated at x(NaVO₃) = 0.975 and t _eut = 617°C. The XRD patterns of samples after thermal analysis revealed the presence of cryolite and NaVO₃ only supporting the above assumption of a simple eutectic binary system.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photochemische Umwandlungen, 45. Mitteilung [1] die 3σ → 3π-route zu oxepin-derivaten

Exemplifying with the 4.5-dicarbomethoxy oxepin 6a the authors describe an oxepin synthesis from furanes and acetylenic dienophiles via Diels-Alder reaction ( 4a ), photochemical oxanorbornadiene-oxaquadricyclane transformation ( 4a → 5a ), and thermal 3σ → 3π opening of the highly strained oxaquadricyclane 5a . With dimethylacetylenedicarboxylate, methylpropiolate, maleic anhydride, and di-methoxycarbonyl-oxanorbornadiene ( 4a ) 5a yields the 1:1 adducts 19a, 19b, 22, 23 and 26 (unstable) by strictly stereospecific addition to the α-positions of the oxygen bridge. With the same dienophiles the oxepin 6a reacts only through its valence-tautomeric benzene-oxide form 7a giving stereospecifically 27, 29, 30 and 31 . No definite conclusions are drawn with regard to the mechanistic implications of the photostep 4a → 5a , the thermal 3σ → 3π-transformation 5a → 6a/7a , and the bishomofurane cycloaddition reactions. Scope and limitations of this oxepin synthesis are briefly discussed.     

Non-Isothermal Kinetics of the Decomposition Reaction of Cluster [Ag3WS3Br]（PPh3）3 and [Cu3WS3Br]（PPh3）3

The thermal behaviors of clusters [Ag3WS3Br](PPh3)3 and [Cu3WS3Br](PPh3)3 (PPh3=triphenyl phosphine) in a nitrogen atmosphere were studied under the non-isothermal conditions by simultaneous TG-DTG-DSC and EDS techniques. The results showed that the evolution of PPh3 generally proceeded before the release of the other moiety in one or two step-mode. The mechanisms, the kinetic and the thermodynamic parameters for decomposition of PPh3 of both clusters were determined and calculated by jointly using several methods, which showed that its evolution was controlled by Avrami-Erofeev equation. The results also showed that there was no new stable phase composed of W-Ag(Cu)-S-Br after release of organic moiety PPh3 and that CVD method was not applicable to their further processing.     

Thermal Decomposition of 3'-Azidothymidine

The kinetics of thermal decomposition of 3'-azidothymidine (AZT) in melt at 140-201°C were studied by the thermogravimetric and manometric methods. The process follows the first-order kinetics and is decribed by the Arrhenius equation: k = 1014.7±0.5 exp[-(38100±900)/RT] (1/s). The kinetic and activation parameters are typical of thermal decomposition of aliphatic azides; they suggest that decomposition of the azido group is the rate-determining stage. The formation of nitrogen (1 mol per mole of AZT), furan, methyl alcohol, water, and carbon dioxide was confirmed by mass spectrometry. Thymine was found to be one of the condensed products of thermal decomposition of 3'-azidothymidine.     

利用原位红外光谱研究钙钛矿复合半导体CH_3NH_3PbI_3的稳定性

利用高压原位红外光谱法实时跟踪监测了CH_3NH_3PbI_3在高压氮气以及不同含量氧气气氛中加热时的变化规律.发现CH_3NH_3PbI_3对氧气十分敏感,当氮气中含有1%(体积分数)的氧气时,CH_3NH_3PbI_3加热到150℃发生分解;继续提高氧气含量到21%,温度升高到100℃时CH_3NH_3PbI_3即发生分解;若在常压高纯氮气中加热,其分解温度则能提高到250℃;若将氮气压力提高到4.0 MPa,CH_3NH_3PbI_3的分解温度进一步提高到270℃.实验结果表明,提高压力和减少环境中的氧含量是改善钙钛矿复合半导体稳定性的有效方法.相应地,复合半导体光电子器件的热处理过程可以在更高的温度下进行,从而有希望获得性能更加优良的钙钛矿复合半导体光电子器件.     

Cu3BiS3: Two-Dimensional Coordination Induces Out-of-Plane Phonon Scattering Enabling Ultralow Thermal Conductivity

The discovery of compounds with low thermal conductivity and the understanding of their microscopic mechanisms are of great challenges and scientific significance. Herein, we report a unique ternary sulfide compound, Cu₃BiS₃, in which all Cu atoms are coordinated within a two-dimensional [CuS₃] triangle plane. This local coordination leads to efficient out-of-plane phonon scattering and an ultralow thermal conductivity. Through DFT phonon spectrum calculations and analyses, we reveal that the lowest vibration frequency decreases from 2 THz for high-dimensional [CuS₄] tetrahedral coordinated Cu atoms in CuBiS₂ (CN=4, with an average Cu−S bond length of 2.328 Å) to 1.5 THz for low-dimensional [CuS₃] triangular coordinated Cu atoms in Cu₃BiS₃ (CN=3, with a shorter Cu−S bond length of 2.285 Å). This is due to the out-of-plane thermal vibration of the Cu atoms in the latter. Consequently,Cu₃BiS₃ exhibits one of the lowest values of κ_lat (0.32 W/m K) among its peer, with a 36 % reduction compared to CuBiS₂ (0.50 W/m K). This groundbreaking discovery highlights the significant role of 2D local coordination in reducing thermal conductivity through characteristic out-of-plane phonon scattering, while also contributing to a large Grüneisen parameter (2.06) in Cu₃BiS₃.     

Thermal change of organic light-emitting ALQ3 thin films

A series of Alq3 thin films with the thicknesses of 50, 100, and 200 nm was deposited on Si substrates at room temperature using the thermal evaporation method. The thermal crystallization process of Alq3 thin films, especially 50 nm thick films, was successfully examined using high-temperature X-ray diffraction (HT-XRD) with the in-plane scan mode. Film thickness, density, and changes in surface roughness while heating were determined using X-ray reflectometry (XRR). The decreased density and increased surface roughness, which were accompanied by sublimation, indicate the instability of the Alq3 film. Thus, thermal instability is a major factor for device failure.     

Thermal studies on solid 1,4-bis(3-carboxy-3-oxo-prop-1-enyl) benzene of lighter trivalent lanthanides

Solid-state compounds of general formula Ln₂L₃·nH₂O, where L represents 1,4-bis(3-carboxy-3-oxo-prop-1-enyl)benzene and Ln = La, Ce, Pr, Nd, Sm, were synthesized. Complexometric titrations with EDTA, thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, elemental analysis and infrared spectroscopy have been employed to characterize and to study the thermal behavior of these compounds in dynamic air atmosphere. The results led to information about the composition, dehydration, crystallinity, and thermal decomposition of the synthesized compounds.