Microstructural characterization and recrystallization kinetics of cold rolled copper

The recrystallization kinetics in pure copper deformed by cold rolling is mainly investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves show exothermic peaks corresponding to the stored energy released during recrystallization process. Variation of the heating rate and application of different methods allowed us to calculate two kinetic parameters of recrystallization: (i) the activation energy of the process was calculated using three different methods and (ii) the Avrami exponent was estimated using the Matusita method. On other hand, the microstructural evolution during recrystallization and grain growth of cold rolled copper were investigated at a temperature of 450 °C by scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD).     

纳米微粒对低温保护剂溶液玻璃化性质的影响

利用差示扫描量热仪(DSC)研究了加入羟基磷灰石(HA)纳米微粒对低温保护剂溶液玻璃化的影响,实验得到了不同粒径和不同质量浓度的HA纳米微粒加入PVP溶液的玻璃化转变温度与反玻璃化温度.实验结果表明加入纳米微粒能显著的影响低温保护剂溶液的玻璃化性质.且随着纳米微粒质量分数的增加,溶液的玻璃化转变温度与反玻璃化温度均显著...     

Organosoluble and thermally stable polyimides derived from a new diamine containing bulky-flexible triaryl pyridine pendent group

A novel kind of aromatic diamine,N-(4-(4-(2,6-diphenyl pyridine-4-yl)phenoxy)phenyl)-3,5-diaminobezamide (DPDAB),was synthesized via aromatic nucleophilic substitution of 3,5-dinitrobenzoylchloride with 4-(4-(2,6- diphenylpyridine-4-yl)phenoxy)aniline(DPPA),followed by palladium-catalyzed hydrazine reduction.This monomer was used to prepare polyimides(PIs)based on reaction with several commerically avaiable tetracarboxylic dianhydrides such as pyromellatic dianhydride(PMDA),benzophenone tetracarboxylic acide dianhydride(BTDA)and bicycle[2.2.2]oct-7-enc- 2,3,5,6-tetracarboxylic dianhydride(BCDA).These PIs had inherent viscosity in the range of 0.34-0.76 dL/g and showed good solubility in various aprotic polar solvents.The glass-transition tempratures(T_gs)of the PIs were in the range of 184-302℃,and showed high thermal stability with 10%weight loss in the temperature range of 360-500℃under nitrogen atmosphere.     

Chemically modified biolubricant basestocks from epoxidized oleic acid: Improved low temperature properties and oxidative stability

Synthetic biolubricant basestocks with improved low temperature and oxidative stability were prepared by chemical modification of epoxidized oleic acid (EOA). Preparation, characterization and physico-chemical properties of mono, di and triester derivatives of 9,10-dihydroxyoctadecanoic acid after the epoxidation of oleic acid, opening of the formed oxirane ring in suitable medium, esterification of carboxylic acid hydroxyl group and acetylation of free hydroxyl group is discussed in this paper. Removal of the double bond from fatty acid acyl group, increase of the molar weight and change of molecular structure resulted in the increase of viscosity index and oxidation stability of synthetic esters.     

Gelation on Heating of Supercooled Gelatin Solutions

Diluted (1.0–1.5 wt%) aqueous gelatin solutions have been cooled to –10 °C at a cooling rate 20 °C min⁻¹ without freezing and detectable gelation. When heated at a constant heating rate (0.5 –2 °C min⁻¹), the obtained supercooled solutions demonstrate an atypical process of gelation that has been characterized by regular and stochastically modulated differential scanning calorimetry (DSC) as well as by isoconversional kinetic analysis. The process is detectable as an exothermic peak in the total heat flow of regular DSC and in the nonreversing heat flow of stochastically modulated DSC. Isoconversional kinetic analysis applied to DSC data reveals that the effective activation energy of the process increases from approximately 75 to 200 kJ mol⁻¹ as a supercooled solution transforms to gel on continuous h eating.     

Thermal,Mechanical and Morphological Behavior of Poly(propylene)/Wood Flour Composites

The comparative studies on the thermal, mechanical and morphological behavior of compression molded poly(propylene) (PP)/wood flour (WF) composites were performed using wood flours (WFs) of different origins. The comparison has been made on the basis of results obtained from thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile testing. It has been demonstrated that an addition of 5 wt.-% of maleic anhydride grafted polypropylene (PP-g-MA) has a significant effect on the morphological and thermomechanical behavior of the composites. Although, microscopic examinations revealed no significant differences in the morphology of the compatibilized composites, a remarkable improvement of thermal degradation behavior was observed. From the view point of mechanical properties, the composites with high amount of filler (60 wt.-%) showed similar behavior irrespective of the origin of wood flour.     

A new mixed multi-metallic calcium–cobalt-phosphotungstate with nano wheel-like polyanion: Na6Ca3[Ca2(H2O)6Co9(OH)3(H2O)6(HPO4)2(PW9O34)3]

A new 3-D wheel-like calcium–cobalt phosphotungstate, Na₆Ca₃[Ca₂(H₂O)₆Co₉(OH)₃(H₂O)₆(HPO₄)₂(PW₉O₃₄)₃], is reported and characterized by IR, UV, and single-crystal X-ray diffraction. The crystal structure consists of an infinite 3-D array of [Ca₂(H₂O)₆Co₉(OH)₃(H₂O)₆(HPO₄)₂(PW₉O₃₄)₃]^12? anions (1) connected by sodium and calcium metal cations. The novel feature is the presence of two Ca²⁺, bonded to oxygen of HPO^4? and to H₂O spanning opposite sides in the complex anion. The stability of the crystalline product and its morphology were studied by SEM-EDX and DSC techniques.     

Phase polymorphism of [Ni(DMSO)6](BF4)2 studied by differential scanning calorimetry

The tetrafluoroborate of hexadimethylsulfoxidenickel(II) was synthesized and studied by differential scanning calorimetry. Seven solid phases of [Ni(DMSO)₆](BF₄)₂ were revealed. Specifically, six phase transitions of the first order were detected between the following solid phases: stable KIb → stable KIa at T _C6 = 335 K, metastable KIIb → metastable KIIa at T _C5 = 368 K, metastable KIII → overcooled phase KI at T _C4 = 378 K, metastable KIIa → overcooled phase KI at T _C3 = 396 K, stable KIa → stable KI at T _C2 = 415 K and stable KI → stable K0 at T _C1 = 433 K. [Ni(DMSO)₆](BF₄)₂ begins decomposition at 440 K with loss of one DMSO molecule per formula unit forming [Ni(DMSO)₅](BF₄)₂ (phase L0) which melts next in two steps in the temperature range 550–593 K. From the entropy changes connected both with melting and with phase transitions, it can be concluded that phases KI, overcooled KI and K0 are orientationally dynamically disordered (ODIC) crystals. Stable phases KIb, KIa and metastable phase KIII are ordered solid phases. Metastable phase KIIa and metastable phase KIIb are more or less ordered solid phases.     

Differential Scanning Calorimetry Evaluates Relative Proportions and Strength of Acid-Sites in Catalytic Materials and Adsorbents Alumina and Amorphous Silica-Alumina

Abstract

Differential scanning calorimetry (DSC) is employed to evaluate the relative proportions and strength of acid-sites in gammaalumina and amorphous silica-alumina through presorption of tri-ethylamine (TEA) followed by its thermal desorption in the DSC equipment. From the data obtained, total acid-sites in silica-alumina is found to be 2.3 times as large as those present in gamma-alumina, and 5–5% of total acidity in alumina is of Bronsted type whereas in silica-alumina this type comprises 28.9%' The Bronsted acidity strength in alumina and silica-alumina is identical although greatly different in quantity. Lewis acidity in silica-alumina is significantly stronger than that in alumina.     

Characterization of surface and porous properties of synthetic hybrid lamellar silica

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications.