Dependence of thermal stability and thermomechanical characteristics of non-crystalline chalcogenides in the Cu-As-Se system on copper content

We have developed a modified power-compensation DSC to evaluate the electrocaloric properties of ferroelectrics. With this apparatus, latent heat of electric-field-induced phase transition in Ba_0.73Sr_0.27TiO₃ (BST) ferroelectric ceramics has been investigated in detail. It varies with temperature and reaches its climax at 25°C, close to the ferroelectric-paraelectric phase transition temperature, when induced by the same electric field of 15 kV cm^-1. The theoretical saturated endothermicity induced by enough high electric field at 25°C is expected to 0.59 J g^-1, which is 84% of the total phase transition latent heat of BST. At last the origins of difference between exothermicity and endothermicity are discussed.     

Effect of composition on the thermal behavior of NiMnGa alloys

The methods to determine martensitic transformation temperature, enthalpy and entropy change, specific heat capacity change with temperature, and transformation activation energies of Ni–%29.5Mn–%21Ga, Ni–%29Mn–%21Ga, Ni–%29.5Mn–%20Ga, and Ni–%28.5Mn–%20.5Ga (atomic percentage) alloys were investigated by differential scanning calorimetry. It was observed that the transformation temperature increased with an increase in atomic nickel ratio. Meanwhile, it was detected that the change in enthalpy increases with the amount of nickel. The highest values of entropy change and the heat capacity at room temperature were observed in the alloy having the least amount of nickel in it.     

Co-B非晶态合金超细微粒的热稳定性与催化性能研究

利用化学还原法制备了Co—B非晶态合金超细微粒，用电感耦合等离子体光谱(ICP)、电子显微镜(TEM)、X射线粉末衍射(XRD)、BET、表面积测试及X光电子能谱(XPS)等手段对新鲜样品及经过不同温度热处理后的样品进行了表征，并用微型催化反应装置评价其CO H2催化性能．结果表明，经过热处理后的样品不仅其表面组成和结构状态发生了变化，而且其催化性能也发生了明显变化，同时还表明非晶态Co—B合金超细微粒具有比其晶态更高的催化活性和独特的选择性。     

Effect of structure on the thermal stability of polyimides

Polyimides with different proportions of m-phenylene and p-phenylene (or p,p′-biphenylene) were prepared by polymerizing different molar ratios of m-phenylene diamine and p-phenylene diamine (or p,p′-diaminobiphenyl) with pyromellitic dianhydride in dimethylformamide at 0°C. Chemical cyclodehydration of polyamic acids resulted in the corresponding polyimides. Polymers were characterized by infrared (IR), viscosity, and density measurements. Viscosity and density of polymers decreased with an increase on m-phenylene groups in the backbone. The thermal and thermooxidative stabilities were investigated by dynamic thermogravimetry. Stability decreased when m-phenylene groups were introduced in the backbone.     

Thermal analysis and longtime stability of amorphous Co100−xBx alloys

Crystallization behaviour of amorphous Co_100?xB_x alloys (17 <x ≤ 40) has been investigated by differential thermal analysis (DTA) and dynamic temperature X-ray diffraction (DTXD) methods in the freshly prepared state and at a period of about eight years after preparation. The crystallization temperatures lie in the range 670 K–760 K. An average decrease of about 1.25 K/year over a period of eight years has been observed to take place in the crystallization temperatures of these materials. The value of heat of crystallization (ΔH _cr) and activation energy lie in the range 2.3 kJ/g-at – 5.9 kJ/g-at and 2.1 eV – 2.4 eV, respectively. The phases obtained at crystallization temperatures during DTXD analysis have been discussed.     

Effect of the soil uses on their thermal stability

Differential scanning calorimetry was applied to assess on seasonally soil organic matter changes. Soils were collected in two sites located in Viveiro (Galicia, Spain). One of them has been used as arable land and the other one was under pinewood. Soil samples were seasonally collected during a year. The heat of combustion and the ignition temperature of the soil organic matter were calculated by analyzing the thermograms obtained by differential scanning calorimetry. The shape and the maximum and end temperatures of the two exothermic peaks observed in the thermograms, yielded information about the relations between the labile and recalcitrant pools, and hence information about carbon stabilization degree in both soils.     

Effect of thermal processing on the flavonols rutin and quercetin

The current research involves the study of the thermal treatment of quercetin and rutin in an aqueous model system (cooking). These substances were heated and their degradation was followed by high-performance liquid chromatography/diode-array detection (HPLC/DAD). The influence of pH and the involvement of oxygen in the degradation were studied. HPLC/electrospray ionization multi-stage mass spectrometry (ESI-MS(n)) was used for the structural characterization of the compounds produced. The influence of the degradation of the phenolic compounds on their antioxidant properties was elucidated by a electron spin resonance (ESR) spectrometry study of the reaction samples mixed with the stabilized radical, Fremy's salt. Strong degradation of the model substances took place under weak basic and oxidative conditions. Quercetin showed the most intense degradation. Protocatechuic acid could be identified as a cleavage reaction product by analyzing its retention time and molar mass during the degradation of quercetin. The structure of a second cleavage product could be identified on the basis of ESI-MS(n) fragmentation data. Also, several structures for reaction products of oxidized quercetin are suggested. The ESR analysis showed a decrease in the antioxidant activity of the reaction samples after heat treatment in aqueous solution.     

Effect oftrans-polyoctenamer on thermal stability of rubbers determined by thermal analysis

An effect of a cyclic low molecular-weight polymertrans-polyoctenamer rubber (TOR) on the thermal stability of diene rubbers and their vulcanizates was investigated. The investigation was carried out in the air and nitrogen atmospheres using thermogravimetry, DSC and simultaneous thermoanalytical methods. The thermal stability indexes:T ₅,T _max and activation energy of degradation (E), as well asT _g andT _m values, have been determined.It was found thattrans-polyoctenamer (TOR) increases of the thermal stability indices of raw diene rubbers and their vulcanizates. The results show that the thermal degradation of diene rubbers occurred at higher temperature if they were blended with TOR. In our opinion, intermolecular structures formed between the cyclic low-molecular weight polymer and some linear rubber molecules may be the reason for the higher thermal stability of these rubber blends.The work was supported by State Committee for Research, Poland. Grant No. 7.T08 E 032-08.     

Effect of heat treatment on thermal stability of limestone

The nature of the anomalous effect exerted by the heat treatment of limestone at 500 and 600°C on its thermal stability at 825°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1435–1437.Original Russian Text Copyright © 2004 by Kabanov.     

Effect of hydration andpH on the thermal stability of proteinase K

The effect of hydration andpH on the thermal stability of proteinase K was studied in the temperature range 310–450 K by differential scanning calorimetry. The dependences of the denaturation temperatureT _d, the specific enthalpy of denaturation H _d and the maximum of excess apparent specific heat capacityC _ex ^max upon the degree of hydrationh and thepH of the buffers used are presented. The relation betweenT _d andh is of the Flory-Garrett's type. By means of Ooi's model, the two components of the denaturation enthalpy arising from hydration and conformational change, respectively, were estimated. The fact that the specific denaturation enthalpy of proteinase K is very low may be attributed to its very low enthalpy of conformational change per heavy atom.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThis major project was supported by the National Natural Science Foundation of China.     

Effect of ethanol on the thermal stability of human serum albumin

The effect of ethanol on human serum albumin stability in aqueous solution was studied by use of differential scanning calorimetry. A deconvolution of DSC traces in 2-state model with ΔC _p=0 and ΔC _p≠0 was performed and analysed to obtain information on the interaction of ethanol with different parts of albumin molecule both fatty acid containing and fatty acid free. The differences in ethanol binding affinity for both kinds of albumin were found. At very low concentrations ethanol was observed to be a stabilizer of the folded state of albumin contrary to the higher concentration where its binding to the unfolded protein predominates.     

Effect of mechanical activation on the thermal stability of polytetrafluoroethylene powder

It was found that processing in a planetary activator leading to amorphization of the structure of polytetrafluoroethylene powder was not accompanied by a noticeable decrease in its thermal stability. It was established that the temperature at the onset of melting drops slightly, the melting rate increases, and the enthalpy of the endoeffect declines noticeably heating.     

Effect of the pH value on the thermal stability of alkaline phosphatase

The thermal stability of bovine and chicken intestinal alkaline phosphatase (IAP) was studied at 60°C over a pH range from 6.7 to 9.0. It was shown that the peaks of stability (at pH 7.5) and activity (at pH 9.0) do not coincide. The pH dependence of the elementary rate constants of dissociative thermal inactivation of the IAP dimers was determined: k ₁ (the rate constant of dissociation of active dimer E₂) and k _d (the rate constant of denaturation of the inactive monomers). At pH 7.5, the stability IAP attains its highest level. As the pH increases, k ₁ increases drastically while k _d does so only slightly. A comparison of the rate constants of dissociation k ₁ and association k ₁ showed that the interrelation between these parameters explains why the stability of the active enzyme is lower at acidic and basic pH values. The pH produces a weaker effect on the stability of the inactive monomers. An analysis of the thermal stability of chicken IAP at an optimum pH value and 55–60°C showed that the thermal inactivation is a three-stage process (including dissociation and denaturation) with an induction period. Measuring the induction period makes it possible to determine the minimum number of latent stages preceding the dissociation of E₂: 6, 4, and 3 at 55, 58, and 60°C, respectively.     

Effect of stearate preheating on the thermal stability of plasticized PVC compounds

Effect of preheating of stearates on the processing and post-processing thermal stability of poly(vinyl chloride) compounds, plasticized with di(2-ethylhexyl) phthalate (DEHP) and epoxidized soybean oil (ESO), using several ratios of calcium/zinc stearates and DEHP/ESO is reported. The compounds were prepared as follows: (1) dry-blending the compound components, (2) pelletizing the dry-blend and (3) extruding the pellets to obtain a ribbon geometry. Processing stability was determined by: (a) mechanical characterization and (b) visual color comparison of extruded samples. Post-processing thermal stability was followed by: (a) measurement of HCl release from heated pellets and (b) color changes in heated ribbon samples. From a practical point of view, the preheating has a negligible effect on the initial color of formulations; except for the case of formulations without both ESO and CaSt₂. However, the effect of the preheating on the post-processing thermal stability is strongly determined by the composition formulation.     

Effect of post-irradiation thermal treatments on the stability of gamma-irradiated glass dosimeter

A commercial window glass has been investigated as a routine high dose dosimeter for gamma irradiation. The irradiated samples showed rapid fading at room temperature immediately after irradiation. This short-term rapid fading was followed by a slow fading at long-term. This strong initial fading is a problem for dosimetry purposes. However, when the dosimeter is measured at the same time interval after irradiation, it maintains proportionality to dose. Calibration curves have to be used for different time intervals after irradiation. In order to improve post-irradiation stability dosimeters were submitted to different post-irradiation thermal treatments from (−20) up to 150 °C. After that, optical absorbance measurements were carried out up to 2 months at room temperature. The heating at 150 °C for 20 min was found to be the most suitable procedure for the removal of unstable entities responsible for the initial rapid fading. Due to these heat treatments, variation of response was found almost negligible 24 h after irradiation for several months. Calibration curves demonstrated the applicability of this glass as routine dosimeter in the dose range of 0.5–90 kGy.     

Effect of industrial water components on thermal stability of nitrocellulose

In order to prevent the spontaneous ignition of nitrocellulose (NC), NC is stabilized by washing with industrial water in its synthesis process. However, there is a possibility that the components in industrial water contribute to the thermal stability of NC. In this way, the purpose of this study is to clarify the effect of industrial water components on the thermal stability of NC. In experiments, a heat flux calorimeter was used to observe the thermal behavior of NC with the residue of vaporized industrial water. The induction period of heat release of NC with 2-mass% residues was approximately 2–5 h shorter than that of NC alone whose induction period was observed at 7 h. Those results indicate that the residue destabilized NC. On the other hand, when the additive amount of the residue was increased, the induction period gradually increased as well. Based upon these results, we assume that inorganic salts contributing to stabilization and destabilization competitively coexist in the industrial water components. The same thermal analysis was performed on NC with CaCO₃, CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl. Those salts are predicted to exist in the industrial water. In the results, the induction period of NC with 2-mass% CaCO₃ was approximately 15-h longer than that of NC alone, while the induction period with the inorganic salts CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl was 4–5-h shorter. Therefore, when the industrial water components accumulate in NC, the destabilization by inorganic salts such as CaSO₄, CaCl, ZnSO₄, NaCl, and CuCl and the stabilization by compounds such as CaCO₃ are thought to countervail against each other.     

电沉积非晶态镍磷合金的研究

本文用电化学方法, X射线衍射及电子能谱方法研究了阴极恒电位沉积非晶态镍磷合金镀层,实验结果表明,影响镍磷合金非晶结构的主要因素是镀层中的磷含量,当磷含量大于9%时,镀层具有良好的非晶结构,镀层中镍和磷主要以元素态形式存在,磷的析出具有诱导共析特点。     

Studies on the thermal characteristics of polymer alloys

PVC: polystyrene alloys of varying compositions were prepared by the film casting technique. Thermogravimetric analysis of these materials showed that the decomposition patterns of the alloys are quite different from those of the constituent polymers. These results are explained in terms of polymer interaction phenomena.

---

Zusammenfassung Mittels eines Feinfoliengiebverfahrens wurden PVC-Polystyrol-Mischungen verschiedener Zusammensetzung gefertigt. Eine thermogravimetrische Analyse dieser Stoffe zeigte, daß sich der Typ der Zersetzung der Mischungen vollständig von dem der reinen Komponenten unterscheidet. Diese Ergebnisse werden als Folge von Polymerwechselwirkungen interpretiert.

     

SAXS study on the structure and crystallization of amorphous metallic alloys

The change in structure of several amorphous alloys as Fe-P-C, Fe-B and Pd-Au-Si alloys during isothermal ageing was examined using small angle X-ray scattering technique as well as transmission electron microscopy. The SAXS intensity was related to two different types of scattering sources depending on ageing period and temperature. As-splatted amorphous alloys and the specimens aged for short period at relatively low temperature, where specimens remained in amorphous state, showed a weak and spreaded SAXS intensity. This indicates an existence of electron density fluctuation in amorphous phase. The dimension of their scattering regions was estimated to be 1.8 to 2.4 nm for Fe-P-C alloys, and 1.2 to 0.8 rim. for Fe-B alloys, respectively, by analysing the electron density-density correlation function derived from observed SAXS intensity. The origin has been discussed based on one dimensional model. A compositional fluctuation was made clear to occur in fine scale of about 1 nm in amorphous Fe-B and Fe-P-C alloys. When the alloys were aged for longer period below their crystallization temperatures, fine crystalline particles precipitate; those are a two phase lamella structure of Fe₃P and-Fe for a Fe₈₃P₁₀C₇ alloy, an Ferich single phase for Fe₈₃B₁₇ alloy, and a Pd-rich single phase for Pd₇₆Au₆Si₁₈8 alloy, respectively. Their size and structure were determined from the analysis of SAXS data and TEM observation.