DIFFERENTIAL SCANNING CALORIMETRY AND X-RAY DIFFRACTION STUDIES ON AGING BEHAVIOR OF Zn-Al ALLOYS

Decomposition processes of the quenched Zn-Al alloys were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the stabilities of supersaturated solid solution (SSS) of Zn-Al alloy and α' phase formed by quenching would reduce with the increase of Zn content and the precipitation of η-Zn phases even when aging at ambient temperature, so that the exothermic precipitation peak in DSC curve would disappear. The activation energy of the η-Zn precipitation and the reaction enthalpy were calculated and measured. The kinetics of α' decomposition or η-Zn formation was determined by XRD. The microstructure change during aging was observed by TEM.

Assessment of parameters for precipitation simulation of heat treatable aluminum alloys using differential scanning calorimetry

Differential scanning calorimetry （DSC） has been used extensively to study different solid state reactions. The signals measured in DSC are associated with the growth and dissolution of different precipitates during a specific heat cycle. The time-temperature dependence of heat cycles and the corresponding heat flow evolution measured in the sample by DSC provide valuable experimental information about the phase evolution and the precipitation kinetics in the material. The thermo-kinetic computer simulation was used to predict the DSC signals of samples taken from 6xxx and 2xxx alloys. In the model, the evolution of different metastable and stable phases and the role and influence of excess quenched-in vacancies in the early stage of precipitation were taken into account. Transmission electron microscopy （TEM） and high-resolution TEM were used to verify the existence of precipitates, their size and number density at specific points of the DSC curves.

Research on thermal decomposition of 1,3,5-trinitro-1,3,5-triazinane based on differential scanning calorimetry

In order to test the thermal decomposition of 1,3,5-trinitro-1,3,5-triazinane(RDX),the linear temperature rise experiment of RDX was carried out by differential scanning calorimeter under different heating rate conditions.The kinetic calculation of RDX thermal decomposition curve was carried out by Kissinger and Ozawa methods,respectively,and the thermal analysis software was used to calculate the parameters such as self-accelerating decomposition temperature.The results show that the initial decomposition temperature range,decomposition peak temperature range,and decomposition completion temperature range of RDX are 208.4-214.2,225.7-239.3 and 234.0-252.4℃,respectively,and the average decomposition enthalpy is 362.9 J·g^-1.Kissinger method was used to calculate the DSC experimental data of RDX,the apparent activation energy obtained is 190.8 kJ·mol^-1,which is coincident with the results calculated by Ozawa method at the end of the reaction,indicating that the apparent activation energy calculated by the two methods is relatively accurate.When the packaging mass values are 1.0,2.0 and 5.0 kg,respectively,the self-accelerating decomposition temperatures are 97.0,93.0 and 87.0℃,respectively,indicating that with the increase of packaging mass,the self-accelerating decomposition temperature gradually decreases,and the risk increases accordingly.

Synthesis kinetics of Mg_2Sn in Mg-Sn powder mixture using non-isothermal differential scanning calorimetry

The non-isothermal heating process of Mg-Sn powder mixture was studied by differential scanning calorimetry(DSC) technique and the synthesis kinetics of Mg2Sn was evaluated by the model-free and model-fitting methods.The activation energy and conversion function of Mg2Sn synthesis reaction are calculated to be 281.7 kJ/mol and g(α)=[-ln(1-α)] 1/4,respectively.The reaction mechanism of 2Mg+Sn→Mg2Sn under non-isothermal condition is regarded as "nucleation and growth" .During the non-isothermal heating process,the phase transformation occurred in the Mg-Sn powder mixture was analyzed by XRD and the microstructure evolution of Mg2Sn was observed by optical microscopy,which is in good agreement with the reaction mechanism of 2Mg+Sn→ Mg2Sn deduced from the kinetic evaluation.

Measurement of Crystallinity of Acrylic Copolymer by Swelling Differential Scanning Calorimetry

In this paper the measurement of crystallinity(C)ofacrylic copolymer(PAC),by Swelling Differential Scan-ning Calorimetry(SDSC)is discussed.Common DSC isonly used for measuring the crystallinity of polymers withmelting point,(T_m),below their decomposition temper-ature,(T_d).As temperature rises,polymers with swell-ing agent added become swollen and dissolved,goingthrough whole process of breaking solid structures.Thus,SDSC makes it possible to measure the crystallini-ty of polymers even with T_d below T_m.But the C mea-sured by WAXD and the total endothermal melting(swelling)heat in SDSC thermograms,(△H_l),are notlinearly correlated.It has been found that,instead of the△H_l,△H_l’obtained from the △H_l by subtracting the en-dothermal heat,△H_l,and the C measured by WAXDare linearly correlated.On the basis of this linear rela-tion,the unknown C of another PAC sample is measuredby SDSC.The result is in good accordance with thatmeasured by WAXD.

Studies of the Energy Release of Mitochondria from Sporophyte Cytoplasmic Male Sterile Rice by Differential Scanning Calorimetry

The differential scanning calorimetric (DSC)curves of the mitochondria isolated from two varieties of sporophyte cytoplasmic male sterile and their fertile lines of Yie Bai and Ma Xie type rice have been determined. The curves show that the energy is released continuously as temperature rise to 70℃. Some thermodynamic and kinetic parameters of the energy release of the mitochondria have been obtained. The presented results showed that the mitochondria from cytoplasmic male sterile rice released more heat and they had higher energy barrier, less rate, and more complicated mechanism than that of their fertile lines in the energy release process.

Comparison between Glass and Stainless-Steel Vessels in Differential Scanning Calorimetry Estimation

Differential scanning calorimetry (DSC) provides easy screening for thermal hazard evaluation. Here, we investigate the difference between using glass and stainless-steel vessels on the DSC measurement of exothermic decomposition energy (QDSC) for 41 chemical substances (containing nitro, halogen, peroxide, and sulfur groups, and hydrazine bonds). Two borosilicate glass vessels (capillary and ampule) and one stainless-steel vessel were used. All QDSC values obtained were investigated with reference to the permissible fluctuation range specified by the ASTM (American Society for Testing and Materials) international Both glass vessels produced very similar QDSC values, despite different sample scales. The QDSC values obtained with the glass vessels were generally roughly within the variation tolerance range of the stainless-steel vessel. Notable exceptions were halogen- or sulfur-containing compounds;these exhibited smaller QDSC values with glass vessels in almost all cases. We will investigate whether certain structures in compounds react with stainless steel. The vessel material choice is crucial in evaluating the true reactivity of a substance.

Application of Single Scan Differential Scanning Calorimetry Technique for Determination of Kinetic Parameters of Crystallisation in Se-Sb-Ag

A single scan has been performed in Differential Scanning Calorimetry (DSC) at a heating rate of 15oC/min under non-isothermal conditions to investigate the crystallization kinetics of glassy Se90Sb10-xAgx alloys (where x = 2, 4, 6, 8). For this purpose, Handerson’s theory based on non-isothermal method for thermal analysis of single-scan DSC data has been used. The activation energy of crystallization and order parameter has been determined and composition dependence of these parameters has been discussed.

Thermal Diffusivity and Thermal Conductivity of Epoxy-Based Nanocomposites by the Laser Flash and Differential Scanning Calorimetry Techniques

Nanocomposites were fabricated by using a commercial two part epoxy as a matrix and multiwalled carbon nanotubes, graphite fibers and boron nitride platelets as filler materials. Multiwalled carbon nanotubes (MWCNTs) that were produced by chemical vapor deposition were found to produce nanocomposites with better thermal diffusivity and thermal conductivity than the MWCNTs that were produced by the combustion method. Compared to the MWCNTs produced by both methods and graphite fibers, boron nitride produced nanocomposites with the highest thermal conductivity. Specific heat capacity was measured by using differential scanning calorimetry and thermal diffusivity was measured by using the laser flash.

New method for analyzing recrystallization kinetics of deformed metal by differential scanning calorimeter

The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrhenius behavior and modifying the baseline of DSC curves, has been proposed. The results show that JMAK exponent and recrystallization activation energy of the drawn copper wires with a strain of 2.77 are about 2.39 and 125 k J/mol, respectively. The line linking the tangency points of DSC curve hypotenuse can be used as the baseline when calculating recrystallization fraction. The JMAK exponent obtained by the DSC method is in a good agreement with that obtained by microhardness measurements. Compared to traditional methods to measure the exponent, the proposed method is faster and less labor intensive.

Application of differential scanning calorimetry to study the interpretation on herbal medicinal drugs:a review

Background:Differential scanning calorimetry as a method of investigating and monitoring the kinetics of herbal medicinal plants.Some instrumental and experimental aspects are discussed.Methods:A brief survey is made of herbal medicinal plants and results of differential scanning calorimetry studies are reviewed and this discussion is presented the effects of the instrumental conditions like heating rate and the sample conditions like sample particle size,sample mass,sample purity,sample stability in the melting region and property of impurities.Conclusion:This study suggests that application of differential scanning calorimetry to study the interpretation on herbal medicinal drugs.

ON A DIFFERENTIAL EQUATION FOR KINETICS OF NON- ISOTHERMAL CRYSTALLIZATION

A new differential equation was derived from the modified first-order kinetic model to describe the polymer crystallization processes. The crystallization experiments were carried out by means of DSC. Poly (ethylene terephthalate) resins were selected as the samples containing different catalysts. The relationships between the parameters obtained from the known Avrami equation and from one in the present paper were discussed. A method for applying the equation to determine the kinetic parameters from a constant heating and a constant cooling curve was proposed.

Formation mechanism of the Zn-5%Al hot-dip coating amorphous alloys(Ⅰ)--The analysis of differential scanning calorimetry

HOT-DIPPING Zn+5% Al + (0.01%-0.2%) RE alloy on steel surface by the gas reductionmethod is a new technology. Owing to its good anti-corrosive and forming properties as wellas good technical periormances, the coating attracts wide interest and has been put into indus-trial production rapidly. The authors successfully produced the coating by the electrolytic ac-tivity aid agent method and put it into industrial production. The products have been used inthe electric power and railway engineerings. Results show that the anti-corrosive

Undercooling and solidification of germanium melts studied by differential scanning calorimeter

Differential scanning calorimeter combined with flux(dehydrated B2O3) processing was used to realize and precisely measure the undercooling of germanium melts.The highest undercooling obtained in this way was 190 K.Relations between the undercooling and cooling rate or overheating tem-perature are analyzed respectively.The undercooling obtained is found to be increased with increasing of the cooling rate in the range from 5 to 40 K/min.At a given cooling rate,the undercooling reached is increased with the increasing of the overheating temperature of the melt,but tends to be constant at last.Crystallization of the undercooled germanium melt is investigated at the same time.It is clearly shown that,the higher the cooling rate,the shorter time is needed for crystallization.

Comparative ultrastructural study of endoplasmic reticulum in colorectal carcinoma cell lines with different degrees of differentiation

The endoplasmic reticulum (ER) consists of a complex system of tubules, lamellae, and flattened vesicles, and has a variety of morphologies in different cells. It is believed to play a central role in the biosynthesis of cholesterol, phospholipids, steroids, prostaglandins, membrane and secretory proteins[1]. Cancer cells have different functions and ultrastmcture from their original cells[2-4]. The studies on ER membrane system of cancer cells are of great significance in understanding their malignant behavior. In the present work, the ultrastructural characteristics of ER in human colorectal carcinoma cell lines with different differentiation degrees were investigated.

Review of MEMS differential scanning calorimetry for biomolecular study

Differential scanning calorimetry （DSC） is one of the few techniques that allow direct determination of enthalpy values for binding reactions and conformational transitions in biomolecules. It provides the thermody- namics information of the biomolecules which consists of Gibbs free energy, enthalpy and entropy in a straightfor- ward manner that enables deep understanding of the structure function relationship in biomolecules such as the folding/unfolding of protein and DNA, and ligand bindings. This review provides an up to date overview of the applications of DSC in biomolecular study such as the bovine serum albumin denaturation study, the relationship between the melting point of lysozyme and the scanning rate. We also introduce the recent advances of the development of micro-electro-mechanic-system （MEMS） based DSCs.

基于特级初榨橄榄油两种不同特性的DSC掺假分析方法研究

该文基于油脂物理特性与氧化稳定性2种特性,利用差示扫描量热法(differential scanning calorimetry,DSC)对市面上常见的特级初榨橄榄油(extra virgin olive oil,EVOO)中大豆油掺假问题进行研究。在物理特性方面,采用DSC冷却曲线来分析EVOO掺假。随着大豆油掺假比例升高,油样在-40~-60℃结晶焓值ΔH由EVOO的29.78 J/g减小为40%掺假混合油的6.133 J/g,对EVOO质量比构建的一元回归方程Y=57.556X-28.44(R2=0.997)。在氧化稳定性方面,氧化温度160℃下,不同油样诱导氧化时间随大豆油掺假比例上升逐渐变短,由EVOO的25.8 min逐渐减小为40%掺假混合油的17.8 min,Y=-19.4X+25.64(R^(2)=0.996),掺假模型相关性较好。这2种DSC检验掺假分析方法都能有效鉴别EVOO中大豆油的掺假且各有特点,可根据实际情况选取合适的方法更好处理EVOO掺假问题。

加热氧化对山茶油热力学及流变学特性的影响

目的探究加热氧化对山茶油热力学及流变学特性的影响。方法山茶油经加热氧化处理后,运用差示扫描量热技术(differential scanning calorimetry,DSC)、旋转流变技术,研究其DSC氧化稳定性,熔融结晶特性及黏度随剪切速率、温度变化等特性。结果山茶油加热时间越长,其DSC热力学氧化稳定性越低,当加热120 min后较初始山茶油的氧化起始温度降低了8.3℃,加热氧化后它的熔融温度及熔融焓降低,主要结晶峰消失。山茶油加热氧化后流动性变差,表现为黏度升高,加热120 min的山茶油较初始山茶油黏度提高了2.8倍,山茶油氧化程度越高,其黏度随温变化的速率越快。结论加热氧化降低了山茶油的热力学稳定性及流变学稳定性,本研究为山茶油精深加工的热力学性能及流变性能提供了一定的理论支撑。

核医学检查在评估中低危分化型甲状腺癌患者术后淋巴结转移中的价值

目的探讨中低危分化型甲状腺癌患者术后刺激状态下甲状腺吸碘率、甲状腺功能及残留甲状腺131I最大计数评估发生淋巴结转移的临床价值。方法随机选取2016年1月—2018年12月就诊于我院临床资料齐全的中低危分化型甲状腺癌术后并欲行131I治疗的182例分化型甲状腺癌(DTC)患者,收集所有患者甲状腺吸碘率、甲状腺功能、颈部超声、131I全身扫描及颈部SPECT/CT断层显像资料。结合淋巴结术后病理、颈部超声、颈部SPECT/CT断层显像及临床随访来最终确定颈部淋巴结转移情况。分析甲状腺吸碘率、功能、131I最大计数诊断淋巴结转移的相关因素。结果二元Logistic回归分析结果显示,中低危分化型甲状腺癌颈部淋巴结转移与术后刺激状态下吸碘率(P=0.048)、Tg(P=0.048)、131I最大计数(P=0.049)有关,与TSH(P=0.256)、FT3(P=0.516)、FT4(P=0.827)、TgAb(P=0.351)、TPOAb(P=0.389)无关。将吸碘率、Tg、131I最大计数对转移进行ROC处理,三者中吸碘率诊断效能最高,131I最大计数效能最差,吸碘率、Tg的临界值分别为1.5、5.28时对评估淋巴结转移有统计意义,131I最大计数临界值为727,但无统计学意义。通过偏相关分析显示,吸碘率、TSH、FT3、FT4、TgAb均与131I最大计数有关,其中吸碘率、FT3、FT4与131I最大计数呈正相关,TSH、TgAb与131I最大计数呈负相关(P<0.05)。结论吸碘率、Tg、131I最大计数对淋巴结转移有一定评估价值;吸碘率、FT3、FT4值越高,提示131I最大计数越高;TSH、TgAb值越高,对应131I最大计数水平越低。

超声在线监测不饱和聚酯树脂固化过程及其动力学行为

为探索不饱和聚酯树脂(UPR)固化体系在不同温度下的超声振幅变化规律,采用超声波穿透技术对UPR固化过程进行在线监测,获得声速、储能模量、松弛时间、凝胶时间等动力学参数变化规律,并得到固化反应动力学方程。结果表明:温度越高,声速与储能模量变化越快,且最终数值也越大,而固化松弛时间与凝胶时间随温度增加而缩短;此外,超声法与差示扫描量热法(DSC)得到的固化度曲线变化高度一致,通过2种方法所得到的反应活化能分别为38.14 kJ/mol和45.3 kJ/mol;最终,通过DSC法确定了UPR固化反应动力学级数为0.92。总之,超声法与DSC法2种方法相互结合,不仅证明了超声结果的准确性,也为UPR固化过程提供一种精准的在线监控技术和量化方法,从而为UPR生产过程提供理论指导。