Thermal Decomposition of Silver Flake Lubricants

There is a thin layer of organic lubricant on commercial silver flake surfaces. This lubricant layer is a fatty acid salt formed between a fatty acid and silver flake surfaces. Thermal decomposition behavior of the silver flake lubricant is investigated in this study. The heat flow and mass loss of a silver flake are studied using differential scanning calorimetry (DSC) and thermogravimetry (TG), respectively. The silver flake is also oven heated to different isothermal temperatures (150,190, 250 and 300°C) for one h. Then chemical nature of the lubricant of the heated silver flake sample are studied using diffuse reflectance infrared Fourier transfer spectroscopy (DRIFTS). Based on the results, a mechanism of thermal decomposition of the silver flake lubricant is proposed. It is found that decomposition of the lubricant - the fatty acid salt -includes the release of the fatty acid, formation of short chain acids by decomposition of hydrocarbon moiety of the fatty acid, and formation of alcohols through decarbonation of the short chain acids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characterization of the poultry fat biodiesel

Chemical composition of oils and fats used in the biodiesel synthesis can influence in processing and storage conditions, due to the presence of unsaturated fatty acids. An important point is the study of the biodiesel thermal stability to evaluate its quality using thermal analysis methods. In this study the thermal stabilities of the poultry fat and of their ethyl (BEF) and methyl (BMF) biodiesels were determined with the use of thermogravimetry (TG/DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), in different atmospheres. The TG/DTG curves of the poultry fat in synthetic air presented three decomposition steps while only one step was observed in nitrogen (N₂) atmosphere. The DSC results indicated four exothermic enthalpic transitions in synthetic air and an endothermic transitions in N₂ atmosphere attributed to the combustion process and to the volatilization and/or decomposition of the fatty acids, respectively. For both biodiesels the TG/DTG curves in air indicated two mass loss steps. In the DSC curves four exothermic transitions were observed in synthetic air besides an endothermic one in N₂ atmosphere.     

Quantitative analysis of some bile acids by differential scanning calorimetry combined with TLC

An analytical method useful for the quantitative determination of some bile acids is proposed. The analysis is carried out in two steps. The first is based on the thin layer chromatographic (TLC) separation of the bile acids on alumina plates. The second is based on the application of differential scanning calorimetry (DSC), which permits the characterization and determination of the amount of compound contained in each spot. The DSC signal is proportional to the amount of sample present in the spot layer, while the various peaks and peak temperatures are used to identify the separated compound.     

Fabrication and characterization of silver nanostructures conformal coating layer onto electrospun N6 nanofibers with improved physical properties

In this communication, colloidal silver (Ag) nanostructures were synthesized and deposited directly onto electrospun nylon 6 (N6) fibers without using surface modifier in the form of an ultrathin conformal coating layer via a hydrothermal treatment. The morphological, structural, and thermal properties of the Ag/N6 nanocomposite membranes were analyzed by field-emission scanning electron microscopy (FESEM), X-ray diffraction, X-ray photoelectron spectroscopy, and differential scanning calorimetry (DSC). FESEM imaging showed that the Ag coating on individual N6 nanofibers was continuous, uniform, and compact. A DSC study of the nanocomposites illustrated a strong interfacial adhesion of the Ag layer with N6 nanofiber surfaces via strong hydrogen bonds. A possible mechanism for hydrogen bond formation during the hydrothermal process was proposed. Further, it was found that the transition of the meta-stable γ-form into the thermodynamically more stable α-form of N6 structure was achieved; therefore, the hydrothermal process did not cause chain degradation.     

Crystallization kinetics of amorphous Fe75−xAgxSi9B16

The influence of Ag admixtures on the crystallization process of amorphous Fe-Si-B alloys of the series Fe_75−xAg_xSi₉B₁₆ (x=0, 1, 2, 3 and 4) was studied by differential scanning calorimetry (DSC) measurements at different heating rates. Two exothermic peaks were observed in the DSC trace when the Ag content was 2-4 at.% and one when it was 1 at.%, respectively. The activation energy was calculated both with Kissinger’s and isoconversional Flynn, Wall and Ozawa methods. The possibility of analysis with the JMA model using the Avrami plot was investigated for the third stage of crystallization.     

Synthesis and structure of colloids and films from Pd–Ag in organic solvents

Pd/Ag bimetallic particles are dispersed in acetone, 2-propanol and 2-methoxyethanol. The colloids are prepared by codeposition of the vapors of metals and solvents at 77 K. The stabilities of the Pd/Ag colloids are in the order acetone>2-methoxyethanol~2-propanol. The particles are studied by transmission electron microscopy to determine their size and also by electron diffraction to study their crystal structure. The Pd/Ag samples exhibit more than one metallic phase in the different solvents, these being Pd, Ag and Pd/Ag. The crystallinity is controlled by the Pd/Ag ratio; the crystalline phases in the bimetallic particles can be observed using the dark field technique. The differential scanning calorimetry of Pd/Ag-2-methoxyethanol solids shows three exothermic peaks in which phase transformation, microcrystal growth and solvent decomposition of the solvent in the solid are observed. However, the differential scanning calorimetry of Pd/Ag-acetone solids shows two exothermic peaks.     

Thermal characteristics of mixtures of cyclonite and nitroglycerine or diazidonitrazapentane

The thermal characteristics of mixtures of cyclonite (RDX) and nitroglycerine (NG) and of RDX and diazidonitrazapentane (DIANP) were studied. The thermal decomposition processes of NG and RDX are not synchronous with those of RDX/NG mixtures. The DSC curves show two obviously exothermic peaks, one at 203°C for NG and other at 240°C for RDX. However, there is only a single exothermic peak in the DSC curves of RDX/DIANP mixtures within certain ratio limits, due to the coincidence of the exothermic decomposition peaks for both RDX and DIANP and their mutual dissolution. The effects of the different thermal characteristics of different explosives on the combustion performance are also discussed.     

壳聚糖液晶溶液的性能

制备了聚糖液晶溶液,并采用偏光显微镜(POM)、流变仪、差示扫描量热仪(DSC)等分别对液晶织构、黏度、相转变性能进行了研究.结果表明:壳聚糖呈现典型的胆甾相液晶织构;其溶液黏度随浓度及剪切力的变化规律符合高分子液晶溶液的变化规律;在DSC升、降温曲线上分别存在吸热峰和放热峰.     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Tracking lubricants during single screw extrusion of uPVC

Lubrication is one of the most important parameters in unplasticized polyvinyl chloride (uPVC) processing apart from the PVC resin and processing equipment. Lubricants are used in specific ratios to ensure effective fusion of PVC particles. The exact mechanism on how these lubricants interact is not yet fully understood. A widely accepted theory is the interaction mechanism proposed by Rabinovic et al. where lubricants are said to act as surfactants and slip agents. In this study a method for tracking lubricants, by simulating the extrusion process within a single screw extruder, was proposed. A three stage fusion simulation consisted of the feeding zone (stage 1), the compression zone (stage 2) and the metering zone (stage 3). The association interactions between the individual components of a typical uPVC formulation were followed throughout the three stages. External polar and nonpolar lubricants in combination with an internal lubricant was studied. Lubricants were successfully tracked using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). In conclusion it was found that the use of an internal lubricant promotes dispersion of external lubrication towards PVC. It was also found that there is a competition between the internal lubricant and polar external lubricant.     

Thermal characteristics and analysis of pyrolysis effects during the mechanical alloying process of Astaloy CrM powders

Mechanical alloying processes are carried out usually with addition of some lubricants, referred to also as a process control agents (PCA). About 1–2 wt% of a PCA (usually stearic acid) is normally added to prevent excessive cold welding amongst the powder particles, especially when powders of ductile metals are milled. However, lubricants (maybe disintegrated after MA process) must be removed in the early stages of heating during the sintering process. The aim of the present study was to determine the effect of the MA process especially (i) milling time and (ii) influence of lubricant addition on thermal effects during heating of iron powder (Astaloy CrM) with the addition of 1 wt% stearic acid measured by differential scanning calorimeter (DSC) and thermogravimetry (TG) techniques. Removal of the lubricants during heating of the blended powders and exhaust gases from the furnace were monitored by quadruple mass spectrometry (QMS). Determination of the physical and technological properties of the powder mixture obtained from MA was performed with a laser particle sizer. Distribution of particle sizes, flow and apparent density were also measured. Furthermore, the shape and morphology of the powders were characterised by a light optical microscope (LOM) and scanning electron microscope (SEM).     

含CL-20的改性双基推进剂的热行为及非等温反应动力学

用DSC和TG方法研究了含六硝基六氮杂异伍兹烷(CL-20)的改性双基推进剂在常压(0.1 MPa)和高压(4和7 MPa)下的热行为和高压下的热分解反应动力学. 结果表明, 该推进剂常压下DSC曲线有3个放热峰, 相应TG曲线有3个失重过程; 而高压下DSC曲线只有一个放热峰, 高压下放热峰的峰温随加热速率增大而升高. 高压下该推进剂放热分解反应机理和反应动力学参数受测试环境压强影响较弱, 反应机理是随机成核和随后生长, 放热分解反应的动力学方程可以表示为, 4 MPa时, dα/dt=1014.5(1-α)[-ln(1-α)]1/3e-17981.7/T; 7 MPa时, dα/dt=1014.7(1-α)·[-ln(1-α)]1/3e-18138.1/T.     

基于差示扫描量热技术的生物质热解两步连续反应模型研究

采用差示扫描量热分析仪对我国的一种生物质试样在空气气氛中进行了实验, 发现试样从常温到923 K高温的低速升温过程中, 经历了两步明显的放热过程. 对放热机理的分析表明, 第一步主要是由半纤维素和纤维素的有氧热解过程控制, 第二步放热过程则受木质素热解和炭的氧化反应的共同作用. 采用等转化率方法和优化计算方法, 对热解过程的动力学模型进行了研究, 结果表明, 两步连续反应机理可用于描述生物质在空气气氛中热解的放热动力学.     

2,4,6-三(羟基苯甲基氨基)-均三嗪的合成及其与双酚A型环氧树脂的固化行为研究

合成了一种含三嗪环结构的环氧树脂固化剂2,4,6-三(羟基苯甲基氨基)-均三嗪(MFP).用动态DSC和原位红外光谱对MFP/DGEBA(双酚A型环氧树脂)体系的固化行为进行了研究.动态DSC研究表明,由于MFP分子结构中存在两种活泼氢(酚羟基氢和仲胺氢),固化反应存在明显的两个峰,相对应的表观活化能分别为70.5 kJ.mol-1和86.5 kJ.mol-1(Kissinger法),通过与另一相似化合物固化DGEBA的比较可知,在MFP固化DGEBA的过程中,酚羟基与环氧基反应相对较难.原位红外动力学结果很好地支持了上述结论.     

差示扫描量热研究水稻线粒体能量释放动力学

线粒体是细胞的一个重要的亚细胞器．它通过呼吸作用为细胞各项活动提供能量，有细胞'动力戒'之称．生物摄取的食物通过代谢分解形成小分子产物之后，被输送至线粒体，经过氧化作用将其中贮存的能量逐步释放出来，并转化为三磷酸腺苦（ATP）以供生命机体各种活动的需要，因而它     

烷基咪唑螯合硼离子液体的合成及摩擦学性能

以1种环境友好的双水杨酸螯合硼为阴离子中心,以咪唑环为阳离子骨架,合成了7种新的具有不同烷基直链的螯合硼离子液体D-C_nImBScB(n=4,6,8,10)和C_nImC8BScB(n=4,6,10).利用核磁共振波谱(~1H NMR)、热重分析(TGA)和差示扫描热量(DSC)等技术对7种双咪唑螯合硼离子液体进行了结构和热稳定性分析.以聚乙二醇(PEG200)作为基础油,双边咪唑螯合硼离子液体D-C_nImBScB(n=4,6,8,10)和C_nImC8BScB(n=4,6,10)作为添加剂,采用四球摩擦磨损试验机、扫描电子显微镜(SEM)和能量色散X射线光谱仪(EDX)分别对油样的抗磨减摩性能、磨斑形貌和磨斑表面元素分布进行了分析表征.结果表明,D-C_nImBScB(n=4,6,8,10)和C_nImC_8BScB(n=4,6,10)可用作在较宽温度范围使用的润滑油添加剂,添加C_6ImC_8BScB的PEG200油样抗磨效果最佳,其磨斑直径为0.712 mm,与PEG200相比降低了27.49%,通过适当调节阳离子咪唑环骨架上的双边烷基链长度可以调控离子液体的摩擦学性能.     

Physicochemical analyses of phase transition and dehydration processes of a new oral 1beta-methylcarbapenem antibiotic agent,CS-834

The characterizations of the anhydrate (A-form), monohydrate (B1-form), and dihydrate (B2-form) of CS-834 were investigated by powder X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetry-differential thermal analysis (TG-DTA), infrared spectroscopy, and Karl Fischer moisture titration. The typical DSC curve of the B2-form showed five endothermic peaks at 35.0, 46.4, 56.2, 99.2, and 190.4 degrees C and an exothermic peak at 123.4 degrees C. In TG-DTA analysis, the three peaks at 35.0, 46.4, and 56.2 degrees C had a total weight loss of 7.3%, corresponding to the release of two water molecules. From morphological observation under thermomicroscopy, the endothermic peak at 99.2 degrees C was attributed to the melting of the dehydrous crystals (B0-form) and the exothermic peak at 123.4 degrees C to the recrystallization to the A-form crystals. The endothermic peak at 190.4 degrees C was due to the melting of the A-form crystals. After incubation for 6.0 h at 35, 50, 60, and 80 degrees C, the powder X-ray diffraction patterns of the B2-form indicated that it was converted into the A-form via the B1-form and B0-form. Thus CS-834 exists in homologous hydrous crystal forms in multiple-phase transformations with the dehydration of two water molecules.     

Impact on lipid membrane organization by free branched-chain fatty acids

Here, we exploit the non-invasive techniques of solid-state NMR (nuclear magnetic resonance) and differential scanning calorimetry (DSC) to study the effect of free iso and ante-iso branched chain fatty acids (BCFAs) on the physicochemical properties of lipid membranes. Free fatty acids are present in biological membranes at low abundance, but can influence the cellular function by modulating the membrane organization. Solid state NMR spectra of dimyristoylphosphatidylcholine (DMPC) lipid membranes containing either free 12-methyltetradecanoic acid (a15:0) or free 13-methyltetradecanoic acid (i15:0), show significant differences in their impact on the lipid bilayer. Chain order profiles obtained by deuterium NMR on fully deuterated DMPC-d(67) bilayers revealed an ordering effect induced by both fatty acids on the hydrophobic membrane core. This behavior was also visible in the corresponding DSC thermograms where the main phase transition of DMPC bilayers-indicative of the hydrophobic membrane region-was shifted to higher temperatures, with the iso isomer triggering more pronounced changes as compared to the ante-iso isomer. This is probably due to a higher packing density in the core of the lipid bilayer, which causes reduced diffusion across membranes. By utilizing the naturally occurring spin reporters nitrogen-14 and phosphorus-31 present in the hydrophilic DMPC headgroup region, even fatty acid induced changes at the membrane interface could be detected, an observation reflecting changes in the lipid headgroup dynamics.     

Silver(I) pyrophosphonates: structural, photoluminescent and thermal expansion studies

The solvothermal reactions of silver(I) salts with mono-organophosphonic acids, i.e. 3-thienylphosphonic acid (3-TPA), phenylphosphonic acid (PPA), α-naphthylphosphonic acid (α-NPA) and cyclohexylphosphonic acid (CPA), yield four new silver(I) pyrophosphonates, namely: [Ag(2)(ptp)] (1), [Ag(2)(ppp)] (2), [Ag(3)(CH(3)CN)(pnp)(pnpH)] (3), and [Ag(3)(pcp)(pcpH)] (4) [ptp(2-) = pyro-3-thienylphosphonate, ppp(2-) = pyrophenylphosphonate, pnp(2-) = pyro-α-naphthylphosphonate, pcp(2-) = pyrocyclohexylphosphoante]. In all cases, the pyrophosphonate ligands are generated in situ from their relative mono-organophosphonic acids, mediated by silver(I) ions. Single crystal structural determinations reveal that compounds 1 and 2 display two-dimensional layer architectures, while 3 and 4 show one-dimensional chain structures. Structure 1 can be best described as a layer made up of Ag(4)O(P)(6) clusters linked by O-P-O units and AgAg contacts, with the organic groups grafted on the two sides of the inorganic layer. A similar layer structure is found in 2 except that the AgAg interactions are absent. Compound 3 shows a chain structure where the silver ions are bridged by the phosphonate oxygen atoms forming an infinite Ag-O(P) chain which is decorated by the pyrophosphonate ligand and CH(3)CN. Compound 4 has another type of chain structure made up of Ag-O(P) with extensive Ag···Ag argentophilic interactions. Solid state photoluminescent properties and thermal expansion behaviors are also investigated.     

Thermal and stability study of tetracene using differential scanning calorimetry

A thermal analysis study was made of tetracene using differential scanning calorimetry (DSC). The effect of different scan speeds was investigated. At scan speeds of 0.625 to 10°C min^?1 two large rounded exothermic peaks were produced. The peaks occurred at an increasingly high temperature as the scan speed increased (for example, the peaks occurred at 128 and 130°C at a scan speed of 0.625°C min^?1 and at 148 and 150°C at a scan speed of 10°C min^?1. When tetracene was heated at a scan speed of 80°C min^?1 only one large sharp exothermic peak was produced. It is believed that the two peaks obtained at scan speeds of 0.625 to 10°C min^?1 represent decomposition of the tetracene in two successive stages, while the one peak obtained at 80°C min^?1 represents an explosion. A stability test for tetracene is proposed that involves heating of the tetracene in aluminum pans from the DSC apparatus in ovens at 100, 75, and 60°C, removing the pans and samples at intervals of 30 min, 24 h, and 7 days, respectively, subjecting the samples to DSC at 1.25°C min^?1, and noting the time interval in the oven that produces a DSC curve that shows obliteration of the second peak. Two lots of tetracene made by different processes showed marked differences in stability characteristics.