Thermomechanical Data Research Articles

Materials for high-temperature fuel cells

The materials incorporated into molten carbonate fuel cells (MCFC) have remained unchanged over the past 20 years. Materials selection is dominated by the need to satisfy performance, cost and stability criteria in the aggressive environment provided by the molten carbonate electrolyte. Accordingly, materials developments associated with the MCFC have been focused on reducing fabrication costs and improving reliability over extended periods. In contrast, materials selection for solid oxide fuel cells (SOFC) is still a very active endeavour due to the different requirements arising from the range of operating temperatures (500-1000 °C), various design configurations and market opportunities. It is expected that electrode-supported thick-film electrolyte technology will satisfy most of the technical requirements, and investigations are urgently required to reduce the associated fabrication costs, and to provide relevant thermomechanical property data. SOFC systems operate on a variety of fuels, and their relative simplicity makes them particularly promising candidates for small-scale combined heat and power applications, and for incorporation into electric vehicles.

A Study of the Mobility of Poly(Methyl Methacrylate)-Silicate Interpenetrating Networks with 2H NMR

Poly(methyl methacrylate) (PMMA)/silicate interpenetrating networks (IPNs) have been synthesized in formic acid solutions. The fast gelation times observed in these solutions reduced the phase separation of the polymer, and the 50% by weight PMMA/silicate hybrid showed virtually no evidence of a glass transition (T{sub g}) from thermomechanical data. {sup 2}H NMR showed that the PMMA is extremely mobile in the wet gels, and liquid-like {sup 2}H NMR spectra are observed even after prolonged aging of the samples. A {sup 2}H static NMR lineshape, indicative of the rigid polymer, does not occur until polymer to solvent ratios of approximately 0.2 (weight basis) are attained. Motional narrowing of the {sup 2}H resonances is not observed in the vacuum-dried IPNs below 180 C. In contrast, pure PMMA shows motional narrowing between 150 and 180 C. There was little evidence of isotropic motion of the polymer chains, for low polymer concentrations, up to the highest temperature studied (200 C). The percentage of polymer undergoing isotropic motion increased with polymer content, and as a function of the aging time before solvent stripping.

等価介在物法による焼結複合材料の熱・機械的性質の推定

The thermomechanical properties of composite materials are influenced by various factors such as defects, reactions between matrix and fillers, orientation of fillers, mismatch of the coefficient of thermal expansion (CTE) between the matrix and the fillers.The effect of these factors on the thermomechanical properties of sintered composites is estimated theoretically and the theoretical evaluations are compared with the experimental data.The theory used in this calculation is based on Eshelby's equivalent inclusion method, with which we can solve the three-dimensional elastic problem by assuming ellipsoidal fillers to be embedded in an infinite elastic body.This method applies to various types of fillers by changing the aspect ratio of the ellipsoidal fillers such as: long fibers, whiskers, spherical particles and so on.Within this formalism, we have analyzed the effects on the thermomechanical properties of composites of interface debonding between matrix and fillers, dispersion of pores, phase reactions among constituent phases, anisotropically dispersed fillers, residual stress induced by shape memory effect, and CTE mismatch between matrix and fillers.The microstructure of the sintered composites, can be controlled widely by changing the mixtures of powders, sintering conditions and the heat treatment, thereby we can obtain specimens with a variety of thermomechanical properties. In this study, the microstructural parameters for Eshelby's analysis have been determined directly from microstructural observations of the composites, and the thermomechanical properties have been predicted theoretically using the observed data.We have got an excellent agreement between the experimentally determined thermomechanical data and the theoretical predictions.It has been shown that the present method will be a versatile tool for the analysis of the properties of the sintered composites, as well as for their material design.

Studies on co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester: Thermomechanical and thermodynamic properties

AbstractA series of co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyesters were prepared by the copolymerization of poly(ethylene terephthalate) (PET) as moiety (II) and p‐acetoxybenzoic acid (POB) as moiety (I). The polymeric products obtained were subjected to solid‐state polymerization. Characterization of the copolyesters by thermomechanical analysis shows that properties such as the coefficient of thermal expansion, transition temperature, and maximum softening rate temperature varied directly as a function of composition as well as did solid‐state polymerization time. All thermomechanical data were found to increase with the solid‐state polymerization time due to the increase in the degree of polymerization and the effect of annealing. The coefficient of thermal expansion behaves in a manner that is interpretable by the crystalline state of the copolyester. The relationship between the free‐volume fraction and thermodynamic properties is further correlated for a more comprehensive discussion on its molecular arrangements. © 1995 John Wiley & Sons, Inc.

Properties of block-copolymers of ethylene with acetylene, prepared on complex organometallic catalysts

The copolymerization products of ethylene with acetylene or phenylacetylene are coloured, nonconductive, can get strongly charged, melt in the range 80–140°C, in the nascent state or in films contain a considerable fraction of the crystalline phase, are completely soluble in tetralin at 130°C, and exhibit low values of the melt flow index. Thermomechanical data and the results of the studies of these copolymers by DSC and thermogravimetry indicate that they undergo crosslinking without initiators or accelerators. The acetylene blocks initiate crosslinking, act as the crosslinking agent and also appear as part of the generated structuralized material. The crosslinked copolymers of ethylene with acetylene differ very little from LDPE concerning their molecular or supermolecular structure, and stress-strain characteristics.

Solute and penetrant diffusion in swellable polymers: X. Swelling of multiethylene glycol dimethacrylate copolymers

AbstractThe swelling behavior of copolymers containing 2‐hydroxyethyl methacrylate and various multiethylene glycol dimethacrylates was examined at 25°C. These highly crosslinked copolymers show some hydrophilic behavior due to the hydroxyl groups of HEMA. Analysis of the swelling data indicates and anomalous water transport in the network, which depends on the degree of crosslinking attained according to the dimethacrylate comonomer molar fraction in the copolymerization feed. Thermomechanical analysis data were used to further characterize the network structure.

Acetylene-Terminated Polyimide Composites for Advanced Electronic Packaging Applications

AbstractSurface mount technology (SMT) is an electronic packaging technology wherein the leads of electronic components are soldered directly to metallized pads on the surface of a printed circuit board (PCB). The SMT with leadless ceramic chip carriers (LCCCs) is used to design, fabricate, and assemble affordable, high-speed, high-density electronic modules with reduced size and weight and improved electrical performance. In surface mount devices, the LCCCs are soldered directly onto the fabric composite PCB substrate. New high-performance composite substrate materials must be developed to take full advantage of SMT. Fabricating a PCB that will perform reliably throughout its intended life is also an increasingly important requirement, especially if the goal is to satisfy the high reliability required in military applications. Consequently, SMT is driving the development of PCB substrate materials with improved thermal and electrical properties. In our continuing effort to meet these military demands, we evaluated high-temperature resistant/high-performance acetylene-terminated polyimide composites for use in SMT PCBs. This paper focusses on the processing and on the thermal, thermomechanical, and dynamic mechanical properties data developed for these acetylene-terminated polyimide composites for their potential evaluation as PCBs. The characterization includes such properties as in-plane coefficient of thermal expansion (CTE), out-of-plane CTE, and glass transition temperature (Tg), which determine the solder joint reliability, plated-through-hole (PTH) reliability, and dimensional stability.

Thermochemical Arsenide-Oxide Equilibria in the System Ni–As–O Determined Electrochemically between 438 and 866°C

An electrochemical technique has been developed for the determination of solid-solid-gas equilibria in metal-bearing arsenic-oxygen systems which are of significance in pyrometallurgy and for which few thermomechanical data are available.Equilibrium electrochemical potentials were measured in an oxygen concentration cell which consisted of (a) an oxygen reference electrode, (b) a solid zirconia-calcia electrolyte and (c) an arsenide-oxide mixture over which was passed argon containing a known partial pressure of As4O6.The technique has been used to determine the free energies of reaction of rammelsbergite (NiAs2), niccolite (NiAs), maucherite (Ni11Asg) and Ni5As2 with oxygen to form bunsenite (NiO) and As4O6 in the temperature range 438–866°C. The thermodynamic functions for these compounds were also calculated from the measurements; those for NiAs are in good agreement with literature values.The literature on the electrochemical determination of thermodynamic equilibria at elevated temperatures in M–S–O systems was also reviewed.

PE-II Scoping Test Results: Solid Breeder Heat Transfer and Stability

Two scoping test stands have been designed, built and installed at GA Technologies to perform single effect type testing to investigate specific thermomechanical and thermal-hydraulic data needs of typical solid breeder blanket designs. An initial test has been completed successfully yielding important information on the stability of Li2O breeder material at typical fusion reactor environmental conditions. Assembly of the second test rig and a pre-testing checkout of the equipment has been completed.

FWBS Program Element II: Blanket and Shield Testing

The First Wall/Blanket/Shield (FWBS) Program has the goal to provide the development and testing of FWBS systems for magnetic fusion reactors. Program Element II of this program is to develop the thermal-hydraulic and thermomechanical data base for blanket and shield components. The critical blanket/shield data needs were identified, alternate techniques to simulate fusion neutron bulk heating were evaluated, and a detailed technical plan was developed. The initial focus is on the critical issues of solid breeder blankets. Two single effect scoping tests are currently in progress to determine the heat transfer characteristics and thermomechanical stability of the solid breeder bed. The design of an integral test to simulate all the non-nuclear aspects of the blanket has been completed. Preliminary planning for a fission reactor-based nuclear test has also been done. Future testing will investigate alternate solid breeder blanket materials and configurations and will begin the investigation of the critical MHD effects of liquid metal blanket concepts.

Thermomechanical modeling and data analysis for heating experiments at Stripa, Sweden : Chan, T; Littlestone, N; Wan, O Proc 21st US Symposium on Rock Mechanics, Rolla, Missouri, 28–30 May 1980, P16–25

Comparisons were made between predicted and measured thermomechanical displacements and stresses for in situ heating experiments at a depth of 340 m in a granite body at Stripa, Sweden. We found that taking into account the temperature dependence of the thermal expansion coefficient and the mechanical properties of the rock substantially improves the agreement between theory and experiment. In general, the displacements calculated using laboratory values of rock properties agree better with field data than in the case of stresses. This may be due to the difference between in situ and laboratory rock modulus. The significance of temperature-dependent rock properties and strength to thermomechanical failure is also discussed.

Structure and properties of acrylonitrile‐[(2‐methacryloyloxy)alkoxy]trimethyl silane copolymers

AbstractDielectric, x‐ray diffraction, density, thermomechanical, and thermogravimetric studies on polyacrylonitrile (PAN), poly[acrylonitrile‐(2 methacryloyloxy)ethoxytrimethylsilane] [poly(AN‐2MAETMS)], and poly[acrylonitrile‐(2 methacryloyloxy)propoxytrimethylsilene] [poly(AN‐2MAPTMS)] copolymers have been carried out for investigating their structure. The glass transition temperature as indicated from the dielectric and thermomechanical analysis data are lower for the copolymers as compared to PAN. Crystallinity is influenced by the introduction of the silylated acrylic comonomer units but the crystalline lattice remains similar to that of PAN. The changes obseved in the various properties of these coplymers clearly suggest a more closely packed structure of poly(AN‐2MAETMS) than poly(AN‐2MAPTMS), and the uninterrupted PAN sequences are longer in the former. Thermal stability of copolymers has also been investigated.

Relations between thermomechanical properties and chain folding of polyethylene terephthalate fibers

The molecular mechanism of the nonlinear relationship between the transition temperatures (T g resp.Tinm) and the outer tensile stress is discussed. On the basis of thermomechanical curves (deformation-temperature) taken at different external tensile force on drawn annealed PET fibers and films it has been shown that the transition temperatures depend nonlinearly on the applied tension stress. The maxima observed for bothT g andT m confirm the theoretical results ofCiferri andSmith andFrenkel assuming a crystallization of oriented polymer with chains in folded or helical conformation. A reasonable explanation is proposed for the increase ofT m followed by decrease and again increase with progressively rising of the applied tension stress using the model ofBonart-Hosemann for structure of semicrystalline polymers: at low tension values an orientation of macromolecules in noncrystalline zones takes place followed by defolding of chains from crystallites and finally (at highest tension values) an extreme stretching with additional orientation proceeds. This mechanism is supported by infra-red measurements. The thermomechanical data plotted as external tension divided by the corresp. melting temperature versus deformation confirm the theoretical curve derived byFlory. The experimental curves demonstrate that (1) the crystallization under strain with negative elongation as well as (2) the regeneration of the amorphous phase and its additional stretching are physically realisable situations when the crystallization is accompanied by chain folding or building of helices. It is shown that the thermomechanical method could be used as a simple tool for investigating the chain folding problem. The data reported are an additional proof of the existence of regular folded chains in the crystalline PET too.

Molecular Relaxations, Molecular Orientation and the Friction Characteristics of Polyimide Films

The friction characteristics of polyimide films bonded to metallic substrates were studied from 25 to 500 C. These results were interpreted in terms of molecular orientation and thermomechanical data obtained by torsional braid analysis (TBA). A large friction transition was found to occur at 40±10 C in a dry argon atmosphere (10 ppm H2O). It was postulated that the mechanical stresses of sliding transform or reorder the molecules on the surface into a configuration conducive to easy shear, such as an extended chain. The molecular relaxation which occurs in this temperature region appears to give the molecules the necessary freedom for this reordering process to occur. The effects of velocity, reversibility, and thermal prehistory on the friction properties of polyimide were also studied. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Miami Beach, Florida, October 21–23, 1975

Material Property Determination for Fast Pulsed Reactor Fuels by Rapid Fission Heating

A new experimental technique has been developed for dynamically measuring the thermomechanical properties of fissile materials. The speed of sound, modulus of elasticity, and coefficient of thermal expansion as a function of temperature for uranium alloys can be determined using the heating conditions that exist in a fast pulsed reactor. The technique was developed to provide thermomechanical property data for pulse reactor fuels under actual use conditions.

High polymers obtained using organometallic complexes containing lithium and titanium

AbstractHigh polymers with a regular chain structure have been produced by polymerization of ethylene with complexes containing crystalline organolithium compounds and titanium tetrachloride in organic solvents. For this purpose RLi compounds have been prepared, R being methyl, ethyl, butryl, dodeeyl, tolyl, mesityl, naphthyl, benzyl, and other aliphatic and aromatic groups. The investigation of the polymerization has led to the elucidation of the influence of the nature of the organic radical bound with lithium on the properties of polythene formed. Thermomechanical data, infrared and X‐ray spectra, as well as viscometric molecular weight determination, have shown all specimens of polyethylene to be highly crystalline and of a regular chain structure. The polymers obtained have mechanical properties characteristic of polyethylenes of this type but with elongations that strongly differ in polymers produced using organolithium complexes with different radicals at the lithium. With some specimen, elongation has been found to reach extremely high values. Some suggestions have been made as to the causes of influence of different organic radicals in RLi on the properties of polymers.