Air-Coupled Ultrasonic Cure Monitoring of Unsaturated Polyester Resins

Air-coupled ultrasound in one-side transmission mode has been applied to monitor the curing process of an unsaturated polyester resin, commonly used as a matrix in glass reinforced composites. The evolution of the resin mechanical properties during cure has been measured from the variation of longitudinal velocity. The technique has demonstrated to be a very powerful tool for detecting the structural changes occurring at gelation and vitrification. The no-contact ultrasonic results have been compared with those obtained using conventional contact ultrasonic measurements, characterized by direct coupling between the transducer and the resin, and with the rheological measurements. The good agreement among the results of the different techniques demonstrates the reliability of air-coupled ultrasound in monitoring the changes of viscoelastic properties occurring during the cure of thermosetting polymers. A further advantage of the proposed one-side ultrasonic technique is the absence of physical contact between the transducers and the sample, which is relevant during composite manufacturing, where probe contact could adversely affect the part quality or access from both sides is not practicable. No-contact ultrasonic cure monitoring is suitable for both stationary and moving liquid or solid samples in several process conditions such as moulding, filament winding, etc., opening the way to new applications of ultrasound in the composite industry.     

Ultrasound monitoring of the cure kinetics of an epoxy resin: Identification,frequency and temperature dependence

In this paper the monitoring of ultrasonic parameters of a thermosetting resin during an isothermal curing process is described. The ultrasonic properties are studied within the context of the monitoring of composite plate production by resin transfer molding (RTM). These ultrasonic characteristics can be related directly to cure kinetic models. An ultrasonic method, based on the measurement of the elastic constant and associated mechanical loss has been developed to identify the variations of the phase transformation. To study the reaction kinetics, the time dependence of the elastic coefficient is modeled using a Weibull distribution. The approximate time derivative form of this Weibull model makes it possible to find the relationship between ultrasonic parameters and the chemical Kamal model. The ultrasonic monitoring of a cooling process was also performed to study the temperature sensitivity after curing. Thanks to experimental measurements of the ultrasonic velocity and attenuation, the power law coefficient variations and their temperature sensitivity can be examined. The resulting viscoelastic Cole-Cole parameters were estimated and a frequency-temperature (f, T) model was proposed.     

Measurement of High Energy Gross Beta and 40K by Cerenkov Counting in Liquid Scintillation Analyser

The Environmental Survey Laboratory is responsible for the monitoring of radioactivity due to natural and artificially produced radionuclides in a variety of samples available around the nuclear facilities at Tarapur. Standard methods of radiochemical separation and counting are followed to determine -emitters in various matrices. To make the measurement simple and detect lower levels of contamination in some of the matrices, a method was developed to measure the high energy gross -activity primarily due to ⁹⁰Y in borehole water and urine samples of occupational workers by Cerenkov counting in a liquid scintillation analyser. Cerenkov counting results of borehole samples were compared with the total gross -activity measured by a low background beta-counter. The combined measurements were used to evaluate ⁹⁰Sr and ¹³⁷Cs levels without chemical separation or gamma-spectrometry. Cerenkov counting technique was also utilised to evaluate ⁴⁰K in drinking water and intercomparison water samples. The paper presents the methodology and results of a few measurements using the technique.     

Matrix reference materials – provision in Australia

 Until quite recently, Australia has not been much involved in the preparation and certification of matrix reference materials for chemical testing. Even today, the vast bulk of chemical reference materials used in Australia are imported from other world producers. Increased international focus on the accuracy, traceability and comparability of chemical measurements has led to the establishment of the National Analytical Reference Laboratory (NARL) within the Australian Government Analytical Laboratories. Part of the work of NARL will be to supply matrix reference materials, not available from existing sources, to meet specific Australian requirements. This need has been addressed in the past by a combination of industry and government initiatives. Examples include a series of certified matrix reference materials for chemical testing of iron ore, coal and mineral sands produced by Standards Australia and a series of three animal fat matrix reference materials certified for a range of pesticide residues produced by the Australian Chemical Standards Laboratory (now part of NARL). To make effective use of limited resources, it will be important for NARL to focus on identified priorities and to maximise the use of available Australian resources and expertise through technical collaboration for reference material production. An important part of this process should be input on needs and priorities from reference material "users" such as government legislators, regulatory authorities, standards setting bodies, industry and the analytical community. The aim will be to produce matrix certified reference materials that are traceable to SI or other international standards at a stated level of measurement uncertainty.     

Wavelength dependencies in interferometric measurements of thin protein films

Summary The evaluation of the spectral modulation in reflectance measurements at thin dielectric films allows the characterisation of layers in the m-range. Diode array spectrometers make this technique a useful tool in sensor development. The variation of the optical pathlength in thin films due to change of refractive index or to change of physical thickness of a homogeneous layer has been applied to refractometry and detection of hydrocarbons by polymer swelling. More recently, the monitoring of solid-phase affinity reactions, like immunoassays has successfully been demonstrated. While the homogeneous layer concept is useful for data evaluation in the first two cases, it has its limitations for the treatment of adlayer formation as in the latter case. This is discussed with respect to results from affinity reactions carried out at optically different interference layers.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Sensor integration in rubber gaskets for structural health monitoring made by compression molding

This research work shows the integration process and characterization of a miniaturized strain gauge sensor in rubber O-rings for structural health monitoring (SHM). Strain gauges have been successfully embedded during compression molding, which is a commonly used fabrication method of rubber components. The sensor signal is correlated with the contact pressure of the gasket that abates over time due to aging processes. This can be exploited for lifetime prediction. Embedding sensors into rubber applying compression molding is a novel method that allows the integration into non-liquid elastomers. The strain gauge resistance correlates linearly to the contact pressure. An artificial aging test exhibits an exponential decrease in the resistance caused by the relaxation processes during the accelerated aging of the elastomer at 70 °C for 72 h. Uniaxial tensile testing with dumbbell specimens reveals the influence of the integrated sensors. It is demonstrated that the influence heavily depends on the sensor size.     

Molecular Interactions in 1,4-Dioxane,Tetrahydrofuran, and Ethyl Acetate Solutions of 1,1′-Bis(4-isopropyloxyacetylphenoxy)cyclohexane on Reological,Density, and Acoustic Behavior

Various thermo-acoustical parameters of 1,4-dioxane, tetrahydofuran and ethylacetae solutions of 1,1′-bis(4-isopropyloxyacetylphenoxy)cyclohexane were determined at different temperatures using density, viscosity and ultrasonic speed and correlated with concentration. Linear increase of ultrasonic speed, specific acoustical impedance, Rao’s molar sound function, Van der Waals constant and free volume with concentration C and decreased with temperature. Linear decrease of adiabatic compressibility, internal pressure, intermolecular free path length, classical absorption coefficient, and viscous relaxation time with concentration and increased with temperature indicated existence of strong molecular interactions in solutions and further supported by positive values of solvation number. Gibbs free energy of activation decreased with C in all three systems. It is decreased with T in 1,4-dioxane, while increased in tetrahydrofuran and ethyl acetate. Both enthalpy of activation and entropy of activation are increased gradually with C in 1,4-dioxane, while they are negative and remained practically independent of concentration in 1,4-dioxane and tetrahydofuran systems.     

Techniques used for determining cure kinetics of rubber compounds

Controlling and assuring the quality of the manufacture of high precision engineering rubber components has led to the need to simulate fundamental industrial processes such as compression molding and injection molding using CAE tools. Both compression and injection molding techniques for the fabrication of rubber products involve crosslinking or vulcanization which is invariably assisted by temperature and pressure. Vulcanization is a chemical process and therefore its simulation necessarily involves characterization of kinetic parameters. The kinetics of curing or vulcanization is somewhat complex as it depends upon the compound formulation, temperature and in some cases pressure. The present paper reports and discusses the application and utility of different techniques for characterizing the cure behavior of rubber compounds. Kinetic data has been fitted to various mathematical models in order to see which of the models can best represent the crosslinking behavior of selected rubber compounds. Finally, the kinetic data is used to simulate the injection molding process for relatively simple geometries.     

Thermal and mechanical characterization of high performance epoxy systems with extended cure times

Five epoxy resins of different chemistry and functionality were cured with DDS (4,4-diaminodiphenyl sulfone) using 2, 8 and 14 h curecycles. Both Differential Scanning Calorimetry (DSC) and Thermomechanical Analysis (TMA) were used to characterize reaction behavior and cured properties of the resin systems. In addition, static mechanical tests and density measurements were integrated with the thermal characterization methods to correlate resin properties with process time. Flexural three-point bending experiments showed that the resins tended to have higher yield stress and toughness values at extended cure times. The improved mechanical properties could be attributed to the full development of the epoxy molecular structure, in the form of cross-linked networks and molecular rearrangement. These results suggest that extended cure times or high temperature post-curing may be required to obtain the resin's ultimate mechanical properties for high performance composites.The authors would like to thank Dr. Andri Filippov of Shell Development Company for his interest in this work. Financial assistance and material support for this research were provided by Shell Development Company while instrument support was provided by TA Instruments through project support to the Polymeric Composites Laboratory of the University of Washington.     

Determination of alpha contaminated soil profiles using Nuclear Track Detectors

Nuclear Track Detectors (NTD's) are a useful option forin situ measurements of the distribution of alpha contamination as a function of soil depth. The contamination profile of alpha emitting elements, e.g. Pu, Am and U, can be determined by detecting their alpha emission at varying depths. This paper discusses a stake type device, containing strips of CR-39 (allyl diglycol carbonate) that can be inserted into the soil up to ten centimeters or more, depending on the firmness of the soil. The CR-39 is exposed directly to the contaminated soil for a few hours. The stake is then withdrawn from the soil, the plastic detectors recovered and the alpha tracks developed by chemical etching with KOH. The distribution of tracks can be used to determine the alpha contamination depth profile as well as for detecting hot spots. It has a sensitivity of less than a pCi/g of soil.Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-ENG-48.     

The role of metrology in chemistry in the upholding of public health and food safety in Hong Kong

The Government Laboratory has been involved in the provision of analytical and advisory services since its formal establishment in 1913 in support of the needs of the community and the commitments of the Government of Hong Kong Special Administrative Region, China. One of the earliest areas of work involves the testing of food samples for maintenance of public health and food safety. Remarkable advances in technology in recent years coupled with the introduction of new policies and regulations, the launching of new international standards and requirements have all contributed to significant and ever-rising demand of accurate, specific, comparable and traceable measurements using the latest technologies for a wide variety of additives, contaminants, residues and genetically modified ingredients in food.Metrology, the science of measurement, has always played a key role in the development and validation of analytical methodologies in the Government Laboratory for the realization of its measurements to the highest level of accuracies and traceability to internationally recognized standards. Besides the application of the latest analytical technologies such as isotope dilution mass spectrometry, tandem mass spectrometry, real-time polymerase chain reactions, etc., the Analytical and Advisory Services Division of the Laboratory develops a quality assurance system in full compliance with the requirements of ISO/IEC 17025 and endeavours to ensure that every analytical methods are validated with the best applicable means and are fit for the intended purposes. In this presentation, the role and application of metrology in chemistry in the measurements pertaining to public health and food safety work undertaken by the Government Laboratory are discussed.Presented at International Symposium on Metrology in Chemistry, 2004 Beijing, China.     

Achieving traceable chemical measurements: inter-laboratory evaluation of a simplified technique for isotope dilution mass spectrometry (IDMS). Part 1: Methodology for high accuracy analysis of trace metals

A high accuracy measurement procedure developed and validated at the Laboratory of the Government Chemist (LGC) has been transferred to a number of expert United Kingdom laboratories and their experience in applying the technique has been evaluated by inter-laboratory comparisons. It is an approximate matching calibration procedure for analysis of trace metals using isotope dilution mass spectrometry (IDMS). Use of a calibration blend and a sample blend having closely matched isotope amount ratios reduces systematic errors. Four comparisons were carried out, each evaluating an increasingly difficult aspect of the methodology. The final study required determination of trace levels of cadmium in an artificial food matrix acid digest containing tin, using both external calibration and approximate matching IDMS. The results of the trials clearly showed the superior accuracy of the IDMS approximate matching procedure; a result within 1% of the target reference value could be achieved. These trials and a training workshop enabled LGC to transfer its methodology to other expert laboratories, helping to improve the United Kingdom delivery of traceable reference measurements.     

Thermal analysis of heritage stones

Many of Sydneys heritage buildings and monuments were built as a result of the first European settlement in the 1800s. These buildings not only display the richness of the Australian culture, but also capture the architectural and historical values of its past. Although many of these buildings still appear to be strong and sound, many signs of deterioration have been detected in recent years. Conservators from various disciplines such as science, architecture and engineering are working closely together to develop suitable solutions to stop or at least slow down the degradation process of these precious buildings. This study demonstrates the usefulness of thermal analysis in determining the weathering mechanisms of marble and sandstone taken from two of Sydneys landmarks, the Captain Arthur Phillips Monument at Sydneys Botanic Gardens and Sydneys St Marys Cathedral. This paper reports the findings of the weathering behaviours of both marble and sandstone samples determined using thermal analysis techniques.     

Characteristic analysis of cavitation bubbles in carbon dioxide fluid

After analysing the characteristics of bubble cavitation in high-pressure carbon dioxide (CO₂) fluid, cavitation conditions and some correlative physical characteristics are investigated. The results show that the ultrasonic intensity of liquid carbon dioxide to make cavitation occur is affected by the initial radius of the bubbles, hydrostatic pressure, temperature and vapour pressure within the bubbles in liquid CO₂. At the low frequency of ultrasound, the phase-speed of the liquid CO₂ gradually approaches the sound speed of the pure liquid when void fraction increases. At high frequency, the phase-speed is nearly equal to the sound speed in the liquid under different void fractions. The attenuation of ultrasound in liquid carbon dioxide reaches a maximum near the resonance frequency and then decreases when frequency either increases or decreases. At the resonance frequency, the phase-speed and the attenuation increase when the void fraction increases.     

Volumetric,Viscometric and Speed of Sound Studies of Binary Mixtures of <Emphasis Type="Italic">Tert</Emphasis>-butyl Acetate with Fluorobenzene,Chlorobenzene and Bromobenzene at (298.15 and 308.15) K and at Atmospheric Pressure 0.087 MPa

Volumetric, viscometric and speed of sound studies of binary mixtures of tert-butyl acetate with fluorobenzene, chlorobenzene and bromobenzene have been made over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure (p?=?0.089 MPa). From the experimental values of density, viscosity, and speed of sound, the excess molar volumes V^E, deviations in viscosity ?η and deviation in isentropic compressibility ΔK _S have been calculated. The V^E and ΔK _S values are negative while the ?η the values are positive over the entire composition range for the binary mixtures. The derived parameters have been fitted with the Redlich–Kister polynomial equation. The interaction parameters of McAllister model are used to correlate the experimental values of density, viscosity and speed of sound.     

Formation of a highly ordered poly (N,N'-bis-phenoxyphenylpyromellitimide) powder using a high pressure curing technique

A high-pressure curing technique was developed to help determine the effects of solvent presence during the thermal curing of the polyimide poly (N,N'-bis-phenoxyphenylpyro-mellitimide) (PMDA-ODA). A powder form of this aromatic polyimide was produced from a polyamic acid solution using the high-pressure thermal curing technique. Preliminary characterization of the powder indicates a high degree of crystallinity with a measured density of 1.46 ± 0.01 g/cm³ and a distinct melting point of 594°C. The addition of chemical curing agents to the polyamic acid solution prior to thermal treatment reduced the amount of crystallinity observed in the cured material. Molecular weight measurements of the polyamic acid precursor and powder suggest that the high degree of order observed in the powder is a result of degradation during cure. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America

     

Gamma-ray signatures for state-of-health analysis and monitoring of widely-arrayed radiation portal monitor systems

Pacific Northwest National Laboratory (PNNL) has deployed a large array of radiation portal monitors for the Department of Homeland Security and U.S. Customs and Border Protection. These portal monitors scan incoming vehicles crossing the U.S. border and shipping containers leaving international ports for radioactive material via gamma-ray and neutron detection. Data produced and captured by these systems are recorded for every vehicle related to radiation signature, sensor/system status, local background, as well as a host of other variables. Within the Radiation Portal Monitor Project at PNNL, state-of-health observation and analysis for the whole RPM array using these data to determine functionality and performance is ongoing. Advanced state-of-health analysis and monitoring algorithms are being developed. Preparations are underway to incorporate the more difficult state-of-health monitoring of the mobile RPM and Advanced Spectroscopic Portals.     

Equation of state of water under negative pressure

We report on the simultaneous measurements of the speed of sound and the density in liquid water under negative pressure. Application of a focused acoustic wave to the bulk liquid is able to generate negative pressures before nucleation of the vapor phase occurs. A method for time-resolved Brillouin scattering is developed to measure the speed of sound during the passage of a 1 MHz ultrasonic wave. This is coupled with a fiber optic probe hydrophone which allows the determination of the density. Together, these methods give an ambient temperature equation of state of metastable liquid water down to the acoustic cavitation threshold. Empirical equations of state of water are based on experimental data at positive pressure; the validity of their extrapolation to negative pressures had been tested only indirectly or with very weakly metastable liquid. We provide thermodynamic data that prove the fidelity of recent equations of state down to -26 MPa. However, this raises questions regarding the nature of the cavitation threshold observed in acoustic experiments, which is far less negative than expected.     

Nuclear decay studies of fission-product nuclides using an on-line mass separation technique

An isotope-separator-on-line (ISOL) system has been developed at the Idaho National Engineering Laboratory to enable a wide variety of nuclear decay studies to be made for fission-product radionuclides. The system is unique in that it utilizes the spontaneous fission source,²⁵²Cf, as the source of fission-product radioactivity. Fission products are transported to the ion source of the mass separator by the helium gas-jet technique. Mass-separated beams of previously unattainable rare-earth nuclides are produced with this system because of the higher yield of fission products with A>150, relative to that for thermal-neutron fission of²³⁵U, and the use of a relatively efficient ion source. Recent decay studies reported here include systematic measurements of rare-earth nuclide half-lives and comparison of them to theoretical prediction, a decay scheme investigation for¹⁵⁴Nd, and -strength function measurements for¹⁴⁰Cs.     

Activation energy determinations from dielectric thermal analysis of reacting polymeric systems

Methods were developed for calculating reaction activation energies from dielectric property measurements during isothermal and nonisothermal cure of thermosetting polymers. These methods were derived by assuming that features of the dielectric response occurred at unique extent of reaction values. Activation energy results were obtained through dielectric analysis for two thermosetting resin systems: a model epoxy system — tetraglycidyl-4, 4-diaminodiphenylmethane cured with 25 parts per hundred of 4,4-diaminiphenylsulfone hardener; and a model dicyanate blend resin, 55% (by weight) of bisphenol A dicyanate and 45% of tetrao-methyl bisphenol F dicyanate. Results were in excellent agreement with activation energies determined from differential scanning calorimetry measurements.

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Zusammenfassung Es wurden Verfahren zur Berechnung der Aktivierungsenergien aus dielektrischen Messungen der isothermen bzw. nichtisothermen Aushärtung von Duroplasten entwickelt. Dabei wurde angenommen, daß die dielektrische Antwort bei einem einzelnen Wert der Reaktionswerte erfolgt. Die Aktivierungsenergie-Ergebnisse wurden für zwei Duroplast-Harze ermittelt: ein Epoxysystem — Tetraglycidyl-4,4-diamonidiphenylmethan, gehärtet mit 25% 4,4-Diaminodiphenylsulfonhärter; und ein Dicyanatmischharz aus 55 Gew.% Bisphenol A Dicyanat und aus 45 Gew.% Tetra-o-methylbisphenol F Dicyanat. Die Ergebnisse stehen in guter Übereinstimmung mit den aus DSC-Messungen erhaltenen Werten.

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The authors would like to thank Dr. M. A. Bachmann of ICI, Dr. R. B. Prime of IBM, and Dr. E. M. Woo of the Polymeric Composites Laboratory and currently with Boeing Commercial Airplane Group, for helpful discussions in the development of this technique. In addition, the expert coordination for the project provided by Ms. Louise Peterson and Dr. Kyujong Ahn, as well as Shangying Zeng in analyzing the dicyanate data at the Polymeric Composites Laboratory, is gratefully acknowledged. Equipment support for this project was provided by Tetrahedron Associates and TA Instruments (formerly DuPont Instruments), through their participation at the Polymeric Composites Laboratory consortium at the University of Washington. Financial assistance for this work was provided by ICI, and the National Science Foundation Grant # MSM 8352414.