Acoustic emission of a crazing polymer

The acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment is described. Acoustic emission appears as a series of bursts which most likely correspond to the initiation and growth of crazes. The emission intensity is characterised by acoustic activity (pulse rate) measured by the ring-down technique. The average activity increases with strain. During repeated loading the acoustic activity shows a measurable intensity and significant rise only beyond the maximum strain of the former runs. This is equivalent to Kaiser's effect in metals. Acoustic emission during the creep experiment occurs in three characteristic periods. They are characterized as the relaxation, fatigue, and breakdown periods. Visual observations indicate that the relaxation period corresponds to the initiation, and the fatigue period to the growth of crazes. In the breakdown period a macroscopic crack develops and the sample fails.     

Acoustic emission in solid-liquid decomposition reactions

The chemical acoustic emission method was used to study solid-liquid decomposition reactions for the example of the interaction of potassium carbonate pellets with solutions of hydrochloric acid (HCl). The reaction was shown to follow different mechanisms at different hydrochloric acid concentrations (the concentration was varied from 0.12 to 12 M). An increase in the concentration of HCl not always caused an increase in the rate of generation of acoustic emission signals and, therefore, the reaction rate. The generation of acoustic emission was studied at various reaction stages. The advantages of the chemical acoustic emission method include measurements in real time (this is of importance for fast reactions, the reaction studied took no more than 5 min) and the possibility of determining rates at separate reaction stages. An automated acoustic emission unit was tested. The unit showed high reproducibility of measurement results, reliability, and rich possibilities for studying chemical acoustic emission in solids.     

Acoustic emission induced by tritium decay

An observation of signals of acoustic emission induced by tritium decay is reported. The equipment consisting of PZT detectors, preamplifiers, low-cut filters and computer evaluation was used in this study as a differential system. The result shows that the two types of clear signals of acoustic emission are induced by tritium decay. They seem to be related to some radiation effects due to tritium irradiation, and not to acoustic waves during tritium decay events.     

Acidic properties of fiberglass materials

Acidic properties of fiberglass materials were investigated using the adsorption of NH₃ and the rate of isopropanol dehydration. It is shown that the specific catalytic activity of such materials and amount of the Br?nsted acid sites per their surface unit (100 ?²) exceed considerably those in zeolite HZSM-5.     

Acoustic emission study of the TDCB test of microcapsules filled self-healing polymer

The failure process of self-healing microcapsule filled epoxy composites was investigated with Acoustic Emission (AE) measurement during tapered double cantilever beam (TDCB) tests. Unfilled, epoxy microcapsule filled and self-healing microcapsule (dual-microcapsules consisting of epoxy capsules and trifluoromethanesulfonic acid (TfOH) capsules) filled epoxy matrix specimens were compared. It was found that, with acoustic emission measurements, reliable data can be retrieved about the nature and progress of crack propagation and failure. Comparing the unfilled and the microcapsule filled specimens, considerably more AE hits were detected in the latter case due to the cracking of capsules and capsule-matrix debonding, which was confirmed by scanning electron microscopy investigations. Also, key differences were observed in the shape of the sum of AE hits curves and amplitude ranges of detected AE hits. Uniform distribution of the healing agent was demonstrated by energy-dispersive X-ray spectroscopy.     

Acoustic emission characterization of tensile damage in 3D braiding composite shafts

The acoustic emission (AE) method was used to monitor the tensile damage in a 3D braiding composite shaft. The 3D braiding composite shaft was manufactured via Vacuum Assisted Resin Transfer Moulding (VARTM) and the tensile experiment was conducted accompanied by AE monitoring. The AE signals were analyzed using the wavelet transformation for time-frequency analysis. The characteristic values of the AE signals were decomposed by the principal component analysis (PCA). The damage mode of the 3D braiding composite shaft under tension was identified and classified by the fuzzy clustering method (FCM). The results showed that the AE method could monitor the damage evolution process of the 3D braiding composite shaft under tension and the FCM combined with the PCA effectively divided the damage mode of the 3D braiding composite shaft. The results will provide an effective method for health monitoring of the 3D braiding composite shaft within engineering.     

Acoustic emission from cavitating solutions: implications for the mechanisms of sonochemical reactions

The acoustic emission from collapsing cavitation bubbles generated using ultrasound of 20 kHz and 515 kHz frequencies in water has been measured and correlated with sonoluminescence and hydroxyl radical production to yield further information on the frequency dependence of sonochemical reactions. A reasonable correlation was found, and the results suggest differences in the predominant types of cavitation observed under laboratory conditions.     

Continuous emission monitoring of metal aerosol concentrations in atmospheric air

Improvements of an apparatus for continuous emission monitoring (CEM) by inductively coupled plasma atomic emission spectrometry (ICP-AES) of metal aerosols in air are described. The method simultaneously offers low operating costs, large volume of tested air for valuable sampling and avoids supplementary contamination or keeping of the air pollutant concentrations. Questions related to detection and calibration are discussed. The detection limits (DL) obtained for the eight pollutants studied are lower than the recommended threshold limit values (TLV) and as satisfactory as the results obtained with other CEM methods involving air-argon plasmas.     

Atomic emission spectroscopy for the on-line monitoring of incineration processes

A diagnostic measurement system based on atomic emission spectroscopy has been developed for the purpose of on-line monitoring of hazardous elements in industrial combustion gases. The aim was to construct a setup with a high durability for rough and variable experimental conditions, e.g. a strongly fluctuating gas composition, a high gas temperature and the presence of fly ash and corrosive effluents. Since the setup is primarily intended for the analysis of combustion gases with extremely high concentrations of pollutants, not much effort has been made to achieve low detection limits. It was found that an inductively coupled argon plasma was too sensitive to molecular gas introduction. Therefore, a microwave induced plasma torch, compromising both the demands of a high durability and an effective evaporation and excitation of the analyte was used as excitation source. The analysis system has been installed at an industrial hazardous waste incinerator and successfully tested on combustion gases present above the incineration process. Abundant elements as zinc, lead and sodium could be easily monitored.     

Acoustic emission spectra from 515 kHz cavitation in aqueous solutions containing surface-active solutes

The effect of adding surface-active solutes to water being insonated at 515 kHz has been investigated by monitoring the acoustic emission from the solutions. At low concentrations (<3 mM), sodium dodecyl sulfate causes marked changes to the acoustic emission spectrum which can be interpreted in terms of preventing bubble coalescence and declustering of bubbles within a cavitating bubble cloud. By conducting experiments in the presence of background electrolytes and also using non-ionic surfactants, the importance of electrostatic effects has been revealed. The results provide further mechanistic evidence for the interpretation of the effect of surface-active solutes on acoustic cavitation and hence on the mechanism of sonochemistry. The work will be valuable to many researchers in allowing them to optimize reaction and process conditions in sonochemical systems.     

Study of thermohumid aging of aircraft fiberglass plastic

The thermohumid aging of aircraft fiberglass plastic over 5.5 years is studied. It is shown that, under conditions that simulate a tropical climate, the controlled parameters (maximal water saturation, moisture diffusion coefficient, shear modulus along the sheet plane) vary to the greatest extent after 1 year of aging, after which they stabilize. The molding conditions under which fiberglass plastic preserves high parameters under long-term exposure to a moist environment are determined.     

Acoustic emission evaluation of the fracture behavior of APS‐TBCs subjecting to bondcoating oxidation

Air‐plasma‐sprayed (APS) thermal barrier coatings (TBCs) under the conditions of without TBC, as‐sprayed and preoxidized, were tested under tensile loading, and their acoustic emission (AE) responses were monitored. AE parameters including event count, amplitude, and frequency spectrum realized by Fast Fourier Transformation (FFT) were analyzed for information regarding the fracture behavior of TBCs. On the basis of AE behavior, the fracture process of TBCs and corresponding cracking patterns in TBCs subjected to tensile tests were evaluated. AE results also showed that the bondcoating oxidation not only promotes the cracking but also changes the failure mode in TBCs. Copyright © 2007 John Wiley & Sons, Ltd.     

Acoustic emission potentialities for characterization of Mullins effect in natural rubber materials filled with carbon black

Acoustic Emission (AE) was investigated in order to monitor in real time the Mullins effect. Cyclic uniaxial tensile tests were carried out on two different natural rubbers. Different behaviour is revealed depending on whether or not the material undergoes the Mullins effect. The acoustic emission activity is very important during the first cycle, but decreases gradually with increasing number of cycles, when the Mullins effect is observed. On the contrary, when there is no Mullins effect no significant AE activity is recorded.     

Synthesis and DNA damaging ability of enediyne-polyamine conjugates

Polyamine-enediyne conjugates were synthesized and exhibited potent DNA damaging ability under physiological conditions. The extent of their activity was shown to depend upon the polyamine length that regulates the DNA binding affinity of the conjugates, and enhanced DNA damaging activities were observed under slightly acidic conditions.     

Detection of DNA damaging agents using layer-by-layer assembly

The layer-by-layer (LBL) electrostatic deposition method was used to fabricate multilayer films of pentaerythritol-based metallodendrimer with Ru^II terpyridine subunits (RuDen) that has a positive charge and ds-DNA (ds, double-stranded) that has a negative charge due to its phosphate backbone. Evidence of assembly was obtained by fabrication of (DNA | RuDen)_n on quartz treated with poly(diallyldimethylammonium chloride), PDDA. The absorbance at 263 nm varied linearly with n in the range 1-6. For electrochemical monitoring of damage by styrene oxide, the assembly was on a glassy carbon electrode that was coated with a monolayer of aminobenzoic acid. The measurement was based upon the RuDen-catalyzed oxidation of sites, e.g. guanine, that are exposed when ds-DNA is damaged. The peak current at 1.07 V versus Ag | AgCl in square wave voltammetry increases with incubation time for 30 min. The process was also monitored by the shift in the spectrum of a long period grating (LPG) fiber coated with (DNA | RuDen)₅. A typical shift, which is due to changes in the refractive index of the coating, was 0.3 and 1.8 nm for 5 and 30 min exposures, respectively, using an algorithm that can measure a shift of 10⁻⁴ nm.     

On mass- and emission spectroscopic CVD process monitoring of organometallics/O2 discharges

Mass spectroscopic analysis of neutrals and ions from a deposition plasma shows that the decomposition of the organometallic precursor compounds [La(thd)₃, Cu(acac)₂, and Al isopropoxide] in the plasma .starts with the abstraction of complete ligands. The mass spectra of plasma ions sensitively indicate the incomplete oxidation of the organic fragments with increasing organometallic partial pressure. The concentration of carbon-rich ions in the oxygen-based deposition plasma correlates with the carbon content of the deposited oxide films. Specific emissions of the precursor compounds (e.g., Cu atomic lines and LaO bands) can be used to monitor the precursor partial pressure; however, there is some interference with sputter emission from the deposited films. During La₂O₃ deposition, optical emission of oxidation products (e.g., OH, CO, CO₂ bands) was used to regulate the precursor partial pressure in the discharge with a closed-loop control circuit.On leave from Friedrich Schiller University, Institute of Physical Chemistry, Lessingstrasse 10, D-O-6900 Jena, Germany.On leave from California State University, Department of Chemistry, 2555 East San Ramon Avenue, Fresno, California 93740-0070.     

On-line monitoring of a frontal chromatographic separation using inductively coupled plasma atomic emission spectroscopy

A test array is described employing a destructive analytical technique for the long-term monitoring of an industrial-scale separation process. As an example, we chose frontal chromatography as the separation and ICP/AES as the analytical method. The feed solution of the process was conveyed by a process pump via the separation unit to a sample station, where a small portion was diverted and transported by a roller pump into the spectrometer. We equipped our array with different loops for operating the process, calibrating the instrument and verifying the calibration. We obtained identical results for the different loops by absorbing the pulsation of the process pump and arranging for identical suction lines of the spectrometer pump. Based on the results, we redesigned the sample station for a technical application using only commercially available parts.     

Mitochondria-targeted fluorescent probe based on vibration-induced emission for real-time monitoring mitophagy-specific viscosity dynamic

Directly monitoring mitophagy-specific viscosity dynamic in living cells is of great significance but remains challenging. Herein, this study reported a novel mitochondria-targeted fluorescent probe DPAC-DY based on vibration-induced emission (VIE) for monitoring viscosity changes during mitochondrial autophagy. This probe contained N,N'-diphenyl- dihydrodibenzo[a,c]phenazine (DPAC) as the VIE core and two positively charged pyridinium moieties for mitochondria anchoring. As the ambient viscosity increased, the vibration of DPAC-DY could be hindered, and subsequently resulting in the enhancement of fluorescence emission. In vitro and intracellular experiments indicated that the probe DPAC-DY showed highly sensitive response to viscosity due to VIE mechanism. Importantly, by virtue of this probe, in situ and real-time visualization of the specific viscosity dynamics during the mitochondrial autophagy process was achieved. Thus, this work provides a novel strategy for VIE-based viscosity response sensors applied to specific organelles and offers a platform for in-depth study of mitochondrial viscosity-related diseases.