RESUMO
The characteristics of the VOCs species in foundry industries based on the production processes were analyzed through gas chromatography-mass spectrometry (GC-MS) after sampling the emissions of VOCs in 9 typical foundry enterprises using air packages and absorption tubes. The source profiles of the VOCs species in foundry industries based on production processes were established for the first time in China. In addition, the emission characteristics of VOCs and the contribution of VOCs emitted by various production processes to ozone generation were also studied. The results showed that the characteristic components of the VOCs in foundry industries were predominantly aromatic hydrocarbons, halogenated hydrocarbons, and oxygenated hydrocarbons. The average concentrations were 50.9%, 20.8%, and 12.6%, respectively. In general, aromatic hydrocarbons, such as toluene, benzene, and m/p-xylene; halogenated hydrocarbons, such as trichloroethylene and dichloromethane; oxygenated hydrocarbons, such as acetone, ethyl acetate, cyclopentanone, and some alkanes, were the primary VOCs species of the foundry industries. The emission characteristics of different production processes were related to the solvents and surface treating agents used by each process. The results also demonstrated that painting was the largest contributor of VOCs concentrations among all the production processes, followed by the modeling procedure and the silica sol and pouring processes. The OFP values for the different production processes ranged from 0.29-96.09 mg·m-3. Painting was the largest contributor to OFP, followed by the modeling procedure and the melting and pouring processes. Aromatic hydrocarbons and oxygenated hydrocarbons were the dominant contributors to OFP, and 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, toluene, and m/p-xylene were the main active components in the foundry industry, with a total contribution to the ozone generation potential of nearly 60%. It is suggested that the painting process should be prioritized regarding control measures to reduce its emissions and impact, while the waste gas from the modeling procedure and the melting and pouring processes should be collected efficiently and treated properly before being discharged to the environment.
RESUMO
In order to improve the mechanical and dielectric properties of radome cyanate, a synergistic reinforcement method is employed to develop a resin-based ternary-composite with high heat-resistance and preferable radar-band transmission, which is expected to be applied to fabricate radomes capable of resisting high temperature and strong electric field. According to copolymerization characteristics and self-curing mechanism, epoxy resin (EP) and bismaleimide (BMI) are employed as reinforcements mixed into a cyanate ester (CE) matrix to prepare CE/BMI/EP composites of a heat-resistant radome material by high-temperature viscous-flow blending methods under the catalysis of aluminum acetylpyruvate. The crystallization temperature, transition heat, and reaction rate of cured polymers were tested to analyze heat-resistance characteristics and evaluate material synthesis processes. Scanning electron microscopy was used to characterize the micro-morphology of tensile fracture, which was combined with the tensile strength test and dynamic thermomechanical analysis to investigate the composite modifications on tenacity and rigidity. Weibull statistics were performed to analyze the experimental results of the dielectric breakdown field, and the dielectric-polarization and wave-transmission performances were investigated according to alternative current dielectric spectra. Compared with the pure CE and the CE composites individually reinforced by EP or BMI, the CE/BMI/EP composite acquires the most significant amelioration in both the mechanical and electrical insulation performances as indicated by the breaking elongation and dielectric breakdown strength being simultaneously improved by 40%, which are consistently manifested by the obviously increased transverse lines uniformly distributed on the fracture cross-section. Furthermore, the glass-transition temperature of CE/BMI/EP composite reaches the highest values of nearly 300 °C, with the relative dielectric constant and dielectric loss being mostly reduced to less than 3.2 and 0.01, respectively. The experimental results demonstrate that the CE/BMI/EP composite is a highly-qualified wave-transmission material with preferences in mechanical, thermostability, and electrical insulation performances, suggesting its prospective applications in low-frequency transmittance radomes.
