Charge storage and relaxation process of polymer film by thermally stimulated discharge current technique

Charge storage and relaxation process of the polymide film electret were investigated using the thermally stimulated discharge current technique. Homo- and heterocharges were mainly observed up to and above the polarization temperature.     

ChargingE-perm for radon measurements

Recharging of commercial E-perm electret detectors used for radon measurement has been investigated. The E-perm was recharged using the poling charging method where a high voltage is applied on a metal nozzle to polarize the electret material. The optimum parameters to recharge the electrets were 5 kV charging voltage and 7 mm height of the nozzle from the electret surface and using an insulator while charging. Under these conditions, charging of E-perm carried out for 15 s attained required voltage and retained the charge for long durations. The response of recharged E-perm for radon activity measurements in a radon calibration chamber and in an open environment was compared with that of CR-39 detectors. Results showed close proximity in radon values.     

Correlation between charge decay and solvent effect for melt-blown polypropylene electret filter fabrics

Melt-blown polypropylene electret fabrics are widely used as air filter media. However, its filtration efficiency gradually decays in application process. This paper is to investigate the correlation between filtration efficiency decay and solvent effect. Experimental results show that filtration efficiency displays a regular decrease when polypropylene electret fabrics are exposed to solvents in the sequence of water, ethanol, isopropanol and acetone. The results can be correlated to solubility parameter difference between polypropylene and solvent according to the Flory–Huggins swelling theory. Smaller solubility parameter difference leads to greater decay of filtration efficiency owing to greater affinity between polypropylene and solvent.     

聚2,6—萘二甲酸乙二醇酯驻极体的研究

实验观察到双轴拉伸聚2,6-萘二甲酸乙二醇酯(PEN)的γ-辐射诱导我流子品种转变现象,检测到发生转变的剂量范围,在γ-辐射诱导陷阱变浅的实验基础上讨论了载流子品种转变的实质,研究了非晶及双拉PEN热驻极体在γ-辐射激励下电荷储存、迁移机理及解驻极效应。     

Influences on indoor radon concentrations in Riyadh,Saudi Arabia

The influences on indoor radon concentrations in Riyadh, Saudi Arabia survey was carried out for 786 dwellings. The measurements were obtained by using a passive integrating ionization system with an E-Perm^® Electret ion chamber. Radon levels ranged from 1 to 195 Bq m⁻³, with a mean value of 24.68 Bq m⁻³, the geometric mean and the geometric standard deviation are 21 and 2 respectively. 98.5% of the results were below the action level recommended by WHO of 100 Bq.m⁻³. The results were found to vary substantially due to types of houses and rooms, ventilation, seasons and building materials. Radon concentrations were higher in houses with no ventilation systems, and central air conditioners, and were relatively lower in well ventilated houses with red bricks and water air conditioners.     

Physical mechanism of the electrical polarization of polyethylene terephthalate

The relation between the structural and dynamical properties of amorphous and partially crystalline polyethylene terephthalate and its electret properties was analyzed. The thermal stability of polarization charges and space charges was found to increase with aging in the glassy state and with increasing degree of crystallinity. The discharge behavior was governed by the interaction of real charges and polarization charges. The combination of different charging techniques resulted in a linear superposition of the respective discharge processes on heating.     

Measuring electrostatic properties of fibrous materials: A review and a modified surface potential decay technique

Electrostatic charging of fibrous materials are of concern for the performance of electret filters and comfort issues of textiles. However there is a huge controversy in the characterization techniques of ion beam irradiated or corona charged fibrous materials. In this study we reported a reliable, simple surface potential measurement method. Large variations in potential measurements were found to be mostly due to structural nonuniformity such as packing density, thickness and fiber–fiber proximity. Test samples were prepared after optimizing those parameters and we were able to reduce coefficient of variation below 15%. Methods that were developed so far were also reviewed.     

Enhancement of filtration efficiency by electrical charges on nebulized particles

There have been few investigations of effects of electrical charge, carried by lab-generated particles, on filtration efficiency testing. Here, we measured the elementary charge on particles and the fraction of particles carrying that charge with a combined electrometer, differential mobility analyzer, and scanning mobility particle sizer. A typical solid NaCl aerosol and liquid diethylhexyl sebacate (DEHS) aerosol were generated with Collison and Laskin nebulizers, respectively. Our experimental results showed that NaCl aerosols carried more charge after aerosol generation. The average net elementary charge per particle was approximately 0.07. The NaCl aerosol was overall positively charged but contained a mixture of neutral and charged particles. Individual particles could carry at most four elementary charges. According to constant theorem, we speculated that original NaCl aerosol contained 17% neutral, 45% positive-, and 38% negative-charged particles in the diameter range from 30 to 300 nm. A Kr-85 neutralizer was used to decrease the charge on the NaCl particles. Our results indicated that the DEHS aerosol was electrically neutral. The effects of electric charge on particle collection by electret and electroneutral high efficiency particulate air (HEPA) filters were analyzed. Theoretical calculations suggested that charges on original NaCl aerosol particles enhanced the filtration efficiency of HEPA filters.     

The effect of humidity on the accuracy of measurement of an electret radon dosimeter

Test has been conducted for the response of electret radon dosimeters with varying levels of humidity. At a constant value of radon concentration, measured values have been found to increase linearly with increasing humidity, from 30% RH up to a value of 85% RH. On this basis we argue for the establishment of a humidity-dependent calibration factor.     

Formation of calcite thin films by cooperation of polyacrylic acid and self-generating electric field due to aligned dipoles of polarized substrates

We demonstrated the formation of calcite thin films on positively and negatively charged surfaces of a hydroxyapatite (HAp) electret coexisting with polyacrylic acid (PAA) and self-generating surface electric fields due to HAp electrets with electrically aligned dipoles. The cooperation of PAA and the self-generating surface electric field due to the electrets favored the formation of calcite thin films and acted remarkably on the negatively charged surface. Calcite thin films, 4–10 μm thick, with a shell-like microstructure were produced on the negatively charged surfaces with a small amount of PAA. In contrast, under other reaction conditions, calcite thin films with a fan-like structure in the cross section formed on the polarized substrates, and their thickness ranged from 2 to 7 μm. The films were composed of hemispheric- or flat island-shaped aggregates that were made of the calcite crystals that elongated along the c-axis. The morphology of the PAA–Ca²⁺ complex assembly, which adsorbed onto the polarized HAp substrates, was controlled by the balance of the spatial charge distribution in its structure and the properties of the self-generating surface electric field, which led to the different morphologies of the calcite thin films. We proposed that the formation mechanism of the films formed coexisting with PAA and the self-generating electric fields.