Albraa A. Jaber

The feasibility of measuring the surface potential decay of polystyrene (PS) film is investigated at room temperature by using Kelvin probe force microscopy (KPFM). The PS film was charged by an ion injection method utilizing Bruker's atomic force microscope (AFM) Nanoman module with a pulse duration of 1 ms, SCM‐PIT electrically conductive probe, and a voltage pulse of −250 mV. The surface potential decayed linearly on a semi‐log scale with time, where the time decay constant was quantified for relative humidity (RH) = 5% by KPFM at room temperature. The surface potential decayed due to the interaction of the PS film with the hydronium ions available in the environment. Furthermore, the effect of the material forms (film vs. microspheres) on the time decay constant at RH = 5% was investigated. The time decay constants measured using different methods exhibited excellent correlation with the AFM‐KPFM. This also confirmed that the results are independent of the material form (microspheres vs. film form). As a result, the proposed method can be used to measure the effect of RH for any PS surface (i.e., particles of various sizes and films) exposed to these environmental conditions.

Fiber sizing is one of the most important components in manufacturing composites by affecting mechanical properties, including strength and stiffness. The sizing of manmade fibers offers many advantages, such as improving fiber/matrix adhesion and bonding properties, protecting fiber surfaces from damage during the processing and weaving stages, and enhancing the surface wettability of polymer matrices. In this work, the influence of fiber sizing levels on carbon fibers’ (CFs) mechanical properties is reported at room temperature using single fiber tensile testing (Favimat+), single fiber pullout testing (SFPO), and interfacial elemental analysis by X-ray photoelectron spectroscopy (XPS). Standard modulus CFs (7 ± 0.2 μm in diameter) were sized using two commercially available Michelman sizing formulations. The average solid content for each sizing formulation was 26.3 ± 0.2% and 34.1 ± 0.2%, respectively. HEXION RIMR 135 with curing agent RIMH 137 was used as a model thermoset epoxy matrix during SFPO measurements. A predictive engineering fiber sizing methodology was also developed. Sizing amounts of 0.5, 1, and 2 wt.% on the fiber surface were achieved for both sizing formulations. For each fiber size level, 50 single-fiber tensile testing experiments and 20 single-fiber pull-out tests were conducted. The ultimate tensile strength (σ_ult) of the carbon fibers and the interfacial shear strength (τ_app) of the single fiber composite were analyzed. The sizing levels’ effect on interfacial shear stress and the O/C (Oxygen/Carbon) surface composition ratio was investigated. Based on our experimental findings, an increase of 6% in fiber performance was recorded for ultimate tensile and interfacial shear strengths. As a result, generalized fiber sizing and characterization methods were established. These developed methods can be used to characterize the strength and interfacial shear strength of manmade fibers with different sizing formulations and solid contents irrespective of the matrix, i.e., thermoset or thermoplastic.

It is well known that fiber sizing is one of the most important component in the manufacturing of composites, and it does affect the mechanical properties including strength and stiffness. In this work, the influence of fiber sizing levels on the mechanical properties of carbon fibers (CF) is reported at room temperature by using single fiber tensile testing (Favimat+), single fiber pullout testing (SFPO), and interfacial elemental analysis using X-ray photoelectron spectroscopy (XPS). Standard modulus of CF (7±0.2 μm in diameter) were sized using two Michelman commercially available sizing formulations. The average solid content for each sizing formulation is 26.3 ± 0.2% and 34.1 ± 0.2%, respectively. HEXION RIMR 135 with curing agent RIMH 137 was used as a model thermoset epoxy matrix during the SFPO measurements. A predictive engineering fiber sizing methodology is also developed. Sizing amounts of 0.5, 1, and 2 wt. % on the surface of the fiber is achieved for both sizing formulations. For each fiber sizing level, 50 single fiber tensile testing experiments and 20 single fiber pull-out tests were conducted. The ultimate tensile strength (σult) of the carbon fibers and the interfacial shear strength (τ_app) of the single fiber composite were analyzed. it is also investigated the effect of the sizing levels on the interfacial shear stress and the O/C (Oxygen/Carbon) surface composition ratio. As a result, generalized fiber sizing and characterization methods were established. The developed methods can be used to characterize the strength and interfacial shear strength of any man-made fibers with different sizing formulations and solid contents, irrespective of the matrix i.e. thermoset or thermoplastic.

The influence of relative humidity on charge decay on polystyrene (PS) particles is investigated at room temperature by using Faraday cup and attenuated total reflection‐Fourier transform infrared spectroscopy (ATR‐FTIR) spectroscopy. The PS (2.8 ± 0.4 μm in diameter) particles were charged by using an ozone setup. The ozone charging source was from the free O‐ radicals generated from O₃ dissociation on the surface of the PS particles resulting in carbonyl groups formation. The charge decayed exponentially, and the decay time constants were quantified using Faraday cup for various relative humidity conditions at room temperature. The charge decay due to the interaction of the PS particles with the environment was also investigated using ATR‐FTIR, where the CO stretching band at 1745 cm⁻¹ was monitored. The decay of the CO on the PS particles is due to the reaction of the carbonyl groups with the hydronium ions [H₃O]⁺. The reaction of CO with [H₃O]⁺ is responsible for the time dependent charge decay. From both methods, the charge decay exhibited an exponential behavior, where the time decay constants measured from the two methods were in excellent correlation. The decay time constant increased linearly with increasing the RH. A generalized master charge decay curve is established for any PS surfaces (particles/films).

There is a strong indication that the dual-cooled LiPb blanket is the preferred concept for many fusion power plants being designed around the world. The ability of the blanket to provide tritium self-sufficiency is among the important issues that we investigated in detail for ARIES-ACT to pinpoint the design elements that degrade the breeding the most, using state-of-the-art neutronics codes. A novel stepwise approach was developed to identify the exact cause of the degradation in the tritium breeding ratio (TBR), initially 1.8 for an ideal system, reaching 1.05 for a practical design. More broadly, this paper gives many insights into the impact that internal components of the blanket as well as essential parts of a tokamak can have on the TBR and the more damaging or enhancing conditions or changes to the breeding. To overcome the challenges of dealing with all tritium-related uncertainties in several subsystems, we suggest adjusting the Li enrichment online during operation to mitigate concerns about the danger of placing the plant at risk due to tritium shortage as well as the problem of handling and safeguarding any surplus of tritium.