Influence of continuous stabilization on the physical properties and microstructure of PAN-based carbon fibers

A continuous stabilization and carbonization process was used to prepare polyacrylonitrile (PAN)-based carbon fibers. The stepwise stabilization of PAN fibers was tried at various temperatures. The effect of stepwise stabilization on the physical properties and microstructure of the final carbon fibers is reported in this article. The fixed temperature in stepwise stabilization is kept below the fusion temperature of PAN precursors to avoid overstabilization of the fibers. The optimum stepwise stabilization process not only increases the amount of ladder polymer in stabilized fiber but also improves the physical and mechanical properties of the resultant carbon fibers. The formation of closed pores from open pores in carbon fiber occurs at 1100°C, but the formation of closed pores occurs at 200°C lower for carbon fiber developed from overstabilized fiber. The effect of continuous stepwise stabilization on the properties of resulting stabilized fibers and the variation in physical properties, element composition, and microstructure of carbon fibers during the carbonization process are also reported in this article.     

Fabrication of SiO2-ZrO2 composite fiber mats via electrospinning

(1 − x)SiO₂-(x)ZrO₂ (x = 0.1, 0.2) composite fiber mats were prepared by electrospinning their sol-gel precursors of zirconium acetate and tetraethyl orthosilicate (TEOS) without using a polymer binder. The electrospun composite fibers were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and mercury porosimetry. The composite fibers having a tetragonal crystalline ZrO₂ were obtained by calcining the electrospun composite fibers at high temperatures. The results show that the structure and crystallization of ZrO₂ in the composite fibers can be controlled by sintering temperature, while the porosity and morphology of the fiber mats did not depend on the sintering temperature.     

Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize active catalysts. Among them, Pt-Ni/γ-Al₂O₃ showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO₂ and ZrO₂ as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A1₂O₃ showed no decrease in CO conversion and CO₂ selectivity for the selective CO oxidation in the presence of 2 vol% H₂O and 20 vol% CO₂. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO₂ selectivity in selective oxidation of CO in H₂-rich stream.     

Dynamic light scattering measurements on the polystyrene/ethyl acetate system at semi-dilute concentrations as a function of temperature

Summary Measurements of autocorrelation functions extending over a broad time range are reported for a sample of polystyrene in ethyl acetate as a function of temperature between –44°C (-temperature) and 70°C. The corresponding spectra of decay times are obtained by two mathematical methods. The existence of three dynamic processes is shown and their temperature and angular behaviour is studied.     

Temperature-dependent transparency of poly(HPMA-co-DMA) hydrogels: effect of synthesis parameters

The acrylic comonomers hydroxypropyl methacrylate (HPMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been used in several earlier studies to produce pH-responsive hydrogels. However, these same monomers can also be used to prepare hydrogels that are highly responsive to temperature. One manifestation of this temperature sensitivity is a sharp decrease in hydrogel optical transparency that occurs when the temperature exceeds a critical transition value. For example, a hydrogel that exhibits a swelling transition at the physiological pH value of 7.4 has a transition temperature of about 45 °C when the environmental salt concentration is 0.15 M. The value of the transparency transition temperature is shown to depend on hydrogel synthesis parameters such as comonomer mole ratio, crosslinker mole ratio, and even initiator concentration. By reducing the mole ratio of the crosslinker tetraethylene glycol dimethacrylate (TEGDMA), the transition temperature can be lowered by as much as 15 °C. Environmental salt concentration and solvent polarity are also shown to influence the transition temperature.     

Bit-level systolic arrays for modular multiplication

This paper presents bit-level cellular arrays implementing Blakley's algorithm for multiplication of twon-bit integers modulo anothern-bit integer. The semi-systolic version uses 3n(n+3) single-bit carry save adders and 2n copies of 3-bit carry look-ahead logic, and computes a pair of binary numbers (C, S) in 3n clock cycles such thatC+S[0, 2N). The carry look-ahead logic is used to estimate the sign of the partial product, which is needed during the reduction process. The final result in the correct range [0,N) can easily be obtained by computingC+S andC+S–N, and selecting the latter if it is positive; otherwise, the former is selected. We construct a localized process dependence graph of this algorithm, and introduce a systolic array containing 3nw simple adder cells. The latency of the systolic array is 6n+w–2, wherew=n/2. The systolic version does not require broadcast and can be used to efficiently compute several modular multiplications in a pipelined fashion, producing a result in every clock cycle.     

Production of NiO,NiO/Ag,NiO/Au,and NiO/Pt hollow spheres by using block copolymer stabilized microspheres as a template

Hollow spheres of nickel oxide (NiO) and silver, gold, and platinum nanoparticle loaded NiO composites were successfully produced by using polystyrene (PS) latexes as hard template. Due to the presence of tertiary amine based diblock copolymer stabilizer on the surface of PS, the tertiary amine functional groups provided homogene deposition of nickel hydroxide, and then the precursor NiO salt production on the surface of PS latexes with a controlled precipitation technique. Then, NiO and NiO/metal NP hollow spheres were produced by calcination at 600 °C. Thermogravimetric analysis indicated that the amounts of NiO and NiO-composite after calcination were in the range of 21.1–29.7 wt%. The diameters of metal oxide spheres were in the range of 2.0–2.7 μm and the shell thickness were in the range of 250–350 nm. These structures had very low densities due to their porous and hollow structures and had outer layers with highly rough surfaces due to formation of nanosheets, which may offer important advantages for catalysis studies.     

Micro-end-milling of single-crystal silicon

Ductile-regime machining of silicon using micro-end-mill is almost impossible because of the brittle properties of silicon, crystal orientation effects, edge radius of the cutter and the hardness of tool materials. Micro-end-milling can potentially be used to create desired three dimensional (3D) free form surface features using the ductile machining technology for single-crystal silicon. There is still a lack of fundamental understanding of micro-end-milling of single-crystal silicon using diamond-coated tool, specifically basic understanding of material removal mechanism, cutting forces and machined surface integrity in micro-scale machining of silicon. In this paper, further research to understand the chip formation mechanism was conducted. An analysis was performed to discover how the chips are removed during the milling process. Brittle and ductile cutting regimes corresponding to machined surfaces and chips are discussed. Experiments have shown that single-crystal silicon can be ductile machined using micro-end-milling process. Forces generated when micro-end-milling single-crystal silicon are used to determine the performance of the milling process. Experimental results show that the dependence of the cutting force on the uncut chip thickness can be well described by a polynomial function order n. As cutting regime becomes more brittle, the cutting force has more complex function.     

Effect of TiO2 on high-temperature thermoelectric properties of ZnO

The as-sintered Zn_1−xTi_xO (0.01 ≤ x ≤ 0.05) samples contained a solid solution of Zn_1−xTi_xO with a wurtzite structure and a small amount of the cubic spinel Zn₂TiO₄. The amount of Zn₂TiO₄ increased with an increase in TiO₂ content. The density and grain size increased with the small TiO₂ content (≤0.01), and then they decreased gradually by further increasing the TiO₂ content. The addition of TiO₂ to ZnO led to a significant increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient, resulting in an increase in the power factor. The highest value of power factor (7.6 × 10⁻⁴ W m⁻¹ K⁻²) was attained for Zn_0.98Ti_0.02O at 1073 K. It is demonstrated that the TiO₂ addition is fairly effective for enhancing thermoelectric properties.     

Advanced compensation technologies for large‐sized UHD OLED TVs

In this paper, we present novel organic light‐emitting diode (OLED) display panel compensation technologies for large‐sized ultra‐high‐definition OLED TVs considering variations of threshold voltage, mobility, channel size, OLED efficiency, and OLED uniformity. Using these technologies, we have successfully launched 55‐, 65‐ and 77‐in. ultra‐high‐definition OLED TVs.