Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

Oxidation Resistance Evaluation of Silicon Carbide Ceramics with Various Additives

Five silicon carbide ceramics with various additives were evaluated for oxidation resistance at 1300°C in flowing dry and wet air. In the dry atmosphere, the oxidation of the five samples was diffusion-controlled, and in wet atmosphere they exhibited a linear relation beween weight gain by oxidation and water vapor content. Water vapor in the atmosphere strongly accelerated oxidation. The influence of oxidation on room-temperature strength was complex, but the samples were not as affected by oxidation.     

Development of a new displacement-measuring ultrasonic sensor based on astigmatic focus error detection-measuring principle and its demonstration

Conventional ultrasonic displacement-measuring systems normally employ the pulse-echo technique. Resultant resolution capability, however, typically is not suitable for meeting high-dimensional, in-process measurement standards used in cutting and grinding operations. This paper presents a new ultrasonic sensor for displacement measurement based on astigmatic focus error detection. The measuring principle and basic analysis applied in the design method are described in detail, after which the validity of the principle is demonstrated by the results of experimental evaluations.     

Record of mercury pollution in sediments of lakes Nakaumi and Shinji in Japan

Two sediment core profiles from lakes Shinji and Nakaumi were studied in order to understand the level of mercury (Hg) pollution in lakes in northwestern Japan. The sedimentation rates were established on the basis of the activity of [²¹⁰Pb] and [¹³¹Cs] in the sediments. In Lake Shinji, the highest level of Hg (130 ng g^–1) in the sediment was found at a depth of 20–22 cm, while 195 ng g^–1 was found at a depth of 10–12 cm in the core profiles from Lake Nakaumi. The relative increase in Hg concentration in lake sediments started after 1960 and significant contamination events occurred in the early 1960s. Mercury profiles in lake sediments from lakes Shinji and Nakaumi are found to reflect the anthropogenic Hg released into the environment in the 1950s and 1960s. A pronounced maximun concentration of Hg is found in both lakes, where sediment accumulation rates differ.     

Precise analysis of H, C, N, and O as dominant impurities in Cu films: complementary use of SIMS and GDMS

Secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS) were used to determine the impurity concentrations of hydrogen, carbon, nitrogen, and oxygen elements in Cu films, and the results of SIMS and GDMS were carefully interpreted. The Cu films were deposited on Si (100) substrates at substrate bias voltages ranging from 0 V to −150 V using a non-mass separated ion beam deposition method. From the results of SIMS using a Cs⁻ ion beam, as a whole, many high intensity peaks were observed in the Cu films deposited without substrate bias voltage. From the quantitative GDMS results, these peaks were determined to be signals detected as a cluster state such as C_xH_x, O_xH_x, C_xO_xH_x. Therefore, using a combination of these dominant impurities, all the unknown peaks observed in the SIMS results could be interpreted. Moreover, it was found that the dominant impurities having a great influence on the film purity were hydrogen, carbon, nitrogen, and oxygen.     

Fabrication of semi-conductive ceramics by combination of gelcasting and reduction sintering

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s⁻¹, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 10⁶ Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details.     

Seismic proof test of a reinforced concrete containment vessel (RCCV): Part 1: Test model and pressure test

In Japan, the Nuclear Power Engineering Corporation (NUPEC), sponsored by the Ministry of Economy, Trade and Industry (METI), has been conducting a series of seismic reliability proving tests using full-scale or close to full-scale models to simulate actual important equipment that is critical for seismic safety of nuclear power plants. The tests are intended to validate the seismic design and reliability with a sufficient margin even under destructive earthquakes. A series of tests was carried out on a reinforced concrete containment vessel (RCCV) for advanced boiling water reactor (ABWR) from 1992 to 1999. A large-scale high-performance shaking table at Tadotsu Engineering Laboratory, the largest in the world, was used for this test. Part 1 reports the test model and the results of pressure and leak tests. Part 2 describes test procedures, input waves and the results of verification tests such as changes of stiffness, characteristic frequency and damping ratio, the failure of the model and the load deflection. Part 3 shows the seismic safety margin that was evaluated from the energy input during the failure test to a design basis earthquake. Part 4 reports simulation analysis results by a stick model with lumped masses.     

Plasma polymerized membranes and gas permeability. II

Thin films were deposited onto porous substrates by plasma polymerization using three kinds of organosilicic compounds, tetramethylsilane (TMS), hexamethyldisiloxane (M₂), and octamethylcyclotetrasiloxane (D₄). Those composite membranes showed different characteristics of gas permeability. When D₄ was plasma-deposited onto a porous substrate, the composites membrane showed the highest oxygen permeability and the lowest oxygen-to-nitrogen permeability ratio. The composite membrane prepared from TMS showed the permeability characteristics opposite to the membrane obtained from D₄. Infrared spectrum of the polymer from D₄ resembles that of dimethylpolysiloxane. The plasma polymers from TMS and M₂ showed different profiles in Si? O absorption bands in the range 1100–1000 cm^-1 or in absorption bands of SiCH₃ groups in the range 850–750 cm^-1 from respective monomers. X-ray photoelectron spectroscopic observation indicated that all the plasma polymers contained more than two species of Si atom with different oxidation states. The greater part of Si atoms in plasma polymers took the same oxidation states in corresponding monomer. The gas permeability characteristics were closely related to the oxidation states of Si atom in the plasma polymers.