TEM Observations on 0.65Pb(Zr0.42Ti0.58)O3‐0.35Pb(Ni0.33Nb0.67)O3 Ceramics with CuO Additive

The microstructural properties and the chemical compositions of a 0.65Pb(Zr_0.42Ti_0.58)O₃‐0.35Pb(Ni_1/3Nb_2/3)O₃ (0.65PZT58‐0.35PNN) ceramic system sintered at 900°C for 4 h with 10 mol% CuO additives were studied using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). CuO pockets were found as new microstructural constituents. The liquid phase has formed by the partial melting of CuO additives at the sintering temperature by reacting with Pb element in the matrix. The reaction started at the interfaces and then proceeded into the pocket through the diffusion of the Pb element. The presence of the Pb‐rich precipitates during cooling was confirmed by EDS analyses. Cu‐rich crystals in the pocket were observed near the boundaries between the matrix grain and the pocket. Rather smaller Pb‐Cu‐O‐contained particle segments were detected around the center of the pocket, demonstrating that the reaction of melting of CuO has occurred with the Pb element which was diffused from the matrix. Due to the existence of the liquid phase, a dense microstructure was achieved during the sintering process and abnormal grain growth occurred in the process.     

Er2O3 Doping Effect on Varistor Properties and Multiimpulse Stress Behavior of ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 Ceramics

The Er₂O₃ doping effects on varistor properties and impulse aging behavior of the ZnO–PrO_1.83–CoO–Cr₂O₃–Dy₂O₃ ceramics were investigated in the range of 0–2.0 mol%. The nonlinear coefficient increased from 42 to 56 with an increase in the amount of Er₂O₃. The clamp voltage ratio (K) decreased with an increase in the amount of Er₂O₃. The varistors doped with 2.0 mol% in the amount of Er₂O₃ exhibited the best clamping characteristics, with K = 1.43–1.83 at an impulse current of 1–50 A. The varistors doped with 0.25 mol% in the amount of Er₂O₃ exhibited the strongest electrical stability, with the variation rate of the breakdown field of ?0.5%, the variation rate of the nonlinear coefficient of ?5.5%, and the variation rate of the leakage current of ?1.5% after applying 400 times at an impulse current of 400 A     

Effect of oxygen vacancy and Mn-doping on electrical properties of Bi4Ti3O12 thin film grown by pulsed laser deposition

An amorphous Bi₄Ti₃O₁₂ phase was formed when films were grown at <400 °C while Bi₂Ti₂O₇ and Bi₂Ti₄O₁₁ transient phases were developed when films were grown at 400–500 and 600 °C, respectively. A homogeneous Bi₄Ti₃O₁₂ crystalline phase was formed in the film grown at 700 °C. The high leakage current density (5 × 10^?7 A cm^?2 at 0.2 MV cm^?1) of the film grown at 300 °C under 100 mTorr oxygen partial pressure (OPP) decreased to 2 × 10^?8 A cm^?2 for the film grown at 200 mTorr OPP, due to the decreased number of intrinsic oxygen vacancies. However, when OPP exceeded 200 mTorr, the electrical properties were deteriorated due to the formation of oxygen interstitial ions. Mn-doping at a suitable level improved the electrical properties of the films by producing extrinsic oxygen vacancies that reduced the number of intrinsic oxygen vacancies. Schottky emission was suggested as the leakage current mechanism of the Bi₄Ti₃O₁₂ film.     

Characteristics of ZnOV2O5MnO2Nb2O5Er2O3 semiconducting varistors with sintering processing

The effects of sintering temperature on the microstructure, electrical properties, and dielectric characteristics of ZnOV₂O₅MnO₂Nb₂O₅Er₂O₃ semiconducting varistors have been studied. With increase in sintering temperature the average grain size increased (4.5–9.5 μm) and the density decreased (5.56–5.45 g/cm³). The breakdown field decreased with an increase in the sintering temperature (6214–982 V/cm). The samples sintered at 900 °C exhibited remarkably high nonlinear coefficient (50). The donor concentration increased with an increase in the sintering temperature (0.60×10¹⁸–1.04×10¹⁸ cm^?3) and the barrier height exhibited the maximum value (1.15 eV) at 900 °C. As the sintering temperature increased, the apparent dielectric constant increased by more than four-fold.     

Effects of K2O Evaporation on the Structural Properties of KSbO3 Compounds

A specimen having a stoichiometric composition of KSbO₃·(KSb) calcined at 800°C has an R rhombohedral structure (RS), and changes to a Pn cubic structure (CS) when calcined at 1100°C. Finally, a <111>‐oriented rhombohedral phase is formed in the specimen calcined at 1230°C. K/Sb ratio decreases from 1.0 in RS, 0.93 in CS, and finally to 0.85 in <111>‐oriented rhombohedral phases. On the other hand, a specimen having a K‐excess composition of K_1.1SbO₃ calcined at 800°C shows a RS that is maintained in the K‐excess specimen calcined at 1230°C. The composition of these specimens is very close to KSb. Therefore, the RS with a space group of R is a stable form of KSbO₃. The formation of Pn cubic and <111>‐oriented R phases can be explained by the evaporation of K₂O during the calcination process at temperatures above 1100°C.     

Enhanced hydrogen storage capacity of Pt-loaded CNT@MOF-5 hybrid composites

We report on an easy synthesis method for the preparation of a hybrid composite of Pt-loaded MWCNTs@MOF-5 [Zn₄O(benzene-1,4-dicarboxylate)₃] that greatly enhanced hydrogen storage capacity at room temperature. To prepare the composite, we first prepared Pt-loaded MWCNTs, which were then incorporated in-situ into the MOF-5 crystals. The obtained composite was characterized by various techniques such as powder X-ray diffractometry, optical microscopy, porosimetry by nitrogen adsorption, and hydrogen adsorption. The analyses confirmed that the product has a highly crystalline structure with a Langmuir specific surface area of over 2000 m²/g. The hybrid composite was shown to have a hydrogen storage capacity of 1.25 wt% at room temperature and 100 bar, and 1.89 wt% at cryogenic temperature and 1 bar. These H₂ storage capacities represent significant increases over those of virgin MOF-5s and Pt-loaded MWCNTs.     

Effect of the Pt precursor on the morphology and catalytic performance of Pt-impregnated on Pd/C for the oxygen reduction reaction in polymer electrolyte fuel cells

We describe how the morphology and electrocatalytic activity of Pt-Pd with low levels of Pt are dependent on the type of Pt precursor that is used for the impregnation on to Pd/C. When a Pt precursor with a negative charge (H₂PtCl₆) is used in the preparation medium (Pt-Pd/C-H), its electrostatic interaction with the carbon surface results in some Pt nanoparticles being deposited on the carbon separately from the Pd surface. Due to the absence of such an electrostatic interaction with the Pt(NH₃)₄Cl₂ precursor, more selective deposition of Pt can be achieved on the Pd surface (Pt-Pd/C-N). Depending on the morphology, different electrocatalytic performance in oxygen reduction reaction would be observed. Compared to Pt-Pd/C-H, Pt-Pd/C-N shows 180% (half-cell at 0.9 V) and 160% (unit-cell at 0.8 V) enhanced performance, which is comparable to that on Pt/C. It is believed that the interaction between the Pt and the Pd substrate is more extensive in Pt-Pd/C-N than in Pt-Pd/C-H, and this is responsible for the large difference in the catalytic performances between these two catalysts.     

Fabrication and properties of macro-porous SiC using Al2O3–Y2O3–SiO2 as bonding additives

Macro-porous SiC was fabricated without using pore-forming agents by an in situ reaction bonding process. A bonding additive, Al₂O₃–Y₂O₃–SiO₂, with a low melting temperature was mixed with SiC particles and sintered at 1500 °C and 1600 °C for 1 h in Ar. Macro-porous SiC with a porosity of 32.7–45.9%, a pore size of 3.4–4.2 μm, and a relatively narrow and uniform pore size distribution was fabricated by varying the amount of bonding additive. The flexural strength of macro-porous SiC prepared at 1500 °C increased from 47.2 MPa to 71.2 MPa while the porosity decreased from 45.9% to 42.8%, respectively. When the sintering temperature of the macro-porous SiC was increased to 1600 °C, the flexural strengths were significantly reduced to 32.6–35.6 MPa, along with a reduction in porosity and pore size. The permeability of macro-porous SiC prepared at 1500 °C varied from 1.59 × 10^?12 m² to 1.26 × 10^?12 m², depending on the porosity. As the sintering temperature increased from 1500 °C to 1600 °C, the permeability decreased to less than 1.00 × 10^?12 m² because of the reduced porosity and average pore size. The electrical resistivity of macro-porous SiC prepared at 1500 °C and 1600 °C varied from 2.7 × 10⁸ Ω-cm to 1.4 × 10⁹ Ω-cm and from 1.3 × 10⁸ Ω-cm to 1.7 × 10⁹ Ω-cm, respectively, with increasing volume percent of bonding additives. The relatively high electrical resistivity was apparently due to neck bonding phase between SiC particles formed by phases consisting of Y₂Si₂O₇, YAG, and residual Al₂O₃.     

Prognostic factors for toluene diisocyanate-induced occupational asthma after removal from exposure

A proportion of strokes are due to intracranial haemorrhage. Their characteristics and treatment are different from ischaemic stroke-surgery is often necessary and thrombolytic or anticoagulant treatment contraindicated. Most intracerebral haematomas (ICH) are hypertensive in origin. Small haematomas are treated with blood pressure control and rehabilitation. Larger ones often need surgery. Treatment must be tailored to the patient's circumstances, taking into account age, general and neurological health, location of haematoma etc. Subarachnoid haemorrhage (SAH) affects younger people and is classically due to aneurysm rupture, requiring urgent neurosurgical referral. Another cause is arteriovenous malformations (AVM), also treated surgically. A major problem is failure to diagnose less severe bleeds, which often precede major haemorrhages.     

Analysis of tube thoracostomy performed by pulmonologists at a teaching hospital

STUDY OBJECTIVE: To evaluate all tube thoracostomies (TTs) done by pulmonary/critical care fellows and attending physicians in the Medical University of South Carolina's health-care system documenting patient demographics, indication for placement, size and characteristics of the tube, and associated problems. DESIGN: Prospective. SETTING: University health-care system, including a university hospital, a Veterans Affairs hospital, and a county hospital. PATIENTS: All adult patients requiring consultation by a member of the pulmonary/critical care staff for a tube thoracostomy. RESULTS: One hundred twenty-six tube thoracostomies were performed over a 24-month period in 91 patients. The most common initial indication for a TT was pneumothorax (69/103, 67%). Overall mortality in the patient population was 35% (32/91). Early problems (< 24 hours following placement) occurred in 3% (4/126); late problems (> 24 h after placement) occurred in 8% (10/126). Problems occurred in 36% (4/11) of small-bore tube placements vs 9% (10/115) of standard TT placements (p=0.02). CONCLUSIONS: Tube thoracostomy can be safely performed by pulmonologists with relatively few associated problems.