Near net-shape, ultra-high melting, recession-resistant ZrC/W-based rocket nozzle liners via the displacive compensation of porosity (DCP) method

Dense, near net-shaped ZrC/W-based composites have been fabricated at modest temperatures and at ambient pressure by a reactive infiltration process known as the Displacive Compensation of Porosity (DCP) method. Porous WC preforms with hourglass shapes (for rocket nozzle liners) were produced by gel casting, whereas simple bar-shaped preforms were produced by uniaxial pressing. The porous preforms were exposed to molten Zr₂Cu at 1200–1300°C and ambient pressure. The Zr₂Cu liquid rapidly infiltrated into the preforms and underwent a displacement reaction with the WC to yield a more voluminous mixture of solid products, ZrC and W. This displacement reaction-induced increase in internal solid volume filled the prior pore spaces of the preforms (displacive compensation of porosity) to yield dense, ZrC/W-based composites. Because the preforms remained rigid during reactive infiltration, the final composites retained the external shapes and dimensions of the starting preforms. A DCP-derived, ZrC/W-based nozzle insert was found to be resistant to the severe thermal shock and erosive conditions of a Pi-K rocket motor test. The DCP process enables dense, ceramic/refractory metal composites to be fabricated in complex and near net shapes without the need for high-temperature or high-pressure densification or for extensive machining (i.e., relatively expensive processing steps are avoided).     

A comparative study of ketorolac (Toradol) and magnesium sulfate for arrest of preterm labor

BACKGROUND: We evaluated the efficacy and safety of ketorolac (Toradol). METHODS: In this prospective trial, 88 women in confirmed preterm labor at < or =32 weeks' gestation were randomized to receive magnesium sulfate given as an initial 6 g intravenous bolus followed by continuous infusion therapy (2 to 6 g/hr) or intramuscularly administered ketorolac (60 mg loading dose) followed by 30 mg every 6 hours for a maximum of 24 hours. RESULTS: The study groups were similar with respect to age, parity, cervical status, and gestational age on admission. Ketorolac was more rapid (2.71 hr+/-2.16) in the arrest of preterm labor than was magnesium sulfate (6.22 hr+/-5.65). No patient required discontinuance of either drug due to adverse effects. There was no difference in the incidence of neonatal complications between the two groups. CONCLUSION: In gestations with preterm labor at <32 weeks, ketorolac appears to be an appropriate first-line tocolytic agent.     

Oxidation und Aufkohlung hochlegierter Werkstoffe für Crackrohre. Teil 1: Das Oxidationsverhalten in Luft

Oxidation and Carburization of High Alloyed Materials for Cracking Tubes. Part 1: The Oxidation Behaviour in Air The oxidation behaviour has been studied of cast materials (German Materials Numbers 1.4848, 1.4857, 2.4813), an experimental melt of 25/20/5 CrNiSi steel and wrought materials (German Materials Numbers 1.4301 and 1.4841) in dry synthetic air between 800 and 1300°C. Only the oxidation of the materials 1.4848 and 1.4841 follows an approximately parabolic law, with the other materials more complex kinetic laws are found. The oxidation rates of all the cast materials are rather similar; the scale layers successively formed on the base material are Cr₂O₃ and MnCr₂O₄. The latter is characterized by clearly distinguishable iron contents. The Cr₂O₃ layer contains SiO₂ inclusions, in particular near the metal boundary. Above 1000°C internal oxidation of silicon is found. An exception to this is the 25/20/5 CrNiSi experimental melt where, because of the high Si content, a continuous SiO₂ layer is formed consistently between base material and Cr₂O₃ layer. The material 1.4301 exhibits locally increased oxidation at temperatures above 1050°C; in this case oxide nodules are formed. The oxidation rate of material 1.4841 at temperatures above 1100°C is higher for the fine grained than for the coarse grained condition; this phenomenon is attributed to the fact that at these temperatures pronounced grain growth occurs which impairs the formation of a protective layer. The scale layers formed contain considerable amounts of iron and the Cr content in the metal at the metal/oxide boundary decreases at a considerable higher rate with increasing temperature than in the case of the coarse grained material 1.4841 and of the cast materials containing about 25% Cr. Below 1100°C the differences in the behaviour are rather small and the oxidation rate is comparable to that of the cast materials. A transition from internal silicon oxidation to external SiO₂ scale formation is found with materials 1.4848 and 1.4841 at 1100°C in H₂/H₂O mixtures below the partial pressure of oxygen corresponding to the Cr/Cr₂O₃ equilibrium.     

Effects of annealing on elemental composition and quality of CZTSSe thin films obtained by spray pyrolysis

The spray pyrolysis was used for the deposition of Cu₂ZnSn(S, Se)₄ (CZTSSe) kesterite thin films. The basic spray pyrolysis solution was prepared from two precursor solutions containing thiourea and cooled to a temperature near 1°C, which leads to minimizing the number of insoluble hydrates of copper chloride. The optimal substrate temperature was 350°C and the distance from the sprayer nozzle 30 cm. The as-deposited Cu₂ZnSnS₄ layers were annealed in S₂ atmosphere for the compensation of the sulfur deficiency and with the addition of Sn in order to avoid tin loss. Cu₂ZnSn(S, Se)₄ thin films were obtained after the annealing of as-deposited films in the (S₂ + Se₂) atmosphere. The surface morphology and composition of obtained thin films were investigated using the energy dispersive X-ray (EDX) microanalysis and Raman spectroscopy measurements. The structural characterization by the grazing incidence X-ray diffraction (GIXRD) showed the presence of Cu_2–x S phases in all of the annealed thin films. For the Se/(S + Se) ratio of the thin films annealed in the (S + Se) atmosphere was established from EDX measurements and analysis of GIXRD data, the results are in satisfactory agreement.     

A randomized prospective trial of the obstetric forceps versus the M-cup vacuum extractor

OBJECTIVE: Our purpose was to determine the efficacy of the obstetric forceps versus the M-cup, a new vacuum extractor cup, and maternal-neonatal complication rates. STUDY DESIGN: Over a 10-month period operative vaginal deliveries were randomized between the obstetric forceps and the M-cup vacuum extractor cup. Maternal demographics, indication for intervention, analgesia, position, station, degree of asynclitism, fetal caput-molding, and time from application to delivery were prospectively recorded. Episiotomy and extensions, lacerations, and the reason for abandonment of the randomized instrument were noted in both groups. Fetal weight, Apgar scores, cord arterial gases, hyperbilirubinemia, phototherapy, and any evidence of fetal trauma were documented at delivery or in the nursery. RESULTS: Six hundred thirty-seven women were randomized, 315 in the forceps group and 322 in the M-cup group. There were no differences in maternal demographic variables. The station, position, degree of asynclitism, or requirement for rotation was not different between the groups. The corrected efficacy rates were forceps 92% and M-cup 94% (p = 0.217). The M-cup deliveries were accomplished more rapidly than forceps deliveries (p < 0.001) and were associated with a lower rate of episiotomy (p < 0.001), third-degree (p < 0.001) and fourth-degree (p = 0.002) lacerations, but blood loss as clinically estimated (p = 0.232) or as measured by hemoglobin levels (p = 0.166) was not significantly different. Forceps deliveries were associated with fewer clinically diagnosed cephalhematomas (p = 0.015) than M-cup deliveries were, but there were no differences in the number of neonates diagnosed with hyperbilirubinemia (p = 0.377) or in the number of infants treated with phototherapy (p = 0.660). CONCLUSIONS: The M-cup vacuum extractor cup appears to be as efficient (and faster) than the obstetric forceps but is associated with significantly more fetal cephalhematomas, whereas maternal injuries are more common with the forceps.     

Synthesis and incorporation of poly(methyl methacrylate) microspheres with UV stabilizers in wood clear coating binder

The durability of clear coatings is an important problem in the coatings industry. This problem can be partly solved with the addition of UV absorbers (UVAs) in the coating formulation. UVAs can absorb part of the UV radiation and convert it into harmless heat. Organic UVAs are prone to photodegradation and can migrate in the binder of a coating formulation. In this study, commercial UVAs have been encapsulated in poly(methyl methacrylate) microspheres using the internal phase separation method. Microspheres have been incorporated into a clear acrylic binder. The acrylic was then applied on wood panels and was placed into an artificial UV chamber. Efficiency of coatings after aging as well as chemical and physical properties were monitored using a colorimeter, FTIR spectroscopy and transmission electron microscopy. This study presents a comparison between the efficiency of free and encapsulated Tinuvin 1130 and 292 commercial absorbers. Results have shown that the coating efficiency is slightly improved when using the encapsulated products.     

The Role of Bulk and Interface Recombination in High‐Efficiency Low‐Dimensional Perovskite Solar Cells

2D Ruddlesden–Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite‐based cells. Herein, 2D (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Pb_nI_3n+1 perovskite cells with different numbers of [PbI₆]^4? sheets (n = 2–4) are analyzed. Photoluminescence quantum yield (PLQY) measurements show that nonradiative open‐circuit voltage (V_OC) losses outweigh radiative losses in materials with n > 2. The n = 3 and n = 4 films exhibit a higher PLQY than the standard 3D methylammonium lead iodide perovskite although this is accompanied by increased interfacial recombination at the top perovskite/C₆₀ interface. This tradeoff results in a similar PLQY in all devices, including the n = 2 system where the perovskite bulk dominates the recombination properties of the cell. In most cases the quasi‐Fermi level splitting matches the device V_OC within 20 meV, which indicates minimal recombination losses at the metal contacts. The results show that poor charge transport rather than exciton dissociation is the primary reason for the reduction in fill factor of the RPP devices. Optimized n = 4 RPP solar cells had PCEs of 13% with significant potential for further improvements.     

Single crystal X-ray structure investigation of Cu2ZnSnSe4

The crystal structure of Cu₂ZnSnSe₄ (CZTSe) has been investigated using two types of structure models known as stannite and kesterite. The single crystal X-ray diffraction study has been performed for two CZTSe single crystals samples obtained by the Bridgman (I) and chemical transport reaction (II) methods. The best refinement was obtained for the model in the space group I-42m, which suggests that cooper and zinc atoms alternate in the d Wickoff position of the space group and statistically occupy it with equal probability.