Reactions in the systems MoSi3N4 and NiSi3N4

The reaction products, formed during annealing of porous powder mixtures of Si₃N₄ with non-nitride forming metals like Ni or Mo, will depend on the partial pressure of N₂ in the atmosphere. In a diffusion couple, however, nitrogen has to be released at the Si₃N₄-interface during the formation of a metal silicide. It cannot escape easily and builds up a higher pressure of nitrogen at this interface. Therefore, the reaction products are different from those in porous pellets. This has been verified for NiSi₃N₄ and MoSi₃N₄ couples. The role of traces of oxygen on these reactions will be discussed.     

Phase Stability and Ionic Conductivity of NASICON-Like Phases in ScPO4-Na3PO4-Li3PO4 Ternary System

Phase formation in ternary system of complex Sc, Na and Li phosphates was studied at 950 ℃ and synthesis of new phases of definite composition was carried out. Obtained specimens were investigated with X-ray powder diffraction, infrared and impedance spectroscopy. Compositions of fields of homogeneity with NASICON-like structure were discovered. Temperature dependency of ionic conductivity was measured.     

Characterization of Ti4AlN3

Bulk samples of Ti₄AIN₃ were fabricated by reactive hot isostatic pressing (hipping) of TiH₂, AlN, and TiN powders at 1275 °C for 24 hours under 70 MPa. Further annealing at 1325 °C for 168 hours under Ar resulted in dense, predominantly single-phase samples, with <1 vol pct of TiN as a secondary phase. This ternary nitride, with a grain size of ≈20 μm on average, is relatively soft (Vickers hardness 2.5 GPa), lightweight (4.6 g/cm³), and machinable. Its Young’s and shear moduli are 310 and 127 GPa, respectively. The compressive and flexural strengths at room temperature are 475 and 350 MPa, respectively. At 1000 °C, the deformation is plastic, with a maximum compressive stress of ≈450 MPa. Ti₄AlN₃ thermal shocks gradually, whereby the largest strength loss (50 pct) is seen at a ΔT of 1000 °C. Further increases in quench temperature, however, increase the retained strength before it ultimately decreases once again. This material is also damage tolerant; a 100 N-load diamond indentation, which produced an ≈0.4 mm defect, reduces the flexural strength by only ≈12 pct. The thermal-expansion coefficient in the 25 °C to 1100 °C temperature range is 9.7±0.2 × 10⁻⁶ °C⁻¹. The room-temperature electrical conductivity is 0.5 × 10⁶ (Θ · m)⁻¹. The resistivity increases linearly with increasing temperature. Ti₄AlN₃ is stable up to 1500 °C in Ar, but decomposes in air to form TiN at ≈1400 °C. graduated from the Department in June of 1999 with an MS thesis.     

Fe_3O_4@SiO_2@Co_3O_4三元核壳结构催化剂的制备及表征

本文中采用均相沉淀法制备了Fe3O4@SiO2@Co3O4核壳结构纳米材料。通过X射线衍射仪,X射线能谱仪,透射电镜,振动样品磁力计,对其结构形貌和磁性能进行了表征。结果表明,所制备纳米粒子包覆结构比较完整,粒径约300nm,内核为磁性Fe3O4,中层为无定形SiO2,外层为Co3O4纳米线,具有海胆状三元核壳结构。该材料有望应用于具有可回收性的磁性纳米催化剂。     

Coumarins XIV: high-resolution mass spectra of 3',4'-disubstituted 3',4'-dihydroseselins

High-resolution mass spectra of 14 3',4'-disubstituted 3',4'-dihydroseselins were examined. The nature of the substituents determinines the mode of fragmentation. Compounds having one or two acyloxy substituents fragment mainly by a pathway leading to the stable coumarinopyrilium ion. Coumarins with alkoxy or hydroxy substituents proceed by way of fission of the chroman ring, accompanied by the loss of two ring carbon atoms. Several generalizations are formulated which will aid in the interpretation of the mass spectra of this class of coumarins from a structural standpoint.     

4-Phenyl-4-oxo-butanoic acid derivatives inhibitors of kynurenine 3-hydroxylase

Kynurenine 3-hydroxylase (KYN 3-OHase) is a key enzyme in the kynurenine pathway of tryptophan degradation and its inhibition may be an effective mechanism for counteracting neuronal excitotoxic damage. We present here a new class of inhibitors derived from a structure-activity relationship (SAR) study of the benzoylalanine side-chain of 1. 2-hydroxy-4-(3,4-dichlorophenyl)-4-oxobutanoic acid (8) and 2-benzyl-4-(3,4-dichlorophenyl)-4-oxo-butanoic acid (10) emerged as the most interesting derivatives. Enantiospecific synthesis for both enantiomers of 8 and diastereomeric salt resolution for those of 10 were successfully applied.     

Simultaneous determination of polyamines, N-acetylated polyamines and the polyamine analogues BE-3-3-3 and BE-4-4-4-4 by capillary gas chromatography with nitrogen-phosphorus detection

IgM paraproteins from patients with CANOMAD (chronic ataxic neuropathy, ophthalmoplegia, M-protein, agglutination, anti-disialosyl antibodies) react with NeuAc(alpha 2-8)NeuAc epitopes on a wide range of gangliosides including GQ1b, GT1a, GD1b and GD3. The tissue distribution of reactive antigens in human peripheral nerve has not been addressed in detail. In addition, the origin of these antibodies is unknown. Here we report that purified anti-disialosyl paraproteins from two affected patients bind a wide array of human peripheral nerve structures including dorsal root ganglia, dorsal and ventral root axons, femoral and oculomotor nerves. We also show that these paraproteins bind lipopolysaccharides of Campylobacter jejuni isolates from 3/3 cases of Miller Fisher syndrome, and to a less frequent extent, from cases of Guillain-Barré syndrome and enteritis controls. In conjunction with our previous studies, these data provide a possible causal link between the origin and pathogenic effects of anti-disialosyl antibodies in human paraproteinaemic neuropathy.     

Bi_3PbSr_3Ca_3Cu_4O_y超导体的颗粒超导性

本文对Bi_3PbSr_3Ca_3Cu_4O_y超导体进行了超导电性、磁阻、输运特性等的测量。并利用结构分析等方法,对超导体的颗粒超导性进行了研究。试验观察到了负磁阻效应、回滞和热激活行为,以及颗粒间晶界对输运特性的影响。并对以上结果进行了较详细的分析。     

Development of a new CuNiTiB brazing alloy for joining Si3N4 to Si3N4

Joining Si₃N₄ to Si₃N₄ was carried out initially with a Cu₃₄Ni₂₇Ti₃₉ brazing alloy prepared by double melting under a vacuum condition. However, the strength of the joints was not as high as expected. The causes were studied. Based on the results of the analysis, a CuNiTiB brazing filler metal was designed. The Si₃N₄/Si₃N₄ joints were then brazed with this new brazing alloy in the paste form, and joints with a three-point bend strength of 338.8 MPa at room temperature were obtained. The interfacial reactions of the joint are also discussed. With the rapidly solidified foils of the brazing alloy, the bend strength of the Si₃N₄/Si₃N₄ joints under the same brazing conditions is raised to 402 MPa at room temperature. The Si₃N₄/Si₃N₄ joints brazed with this newly developed brazing alloy exhibit a rather high and steady bend strength (about 406 MPa) at 723 K.     

THE CaSO4-CaO-Ca3(AsO4)2 PHASE DIAGRAM

Abstract

The phase diagram of the CaSO₄-Ca₃(AsO₄)2-CaO system was measured by differential thermal analysis and by an equilibration and quenching technique. A thermodynamic model was developed giving the Gibbs energy of every phase as a function of temperature and composition. A new ternary compound was observed with a composition near Ca5As2SO13. The Modified Quasichemical Model was used for the liquid solution. Optimized model parameters were obtained by assessing of all available thermodynamic and phase equilibrium data. The model reproduces all the data within experimental error limits. The model was used to calculate the liquidus surface over the temperature range of industrial interest.

Le diagramme de phases CaSO₄-Ca₃(AsO₄)2-CaO a été mesuré par analyse thermique différentielle et par une technique d’équilibration et de trempe. Un modèle thermodynamique a été développé donnant l’énergie de Gibbs pour toutes les phases dans ce système en fonction de la température et de la composition. Une nouvelle phase solide a été observée ayant une composition proche du Ca5As2SO13. La dernière version du modèle quasichimique a été utilisée pour la phase liquide. Les paramètres du modèle ont été obtenus par optimisation en tenant compte de toutes les données thermodynamiques et d’équilibres de phases disponibles pour ce système. Le modèle reproduit toutes les données à l’intérieure des erreurs expérimentales. Le modèle a été utilisé pour calculer la projection du liquidus du système CaSO₄-Ca₃(AsO₄)2-CaO à des températures pouvant être utilisées dans l’industrie.