共查询到20条相似文献,搜索用时 62 毫秒
1.
2.
3.
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. 相似文献
4.
Erwin Rudy 《Metallurgical and Materials Transactions B》1970,1(5):1249-1252
The crystal structures of ε-Hf3N2 and ζ-Hf4N3 were determined from X-ray powder photographs. The structure of both phases is trigonal, space group D 5 3d -R?3m, with unit cells ofa R = 7.972Å, α= 23 deg 12 min (hexagonal axes:a = 3.206Å,c = 23.26Å) for ε-H3H2, and aR= 10.54Å, α = 17 deg 32 min (hexagonal axes:a = 3.214Å,c = 31.12Å) for ζ-Hf4N3. The nine close packed metal layers in ε-Hf3N2 are stacked according to (hhc)3, or ABABCBCAC. The structure of ζ-Hf4sN3, isomorphous with ζ-V4C3,1 consists of twelve close-packed metal layers in a stacking sequence (hhcc)3. The nitrogen atoms occupy octahedral interstices in the metal lattice. The experimentally observed compositions, Hf3N1.69 and Hf4N2.56, shows both phases to be substantially deficient in nitrogen. ε-Hf3N2 is unstable above 2000°C, and ζ-Hf4N3 above 2300°C. 相似文献
5.
6.
The regional distributions of the G protein beta subunits (Gbeta1-beta5) and of the Ggamma3 subunit were examined by immunohistochemical methods in the adult rat brain. In general, the Gbeta and Ggamma3 subunits were widely distributed throughout the brain, with most regions containing several Gbeta subunits within their neuronal networks. The olfactory bulb, neocortex, hippocampus, striatum, thalamus, cerebellum, and brainstem exhibited light to intense Gbeta immunostaining. Negative immunostaining was observed in cortical layer I for Gbeta1 and layer IV for Gbeta4. The hippocampal dentate granular and CA1-CA3 pyramidal cells displayed little or no positive immunostaining for Gbeta2 or Gbeta4. No anti-Gbeta4 immunostaining was observed in the pars compacta of the substantia nigra or in the cerebellar granule cell layer and Purkinje cells. Immunoreactivity for Gbeta1 was absent from the cerebellar molecular layer, and Gbeta2 was not detected in the Purkinje cells. No positive Ggama3 immunoreactivity was observed in the lateral habenula, lateral septal nucleus, or Purkinje cells. Double-fluorescence immunostaining with anti-Ggamma3 antibody and individual anti-Gbeta1-beta5 antibodies displayed regional selectivity with Gbeta1 (cortical layers V-VI) and Gbeta2 (cortical layer I). In conclusion, despite the widespread overlapping distributions of Gbeta1-beta5 with Ggamma3, specific dimeric associations in situ were observed within discrete brain regions. 相似文献
7.
Huaping Xiong Chuangeng Wan Zhenfeng Zhou 《Metallurgical and Materials Transactions A》1998,29(10):2591-2596
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. 相似文献
8.
KA Stauderman LS Mahaffy M Akong G Veli?elebi LE Chavez-Noriega JH Crona EC Johnson KJ Elliott A Gillespie RT Reid P Adams MM Harpold J Corey-Naeve 《Canadian Metallurgical Quarterly》1998,284(2):777-789
Human embryonic kidney (HEK293) cells were transfected with cDNA encoding the human beta4 neuronal nicotinic acetylcholine (ACh) receptor subunit in pairwise combination with human alpha2, alpha3 or alpha4 subunits. Cell lines A2B4, A3B4.2 and A4B4 were identified that stably express mRNA and protein corresponding to alpha2 and beta4, to alpha3 and beta4 and to alpha4 and beta4 subunits, respectively. Specific binding of [3H]epibatidine was detected in A2B4, A3B4.2 and A4B4 cells with Kd (mean +/- S.D. in pM) values of 42 +/- 10, 230 +/- 12 and 187 +/- 29 and with Bmax (fmol/mg protein) values of 1104 +/- 338, 2010 +/- 184 and 3683 +/- 1450, respectively. Whole-cell patch-clamp recordings in each cell line demonstrated that (-)nicotine (Nic), ACh, cytisine (Cyt) and 1, 1-dimethyl-4-phenylpiperazinium iodide (DMPP) elicit transient inward currents. The current-voltage (I-V) relation of these currents showed strong inward rectification. Pharmacological characterization of agonist-induced elevations of intracellular free Ca++ concentration revealed a distinct rank order of agonist potency for each subunit combination as follows: alpha2beta4, (+)epibatidine (Epi) > Cyt > suberyldicholine (Sub) = Nic = DMPP; alpha3beta4, Epi > DMPP = Cyt = Nic = Sub; alpha4beta4, Epi > Cyt = Sub > Nic > DMPP. The noncompetitive antagonists mecamylamine and d-tubocurarine did not display subtype selectivity. In contrast, the Kb value for the competitive antagonist dihydro-beta-erythroidine (DHbetaE) was highest at alpha3beta4 compared with alpha2beta4 or alpha4beta4 receptors. These data illustrate that the A2B4, A3B4.2 and A4B4 stable cell lines are powerful tools for examining the functional and pharmacological properties of human alpha2beta4, alpha3beta4 and alpha4beta4 neuronal nicotinic receptors. 相似文献
9.
G. V. Samsonov A. D. Panasyuk I. M. Finkel'shtein 《Powder Metallurgy and Metal Ceramics》1977,16(5):392-394
Conclusions Refractory silicon nitride materials containing up to 50 wt.% of chromic and zirconium oxides (stabilized with CaO) are suitable for applications involving contact with liquid nickel.Translated from Poroshkovaya Metallurgiya, No. 5(173), pp. 91–93, May, 1977. 相似文献
10.
11.
12.
José Lemus-Ruiz Carlos A. León-Patiño Robin A. L. Drew 《Metallurgical and Materials Transactions A》2006,37(1):69-75
This work focuses on various aspects of diffusion bonding of Ti-foil and Nb-foil interlayers during the self-joining of Si3N4. Joints were diffusion joined by hot-uniaxial pressing at temperatures ranging from 1200 °C to 1600 °C using different holding
times. The microstructural characterization of the resulting interfaces was carried out by scanning electron microscopy, electron-probe
microanalysis (EPMA), and X-ray diffraction. The results showed that Si3N4 could not be bonded to Ti at temperatures lower than 1400 °C; however joining was successful at higher temperatures. On the
other hand, Si3N4 was solid-state bonded to Nb at temperatures ranging from 1200 °C to 1600 °C. Joining occurred by the formation of a reactive
interface on the metal side of the joint. Ti5Si3, TiSi, and TiN were detected at the Si3N4/Ti interface, and Nb5Si3 and NbSi2 at the Si3N4/Nb interface, resulting from high-temperature reaction between Ti or Nb and Si3N4. Four-point bending testing gave a maximum joint strength of 147 MPa for Si3N4/Ti/Si3N4 samples hot pressed at 1500 °C and 120 minutes. However, strong joints were obtained above 1450 °C (>100 MPa). These results
indicated that there is a strong relationship between the thickness of the interface and the mechanical strength of the preceding
joints.
This article is based on a presentation made in the symposium entitled “Processing and Properties of Structural Materials,”
which occurred during the Fall TMS meeting in Chicago, Illinois, November 9–12, 2003, under the auspices of the Structural
Materials Committee. 相似文献
13.
In order to clarify the phenomenon of nitride formation on the surface of iron, highly polished specimens of well refined and coarsened iron grains have nitrided in flowing H2 + NH3 gas. The morphology and the conditions for formation of Fe3N are clarified; it forms only on the surface of {lll}α or near {lll}α grains and grows in {112}α directions during nitriding treatment at temperatures between 450 and 550°C. Fe16N2 and Fe4N are also formed preferentially on the surfaces of {00l}α and {210}α grains, respectively. It is suggested that these iron surfaces are those satisfying the coherency relationships between nitrides and iron matrices. The morphologies and the formation temperature regions of Fe16N2 and Fe4N on the surface of iron are quite different to those observed in iron. In particular, Fe16N2, which has been generally accepted as metastable in bulk iron below 200°C, can exist even at temperatures from 450 to 500°C when it is formed on the surface of iron. 相似文献
14.
Microstructure of coatings obtained by treating Si3N4 and SiC in Cr powders at 1273–1623 K has been studied employing XRD, SEM, AES and TEM. In accordance with thermodynamic calculations and kinetic consideration, the coatings have layered structures and contain metal-rich silicides and metal-rich nitrides or carbides. The microstructure of the coatings has been found to depend on the treatment conditions. The kinetics of the coatings growth obeys a parabolic growth law, the activation energies being close to the activation energies for self-diffusion of the corresponding metals. Thermal stability of the coated and uncoated Si3N4 and SiC in Fe-, Ni- and Co-based matrices has been studied and the coatings have been found to considerably improve the stability of Si3N4- and SiC-metal interfaces. 相似文献
15.
16.
《Acta Metallurgica Materialia》1990,38(5):805-810
The compression creep behaviour of silicon nitride sintered with the aid of Y2O3 and Al2O3 and containing TiN particles was studied between 1260 and 1340°C at stresses ranging from 100 to 300 MPa. The volume fraction Φ of TiN particles was varied from 0 to about 40 vol % and two particle sizes: 1 μm and 2.5 μm were studied. The dominant creep mechanism of the matrix was viscous creep (n = 1) up to 1340°C and 200 MPa. The effect of the TiN addition on the creep behaviour was marked by a decrease of the creep strength with increasing volume fraction and decreasing particle size of TiN. In the same way, the steady state creep rate increased as the ratio Φ/d. In the microstructure, cavities and microcracks along particle/matrix interfaces show that a cavitational mechanism develop from the particles in the composite. 相似文献
17.
通过甲基含氢硅油与乙烯基硅氧烷(A151)的接枝反应,制备大分子硅氧烷偶联剂(HSi-g-A151),并用其对纳米Si3N4粉体进行表面修饰,通过沉降实验、透射电镜分析、粒度测定、热重分析和表面自由能分析等手段对改性前后的粉体进行表征.结果表明:大分子硅烷偶联剂对纳米Si3N4粉体为化学改性,改性后的纳米Si3N4粉体在二甲苯中悬浮稳定,粒径分布在30 nm左右,纳米颗粒表面自由能由79.8 J·m-2下降到39.4 J·m-2. 相似文献
18.
19.