Preparation and Characterization of MM’Si4N6C Ceramics

2008 ◽  
Vol 403 ◽  
pp. 3-6 ◽  
Author(s):  
Derek P. Thompson ◽  
Yue Zhang
Keyword(s):  
Mechanical Property ◽  
High Temperature ◽  
Similar Type ◽  
Trivalent Metal ◽  
Area Of Interest ◽  
Inorganic Crystal ◽  
Powder Samples ◽  
The One ◽  
Dense Product

The preparation of high temperature ceramics simultaneously containing silicon, nitrogen and carbon has only relatively recently become an area of interest for inorganic crystal chemists, and the recent discovery of a new series of carbonitrides with the general formula MM’Si4N6C is of interest because of the good high temperature properties they appear to display. On the one hand, M and M’ can be the same trivalent metal - either rare earth or yttrium; in this case, the resulting compounds display orthorhombic (pseudo-hexagonal) structures. Alternatively the metals may be a mix of di- (Ca,Sr, Ba) and tri-valent (Y,Ln) cations, in which case the carbon is replaced by nitrogen, and the overall symmetry is hexagonal. Other quaternary nitrides of a similar type can be produced if the two metal cations remain trivalent and one of the silicon atoms is replaced by aluminium. The present study describes the preparation of powder samples of Y2Si4N6C and LaYSi4N6C starting from YH2, La, Si3N4 and carbon precursors, and summarises attempts to achieve a dense product by hot-pressing at 1700-1800oC. Some preliminary mechanical property measurements are included.

Spark plasma sintering of self-propagating high-temperature synthesized TiC0.7/TiB2 powders and detailed characterization of dense product

2009 ◽  
Vol 35 (7) ◽  
pp. 2587-2599 ◽  
Author(s):  
Clara Musa ◽  
Antonio Mario Locci ◽  
Roberta Licheri ◽  
Roberto Orrù ◽  
Giacomo Cao ◽  
...  
Keyword(s):  
High Temperature ◽  
Spark Plasma Sintering ◽  
Detailed Characterization ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Dense Product

Rhombohedral-cubic phase transition characterization of (Pb,Ge)Te using high-temperature XRD

2008 ◽  
Vol 23 (2) ◽  
pp. 137-140 ◽  
Author(s):  
J. Sariel ◽  
I. Dahan ◽  
Y. Gelbstein
Keyword(s):  
High Temperature ◽  
Cylindrical Specimen ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Continuous Transformation ◽  
X Ray ◽  
High Temperature Xrd ◽  
Powder Samples ◽  
Powder Metallurgy Approach

Rhombohedral-cubic transformation in Bi2Te3 doped-Pb1−xGexTe alloys is presented. Samples of Bi2Te3 doped Pb1−xGexTe were prepared by powder metallurgy approach. These powder samples were examined by high-temperature X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy. A bulk (pressed powder) cylindrical specimen was used for dilatometery characterizations. According to the XRD examinations it seems that upon increasing the temperatures a continuous transformation occurs from the rhombohedral to the cubic phase, accompanied by the formation of a small amount of the phase Ge0.74Pb3.26Te4.

Electron Microscopy of Silicon Nitride-Based Ceramics

1991 ◽  
Vol 49 ◽  
pp. 926-927
Author(s):  
Gareth Thomas
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
Silicon Nitride ◽  
World Wide ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
High Temperature Strength ◽  
Sintering Additives ◽  
Glass Forming ◽  
Dense Product

Silicon nitride and silicon nitride based-ceramics are now well known for their potential as hightemperature structural materials, e.g. in engines. However, as is the case for many ceramics, in order to produce a dense product, sintering additives are utilized which allow liquid-phase sintering to occur; but upon cooling from the sintering temperature residual intergranular phases are formed which can be deleterious to high-temperature strength and oxidation resistance, especially if these phases are nonviscous glasses. Many oxide sintering additives have been utilized in processing attempts world-wide to produce dense creep resistant components using Si3N4 but the problem of controlling intergranular phases requires an understanding of the glass forming and subsequent glass-crystalline transformations that can occur at the grain boundaries.

scholarly journals Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 108-120
Author(s):  
Simone Barbarossa ◽  
Roberto Orrù ◽  
Valeria Cannillo ◽  
Antonio Iacomini ◽  
Sebastiano Garroni ◽  
...  
Keyword(s):  
High Temperature ◽  
Single Phase ◽  
Nominal Composition ◽  
High Entropy ◽  
Chemical Complexity ◽  
Alternative Processing ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Spark Plasma

Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e., 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual porosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing tantalum, displayed lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) was relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material.

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