Fabrication and Characterization of Aluminum Nitride/Boron Nitride Nanocomposites by Carbothermal Reduction and Nitridation of Aluminum Borate Powders

In order to fabricate aluminum nitride/boron nitride (AlN/BN) nanocomposites by pressureless sintering, the present study investigated the synthesis of AlN-BN nanocomposite powders by carbothermal reduction and nitridation of aluminum borate powders. Homogeneous mixtures of alumina (Al2O3), boric acid (H3BO3), and carbon powder were used to synthesize AlN/BN nanocomposite powders containing 10 and 20 vol% BN. Aluminum borate was produced by reacting Al2O3 and B2O3 above 800 °C, and AlN and turbostratic BN (t-BN) were produced by reacting aluminum borate with carbon powder and nitrogen gas at 1500 °C. Carbothermal reduction followed by nitridation yielded an AlN/BN nanocomposite powder composed of nanosized AlN and t-BN. By pressureless sintering nanocomposite AlN/BN powders containing 5 wt% Y2O3, AlN/BN nanocomposites were obtained without compromising the high thermal conductivity and high hardness.

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Preparation and Characterization of Polycrystalline Cubic Boron Nitride (PcBN) Compacts by a Pressureless Sintering Process

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.105-106.38 ◽

2010 ◽

Vol 105-106 ◽

pp. 38-41 ◽

Cited By ~ 2

Author(s):

Zhen Huo Ren ◽

Rui Zhang ◽

Hai Long Wang ◽

De Liang Chen ◽

Ming Liang Li

Keyword(s):

Boron Nitride ◽

Cubic Boron Nitride ◽

Cost Effective ◽

Sintering Behavior ◽

Pressureless Sintering ◽

X Ray Diffraction ◽

Polycrystalline Cubic Boron Nitride ◽

Air Atmosphere ◽

Sintering Method

A novel cost-effective pressureless sintering method has been developed to prepare polycrystalline cubic boron nitride (PcBN) compacts. The effect of feldspar as sintering aids was analyzed in this paper. Various amounts of feldspar from 5 to 15 wt% were added to cBN powders, and the pressureless sintering was conducted at temperatures ranging from 900°C to 1200°C under an air atmosphere. The microstructure, phase, density and microhardness of the as-obtained PcBN compacts were measured and correlated to amounts of Si added and to sintering temperatures. The sample showed superior sintering behavior in comparison to those fabricated using hot pressed sintering. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that feldspar diffused homogeneously and tightly bonded with cBN. But hBN appeared when the sintering temperature even at 900°C, which dramatically affected the property of PcBN compacts. A PcBN compact with a relative density of 91% was obtained at 1100°C and its microhardness was as high as 1000HV.

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Effects of Carbon Source on Fabrication and Characterization of Porous Silicon Nitride Ceramics by Carbothermal Reduction

Materials Science Forum ◽

10.4028/www.scientific.net/msf.675-677.175 ◽

2011 ◽

Vol 675-677 ◽

pp. 175-178

Author(s):

Shu Wen Yang ◽

Shao Yun Shan ◽

Wen Hui Ma ◽

Hua Wang

Keyword(s):

Phase Composition ◽

Silicon Nitride ◽

Porous Silicon ◽

Carbothermal Reduction ◽

Carbon Sources ◽

Reduction Reaction ◽

Carbon Powder ◽

High Porosity ◽

Nitride Ceramics

Porous silicon nitride ceramics with high-porosity were fabricated by carbothermal reduction reaction between silicon dioxide and carbon. The influences of carbon sources on microstructure and phase composition of the samples were studied. The result showed that the resultant porous silicon nitride ceramics using nano-meter carbon powder (C(n)) had finer microstructure, more uniform pore structure than those using activated carbon powder (C(a)). In order to illuminate the reaction and growth mechanism of b-Si3N4 grains, a series of intermediate sintering processes were investigated. X-ray diffractometry showed a difference in phase composition for the samples using the different carbon sources.

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Construction of plastic contact deformation maps on ceramics: a case study on aluminum nitride

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165641 ◽

1996 ◽

Vol 54 ◽

pp. 636-637

Author(s):

D. L. Callahan

Keyword(s):

Plastic Deformation ◽

Aluminum Nitride ◽

Mechanical Response ◽

Three Dimensional ◽

Bright Field Image ◽

Perfectly Plastic ◽

Contrast Analysis ◽

Deformation Patterns

Modern polishing, precision machining and microindentation techniques allow the processing and mechanical characterization of ceramics at nanometric scales and within entirely plastic deformation regimes. The mechanical response of most ceramics to such highly constrained contact is not predictable from macroscopic properties and the microstructural deformation patterns have proven difficult to characterize by the application of any individual technique. In this study, TEM techniques of contrast analysis and CBED are combined with stereographic analysis to construct a three-dimensional microstructure deformation map of the surface of a perfectly plastic microindentation on macroscopically brittle aluminum nitride.The bright field image in Figure 1 shows a lg Vickers microindentation contained within a single AlN grain far from any boundaries. High densities of dislocations are evident, particularly near facet edges but are not individually resolvable. The prominent bend contours also indicate the severity of plastic deformation. Figure 2 is a selected area diffraction pattern covering the entire indentation area.

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CBED analysis of impurity distributions in AlN

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174205 ◽

1990 ◽

Vol 48 (4) ◽

pp. 214-215

Author(s):

Daniel Callahan ◽

G. Thomas

Keyword(s):

Aluminum Nitride ◽

Bulk Material ◽

Strong Dependence ◽

Lattice Parameter ◽

Promising Technique ◽

Nitride Ceramics ◽

Surface Phases ◽

Convergent Beam ◽

Oxygen Impurities

Oxygen impurities may significantly influence the properties of nitride ceramics with a strong dependence on the microstructural distribution of the impurity. For example, amorphous oxygen-rich grain boundary phases are well-known to cause high-temperature mechanical strength degradation in silicon nitride whereas solutionized oxygen is known to decrease the thermal conductivity of aluminum nitride. Microanalytical characterization of these impurities by spectral methods in the AEM is complicated by reactions which form oxygen-rich surface phases not representative of the bulk material. Furthermore, the impurity concentrations found in higher quality ceramics may be too low to measure by EDS or PEELS. Consequently an alternate method for the characterization of impurities in these ceramics has been investigated.Convergent beam electron diffraction (CBED) is a promising technique for the study of impurity distributions in aluminum nitride ceramics. Oxygen is known to enter into stoichiometric solutions with AIN with a consequent decrease in lattice parameter.

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