A Mechanically-Alloyed Amorphous 2Si-B-3C-N Ceramic with a Crystallization Temperature up to 1800°C

2018 ◽  
Vol 281 ◽  
pp. 323-329
Author(s):  
Peng Fei Zhang ◽  
De Chang Jia ◽  
Bin Yang ◽  
Guang Xin Wang
Keyword(s):  
Crystallization Temperature ◽  
Composite Powder ◽  
Hexagonal Boron Nitride ◽  
Silicon Powder ◽  
Graphite Powder ◽  
Amorphous Structure ◽  
Mechanically Alloyed ◽  
Boron Nitride Powder ◽  
Average Grain Size ◽  
High Crystallization Temperature

A mixture of cubic silicon powder, hexagonal boron nitride powder and graphite powder was mechanically alloyed for 30 hrs in argon. The as-milled 2Si-B-3C-N composite powder was heated up to 1900 °C in nitrogen, with a heating rate of 25 °C/min and under a pressure of 80 MPa. XRD and HRTEM results show that the as-milled 2Si-B-3C-N composite powder has a well amorphous structure. Under the current hot-pressing circumstances, the amorphous ceramic starts to crystallize at a temperature between 1800 °C and 1900 °C. Once the temperature is higher than crystallization temperature, crystallites appear in the amorphous matrix with a great nucleation rate, but a small growth rate. Hot pressed at 1900 °C for 0 mins or 10 mins, the prepared 2Si-B-3C-N bulk ceramic has an average grain size of 8.7 nanometers and 22.3 nanometers, respectively. After an intensive literature search, we believe the present work is the first one to make clear that it is possible to use the mechanical alloying route to prepare amorphous Si-B-C-N ceramic with such a high crystallization temperature.

Research on the Densification Process of the Mechanically-Alloyed Amorphous 2Si-B-3C-N Powder

2018 ◽  
Vol 281 ◽  
pp. 15-21
Author(s):  
Peng Fei Zhang ◽  
De Chang Jia ◽  
Bin Yang ◽  
Guang Xin Wang
Keyword(s):  
Mechanical Properties ◽  
Hexagonal Boron Nitride ◽  
Amorphous Powder ◽  
Silicon Powder ◽  
Graphite Powder ◽  
Densification Process ◽  
Mechanically Alloyed ◽  
Powder Particles ◽  
Average Size ◽  
N Powder

A mixture of the commercially available cubic silicon powder, hexagonal boron nitride powder and graphite powder was mechanically alloyed to prepare amorphous 2Si-B-3C-N composite powder. The amorphous powder was heated up to 1900°C in nitrogen, with a heating rate of 20°C/min and under a pressure of 80 MPa. Careful investigation was carried out on the densification curve, the microstructure and the mechanical properties of the prepared ceramics. Results show that the amorphous 2Si-B-3C-N powder mainly consists of near-spherical agglomerates, with an average size of 3.5±2.4 micrometers. When the amorphous powder was hot pressed, the densification process mainly included three stages, the denser packing of powder particles with the help of axial pressure, the initial sintering at about 1500-1800°C, and the rapid sintering at temperatures approximately higher than 1830°C. When the 2Si-B-3C-N ceramic was hot pressed at 1900°C for 10-30 mins, it exhibited large volume shrinkage, noticeable reduction of pores, and significantly improvement of density and mechanical properties. The applied high temperature and large pressure may give rise to severe plastic deformation, viscous flow and creep of powder particles, which greatly contribute to the rapid densification of the amorphous 2Si-B-3C-N powder.

scholarly journals Crystallization Kinetics and Consolidation of Al82La10Fe4Ni4 Glassy Alloy Powder by Spark Plasma Sintering

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 812
Author(s):  
Nguyen Viet ◽  
Nguyen Oanh ◽  
Ji-Soon Kim ◽  
Alberto Jorge
Keyword(s):  
Nucleation Rate ◽  
Glassy Alloy ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Sample Surface ◽  
Sintered Sample ◽  
Amorphous Structure ◽  
Mechanically Alloyed ◽  
Plasma Sintering ◽  
Spark Plasma

The mechanically alloyed Al82La10Ni4Fe4 glassy powder displays a two-step devitrification characterized by the precipitation of fcc-Al together with small amounts of the intermetallic Al11La3 phase in the first crystallization. The interface-controlled growth mechanism governed the first crystallization event. Calculations of the activation energy, using the methods of Kissinger, Ozawa, and Augis-Bennett gave values of 432.33, 443.2, and 437.76 kJ/mol, respectively. The calculated Avrami exponent (n) for the first crystallization peak was about 1.41, suggesting an almost zero nucleation rate. On the other hand, the value of n for the second peak related to the residual amorphous phase completely transformed into the intermetallic phase Al11La3 was about 3.61, characterizing diffusion controlled three-dimensional crystal growth with an increasing nucleation rate. Samples sintered at 573 K kept an amorphous structure and exhibited a high compressive strength of 650 MPa with a maximum elongation of 2.34% without any plastic deformation. The failure morphology of the sintered sample surface presented a transparticle fracture mechanism, indicating the efficiency of the sintering processing.

Flame-retardant activity of modified boron nitride nanosheets to cotton

2019 ◽  
Vol 90 (5-6) ◽  
pp. 512-522 ◽  
Author(s):  
Hong Liu ◽  
Yang Du ◽  
Shaohua Lei ◽  
Zhuoqun Liu
Keyword(s):  
Boron Nitride ◽  
Flame Retardant ◽  
Hexagonal Boron Nitride ◽  
Cotton Fabrics ◽  
High Yield ◽  
Limiting Oxygen Index ◽  
Boron Nitride Nanosheets ◽  
Boron Nitride Powder ◽  
Coated Fabrics ◽  
Index Value

Boron nitride nanosheets (BNN) were prepared by molten hydroxide-assisted liquid exfoliation from hexagonal boron nitride powder with an effectively high yield, and then modified with hexachlorocyclotriphosphazene (HCCP) to obtain HCCP-BNN. The series of samples were applied to prepare flame-retardant cotton fabrics with the impregnation-drying method, and successful treatment was confirmed by scanning electron microscopy. The combustion performance of the as-prepared cotton fabrics was tested and evaluated. After coating with HCCP-BNN, the combustion rate of the fabric is reduced in vertical and horizontal combustion conditions and the limiting oxygen-index value of cotton fabric increases to 24.1, becoming less flammable than the blank cotton. The fibrous structure of the BNN and HCCP-BNN coated fabrics is relatively complete after combustion, which indicates that BNN have a certain protective effect on the fabric. The results demonstrate HCCP-BNN as an effective flame-retardant for cotton fabrics.

On the Possibility of Occurrence of Anisotropy in Processing of Cu-CNT Composites by Powder Metallurgical Techniques

2012 ◽  
Vol 710 ◽  
pp. 285-290 ◽  
Author(s):  
Anoop Kumar Shukla ◽  
Niraj Nayan ◽  
S.V.S. Narayana Murty ◽  
S.C. Sharma ◽  
Kallol Mondal ◽  
...  
Keyword(s):  
Hot Pressing ◽  
Composite Powder ◽  
Pure Copper ◽  
Multiwall Carbon Nanotubes ◽  
Axial Direction ◽  
High Energy ◽  
Processing Technique ◽  
Structure Property ◽  
Mechanically Alloyed ◽  
Degree Of Anisotropy

Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

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