Heat dissipation of electronic devices was an urgent problem to be addressed. In this paper, magnesium borate whiskers were used as the template for the preparation of the boron nitride submicron tube (BNST). Then the polymerfree supported three-dimensional boron nitride submicron tube skeleton was prepared by sacrificing the material ammonia bicarbonate. Finally, high thermal conductivity boron nitride submicron tube/epoxy resin (BNST/EP) composites were prepared by infiltrating technique. The phase, chemical composition, microstructure, thermal conductivity, and thermal stability of the samples were studied by X-ray diffraction, scanning electron microscopy, and other characterization methods. The results show that BNST has an average diameter was 2 um and the tube length was 5-20 um. The surface of BNST was loaded with a large number of boron nitride nanosheets. The in-plane thermal conductivity of the BNST/EP composite was improved by the three-dimensional BNST skeleton. When the BNST was 39.28 wt%, the inplane thermal conductivity reached 1.632 W/(m K). Compared with pure EP, the in-plane thermal conductivity was increased by 782.2%. BNST played a good physical barrier effect on the matrix, so the thermal stability of the composite was greatly improved. This strategy will open up a new path to prepare heat dissipation materials.

In this paper, the novel boron nitride micron tubes (BNMTs) were used to reinforce commercial boron carbide (B 4 C) ceramics prepared via spark plasma sintering technology. The effects of the sintering parameters, sintering temperature, the holding time, and the BNMTs content on the microstructure and mechanical properties of B 4 C/BNMTs composite ceramics were studied. The results indicated that adding a proper amount of BNMTs could inhibit the grain growth of B 4 C and improve the fracture toughness of the B 4 C/BNMTs composite ceramics. The prepared composite ceramic sample with 5 wt% BNMTs at 1850 • C, 8 min and 30 MPa displayed the best mechanical properties. The relative density, hardness, fracture toughness, and bending strength of the samples were 99.7% ± .1%, 35.62 ± .43 GPa, 6.23 ± .2 MPa m 1/2 , and 517 ± 7.8 MPa, respectively.Therein, the corresponding value of hardness, fracture toughness, and bending strength was increased by 10.3%, 43.59%, and 61.5%, respectively, than that of the B 4 C/BNMTs composite ceramic without BNMTs. It was proved that the high interface binding energy and bridging effect between boron carbide and BNMTs were the toughening principle of BNMTs.