Development of non-shrinkable ceramic composites for use in high-power microwave tubes

Abstract

Al₂O₃-CaO-SiC-based ceramic composites with four different compositions were sintered at 1700°C for 3 h in an air furnace. The phase analysis, microstructural characterization, and elemental composition determination of the developed composites were performed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDAX) analysis, respectively. The shrinkage, thermal properties, and electrical resistivity of the composites were also studied. The experimental results showed the effects of adding silicon carbide and calcia to alumina on the thermal, electrical, and shrinkage properties of the resultant composites. Among the four investigated ceramic composites, the one composed of 99wt% alumina, 0.5wt% CaO, and 0.5wt% SiC exhibited the best characteristics for use as a potting material in a dispenser cathode of a microwave tube. The material exhibited slight expansion instead of shrinkage during drying or firing. Other properties of the composite powder, such as its thermal properties and electrical resistivity, were comparable to those of a commercial alumina powder.

Keywords

Al₂O₃-CaO-SiC composite / expansion / potting material / dispenser cathode / microwave tube

References

[1] L. Wolverton, J.O. Tarter, Thermal, R.E. Eitel, M. Weisenberger, and C. Dowden, Properties of alumina cathode heater potting materials, [in] International Vacuum Electronics Conference (IVEC), IEEE International, USA, 2010, p. 165.

[2] R.B. True, M.F. Kirshner, L. Turek, G.R. Good, R.J. Hanse, T.M. Bemis, and R.J. Bartkowski, Dispenser cathode high power gridded klystron gun, [in] International Vacuum Electronics Conference (IVEC), IEEE International, USA, 2004, p. 328.

[3] T.J. Grant and L.R. Falce, Impact of dispenser cathode thickness on useful operating life, [in] International Vacuum Electronics Conference (IVEC), IEEE International, USA, 2004, p. 305.

[4] Shields VB. Applications of silicon carbide for high temperature electronics and sensors. NASA Jet Propulsion Laboratory, Tech Briefs, 1996, 20, 55.

[5] P. Swartzentruber, M. Collier, R. Dewees, W. Epperson, C. Poole, B. Rupp, D. Bowling, E. Fadde, A. Floyd, P. Rottmann, R. Wilson, T.J. Balk, S. Roberts, J. Tarter, and M. Effgen, Alternative ceramic potting materials for dispenser cathodes, [in] International Vacuum Electronics Conference (IVEC), IEEE International, USA, 2012, p. 483.

[6] Barik RK, Bera A, Raju RS, Tanwar AK, Baek IK, Min SH, Kwon OJ, Sattorov MA, Lee KW, Park GS. Development of alloy-film coated dispenser cathode for terahertz vacuum electron devices application. Appl. Surf. Sci., 2013, 276, 817.

[7] Bhattacharya R, Khatun H, Singh NK, Singh U, Sinha AK. Design of cathode heater assembly for high power gyrotron. Frequenz, 2013, 67(5–6): 163.

[8] Pedrini D, Misuri T, Paganucci F, Andrenucci M. Development of hollow cathodes for space electric propulsion at Sitael. Aerospace, 2017, 4(2): 26.

[9] L. Ives, G. Miram, M. Read, M. Mizuhara, P. Borchard, L. Falce, and K. Gunther, Development of improved cathodes for high power RF sources, [in] Proceedings of the Particle Accelerator Conference, IEEE International, USA, 2003, p. 1113.

[10] Marchewka CD. Non-Uniform Emission Studies of a Magnetron Injection Gun, 2006, USA, Massachusetts Institute of Technology (MIT) 1.

[11] Gilmour AS Jr. Microwave Tubes, 1986, Boston, Artech House 733.

[12] Simmons DF, Fortgang CM, Holtkamp DB. Using multispectral imaging to measure temperature profiles and emissivity of large thermionic dispenser cathodes. Rev. Sci. Instrum., 2005, 76(4): 044901.

[13] Kaczynski DJ, Walsh K A. Beryllium Oxide. Conference of Raw Materials for Advanced and Engineered Ceramics, 1985, 6(9–10): 1261.

[14] Thamaraiselvi TV, Rajeswari SS. Biological evaluation of bioceramic materials—A review trends. Trends Biomater. Artif. Organs, 2004, 18(1): 9.

[15] Lamba OSS, Nangru SC, Joshi LM, Sharma A, Singh VP, Gupta NC. Choice of alumina ceramics for 5MW pulsed power klystron. Indian J. Eng. Mater. S., 2000, 7(5): 443.

[16] S. Roberts, Sources of temperature variance in dispenser cathodes, [in] International Vacuum Electronics Conference (WEC), IEEE International, USA, 2004, p. 299.

[17] Park CW, Yoon DY. Effects of SiO₂, CaO₂, and MgO additions on the grain growth of alumina. J. Am. Ceram. Soc., 2000, 83(10): 2605.

[18] Pal KS, Ghosh S, Dandapat N, Datta S, Basu D, Raju RS. Development of suitable potting material for dispenser cathodes of a high power microwave tube. Mater. Sci. Eng. B, 2012, 177(2): 228.

[19] P. Swartzentruber, M. Collier, R. DeWees, W. Epperson, C. Poole, B. Rupp, D. Bowling, E. Fadde, A. Floyd, P. Rottmann, R. Wilson, T.J. Balk, S. Roberts, J. Tarter, and M. Effgen, Alternative ceramic potting materials for dispenser cathodes, [in] International Vacuum Electronics Conference (IVEC), 2012, IEEE International, Monterey, CA, USA, p. 483.

[20] Kisko A, Talonen J, Porter DA, Kaijalainen LP. Effect of Nb microalloying on reversion and grain growth in a high-Mn 204Cu austenitic stainless steel. ISIJ Int., 2015, 55(10): 2217.

[21] Miao S, Xie ZM, Zeng LF, Zhang T, Wang XP, Fang QF, Liu CS. Mechanical properties, thermal stability and microstructure of fine-grained W-0.5wt% TaC alloys fabricated by an optimized multi-step process. Nucl. Mater. Energy, 2017, 13, 12.

[22] G.E. Jr. Oxidation behavior of silicon carbide. J. Am. Ceram. Soc., 1958, 41(9): 347.

[23] Ogbuji LUJT, Singh M. High-temperature oxidation behavior of reaction-formed silicon carbide ceramics. J. Mater. Res., 1995, 10(12): 3232.

[24] Theerapapvisetpong A, Jiemsirilers S, Thavorniti P, Conradt R. Barium-free glass-ceramic sealants from the system CaO-MgO-B₂O₃-Al₂O₃-SiO₂ for application in the SOFC. Mater. Sci. Forum, 2011, 695, 1.