1980 年 36 巻 7 号 p. 343-349
An effective boronizing process to titanium diaphragm has been developed. The process provides a diaphragm with large specific modulus of elasticity and bending stiffness. Titanium diaphragms are buried in a mixed powder of boron (70wt%), carbon black (20wt%) and sodium carbonate (10wt%) and heated at a required temperature for a required time under 1Pa pressure. By this process, Young's modulus of boronized titanium sheets with 25μm and 35μm thickness are brought up to 2. 5×10''N/m^2 and 2. 3 × 10''N/m^2 respectively. Density of boronized titanium sheets is about 4. 5×10^3kg/m^3, which is almost equal to the density of titanium. Cross section of boronized titanium sheet consists of TiB_2 surface layer, TiB spike and Ti layer which is located in the middle of the section. High frequency resonance of 2. 5 cm diameter dome type loudspeaker with boronized diaphragm reaches to 37kHz which is about 1. 5 times higher than that of the titanium diaphragm loudspeaker with same shape. 12cm cone type loudspeaker using the boronized diaphragm has flatter and wider frequency response and lower harmonic distortion than that of titanium diaphragm loudspeaker with same shape.