For electronic communication, the substrate of printed circuit board must has excellent dielectric properties: low dielectric constant and low dielectric loss[1, 2]. The lower the dielectric constant is, the faster the signal transfers; The lower the dielectric loss is, the better the integrity of signal transfers in the medium[3, 4]. Generally, the substrate is composed of resin and glass fibers. The resin has excellent dielectric properties, its dielectric constant is about 2.8 ~ 3.0 [5]. But the dielectric constant of glass fibers is too higher, such as E glass fiber’s dielectric constant is 6.7 ~ 7.3 at 1 MHz frequency [6]. Therefore, the poor dielectric property of glass fibers is the key factor restricting the improvement of substrate performance. However, the development of low dielectric properties glass fibers has been a bottleneck all along, so it is imperative to find a substitute.
Just like glass fibers, the basalt fiber can also be used as reinforced materials [7]. Compared with glass fibers, the basalt fiber has some better properties such as good modulus [8], high temperature resistance [9], high strength and capable of chemical resistance [10, 11]. Basaltic rocks are the only raw materials for basalt fiber production. Basalt is an igneous rock and it is the main component of the earth's oceanic crust, so basaltic rocks are abundant and low cost. However, there are no reports on the dielectric properties of basalt fibers, to the best of my knowledge.
In general, the dielectric properties of glass fibers can be suggested through measuring its amorphous glass blocks without crystallization [12]. Similarly, the dielectric properties of basalt fiber can also be obtained through evaluating the properties of amorphous basaltic glass [13]. So the preparation of amorphous basaltic glass is the key to get the dielectric properties of its basalt fiber.
But basaltic glass is easy to crystallize and form glass-ceramics during the annealing process[14]. Basaltic glass that contained 46 ~ 50% SiO2 and 9% FeO gave monophasic omphacite pyroxene at 950℃ [15]. Basaltic glass containing 49% SiO2, 3.81% Fe2O3 and 2.68% FeO formed pyroxene glass-ceramic with small portions of a glassy phase [16]. Crystallization of basaltic glass from the northern Harrat area in the temperature range of 800 ~ 1000 °C gave augitic pyroxene as the major phase with small amounts of olivine, haematite and magnetite [17]. The magnetite was easy to crystallize from basalt glass at 650℃ and augite at 860℃ [18]. In view of the fact that basaltic glass is easy to crystallize during high temperature annealing progress, the annealing temperature is set at 650 ℃ in our experiment to avoid crystallization.Therefore, the major purpose of this paper is to prepare amorphous basalt glass and measure its dielectric properties.