Figure 1 The diagram of electrospray experiment

2.3 Characteristics Analysis

The structures and morphologies of samples prepared from electrospray method are observed by using field emission scanning electron microscopy (FE-SEM) (HITACHI High Technologies Corporation, S-4800II Japan). The secondary electron images are captured at 15 kV accelerating voltage. As for thermal analysis, thermogravimetric-differential scanning calorimetry (TG-DSC) (NETZSCH STA 449C Germany) is introduced to study the thermal properties of samples. The heating rate is 15 ^oC min^-1 from room temperature to 800^oC at argon atmosphere. The mass of sample in an 80 uL corundum crucible is about 3 mg. Finally, the X-ray diffraction (XRD) (Bruker, D8 Advance, Germany) analysis is used to figure out the phase in residues after thermal analysis.

2.4 Onset combustion test

To verify and record the characteristics of samples combustion, the heating wire ignition combustion system is designed and made, as shown in Figure 2. The diameter of heating wire is about 0.1 mm. The DC is employed as the power supply. Ignition and combustion processes are recorded by the high-speed camera (FASTCAM SA-Z Japan) with shutter speed at 50 us per picture. In each ignition and combustion test, the mass weight of sample is about 10 mg (±1 mg) directly touching with the heating wire. Then, the current value on the heating wire increases slowly and gradually. At the moment of ignition, the corresponding current value is recorded, which is set as ignition energy threshold, and in the meanwhile the shutter of high-speed camera is also pressed. A time period of 200 ms before the shutter time can be also recorded which ensures that we can fully document the process from the ignition moment to its extinction. In order to protect the camera from the burning sparks, a transparent tempered glass is placed between the sample and camera.