## 3 Results and Discussion  
The purity of quartz sand is one of the key factors affecting the quality of quartz glass. The quality of the quartz sand will directly affect the quality of the quartz glass. Therefore, it is especially important to choose a suitable quartz sand. Table 1 shows the impurity content of two kinds of high-purity quartz sand. The SiO\({}_{2}\) content of sample I (99.997%) is higher than that of sample II (99.982%). The content of the alkali metal impurities (Li, Na, and K) of sample I is only 3.77 ppm, and the content of the alkali metal impurities will directly affect the loss of permeability and the thermal stability of the quartz glass. Figure 2 shows the morphology photo of the quartz sand under a laser confocal microscope. The morphology of sample I is lumpy with a similar aspect ratio. The morphology of sample II is mostly long columnar. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline Sample & \begin{tabular}{c} **SiO\({}_{2}\)** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **Al** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **B** \\ **Ca** \\ \end{tabular} & \begin{tabular}{c} **Ca** \\ \end{tabular} & \begin{tabular}{c} **Cu** \\ \end{tabular} & \begin{tabular}{c} **Fe** \\ \end{tabular} & \begin{tabular}{c} **K** \\ \end{tabular} & \begin{tabular}{c} **Li** \\ **Li** \\ \end{tabular} & \begin{tabular}{c} **Mg** \\ **Mg** \\ \end{tabular} & \begin{tabular}{c} **Mn** \\ \end{tabular} & \begin{tabular}{c} **Na** \\ \end{tabular} & \
\begin{tabular}{c} **Ni** \\ \end{tabular} &
\begin{tabular}{c} **Ti** \\ \end{tabular} \\ \hline I & 99.997 & 17.28 & 0.04 & 0.58 & \textless{}0.01 * & 0.02 & 0.17 & 0.15 & 2.32 & \textless{}0.04 * & \textless{}0.01 * & 1.43 & \textless{}0.02 * & 1.52 \\ \hline II & 99.982 & 128.6 & 1.39 & 0.7 & \textless{}0.03 * & 0.04 & 0.17 & 0.92 & 42.3 & \textless{}0.08 * & 0.14 & 12.1 & \textless{}0.03 * & 0.07 \\ \hline \end{tabular}
\end{table} 
Table 1: Content of impurity elements in different types of high-purity quartz sand. Figure 1: Process flow diagram. Figure 3 shows photographs of the bubble distribution of the quartz glass prepared using different quartz sands. As can be seen from Figure 3, the number of bubbles in the quartz glass prepared from raw material I is smaller than in the quartz glass prepared from raw material II, and the average size of the bubbles is much smaller than in raw material II. The bubble defects in quartz glass due to residual impurities can be greatly reduced because of the lower content of residual impurities in raw material I. Therefore, the high-purity quartz sand of type I was selected as the raw material of the quartz glass. Compressive strength and tensile strength are two important characteristics of quartz glass. The compressive strength of the samples was tested by the indentation method, and the results are shown in Table 2. The compressive strength of the samples was in the range of 737.7-767.1 GPa. The samples were processed to measure the tensile strength, and the dimensional error of the quartz glass processing was \(\pm\)0.05 mm. The testing instrument recorded the tensile value of each test sample in real time from the beginning of stretching to the occurrence of rupture. In order to minimize the testing error, five samples of quartz glass were tested, and the tensile strength was calculated according to Equation (1). \[R_{m}=\frac{F_{m}}{A} \tag{1}\]  
where \(R_{m}\) denotes the tensile strength of the sample; \(F_{m}\) denotes the value of the maximum tensile force corresponding to the occurrence of a fracture in the sample; and A denotes the cross-sectional area of the fracture zone. The tensile strength of the samples was 6.88-9.64 MPa, only one-seventieth of the compressive strength, which is consistent with the general results for materials such as glass and ceramics, i.e., compressive strength is much greater than tensile strength.