Rapid identification method for inclusions in evaluating high-purity quartz

Abstract

The rapid growth of semiconductor, photovoltaic, and other emerging industries has led to a sharp increase in the demand for high-purity quartz in China, particularly 4N5-grade (99.995% pure SiO2). However, heavy reliance on imported high-purity quartz poses a significant risk to the security of key national strategic industries. To address this challenge, China is focusing on identifying domestic sources of high-purity quartz and developing efficient evaluation methods. This study investigates the inclusion content in three types of quartz: pegmatite, vein quartz, and white granite. A grading system based on the transmittance of quartz grains was established by analyzing the number of inclusions. Five quartz ore samples from different regions were purified, and the resulting concentrates were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The relationships among the inclusion content of raw quartz, impurity composition of purified quartz, and quality of sintered fused quartz products were examined. The findings demonstrate that quartz with fewer inclusions results in lower impurity levels after purification, higher SiO2 purity, and more translucent glass, as confirmed by firing tests. Herein, this study establishes a clear connection between quartz inclusions and the overall quality of high-purity quartz. The proposed approach enables the rapid assessment of quartz deposit quality by identifying inclusions, offering a practical and efficient method for locating high-quality quartz resources.

1. Introduction

High-purity quartz is an essential material widely used in semiconductors, optical fibers, photovoltaics, aerospace, military technology, laboratory equipment, and other advanced fields [1–5]. Its critical role in these industries makes it a highly sought-after material, with demand continuing to grow rapidly as global science and technology advance [6–7]. However, the number of deposits capable of producing high-purity quartz is limited and unevenly distributed worldwide [8]. Currently, China relies heavily on imports of high-purity quartz (above 4N5 grade) for strategic applications. To reduce this dependency, it is an urgent need to identify domestic sources of high-quality quartz quickly and efficiently.

High-purity quartz is distinguished by an exceptionally high SiO2 content compared with the standard quartz. The international standard for high-purity quartz requires a minimum SiO2 concentration of 99.995% [9]. In addition to SiO2, trace amounts of impurity elements, such as Al, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, and Ti, as well as small molecules, like CO2 and H2O, are presented in high-purity quartz [10–11]. According to the standards for the IOTA-series products from Sibelco North America (formerly Unimin), among these 13 key impurity elements, Al and Ti typically have slightly higher concentrations, in the range of 7–16.2 and 1.1–1.4 μg·g−1, respectively, while the concentrations of the other impurities are below 1.0 μg·g−1 [12]. To qualify as high-purity quartz, the total impurity content must be less than 19.66 μg·g−1, and SiO2 purity must exceed 99.998%. Such high-grade quartz products are in high demand globally [13]. Götze and Möckel [14] established additional concentration limits for impurity elements in high-purity quartz sourced from Norwegian deposits. The maximum allowable concentrations of elements include Al < 30 μg·g−1, Ti < 10 μg·g−1, Na < 8 μg·g−1, K < 8 μg·g−1, Li < 5 μg·g−1, Ca < 5 μg·g−1, Fe < 3 μg·g−1, P < 2 μg·g−1, and B < 1 μg·g−1, with the total concentration of these elements not exceeding 50 μg·g−1. In response to evolving domestic and international market demands, Wang [15] proposed a refined classification for high-purity quartz in China based on SiO2 purity levels (Table 1). This classification includes high-end quartz with ...