XRF Detects Metallic Oxides in Glasses

X-ray fluorescence (XRF) technology is well known for analyzing elemental composition in a variety of applications, including scrap metal, oil and gas piping, manufacturing quality control, precious metal analysis, and even glass analysis.

Glass can be colored by the addition of various metal oxides. According to geology.com, the technique has been around for centuries: As early as 3500 BCE, colored glass beads and small blown-glass vessels were being made in Mesopotamia and Ancient Egypt. In the eighth century, the Persian chemist Geber, the “father of chemistry,” realized that metal oxides were the key ingredients for coloring glass.

In-depth coloring is obtained by adding various metallic oxides, sulfide, or other compound of that metal to molten glass. Metals used to impart color include cadmium sulfide for yellow, gold chloride for red, nickel oxide for violet, and cobalt oxide for blue. Slight coloration can be achieved by adding ppm levels of cobalt oxides and selenium, which may be applied in the manufacture of glass for car windshields, for example. Manganese dioxide and sodium nitrate are used as decoloring agents to neutralize the coloring impact of impurities in the glass.

The simplest form of glass is the single component fused silica (SiO₂), which is difficult to process and expensive. To reduce these difficulties, other oxides are added imparting specific properties to the glass. Glasses used in construction are referred to as flat glasses. Most of them are composed of about 70% silica, which is a glass former, soda as a flux in the form of carbonate and sulfate (about 14%), lime as a stabilizer in the form of limestone (about 10%). Other types of oxides like alumina or magnesia improve the physical characteristics of glass, particularly the resistance to atmospheric conditions.

Read Analysis of Glass see study results demonstrating that XRF analysis is well suited to produce high precision results for the determination of the main oxides and the coloring agents in glasses. In this experiment, a series of flat glass standard samples were measured on lab-based XRF analyzer. Calibration curves were derived by relating intensities for each oxide (or element) to concentrations in the standard samples. X-ray fluorescence measures elements, but the results can be related directly to the oxide forms of these elements when only one single form is present in the sample. Using the calibration curves, limits of detection were derived for the most common oxides found in flat glasses.

Read Analysis of Glass