PROBLEM TO BE SOLVED: To provide a BaO-free and PbO-free X-ray opaque glass which is suitable as dental glass or optical glass and has zirconium having a relatively low refractive index nd.SOLUTION: The BaO-free and PbO-free X-ray opaque glass is the system SiO2-B2O3-Al2O3-R2O-RO-La2O3-ZrO2, mass% in terms of oxide, wherein the glass comprises 48-56% of SiO2, 3-8% of B2O3, 0.5-4% of Al2O3, 0-5% of Li2O, 1-4% of Na2O, 2-7% of K2O, 10-16% of Cs2O, 5-9% of CaO, 0-5% of MgO, 0.5-13% of ZrO2, 5-12% of La2O3, 0-4% of SnO2, 16-21% of &Sigma alkali metal oxides, and the amount of Cs2O+La2O3+SnO2&ge19%, wherein the glass has a refractive index nd of 1.54-1.58 and an aluminium equivalent thickness of at least 500%.COPYRIGHT: (C)2011,JPO&INPIT【課題】特に歯科用ガラスとして及び光学ガラスとして適し、比較的低い屈折率ndを有するジルコニウム含有でBaO-フリー及びPbO-フリーのX線不透過性ガラスを提供する。【解決手段】BaO-フリー及びPbO-フリーのX線不透過性ガラスは、SiO2-B2O3-Al2O3-R2O-RO-La2O3-ZrO2系であり、酸化物基準の質量%表示で、SiO2 48~56%、B2O3 3~8%、Al2O3 0.5~4%、Li2O 0~5%、Na2O 1~4%、K2O 2~7%、Cs2O 10~16%、CaO 5~9%、MgO 0~5%、ZrO2 0.5~13%、La2O3 5~12%、SnO2 0~4%、Σアルカリ金属酸化物 16~21%、Cs2O+La2O3+SnO2 ≧19%を含有し、1.54~1.58の屈折率nd及び少なくとも500%のアルミニウム等価厚を有する。【選択図】なし
