One of the main uses of ruthenium is in alloys with platinum, palladium or titanium. It hardens the platinum and palladium, which makes it useful for making durable electrical contacts. When used with titanium it increased the corrosion resistance of the metal. It is also alloyed with gold to make gold jewelry more stable. It may also be used in some superalloys, which are most commonly used in the aerospace industry. Alloys containing ruthenium may also used in the nib of a fountain pen. Ruthenium dioxide is used in creating thick film chip resistors, which are used to produce many electronic devices such as integrated circuits and sensors. The isotope 106Ru is used in radiotherapy treatment of some eye tumors. Complexes of ruthenium are also being tested for anticancer properties. Ruthenium is used in mixed-metal oxide anodes, which are used to protect submerged structures and to generate chlorine from salt water. It is also used in some optical sensors to measure oxygen. Ruthenium red is a stain used to study certain molecules with a microscope. Ruthenium is an important catalyst and is used in many different industries. It is also being tested for use in solar energy conversion and data storage.