Computed Tomography (CT) scanner in hospital

Glass 8245 for X-Ray Sources

Used in a wide range of radiographic diagnostics devices, glass 8245 for X-ray tubes not only reliably ensures the required high vacuum but also forms a mechanically stable connection to metal and insulates anodes from cathodes, particularly at high voltages.

Linked by location and technology

A distance of just 40 km separates the home of SCHOTT AG in Jena, Thuringia from the Siemens Healthineers facility in Rudolstadt, Germany. Both tech companies can look back on more than 100 years of history and are now linked by close technological cooperation. Siemens Healthineers uses glass 8245 to manufacture vacuum components, X-ray tubes and X-ray beams, as well as detectors for diagnostic devices such as Computed Tomography (CT) scanners. The glass forms a gas-tight seal and insulator between the anode and cathode of the X-ray tube.

Logo Siemens Healthineers

Task

In an X-ray tube, a voltage of 25 to several hundred kilovolt (kV) in a high vacuum accelerates electrons from the cathode to the anode, where they crash into the anode metal and emit the characteristic X-rays. Glass is an ideal barrier also in form of a seal with metals since it prevents the entrance of air molecules that would inhibit the x-ray formation in the tube, the high ohmic resistance of the borosilicate glass SCHOTT 8245 (107.4 to 105.9 Ω.cm even at temperatures of 250 °C to 350 °C) electrically separates cathodes and anodes.

Solution

Siemens Healthineers acquires the glass as cylinders in a variety of diameters, for example, 75.5 mm. The further processing includes bonding rings made of the nickel-iron-cobalt alloy Kovar being connected at both ends and later assembled into the x-ray tube. The rings are first roughened and cleaned by sandblasting, then annealed. The glass is then heated, 3d formed according to the needs and fused with the sealing rings, which creates a vacuum-tight glass-metal connection. 
    Four clear tubes of SCHOTT Glass 8245
    1/5
    Due to its sealing and electrical properties, the borosilicate glass SCHOTT 8245 is ideally suited for X-ray tubes.
    A glass tube being heated to be widened
    2/5
    In the first optional step the glass tube is heated and widened or blown into a mold to abtain the desired contour.
    A sealing ring being fused to a glass tube
    3/5
    The glass is then fused with the sealing rings to create a vacuum-tight glass-metal connection.
    Siemens Heathineers: Glasrohr wird gegen eine Form aufgeblasen, um die gewünschte Kontur zu erstellen
    4/5
    Finally, the glass tube is blown into a mold to obtain the desired contour.
    Glass X-ray flask with angled rings
    5/5
    The final product is used for some of the most technically advanced radiographic devices in medicine.

    Long-term stability and reliability

    The stable vacuum-tight bond is particularly crucial to the long-term function of X-ray tubes. This is because high mechanical forces can occur in the glass tube at the glass-metal seal when the X-ray source is moved around the patient computed tomography. Moreover, unavoidable vibrations occur. “We need a glass of very high quality, without airlines or other impurities,” explains Daniel Kutschbach, a process engineer at Siemens Healthineers in Rudolstadt, who’s responsible for the components of X-ray tubes and glass processing. “We ensure this by closely monitoring each processing step.”
    Daniel Kutschbach, Process Engineer/Production Management Vacuum Components, Siemens Healthineers
    The high quality of the glass already meets our requirements. Nevertheless we have recently working with SCHOTT to improve yield in our production processes and save resources and costs.
    Wide glass X-ray flask with angled rings

    SCHOTT offers glass tubes in various dimensions to meet each customer's requirements.

    View from the control room of a CT scanner in a hospital

    X-ray tubes made from SCHOTT glass are vital for diagnosis in medical centers and hospitals.

    Used materials

    The permanent sealing of the borosilicate glass SCHOTT 8245 with a metal alloy is only possible because both materials have the same thermal coefficient of expansion as they are heated to 400 °C during operation. If the glass and metal expanded at different rates, mechanical stresses will occur and eventually lead to breakage.

    Unlike many applications, the optical specifications of the glass are irrelevant since radiation can exit the tubes also through a radiolucent titanium window. During a typical three-year service time the glass even turns brown, but this does not impair its functionality.

      Sealing glass tubing for Kovar
      Sealing glass tubing for Kovar
      Glass types for direct sealing to Kovar

      SCHOTT 8250

      This borosilicate glass is ideal for sealing to Kovar and molybdenum, and it offers outstanding electrical insulation. Popular applications for this glass include X-ray and transmitting tubes, image amplifier tubes, cladding tubes for optical fibers, ozone generators, and helium-neon (He-Ne) laser systems.

      SCHOTT 8245

      A borosilicate glass suited to sealing to Kovar, metals and molybdenum, SCHOTT 8245 offers outstanding low background noise for sensors and provides minimal X-ray absorption similar to SCHOTT 8250. Popular applications include X-ray and photomultiplier tubes.

      SCHOTT 8800R

      This highly chemically resistant glass is suitable for outdoor use in ambient conditions such as solar thermal power stations.
       

      Glass types for transition from DURAN® to Kovar

      SCHOTT 8447

      This intermediate glass is a sealing partner for SCHOTT 8449 and the alloy Kovar. It’s suitable for use in transmitter and X-ray tubes, as well as other electronic systems.

      SCHOTT 8448

      SCHOTT 8448 is an intermediate sealing glass that bonds effectively to DURAN® borosilicate glass tubing, SCHOTT 8449, and tungsten. It is suitable for use in transmitter and X-ray tubes, as well as other electronic systems.

      SCHOTT 8449

      This intermediate glass offers glass-to-glass sealing with SCHOTT 8447 and 8448, enabling it to be used in the same applications as SCHOTT 8448 and SCHOTT 8447 as a graded seal containing all three glass types.

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      A successfull joint team

      Glass made by
      SCHOTT

      Installed by
      Siemens Healthineers

      Want to know more? Let’s talk

      Whether you need more information, samples, a quote, or advice for a project, we would be delighted to talk to you.

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