In modern medical imaging and industrial testing, the X-ray tube is an indispensable core component. The mainstream product today—the Ceramic Envelope X-ray Tube—did not exist from the very beginning; its emergence went through an evolutionary process from glass to ceramic.
The Age of Glass Tubes
Going back to 1895, when Wilhelm Röntgen discovered X-rays, the device he used was exactly a Crookes tube with a glass envelope. For a long time thereafter, glass remained the standard material for X-ray tube envelopes. Glass is easy to shape, low in cost and mature in processing, so almost all early X-ray imaging equipment relied on glass tubes.
However, with the advancement of technology, the drawbacks of glass have gradually come to light. First of all, its mechanical strength is insufficient. It is prone to cracking when subjected to mechanical vibrations and impacts during transportation and installation, resulting in equipment scrappage. Secondly, its extremely low fracture toughness and thermal conductivity lead to poor thermal shock resistance. When an X-ray tube is in operation, significant temperature gradients form across different parts of the glass envelope, generating thermal stress. Changes in the operating power of the X-ray tube will further exacerbate the accumulation of thermal stress, causing the glass to develop cracks or even shatter. What is worse, glass has poor high-temperature stability. High temperatures can soften the glass, severely impairing its electrical insulation performance, which is likely to induce leakage current and electrical breakdown. All these issues have become bottlenecks restricting the further development of X-ray imaging.
The birth of ceramic tubes
To overcome these limitations, researchers turned their attention to ceramics. In the middle and late 20th century, ceramic-envelope X-ray tubes began to emerge onto the historical stage. High-purity alumina ceramics are usually the material of choice, which boast comprehensive properties far superior to those of glass: their extremely high strength and relatively high toughness enable ceramic tubes to withstand stronger mechanical impacts; their better thermal conductivity keeps internal thermal stress low and enhances thermal shock resistance; their excellent electrical insulation performance and high-temperature stability allow ceramic tubes to be more compact and operate at higher power levels without suffering electrical breakdown. On the other hand, the increasingly mature metal-ceramic vacuum sealing technology is also the key to the practical application of ceramic tubes.
Thus, ceramic tubes have brought about innovations in multiple aspects: their reliability is significantly improved, and their service life far exceeds that of glass tubes; their higher power and thermal load capacity enable high-end equipment such as computed tomography (CT), digital radiography (DR), and digital subtraction angiography (DSA) to achieve high-speed and high-resolution imaging; at the same time, ceramic tubes are smaller in size and lighter in weight, making them particularly suitable for the needs of mobile equipment. In terms of safety, even if they break under extreme conditions, ceramic fragments are far more controllable than glass shards. It can be said that ceramic materials have completely solved the fundamental defects that have plagued glass tubes.
Present and Future
Nowadays, ceramic X-ray tubes have become the mainstream equipment in the fields of medical imaging and industrial non-destructive testing. Ranging from stationary anodes to rotating anodes, from conventional focal spots to micro-focal spots, and even to megawatt-class high-power industrial tubes, ceramic envelope technology can cover them all. Continuous optimizations of anode target materials, cathode electron guns, cooling technologies and bearing structures have enabled ceramic tubes to constantly push the limits of power density and imaging performance.
Looking ahead, the development trends of ceramic X-ray tubes are mainly focused on several directions. First is the achievement of higher power density to meet the requirements of ultra-high-speed CT scanning and low-dose imaging, which involves new types of target materials and more advanced cooling designs. Second is the development of more compact and lightweight designs to adapt to emerging applications such as portable equipment and surgical robots. Intelligence is also a major trend: by integrating sensors to monitor real-time status including vacuum level and temperature, predictive maintenance can be realized. Meanwhile, the introduction of new processes such as advanced ceramic matrix composites, nano-coatings and even 3D printing is expected to further enhance the performance and service life of the tubes.
Summary
It can be said that glass tubes laid the foundation, while ceramic tubes represented a leap forward. Glass tubes brought X-ray imaging from scratch, yet due to their fragility and performance limitations, they gradually faded out of mainstream application scenarios. In contrast, ceramic tubes have become the cornerstone of modern imaging technology by virtue of their outstanding performance. Looking ahead, with the continuous emergence of more efficient materials and smarter designs, ceramic X-ray tubes will continue to play a core role for a long time to come, driving medical imaging and industrial testing to new heights.