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A glass-ceramic-to-metal seal is a type of mechanical seal which binds glass-ceramic and metal surfaces. They are related to glass-to-metal seals, and like them are hermetic (airtight).
Glass-ceramics are polycrystalline ceramic materials prepared by the controlled crystallization of suitable glasses, normally silicates. Depending on the starting glass composition and the heat-treatment schedule adopted, glass-ceramics can be prepared with tailored thermal expansion characteristics. This makes them ideal for sealing to a variety of different metals, ranging from low expansion tungsten (W) or molybdenum (Mo) to high expansion stainless steels and nickel-based superalloys.
Glass-ceramic-to-metal seals offer superior properties over their glass equivalents including more refractory behaviour, in addition to their ability to seal successfully to many different metals and alloys. They have been used in electrical feed-through seals for such applications as vacuum interrupter envelopes and pyrotechnic actuators, in addition to many applications where a higher temperature capability than is possible with glass-to-metal seals is required, including solid oxide fuel cells.
In the formation of a glass-ceramic-to-metal seal, the parts to be joined are first heated, normally under inert atmosphere, in order to melt the glass and allow it to wet and flow into the metal parts, in much the same way as when preparing a more conventional glass-to-metal seal. The temperature is then normally reduced into a temperature regime where many microscopic nuclei are formed in the glass. The temperature is then raised again into a regime where the major crystalline phases can form and grow to create the polycrystalline ceramic material with thermal expansion characteristics matched to that of the particular metal parts.
The white opaque "glue" between the panel and the funnel of a colour TV cathode ray tube is a devitrified solder glass based on the system PbO-ZnO-B
2O
3. While this is a glass-ceramic-to-glass seal, the basic patent of S.A. Claypoole considers glass-ceramic-to-metal seals as well.
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick.
Glass-ceramics are polycrystalline materials produced through controlled crystallization of base glass, producing a fine uniform dispersion of crystals throughout the bulk material. Crystallization is accomplished by subjecting suitable glasses to a carefully regulated heat treatment schedule, resulting in the nucleation and growth of crystal phases. In many cases, the crystallization process can proceed to near completion, but in a small proportion of processes, the residual glass phase often remains. Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so-called "controlled crystallization" in contrast to a spontaneous crystallization, which is usually not wanted in glass manufacturing. Glass-ceramics have the fabrication advantage of glass, as well as special properties of ceramics. When used for sealing, some glass-ceramics do not require brazing but can withstand brazing temperatures up to 700 °C. Glass-ceramics usually have between 30% [m/m] and 90% [m/m] crystallinity and yield an array of materials with interesting properties like zero porosity, high strength, toughness, translucency or opacity, pigmentation, opalescence, low or even negative thermal expansion, high temperature stability, fluorescence, machinability, ferromagnetism, resorbability or high chemical durability, biocompatibility, bioactivity, ion conductivity, superconductivity, isolation capabilities, low dielectric constant and loss, corrosion resistance, high resistivity and break-down voltage. These properties can be tailored by controlling the base-glass composition and by controlled heat treatment/crystallization of base glass. In manufacturing, glass-ceramics are valued for having the strength of ceramic but the hermetic sealing properties of glass.
A cermet is a composite material composed of ceramic (cer) and metal (met) materials.
Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms from bulk solid-state components to high surface area forms such as thin films, coatings, and fibers. Such devices have found widespread use for various applications in the electro-optical field including: optical fibers for guided lightwave transmission, optical switches, laser amplifiers and lenses, hosts for solid-state lasers and optical window materials for gas lasers, and infrared (IR) heat seeking devices for missile guidance systems and IR night vision.
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion, making them more resistant to thermal shock than any other common glass. Such glass is subjected to less thermal stress and can withstand temperature differentials without fracturing of about 165 °C (300 °F). It is commonly used for the construction of reagent bottles and flasks as well as lighting, electronics, and cookware.
A hermetic seal is any type of sealing that makes a given object airtight. The term originally applied to airtight glass containers, but as technology advanced it applied to a larger category of materials, including rubber and plastics. Hermetic seals are essential to the correct and safe functionality of many electronic and healthcare products. Used technically, it is stated in conjunction with a specific test method and conditions of use.
In materials science, the sol–gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon (Si) and titanium (Ti). The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network of either discrete particles or network polymers. Typical precursors are metal alkoxides. Sol-gel process is used to produce ceramic nanoparticles.
Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.
The role of the substrate in power electronics is to provide the interconnections to form an electric circuit, and to cool the components. Compared to materials and techniques used in lower power microelectronics, these substrates must carry higher currents and provide a higher voltage isolation. They also must operate over a wide temperature range.
A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.
Thermal barrier coatings (TBCs) are advanced materials systems usually applied to metallic surfaces operating at elevated temperatures, such as gas turbine or aero-engine parts, as a form of exhaust heat management. These 100 μm to 2 mm thick coatings of thermally insulating materials serve to insulate components from large and prolonged heat loads and can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications. Due to increasing demand for more efficient engines running at higher temperatures with better durability/lifetime and thinner coatings to reduce parasitic mass for rotating/moving components, there is significant motivation to develop new and advanced TBCs. The material requirements of TBCs are similar to those of heat shields, although in the latter application emissivity tends to be of greater importance.
Glass-to-metal seals are a type of mechanical seal which joins glass and metal surfaces. They are very important elements in the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass-encapsulated semiconductor diodes, reed switches, glass windows in metal cases, and metal or ceramic packages of electronic components.
Ultrasonic soldering is a flux-less soldering process that uses ultrasonic energy, without the need for chemicals to solder materials, such as glass, ceramics, and composites, hard to solder metals and other sensitive components which cannot be soldered using conventional means.
Solid is one of the four fundamental states of matter. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.
Soldering is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.
AlSiC, pronounced "alsick", is a metal matrix composite consisting of aluminium matrix with silicon carbide particles. It has high thermal conductivity, and its thermal expansion can be adjusted to match other materials, e.g. silicon and gallium arsenide chips and various ceramics. It is chiefly used in microelectronics as substrate for power semiconductor devices and high density multi-chip modules, where it aids with removal of waste heat.
Glass frit bonding, also referred to as glass soldering or seal glass bonding, describes a wafer bonding technique with an intermediate glass layer. It is a widely used encapsulation technology for surface micro-machined structures, e.g., accelerometers or gyroscopes. This technique utilizes low melting-point glass and therefore provides various advantages including that viscosity of glass decreases with an increase of temperature. The viscous flow of glass has effects to compensate and planarize surface irregularities, convenient for bonding wafers with a high roughness due to plasma etching or deposition. A low viscosity promotes hermetically sealed encapsulation of structures based on a better adaption of the structured shapes. Further, the coefficient of thermal expansion (CTE) of the glass material is adapted to silicon. This results in low stress in the bonded wafer pair. The glass has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures occurs. The usual temperature of achieving flowing and wetting is between 450 and 550 °C.
Materials for use in vacuum are materials that show very low rates of outgassing in vacuum and, where applicable, are tolerant to bake-out temperatures. The requirements grow increasingly stringent with the desired degree of vacuum to be achieved in the vacuum chamber. The materials can produce gas by several mechanisms. Molecules of gases and water can be adsorbed on the material surface. Materials may sublimate in vacuum. Or the gases can be released from porous materials or from cracks and crevices. Traces of lubricants, residues from machining, can be present on the surfaces. A specific risk is outgassing of solvents absorbed in plastics after cleaning.
Ultra-high-temperature ceramics (UHTCs) are a type of refractory ceramics that that can withstand extremely high temperatures without degrading, often above 2,000 °C. They also often have high thermal conductivities and are highly resistant to thermal shock, meaning they can withstand sudden and extreme changes in temperature without cracking or breaking. Chemically, they are usually borides, carbides, nitrides, and oxides of early transition metals.
Lithium disilicate (Li2Si2O5) is a chemical compound that is a glass ceramic. It is widely used as a dental ceramic due to its strength, machinability and translucency.
