Speciality –hydroxide catalysis bonding (HCB).
Both science and industry are always interested in finding new technologies to join materials together with as much ease and reliability as possible. One of the relatively new kids on the block - hydroxide catalysis bonding (HCB) – is such a technique. It is a chemical technique used primarily to bond glass (e.g. fused silica) parts together, but can be used to join many other materials as well, like sapphire and silicon.
In HCB an alkali solution like sodium hydroxide is placed between two parts to be jointed. The alkali solution disconnects some of the silica molecules from the substrates and reacts chemically with them to form siloxane chains that interconnect the two substrates while water dissipates away from the bond. This technique can be used at room temperature, is quite safe and allows for very accurate alignment of components.
Field –gravitational wave astronomy and more specifically development of ground based interferometric gravitational wave detectors.
Gravitational waves as predicted by Einstein’s Theory of General Relativity are expected to cause extremely small positional changes of objects on Earth. Therefore any gravitational wave detector needs to be extremely sensitive. One of the most promising techniques is to use a laser interferometer such that the minute relative distance change between two paths (due to gravitational waves passing by) travelled by laser light can be measured. The paths are formed between mirrors suspended as pendulums which are a few kilometres apart. One can imagine that a lot of other things affect the position of the mirrors more than a gravitational wave; e.g. thermal fluctuations. One of the things done to reduce these noise sources is to make the mirror pendulum as one almost monolithic piece of silica (extremely pure glass). To achieve this, silica interface pieces are hydroxide catalysis bonded to the sides of the mirrors and thin silica fibres are welded to those pieces.
Beyond gravitational wave detectors HCB is of huge interest for other (optical) applications
Up to now it has been used primarily for mechanical applications like in gravitational wave detectors and for example to construct a telescope for the Gravity Probe B mission and for all-glass optical systems for precision measurement experiments. However, we are only just discovering the potential of HCB for optical applications.
Recent measurements show reflectivity of bonds is very low when you join silica parts together, which means HCB is a great technique for transmissive optical applications, particularly where other jointing techniques do not work. Here we think for example of optical components used in the laser industry, where high power laser light is sent through optical components that are joined together.
Focus – to develop HCB for gravitational wave detectors and optical applications
Marielle’s research team therefore measures and tailors properties of HCBs like strength, mechanical loss, reflectivity and transmission and working on measuring Young’s modulus, bond thickness and refractive index for the various applications discussed above. Materials of particular interest include fused silica, silicon, sapphire and YAG.