Laboratory gases have always played an important role in the daily life of any laboratory worker. A gas chromatograph (GC) or mass spectrometer (MS) is just a rather large paperweight without gases. But with a myriad of gases and gas grades to choose from, and gas company representatives not always keeping up with the high end of the specialty gas spectrum, how do you make the best choice?
Standard gases used for tasks such as welding or metal cutting are known as 'industrial gases'. The tanks are filled with the gas of choice for the application and delivered to the customer. When the tank becomes empty, it is simply refilled and out the door again.
This is not the case with speciality gases. Speciality gases must meet or exceed a specific set of specifications and are never allowed to leave the gas company's gas laboratory until the relevant cylinders have been rigorously reviewed to prove their worth.
Most typically, speciality gases are individually produced combinations, designed for use by a single customer, and require more effort than packaged industrial gases. Speciality gases typically involve gas calibration, gauge gases, transport gases, ventilated test gases and zero gases. These can be pure gases or gas mixtures with a composition of 100% to parts per billion, sometimes even parts per trillion. Customised or off-the-shelf speciality gases can be supplied.
In the case of Ultra High Purity (UHP) Helium, let's take a look at the process involved in achieving the coveted "Ultra High Purity" status. Firstly, the cylinder is fitted with an active on/off valve, which ensures a high level of leak integrity. Secondly, the cylinders must be baked to remove any contaminants from the inside of the cylinder walls. The cans are placed in an oven and baked at 140ºF for eight hours. During the baking process, the cans are purged with inert ultra-high purity gas and then quickly placed under vacuum.
The purpose of this process is to break the polar bonds of any existing moisture molecules that have attached themselves to the interior of the cylinder walls. This heat transfer releases the molecules from the cylinder walls and the purge/vacuum process removes the contaminants from the tank. Trapped within these moisture molecules are other harmful contaminants such as hydrocarbons and particulates. When this process is complete, the inside of the cylinder is clean enough to accept and maintain the integrity of the UHP gas. We can introduce the prepared cylinder (now under vacuum) to its new member, UHP Helium.
Once the cylinder is filled, it is sent to the laboratory where a chemist performs a series of tests on the cylinder to check for contaminants such as moisture, total hydrocarbons and oxygen. Once the cylinder has passed that test, it moves on to a gas chromatograph to prove its worth again. After passing the GC analysis, the tank is given a shrink-wrap valve and a place in the "special gases" range. If these procedures are not followed, it is like putting clean milk in a dirty hot water bottle - you will pour out the dirty milk. Dirty gas delivered to equipment intended for use with UHP gases will lead to unfavourable results
For further technical information talk with our specialist or visit our website https://www.taiyugas.com. We can help you to identify the best solution for your application.
