Pyrolytic graphite-coated graphite tubes are made by depositing the pyrolysis product of organic matter, pyrolytic graphite, on the inner surface of an ordinary graphite tube.

Siemer and Woodriff et al. Presented a very simple method of depositing pyrolytic graphite on carbon components. On a wall of an insulated, thermally resistant glass tube with a diameter of 17 mm, wrap about 50 turns of nickel chrome wire as the sample chamber. In the tube through nitrogen, power, with an adjustable autotransformer heating nickel chrome wire, the temperature reached 1000 ℃. Place the object to be coated in the tube, stop the nitrogen stream, change the methane (39 ~ 200 mL / min). The flow rate of methane varies depending on the object. Depending on the size of the element, the deposition rate of pyrolytic graphite is generally 0.01 to 0.1 mm / h. The pyrolytic carbon was also deposited on a graphite tube using Kntlensky's method. Gas hydrocarbons (usually with methane) diffuse through the multi-porous graphite slowly deposited in the larvae to form a pyrolytic carbon coating. At high temperatures (2300 ° C), the graphite surface is preferentially coated, and at low temperatures (1400 ° C) and low pressure, the pores inside the graphite are preferentially coated until the voids are completely closed. The graphite produced in this way has a density of 2.1 g / cm3 close to the theoretical density. It can also be heated to a graphite tube (2300 ° C) for 60 s at a flow rate of 0.3 L / min with argon or nitrogen containing 10% methane, followed by heating at 2350 ° C for 6 s and then repeated 10 times.

It has been suggested to coat the graphite tube with a pyrolytic graphite coating before or after each analysis. C1vburn et al. Proposed that methane be blown into argon at each atomization stage so that the pyrolytic graphite coating can be continuously re-coated. Allen et al. Incorporated acetylene into the nitrogen stream, claiming a lower detection limit, and 10 times longer life of the graphite tube. Steinev and Kramer have improved the gas inlet and jacket protection systems for conventional CRA-90 graphite tubes to enable continuous pyrolytic coating of graphite tubes.

Many people studied the surface of the pyrolytic coated graphite tube with a scanning electron microscope. Experiments with HGA-2100 graphite tubes indicate that the deposition temperature must be higher than 2300 ° C. It has been pointed out that the ability of pyrolytic graphite to eliminate interference is related to its surface smoothness.