The graphite heater has three kinds of common shape, cylindrical, cup, spiral, the vast majority of the heater is a cylinder.
Made of high purity graphite heater with carbon content of more than 99.9%; the graphite bowl wall thickness is generally 3 mm - 6 mm; after a long period of practice, the effective length of the quartz crucible heater is 1.6 times the height to 1.8 times.
Now more and more of the graphite heater used to heat treating and brazing furnace, thermal field generally used coarse graphite in the fine structure of the bottom prop up the market, the thermal insulation cover, upper cover and a lower cover; imported isostatic graphite as a heater.
The heating principle of graphite heater:
The sample injector with quantitative injection into the graphite tube, and the graphite tube as the body heat resistance, rapid heating power, make the sample to achieve atomic purpose.
It consists of heating power and protection gas control system and graphite tubular furnace.
The external power supply to both ends of the graphite tube atomizer, energy, current high temperature of 3000 DEG by graphite tube, which is arranged in the graphite tube measured element into the atomic vapor.
Protection gas control system is the control of protective gas, start the instrument, protection of Ar gas flow, air burning is completed, shut off the flow of argon. Outdoor road in Ar gas along the graphite tube outer wall flow, to protect the graphite tube is ablated, the road of Ar gas from the tube at both ends of the flow tube center, consists of a central orifice discharge pipe, to effectively remove matrix vapor generated in the drying and ashing process and protect have atoms of the atoms are no longer oxidation.
In the atomization stage, stop ventilation, in order to prolong the average residence time of the atom in the absorption region, and avoid the dilution of the atomic vapor.
In the graphite furnace atomic system, the flame will be placed in argon electrically heated graphite tube replaced. Argon can prevent graphite tube under the condition of high temperature rapid oxidation and in drying and ashing stage will matrix components and other interfering substances from the light path in addition to. A small amount of sample (1 to 70 ml, usually in about 20 ml) was added in pyrolytic coated graphite tube. Pyrolytic coating graphite tube can effectively prevent the oxidation of the graphite tube, from and prolong the service life of the graphite tube. Meanwhile, the coating can also be prevent sample intrude graphite tube, so as to improve the sensitivity and reproducibility.
Graphite tube heated by the current and by the size of the current programmable control circuit control, resulting in the heating process according to a series of heating steps on the graphite tube in the samples heated to remove solvent and most of the matrix components then to product atoms have ground state free. Molecular decomposition depends on the atomic transition temperature, heating rate and heat graphite tube wall surrounding environment and other factors.
