The US company Raytheon produced industrial-scale pyrolytic graphite products in 1956, which were successfully applied to the aerospace industry. Compared with ordinary graphite crucibles (made from natural flake graphite as the main raw material and plastic refractory clay or carbon as the binder), pyrolytic graphite crucibles are made from a new type of carbon material - pyrolytic graphite. Pyrolytic graphite is pyrolytic carbon with high crystal deposited by high purity hydrocarbon gas on the graphite matrix at 1800 ℃~2000 ℃ under a certain furnace pressure through chemical vapor deposition. It has high density (2.20g/cm ³）, high purity (impurity content (0.0002%) and anisotropy of thermal, electrical, magnetic and mechanical properties. The 10mmHg vacuum degree can still be maintained at about 1800 ℃. Therefore, the crucible made by this material has better performance, such as better thermal conductivity, stronger corrosion resistance to acid and alkali solutions, smoother and more compact surface, less permeability,broader application prospect.
1. Production process:
Pyrolytic graphite crucible is different from ordinary graphite crucible. It is made of carbon atoms directionally deposited on the mold after pyrolysis of hydrocarbons under high temperature, low pressure and nitrogen atmosphere, and being demoulded after cooling.
2. Main features:
(1) High temperature resistance and low ablation rate;
(2) Resistance to acid and alkali corrosion at high temperature (700 ℃);
(3) The surface is smooth and compact with low permeability; easy to clean and decontaminate;
(4) Have certain mechanical strength;
(5) It has high purity and it does not stain the sample. It can be used repeatedly.
Pyrolytic graphite crucible can not only be used for pre-treatment of samples in the field of minerals, building materials and glass, but also be used in the preparation of high-purity metal oxides, ion plating and other fields. For example, some researchers used pyrolytic graphite (PG) crucibles instead of platinum, quartz and other crucibles to prepare high-purity yellow lead oxide with ideal results.