Hydro-thermal

Introduction

Geologists started to study hydrothermal in Mid-19th century. After 1900, scientists established a hydrothermal synthesis theory, and later turned to the study of functional materials. Currently hydrothermal method has prepared over a hundred kinds of crystals. Hydrothermal is a category of liquid chemical method. It means chemical reaction happens in a sealed pressure vessel with water as a solvent, and at high temperature and pressure conditions. Depends on the type of reaction, hydrothermal reaction can be divided into hydrothermal oxidation, hydrothermal reduction, hydrothermal precipitation, hydrothermal synthesis, thermal hydrolysis, hydrothermal crystallization. Hydrothermal crystallization is the most common way.

Advantage

MoS2 made by hydrothermal which is prepared through heating and press with molybdate and vulcanizing agent. According to hydrothermal reaction temperature, it can be divided into sub-critical and super-critical reaction, the former reaction temperature is between 100 ~ 240 ℃, which is suitable for industrial or laboratory. The latter test temperature has reached 1000 ℃, pressure up 0.3Gpa. Under hydrothermal conditions, water can act as a chemical component and participate in the reaction, it is the solvent and mineralizing agent and it can also used as medium to transfor press. Overcome some hard agglomerate produced at the high-temperature, whis method has a fine powder (nano-scale), high purity, good dispersion, uniform, narrow distribution, without agglomeration, good crystal form, shape controllable and other features.

Disadvantage

The disadvantage of the hydrothermal method are as follows:
1)Crystal havs a crystal face, the thermal stress is small, internal defects are less. Inclusions are very similar with its natural gemstones.
2) It is unable to observe the growth process in a closed vessel.
3) High equipment requirements (high pressure high temperature steel, corrosion-resistant lining), technical difficulties (strict control of temperature and pressure), high cost; 4)Safety performance is poor;