Technical Background of Hexagonal Boron Nitride Ceramic Synthesis
White graphite, or hexagonal boron nitride, is so named for its resemblance to graphite and its usage as a graphite substitute in several applications. Under high-temperature circumstances, its performance is clearly superior to graphite. It is an innovative form of inorganic material that possesses desirable chemical and physical properties. It can be used as a release agent, as a lubricant for high temperatures, or as an additive for composite ceramic materials. Boron nitride is a crucial raw ingredient for the production of cubic boron nitride at the same time. The synthetic approach of high quality, low cost, and low energy consumption has become the research direction of scientific and technological people in light of the ever-increasing scope of applications for boron nitride materials and the corresponding rise in demand.
Limitations of Traditional Synthesis of Hexagonal Boron Nitride Ceramics
Currently, boron nitride is produced using a variety of techniques, such as the ammonium chloride-anhydrous borax method, the borax-urea method, the boric acid-melamine approach, etc. Traditional procedures have poor crystallization and cause air pollution, thus intermittent high-temperature synthesis is used. For the purpose of material synthesis, either a high-temperature furnace or a tube furnace is utilized. The furnace is turned off and allowed to cool down when the synthesis has been completed. As a result, there is a significant cost and energy need for production, and the conventional synthesis process necessitates the use of a protective atmosphere of ammonia gas or inert gas, which places limitations on the available manufacturing technology. Most sophisticated one-step synthesis of hexagonal boron nitride is to synthesize borax and melamine in an inert gas environment at 1100-2200 ° C, then wash with dilute mineral acid till PH 1. Then, wash in water until it reaches a pH of 5-7. This approach is also a batch method, which has the disadvantages of high energy consumption and inert gas equipment limits.
In response to the aforementioned, this article describes a method for synthesizing hexagonal boron nitride adopting anhydrous borax and melamine as raw materials, a tunnel kiln as equipment, and continuous reaction in a calcining kiln. This approach can cut manufacturing costs while simultaneously producing hexagonal boron nitride of a high purity.
Basic Steps for Synthesis of Hexagonal Boron Nitride Ceramics
Material Mixing
Raw materials: anhydrous borax 0.7-1.5; melamine 1.
Combine the two raw ingredients in the proportions specified in the recipe.The mixing process should take between two and five hours.
Pressing
The combined material is compressed and shaped in a briquetting machine, and the shaped material is then placed in a graphite crucible.
Synthesizing
Graphite crucibles are heated to between 700 and 1300 degrees Celsius in an air environment at the beginning of a tunnel kiln, where they are pushed every 20 minutes; the tunnel kiln's response time for each crucible is 6 to 10 hours.
Post-processing
The reacting material is crushed in a pulverizer and then introduced to a reactor with 3-10% hydrochloric acid at a temperature of 20-100 ° C while being agitated for 2 hours. After drying, wash two to five times with deionized water to achieve fluffy white powder. Test results show that there is more than 99% boron nitride present, and the amount of free boron is less than 0.5%.
The production results are compared in the following table: (a picture)
Conclusion
The synthesis method for hexagonal boron nitride described in this article is simple and straightforward. The goods are constantly synthesized utilizing anhydrous borax and melamine as raw materials and an ordinary tunnel kiln as manufacturing equipment. The manufacturing cost is significantly decreased since the calcination temperature is substantially lower than the current synthesis method and intermittent high-temperature synthesis is not necessary. There's no need to wear an inert gas mask. Since the synthesis is performed in an air environment, there are no equipment requirements or limits. Additionally, the synthetic product has a consistently good quality and flavor, and its purity can exceed 95%.According to the method introduced in this paper, the problems existing in the traditional production methods can be effectively solved.