HPHT Manufactures Synthetic Diamonds Part 1

Natural diamonds have extreme hardness and scarcity, combining jewelry and industrial value. But the bottleneck of natural diamond production capacity was not broken until the mid-20th century with the emergence of "high temperature and high pressure (HPHT) technology" - and HPHT equipment is the core "mother machine" for replicating the earth's core environment and mass producing synthetic diamonds.

 

HPHT stands for High Temperature and High Pressure Manufacturing Technology

 

Part One: Core Principle 

The essence of HPHT technology, which replicates the "diamond generation field" of the Earth's core, is to reproduce the natural formation conditions of diamond in an artificial cavity and promote the conversion of carbon source to diamond.

• Natural formation benchmark: Natural diamonds are born at depths of 150-200 kilometers in the mantle, requiring high temperatures of 1100-1500 ° C and high pressures of 4.5-6 GPa (approximately 45000 to 60000 times atmospheric pressure). Carbon atoms are arranged in a cubic lattice to form diamonds in this environment.

• Thermodynamics core logic: The carbon phase diagram shows that under high pressure and high temperature, graphite (common carbon form) is in a metastable state, and diamond is the stable phase. The core mission of HPHT equipment is to precisely construct this "diamond stable zone" and promote the directional conversion of carbon sources (such as graphite) 

 

 

Part 2: Technical Core -

Three Mainstream Routes of HPHT Equipment
HPHT equipment achieves extreme conditions through "mechanical pressurization+electric heating", and the mainstream technology route has significant positioning differences due to structural differences.

 

1. Double sided pressing machine: early commercialized main force 

• Structure: 2 tungsten carbide anvil blocks for relative pressure, metal tube resistance heating.
• Features: Simple structure, low cost, but uneven pressure distribution, unable to produce large single crystals.
• Current positioning: Mainly used for manufacturing small-sized products of diamond micro powder and polycrystalline diamond (PCD).

 

2. Six sided top press machine: the absolute core of the current industry (led by China)

• Structure: Six hydraulic cylinders drive the tungsten carbide top hammer, which squeezes the cubic pressure medium (Yelaishi) from six directions, synchronously achieving high pressure and uniform heating.
• Core advantages: uniform pressure distribution, large cavity volume, suitable for industrial mass production (gem/tool grade large single crystals).

 

Simplified workflow: 

• a. Assembly: carbon source (high-purity graphite), metal catalyst (iron/cobalt/nickel), seed crystal embedded in pyrophyllite cavity;
• b. Pressurization: Six hammers are synchronously pushed forward, forming a static water pressure of 5-6 GPa inside the chamber;
• c. Heating: The electrode is electrified and heated to above 1400 ° C to melt the catalyst;
• d. Growth: The catalyst dissolves graphite and precipitates diamond on the seed crystal;
• e. Crystallization: Remove the finished product after cooling and reducing the pressure. 

 

3. Splitting ball/multi-faceted pressing machine: specialized for cutting-edge scientific research.

• Structure: 8 or more anvil blocks form a spherical surface and squeeze the spherical cavity. 
• Features: The most uniform static water pressure and strong adaptability of the chamber, but the equipment cost is extremely high (in the tens of millions). 
• Positioning: Used for cutting-edge research on superhard materials and special diamond synthesis (non mass production). 

 

 

For the second half of the sharing about the method and process of HPHT manufacturing synthetic diamonds, please continue to pay attention to this website. Thanks for your support.