Industrial artificial sapphire and ruby are gem-quality synthetic forms of Al2O3 or Corundum with a hardness of 9 on the Moh's hardness scale which is second only to diamond, they are extremely durable and wear resistant, besides, they features zero porosity, high degree of polish, heat resistant, low friction coefficient, chemical inertness and shock resistant. The durability and hardness of corundum makes synthetic ruby and sapphire resistant to abrasion and damage, thus, they are quite suitable to work under ultra-high pressure water environment and are adopted for orifice of nozzles including water-jet nozzle, spray nozzle, Ultra-dry fog nozzle, pin jet nozzle, needle jet nozzle and trim squirt nozzle.

Synthetic ruby orifice and synthetic sapphire orifice are nearly identical, they are the same hardness, same wear resistant, same sliding co-efficient of friction, same everything, except for the color. White sapphires are inherently transparent and more convenient for a visual inspection with a naked eye via microscope.

Other hard materials can also be adopted to make nozzle orifice, but synthetic ruby and sapphire are the best choice. You can refer to the approximate abrasion resistance ratios comparing to other materials as below:

Crystal lattice: hex-sided monocrystalline
Chemical composition: Al2O3
Purity: 99.99%
Percentage: 3.99 - 3.98

Hardness: Mohs class 9, Knoop hardness=1700kg/mm2
Elasticity modulus: 3.5X106 to 3.9X106kg/cm2
Pressure-resistance: 2.1X104 kg/cm2
Tensile strength: 1.9*103 kg/cm2

Melting point: 2050°C
Specific heat: 0.18(at 25?)
Soften point: 1800°C
Thermal expansion: 6.7*10-6 // C-axis 5.0*10-6?C-axis

Acid- and alkali-proof: can not be eroded by acid or alkali, but hydrofluoric acid.

Electric constant:7.5 to 10 electric constant
Impedance:1011O/cm at 500?, 106O/cm at 1000?, 103O/cm at 2000?,

Refractive index:1.769 // C-axis,1.760 ?C-axis, 0.5893µm
Visible light: fine
Infrared ray:85% 0.75 - 4µm, 70% 4.7µm, 50% 5.2µm
Ultraviolet ray:80% 0.4-0.3µm, 60% 0.28µm, 50% 0.2µm