CERAMIC BALLS
Si3N4 SILICON NITRIDE
The most widely used type of ceramic due to very
high resistance to wear and abrasion in general.
It has a low coefficient of thermal expansion (25%
of that of steel balls) and a weight 60% lower than
steel. It has a micro-structure specially designed
for applications subject to great stress. It does
not require lubrication, it is resistant to corrosion,
anti-magnetic and electrically insulating, and it
continues to be efficient at high temperatures up
to +1400 °C. It combines extreme hardness with a
high precision ball. Si3N4
balls are widely used in high precision bearings
in the airspace industry, for machine tools, measurement
instruments, mechanical centrifuges, radar and
missiles, pumps and compressors.
Al2O3 99,5% ALUMINA (ALUMINA OXIDE)
This material has a multi-crystal structure and
excellent resistance to abrasion and high temperatures.
It is resistant to most corrosive agents, but it
is not recommended for use in contact with hydrochloric
and hydrofluoric acid or strong alcaline solutions.
Al2O3 balls are used in valves,
pumps and ball bearings.
ZrO2 ZIRCONIUM OXIDE
This material, compared has a high degree of compactness and considerable flexural strength, which makes it very reliable. It also has a low modulus of elasticity, close to that of steel, together with an extraordinarily low thermal conductivity.
Al2O3 99,99% RUBY
This material has a non porous single crystal structure
used where particular hardness and extreme resistance
to wear are required together with a low specific
weight and properties of chemical inertia. The material
consists of pure aluminium oxide with a small percentage
of chrome oxide which gives it its characteristic
red colour, which is the most visible feature of
these balls in many applications as measurement
and control instruments, valves and pumps.
Al2O3 99,99% SAPPHIRE
This material has a single crystal structure and unlike ruby is transparent. Because of its optical properties and high refraction index. Balls made of this material are currently used as chemically inert lenses.
CERAMIC BALLS - PROPERTIES OF MATERIALS
| PHYSICAL PROPERTIES |
SAPPHIRE AND RUBY |
ALUMINA OXIDE |
SILICON NITRIDE |
ZIRCONIUM OXIDE |
| STRUCTURE |
single crystal |
multi-crystal |
multi-crystal |
multi-crystal |
| CHEMICAL FORMULA |
Àl2Î3 |
Àl2Î3 |
Si3N4 |
ZrO2 |
| PURITY % |
99,99 |
99,8 |
95,00 |
97,00 |
| DENSITY g/cm3 |
3,99 |
3,90 |
3,20 |
5,50 |
| PHYSICAL PROPERTIES |
SAPPHIRE AND RUBY |
ALUMINA OXIDE |
SILICON NITRIDE |
ZIRCONIUM OXIDE |
| OPERATING TEMPERATURE °C |
|
1800 |
1100 |
1000 |
| MELTING POINT |
2050 °C |
2050 °C |
1900 °Ñ |
|
| SOFTENING POINT |
1800 °C |
1725 °Ñ |
1400 °Ñ |
|
SPECIFIC HEAT AT 25 °C (CAL/g/°C)
THERMAL CONDUCTIVITY |
0,18
36 W/m°k |
0,25
29 W/m°k |
0,17
29 W/m°k |
9
W/m°k |
| MECHANICAL PROPERTIES |
SAPPHIRE AND RUBY |
ALUMINA
OXIDE |
SILICON NITRIDE |
ZIRCONIUM OXIDE |
| VICKERS HV10 HARDNESS (N/mm2) |
17000 |
16500 |
24000 |
20000 |
| MODULUS OF ELASTICITY (N/mm2) |
4,3õ105 |
3,5õ105 |
3,1õ105 |
2õ105 |
| BREAKING MODULUS AT 25 °C (N/mm2) |
392 |
470 |
700 |
600 |
| COMPRESSIVE STRENGTH AT 25 °C (N/mm2) |
2060 |
2354 |
2500 |
2100 |
| CHEMICAL RESISTANCE |
| SAPPHIRE / RUBY: inert to most acids at very high temperatures. |
| ALUMINA (OXIDE): inert to
most acids, but not recommended in environments
with hydrochloric or hydrofluoric acids or strong
alcaline solutions |
| SILICON NITRIDE: inert to most acids. |
| ZIRCONIUM OXIDE: inert except to hydrofluoric acid and strong concentrations of sulphuric acid. |
| 
