The Hollow Corundum Microspheres (HCM) are made of aluminum oxide with purity of 99.6%, has a round shape with wide surface, particle size from 5 to 180 microns, density from 0.8 to 2.0 gram per cm3, refractoriness 1800 °C and cold crushing strength from 40 to 120 MPa. In the photos taken by an optic and an electron microscope is visible a wide surface of HCM, a particle size and the crashing walls of the HCM.
Main proporties of Hollow Corundum Microspheres:
- Material: gamma- and alpha-aluminium oxide Al2O3 (corundum);
- Chemical purity – 99,7%;
- Spherical shape;
- Wide spec. surface area, cm2/cm3;
- Particle size 20-180 micron;
- Bulk density – 0.8-2.0 g/cm3;
- Refractoriness – 1700-1800 °С;
- Cold crushing strength up to 120 MPa;
- Thermal conductivity – 0.1-3 W/(m•K);
- Dielectric Constant – 3.0.
Surface of the HCM is like an orange – it is very wide (to compare with glass bubble). The mix of big- and small-sized (160 microns and 20 microns) HCM and standard grains of the fuzed white or red Al2O3 can help to obtain a porose matrix in filters or high porose grinding wheels with a pore size less than 0.1-10 microns.
Porose matrix for ceramic products.
An example of different distribution of alumina grains and HCM particles. Ceramics with a mix of big HCMs and small alumina grains and a mix of small HCMs and big alumina grains will have absolutely different mechanical properties and porosity. Moreover, it is possible to gain other properties using a bifractal mix of big and small HCM.
Hollow Corundum Microspheres sized up to 180 microns which have a crush strength from 40 to 120 MPa allow to make the final products – for example, during producing a crucibles, casting molds for molding or grinding wheels produced by isostatic or hot isostatic pressing the microspheres will not be crushed.
The final products with the addition of the microspheres obtain the low density, the low-heat-conductivity and the high mechanical crush strength.
By the spherical shape of microspheres the final product with HCM like ceramic crucibles, casting molds, grinding wheels or ceramic filters will have minimum reduction of blank volumetric deformation while drying and sintering. Addition of 5-20% of the Hollow Corundum Microspheres allows to lower reduction of blank volumetric deformation after sintering in 2-3 times in comparison with conventional materials.
Main application of HCM:
- refractors;
- ceramic filters – as a filler (pore agent) to reduce the weight and thermal conductivity of the final product;
- casting molds in metal industry;
- filler for refractory concrete and mortars;
- heat-insulating coatings and paints;
- abrasive products (disks, sticks, abrasive cloth);
- fillers for rubber and plastic – to increase durability of industrial rubber goods;
- fillers for car tires – to improve road-holding;
- plasma spraying;
- catalyst carriers (as base for spray coating and coating deposition).
| Fraction |
micron |
0,1-5 |
5-100 |
40-180 |
5-40 |
40-70 |
70-100 |
100-140 |
140-180 |
140-180 |
140-180 |
|
Сhemical composition |
|
Al2O3 |
% |
99,6 |
|
Fe2O3 |
% |
0,003 |
|
CaO |
% |
0,01 |
|
SiO2 |
% |
0,025 |
|
Na2O |
% |
0,26 |
|
ППП (ГОСТ 8136-85) |
% |
0,48 |
|
a-AI2O3 |
% |
28 |
|
Bulk density (ISO 903-76) |
г/см3 |
0,2 |
1,5-1,7 |
1,6-1,8 |
1,5-1,7 |
1,5-1,7 |
1,6-1,8 |
1,6-1,8 |
1,6-1,8 |
0,7-0,9 |
0,45 |
|
True density* |
г/см3 |
- |
- |
- |
3,70 |
3,65 |
3,55 |
3,63 |
3,60 |
- |
- |
|
Thermal conductivity at room temperature** |
Вт/(м·К) |
0,033 |
|
|
0,107 |
0,147 |
0,163 |
0,217 |
0,231 |
0,198 |
0,187 |
ППП percentage after calcination (GOST 8136-85) 20°C / 700°C, %
* Gas measurement method (helium) device Pycnomatic ATC (Thermo Scientific)
** Thermal conductivity measurements were carried out on the device ITS-1 (Russia) at room temperature
