What additives can do to kiln furniture

In the chemical world, additives will surely exert certain impacts on the main raw materials, which gives us more space for improvement of our products, actually, Today, let’s dive into the world of additives and see how trace additives of LiCO3, aluminum, zircon etc. will influence the performance of most widely used kiln furniture materials: cordierite and corundum mullite. Here is an exclusive interview of our engineer crew members John and Kim by our office clerk, Cathy.

1.Impacts of additives on thermal expansion coefficient of kiln furniture series--cordierite materials.

Experiment 1:

Cathy: So what’s your first experiment?

John: OK.Just for heads-up, the chemical formula of cordierite is 2MgO·2Al2O3·5SiO2, and the experimented additives are TiO2, TiCl4,Y2O3,and LiCO3. Our first experiment is about the impacts of additives on cordierite products. Here are some graphs to specify the impact.

After adding 1% of TiO2:

After adding 1% of TiCl4:

After adding 1% of Y2O3:

After adding 1% of ZrO2

After adding 1% of LiCO3

Kim: TiO2，TiCl4，Y2O3 ，ZrO2，and LiCO3 were added into cordierite as additives to study the effect of different additives on the expansion coefficient of cordierite. The results showed that the addition of TiO2，TiCl4 and ZrO2 can reduce the coefficient of thermal expansion of the samples. The expansion coefficient of cordierite samples with addition of Y2O3 and LiCO3 was small below 100 °C, when it was above 100 °C, the coefficient was larger and increases in a straight line and eventually exceeded the final coefficient of expansion of the sample product without and additives.

John: Indeed, the results showed that TiCl4 is the best, but the expansion coefficient of TiO2 is similar to that of TiCl4.

Experiment 2:

Cathy: Now we know that TiCl4 addition attributed best to the improvement of thermal expansion coefficient at 1%, did you further the experiment?

John: Sure we do. The second experiment tested what percentage of TiCl4 worked best and the results are as follows:

Kim: We have analysed the reasons behind the results. Firstly, the structure of cordierite is sparse and there is a large gap in between. When the temperature rises, the atom can vibrate toward the open part of the structure and be contained by the gap inside the structure. Therefore, in a certain temperature range, it shows a lower thermal expansion.

John: Yes, and secondly, cordierite creates stress and stores strain energy in the crystal during sintering and cooling. If this is sufficient to counteract the increase in surface energy caused by crack initiation, grain boundaries or grains will crack, causing microcracks to form within them. As the temperature rises further, and as more and more micro cracks are closed in the material, there are fewer and fewer micro cracks left, which is why the coefficient of thermal expansion increases gradually.

Cathy: Thank you, guys, so to sum up, the results show that the expansion coefficient of cordierite sample is best when adding 4% of TiCl4.

2. Impacts of additives on thermal shock resistance of kiln furniture series 2--corundum mullite materials

Experment 1:

Cathy: High temperature kiln furniture of corundum-mullite materials is widely used for its high melting point, good creep resistance and thermal shock resistance. In order to improve its properties, let’s hear what our engineers have done.

John: we applied andalusite, plate corundum, alumina powder and silica powder as raw materials under the guidance of transition plastic phase technology. The effects of two different additives on the properties of corundum-mullite materials were studied by adding 0,1% , 2% and 3% aluminum or silicon, respectively.

Kim: The effects of aluminum and silicon on the density, strength, toughness and thermal shock resistance of corundum-mullite materials were studied. It was found that the addition of aluminum and silicon to corundum-mullite materials could form plastic mould, and was oxided with their original chemical valence in the sintering process resulting in the formation of oxide filling part of the pores. It was beneficial to reducing the apparent porosity of the material, and the mullite crystals formed were needle-like structure, interpenetrating, bridging and interlocking, which help to improve the strength, toughness and thermal shock resistance of the material.

John: However, the addition of the two additives reduce the volume density of the material since the additives were not as dense. Comparing the effect of aluminum and silicon on the properties of corundum-mullite materials, it was found that aluminum had better plasticity and lower melting point than silicon, and it helped to improve the kiln furniture’s strength, toughness and thermal shock resistance better than that of silicon.

Experment 2:

John: So we also did another experiment used fused mullite as coarse particles, α-al2o3 powder, sillimanite powder and a small amount of bonded clay as matrix, and carboxymethyl cellulose as binder. Researchers added titanium dioxide powder and zircon powder respectively and then added these two kinds of powder at the same time. After mixing, hydroforming, the bearing plate specimens were fired at 1530 °C for 2 hours. Kim: Our group used fused white corundum and mullite of medium particles respectively to analyse the effect of the addition of titanium dioxide (4% , 6% , 8%) , the addition of zircon powder (4% , 6% , 8%) and the simultaneous addition of two powders (zircon powder 6% , titanium dioxide 4% , 6% , 8%) on the thermal shock resistance of bearing plate.

John: The results showed that the thermal shock resistance of corundum samples of medium particles was better than that of mullite samples, and the thermal shock resistance of samples with zircon powder or titanium white powder was improved obviously. When both of them were added simultaneously, the thermal shock resistance of the specimen was improved remarkably.

Kim:SEM analysis showed that the zircon phase was precipitated by adding zircon powder, aluminum titanate was formed by adding titanium dioxide, zircon phase and aluminum titanate crystals were formed by adding both zircon powder and titanium dioxide. The existence of these phases led to microcracks and intergranular cracks, which was helpful to improve thermal shock resistance.

Cathy: Since there are various effects of additives on the performance of ceramic materials, as well as on the sintered products, we have been doing R&D to improve our products while finding out better solutions to meet our customers’ need.

Now we provide primary KF and secondary KF. BATTS, SiC beams, props, saggers, crucibles, boats and plates of various sizes and shapes are all within our production span in a bespoken way. Please do contact us and we will be committed to providing you with our best service.