KR20030070703A - Renewed alumina ceramics - Google Patents

Abstract

PURPOSE: Provided are recycled alumina ceramics with low manufacturing costs by adding waste alumina ceramic powder used as structure materials and absorbents to conventional alumina powder. CONSTITUTION: The recycled alumina ceramics are manufactured by adding less than 30wt.% of waste alumina powder(recycled alumina, RA) with a size under 40micrometer, less than 20wt.% of waste alumina powder(recycled alumina, RA) with a size of more than 40micrometer, or less than 10wt.% of waste alumina adsorbent powder(WA) to alumina powder(PA) with a 10micrometer size. The RA powder, obtained by quenching alumina for structure materials sintered at 1650deg.C and grinding, has more than 95% of Al2O3 and alpha-Al2O3 crystal structure, and The WA powder, generated from oil refinery, has more than 97% of Al2O3 and gamma-Al2O3 crystal structure.

Description

Regenerated Alumina Ceramics

The present invention relates to regenerated alumina ceramics, and more particularly, to regenerated alumina ceramics produced by recycling waste alumina ceramic powder for structural materials and waste adsorbent alumina powder.

Alumina Since ceramics have excellent mechanical, electrical, chemical and thermal properties, they have a wide range of applications such as structural materials, electrical, electronic materials, and biomaterials. Due to problems such as excessive consumption of energy, there are many difficulties in practical use.

Currently, alumina ceramics used as structural adsorbents and catalysts for refining air in refineries or refineries are being disposed of entirely by landfill after use, but alumina ceramics that are discarded after a certain period of time are used. It can be an important resource because the content of ₂ O ₃ is over 95%.

Moreover, due to domestic circumstances, it is difficult to secure landfills, which leads to problems with landfills. Therefore, research on recycling of alumina ceramics is required in order to solve such landfills and solve economic losses due to the disposal of valuable valuable resources imported from abroad. .

However, the research on the recycling of structural ceramics using glass, slag and stone sludge has been extensively studied and some practical steps have been taken. However, there is no research on the recycling of structural alumina ceramics.

The present invention has been made to solve the problems of the prior art as described above, the object is to produce a cheap alumina ceramics by lowering the manufacturing cost by reducing the manufacturing cost and energy.

Another object of the present invention is to recycle waste alumina ceramics or waste alumina adsorbents for structural materials.

1A and 1B are graphs showing the results of XRD analysis according to the sintering temperature of the regenerated alumina ceramic specimens according to Examples 1 and 4 of the present invention.

2A to 2C are graphs showing the three-point bending strength change of the specimen according to the addition amount of the recycled powder (RA) and the waste adsorbent powder (WA) and the sintering temperature.

3A to 3F are specimens prepared according to Example 1, Example 3, and Comparative Example 2, and Examples 1 and 4 using RA having a particle size of less than 40 μm, respectively, using P10 specimens and particles having a particle size of 40 μm or more Scanning electron micrograph showing the microstructure of the.

In order to achieve the above object, in the present invention, 30 wt% or less for recycled alumina having a particle size of less than 40 μm, 20 wt% or less for recycled alumina having a particle size of 40 μm or more, and 10 wt% or less for waste alumina adsorbent. To add alumina ceramics.

Hereinafter, the method for producing regenerated alumina ceramics according to the present invention will be described in detail.

In the present invention, recycled alumina powder is mixed with alumina powder and waste alumina powder such as waste adsorbent in a predetermined ratio to produce regenerated alumina ceramics. Among the waste alumina powders, recycled powder refers to the pulverization of general alumina ceramics. For example, alumina ceramics for waste structural materials are pulverized. do. This recycled powder has a chemical composition of more than 95% by weight of Al ₂ O ₃ content.

Another closed-alumina powder of waste adsorbent refers to alumina previously used in refineries as adsorbent and catalyst for the purification of air, which includes when the content of Al ₂ O ₃ except for the loss on ignition 10.84% by weight in terms of 88.76% by weight Al ₂ The content of O ₃ is a chemical composition of at least 97% by weight. In addition, the waste adsorbent is a test method that predicts the degree of elution of contaminants contained in workplace wastes after landfill disposal, and is used as judgment data for determining designated wastes or landfill methods for nine field wastes. Heavy metal dissolution test is used, the heavy metal leaching amount is less than the reference value, heavy metal contamination problem should be used.

In the case of recycled powder, it is added at 30% by weight or less, in the case of recycled powder is added at 20% by weight or less, and in the case of waste adsorbent, at 10% by weight or less. At this time, the reason for limiting these powders to 30 wt% or less, 20 wt% or less, and 10 wt% or less, respectively, is that when more than this is added, the strength of the recycled alumina ceramics becomes lower than the practical strength of the structural alumina ceramics. Because. In this case, the practical strength for structural materials of alumina ceramics means that the three-point bending strength is 200 MPa at the sintering temperature of 1650 ° C.

Regardless of the amount of recycled powder and waste adsorbent powder added, the recycled alumina ceramics increased in density and three-point bending strength as the sintering temperature increased from 1200 ° C to 1650 ° C. As a result, density and three-point bending strength decrease. This is because the particle size of the recycled powder and the waste adsorbent powder added is larger than that of the general alumina powder, so that the filling rate of the molded body decreases during molding, and the pores remain in the specimen after sintering.

Table 1 shows the average particle size of the recycled powder, which is the waste alumina powder, and the waste adsorbent powder, together with the average particle size of the general alumina powder.

Average particle size (㎛) Alumina powder 10.5 Waste alumina powder Recycled Powder (less than 40 μm) 33.8 Recycled Powder (40㎛ or More) 74.3 Waste adsorbent powder 32.5

As shown in Table 1, since waste alumina powders such as recycled powder and waste adsorbent powder have a larger particle size than general alumina powder, the smaller the particle diameter of the added waste alumina powder is, the densified by decreasing the specific surface area of the particles. The strength of the recycled alumina ceramics produced is increased.

In particular, since the main crystalline phase of the waste adsorbent powder is the γ phase, unlike the main crystalline phase of the alumina powder and the recycled powder, the crystalline phase is sequentially phase-shifted into the θ phase and the α phase during sintering, resulting in volume differences due to shrinkage of the particles themselves. Pores are formed and also pores are formed during sintering by the loss of ignition of 10.84% by weight. Since the pores thus formed are distributed within the grain boundary and are not easily removed, the density is reduced. Also, the addition of the waste adsorbent has a lower strength than the case where recycled powder is used due to the lack of crystallinity of the α phase, which causes the development of strength.

For the above reasons, in general alumina powder, up to 30% by weight for recycled alumina powder with a particle size of less than 40 μm, up to 20% by weight for recycled alumina powder with a particle size of 40 μm or more, and 10 for waste alumina adsorbent powder. The regenerated alumina ceramics according to the present invention are prepared by adding and mixing in an amount of up to% by weight, followed by molding and sintering.

Hereinafter, the present invention will be described in more detail with reference to Examples.

In the embodiment of the present invention, commercially available industrial Al ₂ O ₃ powder (Daejeong Chemical, purity 96%, average particle diameter of 10 ㎛, hereinafter referred to as PA) was used as alumina powder, and recycled alumina powder using such PA powder. Was prepared.

That is, PA powder is first molded into a columnar specimen of 12 × 5 × 60 mm ³ at a pressure of 50 MPa using a uniaxial hydraulic press, and then a cold hydrostatic molding machine (CIP, Reaction Eng. ROK) is used. Secondary molding was performed at a pressure of 150 MPa. The secondary molded specimen was sintered at 1,200 to 1,650 ° C. for 5 hours at a temperature increase rate of 5 ° C./min, and then cooled to prepare an alumina ceramic specimen (P10).

As an alternative raw material of alumina ceramics for waste structural materials, P10 specimens sintered at 1,650 ° C for 5 hours were quenched to generate cracks on the surface of the specimens, and then pulverized to a particle size of less than 40 µm and a particle size of 40 µm or larger (hereinafter referred to as recycled alumina powder). , Named RA).

In Examples 1 to 3, 10, 20, 30 wt% of such recycled alumina powder (RA) and 90, 80, 70 wt% of alumina powder (PA) were mixed, respectively, and regenerated alumina was prepared in the same manner as in the preparation method of the P10 specimen. Ceramics were prepared, and the content of each is summarized in Table 2.

In Example 4, as shown in Table 2, 10% by weight of waste alumina adsorbent powder (named WA) and 90% by weight of alumina powder (PA) generated in a domestic refinery were mixed and regenerated in the same manner as in the preparation method of the P10 specimen. Alumina ceramics were prepared.

Alumina Powder (PA) Recycled Alumina Powder (RA) Waste Adsorbent Powder (WA) Example 1 (P9R1) 90 10 - Example 2 (P8R2) 80 20 - Example 3 (P7R3) 70 30 - Example 4 (P9W1) 90 - 10 Comparative Example 1 (P6R4) 60 40 - Comparative Example 2 (P5R5) 50 50 - Comparative Example 3 (P8W2) 80 - 20 Comparative Example 4 (P7W3) 70 - 30 Comparative Example 5 (P6W4) 60 - 40 Comparative Example 6 (P5W5) 50 - 50 P10 100 -

Meanwhile, in Comparative Examples 1 to 6, RA or WA was added in an amount exceeding the range in the present invention to prepare regenerated alumina ceramics, and the content thereof is shown in Table 2 together.

Characterization of the raw materials used in the examples of the present invention, PA, RA and WA was performed, first chemical composition was analyzed using XRF (Philips, PW 140, Holland) and the results are shown in Table 3.

(weight%) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO TiO ₂ K ₂ O Na ₂ O P ₂ O ₅ LOI Alumina Powder (PA) 1.42 95.45 0.33 0.48 0.45 0.44 0.48 0.40 - 0.55 Recycled Powder (RA) 1.40 95.77 0.16 0.45 0.39 0.41 0.46 0.43 - 0.56 Waste Adsorbent Powder (WA) 0.12 88.76 0.05 0.04 0.07 0.02 - 0.10 - 10.84

As shown in Table 3, the chemical composition of PA and RA is was the content of Al ₂ O ₃ less than 95% by weight, WA is if the content of Al ₂ O ₃ except for the loss on ignition 10.84% by weight in terms of 88.76% by weight Al ₂ The content of O ₃ was at least 97% by weight.

In addition, the particle size of each powder raw material was measured using a particle size analyzer (SA-CP3, Shimazu, Japan) and the results are shown in Table 4.

Average particle size (㎛) Particle Size Distribution (㎛) Alumina Powder (PA) 10.5 3-50 Recycled powder (RA, less than 40 μm) 33.8 3 to 200 Recycled powder (RA, 40㎛ or more) 74.3 5 to 250 Waste Adsorbent Powder (WA) 32.5 3 to 300

In addition, pulmonary alumina heavy metals of the adsorbent after 45 days the sample 1g of distilled water 100 ml bearing according to hwangyeongcheo Notice waste process test, a solution prepared by the addition of _{HNO 3 ICP / MS (HP-} 4500 series, USA) The heavy metal components of Mg, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, and Pb were measured using the results, and the results are shown in Table 5.

(ppm) As CD Pb T-Cr Cr ⁶⁺ Hg Zn Fe Cu Reference value 1.5 0.3 3 1.5 1.5 0.005 - - 3 Waste Adsorbent Powder (WA) ND 0.003 0.194 0.077 ND ND 0.034 0.015 0.004

As shown in Table 5, WA was used in the embodiment of the present invention, so the amount of heavy metal elution was very low, when using the recycled alumina ceramics using it was found that there is no problem of heavy metal contamination.

Next, the characterization of the regenerated alumina ceramics specimen prepared according to the embodiment of the present invention was carried out. First, the crystal phase analysis was performed using a Cu Kα, Ni filter using an X-ray diffraction analyzer (Philips. Co. Pw1720, Holland). , 30 kV, 20 mA. XRD analysis results according to the sintering temperature of the regenerated alumina ceramic specimens prepared in Examples 1 and 4 are shown in FIGS. 1A and 1B, respectively. Where? Is α-Al ₂ O ₃ , ○ is γ-Al ₂ O ₃ , and ■ are θ-Al ₂ O _3. Peaks.

As shown in FIG. 1A, the main crystal phases of PA and RA are α-Al ₂ O ₃ , and only peaks of α-Al ₂ O ₃ were confirmed in the specimens according to Example 1 at 1,500 and 1,650 ° C. As shown in FIG.

Meanwhile, as shown in FIG. 1B, the main crystal phase of WA was γ-Al ₂ O _3, and in the siphon according to Example 4, peaks of α-Al ₂ O ₃ and γ-Al ₂ O ₃ were observed at 700 ° C. FIG. , in addition to α-Al ₂ O ₃ and γ-Al ₂ O ₃ is in the θ-Al ₂ O ₃ peaks due to the transition of the γ-Al ₂ O ₃ were observed in the 800 ℃. 1,000 ℃ the α-Al ₂ O ₃ and θ-Al ₂ O was only observed in the _third peak, is of 1,100 ℃ specimen θ-Al ₂ O ₃ of α-Al by a transition to the _{2 O 3 α-Al 2 O} 3 Only the peak of was observed.

Next, the density of the regenerated alumina ceramic specimens was measured using the Archimedes method (confidence interval 95.45%, standard uncertainty k = 2, expansion uncertainty = 0.002). As a result, as the sintering temperature was increased, it was found that the density of the specimen increased regardless of the amount and particle size of RA and WA, and the density of Example 1 was observed to be 3.89 g / cm ³ . It showed a high relative density of 99% of the theoretical density of 3.93 g / cm ³ .

However, at the same sintering temperature, the density decreased as the amount of RA and WA added increased. Since the average particle diameter of RA and WA added was larger than that of PA, the filling rate of the molded body decreased during cold hydrostatic molding, This may be due to the pores remaining in the specimen.

In the case of RA, the density of the specimens added with a particle size of 40 μm or more was decreased compared to the specimens added with a particle size of less than 40 μm, which was caused by the decrease of the specific surface area of the particle due to the increase of the average particle diameter. This is because the densification of the was not completed completely. Therefore, it was found that the physical properties of the recycled alumina ceramics improved as the particle size of the used raw material was smaller.

The density of Example 4 specimens with WA was 3.86 g / cm ³ and lower than that of Example 1 with recycled powder, but still high relative density of 98% of 3.93 g / cm ³ , the theoretical density of alumina ceramics. Indicated.

Next, the three-point bending strength of the regenerated alumina ceramics specimens was measured using a cross-section speed of 0.5 mm / min using a universal testing machine (SFM, United Co., USA) according to KS L 1591. ) (Confidence interval 95.45%, standard uncertainty k = 2, extended uncertainty = 0.009), The microstructure of the specimen was observed using a scanning electron microscope (Akashi Co. SS130, Japan) by coating Au on the fracture surface of the specimen subjected to the three-point bending strength test.

The three-point bending strength change of the specimen according to the addition amount of RA and WA and the sintering temperature is shown in FIGS. 2A to 2C. Here, FIG. 2A is a case where RA having a particle size of less than 40 μm is used, FIG. 2B is a case where RA having a particle size of 40 μm or more is used, and FIG. 2C is a case where WA is used. In each specimen, the three-point bending strength increased with increasing sintering temperature, but at the same sintering temperature, the three-point bending strength decreased with increasing amounts of RA and WA powders. In addition, if the sintering temperature and the addition amount of RA and WA powder were the same between the particle size of RA and WA powder and the addition amount of RA and WA powder, the smaller the particle diameter was, the densified by decreasing the specific surface area of the particles, the three point bending strength increased. As described above, the smaller the particle diameters of the RA and WA powders, the higher the three-point bending strength is considered to be because it is possible to maintain a certain strength or more close to the average particle diameter of the PA powder.

If the practical strength of the alumina ceramics for structural materials is expected to be 200 MPa, the specimen sintered at 1,650 ° C. using RA powder having a particle size of less than 40 μm, as shown in FIG. 2A, may contain up to 30% by weight of RA powder instead of PA powder. It can be seen that it is possible to replace, when using a powder having a particle size of 40 ㎛ or more as shown in Figure 2b it can be seen that up to 20% by weight of RA powder can be replaced.

Specimen with WA powder added three-point bending strength due to lack of crystallinity of α-Al ₂ O ₃ , which is the cause of strength due to phase transition of γ-Al ₂ O ₃ , the main crystal phase of WA powder. It decreased compared with that. As shown in Figure 2c, it was found that the specimen sintered at 1,650 ℃ by adding the WA powder can replace the WA powder by up to 10% by weight instead of the PA powder.

On the other hand, the microstructure of the regenerated alumina ceramic specimens is shown in Figures 3a to 3f, Figure 3a shows the microstructure of the P10 specimen, Figure 3b is a microstructure of Example 1 specimen using a RA having a particle size of 40㎛ or more 3e shows the microstructure of Example 3 specimens, FIG. 3d shows the microstructure of Comparative Example 2 specimens, FIG. 3e shows the microstructure of Example 1 specimens with RA having a particle size of less than 40 μm, and FIG. 4 shows the microstructure of the specimen.

In the specimen of Example 1 shown in FIG. 3B, no significant change was observed in comparison with the microstructure of the P10 specimen of FIG. 3A, but in FIG. 3C and 3D, the pores in the specimen increased as the amount of RA powder increased. In FIG. 3d, Comparative Example 2, the pores were observed to be too large. In addition, an increase in pores was observed in FIGS. 3E and 3F compared to FIG. 3B, which means that pores increase when RA and WA having a large particle size are used even with the same amount.

Through observation of these microstructures, it is believed that the decrease in three-point bending strength as the amount of RA and WA powder is increased is due to the size and shape of internal defects caused by the connection of pores formed in the specimen.

As described above, in the present invention, since recycled alumina ceramics are manufactured by adding waste alumina ceramics or waste alumina adsorbents used for structural materials to general alumina powder, manufacturing cost is reduced.

In addition, since the waste alumina powder is recycled, the landfill shortage problem is solved, and the economic power loss due to the disposal of valuable valuable resources is solved. In particular, it is effective to realize the recycling of alumina ceramics used for structural materials.

Claims (1)

A recycled alumina ceramics comprising any one of recycled alumina having a particle size of less than 40 μm and up to 30 wt%, recycled alumina having a particle size of at least 40 μm and up to 20 wt%, and up to 10 wt% of spent alumina adsorbent.