Geopolymers as a material suitable for immobilization of fly ash from municipal waste incineration plants

ABSTRACT

This paper discusses the possibility of using the process of geopolymerization to immobilize ash from municipal waste incineration plants. Fly ash used in the related research came from the same incineration plant, one of the biggest in Poland. The examination was conducted on the waste samples labeled as 190107* and 190113*. The comparison included such properties of waste as chemical composition, dioxin content, and size and morphology of particles. The waste was solidified in geopolymer matrix made from (i) fly ash from the combustion of bituminous coal or (ii) metakaolin. The waste percentages were 50 mass% and 70 mass%, respectively. Moreover, leaching tests were carried out and mechanical properties of the geopolymers materials containing immobilized ashes were analyzed. It was proved that geopolymerization process allows for the high-level immobilization of compounds and elements such as chlorides, sulfates, fluorides, barium, and zinc. Additionally, it was observed that in the case of the geopolymer samples containing 70 mass% of 190107* waste, the average compressive strength exceeded 18 MPa.

Implications: A novel aspect of the results presented in this paper is the comprehensive investigation of the immobilization of large amounts of hazardous waste by means of the synthesis of geopolymers from metakaolin or coal fly ash. According to these results, it was determined that the level of immobilization is much higher in the case of the geopolymers based on metakaolin in comparison with geopolymers made from coal fly ash.

On the basis on the obtained results, investigated geopolymers may be successfully used, e.g., as barriers or linear drains in landfills.

Introduction

Every year in the world, more and more money is spent on the development and construction of municipal waste incineration plants. Incineration allows for the reduction of the volume of the waste by 80–95%. However, the combustion inevitably results in the production of secondary waste, i.e., various postprocessing materials. For instance, the amount of hazardous waste produced in Poland by means of incineration is expected to reach 430,000 kg/yr after 2020. At the same time, 160,000 kg of hazardous waste per year is expected to come from the process of cleansing of industrial gases (Wielgosiński and Naniecińska 2016). The above-mentioned by-products contain large amounts of heavy metals and dioxins removed during the process of cleansing of flue gases. They have to be somehow secured in order not to pose a threat to the environment. Nowadays, research is focused on the improvement of old and development of new technologies, allowing for the safe use or storage of such hazardous materials (Feng-Yim and Ming-Yen 2006; Oehmig et al. 2015; Tang et al. 2015).

One of the methods of immobilization of postprocessing waste from the municipal waste incineration plants is their geopolymerization. It is more and more widely used in various branches of the industry (Davidovits, 2002; Davidovits 2008; Provis and Deventer 2009). The application of geopolymerization to hazardous waste not only contributes to the best technological practices and legal provisions but also is ecologically effective. Geopolymerization is very often the best and the cheapest solution in long-term waste management. It has many advantages, such as the effectiveness of immobilization, economical, or possibility to apply to different kinds of postprocessing waste, in comparison with the alternative available technologies. Therefore, this process is filling a market gap in this area. Its additional benefit is the possibility of using the immobilized materials, e.g., in the construction industry. Moreover, because they are highly resistant to the environmental conditions, one may use them, e.g., as an impermeable barrier preventing the landfills from penetrating the environment (Korniejenko and Mikuła 2014).

The postprocessing materials from the combustion of solid municipal waste usually contain heavy metals such as Pb, Cd, Cr, and Zn, which may be successfully immobilized by means of geopolymerization based on the matrix made of fly ash (Ferone et al. 2013; Jing et al. 2016; Lancellotti et al. 2015; Lee et al. 2016; Nikolić et al. 2014; Yunsheng et al. 2007; Zhang et al. 2008a, 2008b). Moreover, Galiano, Pereira, and Vale (2011) proved that the compressive strength of geopolymers increases in time. Improvement of the geopolymer properties also occurs after addition of Portland cement and lime. However, the addition of blast furnace slag (BFS) caused the biggest increase in the compressive strength of the examined samples. High-efficiency immobilization of heavy metals from the postcombustion waste was determined in the concretes made from Portland cement (Deja 2002; Hui-Sheng and Li-Li 2009). Furthermore, Cyr, Idir, and Escadeillas (2012) proved that the addition of metakaolin decreases the leaching of heavy metals from concretes made from cement. Portland cement was also used for immobilization of fly ash and bottom ash (slag) from a medical waste incineration plant (Anastasiadou et al. 2012). Owing to this method, such products may be placed in landfills, together with nonhazardous wastes, or serve as construction materials.

However, as regards heavy metals, much better results can be obtained by use of immobilization process in geopolymer matrix or alkali-activated binders. Deja et al. proved that alkali-activated slags are suitable for such application. In comparison with the pastes based on Portland cement, their microstructure comprises more gel pores and much less capillary pores. Consequently, such materials are characterized by reduction of water absorption as well as decrease in leaching of the solidified product. This type of material has practical applications, and it may heavily affect the whole waste management process. It is worth noting that in the case of immobilization of Cr(VI) in geopolymer matrix, the key factor is S²⁻ ions, as they reduce Cr(VI) to Cr(III) and allow obtaining the insoluble forms (Zhang et al. 2008a, 2008b).

Currently, no universal method has been developed yet that allows for the complete immobilization of postprocessing waste regardless of their source and the degree of hazardousness. The developed methods, apart from research using geopolymers as materials inside which the waste is enclosed, concern elucidation of their chemical processing, stabilization in concrete, or vitrification. One of the common problems in all of Europe is the secondary waste, from municipal waste incineration plants (Lach, Mikula, and Hebda 2016; Liu et al. 2015). This study examines the possibility of immobilizing 50 mass% or 70 mass% of this type of waste using geopolymerization process. It is important that geopolymers with encapsulated waste are characterized not only by the acceptable strength properties but also by the low values of leaching of hazardous substances. This is extremely important due to the possibility of further use and storage of these types of materials. Moreover, the presented results may be used for further research focused on the development of waste stabilization processes in geopolymers matrix that allow obtaining useful products from them. The paper presents the results of analysis of such properties of waste as chemical composition, dioxin content, and size and morphology of particles. The waste was solidified in geopolymer matrix made from (i) fly ash from the combustion of bituminous coal or (ii) metakaolin. Furthermore, leaching tests were carried out and compressive strength of the geopolymers containing immobilized ashes were also investigated.

Materials and methods

Materials

Fly ash used in this study came from the municipal waste incineration plant, located in Warsaw in Poland, whose efficiency is 60,000 10³kg/yr. The technological line dedicated to thermal waste utilization consisted of furnace and the flue-gas cleansing system reducing the nitrogen oxides, dust, acid pollutants, and heavy metals. The waste incineration was conducted at the temperature of 850–1150 °C. The oxygen content in flue gases amounted to 6–11%, and the flue gases resided in the afterburner chamber for 2 sec.

The analyses were conducted on hazardous ashes marked in accordance with applicable law with the following symbols: (i) 190107*, i.e., solid waste from the process of cleansing waste gas, and (ii) 190113*, i.e., fly ash containing hazardous substances. They were labeled as W1 and W2, respectively. Selected ashes are one of the most common types of postprocessing waste coming from various types of installations for the thermal degradation of waste.

The geopolymers were made from the following raw materials: (i) fly ash from bituminous coal combustion in the combined heat and power (CHP) plant in Skawina and (ii) metakaolin whose trade name was Boltin Rapid (delivered by Prechel GmbH, Schwetzingen, Germany).

Taking account of the economic aspects and profitability of the above technology, one of two different amounts of the waste-to-immobilize was applied: 50 mass% or 70 mass%, depending on the particular geopolymer matrix. Metakaolin matrix has better immobilizing capability; therefore in that case, 70 mass% of waste was used. The labels used and their descriptions are included in Table 1.

Table 1. Labels and descriptions of samples.

Sample label	Sample description
FA	Coal fly ash (as delivered)
MK	Metakaolin (as delivered)
W1	Waste no. 190107* as delivered (Waste 1)
W2	Waste no. 190113* as delivered (Waste 2)
G-MK	Geopolymer obtained from metakaolin
70W1-G-MK	Geopolymer obtained from 70 mass% W1 and 30 mass% metakaolin
70W2-G-MK	Geopolymer obtained from 70 mass% W2 and 30 mass% metakaolin
50W1-G-FA	Geopolymer obtained from 50 mass% W1 and 50 mass% coal fly ash
50W2-G-FA	Geopolymer obtained from 50 mass% W2 and 50 mass% coal fly ash

Synthesis of the geopolymers

Coal fly ash or metakaolin was mixed with the measured-out amounts of W1 and W2 in the ratios included in Table 1. To produce geopolymers, flakes of technical sodium hydroxide and an aqueous solution of sodium silicate (R-145) with molar ratio of 2.5 and density of about 1.45 g/cm³ were used. Tap water was used instead of distilled water. The alkaline solution was prepared by means of pouring the aqueous solution of sodium silicate over the solid sodium hydroxide. The solution was thoroughly mixed for 15 min in a low-speed mixer and allowed to equilibrate to a constant concentration and temperature. Next, the obtained paste was poured into cubic molds of 150 × 150 × 150 mm. The solidification was conducted on the vibratory table. Then the molds were heated for 24 hr at 75 °C, cooled to the ambient temperature, taken out of the molds, and stored for 28 or 90 days.

Methods of examination

Particle size distribution was determined by laser diffraction wet-dispersion method, using Fritsch Analysette 22 MicroTec plus (Fritsch GmbH, Idar-Oberstein, Germany). Volume size distribution was calculated automatically and expressed as D₁₀, D₅₀ (median), and D₉₀. Five measurements were carried out for each sample.

The morphologies of the samples were examined using scanning electron microscopy (SEM; JEOL 6510LV, delivered by JEOL, USA). The ashes had been properly prepared before, i.e., dried to the constant mass, put on the coal tape to carry the electric charge of the sample away, and covered with thin layer of gold with the JEOL JEE-4X vacuum evaporator.

The oxide content was measured using x-ray fluorescence the Zetium spectrometer XRF WDX delivered by PANalitycal.

The dioxin content was determined using gas chromatography coupled with mass spectrometry (GC-MS/MS) in the Laboratory of Trace Analysis at the Cracow University of Technology. The examination was carried out according internal testing procedure of an accredited laboratory, certificate no AB 749. The results were expressed as the upper limit of toxic equivalency (TEQ) according to the European Standard - EN 1948-3 “Stationary source emissions. Determination of the mass concentration of PCDDs/PCDFs and dioxin-like PCBs. Identification and quantification of PCDDs/PCDFs”.

The fineness tests were conducted according to the European Standard - EN 451-2 “Method of testing fly ash - Part 2: Determination of fineness by wet sieving” using wet screening. Moisture content from the delivery condition was determined by drying the ashes using the moisture analyzer until a constant weight was obtained.

Compressive strength tests according to European Standard  - EN 12390-3 “Testing hardened concrete - Part 3: Compressive strength of test specimens”, using cement compression machine Matest, model 3000 kN (Italy), were conducted on cubic samples 150x150x150 mm conditioned at room temperature for 28 or 90 days.

Leaching tests were conducted according to the European Standard EN12457-4 “Characterisation of waste - Leaching - Compliance test for leaching of granular waste materials and sludges - Part 4: One stage batch test at a liquid to solid ratio of 10 I/kg for materials with particle size below 10 mm”. The samples were prepared according to the European Standard EN15587-2 “Water quality - Digestion for the determination of selected elements in water - Part 2: Nitric acid digestion”. Depending on the type of analyzed substance, one of the following methods was used: gravimetry, spectrophotometry, ion chromatography, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The mass of each sample was approximately 2.5 kg.

Results and discussion

Table 2 presents the results of the chemical composition of the waste as well as the raw materials used as a geopolymer matrix. It is well known that the amounts of SiO₂ and Al₂O₃ are crucial in the geopolymer synthesis. Moreover, the CaO content influences the rate of binding processes as well as hydration of binders (Davidovits 2008; Lei, Wei, and Yunchun 2010; Provis and Deventer 2009). The quantity of CaO in both samples W1 and W2 was high and exceeded 40 mass%. The amount of SiO₂ in waste W2 was 4 times higher than in the case of W1 (10.1% vs. 2.5%, respectively; Table 2). The Al₂O₃ content in W2 was 7 times higher than in the case of W1 (7.2% vs. 1.0%, respectively). From Table 2, it can be concluded that the component contents in waste labeled as W2 are more suitable for geopolymerization.

Table 2. Chemical composition of coal fly ash (FA), metakaolin (MK), and waste fly ashes (W1, W2).

Component	mass% of components in the investigated samples
	FA	MK	W1	W2
SiO2	50.5	51.7	2.5	10.1
Al2O3	25.3	32.1	1.0	7.2
Fe2O3	13.9	1.5	0.4	1.0
Na2O	1.1	0.1	6.8	5.4
K2O	3.2	0.3	3.0	2.2
CaO	3.6	0.3	43.6	41.6
MgO	2.2	0.3	0.5	1.8
TiO2	1.0	1.4	0.3	1.6
SO3	0.4	0.1	5.8	14.0
Cl	—	—	18.6	6.9
LOI	2.4	6.1	16.2	6.0
Residuals	1.9	6.2	1.6	2.2

Table 3 presents selected physical properties of wastes that are important from the technological point of geopolymer production.. The water demand and workability of geopolymer paste depend on the moisture content of the particular waste and on its fineness (particle size). Generally, the drier and bigger the particles, the easier they can be introduced into the geopolymer matrix. It was found that the examined waste differed from each other in terms of fineness, i.e., residue on the sieve (0.045 µm, wet screening). The W2 waste had 5 times higher fineness in comparison with the results obtained for the W1 waste. This effect can stem from the considerable difference in particle size of both samples. The results of particles size distribution by laser diffraction are shown in Table 3 and Figure 1. Gaussian distribution was observed for both samples W1 and W2. According to the results, waste W1 contained the finest particles. The proof is the extremum on the curve where the recorded maximum was 18.2 µm. Ten percent of the particles did not exceed 3.8 µm, and there were no particles larger than 110 µm. On the other hand, sample W2 contained the largest particles. They were up to 360 µm (Figure 1). The maximum on the curve was observed at 78.9 µm. Moreover, sample W2 had the widest span of particles (span = 2.6). On the other hand, the moisture content of W1 was 3 times higher than in the case of W2. The moisture content depends mainly on the used method of flue-gas cleansing or on the method of reduction of multiparticle compounds (e.g., wet or semidry). On the other hand, results may be dependent also on the conditions of storage or transport. Table 3 presents also the results of the dioxin content tests. The waste W1 contained 19 times more dioxins than W2. However, the amount of dioxins in both samples was low.

Table 3. Selected physical properties of the investigated wastes.

Property	W1	W2
Fineness (%)	13.1 ± 0.6	64.2 ± 1.2
Moisture content, as delivered (%)	1.1 ± 0.1	0.3 ± 0.1
The quantity of dioxins (ng/g)	0.0170 ± 0.0044	0.0009 ± 0.0002
D10 (µm)	3.8 ± 0.6	10.2 ± 1.1
Median D50 (µm)	14.9 ± 5.1	59.1 ± 4.6
D90 (µm)	30.6 ± 8.2	164.1 ± 7.6
Span (D90 − D10)/D50 (µm)	1.8 ± 0.5	2.6 ± 0.2
Mean (µm)	16.6 ± 5.0	75.1 ± 4.3
Mode (µm)	18.2 ± 6.9	78.9 ± 5.0

Figure 1. Particle size distributions and cumulative curves of the samples W1 and W2.

The observed morphologies of the examined samples of the ashes W1 and W2 were similar. Figure 2 presents the representative morphologies of the particles of the examined samples of waste. It was observed that the morphology of the most common fraction of particles was jagged/feathery and that larger particles were probably conglomerates of the smaller ones and included polyhedral or oval crystalline precipitates. The observed surface morphology was independent of the particle size.

Figure 2. SEM images of the wastes: (a) W1 and (b) W2, as delivered.

Table 4 presents the results of water leaching tests applied to samples W1 and W2. On the basis of the obtained results, it was determined that W1 waste contains significant amounts of dissolved organic carbon (DOC), Pb, as well as Ba. The measured values were several times higher than in the case of sample W2. Furthermore, in the case of sample W1, the concentration of leached chloride ions was 4 times higher (171,930 mg/kg) and the concentration of total dissolved solids (TDS) was 3 times higher (373,980 mg/kg) in comparison with sample W2. On the other hand, W2 waste contained significant amount of chromium, which was almost absent in sample W1. Due to the high leaching of harmful substances from W1 waste, the washing process was conducted. It had been proved before that in case of the highly leaching, the pretreatment by means of washing is necessary to make successful and economically efficient the process of immobilization (Ferone et al. 2013). The results of leaching tests of sample W1 after pretreatment by washing for 2 hr (the ratio water/waste was 2/1) are presented in Table 4. Owing to the above procedure, the concentration of chlorides decreased 6 times (to 29,000 mg/kg) and the concentration of sulfates decreased 2 times in comparison with the examination of the same waste before washing. Besides, TDS and DOC were washed out, as well as fluorides and such elements as lead, barium, and zinc. The pretreatment was not applied to the sample W2 because it did not contain large amounts of chlorides and sulfates prone to leaching.

Table 4. Leaching of the examined waste samples as delivered and after washing of W1.

Analyzed substance		Leaching (mg/kg)
	Criteria for admission of waste for storage at a hazardous waste landfill	W1	W1 after washing	W2
Antimony (Sb)	5	<0.5	<0.5	<0.5
Arsenic (As)	25	<0.5	<0.5	<0.5
Barium (Ba)	300	54.4	7.6	2.3
Chlorides (Cl^−)	25,000	171,930	29,000	43,190
Chromium(VI)	—	0.5	<0.5	42.1
Cr (total amount) (Cr)	70	<1	2.3	42.6
Zinc (Zn)	200	31.5	7.2	12.9
Fluorides (F^−)	500	73.3	20.2	83.7
Cadmium (Cd)	5	<1	<1	<1
Copper (Cu)	100	<1	<1	<1
Molybdenum (Mo)	30	<0.5	<0.5	2.8
Nickel (Ni)	40	<1	<1	1
Lead (Pb)	50	191	<1	13.7
Dissolved organic carbon (DOC)	1000	2300	<300	<300
Selenium (Se)	7	<0.5	<0.5	<0.5
Sulfates (SO4^2−)	5000	16,500	8510	23,910
Total dissolved solids (TDS)	100,000	373,980	107,000	135,530

Table 5 presents the results of the leaching tests of the geopolymers made from fly ash and metakaolin and containing the wastes W1 and W2. For the sake of comparison, the results of the leaching tests of geopolymer made from metakaolin without the addition of fly ash from the waste incineration plant are also shown.

Table 5. Leaching of geopolymers made from fly ash or metakaolin containing W1 and W2 wastes.

Analyzed substance	Leaching (mg/kg)
	50W1-G-FA	50W2-G-FA	70W1-G-MK	70W2-G-MK	MK-G
Antimony (Sb)	<0.5	1.7	1.5	<0.5	<0.5
Arsenic (As)	42.0	1.8	<0.5	<0.5	8.2
Barium (Ba)	<0.5	<0.5	<0.5	<0.5	1.3
Chlorides (Cl^−)	5530	21,050	2460	5400	367
Chromium(VI)	<0.5	25.5	<0.5	4.9	0.5
Cr (total amount)	<1	27.4	<1	5.9	<1
Zinc (Zn)	<1	<1	<1	<1	<1
Fluorides (F^−)	46.3	38.2	18.6	62.0	17.1
Cadmium (Cd)	<1	<1	<1	<1	<1
Copper (Cu)	<1	<1	<1	<1	<1
Molybdenum (Mo)	17.8	3.9	<0.5	0.5	<0.5
Nickiel (Ni)	<1	<1	<1	<1	<1
Lead (Pb)	<1	<1	<1	<1	<1
Dissolved organic carbon (DOC)	<300	<300	<300	615	491
Selenium (Se)	4.9	1.7	<0.5	<0.5	<0.5
Sulfates (SO4^2−)	7720	55,440	617	17,070	401
Total dissolved solids (TDS)	43,180	116,150	21,200	50,440	15,380

According to the obtained results (Tables 4 and 5), it was determined that the immobilization of hazardous waste was much better in the geopolymers made from metakaolin than in those made from fly ash. This is related to the leaching of heavy metals from the geopolymer matrix (also made from fly ash). As regards the geopolymers based on metakaolin, the leaching of sulfates, TDS, and chlorides from them was much lower regardless of the type of waste introduced into them. In this case, the higher amount of the waste (by 20%) hardly affected the results, as well. Comparing the results of leaching tests conducted for the wastes (Table 4) with those of the leaching tests carried out for geopolymer matrix including the introduced waste (Table 5), it was observed that in the case of sample W1, geopolymerization contributed to the high level of immobilization of such elements as barium, zinc, and lead and of fluorides.

Table 6 presents the compressive strength tests of two solidified geopolymer matrix including the introduced waste and examined after 28 and 90 days of conditioning.

Table 6. The compressive strength tests of two geopolymer matrices with the introduced wastes, examined after 28 and 90 days of curing.

Label of the sample	Compressive strength after 28 days of curing (MPa)	Compressive strength after 90 days of curing (MPa)
50W1-G-FA	4.6 ± 0.3	10.1 ± 0.2
50W2-G-FA	13.2 ± 0.2	18.9 ± 0.1
70W1-G-MK	18.2 ± 0.4	18.9 ± 0.3
70W2-G-MK	14.4 ± 0.4	14.4 ± 0.4
G- MK	57.3 ± 0.7	62.1 ± 0.5

In the case of geopolymer matrix made of metakaolin and including 70 mass% of W2 waste, the compressive strength exceeded 14 MPa. If the same matrix included 70 mass% of W1 waste, the compressive strength reached 18 MPa. The results were the same regardless of the time of curing. On the other hand, the compressive strength of the obtained materials depended on the introduced waste sample in the case of geopolymers made from fly ash. The lowest compressive strength, about 4.6 MPa, was determined in the case of the geopolymer with the addition of W1, after 28 days of hardening. However, after the next 62 days of curing, this value had doubled. By contrast, the compressive strength of the matrix with the addition of W2 after 28 days of hardening was 13.2 MPa, which is a result comparable to that obtained for the matrix based on metakaolin. Furthermore, it was observed that the compressive strength of the geopolymers made from fly ash rose by approximately 5 MPa after 62 days of curing. The compressive strength of the geopolymer 50W2-G-FA reached about 19 MP after 90 days of curing, which hardly diverged from that of 70W1-G-MK obtained after 28 days of hardening. Wastes introduced into the geopolymer are only its filling, and they do not take part in the geopolymer matrix formation processes. As a consequence, they reduce the cross-section of the geopolymer, which makes waste-containing geopolymers be characterized by much lower strength properties compared with unmodified geopolymers. Moreover, the presence of chloride and sulfate compounds further reduces the properties of geopolymers (Zheng et al. 2011). Chloride could clearly retard the solidification of geopolymer gel (Lee and Van Deventer 2002a) and lower the strength by causing structural discontinuity within the gel (Lee and Van Deventer 2002b). In order to improve the geopolymer strength properties, as an activator of the geopolymerization process, one could try to use potassium hydroxide instead of sodium hydroxide (Hosan, Haque, and Shaikh 2016; Luna et al. 2009).

Conclusion

A novel aspect of the results presented in the paper was the comprehensive investigation of the immobilization of large amounts of hazardous waste by means of the synthesis of geopolymers from metakaolin or coal fly ash. According to these results, it was determined that the level of immobilization is much higher in the case of the geopolymers based on metakaolin in comparison with geopolymers made from coal fly ash.

The postprocessing materials from municipal waste incineration plants containing large amounts of soluble substances should be first subjected to pretreatment by means of washing and then immobilized in geopolymer matrix. It allows for obtaining the best results and for immobilizing large amounts of waste.

As regards the secondary waste from the incineration plant and solidified in the geopolymer matrix made from fly ash, the desirable values of compressive strength are obtained after 90 days of curing. In the case of metakaolin-based geopolymers, it takes only 28 days.

On the basis on the obtained results, the investigated geopolymers may be successfully used, e.g., as barriers or linear drains in landfills.

Additional information

Funding

This work was supported by the National Centre for Research and Development and the National Fund for Environmental Protection and Water Management (GEKON1/05/213240/35/2015).

Notes on contributors

Michał Łach

Michał Łach is an assistant professor at the Cracow University of Technology, Faculty of Mechanical Engineering, Institute of Materials Science and Engineering.

Dariusz Mierzwiński

Dariusz Mierzwiński is an assistant professor at the Cracow University of Technology, Faculty of Mechanical Engineering, Institute of Materials Science and Engineering. Functions: Deputy Director for Didactics at the Institute of Materials Science and Engineering. OECD Scientific Discipline: Materials Engineering.

Kinga Korniejenko

Kinga Korniejenko is a researcher at the Cracow University of Technology, Faculty of Mechanical Engineering, Institute of Materials Engineering.

Janusz Mikuła

Janusz Mikuła is an associate professor at the Cracow University of Technology with 30 years of experience in conducting research - and development. He currently works as Director of the Institute of Materials Science and Engineering.

Marek Hebda

Marek Hebda is an assistant professor at the Cracow University of Technology, Faculty of Mechanical Engineering, Institute of Materials Science and Engineering.