Submitted:
11 September 2026
Posted:
14 September 2026
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Abstract
This article presents scientific research on developing the optimal composition of ceramic wall materials based on local raw materials. The aim is to develop an optimal composition of a ceramic material with improved thermal insulation properties by adding a diatomite additive to the local raw materials to increase porosity and reduce density. During the research, the physicochemical properties of the raw materials, namely the clay from the Roman deposit and the diatomite from the Zhalpaq deposit, were determined. Test samples were prepared by adding 5–15% diatomite to the clay. Their physicomechanical, chemomineralogical, and structural properties were determined. For sample analysis, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), equipped with a JSM-6490LV energy-dispersive microanalyzer, was used. X-ray diffraction (XRD); and Raman spectroscopy methods were used. According to the research results, adding 5-15% the addition of diatomaceous earth in the amount of 5–15% was shown to significantly affect the surface morphology, degree of porosity, structural uniformity, and agglomerate size of the studied samples, as well as the uniform distribution of elemental composition, The addition of 10% diatomite to the clay was shown to affect the change in crystalline phases and its physicomechanical properties. In conclusion, it was determined that adding 10% diatomite to the clay achieves the relatively highest degree of crystallinity, a uniform microstructure, and a relatively high compressive strength of 26.1 MPa. This showed that compared to other samples, the compressive strength increased by 15–23% and the thermal conductivity coefficient decreased by 1–11%. Thus, adding 10% diatomaceous earth to the clay was found to be an effective modifier.
Keywords:
diatomite
; clay
; ceramic materials
; physico-mechanical properties
; microstructure
; XRD analysis
; SEM
; EDS
; Raman spectroscopy
; compressive strength
; building materials
1. Introduction
Currently, the construction industry is developing rapidly. In particular, the development of residential construction is one of the indicators of the population's welfare. In this context, scientific research in the construction industry is primarily focused on developing energy-saving, lightweight building materials for use in enclosing structures characterized by low labor intensity, high strength, and ease of repair [1].
At present, the use of natural raw materials is considered a primary task in the construction materials production sector. Research is being conducted to use raw materials efficiently and to reduce their environmental impact. In particular, demand for efficient and environmentally safe wall materials is increasing [2,3,4,5].
In recent years, developing new energy-saving materials and technologies has been one of the main priorities in international research. In Kazakhstan, heating one square meter of floor area uses four times more fuel than in cold, similarly climatic Finland. That is, the main share of energy consumption is associated with building heating [6].
Therefore, reducing operating costs is considered one of the most important scientific and practical tasks facing modern construction professionals [7]. The works prove the possibilities of obtaining porous ceramic materials using effective technological approaches and formulations that exclude the possibility of obtaining porous ceramic materials with a coefficient of thermal conductivity three times lower than that of traditional bricks [8].
In addition, the works [1,9,10,11,12,13,14,15,16,17,18,19,20,21] have examined the possibilities of obtaining porous ceramic materials by incorporating industrial and agricultural waste. That is, Shubarkol coal, ash from the Ekibastuz Power Plant, wood ash, vermiculite, tobacco waste, rice husks, additives such as olive mill waste, wheat bran, paper processing waste, and date stone form pores during firing, reducing the brick's density and thermal conductivity. Furthermore, if these additives are not removed to a certain extent, they can increase water absorption and reduce the material's strength. Therefore, the amount of additives and the drying and firing procedures need to be precisely studied [22,23].
Ash, bottom ash, sludge from construction and demolition waste, carbonate sludge, additives such as calcite and calcium carbonate affect the porosity, water absorption, strength, thermal conductivity, and firing process of ceramic bricks [17,24,25,26]. By using waste as an additive, the oxides obtained can reduce the firing temperature by improving the density of the clay body [27]. This, in turn, reduces production costs and leads to changes in the product's composition and its physical and mechanical properties [28]. Therefore, the composition and adequate properties of the clay used in ceramic brick production lead to an increase in quality in the construction materials industry.
The West Kazakhstan region has raw material deposits of diatomite, opoka, and terpel for the production of thermal insulation products. They are located in Zhaplaq, Otesay, Kyrgyz, Taskala, and Shipov, They are located at the Zhalpaq, Otesay, Kyrgyz, Taskala, Shipov, Kök-Norin, Akbulak, Ispay-Bulyak, and Aksu deposits [1].
In addition to using diatomite as an additive, it can also be used as a primary raw material. Its low density and porous structure indicate that its thermal insulation properties are also high. The works investigated how using diatomite during calcination leads to mineral transformations that improve the composition of the mixture [2,29,30,31].
Diatomite has also attracted the interest of Kazakh scientists. It has been studied for its ability to reduce the average density and thermal conductivity of wall ceramics [32]. The diatomite from the Otesay deposit is suitable for producing ceramics with low thermal conductivity. The addition of clay, however, was shown to increase its strength and reduce water absorption and shrinkage [33]. Furthermore, it was determined that the West Kazakhstan diatomite can also be considered a raw material to replace quartz sand in borosilicate glass research [34].
As shown by a review of the literature, minerals and waste materials can be used as additives to produce wall ceramics. To this end, by optimizing the material composition with diatomite as an additive, it is possible to influence product quality. The main objective of this study is to develop an optimal composition of a ceramic material with improved thermal insulation properties by adding a diatomite additive to a local raw material base, thereby increasing its porosity and reducing its density. The objectives of this study are to determine the physicochemical properties of the raw materials, prepare samples with various compositional ratios, determine the physico-mechanical, chemico-mineralogical, and structural properties of the samples, and select an optimal composition.
2. Materials and Methods
As the research subject, the clay from the Roman deposit in Kazakhstan and the diatomite from the Zhalpaq deposit were selected as natural raw materials (Figure 1).
The clay from the Roman deposit is a light brown-colored natural aluminosilicate raw material. According to its mineral composition, the clay mainly consists of silica, alumina, calcium oxides, iron oxides, and magnesium compounds.
Diatomite is a light gray, silica-rich, porous sedimentary rock. The diatomite of the Zhalpak deposit, northeast of the city of Embi, covers an area of 84 km². Here, the diatomite rises 20 meters above the ground surface, topped by 0. It forms a plateau, with the diatomite rising 20 meters above the surrounding terrain and being covered by overlying rocks of 0.5–1 meter thickness. The diatomite layer is up to 40 meters thick, and the estimated diatomite reserves amount to 1.8 billion tons [35].
Physicochemical studies were conducted to determine the main properties of the raw materials. The chemical-oxide composition of the raw materials was determined at the M. Äuezov South Kazakhstan University using standard laboratory methods. The elemental composition of the raw materials was analyzed using scanning electron microscopy equipped with an energy-dispersive X-ray microanalyser, model JSM-6490LV. The X-ray spectroscopy spectra of the obtained diatomite and Roman clay are presented in Figure 2, and the elemental quantitative content is given in Table 1.
The chemical-oxide composition was determined in accordance with the requirements of GOST 22551-2019 and GOST 21216-2014, and its results are shown in Table 2.
The determination of the physicomechanical properties was carried out in the Laboratory of Construction Materials and Construction Thermal Physics of the Department of Architecture and Construction at the Western Kazakhstan Innovative-Technological University's Industry Technology Institute, and is presented in Table 3.
The following compositions of the raw material mixture were selected for conducting scientific experimental work, and their values are presented in Table 4.
The raw materials were weighed according to the composition under study and mixed in a laboratory mixer until a homogeneous mixture was obtained. After reaching a uniform composition, water was added to form a semi-dry mass. The ceramic mass was shaped into 50×50×50 mm cylinders using the semi-dry pressing method. The resulting specimens were air-dried under natural conditions and are shown in Figure 3.
The obtained cylindrical samples were calcined in a laboratory muffle furnace at 1000 °C. The calcination temperature was ramped at 1000 °C per hour. The exposure was then held at that temperature for 1 hour. The samples were left in the cooled furnace until they reached room temperature. The cylindrical samples heat-treated at 1000 °C are shown in Figure 5.
Compressive strength and density of the heat-treated samples (GOST 8462–85. Wall materials. Methods for determining compressive and flexural strength limits.) was determined in accordance with the requirements of GOST 530-2012. The compressive strength was determined on a PGM-1500MG4 hydraulic press. The test procedure is shown in Figure 6.
Water absorption and density tests were conducted on the fired cylindrical samples in accordance with the requirements of GOST 7025-91 for ceramic and silicate bricks and stones. To determine the sample's water absorption, the test was performed on three specimens for each variant, and the average value was calculated. The cylindrical sample was pre-dried to a constant mass. The samples were saturated for 48 hours in water that was 2 cm below the bottom and 2–10 cm above the samples, in accordance with the requirements.
The water-saturated samples were wiped with a damp cloth and weighed. Each sample was weighed no later than 2 minutes after being removed from the water, and the water absorption was determined in accordance with the requirements.
The thermal conductivity coefficient of the samples was measured using an ITP-MG4 type thermal conductivity meter over the temperature range of 173–4230 K.
The structural and physicochemical properties of the samples were determined in the laboratory of the Institute of New Materials and Energy Technologies, a private institution at Nazarbayev University in Astana. Ceramic samples were prepared for testing in powder form and as freshly fractured specimens. The samples were analyzed using the following methods:
- -
- Energy-dispersive X-ray spectroscopy (EDS) with scanning electron microscopy (SEM);
- -
- X-ray diffraction (XRD);
- -
- Raman spectroscopy.
3. Results
3.1. Scanning Electron Microscopy
Surface morphology was characterized using scanning electron microscopy with EDS analysis (SEM, JEOL).
SEM analysis was performed at various magnifications. Figure 7 shows the SEM images of the samples at 2000× magnification.
The obtained results showed significant differences in the surface morphology, porosity, structural uniformity, and agglomerate size of the studied samples.
a) Sample 1, compared to samples 2–4, has a partially smoother and denser surface. The morphology shows large interconnected regions, i.e., individual pores, microcracks, and defective areas are observed among them. While maintaining local heterogeneity, the surface appears compact. The surface features measured have characteristic dimensions ranging from approximately 1.04 to 7.99 µm, with an average value of about 4.1 µm. Compared to sample d, the surface is more densely packed and less porous.
b) The two sample surfaces exhibit the roughest and most heterogeneous morphology due to large, unstable agglomerates, open pores, cavities, and locally interconnected voids. The measured sizes of the surface features range from approximately 1.57 to 11.17 µm, with an average size of about 5.1 µm. Some porous and defective regions are significantly larger compared to other samples. This reduces the mechanical stability of the material.
c) Among the three studied samples, sample 3 exhibits the finest grain size and the most uniform morphology. The surface consists of finely divided agglomerates and fine particles. Compared to the other samples, fewer large cavities, deep holes, and significant defect areas are observed. The average of the measured surface features is approximately 2.7 µm, which falls within a narrow range of approximately 2.25 to 3.45 µm. This narrow size distribution indicates a relatively high degree of morphological uniformity. Overall, compared to the other samples, sample 3 can be described as the most uniform in terms of microstructure.
d) Sample 4, a 15% diatomite sample, exhibited a coarse, heterogeneous morphology with a distinct porous structure on its surface. The structure consists of fine-grained material interspersed with coarse-grained agglomerated zones. The surface exhibits depressions, open pores, and local cavities. The measured functional dimensions range from approximately 2.48 to 9.69 µm, with an average size of about 4.9 µm. The wide distribution of sizes indicates significant morphological heterogeneity, which reduces the mechanical homogeneity of the material.
3.2. Energy-Dispersive X-Ray Spectroscopy (EDS)
The chemical composition of the ceramic samples was determined using this method. Figure 8 shows the results of the EDS analyses of the samples.
Sample a shows an oxide–silicate composition dominated by O and Si. Its Ca and Fe contents are somewhat higher compared to sample d, while Ti is almost undetectable in the total spectrum.
Sample b shows the highest Ca content among the samples presented. This composition indicates an oxide–silicate matrix with potential contributions from iron, titanium, and calcium phases.
The distribution of O, Si, Ca, Fe, Al, Ti, and Mg in sample c shows a relatively uniform pattern.
Sample d is characterized by high O and Si content and significant amounts of Ca, Al, Fe, and Ti. The elemental distribution map shows some heterogeneous regions. The main components are generally widespread on the Earth's surface.
3.3. X-Ray Diffraction Analysis (XRD)
The crystalline structure and phase composition of all thin-film anodes were analyzed by X-ray diffraction (XRD, SmartLab Rigaku) using CuKα1 radiation (λ = 0.15406 nm) and are shown in Figure 9. Measurements were performed over a 2θ range of 10° to 80° with a scanning speed of 0.02°/s, a tube voltage of 30 kV, and a tube current of 25 mA.
According to the obtained XRD patterns, Figure 9 shows the samples 4, 3, 1, and 2 displaying distinct crystal peaks indicating the presence of crystalline phases. The main intense reflections are observed in the 26–29° 2θ range, while additional low-intensity peaks appear at around 35–37°, 42–43°, 50°, 60°, and 68° 2θ.
Sample c is characterized by the most intense and narrow main peak in the 26-27° 2θ region, and this indicates a higher degree of relative crystallinity compared to the other samples. Although samples d, a, and b also indicate the presence of crystalline phases, the lower intensity of their main peaks suggests a lower degree of crystallinity and heterogeneity in the phase composition.
3.4. Raman Spectroscopy
The Raman spectroscopic analysis of the external sample was performed using a Raman spectrometer (Cora 5001, a standard fiber-optic dual-wavelength instrument with a fiber-optic probe), and the results are presented in Figure 10.
The spectra of the ceramic samples show broad vibration bands in the range of approximately 150–1200 cm⁻¹. The analysis results indicate that the studied materials belong to the silicate-ceramic system. The highest crystalline phase was identified in sample 3 and fully corresponded with the XRD analysis results. The Raman spectroscopy analysis results determined the proportion of amorphous silicate phases in samples 1, 2, and 4, indicating a partially crystalline structure.
3.5. Physicomechanical Properties
The results of the physicomechanical analysis of the scientific experimental work conducted in the Construction Materials and Building Thermal Physics Laboratory of the Department of Architecture and Construction at the Western Kazakhstan Innovation and Technological University's Industry Technology Institute are presented in Table 5.
4. Discussion
The results of the microstructure, elemental composition, phase composition, and physicomechanical properties of ceramic samples heat-treated at 1000°C, which vary depending on the composition of the components, make it possible to determine the main laws. SEM analysis shows that the pores and open voids of various sizes on the surface of the 4 samples with 15% diatomite, while improving the material's thermal insulation properties, weakening the structural integrity of the material and reducing its mechanical properties. As a result, this sample exhibited the lowest compressive strength, at 21.83 MPa. The single sample made from pure clay exhibited a compressive strength of 26.7 MPa and a relative density of 1841.61 kg/m³, despite the presence of microcracks and individual pores. SEM studies of sample 3, which contained 10% diatomite, showed a narrow size distribution of structural components and few large defects, indicating the most uniform microstructure. Furthermore, XRD analysis results for this particular sample showed the most intense and narrow diffraction peak in the 26–27° region, demonstrating a high degree of crystallinity. Moreover, despite the low density of sample 3, the well-developed crystalline phases and the uniformity of the structure ensured high compressive strength, reaching 26.71 MPa. Sample 2 exhibited the highest morphological heterogeneity according to SEM studies. The presence of large-sized pores and agglomerates weakened the structural integrity of the material, negatively affecting its strength. Overall, adding up to 10% diatomaceous earth was shown to improve microstructural uniformity, crystallinity, and mechanical strength. However, increasing it to 15% had a negative effect on its strength due to excessive porosity.
5. Conclusions
EDS results showed that silicon and oxygen predominated in all samples. The presence of iron, titanium, calcium, magnesium, and aluminum also confirmed the potential formation of complex aluminosilicate and calcium phases. XRD studies revealed the highest degree of crystallinity in the sample containing 10% diatomite. Furthermore, SEM analysis showed that the sample with 10% diatomite developed the most uniform, stable microstructure. Furthermore, the results of the physicomechanical studies showed a relative maximum strength of 26.71 MPa. This indicates that adding diatomite in an optimal amount strengthens the material's structure.
According to the research results, the composition containing 10% diatomite was found to be the most developed system in terms of phase and microstructure. Moreover, it was identified as the most effective and optimal composition due to its high crystallinity, highest compressive strength, and low thermal conductivity. In other words, adding 10% diatomite proved to be an effective modifier.
Author Contributions
Author Contributions: Conceptualization, Q.N. and B. Sh.; Supervision, Q.N. and B.Sh.; Project administration, Q.N. and B. Sh.; Methodology, S.Zh. and B.I.; Investigation, S.Zh., B.I. and K.D.; Formal analysis, S.Zh. and B. I.; resources, K.D. B.A. L.K. ; Data curation, S.Zh. and B.I.; Writing—original draft preparation, S.Zh. and B.I.; Writing—review and editing, B. Sh., Q.N., S.Zh. and B.I.; B. Sh., and Q.N. contributed equally to this work. S.Zh. and B.I. are corresponding authors. All authors have read and agreed to the published version of the manuscript.
Funding
Please add: This research received no external funding.
Data Availability Statement
The data presented in this study are contained within the article.
Acknowledgments
The authors would like to express their deep gratitude to Kazbay Karaevich Bozymov, Founder of West Kazakhstan Innovation and Technological University, for his comprehensive support in the implementation of this research, including the provision of financial assistance, laboratory materials, and equipment necessary for conducting the study.
Conflicts of Interest
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
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Figure 1.
Raw materials: a) clay from the Roman deposit; b) diatomite from the Zhalpaq deposit.
Figure 2.
Energy-dispersive X-ray spectroscopy (EDS) spectra based on the elemental composition of the raw materials: (a) clay from the Roman deposit, (b) diatomite from the Jalpak deposit.
Figure 2.
Energy-dispersive X-ray spectroscopy (EDS) spectra based on the elemental composition of the raw materials: (a) clay from the Roman deposit, (b) diatomite from the Jalpak deposit.
Figure 3.
Laboratory naturally dried cylindrical samples.
Figure 5.
Thermal treatment of cylindrical samples at 1000°C.
Figure 6.
Determination of compressive strength in a PGM-1500MG4 press.
Figure 7.
SEM images of the samples: (a) 100 clay; (b) 5 diatomite + 95 clay; (c) 10 diatomite + 90 clay; (d) 15 diatomite + 85 clay.
Figure 7.
SEM images of the samples: (a) 100 clay; (b) 5 diatomite + 95 clay; (c) 10 diatomite + 90 clay; (d) 15 diatomite + 85 clay.
Figure 8.
SEM-EDS images of the samples: a) 100% clay; b) 5% diatomite + 95% clay; c) 10% diatomite + 90% clay; d) 15% diatomite + 85% clay.
Figure 8.
SEM-EDS images of the samples: a) 100% clay; b) 5% diatomite + 95% clay; c) 10% diatomite + 90% clay; d) 15% diatomite + 85% clay.
Figure 9.
XRD patterns of the samples: ceramic samples.
Figure 10.
Raman spectra of the samples: (a) 100% clay; (b) 5% diatomite + 95% clay; (c) 10% diatomite + 90% clay; (d) 15% diatomite + 85% clay.
Figure 10.
Raman spectra of the samples: (a) 100% clay; (b) 5% diatomite + 95% clay; (c) 10% diatomite + 90% clay; (d) 15% diatomite + 85% clay.
Table 1.
Results of SEM elemental analysis of the raw materials.
| Element | Raw material name | |||
| clay from the Roman deposit | diatomite from the Jalpak deposit | |||
| Weighting | Atomic | Weighting | Atomic | |
| O | 54.12 | 68.21 | 54.67 | 70.18 |
| Na | 1.01 | 0.88 | 0.80 | 0.71 |
| Mg | 1.01 | 0.84 | 1.79 | 1.51 |
| Al | 7.70 | 5.76 | 6.60 | 5.02 |
| Si | 29.52 | 21.19 | 21.70 | 15.86 |
| S | 0 | 0 | 0.29 | 0.19 |
| Cl | 1.87 | 1.06 | 0 | 0 |
| K | 1.62 | 0.84 | 1.73 | 0.91 |
| Ca | 0.33 | 0.17 | 7.02 | 3.60 |
| Ti | 0.58 | 0.24 | 0.49 | 0.21 |
| Fe | 2.23 | 0.81 | 4.92 | 1.81 |
Table 2.
Results of energy-dispersive X-ray spectral analysis of raw materials.
| No. | Indicator Name | clay from the Roman deposit | diatomite from the Jalpak deposit |
|---|---|---|---|
| 1 | PMP | 11,56 | 12,64 |
| 2 | SiO2 | 54,59 | 62,25 |
| 3 | Al2O3 | 11,54 | 14,01 |
| 4 | Fe2O3 | 4,32 | 2,99 |
| 5 | TiO | 0,64 | 0,62 |
| 6 | CaO | 9,37 | 2,8 |
| 7 | MgO | 4,36 | 4,43 |
| 8 | Moisture | 2,4 | 3,3 |
Table 3.
Physico-mechanical properties of raw materials.
| No. | Model name | Liquid limit |
Rolling thread method |
Plasticity | Forming moisture content |
Bulk density |
|---|---|---|---|---|---|---|
| 1 | Clay from the Roman deposit | 36,40 | 23,52 | 12,88 | 28,04 | 1216 |
| 2 | Diatomite from the Jalpak deposit | 90,50 | 83,13 | 7,37 | 65,40 | 430 |
Table 4.
Compositions of the samples studied.
| No. | Designation | Clay, % | Diatomite, % |
|---|---|---|---|
| 1 | a | 100 | 0 |
| 2 | b | 95 | 5 |
| 3 | c | 90 | 10 |
| 4 | d | 85 | 15 |
Table 5.
Physico-mechanical properties of ceramic samples heat-treated at 1000°C.
| Composition | Bulk density, kg/m³ | Compressive strength limit, MPa | Water absorption, % | Total porosity, % | Thermal conductivity coefficient λ, W/(m·°C) |
|---|---|---|---|---|---|
| а | 1841,61 | 21,7 | 15,5 | 29 | 0,595 |
| b | 1826,61 | 23,25 | 16,22 | 30 | 0,589 |
| c | 1652,92 | 26,71 | 18,77 | 31 | 0,528 |
| d | 1663,42 | 21,83 | 20,3 | 34 | 0,532 |
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