Ingunda Šperberga

Characterisation of mullite – ZrO2 ceramics prepared by various methods

Mullite – ZrO2 ceramics was sintered from variously prepared powder mixtures -different time milled and hydrothermal synthesized. As sintering aid 8 wt. % illite clay for one part of starting mixtures was added. Two sintering routes was applied for consolidation of powder – spark plasma sintering (SPS) technique and conventional sintering reactions in air. It is shown that the structure of sintered samples for SPS was completed at 1250°C and by conventional - at 1300°C. The developed microstructure both conventional and SPS can be characterized by mullite matrix with evenly distributed ZrO2 grains. For conventionally prepared and sintered samples corundum and ZrO2 tetragonal grains are observed, but for SPS dominates ZrO2 cubic. The microstructure of ceramic samples from hydrothermal synthesized powders and consolidated by SPS is amorphous like, with xenomorfic crystals of mullite and inclusions of ZrO2 cubic grains. It is stated that additive of illite clay promotes the densification. At conventional sintering clay prevents the transformation of ZrO2 tetragonal to ZrO2 monoclinic by cooling of samples, but for SPS promotes formation of ZrO2 cubic. SPS sintered samples processed from conventionally milled powder mixture are characterized by pressure strength.

Ceramic of the Mullite–ZrO2–SiAlON System During Spark Plasma Sintering

Results are provided for a study of ceramic of the mullite–ZrO2–SiAlON system formed from oxide mixtures with addition of SiAlON nanopowder during spark plasma sintering (SPS) compared with properties of similar ceramic prepared by traditional sintering. It is shown that ceramic prepared by the SPS-process (compared with traditional sintering) has high indices for density (3.10 – 3.32 g/cm3), ultimate strength in compression (295 – 305 MPa), and also a high elasticity modulus (170 – 180 MPa) after ten thermal shock cycles. This is due to the packing density of mullite formations within sintered specimen microstructure, including ZrO2 inclusions of cubic modification.

Porous Cordierite Ceramics from Natural Clays / Poraina kordierīta keramika no dabiskiem māliem

Abstract In this report the obtaining and properties of hightemperature porous ceramic materials using local carbonate clays and quartz sand resources was studied. Materials with two different porosities were obtained by using different synthesis temperatures. The test results show that these materials contain cordierite as their main crystalline phase. The porosity directly influences the compressive strength and it is greatly reduced when overall porosity increases. The CTE of obtained materials is low − about 3-10−6 1/°C. Keramikas materiāliem, kas veidoti sistēmā MgO-Al2O3-SiO2 ir plašs pielietojums dažādās jomās. Tā tas, piemēram, ir termiski stabilajai fāzei kordierītam (2MgO·2Al2O3·5SiO2). Kordierīta keramika ar tās zemo termiskās izplešanās koeficientu - TIK (α ≈ 1,0·10−6 -4,0·10−6 1/°C) droši iztur straujas temperatūras izmaiņas, tāpēc tā var tikt izmantota kā ugunsizturīgs materiāls. Dabā kordierīts ir reti sastopams minerāls, tādēļ šis kristāliskais materiāls ir jāiegūst sintētiski. Visplašāk izmantotā metode ir augsttemperatūras cietfāžu sintēze, retāk - sola-gēla sintēze un rekristalizācija no stiklveida kausējuma. Sintēzei tiek izmantotas dažādas magnija, alumīnija un silīcija oksīdus saturošas izejvielas, no kurām visbiežāk lietotās ir talks un kaolīns. Lai samazinātu nepieciešamo sintēzes temperatūru, oksīda maisījumiem tiek pievienoti dažādi kušņi, piemēram, B2O3. Šajā pētījumā ieguva augsti porainus kordierīta keramiskos materiālus, izmantojot vietējās izejvielas - karbonātu mālu un kvarca smiltis. Ieguva dažādas porainības materiālus, mainot sintēzes temperatūru. Rentgenfāžu analīzes rezultāti liecināja, ka šie materiāli saturēja kordierītu kā galveno kristālisko fāzi. Porainībai palielinoties, tā tieši ietekmēja spiedes stiprību, to ievērojami samazinot. Iegūto materiālu termiskās izplešanās koeficienti bija zemi (ne augstāki par 3,0·10−6 1/°C visā pētītajā temperatūras diapazonā), neskatoties uz poru un stiklveida fāzes klātbūtni.

Mechanical properties of materials obtained via alkaline activation of illite-based clays of Latvia

Materials has been synthesized in the temperature range from 60-100 °C from two illite based clays of Latvia under activation of KOH and NaOH solutions (4-6 M). Compressive strength and apparent porosity were measured. The effect of concentration of KOH and NaOH solutions on the material mechanical properties was investigated by means of infrared spectroscopy (IR). Compressive strength data of the materials showed that via such activation could obtain building materials with good quality.

Comparative study of illite clay and illite-based geopolymer products

Quaternary (Q-clay) clayey deposits are one of the dominating parts of mineral raw materials of the sedimentary cover at present area of Latvia. These clays can be characterised by illite content up to 75-80 %. Two ways for use of illite clays were studied: conventional and geopolymers method. Purpose of the second mentioned method was showing the influence of alkali (KOH) on the transformation of Q-clay/illite structure. Obtained products were investigated by IR–spectroscopy, DTA and XRD, pore size distribution was determined as well. Some ceramic properties and compressive strength were determined and compared. IR-spectrum showed the effect of alkali on the transformation of Q-clay/illite structure in three main absorption bands: 3620-3415 cm−1 which is related to the vibrational modes of adsorbed water between SiO4 and AlO6 layers; new stronger absorption bands at 1635 cm−1 and 1435 cm−1 indicate on the appearance of vibrations in Q-KOH and are related to the K-O-Si bonds; the most essential changes are vibrations at 850 cm−1 showing the changes in the coordination number of Al from 6 to 4 for Q-KOH. Investigations of the bulk density in dependence on temperature showed the small increase of bulk density for Q-clay while - the relatively remarkable decrease for Q-clay/KOH. Mentioned values correlate with the compressive strength of Q-clay and Q-KOH products.

Phase Formation and Structure of Mullite-Alumina-Zirconia and Spinel-Enstatite Ceramics Developed from Synthetic and Mineral Raw Materials

New dense and porous ceramics are developed using two formulation approaches. These are ceramics with remarkable content of mullite, corundum and ZrO2 - tetragonal and monoclinic in crystalline phase and porous (average size of pores up to 150-350μm) spinel-enstatite/forsterite ceramics. To promote the phase development by high-temperature synthesis of these ceramics the mineral raw materials – illite clay and illite clay together with dolomite are used. Bulk density for mullite (corundum) – zirconia ceramics is increased by equal addition of illite clay (8.2 wt.%) as well as ZrO2 and especially ZrO2 +Y2O3 to starting mullite mixtures. Contrary the addition of different kind and amount of illite clay together with dolomite trends to formation of spinel – enstatite (forsterite) ceramics and decrease the bulk density to the value up to 0.35 g/cm3. The XRD results indicate that ZrO2 monoclinic/tetragonal incorporation in mullite (corundum) structure realizes through the liquid phase. Development of the spinel MgAl2O4 and enstatite MgSiO3 crystalline phases along with the sufficient amount of glassy phase in microstructure and even distributed pores are proper for spinel-enstatite (forsterite) ceramic samples.

Chemically and Thermally Activated Illite Clay from Latvia / Ķīmiski un termiski aktivēts Latvijas illīta māls.

Abstract Materials were synthesized from illite based clay from Latvia by chemical and thermal activation using both NaOH and KOH solutions (4−6 M). Compressive strength and apparent porosity were measured. Effect of concentration of both solutions on the mechanical properties of the material was investigated by means of infrared spectroscopy (IR). Compressive strength data showed that alternative building materials could be obtained via alkaline activation. Rakstā aplūkota Latvijas kvartāra illītа māla kīmiska aktivēšana ar dažādas koncentrācijas KOH un NaOH šķīdumiem un tā piemērotība materiālu izstrādei dažādās temperatūrās (60−80 °C) un (600−800 °C). Illīts un plagioklāzs ir alumosilikāti, kas var reaģēt sārmainos apstākļos; to klātbūtnei mālos ir svarīga loma ģeopolimerizācijas procesā. Kā galvenais rādītājs ģeopolimerizācijas procesa sekmīgai norisei izvēlēta iegūto materiālu spiedes stiprība, kas pieauga līdz ar temperatūras paaugstināšanu (no 600 °C līdz 800 °C) karbonātus saturošos kvartāra mālos. Kā aktivētājs tiek izmantots KOH vai NaOH šķīdums. Šo mālu materiālu augstākā spiedes stiprība (23,8 MPa) tiek sasniegta apstrādājot 800 °C, ja kā ķīmiskais aktivators tiek izmantots 4 M KOH šķīdums. Ķīmiskās aktivācijas procesā ar NaOH šķīdumu tiek iegūti materiāli, kuru spiedes stiprības rādītāji ir zemāki par rādītājiem, kas iegūti izmantojot KOH šķīdumu. Tomēr salīdzinot ar ķīmiski neaktivēta māla spiedes stiprību (16 MPa), šajā gadījumā ir iegūts materiāls, kura spiedes stiprība ir 1,5 reizes lielāka (22 MPa) - kā šķīdums ķīmiskajai aktivācijai tiek izmantots 4 M NaOH un termiskās aktivācijas temperatūra ir 800 °C. Pētījumi parādīja, ka viena vai otra sārmu hidroksīda izmantošana ģeopolimerizācijas procesā deva dažādus rezultātus. Iegūto materiālu īpašības bija atkarīgas no vairākiem faktoriem, no kuriem svarīgākais bija termiskās apstrādes temperatūra. Sakarā ar katjonu katalītisko lomu, svarīgs ir katjons, kas ietilpst hidroksīda (NaOH vai KOH) sastāvā un ar kuru māls tiek ķīmiski aktivēts. Iegūto materiālu varētu izmantot kā tradicionālo būvmateriālu aizstājēju. Pētītais materiāls tiek iegūts zemākā temperatūrā, bet tas nemazina tā spiedes stiprību, salīdzinot ar tradicionāliem būvmateriāliem.

Influence of Bacteria Pseudomonas Fluorescens on the Properties of Latvian Clay

Wide varieties of bacteria are able to produce extracellular polymeric substances (EPS) which are mostly composed of polysaccharides. It is suggested that EPS substances can alter certain clay soil properties due to their ability to adhere to the surface of mineral particles. Most common used microorganisms by the researchers for this purpose are of either genus Bacillus or genus Pseudomonas. In this study growth of bacteria P. fluorescens AM PS11 culture in locally obtained clay is studied for the purpose of establishing their influence on rheological properties of clay. An attempt to evaluate it has been made using FT-IR and XRD. Change in plasticity of clay using Atterberg limits method and coefficient of drying sensitivity has also been determined.

Different Treatment Application of Illite Clay for Low Temperature Ceramics

Impact of chemical treatment by alkali of raw, dehydroxylated at 600 °C and intensively milled illite clay on structure, phase composition and some properties of sintered at lower temperatures ceramic materials were studied using DTA, X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) and mercury intrusion porosimetry. DTA and XRD results show that alkaline activation of illite clay by sodium hydroxide leads to the slight structural changes of illite characterized by structural water losses showed from DTA and negligible decrease of illite and kaolinite, as well dolomite diffraction peaks on XRD. Additional treatment, intensive milling and in particular dehydroxylation, contributes to the considerable changes in intensities of all effects on DTA-curves, especially for dehydroxylation endo-peak. It is shown that chemical treatment promotes the formation of rather amorphous and homogenous structure of sintered at 600°C respective ceramic samples and leads to the growth of the compressive strength.

Development of Cordierite Ceramics from Natural Raw Materials

Cordierite ceramics are known for their low CTE and high compressive strength values which affords them place in fields where demanding thermal and mechanical properties are required. Development of such ceramics is greatly dependent on materials used. If raw materials are used formation of additional phases and pore/glass formation is expected. The purpose of this research is to examine the process of cordierite development from mixed compositions formed from precursors of the natural raw materials as illite clay, dolomite and quartz sand and synthetic additives – MgO, γ-Al2O3 and their influence on thermal and mechanical properties. It is verified that the addition of 10 wt.% of illite clay and about 20-21 wt.% dolomite in staring compositions at the sintering temperature of 1200 °C results in the development of dense ceramic material with perfect-shaped crystalline cordierite phase and secondary anorthite phase. Sintered cordierite ceramics have been tested, among other properties, for their compressive strength, coefficient of thermal expansion and modulus of elasticity after 20 cycles of thermal shock treatment.