Minerālo izejvielu piedevu ietekme uz kordierīta keramikas īpašībām

Šī darba mērķis ir ir izmantot Latvijā pieejamās minerālās izejvielas, lai aizstātu daļu no nepieciešamajām sintētiskajām izejvielām, kas jālieto kordierīta keramikas sintēzei, un izpētītu šo izejvielu ietekmi uz iegūtās keramikas īpašībām

Porous Cordierite Ceramics from Natural Clays

In this report the obtaining and properties of high-temperature 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

Minerālo piedevu un izejvielu dispersitātes ietekme uz kordierīta keramikas īpašībām

Darbā apskatītas kordierīta keramikas iegūšanas iespējas, aizstājot daļu nepieciešamo sintētisko izejvielu ar māliem un dažādiem Latvijas dolomītiem. Iegūtie izejvielu pulveri tika malti divos režīmos, pēc malšanas noteikts efektīvais daļiņu diametrs. Šī darba rezultāti parādīja, ka mālu pievienošana konkrēta sastāva paraugiem uzlabo to spiedes izturību. LTIK un SEM attēlu analīze norāda uz malšanas laika palielināšanas pozitīvo ietekmi, samazinot iegūstamo keramisko paraugu porainību un uzlabojot graudu sablīvēšanos

Porous and Dense Cordierite Ceramic from Raw Illite Clay

Ternary system MgO-Al2O3-SiO2 contains many technically valuable crystalline phases such as enstatite, forsterite, spinel and cordierite. For most of these phases coefficient of thermal expansion (CTE) is extremely low (as low as 1.5·10-6 K -1 ) which allows for them to be used in conjunction with other thermally demanding materials like quartz, for example. Also, other important properties like their high mechanical strength and good dielectric permeability is of value for potential use in practical applications. Cordierite ceramic materials, for example, are good candidates for both electronic circuitry substrates, when prepared as dense material and for use in filtration systems, when prepared as porous material. Formation of cordierite from oxide powders takes place above 1350 °C. Rational preparation of such material requires modifications in synthesis rout, i.e., addition of flux forming agents or presence of volatile compounds. In this work the use of Latvian illite clay as partial raw material for preparation of both dense and porous cordierite ceramics was studied. No additional artificial flux and/or volatiles were used. Obtained dense ceramic samples were tested for their mechanical strength, and porous samples – for their pore morphology and porosity. It was determined that the use of illite clay of no less than 1/3 of total mass was enough to form both extremely dense and tough (compressive strength of about 400 MPa) and extremely porous (about 96% apparent porosity) materials by just adjusting thermal treatment regime. The X-Ray diffraction of the samples showed that formation of single-phase crystalline cordierite can also be achieved in relatively lower temperatures, e.g., as low as 1300 °C

Blīva augsttemperatūras mullīta-ZrO2 keramika

Parādīta piedevu (mālu minerāla – illīta, Si3N4, SiAlON), kā arī izejas pulveru izstrādes veida ietekme uz mullīta-ZrO2 keramikas saķepināšanas procesu (pielietojot tradicionālo saķepināšanas procesu un plazmas izlādes saķepināšanas procesu jeb SPS), fāžu sastāvu, struktūru, mehāniskajām un keramiskajām īpašībām.Mālu piedeva sekmē pulvera  daļiņu  izmēru  samazināšanos,  veicina  keramikas paraugu sablīvēšanos tradicionālā saķepināšanas procesā, bet dod pretēju efektu, pielietojot SPS procesu. Silīcija  nitrīda un  SiAlON nanopulveru  piedevas ir efektīvas SPS procesā, sasniegta paraugu spiedes izturība ap 600 MPa Si3N4 piedevas gadījumā, termiskā trieciena izturību un elastības moduļa  vērtības 180 – 220 GPa, kuras termiskā trieciena 1000/20 °C rezultātā samazinās pieļaujamās robežās. Šīs vērtības ir par aptuveni 20–25 % zemākas, pielietojot SiAlON piedevu.Keramikas paraugu, kas saķepināti tradicionāli un pielietojot SPS procesu, mikrostruktūrā ir mullīta vai pseidomullīta kristāliski veidojumi ar ieslēgtiem ZrO2 graudiem, kas pārsvarā ir kubiskā modifikācijā. Galvenā atšķirība starp abos saķepināšanas procesos iegūtajiem paraugiem ir tā, ka tradicionāli saķepināto paraugu mikrostruktūrā ir novērojama ‘tukšumu’ veidošanās, kuri aizpildās ar mullīta kristāliem, it sevišķi palielinoties Si3N4 piedevai. Mikrostruktūra keramikas paraugiem, kas saķepināti ar SPS tehnoloģiju ir blīvāka – mullīta kristāli ir blīvi izvietojušies, un tiem nav mullītam raksturīgās prizmatiskās formas.Dense high-temperature mullite-ZrO2 ceramicsThe influence of some additives (clay mineral illite, Si3N4, SiAlON) and the processing of the initial powders on sintering of mullite-ZrO2 ceramics (using traditional or plasma dispersion sintering processes), composition, structure, mechanical and ceramic properties of phases is shown.The clay additive contributes to the reduction of the particle size of the powder, facilitates the densification of the ceramic samples in the traditional sintering process, but vice versa if SPS is used. Silicon nitride and SiAlON nanopowder additives are effective in the SPS process; samples reach a compressive strength of approximately 600 MPa in the case of Si3N4 additive; thermal shock resistance and elastic modulus are in the range of 180–220 GPa, which under a thermal shock of 1000/20 °C will reduce within the permissible limits. These values are about 20–25 % lower if SiAlON additive is used.The microstructure of the ceramic samples traditionally sintered or sintered using a SPS process is formed by crystalline mullite or pseudomulite crystals with enclosed ZrO2 grains that mostly are in the cubic modification. The main difference between the samples obtained in both sintering processes is that formation of voids filled with mullite crystals can be observed in the microstructure of traditionally sintered samples, especially if the amount of Si3N4 additive is increased. The microstructure of the ceramic samples sintered with SPS technology is denser – the mullite crystals are densely distributed and do not have the prismatic shape that is characteristic to mullite

Latvijas minerālās izejvielas eko-keramikas izstrādei

Darbā dots ieskats par iespējām izmantot Latvijas minerālās izejvielas kā bāzi vai  piedevu  keramikas  materiālu  (eko-materiālu)  izstrādei ar dažādu pielietošanas aspektu, to skaitā parādīt iespēju šo materiālu ieguves tehnoloģisko procesu optimizēšanai virzībā uz to apdedzināšanas temperatūras samazināšanu, līdz ar to reducējot kaitīgu gāzveida izmešu nonākšanu vidē. Parādīti darbu rezultāti laika periodā no 2007. g. līdz 2017. g. Tiek apskatīti un analizēti sekojoši pētījumi:neapstrādāta māla pielietošana atkritumu deponēšanas vietu noblīvēšanai;daļēji dehidratizēta māla pielietošana Cr3+, Cr6+, Zn2+ un Cu+ jonu sorbcijai, kas veidojas galvanisko procesu notekūdeņos; poru saturošas augsttemperatūras keramikas izstrāde no jauktiem izejvielu maisījumiem, kas nodrošina pietiekamu gāzveida fāzes izveidošanos keramikas apdedzināšanas procesā, veidojot poras, lai pielietotu par filtrēšanas/attīrīšanas materiālu;illīta māla piedevu izmantošana, lai pazeminātu augsttemperatūras blīvas keramikas saķepināšanas/apdedzināšanas temperatūru, iegūstot ilgspējīgu mehāniski un termiski izturīgu produktu; kā arī tehnoloģiskie procesi, kas nodrošina porainas, siltumu izolējošas keramikas materiāla ieguvi pie pazeminātām temperatūrām (ģeopolimēru metode).Mineral Raw Materials of Latvia for Development of Eco-CeramicsThe paper gives an insight into the possibilities to use Latvian mineral raw materials as a base or additives for the development of ceramic materials (eco- materials) with different application aspects, including showing the possibility of optimizing the technological processes of these materials towards the reduction of their firing temperature, thereby reducing the release of harmful gaseous effluents into the environment.The results of the works that are reported in the period were obtained from  2007 to 2017. The following studies are reviewed and analyzed: the use of untreated clay for the sealing of waste deposits; the use of partly dehydrated clay for sorption of Cr3+,6+, Zn2+ and Cu2+, which have formed in galvanic processes; the development of porous high temperature ceramics from mixes  of mineral raw materials and synthetic additives that provide a sufficient gas phase  formation in the firing process and consecutively to form pores in obtained ceramic material; the use of illite clay additives to reduce the temperature of sintering of high temperature dense mechanical and thermally durable ceramics, as well as technological processes that ensure the production of porous, heat-insulating ceramic materials at reduced temperatures (geopolymer method)

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

Different Treatment Application of Illite Clay for Low Temperature Cermics

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

Jauni keramikas materiāli un tehnoloģijas

Dots pārskats par rezultātiem enerģiju taupošutehnoloģiju un relatīvi jaunu keramikas materiālu izstrādi,izmantojot Latvijas minerālās izejvielas. Parādīts, ka illītu māluķīmiskā apstrāde ievērojami samazina materiāla saķepināšanastemperatūru un nodrošina augstu spiedes pretestību, salīdzinotar tradicionāli iegūtiem keramikas materiāliem.Mikrobioloģiskā mālu apstrāde maz ietekmē plastisku māluplasticitātes/plūstamības izmaiņas. Izstrādāti mullīta-ZrO2augstas stiprības keramikas materiāli ar illīta mālu piedevu, kāarī augsttemperatūras, kordierīta un paaugstinātas porainībaskeramikas materiāli

Effect of Sintering Process and Additives on the Properties of Cordierite Based Ceramics

It is possible to obtain cordierite ceramics with high temperature synthesis using both synthetic and natural raw materials. This paper discusses the possibilities to obtain cordierite ceramics replacing part of required oxides with raw materials from various Latvian deposits of dolomite and clay. The obtained raw cordierite powders were ground in two modes (3 and 12 hours) and fired at 1200 oC. Ceramic samples were characterized by hydrostatic wieghting method, crystalline phase composition was studied by XRD. Obtained samples were evaluated by their mechanical (compressive) strength and linear coefficient of thermal expansion (CTE). Thermal shock resistance was tested using water quenching method and afterwards evaluated by using ultrasonic method to test changes in Young's modulus of elasticity. Results show that increase in grinding time causes samples to densify and promote formation of cordierite crystalline phase which corresponds to increase in total compressive strength and decrease of CTE values. CTE values of samples ground for 12 hours conform to that of obtained in other researches