Celsian Ceramics Research Articles

Radio-transparent celsian ceramics modified with glass in a pseudoternary system BaO–Al2O3–SiO2: synthesis, microstructure, thermal and physical properties

The article presents the results of the study of radio-transparent celsian ceramics, in which part of the components were introduced using eutectic glass of the pseudoternary BaO–Al2O3–SiO2 system. The bonding of the components of the experimental glass into the celsian phase was realized according to the principle of reactive structure formation by adding the missing components (crystalline fillers). In this case, the obtained dense sintered water-resistant ceramic, the only crystalline phase in the composition of which is the monoclinic form of celsian, which forms a microhomogeneous structural matrix of the material. Celsian is represented by distinct prismatic crystals of tetragonal and hexagonal shape. The size of celsian crystals increases from 3–5 m to 7–10 m with increasing the content of eutectic glass. The developed celsian ceramic has a set of enhanced physical and thermal properties: zero water absorption and open porosity, mechanical compressive strength (up to 157 MPa), refractory index is 1540–15800C. Celsian ceramic is characterized by a coefficient of linear thermal expansion of 3410–7 0C–1, which provides a sufficiently high thermal shock resistance of 7000C. In terms of the level of relative dielectric permittivity (5.5) and dielectric losses (0.0005) at a frequency of 1010 Hz, the developed ceramic meets the requirements for ultra-high-frequency radio-transparent materials for aviation and rocket technology, which operate under conditions of high-speed high-temperature heating.

CALCULATION OF GAS-DYNAMICS PARAMETERS AND STRESS-STRAIN STATE OF CELSIAN CERAMICS PRODUCTS

In the work using the finite element method, an analysis of the behavior of nose fairings made of radio-transparent ceramic materials of celsian composition was carried out. Determination of parameters of gas dynamics and stress-strain state was carried out using licensed ANSYS software. SSG Reynold Stress turbulence model was chosen for accurate air flow simulation. Geometric and finite element models were used to calculate strength and temperature fields. The analysis of the results of gas-dynamic calculations shows that at the point of transition of the conical part of the rocket into the cylindrical part, there is a sharp change in the flow conditions and a disruption of the flow in the range of speeds of 100-1100 m/s. As a result of modeling the distribution of temperature fields with the stated task, it was established that the temperature on the inner surface of the fairing differs from the temperature on the outer surface by no more than ±1 °C on average, and the maximum surface heating temperature does not exceed 550 °C. According to the results of calculations of the stress-strain state under temperature regimes that simulate the conditions of their operation, it was concluded that under the considered conditions the equivalent (≤ 69.3 MPa) and main (≤ 40 MPa) stresses occurring in the nose fairing are not exceed the bending strength limit for celsian ceramics (290 MPa). It can be observed that the maximum temperature difference in thickness corresponds to the part of the fairing with the minimum radius. Movements on the surface of the fairing do not exceed 0.25 mm, which is acceptable according to the specified parameters. The parametric model provides advantages in justifying rational technical solutions. Ultimately, the nose fairing, made of celsian ceramics, will maintain its integrity in real operating conditions. Keywords: radiotransparent celsian ceramics; nose fairing; finite element method; gas dynamics; thermophysical calculations; strength; stress-strain state

Thermodynamic analysis of reactions of the celsian phase formation during the synthesis of thermal shock resistance ceramics based on eutectic glasses of the BaO–Al2O3–SiO2 system

The search for effective ways of obtaining densely sintered celsian ceramics at low firing temperatures usually requires a large volume of experimental research. The object of our research is the reactions of the formation of the celsian phase with the participation of glass components of eutectic compositions of the BaO–Al2O3–SiO2 system under low-temperature firing conditions. In this case, thermodynamic analysis was used as a tool to assess the probability of chemical reactions. This paper reports the results of theoretical and experimental studies into the features of the course of chemical reactions with the participation of glass components of eutectic compositions of the BaO–Al2O3–SiO2 system. It was revealed that once the stoichiometric ratio is maintained, the final product of the interaction between the components of eutectic glasses E-4, E-5 and E-6 with crystalline fillers is the celsian phase. The most probable is the formation of celsian when the components of eutectic glasses interact with Al2O32SiO2, which is a product of kaolinite (Al2O32SiO22H2O) dehydration. It was found that barium orthosilicate, in comparison with other barium silicates, exhibits the highest activity when interacting with charging components in the direction of formation of the сelsian phase already at the temperature of 7500С. At the temperature of 9000C, such a composition is noted to have an active transition of hexagonal celsian to monoclinic celsian. As a result, the content of monoclinic celsian increases significantly. The determined patterns allow making a reasonable choice of glasses in the BaO–Al2O3–SiO2 system with the lowest melting temperatures for the subsequent production of low-temperature сelsian ceramics.

The Receiving and Study of Celsian Electrotechnical Ceramics with Innovation One Stage Simplified Technologies in the Bao-Al2O3-Sio2 System

Goal: Barite based celsian ceramics with phase composition accordingly (mass%): of celsian 93; Barium Aluminate and Barium Silicate-4; Glass phase - 3, has been synthesized on the bases of local raw materials with single stage innovation technology. Method: One burn at 16000C we have take out from standard technology in which barium carbonate is used. The material displays the best properties in conditions of synthesis at 1410-1460°C Results: Its properties have been studied in complex. The material shows high resistanse to heat shock. A completely new mechanism of ceramic production is proposed. Structure of celsian ceramics in BaO-Al2O3-SiO2 system is studyd with electron microscope, X-ray, crystalline phase content, optical microscope. Water absorbtion, W%=O. Bending strength of non glazed, δ N/mm2 – 69. CLTE, α20-700 106C-1 temperature areas-3.7. Tanget of a dielectric loss angle at 50 Hz and 20°C and tg δ 10-4=107. HV GPa-18.0. Volume resistivity, ρ ohm/cm 200C-3000C=1016-1012. Elastic modulus, E N/mm2-74.5. The process of pores filling, full consolidation of material and hardness growth at comparatively high temperatures of baking interval are studied. Conclusion: High refractoriness of celsian, (1740°C), low thermal coefficient of linear expansion of synthesized materials, high thermal resistivity enable this ceramics to be recommended for introduction in electronical and electrotechnical industry.

INTENSIFICATION OF THE SINTERING PROCESS OF CERAMIC MATERIALS BASED ON THE BaO – Al2O3 – SiO 2 SYSTEM

The article examines the effect of additives on the intensification of the sintering process of ceramic materials based on the BaO – Al2O3 – SiO2 system. Taking into account different mechanisms of interaction of additives with the main matrix, modifiers – MgO, Cr2O3, ZrSiO4, TiO2 and mineralizers – CaCO3, B2O3, MoO3, SnO2 : Li2O were selected for research. On the basis of the conducted complex of studies, it was established that the most promising intensifier for the celsian sintering process is the eutectic additive SnO2 : Li2O in the amount of 1 wt.% with the following characteristics: water absorption – 5.1%, porosity – 13.4%, apparent density – 2.62 g/cm3. The results of the X-ray phase analysis show that the celsian synthesis reaction is complete at a synthesis temperature of 1200 °С, which is a confirmation of a decrease in the synthesis temperature of the phase by 100 °С. The obtained celsian ceramics meet the requirements for radio-transparent materials and can be used for the manufacture of individual parts in the aerospace industry.

Features of formation of the celsian phase during firing of heat-resistant ceramics in the system BaO–Al2O3–SiO2

In the synthesis of heat-resistant ceramics in the system BaO–Al2O3–SiO2 (BAS), it is important to find ways of intensifying the process of transition of hexagonal celsian to monoclinic celsian without an increase in sintering temperature. Monoclinic form of celsian is characterized by higher thermal, electro-insulating, and mechanical properties. This paper deals with the features of formation of the phase composition of celsian ceramics when using BAS glass of eutectic composition and glass in the system Li2O–Al2O3–B2O3–SiO2 (LABS) of spodumene composition as modifying components. It is shown that monoclinic celsian is the final crystalline phase formed in ceramics synthesized on the basis of barium carbonate and kaolin. Monoclinic celsian is formed stepwise; and the hexagonal celsian appears first. The complete transition hexagonal celsianmonoclinic celsian occurs only in the process of high temperature firing at 12500C. Notably, the degree of ceramic sintering remains low (water absorption is 11.0%). Introduction of BAS glass contributes to the complete transition of hexagonal celsian to monoclinic celsian at a reduced temperature of 11000C. Maximum effect in the formation of monoclinic celsian is achieved by the introduction of LABS glass. As a result, the temperature of formation of this modification maximally decreases to 8000C. In this case, complete sintering of celsian ceramics is achieved at the temperature of 12500С.

Chemical resistance of celsian ceramics in acid and alkaline reagents

In the article, the chemical stability of celsian ceramics at different firing temperatures was investigated and the structural-phase features of the obtained samples before and after interaction with alkaline and acid media were studied.
 The technology of obtaining test samples was two-stage. The first stage was the synthesis of the celsian phase in a muffle furnace at a temperature of 1200 °C with a holding time of 2 hours and subsequent cooling together with the furnace. The second stage took place in a silitic furnace at temperatures of 1300, 1350 and 1400 °C with a set rate of 15 deg/min and holding at a maximum temperature of 4 hours. The chemical resistance of celsian ceramics was determined in relation to 20 % solutions of HCl and NaOH. The phase composition of the test samples was determined using the method of X-ray phase analysis (X-ray diffraction) using a DRON-3M diffractometer. The studies of the experimental samples microstructure and the surface morphology of their faults were carried out by the direct method of scanning electron microscopy using a scanning electron microscope PhenomPro.
 It was found that in relation to the 20 % solution of NaOH celsian ceramics was insoluble and has a value of alkali resistance in the range of 99.47—99.67 %. The study of microstructure and phase composition of celsian ceramics samples after treatment with 20 % NaOH solution showed that in all studied samples there was only a crystalline phase of celsian, the corrosion process didn’t occur. In relation to the 20 % HCl solution, the process of celsian ceramics corrosion was observed with the complete chemical interaction of the celsian phase with hydrochloric acid and the subsequent formation of the barium chloride dihydrate phase.

Effect investigation of a thinning additive on the physical and mechanical properties of celsian ceramics obtained by slip casting

The article discusses the physical and mechanical regularities of ceramics formation based on the BaO—Al2O3—SiO2 system by slip casting into gypsum molds, and also investigates the rheological properties of a slip based on сelsian and the physicochemical properties of products made from it.
 The samples were made according to the following technology: the first stage is synthesis of celsian in a muffle furnace at a temperature of 1200 °C with a maximum temperature holding for 2 hours. The synthesis products were ground in a planetary mill to a residue on the № 0063 sieve of no more than 0.2 %. Then, slips with different moisture content without additives and with the addition of 0.10, 0.15 and 0.20 wt. % thinning additive Dolapix PC 67 were made. The second stage is to obtain samples by casting slip into gypsum molds. Firing of products took place in a muffle furnace at a temperature of 1350 °C with a two-hour holding.
 The optimal amount of thinning additive in the celsian slip was determined, which corresponds to 0.10 wt. %. It was found that, in the studied area of technological parameters, the material acquires the best properties at a sample firing temperature of 1350 °C and is characterized by the following indicators: water absorption — 10.20 %, apparent density — 2.15 g/cm3, open porosity — 21.04 %.

Effects of Ni2+ substitution on the crystal structure, bond valence, and microwave dielectric properties of BaAl2–2xNi2xSi2O8–x ceramics

BaAl2−2xNi2xSi2O8−x (x = 0, 0.005, 0.01, 0.02, 0.03) ceramics were prepared using traditional solid phase reaction method. The microwave dielectric properties, including permittivity (εr), quality factor (Q × f), and temperature coefficient of resonant frequency (τf), were discussed based on the bond valence theory. The first-principle calculation was adopted to determine the site (Ba, Al, and Si) where doping element (Ni2+) would be inclined to occupy. The substitution of Ni2+ for Al3+ contributed to the breaking of Al-O and Si-O bonds and then facilitated the BaAl2Si2O8 (BAS) hexacelsian-celsian transformation. Moreover, this substitution could change the bond strength between cation and oxygen anion due to the variation of the bond valence, which reasonably explained the variation of εr, Q × f, and τf values. Well-sintered and completely transformed celsian ceramics can be obtained after doping with Ni2+. When x = 0.01, compact BaAl1.98Ni0.02Si2O7.99 ceramic exhibited highly promising microwave dielectric properties: εr = 6.89, Q × f = 53, 287 GHz and τf = -25.31 × 10−6 /°C.

Monoclinic-celsian ceramics formation: Through thermal treatment of ion-exchanged 3D printing geopolymer precursor

Based on conventional ion exchange method from zeolite materials, we herein report a facile synthetic procedure to prepare monoclinic celsian ceramics through thermal treatment of ion-exchanged 3D printing geopolymer precursors. In this contribution, both ion exchange process and thermal evolution of celsian precursors were systematically investigated. The results proved 3D printing Na- and K- based geopolymer were ideal precursors with low residual Na+ content (0.10 meq/g) and K+ content (0.05 meq/g) and translated into monoclinic celsian after being heated at 1400 °C. With increasing Sr2+ doping concentration from 20% (mole ratio) to 30% (mole ratio), more significant phase transition results (hexagonal → monoclinic) were observed. All 3D printing geopolymer precursors kept fine integrity and stable 3D structure upon ion exchange process and heating, indicating the combination of geopolymer technique and 3D printing opens up a versatile and robust way to yield monoclinic celsian ceramics and related components of complex shapes.

Celsian formation from barium-exchanged geopolymer precursor: Thermal evolution

In this paper, thermal evolution, including element & phase composition and microstructure, of Ba2+ exchanged K-based geopolymer precursor (BaGP) were systematically investigated during high-temperature treatment. The results proved that celsian precursor with lower residual alkaline cation content were obtained through amorphous geopolymer than traditional ion-exchanged celsian through crystallized zeolite. With the increase in temperature, weight loss of BaGP was due to evaporation of OH groups and decomposition of BaCO3. Similar to K-based geopolymer, BaGP showed amorphous structure, and nanometer-sized celsian nucleuses first crystallized from the amorphous BaGP matrix after it was treated at 900°C. In the treatment temperature range from 1000 to 1400°C, hexagonal celsian became the main phase. After being treated at 1400°C, hexagonal celsian grains were clearly noticeable with extra SiO2 locating between celsian grains. It was therefore concluded that geopolymer precursor technique provides an alternative route for the preparation of celsian ceramics.

Preparation and dielectric properties of celsian ceramics based on hexagonal BaAl2Si2O8

Celsian ceramics based on hexagonal BaAl2Si2O8 have been prepared through synthesis at 1450°C followed by firing at 1500°C. The unit-cell parameters of BaAl2Si2O8 and principal bond distances in its structure have been determined by the Rietveld method. Using differential thermal analysis and temperature-dependent dielectric measurements, we have determined the temperature of the α (hexagonal) to β (hexagonal) phase transition in our samples: 280–320°C.

Thermal Behavior of Celsian Ceramics Synthesized from Coal Fly Ash

ABSTRACTCelsian with a chemical composition of Ba0.75Sr0.25Al2Si2O8, is synthesized by using coal fly ash (byproduct of a Mexican coal-burning power plant, composed mainly by SiO2 and Al2O3) as main raw material. The thermal behavior of the synthesized material is evaluated by differential (DTA) and gravimetric (TGA) thermal analyses as well as by heating microscopy; its coefficient of linear thermal expansion (CTE) is also determined. Heating microscopy shows that cylinders of compacted powdered Celsian start sintering at ∼1140 ºC, which is associated with a considerable contraction occurring up to 1500 ºC. The mean CTE value of the material in the temperature range of 30-1100ºC is slightly affected by the synthesis conditions employed. Synthesis at 1400 or 1300 ºC during 10 h, with a pre-calcination step at 900 ºC/5h in both cases, produce mean CTE values of 5.15 x 10-6 and 5.43 x 10-6 ºC-1, respectively. On the other hand, Celsian synthesized at 1400 ºC/10 h, without the pre-calcination step, has a mean CTE value of 5.25 x 10-6 ºC-1. Lastly, the DTA/TGA analysis of the synthesized material shows that a slight weight gain takes place from room temperature to 1100ºC, which is followed by a slight weight loss up to 1300ºC. This is attributed to oxidation and evaporation of some of the impurities present in the material.

Development of celsian ceramics from fly ash useful for X-ray radiation-shielding application

For the first time the capability of fly ash to produce barium containing radiopaque materials has been demonstrated. Fly ash which is a waste generated in power plants due to combustion of pulverized coal, has been utilized a a Patent applications for the developed process have already been flied in USA as well as in India vide Application No. US PTO-2646690000/03/30/06 #20060066013 and 1888/Del/04, respectively. for making X-ray radiation-shielding materials. A novel method for making radiation-shielding materials utilizing fly ash and barium compound has been developed by ceramic processing route using phosphate bonding. The fly ash based radiopaque materials (FARM), i.e. shielding materials are characterized for their X-ray attenuation characteristics. The shielding, i.e. half value thickness (HVT) for different energies of X-ray photons for FARM have been computed and compared with conventionally used shielding materials, namely concrete and lead, it is found that the HVT of the fly ash based shielding materials, in comparison to concrete, is significantly very less for the various energies of X-ray photons. The X-ray powder diffraction studies confirmed the presence of monoclinic and hexagonal celsian and sanbornite as the major shielding phases and potassium aluminosilicate, sodium aluminosilicate and silicophosphate as the binder phases in the FARM and are responsible for providing bonding to the ceramic matrix leading to the effective shielding and mechanical properties. Scanning electron microphotographs have revealed the compacted plate like particles with hexagonal morphological characteristics of the various barium silicate and barium aluminosilicate (BAS) shielding phases in the matrix of radiopaque materials. The mechanical properties, namely compressive strength and impact strength evaluation test showed that FARM meets the standard specifications laid down for radiation-shielding concrete and ceramic tiles. Based on the above studies, it is found that FARM, can preferably be used for the construction of X-ray diagnostic and CT-scanner room to provide adequate shielding against X-ray photons.

Preparation of reactive Sr-celsian powders by solid-state reaction and their sintering

In order to develop dense Sr-celsian (SrO·Al 2O 3·2SiO 2) and hexacelsian ceramics, thermal reactions between kaolin and strontium carbonate were investigated. Sintering characteristics of powders and phase transformation from hexacelsian to celsian were clarified. Reactive amorphous powder could be prepared by calcination of the mixtures at 800 °C. Dense hexacelsian and celsian ceramics with a relative density of about 97% were successfully obtained by heat-treatment between 950 and 1200 °C. Relative dielectric constant and dielectric loss of hexacelsian ceramics was measured to be 5.3 and 0.5 × 10 −4 (1 MHz), respectively, showing possibility for electrical applications.

Fabrication and Mechanical Properties of Dense Celsian Ceramics.

Synthesis and densification of celsian was investigated. The mixture which was measured to be the stoichiometric ratio of celsian was melted by using arc melting technique to synthesize the material in glass state. Milled powder of the glass was mold pressed and CIPed to obtain green compacts. Dense celsian ceramics composed of monoclinic crystalline phase could be obtained by heat-treating the compact at 1500°C for 4h in air. Enhanced densification of the present material was ascribed to the viscous deformation of the glass phase. Existence of zirconia, which was dissolved into the glass from refractory bricks during arc melting, was considered to promote the crystallization of monoclinic phase of celsian which was required to exhibit low thermal expansion behavior. Fracture strength and the Young's modulus of the resultant celsian were 148MPa and 138GPa at room temperature, respectively. Thermal expansion coefficient of the sample was 4.0×10-6/°C between room temperature and 1000°C.

Fabrication of Dense Celsian Ceramics by Reaction of Kaolin with SrCO3 and BaCO3.

Fabrication of Dense Celsian Ceramics by Reaction of Kaolin with SrCO3 and BaCO3.

ChemInform Abstract: Microstructural Development, Densification, and Hot Pressing of Celsian Ceramics from Ion‐Exchanged Zeolite Precursors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Microstructural Development, Densification, and Hot Pressing of Celsian Ceramics from Ion‐Exchanged Zeolite Precursors

Dense monoclinic celsian ceramics (melting point of 1760°C) have been fabricated utilizing zeolite precursors. A sodium zeolite (Na86Al86Si106O384H2O) was ion‐exchanged in aqueous solutions to replace Na with Ba ions. The ion‐exchanged powders were then heat‐treated to effect the collapse of the zeolite structure and formation of an amorphous phase at 627°C, followed by crystallization of the celsian ceramic at 990°C. Inducing viscous flow from a thermal soak above the glass transition temperature was necessary to form a dense body from cold‐pressed powders. Hot pressing at a pressure >5 MPa and above the crystallization temperature resulted in densities >90% of theoretical and eliminated the necessity of adding seed particles to form monoclinic celsian. To fabricate shaped bodies, the amorphous phase was molded at a temperature just above the glass transition temperature and then crystallized to monoclinic celsian at 1050°C. This processing technique demonstrates the potential of using zeolites as precursors for the low‐temperature fabrication of shaped refractory parts.

Synthesis of celsian ceramics from zeolite precursors

Abstract A novel low temperature technique has been developed for the synthesis of celsian glass-ceramics. The technique involves ion exchange of zeolites, their subsequent heat treatment to form a glassy phase from which celsian is crystallized. Monoclinic celsian was produced at temperatures as low as 1000°C at heat treatment times of 6 h.