Ceramic with a Low Tcle for Deposition of Protective Coatings Made of Nb2O5

The thermal expansion of mullite-cordierite, mullite, and quartz ceramics used in production of materials with a protective Nb₂O₅ coating is investigated. It is demonstrated that fused quartz glass and quartz ceramics not containing the cristobalite phase are the closest to Nb₂O₅ in their thermal expansion. Variable-composition alloys (Nb₂O₅)_x – (SiO₂)_1–x have intermediate TCLEs and can serve to compensate stresses caused by the discrepancy between the coating and the quartz ceramic substrate.     

Rheology in the technology of ceramics and refractories. Part 5. Dilatancy: Classification and types of dilatant systems

A great majority of high-density ceramic binding suspensions (HDBS) and the related molding systems, characterized by a volume fraction of the solid phaseC _v=0.80−0.85, exhibit a strongly pronounced dilatancy that is a source of difficulties for the production and use of these materials. The effect of dilatancy and the mechanism of dilatant flow are analyzed from the standpoint of thermodynamics and colloid chemistry. Original experimental results and published data are generalized and a classification of the main types of dilatancy is proposed. The effects of some important factors on the character of dilatant flow in high-density ceramic binding suspensions based on quartz glass, quartz sand, mullite, and titanium dioxide are considered. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 8–16, February, 1997. For the previous articles of this series see No. 3 (1994), No. 12 (1995), and Nos. 1 and 10 (1996).     

Certain Specifics of Quasi-Isostatic Molding (A Review)

The author considers specifics of the method of quasi-isostatic molding, which is the most perfect, economical, and simple method for molding products from powder materials providing for a high quality of products due to the volume compression of the molding material. The method can be used for molding articles from ceramic, metal, and graphite powders, glass ceramics, ferrite, abrasive materials, and in production of refractory articles.     

A freeze method of obtaining ceramic based on fused quartz

Conclusions The technology of producing materials based on fused quartz by freezing the blank in a liquid nitrogen medium has been studied.The advantages of this method over slip casting in porous molds are: a reduction in the molding time; the production of articles with a large variety of wall thicknesses and complexity of surface; the possibility of firing the blanks immediately after molding; the production of strong articles with a porosity of 40-0%; the possibility of making articles with specified dimensions without mechanical treatment; and the simplicity of the process.Assistance was given in the manufacture of the molds and the molding of the specimen material.Translated from Ogneupory, No. 7, pp. 49–52, July, 1980.     

Fabrication of high-density NiFe2O4 ceramics by slip casting and pressureless sintering

High-density NiFe₂O₄ ceramics with homogeneous microstructure were produced by slip casting and pressureless sintering. The slurry stability, sintering behavior, and microstructure of NiFe₂O₄ ceramics were investigated. A stable slurry can be obtained by adding 12.5 wt% NiFe₂O₄ nanoparticle and 5 wt% nano-binder at a slurry pH around 11.0. The linear shrinkage and linear shrinkage rate for both NiFe₂O₄ ceramic green bodies shaped by cold press molding and slip casting showed nearly the same trends. The temperature associated with the maximum linear shrinkage rate of slip casted green body was 1263.5°C, which was lower than that of cold press molded sample (1272.0°C). The sintering activation energy of slip casted green body was also lower than that of cold press molded sample (279.18 vs 288.47 kJ mol⁻¹), owing to high density and homogeneity of slip-casted green compact. A high-density NiFe₂O₄ ceramics with uniform grain size distribution can be produced by slip casting and pressureless sintering at 1350°C for 6 hours, attributed to the ability of slip casting to minimize agglomerates and micropores. It demonstrated that slip casting was more suitable to prepare high-density NiFe₂O₄ ceramics with good homogeneity.     

Phase-separation engineering in fluorozirconate glass for designing and fabricating of transparent perfluorinate glass ceramic

Perfluorinate glass ceramics with ultra-low phonon energy are very important optical and photonic materials. Unfortunately, there is no suitable method to obtain transparent perfluorinate glass ceramics due to poor thermal stability of fluoride glass. As a result, wide applications of glass ceramics in advanced infrared systems are restricted. Here, an effective method based on phase-separation engineering is used to develop transparent perfluorinate glass ceramics. In this article, a novel transparent Er³⁺-doped ZnZrF₆-Ba₆Zn₇F₂₆ perfluorinate glass ceramic was designed and fabricated by phase-separation engineering. The sample exhibits low phonon energy (564 cm⁻¹), ultra-wide transmission range (0.33–8.2 μm, T ≥ 50 %), and strong infrared emission, which is better than that of ZBLAN glass, oxide-, and oxyfluoride-glass ceramics. These good properties of the perfluorinate glass ceramic demonstrate that phase-separation engineering not only offers an effective approach to obtain perfluorinate glass ceramics but also provides wide-ranging opportunities for advanced infrared optical and photonic materials.     

Growth behavior,morphology and properties of lithium aluminosilicate glass ceramics with different amount of CaO,MgO and TiO2 additive

Li₂O–Al₂O₃–SiO₂ glass with CaO, MgO and TiO₂ additive were investigated. With more CaO + MgO addition, the crystallization temperature (T_p) and the value of Avrami constant (n) decreased, the activation energy (E) increased. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. With more TiO₂ addition, the crystallization temperature decreased, E and n had a little change. The crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization. Plate-like, high mechanical properties spodumene-diopside glass ceramics were obtained. The mechanical properties related with crystallization and morphology of glass ceramics.     

Photoluminescence properties of rare-earth ion-doped Na5YSi4O12-based glass ceramics

We developed herein photoluminescent glass ceramics based on rare-earth ion-doped Na₅YSi₄O₁₂-type materials according to the Na_3+3xY_1?x?yR_ySi₃O₉ (R: Sm³⁺, Eu³⁺, Dy³⁺, Tb³⁺) composition. Glass ceramics generally have the advantages of excellent chemical durability, heat resistance, and moldability over sintered ceramics. Upon irradiation with near-ultraviolet light, Sm³⁺-, Eu³⁺-, Dy³⁺-, and Tb³⁺-doped glass ceramics emit purplish orange, reddish orange, yellow, and green lights, respectively. The photoluminescent emission intensity of glass ceramics is higher than that of the original glasses, and the emission intensity depends on the crystalline phase. The highest emission intensity of various rare-earth ion-doped glass ceramics is obtained when the parameter y is equal to 0.03, 0.16, and 0.02 for the Sm³⁺-, Eu³⁺-, and Dy³⁺-doped glass ceramic samples, respectively. The internal quantum efficiency is 3%, 37%, 7% and 23% for the Sm³⁺-, Eu³⁺-, Dy³⁺-, and Tb³⁺-doped samples, respectively. Thus the Na superionic conducting Na₅YSi₄O₁₂-type glass-ceramics were proved to have potentiality as novel phosphors.     

Sealing Glass‐Ceramics with Near‐Linear Thermal Strain,Part II: Sequence of Crystallization and Phase Stability

The sequence of crystallization in a recrystallizable lithium silicate sealing glass‐ceramic Li₂O–SiO₂–Al₂O₃–K₂O–B₂O₃–P₂O₅–ZnO was analyzed by in situ high‐temperature X‐ray diffraction (HTXRD). Glass‐ceramic specimens have been subjected to a two‐stage heat‐treatment schedule, including rapid cooling from sealing temperature to a first hold temperature 650°C, followed by heating to a second hold temperature of 810°C. Notable growth and saturation of Quartz was observed at 650°C (first hold). Cristobalite crystallized at the second hold temperature of 810°C, growing from the residual glass rather than converting from the Quartz. The coexistence of quartz and cristobalite resulted in a glass‐ceramic having a near‐linear thermal strain, as opposed to the highly nonlinear glass‐ceramic where the cristobalite is the dominant silica crystalline phase. HTXRD was also performed to analyze the inversion and phase stability of the two types of fully crystallized glass‐ceramics. While the inversion in cristobalite resembles the character of a first‐order displacive phase transformation, i.e., step changes in lattice parameters and thermal hysteresis in the transition temperature, the inversion in quartz appears more diffuse and occurs over a much broader temperature range. Localized tensile stresses on quartz and possible solid‐solution effects have been attributed to the transition behavior of quartz crystals embedded in the glass‐ceramics.     

Domogneupor joint stock company as a unique enterprise producing modern refractory ceramics

AO Domogneupor is a unique enterprise for producing modern high-technology ceramics for different branches of industry. A wide assortment is manufactured by broaching from dense mullite-siliceous ceramics (52% Al₂O₃). Some parts are produced from corundum ceramics (95% Al₂O₃). The enterprise possesses a unique technology of semi-dry pressing from fused quartz glass on a silicon organic binder (> 98% SiO₂).Translated from Ogneupory, No. 10, pp. 28 – 29, October, 1994.AO Domogneupor.     

Effects of CaO–B2O3–SiO2 glass additive on the microstructure and electrical properties of BCZT lead-free ceramic

Addition of CaO–B₂O₃–SiO₂ (CBS) glass was performed to lower the sintering temperature of lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ceramics. Orthorhombic and tetragonal phases coexisted in CBS-free BCZT ceramics. The BCZT ceramics transformed into a pseudo-cubic phase when sintered at 1300 °C with increasing CBS glass content. Additionally, the secondary phase, Ba₂TiSi₂O₈, was observed when CBS glass was added. The density initially increased, reached a maximum value with 2 wt% CBS glass, and then decreased rapidly with further increase in CBS glass content, which was consistent with the microstructure. The ɛ, T_c, P_r, and d₃₃ depend on microstructure, and the results agree with the density. Evident relaxation behavior was observed. Observed results were inferred to be dependent on the microstructure, phase structure, lattice distortion, and secondary phase. The sample with 2 wt% CBS glass showed the excellent performance, which could be a promising substitute to lead-free piezoelectric ceramics for lead-based materials.     

A novel and green preparation of porous forsterite ceramics with excellent thermal isolation properties

This work provides a novel and green approach to preparing porous forsterite ceramics by a transient liquid phase diffusion process based on fused magnesia and quartz powders without detrimental additives. The size of quartz particles markedly affected the sintering behaviors, phase composition, microstructure and properties of the porous forsterite ceramics. Fine quartz particles (D₅₀, 3.87?µm) accelerated the rate of the forsterite formation at elevated temperatures and promoted solid-state sintering behavior of the porous ceramics. Conversely, coarse quartz particles (D₅₀, 25.38?µm) reduced the rate of the solid state reaction and a large amount of unreacted SiO₂ and enstatite (MgSiO₃) phases transformed into a transient liquid-phase during the firing process. This effect resulted in a high porosity (approximately 58.89%) and formation of many large pores (mean pore size of 42.36?µm). These features contributed to the excellent thermal isolation properties of the prepared porous forsterite ceramics. The strength of the obtained porous ceramics (about 23.6?MPa) is relatively high compared with those of conventional ceramics.     

Parametric optimization of dry sliding wear and friction of germanium doped lead calcium titanate borosilicate glass ceramic

In this study, specific wear rate (SWR) and coefficient of friction (COF) of the synthesized samples in 55[(Pb_xCa_1?x)O.TiO₂]?44[2SiO₂.B₂O₃]?1Ge with (0 ≤ x ≤ 0.7 mol%) system of glass ceramics was optimized using Taguchi method. The ASTM standards were used for preparing the samples for friction and wear tests on a pin-on-disc tribometer. The glass ceramic samples were used as pin materials that slid against a disc made up of EN32 steel. For assessing the tribological properties of the glass ceramics, three control factors, viz. material-compositions with varying fraction of x (x = 0.0, 0.1, 0.3, 0.5 and 0.7 mol%), sliding speeds (2.61, 3.14, 3.66, 4.18 and 4.71 m/s) and loads (10, 15, 20, 25 and 30 N) were considered in an L₂₅ orthogonal array design. The optimum input parameters for the minimum SWR and COF were selected based on signal to noise ratios and main effect plots. Analysis of variance (ANOVA) revealed that the sliding speed and lead oxide content of the material are the most contributing factors on SWR and COF, respectively. The optimization for minimizing the SWR and COF was carried out and confirmed. The surface morphologies of the tested glass ceramic sample were studied using scanning electron microscope (SEM) and the elemental analysis of the samples was done using energy dispersive analysis of X-rays (EDAX). The Vickers hardness at the free surface of the glass ceramic samples increased up to 9.59 mol% of lead oxide with the maximum hardness of 23.59 GPa. The compressive strength of glass ceramic samples could reach up to 190 MPa.     

Effects of glass additions on the microstructure and dielectric properties of barium strontium titanate (BST) ceramics

Commercial glass frits (lead borosilicate glasses) were employed as the sintering aids to reduce the sintering temperatures of BST ceramics. The effects of the glass content and the sintering temperature on the microstructures, dielectric properties and tunabilities of BST ceramics have been investigated. Densification of BST ceramics of 5 wt% glass content becomes significant from sintering temperature of 1000 °C. The glass content shows a strong influence on the Curie temperature T_c, permittivity and the diffuse transition. X-ray results show all BST ceramics exhibit a perovskite structure and also the formation of a secondary phase, Ba₂TiSi₂O₈. The shift of BST diffraction peaks towards higher angle with increasing the glass content indicates the substitution of Pb²⁺ in Ba²⁺ site, which mainly accounts for the diffuse transition observed in these BST ceramics. BST ceramics with 10 wt% glass additives possess the highest tunability at all four sintering temperatures. A tunability of 12.2% at a bias field of 1 kV/mm was achieved for BST ceramics with 10 wt% glass content sintered at 900 °C.     

Molded Glass–Ceramics for Infrared Applications

In this paper, the feasibility to make molded glass–ceramics transparent in the second and third atmospheric window has been investigated. The thermodynamical and viscosity properties of the base glass have been measured confirming the possibility of generating crystals during molding at different temperatures. ⁷¹Ga nuclear magnetic resonance confirms that gallium plays the role of nucleating agent of gallium in this glass. Examination of X-rays diffraction patterns and optical properties indicates that the generation of nanocrystals of GeGa₄Se₈ allows the glass–ceramics to keep a wide transparency in the infrared range from 2 to 15 μm. The crystallization of large GeSe₂ crystals of at higher temperature induces scattering and a reduced transparency window. The mechanical and structural properties of the as-prepared glass ceramics show an increase of toughness from 0.188 to 0.387 MPa m^1/2 and elastic modulus from 22.7 to 26.55 GPa while the number and size of crystals increase. As a result, the preparation of molded IR glass–ceramics with high resistance to thermal and mechanical shocks has been clearly demonstrated.     

Highly concentrated suspensions of nontransparent fused quartz and materials based on them

Conclusions On the basis of nontransparent quartz glass, using the wet milling method in a porcelain mill and uralit balls, we obtained casting suspensions with volume concentrations of solid phase equal to 70–73%. By means of stabilization with mechanical gravitation stirring we attained a sharp reduction in the slip's viscosity, and increases in density and strength.We demonstrated the considerable influence of the concentration of the suspension during wet milling on the porosity and strength of the cast. A technology was developed with which, on the basis of the suspension of nontransparent quartz glass, we can obtain green articles with a porosity of 13.3–15% and a bending strength of up to 2 MPa. Using this slip we prepared samples of unfired ceramic with _bend up to 30 MPa which is comparable with the strength of fired materials.Translated from Ogneupory, No. 6, pp. 14–19, June, 1986.     

Synthesis,characterization, bioactivity and cytotoxicity assessment of nano ZrO2 reinforced bioactive glass ceramics

Bioactive glass and glass ceramics have travelled a long way as biomaterials. Several research works have been devoted to improving mechanical properties, especially using various additives. Out of these, ZrO₂-containing glass and glass ceramics have shown promising outcomes. In this present work, a set of 3 Nano-ZrO₂ containing novel bioactive glass and glass ceramics of composition 37.5 nano-SiO₂–(17-X)Al₂O₃–26.5CaO–11.5CaF₂–7.5P₂O₅–X nano-ZrO₂ (where, X= 0.75, 1.7, 2.7, all in mol %) were synthesized by melt-quenching technique. Standard characterization procedures were performed to assess the physical and chemical properties, structure and surface morphologies. In vitro bioactivity and cytotoxicity assessments were also done. Fluorapatite (Ca₅(PO4)₃F) and Anorthite (Ca(Al₂Si₂O₈)) along with tetragonal Zirconia (t-ZrO₂) at higher nano-ZrO₂ content of 2.7 mol% were discovered as the primary crystalline phases. Adding nano-zirconia enhanced the glasses' thermal stability and the glass ceramics' micro-hardness. The formation of nanometer-size hydroxyapatite (HAp) on the glass-ceramics samples confirmed the good bioactive nature. The non-toxic nature of the samples towards living cells was demonstrated by cytotoxicity assessment.     

Effect of MgO addition on the properties of PbO –TiO2–B2O3 glass and glass–ceramics

Glass samples with composition of (50?X) PbO–X MgO–25 TiO₂–25B₂O₃ (where X=0, 5, 10 and 15 mol%) were prepared using conventional quenching technique. The amorphous nature of glass samples were confirmed by XRD. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. It has been observed that the addition of MgO enhances the T_g. The rise in T_g with MgO content may be attributed to the greater field strength of Mg²⁺ cation (as compared to Pb²⁺) which leads to the formation of stronger bonds. These glass samples were converted to glass–ceramics by following a two-stage heat treatment schedule. It was observed that there was good correlation between the density and CTE results of the glass–ceramics. The XRD results revealed the formation of tetragonal lead titanate as a major crystalline phase in the glass–ceramics. The addition of MgO to the glass contributes to the formation of MgB₄O₇. The dielectric constant for all the glass–ceramic samples was observed to be higher than that of corresponding glass samples. Further, with addition of MgO the room temperature dielectric constant for glass–ceramic samples increases up to 10 mol% of MgO and then decreases for 15 mol%. It has been further observed that the variation of dielectric constant of glass–ceramic samples with MgO content is exactly opposite to the variation of crystallite size of PbTiO₃ embedded in the glass ceramic-samples.     

Pressure-molded high-alumina ceramic castables. 2. Compaction and properties of materials based on plasticized bauxite HCBS,reactive alumina,and their binary mixtures

The effect of compacting pressure (20–100 MPa) on the densification of refractory clay plasticized molding mixes based on bauxite HCBS containing 10% highly dispersed quartz glass, reactive STS-30 alumina, and their binary compositions has been studied. The properties of these materials subjected to heat treatment are discussed. Optimum compositions for binary systems are formulated that show promise as matrices for refractory materials and for preparation of engineering ceramics. __________ Translated from Novye Ogneupory, No. 11, pp. 25–31, November, 2005.