Glass and Ceramics最新文献

A method has been developed for securing an optical fiber in a quartz connector by using sodium polysilicate hydrogel formed in a cylindrical gap between a connector and an optical fiber by means of alkaline decomposition of the quartz surfaces of manufactured components. The conditions for the thermal decomposition of hydrogel are determined, and it is shown that hydrogel decomposition with cellular structure formation is possible at temperatures below the thermal decomposition temperature of the polymer coating of the optical fiber. The hydrogel formation conditions and the thermal properties of the hydrogel are determined. Conclusions regarding the suitability of the proposed method for securing an optical fiber in a quartz connector are drawn.

The influence of the modification of glass in the strontium-aluminum-boron-silicate system (SABS) on technological and physicochemical properties was investigated. Introducing two alkalis into the glass makeup significantly lowered the melting temperature, from 1500 to 1450°C, which effected changes in the properties of the glass. On introducing alkalis in amounts up to 5 mol.% the thermal linear expansion coefficient (LTEC) decreased from 58 to 50 (α × 10 ^{– 7} K^{– 1}) and the refractive index n_D from 1.551 to 1.528. However, alkaline components adversely affect the hydrolytic resistance of the glass, transferring it from hydrolytic class I to II. The solution to this problem was to: (1) employ the polyalkaline effect, (2) maintain high radiopacity of the glass by introducing a small amount of highly effective radiopaque barium oxide into the makeup and significant strontium oxide reduction, and (3) increase the aluminum oxide content, which ordinarily increases the chemical resistance of the glass. The result was improved melting properties on lower melting temperatures and glass with high values of x-ray contrast (about 550%), light transmission (T = 90%), refractive index values n_D = 1.530 and LTEC = 56 (α × 10 ^{– 7} K^{– 1}) were obtained while maintaining chemical stability with respect to water the corresponding hydrolytic class I.

It was found that the high decomposition temperature of amorphous Al(OH)₃ makes it possible to sinter corundum ceramics directly from aluminum hydroxide, bypassing the stage of its preliminary thermal dehydration. Using the cold isostatic pressing method at 200, 600, and 1000 MPa, compacts with densities of 62, 69, and 79% of the theoretical value were obtained. The temperature dependence of the shrinkage of amorphous Al(OH)₃ compacts was studied as a function of the cold isostatic pressing pressure. An area of intense shrinkage was discovered in the range 1050 – 1150°C, which coincides with both the temperature of complete decomposition of amorphous Al(OH)₃ and the transition γ → α-Al₂O₃.

The local Abrio method of birefringence assessment was applied for the first time to strengthened glasses, and it was used to investigate the micro-stress distribution in float glass subjected to ion-exchange strengthening. It is demonstrated that the thickness of the stressed layer can be determined with great precision, and a correlation is found between the depth of the stressed layer and the penetration depth of potassium cations in the course of ion exchange.

The effect of the eutectic additive of the system Li₂O–B₂O₃ on the sintering process and the dielectric properties of Li₂MgTi₃O₈-based ceramics was studied. It was found that the introduction of an additive in amounts 10.0 – 15.0% promotes sintering of ceramics by means of a liquid-phase mechanism. Li₂MgTi₃O₈-based ceramic, containing a sintering additive in the amount 15.0% and fired at 900°C, demonstrates the following property levels: average density ρ_av = 3.04 g/cm³, open porosity P_o = 5.7%, relative dielectric constant ε_r = 19.0, and dielectric loss tangent tan δ = 0.028. The lowered sintering temperature of the ceramic will allow the manufacture of different electronic components based on it, using low-temperature co-firing ceramic (LTCC) technology, and the a specified level of dielectric properties will allow the miniaturization of devices.

The main commercial method of preparing precision metal parts with a high surface finish, for example, the blades of a turbo-ram jet engine, is lost waste casting. On preparing a wax model, a ceramic immuring element (rod) is placed in side the model in order to form cavities of complex shape, intended to reduce the mass of the casting and for forming channel of the cooling system of the blades cooled by the secondary air flow after a rod is removed. The main technological problems on removal of the inner rods are their strength and high chemical inertness, as a result of which their removal time and labor costs are quite large. This article investigates a method of preparing ceramic rods whose strength is not uniform along depth, which makes it possible, first of all, to remove (quite easily) the soft center and then to dissolve the stronger periphery.

The morphology and degree of agglomeration of the precursor and YAG-ceramic powders were investigated as functions of the grinding conditions, followed by an assessment of the influence of these parameters on the optical properties and structure of the ceramic. YAG-precursor powders were obtained by chemical coprecipitation. The morphology and size of the agglomerates and crystallites were assessed by means of scanning electron microscopy, laser diffraction analysis, x-ray diffraction analysis, and Brunauer–Emmett–Teller gas adsorption. It was discovered that grinding of the YAG precursor powders can decrease the degree of agglomeration of the ceramic powder. It was found that with a mass ratio of grinding balls to precursor powder of 6.75/1 and a mass ratio of the grinding medium to the mass of the precursor powder of 4.5/1, optimal conditions obtain for providing the necessary granulometric characteristics and the highest mono-dispersity. In summary, by such means the properties of YAG optical ceramic can be improved by using of an additional grinding stage for the powders synthesized by chemical deposition and by selecting suitable grinding modes.

The intent of this work is to investigate the influence of scandium occupying dodecahedral and octahedral positions of the garnet crystal lattice on the aspects of vacuum sintering of the optical ceramic Y_3–xSc_xAl_2–ySc_yAl₃O₁₂:Cr as well as on its optical and luminescent properties. As part of this investigation, YSAG:Cr optical luminescent ceramic was produced for the first time from ceramic powders of metastable compositions with a high content of scandium in the dodecahedral position. The compositions considered were described by the general formula Y_3–xSc_xAl_2–ySc_yAl₃O₁₂, where 0.12 ≤ x ≤ 1.50 and 0.08 ≤ y ≤ 1.00 p.u. [physical units] with total scandium content 0.12 – 1.70 p.u. The following investigations of YSAG:Cr ceramic samples were conducted: x-ray diffractometry, measurement of the shrinkage kinetics of ceramic compacts using dilatometry, and investigation of the morphology and elemental composition of the ceramic surface by means of scanning electron microscopy. The spectra of light transmission and luminescence were measured. It was shown that ceramic made from compositions with scandium content predominating in the dodecahedral positions reach maximum density at lower temperatures compared to compositions containing a larger amount of scandium in the octahedral positions. It was found that as the sintering temperature of YSAG:Cr ceramic increases, compositions with a high content of scandium in the dodecahedral position become unstable.

The possibility of obtaining a new alternative source of clay raw materials for making ceramic materials based on muddy deposits, possessing functional properties, from reservoirs is considered. The physicochemical properties of sediments from the muddy bottom of the Tuyamuyun reservoir in Uzbekistan were studied. It was found that the ceramic bodies developed based on the dual muddy-kaolin composition can be used to produce ceramic materials intended for construction.

Methods of laser micro- and nano-modification of the structure of transparent dielectrics offer much for the creation of a new type of glass-crystalline materials and new applications. In the present work, after a brief excursion into the history of glass-ceramics, transparent aluminosilicate sitalls [glass-ceramics] are discussed, mainly for the example of the Li₂O–Al₂O₃–SiO₂ system, and the areas of their new applications. The recently discovered possibilities of laser micro-modification of the structure of sitalls and the writing of elements of photonics and integrated optics in their interior volume are considered. Special attention is given to transparent glass-ceramics with thermal expansion coefficient close to zero.