Low Expansion Glass-ceramics Research Articles

Low Expansion Glass-Ceramics Using Industrial Waste and Low-cost Aluminosilicate Minerals: Fabrication and Characterizations

The recycling of the wastes towards value added product development has become a prime challenge. In this work, a low thermal expansion glass-ceramic material based on ternary LAS (Li2O-Al2O3-SiO2) system has been prepared by adopting meltquenching route using industrial waste (blast furnace slag) and low-cost aluminosilicate minerals (China clay and pyrophyllite) at relatively low melting temperature (∼1450°C). A part of the precursor powder for pristine glass has also been prepared by sol-gel processing utilizing Li2CO3 and Al(NO3)3.9H2O to obtain better homogeneity in the glass composition vis-à-vis glass-ceramics at lower melting temperature. Thermal properties of the material have been characterized to optimize the nucleation and crystallization temperatures for converting glass to glass-ceramics. Phase structure and surface morphology of the glass-ceramics have been analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy. XRD study reveals the presence of lithium aluminosilicate as a major phase at the crystallization temperature of 730°C. The developed glass-ceramics show a low thermal expansion coefficient (CTE) value of (19±0.5)×10–7/°C in the temperature range of 30°-500°C. The present work can unfold an avenue towards conversion of waste into wealth in the form of low CTE glass-ceramics for possible application as cook-top plate of LPG gas oven.

Processing Li2O-Al2O3-SiO2 (LAS) glass-ceramic with and without P2O5 through bulk and sintering route

Commercially significant Li2O-Al2O3-SiO2 (LAS) glass composition with P2O5 content varying between 0 – 6.8 mol% were prepared through the conventional melt-quenching route. From high-temperature dilation results, it was found that different amount of P2O5 in the LAS glass greatly influences the phase transformation (glass transition, softening and melting) characteristics. Two LAS glass systems, namely 3.1 mol% of P2O5 (P3.1) and without P2O5 (P0) were considered further towards making low expansion glass-ceramic using bulk and sintering route due to their contrary thermal behaviour. The optimum nucleation temperature for P0 and P3.1 glass system was determined to be 640 and 700 °C, respectively using the Marotta method. Effect of heat-treatment temperature on the thermal expansion behaviours of the LAS glass-ceramic is explained in detail. Negative thermal expansion (NTE) and low expansion glass-ceramics were produced from bulk and sintering route. Transparent β–quartz s.s. based ultra-low thermal expansion (0.04 ×10–6 °C–1 between –60 °C and 400 °C) glass-ceramic was produced.

Low Li2O content study in Li2O-Al2O3-SiO2 glass-ceramics

The price of lithium-containing minerals and other chemical materials continues to increase, resulting in an increase in the production cost of Li2O-Al2O3-SiO2 (LAS) system glass-ceramics. In the LAS glass-ceramics component, the reduction in the amount of Li2O used can reduce the cost of the product. It is worthwhile to study whether it is possible to prepare glass-ceramics with low expansion properties under low Li2O content. The effect of Li2O content on the glass-ceramics of LAS system was studied. In this paper, spodumene was used as the main raw material, and TiO2 and ZrO2 were added as crystal nucleating agents to prepare transparent glass-ceramics with low expansion coefficient. The effects of the change of Li2O content on the crystal phase and microstructure of glass-ceramics were investigated by XRD, DSC, FTIR and SEM. The results show that the main crystalline phase of the low expansion transparent glass-ceramics is β-quartz solid solution. When Li2O content is in the range of 2.99 wt% to 4.13 wt%, low expansion glass ceramics can be prepared by an appropriate method. With the increase of Li2O content, the average coefficient of thermal expansion (CTE) in the temperature range of 30 °C–300 °C shows a decreasing trend. When Li2O content is in the range of 3.51 wt% to 4.13 wt%, the thermal expansion coefficient of the glass ceramics is extremely small, and even a negative expansion coefficient occurs.

Coloration Mechanism of Fe Ions in β-Quartz s.s. Glass-Ceramics with TiO2 and ZrO2 as Nucleation Agents

Transparent Li2O-Al2O3-SiO2 low-expansion glass-ceramics have an undesirable brown color owing to Fe ions as a contaminant, whereas the mother glass normally has a clear appearance. Elucidation of the coloration mechanism during crystallization is important for industry to develop highly transparent materials. In this study, the mother glass contained SiO2, Al2O3, and Li2O as its principal constituents and TiO2 and ZrO2 as nucleation agents. The amount of contaminant Fe ions in the form of Fe2O3 was 0.03 wt%. It was confirmed that the coloration was appeared by the coexistence of Fe and Ti ions in the glass matrix based on the experimental results using Ti-containing and Ti-free glasses with a composition identical to that of the glass matrix. The coordination and oxidation state of the Fe ions were not changed by the coexistence of Ti ion according to the results of XANES measurement. The coloration is considered to be due to the formation of Fe-O-Ti by the concentration of Fe and Ti ions in the glass matrix phase during the crystallization process.

Mechanism of compound fracture and removal in grinding process for low-expansion glass ceramics

The mechanism of fracture and its removal for low-expansion glass ceramics processing was studied through grinding experiments. A dynamic coefficient Kd was proposed to characterise the brittle material processing property. Using surface roughness as the evaluation index, the limitations of the empirical model and the brittle fracture model were analysed. On the basis of simple single-factor tests, two-step changes on the processing surface of brittle materials were observed for the first time, which could be described in terms of the critical depth of ductile and ductile–brittletransition (hc1) and the critical depth of ductile–brittle and brittle transition (hc2). The brittle material fracture processing and removal could be divided into three phases: ductile fracture, ductile–brittle fracture and brittle fracture. Furthermore, a compound grinding factor Q and a model of compound regime were proposed in this study, in order to comprehensively test the variation tendency of surface roughness and improve the model accuracy. A multi-factor cross-validation test also was conducted, and the results of the three models were compared with the test results. The model of compound regime (Ra3) showed the highest precision.

Chemical Mechanical Polishing on Extremely Low Expansion Glass Ceramic Wafers

Extremely low expansion glass ceramics are widely used in integrated circuit (IC), liquid crystal display (LCD) lithography, high-precision measurement and astronomy, due to their excellent mechanical properties and chemical stability at higher temperatures. Nevertheless, the extremely low expansion glass ceramics are hard-to-machine materials due to their hard-brittle nature, resulting in cracking, chipping and scratching induced in conventional machining. This leads to higher surface roughness, and is not qualified for high-performance devices. In this study, surface roughness of 0.447 and 4.904 nm are achieved for Ra and peak-to valley (PV), respectively with a measurement area of 70×53 μm2 after chemical mechanical polishing (CMP). Firstly, the glass ceramic wafers are lapped using silicon carbide (SiC) abrasives on a cast-iron plate. After lapping, the wafers are polished by CeO2 slurry in a sequence of 3 μm and 500 nm in diameter, and polyurethane and floss pads are used correspondingly. Finally, CMP is employed on the glass ceramic wafers. Floss pad and silica slurry are used in CMP in an alkaline solution with a pH value of 8.5. After CMP, the wafers are cleaned and dried by deionized wafer and compressed air, respectively.

Fracture toughness of hydroxide catalysis bonds between silicon carbide and Zerodur low thermal expansion glass-ceramic

In many optical and precision engineering applications, low thermal distortion materials need to be bonded together reliably. Since high temperature bonding process ultimately introduce stresses in the bond, rendering it dimensionally instable, room temperature or near room temperature processes are preferred. Low thermal distortion materials such as silicon carbide and low thermal expansion glass ceramics are bonded at room temperature using hydroxide catalysis bonding with a silicate bonding material. The bonding procedure is explained and fracture toughness results are presented for SiC–SiC, Zerodur–Zerodur and SiC–Zerodur bonds. A surface treatment technique for hydrating the SiC surface is presented, which eliminates the need for pre-oxidized SiC surfaces when using HCB bonding. The bonds between surface treated bare SiC surfaces and thermally oxidized SiC surfaces are found to have comparable fracture toughness.

The effect of aluminum sources on synthesis of low expansion glass–ceramics in lithia–alumina–silica system by sol–gel route

This paper investigated the effect of different aluminum sources on the crystallization behaviors, thermal expansion and morphology of lithium aluminosilicate glass–ceramics sintered at different temperatures. Specimens were prepared by sol–gel technology. The crystalline phase in the specimen with Al(NO 3) 3⋅9H 2O aluminum source sintered at 1300 °C has shown a major phase of Li 2Al 2Si 3O 10 accompanied by minor phase of LiAl 5O 8 and trace amount of SiO 2. The β-eucryptite appeared as the only phase in the specimens with aluminum isopropoxide or aluminum isopropoxide mixed with Al(NO 3) 3⋅9H 2O aluminum sources sintered at 1300 °C. The sintering temperature has significant effect on the thermal expansion behavior of all the specimens. SEM indicated that microstructures were spherulitic crystals and no distinct differences were observed in the specimens with different aluminum sources.

Crystallization Kinetics and Mechanism of Low‐Expansion Lithium Aluminosilicate Glass‐Ceramics by Dilatometry

The crystallization kinetics and mechanism of a precursor glass of lithium aluminosilicate (LAS)‐based commercial low‐expansion glass‐ceramics were investigated using a dilatometer. The isothermal crystallization behavior of β‐quartz solid solution (ss) was found to obey the Avrami equation. Nonisothermal crystallization data were analyzed by the Ozawa method and modified Kissinger equation. The value of the Avrami exponent (n) was ∼1.5, and the apparent activation energy (Ea) was ∼500 kJ/mol, which was close to that of the diffusion of silicon and aluminum ions as well as metal–oxygen bond strengths, suggesting a three‐dimensional (3D) diffusion‐controlled reaction mechanism.

00/02133 Study on low expansion glass-ceramics of Cu 2O-Al 2O 3-nSiO 2 system

00/02133 Study on low expansion glass-ceramics of Cu 2O-Al 2O 3-nSiO 2 system

Glass ceramics: State-of-the-art

Recent development and research trends in three important areas are discussed. These are: (1) developments in well established low thermal expansion glass ceramics, (2) diverse approaches to create glass ceramics with high fracture toughness and (3) sintered glass ceramics. Developments are discussed in the light that glass ceramics are more expensive than glasses and therefore will be commercially successful only when the benefit from a glass ceramic component is sufficiently high.

Dimensional stability tests over time and temperature for several low-expansion glass ceramics

The dimensional stabilities of five commercially available low-expansion glass ceramics have been measured between -40 °C and +90 °C. Materials tested include Zerodur, Zerodur M, Astrositall, Clearceram 55, and Clearceram 63. With the use of a standardized thermal testing procedure, the thermal expansion, isothermal shrinkage, and hysteresis behavior of the various materials are compared with one another. A detailed comparison of three separate melts of Astrositall, two separate melts of Zerodur, and one melt of Zerodur M indicates that between -40 °C and +90 °C the dimensional stability and uniformity characteristics of two of the melts of Astrositall are somewhat better than those of the other two materials. To my knowledge, this is the first published comparison of data from these glass ceramics taken with identical test procedures.

Hysteresis effects in low expansion glass-ceramics

Li 2OAl 2O 3SiO 2-based low expansion glass-ceramics with a h-quartz solid solution crystalline phase often show very small hysteresis effects in two different temperature intervals, one lying in the temperature range from -100 to +40°C, the other in the range from +130 to +320°C. It is assumed that the observed hysteresis effects are due to some yet unspecified relaxation phenomena. The effects in both temperature intervals have been investigated intensively by dilatometry and to a lesser extent by dielectric measurements. Investigations performed include experiments with constant heating and cooling rates, isothermal holding periods within the hysteresis intervals, and property changes at temperatures below the hysteresis intervals after different cooling rates from temperatures above the respective hysteresis intervals. While dilatometry is the more versatile method when investigating the glass-ceramic materials, it cannot be applied for the investigation of the glass-ceramic base glasses or partially crystallized glass-ceramics, since these materials have large CTE-values compared with the corresponding glass-ceramics; possible hysteresis effects are therefore masked by the large length changes with temperature. The hysteresis effects in these latter materials are therefore investigated by dielectric measurements.

Glass and its history of service

The review considers various examples of the interactions between glass science and technology on the one hand and electrical and electronic engineering on the other. The historical introduction leads up to the development of special glasses, mainly to meet the needs of lens designers, at the end of the nineteenth century. An elementary account is given of glass formation, of the structure of glasses and of controlled nucleation and crystallisation to make glass ceramics. Most of the particular applications of glass considered are recent developments. They include low-expansion glass ceramics for laser gyroscopes, photosensitive glasses, glasses for optical communication fibres, glasses as electrolytes in high temperature batteries, semiconducting glass switches, magnetic glasses, new sealing techniques, and the use of glass as a substrate. Sufficient references are given to make it possible for the reader to follow up any of these topics in more detail.

Structural changes of glass-ceramics of the Cu2O-Al2O3-SiO2 system on heating in air

The behaviour of copper ions in low thermal expansion glass-ceramics prepared from Cu2O · Al2O3 ·nSiO2 glasses, or inβ-spodumene type Cu2O · Ae2O3 ·nSiO2 crystals included in the glass-ceramics on heating in air was investigated. On hewing at 300 to 500° C, the copper ions behaved as in the corresponding glasses. Cuprous ions in the glass-ceramics orβ-spondumene type crystals were oxidized into the cupric state, and at the same time an equal amount of cuprous ions to those oxidized were expelled out of the specimen for the requirement of electrical charge neutrality and then reacted with oxygen to form CuO on the surface. The oxidation of cuprous ions and the decrease of the copper content of theβ-spondumene type crystals brought about a considerable decrease in the lattice spooings.