Low Thermal Expansion Ceramics Research Articles

Preparation study for the low thermal expansion spodumene/mullite composites

AbstractIn this work, spodumene/mullite ceramics with low thermal expansion were successfully prepared from spodumene, quartz, talc, and clay. The effects of spodumene content and sintering temperature on the mechanical properties of spodumene/mullite ceramics were investigated. The formed phases were then detected by X‐ray diffraction analysis and the microstructures of the sintered bodies were determined by scanning electron microscopy. The interaction effects of the spodumene content and sintering temperature on the apparent porosity and bulk density were studied by response surface methodology. The results demonstrate that an appropriate sintering temperature and spodumene content can promote densification, improve the mechanical properties, and reduce the coefficient of thermal expansion (CTE) of spodumene/mullite ceramics. At the spodumene content of 40 wt.%, the sintering temperature of 1270°C, and the holding time of 90 min, the bending strength was 60.45 MPa, the CTE was 1.73 × 10–6/°C (α[25–650°C] < 2 × 10–6/°C), the bulk density was 2.28 g cm‐3, and the apparent porosity was 0.43%. Therefore, this study was of guiding significance for reducing the production cost of spodumene low thermal expansion ceramics and improving product quality.

Ultra-precision finishing of low expansion ceramics by compliant abrasive technologies: A comparative study

Advanced ceramics have many attractive features such as high stability and wear resistance that find broad applications in various fields, e.g. optics, aerospace, etc. However, the accompanying difficult-to-machine property with complex geometry brings great challenges to the commonly used laser machining and rigid wheel based grinding in industry. To achieve optical surface quality with surface roughness below 10 nm Ra, three promising ultra-precision compliant machining technologies using adaptive elastic tools are presented in this paper, including bonnet polishing, compliant pitch polishing and shape adaptive grinding with fine grain size. A comparative study was conducted by machining three different low thermal expansion ceramics while continuously increasing attack angle, spindle speed and tool offset across rectangular regions. Material removal rate (MRR) and surface roughness (Ra) with respect to different process conditions are compared. With sufficient data, the processing ability using above three compliant machining technologies is summarized based on the MRR-Ra plots for different ceramics. In addition, microscopic observation and X-ray diffraction analysis are conducted to characterize differences in material behavior.

Thermal Expansion of SrZr<sub>4-x</sub>Ti<sub>x</sub>(PO<sub>4</sub>)<sub>6</sub> Ceramics

Low thermal expansion ceramics have been widely applied in multiple fields. In this paper, a series of low thermal expansion ceramics SrZr4-xTix(PO4)6 was prepared and characterized. The SrZr4-xTix(PO4)6 ceramics could be well sintered in the temperature range of 1400~1500 °C. The effect of the addition of Ti substituting Zr and the sintering temperature was studied. The Ceramic with x =0.1 sintered at 1450 °C, the SrZr4-xTix(PO4)6 had a high relative density. The thermal expansion coefficients were about 3.301×10-6 °C-1. It was demonstrated that the microstructure of the SrZr4-xTix(PO4)6 could be altered by adding varying amount of Ti to tailor the thermophysical properties of the material.

Synthesis, microstructure and thermal expansion studies on Ca0·5+x/2Sr0·5+x/2Zr4P6−2x Si2x O24 system prepared by co-precipitation method

We report on the synthesis, microstructure and thermal expansion studies on Ca0·5 + x/2Sr0·5 + x/2Zr4P6 − 2x Si2x O24 (x = 0·00 to 1·00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0·37. For x ≥ 0·5, in addition to NZP phase, ZrSiO4 and Ca2P2O7 form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 °C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0·75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0·00 to 0·37 and then decreases for x > 0·37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.

Comparision of the Preparation Methods of Mesoporous Phosphate Compounds Belonging to NZP Family

Using polyethylene oxide (PEO) as template, the new types of mesoporous phosphate compound which belongs to NaZr2(PO4)3(NZP) family were synthesized by copreciptate, sol-gel and mechanochemical activation(MA) route respectively. The physical phase and pore structure of the synthesized powder materials were characterized by X-ray diffraction (XRD) and N2 adsorption–desorption. The results showed that the crystalline NZP family compound with mesoporous structure is formed by sol-gel route followed with calcination as well as MA method followed with hydrothermal treatment when the mole ratio of PEO to Zr is 1:10, and the specific surface area, average pore diameter and pore volume of the synthesized powder is 20-50m2/g, 3-6.nm and 0.05-0.12cm3/g respectively. The above research results indicate that it is promising to expand the application field of the powder of NZP family from low thermal expansion ceramics to catalytic materials.

Synthesis and Characterization of Ca1-xSrxZr4(PO4) (0≤x

Different low thermal expansion ceramics of Ca1-xSrxZr4(PO4)6 system with x = 0, 0.25, 0.5 and 0.75 were synthesized by the solid state reaction method. After several heat treatments finished products were obtained at 1300°C. These were characterized for phase purity by X-ray Diffractometry and IR Spectroscopy. Densification parameters of the compositions with 3 and 5 wt% ZnO added as sintering aids were studied at 1100°, 1200° and 1300°C under soaking periods of 2-6 h. The corresponding effects on the physical, thermal and mechanical properties were observed. A maximum of 98% of theoretical density was obtained and flexural strength as high as 70 MPa was achieved. Thermal expansion varied from -0.47 to 2.65 x 10−6/°Cwith increase in Sr content. The results are discussed in the light of the microstructures.

Synthesis of low thermal expansion ceramics based on CaZr 4(PO 4) 6–Li 2O system

Ultra-low thermal expansion ceramics based upon CaZr 4(PO 4) 6–Li 2O system were synthesized through solid state sintering. Lithium oxide was introduced to the CaZr 4(PO 4) 6 lattice to promote liquid phase sintering to form CaZr 4(PO 4) 6 with strongly negative thermal expansion. A small addition of Li 2O has improved the densification rate, but also caused an excessive grain growth, which resulted in extensive microcracking. The microcracking lowered the bulk thermal expansion to −6×10 −6°C −1. Excessive amount of Li 2O content also led to formation of the secondary phase, Li 2Zr(PO 4) 2, and also caused the swelling of the CaZr 4(PO 4) 6 phase to lower the sintered density. An addition of over 5% of lithium oxide, the glass phase surrounding the CaZr 4(PO 4) 6 grain, together with the secondary phase increased the thermal expansion. At 2.5% addition, there was an indication that the viscous glassy phase has partially relieved the stresses associated with the thermal expansion anisotropy during cooling from the processing temperature. It was demonstrated that the microstructure of the CaZr 4(PO 4) 6 could be altered by adding varying amount of lithium oxide to tailor the thermophysical properties of the material.

NZP: A New Family of Low Thermal Expansion Ceramics

The NZP family, which gets its name after the prototype composition NaZr2P3O12, has received much attention in recent times because of their very low coefficient of thermal expansion (CTE), controlled lattice thermal expansion anisotropy, fast ionic conductivity, high thermal and chemical stability and flexibility towards ionic substitutions. Such materials can find widespread applications as exhaust components in automobiles, mirror blank for optical telescope, substrate materials for electronic packaging, as well as in sulphur batteries, nuclear waste immobilization, port-liners for diesel engines, braze fixtures for aircraft engines etc. The low expansion behaviour of NZP materials has been attributed to: (i) strongly bonded 3—dimensional network structure, (ii) existence of structural holes which may absorb some of the thermal vibrations and (iii) anisotropy in the thermal expansion of the lattice. In this overview the crystal structure, synthesis, thermal expansion behaviour and possible applications...

Translucent low-thermal expansion ceramics

The optical transmittance of pressureless sintered KZr2P3O12 (KZP) ceramics was studied in the ultraviolet, visible light, and near infrared spectrum ranges. Thermal expansion, strength, and thermal shock resistance of the ceramics were also studied. KZP ceramics with different additives (0–8 wt% of MgO, ZnO or SrO) show a 30–70% transmittance from 0.4–2 μm, a low thermal expansion coefficient and high thermal shock resistance. These polyfunctional ceramics might be useful as optical windows.

Successful Design of New Very Low Thermal Expansion Ceramics

AbstractIn the last few years we have succeeded in developing three separate groups of near-zero-expansion ceramics. These are based on: (1) Modification by crystalline solution of GeO2 for SiO2 in the well-known cordierite phase. (2) Discovery of a new structural family known as [NZP] or [CTP], many members of which have near-zero values of a and very extensive crystalline solution possibilities permitting continuous control of α. (3) Di- (or multi) pfiasic composites of phases, one with negative and one with positive a to give a net-zero-α ceramic material.

Fabrication Techniques for Ceramic X-Band Cavity Resonators

Techniques are described for constructing cavity resonators at X band from low-thermal expansion ceramics. A variety of mechanical arrangements is discussed. Q values as high as 14 000 and frequency-temperature coefficients as low as 1 part in 100 million per °C have been obtained using simple processes.