烧成温度对MgO-TiO2复合无机陶瓷微滤膜支撑体性能的影响

采用添加造孔剂高温烧结法制备了氧化镁-二氧化钛（MgO-TiO₂）复合无机陶瓷微滤膜支撑体。分别研究了相同烧结制度下不同最高烧结温度、相同最高烧结温度不同的烧结制度下样品的孔隙率、抗弯强度及纯水通量的变化情况。采用热重分析（TG-DSC）、电子扫描电镜（SEM）和万能试验机等对样品进行热分析、观察样品形貌及抗弯强度等性能测试。研究表明,最高烧结温度和烧结制度对样品的性能有很大影响,采用最高烧结温度为1 400 ℃、升温速率分别为4、8、2 ℃/min的1400-482烧结制度所制备的支撑体的性能最佳,孔隙率为37.57%,抗弯强度为108.65 MPa,纯水通量为4 040 L/（m²?h?MPa）。     

Low firing temperature ceramic for microcircuit substrates

Methods for fabricating substrates based on low-temperature (firing temperature below 1000°C) ceramic, fired together with a deposited metal coating, are examined. Materials which are promising for use as low-temperature simultaneously fired ceramic (LSC) in the systems B₂O₃-CaO-SiO₂ and B₂O₃-CaO-Al₃O₃ are proposed.     

Ceramic for grinding bodies with low firing temperature

Translated from Stekli i Keramika, No. 9, p. 19, September, 1988.     

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.     

Effect of processing technique on the transport and mechanical properties of vapour grown carbon nanofibre/rubbery epoxy composites for electronic packaging applications

Vapour grown carbon nanofibre (VGCNF)/rubbery epoxy (RE) composites were produced, by either mechanical mixing, three-roll milling (RM) or combined ultrasonication/mechanical mixing. Incorporation of VGCNFs resulted in significant enhancements in the thermal and electrical conductivities of the material. Appropriate selection of processing technique and parameters can help to maximise the potential of VGCNF additions by improving their dispersion in the matrix. The composites produced by RM have superior transport properties compared with those produced by other techniques. The thermal conductivity of such composites at 40 wt.% VGCNFs reached 1.845 W/m K, a 10-fold increase compared to RE alone. The thermal conductivity data of VGCNF/RE composites best fits to the Hatta–Taya model. The lowest electrical percolation threshold is at 2 wt.%, obtained for composites produced by RM. The thermal conductivity of VGCNF/glassy epoxy (GE) composites at 12 wt.% is 10% lower than the corresponding RE composite but its electrical conductivity is 2 orders of magnitude higher than the corresponding RE composite. VGCNFs at 40 wt.% increase the compressive strength of rubbery epoxy by ～5× but the compressive modulus of 40 wt.% VGCNF/RE composite is 12 times lower than that of 12 wt.% VGCNF/GE composite, demonstrating highly compliant nature of RE composites.     

Criteria of temperature conditions control in firing of ceramic articles

Three groups of criteria of temperature control in firing of ceramic articles are considered. An assessment of the effect of the main control criteria on the firing process is provided for a furnace with radiating walls. Translated from Steklo i Keramika, No. 5, pp. 3 – 5, May, 1998.     

High-power properties of piezoelectric hard materials sintered at low temperature for multilayer ceramic actuators

0.05Pb(Mn_1/3Sb_2/3)O₃–0.05Pb(Al_1/2Nb_1/2)O₃–0.9Pb(Zr_0.48Ti_0.52)O₃ (PMS–PAN–PZT) high power piezoelectric system with both La₂O₃ as a hardener and CuO as a low sintering agent had been synthesized at 900 °C for 2 h. When La₂O₃ doping of the main composition went over 0.5 wt%, the mixed tetragonal and rhombohedral perovskite structure changed to pure rhombohedral perovskite structure. In case of the CuO, 1.0 and 1.5 wt% CuO content significantly improved the sinterability of the PMS–PAN–PZT system processed at 900 °C for 2 h. When La₂O₃ and CuO co-doped in PMS–PAN–PZT ceramics, piezoelectric constants (d₃₃), quality factor (Q_m), electromechanical coupling factor (k_p) and dielectric constant (${\epsilon }_3^{\text{T}}/{\epsilon }_0$) of the piezoelectric ceramics sintered at 900 °C for 2 h were optimized, such as 336 pC/N, 841, 60%, and 1358, respectively. New developed piezoelectric materials are promising for high power multilayer ceramic actuators.     

Gas release during clay firing and evolution of ceramic properties

Gas release, crystalline structure and ceramic properties were analysed during firing of clay raw materials and extruded bricks. Carbon monoxide, carbon dioxide, nitrogen oxides, and methane emissions were measured during the firing cycle. Ammonia and sulphur dioxide were not observed within the detection limits. The evolution of crystalline phases, open porosity, volumetric shrinkage, rupture tension and apparent density were correlated to the amount of gases produced at different temperatures, ranging from 300 to 1200 °C. These results can be applied for optimising the production process.     

Oxyfluoride glass-silica ceramic composite for low temperature co-fired ceramics

Glass/ceramic composite materials based on CaF₂–AlF₃–SiO₂ oxyfluoride glass and silica ceramic filler were prepared. The sintering behavior, phase composition and dielectric property of oxyfluoride glass/silica ceramic composites, as well as its compatibility with Ag electrode, were investigated. The results show that the glass/ceramic composite system can be sintered at 825 °C. When the amount of SiO₂ increased from 0 to 20 wt.%, the shrinkage decreased from 17.0 to 14.5%, and the dielectric constant decreased from 5.9 to 5.4, while the thermal expansion coefficient (20–200 °C) increased from 6.0 to 10.1 ppm/°C. The sintered samples had low dielectric losses less than 0.002 and high flexural strengths. This novel glass/ceramic composite system exhibits good sintering compatibility with silver paste, which makes it a promising candidate for low temperature co-fired ceramic application.     

Microstructure and mechanical properties of an alumina–glass low temperature co-fired ceramic

The microstructure and mechanical properties of an alumina–glass low temperature co-fired ceramic (LTCC) have been investigated. The microstructure was studied by using optical microscope, scanning electron microscope, energy spectrum analysis and X-ray diffraction. The Young's modulus, hardness, flexure strength and fracture toughness were measured by three-point bending, indentation and nanoindentation tests. The LTCC can be regarded as a particle-reinforced composite with macroscopically isotropic properties: particles mainly composed of synthetic corundum and matrix mainly of corundum and silica. The particles with irregular shape and an average radius of 0.71 μm are homogeneously dispersed in the matrix. The properties of the individual particle and matrix were successfully measured and further used to obtain the effective properties of the composite by micromechanics methods. The existence of rigid particles improves not only the modulus, hardness and strength but also the fracture toughness of LTCC materials.     

Effect of firing temperature on the properties of sol-gel films of the CuO-TiO2 system

The viscosity, surface tension, and refractive index of 2-day-old film-forming solutions of the CuO-TiO₂ system of different composition were compared with the structure and properties of coatings on float glass made from them. Regardless of the composition and firing conditions, the film thickness remained constant. The refractive index and mirror reflection coefficient of the coatings are correlated by a directly proportional dependence. Increasing the firing temperature does not change or increases the values of the refractive index and mirror-reflection coefficient of the films. The chemical resistance of the coatings to water or hydrochloric acid solution is not a function of or improves with an increase in the firing temperature.     

低温陶瓷釉的制备

低温烧结工艺是目前陶瓷行业节约能源、降低燃耗、提高生产效率的有效途径,因此在低温条件下烧制陶瓷釉逐渐成为研究热点。为大幅度降低烧结温度,采用磷酸钠代替基础釉中的二氧化硅的方法,促使液相在低温形成,成功研制了烧成温度为890 ℃的基础釉。当磷酸钠质量分数达到33.25%时,基础釉的烧成温度降低了290 ℃。采用场发射扫描电镜分析了样品的表面和断口形貌,实验结果表明磷酸钠能够显著降低陶瓷釉的煅烧温度。通过在基础釉中加入显色剂,实现了在低温下制备红色陶瓷釉,并且烧成温度降低了350 ℃。实验结果表明,磷酸钠在低温陶瓷釉的制备过程中起到降低温度的重要作用。这些研究结果有助于彩色陶瓷釉的研制。     

Microwave dielectric properties of a low firing and temperature stable lithium magnesium tungstate (Li4MgWO6) ceramic with a rock-salt variant structure

The Li₄MgWO₆ ceramic was synthesized by the conventional solid-state reaction method, and its sintering behavior and microwave dielectric properties were studied for the first time. The XRD patterns and structural refinements indicated that Li₄MgWO₆ formed an orthorhombic phase at temperatures above 900 °C, and TEM analyses confirmed the ordered and layered rock-salt superstructures for the orthorhombic Li₄MgWO₆. The SEM photographs and relative density curve showed that the sample sintered at 950 °C had the highest densification. When sintered at 950 °C in a WO₃-rich atmosphere for 4 h, Li₄MgWO₆ had the following optimum properties: ε_r = 15.06±0.33, Q×f = 28,300±600 GHz (f = 10.1 GHz), and τ_f = 0.9±3.4 ppm/°C. Compared with other reported low permittivity compounds, Li₄MgWO₆ shows more potential for the Low-Temperature Cofired Ceramics (LTCC) substrate materials due to its intrinsic low sintering temperature, novel temperature stability, and relatively low dielectric loss.     

烧成温度对Al2TiO5-ZrO2复合材料性能的影响

首先以平均粒径为6 μm的预合成Al2TiO5为初始原料,分散在Zr4 浓度为0.06 mol·L-1的氧氯化锆溶液中,以氨水为沉淀剂,将液相共沉淀形成的前驱体经650℃焙烧1 h,制得纳米ZrO2含量(w)分别为2%、5%、8%的Al2TiO5-ZrO2复合粉体;然后在复合粉体中加入6%聚乙烯醇(PVA)结合剂,以100 MPa压力制成53 mm×10 mm×10 mm试样,1 10 ℃干燥2 h后,经1 350、1 400、1 450、1 500℃保温2 h烧成制备了Al2TiO5-ZrO2复合材料.对烧后试样的显气孔率、抗折强度、热膨胀率进行了分析测定,借助XRD、SEM分析了Al2TiO5粉体物相组成及烧后部分试样的物相组成和显微结构,并研究了烧成温度对不同ZrO2含量试样的烧结性能、热膨胀性能、抗热震性能与显微结构的影响.结果表明:随着烧成温度的提高和ZrO2含量的增加,显气孔率与抗折强度呈现不规则的变化趋势,此种情况与预合成Al2TiO5粉磨后微粉的物相变化有关;烧成温度为1 500℃时,ZrO2含量为2%的试样,在1 250℃的热膨胀卒为0.16%,显微结构致密,抗热震性能好.     

Effect of ceramic powder fineness on mullite-zirconium ceramic properties

Results are provided for a study of the development of high-temperature mullite-zirconium ceramic with use of activated ceramic powders prepared by grinding for different times with addition of illite clay, and from pure oxide powders. It is shown that increased activity and amorphicity of ground particles considerably promotes formation of mullite phase at 1200°C, and also transition of the monoclinic modification of ZrO₂ to tetragonal, particularly with an increase in firing temperature. It is proposed that as a result of rapid “freezing” the structure retains the high-temperature modification of ZrO₂, having a tendency with slow ceramic cooling to transform into the monoclinic modification.     

Effect of aldehydes on thermomechanical properties of gluten-based bioplastics

Protein–protein crosslinks play an important role in the design of biodegradable polymeric materials requiring suitable rheological and mechanical properties. The addition of aldehydes to the bioplastic formulation may result in their involvement in some form of protein cross-linking. The objective of this contribution is to evaluate the effect of adding some aldehydes (formaldehyde, glutaraldehyde and glyoxal) on the thermomechanical properties of gluten-based biodegradable polymeric materials processed by a mixing stage followed by compression moulding at 9 MPa and 130 °C. Different bioplastic probes were evaluated by means of DMA measurements, recording the elastic and loss moduli as a function of temperature and uniaxial tensile strength tests. Water absorption capacity and solubility under different extraction media of bioplastic specimens, were also evaluated. Solubility measurements were carried out in order to analyse the effect of the aldehyde on the nature of the interactions taking place in the system, being compared to those performed on blends previous to the moulding process. Glyoxal is the aldehyde that seems to produce bioplastics with best thermal and mechanical properties. This study would contribute to evaluate the potentials of adding aldehyde to gluten/plasticiser systems to control the microstructure and properties of the final bioplastics.