Cordierite Composition Research Articles

Synthesis and Sintering of Cordierite from Kaolinite and Basic Magnesium Carbonate

Sintering behavior of the mixtures of kaolinite and basic magnesium carbonate (BMC) was investigated to obtain dense cordierite ceramics. Kaolinite and BMC were mixed by ball-milling in a molar ratio of nMgO⋅Al2O3⋅2SiO2 (n=0.8-1.4). Particularly fine mixtures were prepared by beads-milling after calcination. During firing of fine mixtures, magnesia disappeared completely by reaction with metakaolin to form amorphous particles below 900°C. Since the amorphous particles were very sinterable, the pressed specimens were densified up to about 90% at 900°C, and then μ-cordierite crystallized at about 940°C. Dense α-cordierite ceramics with relative density of≥95% were obtained at 1300°C from the mixtures of n=1.0-1.4, and the lowest linear thermal expansion coefficient was 2.2×10-6/K in the case of n=1.0, which is close to the composition of cordierite.

Phase Formation Kinetics in a Glass Ceramic Studied by Small-Angle Scattering of X-rays and Neutrons and by Visible-Light Scattering

The kinetics of the primary phase formation in a glass ceramic base glass near the cordierite composition in the MgO–Al2O3–SiO2 system, with additions of ZrO2 and TiO2 as nucleating agents, have been investigated by combining different small-angle scattering techniques. Phase formation in the base glass heated isothermally at 1093 K has been studied in order to elucidate the structural processes that take place during controlled nucleation before volume crystallization begins. Complementary results of X-ray diffraction, transmission electron microscopy and electron microprobe analysis reveal that in the final stages of annealing, different crystalline phases, which are dispersed in the residual glassy phase, are developed. The largest particles have sizes of the order of several hundreds of nanometers and consist of magnesium petalite as well as a high-quartz solid solution. Besides these crystals, two populations of smaller particles, the sizes of which can be resolved by small-angle scattering, were detected and found to be enriched with TiO2 and/or ZrO2. The growth of particles of intermediate size was studied in situ. The radius, R, of each of these particles increases with increasing treatment time, t, according to the power law R ∝ t1/2, indicating diffusion-limited independent growth. The scattering patterns are modified by diffusion zones surrounding the growing particles. The characteristics of the diffusion zones are evaluated by fitting appropriate model scattering curves to the experimental scattering data. The structural arrangement of the Ti and Zr ions was studied by contrast variation with the help of anomalous small-angle X-ray scattering and small-angle neutron scattering. As revealed by the contrast variation experiments, Ti ions are concentrated in the interface between the intermediate-sized particles and the glass matrix, whereas Zr is homogeneously distributed in these particles. Additionally, the Zr ions participate in the formation of the smallest particles, which are crystallites enriched with ZrO2. Finally, the catalyzing effect of TiO2 and ZrO2 on the nucleation and volume crystallization of the glass ceramic is discussed.

The effects of some processing parameters on the sinterability, microstructures operties of sintered cordierite glass ceramics

The paper presents some preliminary studies on the effect of processing parameters on the sinterability, microstructures and dielectric properties of glass ceramics in the cordierite phase field. It is found that the nature of the precursors have a very marked effect on the densification, microstructures, and dielectric properties of the sintered components. The addition of about 5% titania to a cordierite composition reduces the densification and lowers the overall dielectric permittivity. The results are presented and discussed in terms of the microstructures evolved.

An Experimental Investigation of the Failure Modes in Hybrid Ceramic Matrix Composites

A material system has been developed that employs the benefits of both fiber and whisker reinforcement in the strengthening and toughening of ceramics. Testing was performed on this hybrid material system in three-point flexure using a combination of acoustic emissions analysis and microscopy techniques for damage analysis. It is shown that the hybrid material system will withstand a higher stress before microcracking occurs in the matrix and has improved transverse strength. In the longitudinal direction, microcracking occurred at 121 MPa for the hybrid composite, compared to 47 MPa for composites reinforced solely with fibers. The transverse flexure strength was 62 MPa for the hybrid, compared with 24 MPa for fiber-reinforced composites. The hybrid composite also had higher stiffness and better damage tolerance in both the longitudinal and transverse directions. Material properties are presented for three material systems: a whisker-reinforced cordierite composite, a fiber-reinforced cordierite composite, and a fiber/whisker hybrid-reinforced cordierite composite.

Characterization Of Glass-Ceramic Dielectric Thick Films With Cu Conductors for Multilayer Packages

AbstractCompatibility and characteristics of multilayer dielectric thick films with Cu interlayers are influenced by composition and processing parameters. In this work, cordierite based dielectric thick films on a Cu plated alumina substrate were investigated in terms of microstructure and property by changing composition of oxide additives, PbO and Cu2O for a given heating schedule. A nonstoichiometric cordierite composition, 2.4MgO 2Al2O3 5SiO2 was used with nucleating agents, B2O3 and P2O5. The dielectric ink consisting of cordierite glass frit and acrylic based binder vehicles was deposited on oxidized Cu layers via screen printing. The thick film layers were fired at 950°C for 30 min in N2 atmosphere. Dissolution of the oxidized Cu into the cordierite layer was observed. The addition of a small amount of Cu2O to the cordierite layer was effective in preventing the dissolution and enhancing thermal expansion. Crystallization was also influenced by the Cu2O addition. A lower activation energy value of 79 kcal/mol for crystallization, calculated from DTA runs, suggested that Cu20 could be used to form the cordierite glass-ceramic at a lower temperature. In the case of no additive, the activation energy for crystallization was 98 kcal/mol. The addition of Cu2O increased dielectric constant. For 3wt% PbO and 1wt% Cu2O, the dielectric constant and loss were determined at 1 MHz as 6.1 and 0.0046, respectively.

Heat-Resistant ceramics based on quatrz-kaolinite-pyrophyllite rocks of the Boinaksaiskoe Deposit

Results on the development of heat-resistant ceramics based on quartz-kaolinite-pyrophyllite rocks of the Boinaksaiskoe Deposit (Uzbekistan) are presented. The structure of the materials is represented by cordierite and cordierite-mullite compositions. Technological aspects of the problem, physical and engineering properties of the developed materials, and results of experiments on the effect of thermal loads on the mechanical strength are described.

Genetic and chemical relationships between berthierine, chlorite and cordierite in nodules associated to granitic pegmatites of Sierra Albarrana (Iberian Massif, Spain)

Chlorite and berthierine occur through alteration of cordierite within enclaves of metamorphic rocks transformed by the Sierra Albarrana pegmatites. The coexistence of both phyllosilicates allows us to study their stability relationships and to compare their chemical compositions. Samples showing incipient replacement of cordierite by small cryptocrystalline aggregates can be identified by X-ray diffraction (XRD) as berthierine with small quantities of chlorite. Electron Microprobe (EMP) analyses give mixed compositions of berthierine and cordierite. Samples with extensive replacement of cordierite by aggregates show similar characteristics to those with incipient replacement, but some small crystals are present. The last type of sample shows complete replacement of cordierite by crystals showing optical properties of chlorite and EMPA compositions coherent with chlorite or berthierine. Their XRD pattern corresponds to chlorite and their high resolution transmission electron microscopy (HRTEM) images only show perfect sequences of 14 A lattice fringes. The cryptocrystalline aggregates of the samples with incipient and extensive replacement present coexistent areas of 14 A and 7 A lattice fringes that are intergrown at different levels: (1) large areas (> 1 μm) of 7 A layers; (2) packets of 7 A layers between 14 A layer areas, with visible 7 A to 14 A lateral changes; (3) random mixed-layers 7 A/14 A. Chlorite is the final stable product of alteration of cordierite, with berthierine as an intermediate metastable phase. Energy dispersive X-ray spectrometry microanalyses of 14 A, 7 A and (14+7) A areas show lack of systematic differences in chemical compositions between both phyllosilicates which may be considered as true polymorphs.

The crystallization kinetics of a glass based on the cordierite composition studied by DTA and DSC

The crystallization kinetics of a glass based on the cordierite composition have been studied by DTA and DSC. Crystallization has been observed to be very dependent on the particle size of the glass employed, indicating a strong dependence on surface crystallization. For coarse particle sizes (eg. 600–1000 Μm) a single crystallization exotherm is obtained, corresponding to the formation of α-cordierite. For smaller particle sizes (eg ≤ 212Μm) two distinct crystallization exotherms are resolved corresponding to the initial formation of metastable Μ-cordierite, followed by its transformation at higher temperatures to the α-cordierite phase. Activation energies for crystallization have been determined for different particle sizes of glass using a number of isothermal and non-isothermal methods, and the results compared. In general, agreement between DTA and DSC, and the various methods employed, is good, although the isothermal methods appear to reflect more strongly theearly crystallization processes, i.e. they relate more closely to the activation energy for the formation of the Μ-cordierite phase. A value for the activation energy corresponding to structural relaxation at temperatures around the glass transition has also been determined for this cordierite glass.

Combustion synthesis, characterization, sintering and microstructure of mullite-cordierite composites

Mullite and cordierite are promising materials for electronic packaging due to their dielectric constant and coefficient of thermal expansion being lower than that alumina [1-5]. Recent advances in very large scale integrated circuits (VLSI) have led to materials with low dielectric constant and thermal expansion tailored over a wide range. Cordierite- dispersed-mullite composites allow a selection of materials with a wide range of values of dielectric constant and thermal expansion [6]. Mullite/ cordierite composites have been prepared by the sol-gel method using metal alkoxides [7] or by the use of composite sols [8, 9]. Such composites have aslo been prepared by solid state mixing of mullite and cordierite in the desired ratio [10].

Chemical variability of Al-Ti-Fe-Mg minerals in peraluminous granitoid rocks from Central Spain

Two broad series of peraluminous granite types can be distinguished in the Central System of Spain. The first group consists of cordierite-bearing granites that are moderately peraluminous in composition (peraluminous S-type granites, PS). The second is composed of amphibole/allanite-bearing granites, weakly peraluminous in composition (peraluminous I-type, PI). These granite types evolved through complex igneous fractionation processes. Both peraluminous granite types show differences in the chemical composition of biotite and cordierite; cordierite is common in PS granites but restricted to some highly fractionated PI granites. Garnet and ilmenite cannot be used as chemical criteria for distinguishing the two series. The Al and Na content of biotite and cordierite correlate well with the granite type (PS and PI). The higher Na content in biotite (and cordierite) of PS granites is noteworthy. When plotted in a Na vs. [VI1A1 diagram biotites are located in different fields according to the peraluminosity degree of the granite type. The estimated Fe3+/(Fe3++Fe2+) ratio of biotite is higher in PI than in PS granites, although this value is very pluton-dependent. Several compositional variations of Al-Ti-Fe-Mg (ATFM) minerals are functions of the degree of fractionation or evolution of the magma, irrespectively of its peraluminosity. Other chemical features of ATFM phases, such as XFe or XMΠ, can be used as fractionation indices. Thus, the more acid the magma, the higher XFe and XMΠ in ATFM minerals. This correlation is not linear showing a rapid increase for silica values of SiO2 ≥ 74 %. Usually, XFe garnet > XFe biotite > XFe cordierite, and XMΠ ilmenite = XMΠ garnet > XMΠ cordierite > XMΠ biotite, while XFe and XMΠ of whole rock are very close to biotite values. The high increase in Mn content, more marked than in Fe, in all AFM phases in the silica-rich granites (SiO2 = 74 %), can be interpreted as a consequence of the incompatible behaviour of this element in highly evolved granites, that are sufficiently poor in Ti, Mg and Fe to prevent or diminish crystallization of ore-minerals, such as ilmenite.

Synthesis of cordierite and cordierite-ZrSiO4 composite by colloidal processing

Cordierite powder of high purity and cordierite-ZrO2 composite powder were synthesized by colloidal processing. Cordierite was synthesized by calcining a precursor gel obtained by gelation and coprecipitation of AlOOH sol, SiO2 sol and Mg(NO3)2. The calcination temperature affected the constituent phases in the powders. The phase assemblage in calcined powder affected the sintering conditions. The optimum sintering temperature of the powder with cordierite single phase was 1440–1450 °C when it was calcined at 1270 °C. The sintered body had a dense microstructure with submicrometre grains. Addition of ZrO2 sol resulted in reaction with cordierite to form mostly ZrSiO4 at the sintering temperature. Several properties of cordierite and cordierite-ZrSiO4 composite, such as thermal expansion coefficient, bending strength, dielectric constant and insulation properties at high temperature, were investigated. Thermal expansion and electric properties were degraded by an increasing amount of ZrO2 additive, whereas the bending strength was improved by the addition of ZrO2.

Processing of ZrO2 reinforced cordierite composites by infiltration of ceramic felt with sonosols

ZrO2 ceramic felts and low viscosity sols of cordierite were used to obtain ceramic-ceramic composites. Ultrasonic treatments were applied to prepare cordierite sol containing different quantities of nucleating TiO2. Sintering of the composites was accomplished by the hot-pressing of several infiltrated ZrO2 felt layers. Relative densities were around 99%. The reinforcing phase was distributed in an anisotropic way in the densified samples. The mechanical strength of the composites was influenced by the polymorphic form and microstructure of the matrix, and also by the matrix volume fraction introduced by infiltration.

Mechanical Properties of Glass and Polycrystalline Ceramic with Cordierite Composition

The Vickers hardness (Hv), Young's modules (E), fracture toughness (KIC) and bending strength (σf) of a glass and an α-type polycrystalline cordierite with the cordierite composition (2MgO⋅2Al2O3⋅5SiO2) were measured using Vickers indentation, resonance method, various indentation techniques and 3-point bending test. The polycrystalline cordierite was fabricated by densification and subsequent crystallization of compacted cordierite glass powder. The Hv, E and KIC of a polycrystalline cordierite were 7.5GPa, 127.5GPa and 2MPa⋅m1/2, while those of cordierite glass were 5.9GPa, 98.7GPa and 1.0MPa⋅m1/2, respectively. On the other hand, the σf (113MPa) of a polycrystalline cordierite was smaller than that (149MPa) of a cordierite glass.

Heterogeneous Nucleation of Superparamagnetic Phases in “Fe-Bearing Cordierite-Glasses

ABSTRACTGlasses of stoichiometric cordierite composition Mg2(Al1−xFex)4Si5O18, containing very low iron contents (x=0.015 and 0.005) have been investigated by 57Fe Mössbauer spectroscopy. At higher Fe concentrations spinel exsolution has been observed in X-ray powder patterns. To allow Mössbauer spectroscopy at very low Fe-concentrations (<0.8 weight* Fe2O), starting materials were doped with 100% 57Fe. Glasses prepared in air at 1560°C were also oxidized In water saturated O2 stream. Glasses were crystallized to cordierite by heating In air at 1100 to 1400°C. 57Fe-Mössbauer spectra of all samples are governed by a doublet typical for Fe2+ in octahedral coordination (IS: 1.09–1.15, QS: 2.00–2.31 in MM/s relative to metallic iron). X-ray powder patterns exhibit no additional phases. But, the 295 K and 5 K Mössbauer spectra of treated and untreated glasses and of cordierltes exhibit broad lines, which have been fitted by applying internal magnetic hyperfine fields H of ca. 500 kG. These lines are attributed to heterogeneously nucleated, superparamagnetic (MgFe) (AlFe)2O4 spinels of complex compositions. From the calculated subspec-tra one may conclude that 35 to 65% of the total iron, depending on preparation conditions, is incorporated in the spinels.

Influence of sintering conditions on mechanical and thermal properties of cordierite-ZrO2 composites

Abstract Bend strength, fracture toughness and thermal diffusivity of cordierite composites with 30 vol.% of either unstabilized or Y2O3-stabilized ZrO2 sintered at 1400°C have been determined as a function of sintering time. Depending on sintering time, the phase composition varies from cordierite + monoclinic ZrO2 to spinel + zircon. Cordierite with tetragonal ZrO2 sintered for 1 h exhibits a fracture toughness of ∼4·1 M Pa m , while composites consisting essentially of spinel and zircon with both inter- and intragranular monoclinic ZrO2 particles show the highest fracture toughness ( ∼4·7 M Pa m ). These composites are obtained when cordierite is sintered with unstabilized ZrO2 at 1400°C for >4h. They also exhibit the highest thermal diffusivity (48 × 10−3 cm2/s).

Preparation of cordierite ceramics by sol-gel technique

Xerogel with cordierite composition Mg2Al3[AlSi5O18] from aluminium and magnesium 2-ethoxyethoxides and tetraethylortosilicate have been prepared, the latter being not previously partially hydrolized. Conditions to obtain not only homogeneous but also sinterable gel have been determined. All the powders derived were characterized by DTA, TG, BET and X-ray diffraction. Bulk α-cordierite material of 97% from theoretical density have been obtained by sintering.

Sic-Reinforced Cordierite Composites Formed by Viscous Sintering of Cordierite Powders

ABSTRACTOne approach for improving mechanical properties of ceramics is to add reinforcing whiskers; however, addition of whiskers often inhibits densification. Formation of SiCcordierite composites by pressureless sintering was studied. The cordierite composites densified by viscous sintering; after densification the amorphous matrix then crystallized. It was shown that high green density composites obtained by using small particle size powder gave the highest sintered density composites. Reducing the aspect ratio of the SiC phase also improved sintered composite densities. Densities greater than 96% were obtained using small particle size cordierite powder formed by a sol-gel process and either classified SiC whiskers or SiC powder at SiC loadings of 20 vol%

Whisker reinforcement of glass-ceramics

Silicon carbide whisker reinforcement of anorthite and cordierite glass ceramics has been studied. At 25 vol% whisker loading the flexural strengths increased from 65–103 MPa to 380–410 MPa, the fracture toughnesses increased from 1.0–1.5 MPa m1/2 to 5.2–5.5 MPa m1/2. The strengths decline to 240–276 MPa at 1200 °C. The reasons for the decrease in strength with temperature are discussed. Whiskers from two different sources with differences in diameters and aspect ratios were evaluated and the effect of the whisker morphology on the composite properties was studied. It was found that larger diameter, higher aspect ratio whiskers result in improved composite performance. The composites were also characterized in terms of their thermal properties, i.e. thermal expansions and thermal conductivities. The thermal expansion coefficient from 25–1000 °C for anorthite-based composite was 4.6×10−6 °C−1 and that for the cordierite-based composite was 3.62×10−6 °C−1. The thermal conductivities at 1000 °C were 3.75 and 4.1 Wm−1 K−1 for cordierite and anorthite composites, respectively.

Phase transformation in AlSiMg gels: Effect of additions of Ti, Ce and Zr

Abstract Phase transformations in polymeric AlSiMg gels of cordierite composition with addition of 5 wt% TiO 2 , ZrO 2 and CeO 2 have been investigated. An addition of TiO 2 and CeO 2 stimulates the formation of petalite phase (Al 2 O 3 .MgO.3SiO 2 ) instead of μ-cordierite in the range 700–1000°C. TiO 2 and CeO 2 reduce the crystallization temperature of μ-cordierite, whereas ZrO 2 produce no essential effect on the phase transformations in AlSiMg gels.

Glass formation and crystallization in high-temperature glass-ceramics and Si 3N 4

The softening of glassy grain boundaries in ceramic matrix composites and silicon nitride at high temperatures reduces mechanical strength and the upper-use temperature. By crystallizing this glass to more refractory crystalline phases, a material which performs at higher temperatures may result. Three systems were examined: a cordierite composition with zirconia as a nucleating agent; celsian compositions; and yttrium silicate glasses both in bulk and intergranular in silicon nitride. For the cordierite compositions, a series of metastable phases was obtained. The crystallization of these compositions was summarized in terms of metastable ternary isothermal sections. Zircon formed at the expense of zirconia and spinel. In SiC composites the transformations were slower. In celsian, two polymorphs were crystallized. One phase, hexacelsian, which always crystallized, even when metastable, had an undesirable volume change. The other phase, celsian, was very difficult to crystalline. In yttrium silicate bulk glasses, similar in composition to the intergranula rglass in silicon nitride, a number of polymorphs of Y 2Si 2O 7 were crystallized. The conditions under which these polymorphs formed are compared with crystallization in silicon nitride.