Effect of spinel content on hot strength of alumina-spinel castables in the temperature range 1000–1500°C

Hot modulus of rupture of Al₂O₃-spinel castables containing 5–15 wt% alumina-rich magnesia alumina spinel and 1·7 wt% CaO generally increases with increase in spinel content and temperature from 1000 to 1500°C. The magnitudes of hot modulus of rupture of castables containing 15 wt% spinel and 1·7 wt% CaO are 14·3 MPa at 1400°C and 15·6 MPa at 1500°C, while those of castables containing 20 wt% spinel and 1·7 wt% CaO are 12·5 MPa at 1400°C and 14·7 MPa at 1500°C. The former castables contained 15 wt% spinel of −75 μm size, while the latter contained 10 wt% spinel of +75 μm size and another 10 wt% spinel of −75 μm size. The bond linkage between the CA₆ and spinel grains in the matrix is believed to cause both the spinel content and temperature dependence of hot strength of Al₂O₃-spinel castables, as well as fine grain spinel even in amount less than coarser grain spinel to be more effective for enhancing hot strength. The trend of the magnitude of thermal expansion under load (0·2 MPa) above 1500°C of the castables is not necessarily indicative of the magnitude of hot modulus of rupture at 1400 or 1500°C. ©     

Soft chemistry preparation of layered Al0.3V2O5·5H2O

A novel layered compound Al_0.3V₂O₅·5H₂O was successfully prepared and characterized using powder X-ray diffraction, Thermal analysis, scanning and transmission electron microscopes. The new layered Al_0.3V₂O₅·5H₂O has like-nanowires shape and the layered structure was stable until 400 °C. At higher temperature (500 °C), it decomposes to orthorhombic Al_xV₂O₅ and triclinic AlVO₄.     

Transparent mullite ceramic from single-phase gel by Spark Plasma Sintering

Monophasic mullite precursors with composition of 3Al₂O₃·2SiO₂ (3:2) were synthesized and then were sintered by Spark Plasma Sintering (SPS) to form transparent mullite ceramics. The precursor powders were calcined at 1100 °C for 2 h. The sintering was carried out by heating the sample to 1450 °C, holding for 10 min. The sintered body obtained a relative bulk density of above 97.5% and an infrared transmittance of 75–82% in wavelength of 2.5–4.3 μm without any additive. When the precursor powders were calcined at below 1100 °C, it was unfavorable for completely eliminating the residual OH, H₂O and organic compound. However, when calcined temperature was too high, it was unfavorable either for full densification due to the absence of viscous flow of amorphous phase. At the same calcined temperature, the transmittance of sintered body was decreased with the increase of the sintering temperature above 1450 °C owing to the elongated grain growth.     

Synthesis and characterization of Li-type EDI zeolite

A Li-type EDI zeolite (Li-EDI) was successfully synthesized in the Li₂O–Al₂O₃–SiO₂–H₂O system using a silica–alumina mixed sol as the starting material in the absence of other chemical species. The characterization of the obtained Li-EDI was compared with that of the Li-exchanged Linde F zeolite (K-type EDI zeolite). Starting gels with the batch composition of xLi₂O·Al₂O₃·2SiO₂·275H₂O (x = 2–5) were prepared by adding a LiOH solution to a silica–alumina mixed sol. A hydrothermal reaction of the gels was carried out at various temperatures. Li-EDI formed from all of the batches in the range of 60–100 °C. However, the ABW-type zeolite co-crystallized in the composition of Li₂O/Al₂O₃ of 2.0–3.0 above 90 °C. The crystal morphology of Li-EDI was a prism shape. The average particle size of Li-EDI is 0.69 μm in length and 0.23 μm in width. The crystal structure of the Li-EDI collapsed at 300 °C, which indicated that the thermal stability of Li-EDI is significantly lower than that of the Linde F zeolite, which is stable up to 1000 °C.     

Capillary rise properties of porous geopolymers prepared by an extrusion method using polylactic acid (PLA) fibers as the pore formers

The geopolymers were prepared from sodium silicate, metakaolinite, NaOH and H₂O at SiO₂:Al₂O₃:Na₂O:H₂O of 3.66:1:1:x, where x = 8–17, and curing temperatures of 70–110 °C. Since the bending strength of the geopolymers was highest (36 MPa) where H₂O/Al₂O₃ = 9 and the curing temperature = 90 °C, these conditions were adopted. The porous geopolymers were prepared by kneading PLA fibers of 12, 20 and 29 μm diameter into the geopolymer paste, at fiber volumes of 13–28 vol%. The resulting paste was extruded using a domestic extruder, cured at 90 °C for 2 days then dried at the same temperature. The PLA fibers in the composites were removed by alkali treatment and/or heating. The highest capillary rise was achieved in the porous geopolymers containing 28 vol% of 29 μm fibers. The capillary rise of this sample, estimated by the equation of Fries and Dryer¹ was 1125 mm.     

Co0.35Mn0.65Fe2O4 magnetic particles: Preparation and kinetics research of thermal process of the precursor

Precursor of nanocrystalline Co_0.35Mn_0.65Fe₂O₄ was synthesized by solid-state reaction at low heat using CoSO₄·7H₂O, MnSO₄·H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. Nanocrystalline Co_0.35Mn_0.65Fe₂O₄ with spinel structure was obtained via calcining the precursor. The precursor and its calcined products were characterized using TG/DSC, FT-IR, XRD, SEM, EDS, and vibrating sample magnetometer. The results showed that the precursor dried at 353 K was a mixture consisted of CoC₂O₄·2H₂O, MnC₂O₄·2H₂O, and FeC₂O₄·2H₂O. However, when the precursor was calcined at 623 K for 2 h, highly crystallization Co_0.35Mn_0.65Fe₂O₄ [space group R-3 m (166)] was obtained with a crystallite size of 22 nm. Magnetic characterization indicated that the specific saturation magnetization of Co_0.35Mn_0.65Fe₂O₄ obtained at 773 K was 66.14 Am²/kg. The thermal process of precursor experienced two steps, which involves the dehydration of the waters of crystallization at first, and then decomposition of Co_0.35Mn_0.65Fe₂(C₂O₄)₃ and formation of crystalline Co_0.35Mn_0.65Fe₂O₄ together. Based on the Kissinger equation, the values of the activation energy associated with the thermal processes of the precursor were determined to be 78 and 146 kJ/mol for the first and second thermal process steps, respectively.     

Experimental investigations of the structural transformations induced by the heat treatment in manganese ferrite synthesized by ultrasonic assisted co-precipitation method

Manganese ferrite powder has been synthesized by ultrasonically assisted co-precipitation method using Fe(NO₃)₃·2H₂O and Mn(NO₃)₂·H₂O as precursors. The precipitate was washed and dried in oven at 80 °C for 2 h to obtain the initial MnFe₂O₄ powder (denoted by sample S1). Subsequently, other three samples (denoted by S2, S3 and S4) were prepared starting from the initial powder, which was subjected to heat treatment (for 2 h in air) at 400 °C (for sample S2), 700 °C (for sample S3) and 1000 °C (for sample S4). The structural and morphological analysis of samples has been studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). From the XRD analysis of samples one finds that the samples S1 and S2 consist of MnFe₂O₄ with cubic spinel structure, whilst the samples S3 and S4 consist of FeMnO₃ with perovskite structure and Fe₂O₃; meaning that the thermal treatment of MnFe₂O₄ induces chemical and structural transformation. The complex impedance measurements, over the frequency range 20 Hz–2 MHz and magnetic measurements have confirmed the structural transformation in the samples subjected of heat treatment.     

Effect of early hydration temperature on hydration product and strength development of magnesium phosphate cement (MPC)

This paper investigates the effect of early hydration temperatures on hydration products and strength development of magnesium phosphate cement (MPC). MPC paste specimens with borate contents of 3%, 6%, 9% and 12% are prepared and cured in different air temperatures and in the adiabatic condition. The internal hydration temperatures are measured by pre-embedded temperature probes. MPC samples with different hydration temperatures are also obtained by using thin slice samples. The hydration products in MPC samples with different hydration temperatures are analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM) and the strength development is also measured. The results show that NH₄MgPO₄·6H₂O is the major hydration product and beneficial to strength development of MPC at hydration temperature below 70 °C. NH₄MgPO₄·H₂O is another major product, which significantly decreases the strength, when the temperature is higher than a critical temperature between 70 °C and 75 °C. NH₄MgPO₄·H₂O can directly form in the MPC paste, and comes from the decomposition of NH₄MgPO₄·6H₂O when the temperature is above 75 °C. With temperature elevation and duration extension, NH₄MgPO₄·6H₂O decomposes rapidly, and even entirely when the temperature is above 100 °C. The borate content has no effect on the types of major hydration products and the critical temperature.     

A new and economic approach to fabricate resistant porous membrane supports using kaolin and CaCO3

This new and economic approach to fabricate resistant porous membrane supports consists of Algerian kaolin and calcite (CaCO₃) instead of Al₂O₃. The porous mullite (3Al₂O₃·2SiO₂) and anorthite (CaO·Al₂O₃·2SiO₂) based ceramics were obtained by solid state reaction. Different calcite amounts (10–28 wt%) have been added into kaolin halloysite type (Al₂O₃·2SiO₂·4H₂O) in order to control pores forming with appropriate distribution and sizes. Based on a pore distribution and formed phases, a kaolin + 15 wt% calcite (K15C) mixture was selected for flat and tubular configurations. A porosity of 45–52% was also obtained when K15C compacts were sintered at 1100–1250 °C. For example, porosity, average pore size (APS) and 3 point flexural strength were 49%, 3 μm and 87 MPa (same as Al₂O₃ value), respectively when K15C compacts were sintered at 1250 °C for 1 h. Finally, a correlation between microstructure and mechanical properties of elaborated supports has been discussed.     

Mullite whiskers derived from kaolin

Short mullite whiskers prepared by firing compacts of kaolin and NH₄Al(SO₄)₂·12H₂O powders, with a small addition (0.8, 1.5 wt%) of NaH₂PO₄·2H₂O, in air 1300 and 1400 °C for 15 h have been characterized in terms of whisker morphology, composition and structure. Relatively uniform whisker shaped crystals grew within the silicate glass matrix. After chemically leaching the glass matrix with HF solution using a microwave heating source, the resulting whiskers were exposed as isolated crystals and exhibited an aspect ratio of >17 (～0.5 μm in diameter). The mullite whiskers had a composition of 51.06 mol% Al₂O₃ and 48.94 mol% SiO₂, with an orthorhombic crystallographic structure.     

Copper–cobalt heterobimetallic ceramic oxide thin film deposition: Synthesis,characterization and application of precursor

Thin films of halide free Cu–Co mixed metal oxide have been prepared at 390 °C from the heterobimetallic complex Co₄(THF)₄(TFA)₈(μ-OH)₂Cu₂(dmae)₂ · 0.5C₇H₈ (1) [dmae = N,N-dimethylaminoethanol ((CH₃)₂NCH₂CH₂O⁻), TFA = triflouroacetate (CF₃COO⁻), THF = tetrahydrofurane (C₄H₈O)] which was prepared by the reaction of [Cu(dmae)Cl]₄ and Co(TFA)₂ · 4H₂O. The precursor was characterized for its melting point, elemental composition, FTIR and X-ray single crystal structure determination. Thin films grown on glass substrate by using AACVD out of complex 1 were characterized by XRD and SEM. TGA and AACVD experiments reveal it to be a suitable precursor for the deposition of halide free Cu–Co mixed-metal oxide thin films at relatively low temperatures.     

The effect of Cr2O3 as a nucleating agent in iron-rich glass-ceramics

In this work, the effect of Cr₂O₃ as a nucleating agent, in iron rich glasses has been investigated by means of DTA, XRD and density measurements. By Cr₂O₃ addition, from 0·4 to 1·0 wt%, a lowering of the crystallisation peak temperature resulted in the DTA trace, the maximum effect corresponding to 0·7 wt%. By evaluating the degree of crystallisation of the glass at 0·7 wt% Cr₂O₃, the highest efficiency in the nucleation process also corresponds. The optimum values for the nucleation and crystallisation time and temperature, determined for 0·7 wt% Cr₂O₃ addition, have been 70 min at 630°C and 30  min at 800°C. The crystalline phases formed at different thermal treatment temperatures of the parent glass have been investigated by XRD; the spinel is the only phase after the nucleation; pyroxene is the major phase after the crystallisation. The results of this study have highlighted that a small percentage of Cr₂O₃ strongly affects the spinel formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallisation of high iron content glasses. ©     

Effect of steam on the acid strength of H3PW12O40/SiO2 · nH2O and its application in skeletal isomerization of n-butane

The effect of steam on the acid strength of H₃PW₁₂O₄₀ (HPW)/SiO₂ · nH₂O was determined by the Hammett indicators. When the steam content in N₂ was 1.6%, the acidity (H₀ > −13.7) of HPW/SiO₂ · nH₂O could be kept for over 10 h at 300 °C, but for only 2 h when steam was lacking. When it was used as a catalyst for skeletal isomerization of n-butane to isobutane at 300 °C, the HPW/SiO₂ · nH₂O showed stability in the presence of steam (1.6% in feed) better than that without steam, due to a suppression of the loss of crystalline water.     

Multiple functions of amines in the synthesis of anionic,cationic, and neutral indium oxalates

Three new indium oxalates, formulated as H₃dpta·In(C₂O₄)(H₂O)₃·2SO₄ (1), In(qd)(C₂O₄)_1.5·1.5H₂O (2), and H₂bpp·In₂(C₂O₄)₄ (3) in which dpta = dipropylenetriamine, qd = quinoxaline-2,3(1H,4H)-dione, and bpp = 1,3-bis(4-piperidyl)propane, were prepared in the presence of different amines. These compounds have cationic, neutral, and anionic frameworks, respectively. Topological analyses reveal that compound 2 has an hcb net, while compound 3 has a dia net. The photoluminescent property of compound 2 was also investigated.     

Facile synthesis of metal-doped Ni-Zn ferrite from treated Zn-containing electric arc furnace dust

Metal-doped Ni-Zn ferrite with a spinel structure was directly synthesized from treated zinc-containing electric arc furnace dust (Zn-containing EAFD) by solid state reaction method, realizing the transformation of solid waste to high value-added material. First, NiCl₂·6H₂O was added to the treated Zn-containing EAFD before calcination. Then, the effects of the mass ratio of treated Zn-containing EAFD to NiCl₂·6H₂O (R_TZE/N, g g⁻¹) and the calcination temperature on the synthesis and magnetic properties of as-synthesized samples were systematically investigated by X-ray diffraction, Raman spectroscopy and physical property measurement. It was found that R_TZE/N and calcination temperature significantly influenced the synthesis of single-phase spinel ferrite and their magnetic properties. Pure metal-doped Ni-Zn ferrite, exhibiting good magnetic properties of higher saturation magnetization (Ms, 60.5 emu g⁻¹) and lower coercivity (Hc, 49.8 Oe), was obtained when the calcination temperature was controlled at 1100 °C for 2 h with a R_TZE/N of 1:0.9.     

Fracture toughness,strength and creep of transparent ceramics at high temperature

Fracture toughness, four-point bending strength of transparent spinel, Y₂O₃ and YAG ceramics in function of temperature (from room temperature up to 1500° C) were measured. Creep resistance at 1500–1550° C was studied too. Grain size distribution was determined on polished and etched surfaces of samples. Fracture surfaces after tests were examined by scanning electron microscopy. The obtained results showed that: in the case of spinel ceramics fracture toughness and strength decreased from 20 to 800° C, increased from 800 to 1200° C and decreased at higher temperature; in the case of Y₂O₃ ceramics they increased from 400 to 800° C, and next kept constant up to 1500° C; in the case of YAG ceramics they kept constant from 20 to 1200° C and then decreased. The creep strain rate was measured for spinel and YAG but not for Y₂O₃ ceramics which appeared creep resistant. The hypotheses concerning toughening and creep mechanisms were proposed.     

Mullite interaction with bismuth oxide from minerals and sol–gel processes

Mullite compounds with bismuth oxide in the SiO₂–Al₂O₃–Bi₂O₃ ternary system were synthesized from TEOS (C₂H₅O)₄Si, aluminum nitrate Al(NO₃)₃·9H₂O and bismuth nitrate Bi(NO₃)₃. Thermal and structural transformations were studied at temperatures ranging from 1000 to 1400 °C. The coexistence of Al₄Bi₂O₉ and Bi₄Si₃O₁₂ phases at temperatures up to 1000 °C was observed in compositions containing 5–31 mol% Bi₂O₃. Mullite is observed at temperature higher than 1000 °C in composition not exceeding 5 mol% of Bi₂O₃. Corundum coexist with a liquid above 1000 °C in all compositions containing more than 5 mol% Bi₂O₃. The liquid temperature is slightly above 1000 °C for all compositions. A tentative pseudo-binary diagram mullite-Bi₂O₃ is proposed. A similar system was studied with silico-aluminate compositions containing kaolinite and muscovite minerals. The occurrence of a liquid when Bi₂O₃ is added highly favors the mullite growth at temperature below 1200 °C. It is favored by local concentrations at interfaces of a transient liquid phase, which enhance the mobility of species.     

Hydrothermal synthesis of dumbbell-shaped ZnO microstructures

Dumbbell-shaped ZnO microstructures have been successfully synthesized by a facile hydrothermal method using only Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials at 150 °C for 10 h. The results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the prepared ZnO samples exhibit dumbbell-shaped morphology and hexagonal wurtzite structure. The length of ZnO dumbbells is about 5–20 μm, the diameters of the two ends and the middle part are about 1–5 μm and 0.5–3 μm, respectively. The dumbbell-shaped ZnO microstructures may be formed by self-assembly of ZnO nanorods with 1–5 μm in length and 100–200 nm in diameter. The photoluminescence (PL) spectrum of dumbbell-shaped ZnO microstructures at room temperature shows three emission peaks at about 362, 384 and 485 nm.     

Synthesis,structure and magnetic properties of spinel ferrite (Ni,Cu, Co)Fe2O4 from low nickel matte

Spinel ferrite (Ni, Cu, Co)Fe₂O₄ was synthesized from the low nickel matte by using a co-precipitation-calcination method for the first time. The influences of the added amount of NiCl₂·6H₂O, calcination temperature and time on the structure and magnetic properties of the as-prepared ferrites were studied in detail by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy, and Vibrating sample magnetometer (VSM). It is indicated that pure (Ni, Cu, Co)Fe₂O₄ with cubic phase could be obtained under the experimental conditions (NiCl₂·6H₂O added amount of 3.0: 100 g mL⁻¹, calcination temperature from 800 to 1000 °C and calcination time from 1 to 3 h). With increasing calcination temperature and time, saturation magnetization (M_S) of the synthesized (Ni, Cu, Co)Fe₂O₄ increased and the coercivity (H_C) decreased. Under the optimum conditions (i.e. NiCl₂·6H₂O added amount of 3.0: 100 g mL⁻¹, 1000 °C, 3 h), the M_S and H_C values of the product were approximately 46.1 emu g⁻¹ and 51.0 Oe, respectively, which were competitive to those of other nickel ferrites synthesized from pure chemical reagents. This method explores a novel pathway for efficient and comprehensive utilization of the low nickel matte.     

Crystallisation of amorphous spray-dried precursors in the Al2O3–SiO2 system

The crystallisation of amorphous precursors has been studied in the whole range of composition in the Al₂O₃–SiO₂ system. The amorphous precursors have been obtained by hydrolysing TEOS directly in a diluted aqueous solution of aluminium nitrate, spray drying the clear solution and heating the resulting powder. Up to 70 mol % Al₂O₃, only mullite crystallises around 980–1000 °C; between 70 and 80 mol % Al₂O₃ mullite and spinel crystallise together; and for more than 80 mol % Al₂O₃ only spinel is formed. In the 70–80 mol % Al₂O₃ range of composition, when both mullite and spinel crystallise, low heating favours the crystallisation of mullite and it is nearly possible to crystallise only mullite from a 75 mol % Al₂O₃ sample. By rapid heating it is also possible to crystallise only spinel from the same 75 mol % Al₂O₃ precursor. The enthalpy and the activation energy for crystallisation are maximum for 60–80 mol % Al₂O₃. Heating the samples up to 1700 °C for 1 h, the phase equilibrium is not reached, particularly when both mullite and spinel crystallise together, and θ-Al₂O₃ is still present.