A lightweight CNWs-SiO2/3Al2O3·2SiO2 porous ceramic with excellent microwave absorption and thermal insulation properties

To obtain excellent microwave absorption and thermal insulation properties, carbon nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramics (CNWs-SiO₂/3Al₂O₃·2SiO₂) were fabricated by catalytic chemical vapor deposition (CCVD) using C₂H₄ as the carbon source. The content of CNWs in SiO₂/3Al₂O₃·2SiO₂ porous ceramics can be adjusted by controlling the concentration of the catalyst precursor and the CCVD time. A higher concentration of catalyst precursor and longer CCVD time are beneficial for the growth of CNWs and for improving the electromagnetic wave (EMW) absorption properties of CNWs-SiO₂/3Al₂O₃·2SiO₂. However, CNWs are harmful to impendence matching due to the strong reflection and weak absorption when the content exceeds the threshold (30 wt%) in SiO₂/3Al₂O₃·2SiO₂ porous ceramics. CNWs are also harmful to the thermal insulation properties due to their high thermal conductivity. The results show that CNWs-SiO₂/3Al₂O₃·2SiO₂ can attain good EMW absorption and thermal insulation properties if the content of CNWs is 30 wt% when the concentration of the catalyst precursor is 3 wt% and the CCVD time is 15 min. The effective absorption bandwidth (EAB) can cover from 8.2 to 12.4 GHz (the whole X-band), and the minimum reflection coefficient (RC_min) is -31 dB at 9.1 GHz. The temperature gradient is 218 °C, which can satisfy the design requirement. Thus, the dielectric and thermal insulation properties are designable for CNWs reinforced SiO₂/3Al₂O₃·2SiO₂ porous ceramics to obtain excellent EMW absorption and thermal insulation properties.     

Dissolution mechanism of alumina inclusions into CaO–SiO2–Al2O3–FetO–MgO slag via a converter tapping process

Reducing the amount of inclusions during the steelmaking process as much as possible and much earlier plays a vital role in improving the quality of steel products. To reveal the dissolution mechanism of inclusions in slag during the converter tapping process, some comparison experiments were conducted by adding isolated spherical alumina balls as inclusions in CaO–SiO₂–Al₂O₃–Fe_tO–MgO slag, and Fe_tO content up to 10% was contained in slag. The results showed that the dissolution rate of alumina balls in the slag was mainly affected by the diffusion of Al₂O₃, and the diffusion coefficients of Al₂O₃ were 4.2 × 10^–11, 7.5 × 10^–11, and 1.5 × 10^–10 m²/s at 1500℃, 1550℃, and 1600℃, respectively. In addition, the upgraded diffusion-distance-controlled dissolution model (DDD-Model), in which Fe_tO content was introduced and applied in the study. The results illustrated that the Al₂O₃ inclusion apparent dissolution rate was improved by a high Fe_tO content, increasing CaO/SiO₂ and raising the temperature as soon as possible at the early stage of the converter tapping process. It is not necessary to increase the Fe_tO content in the slag to enhance the dissolution rate of the Al₂O₃ inclusion at the last tapping stage. The predicted complete dissolution time of spherical Al₂O₃ inclusions with 1000 µm in diameter based on the upgraded DDD-Model was approximately 1796 s during the actual converter tapping process.     

Selective laser sintering of porous Al2O3-based ceramics using both Al2O3 and SiO2 poly-hollow microspheres as raw materials

Porous Al₂O₃-based ceramics with improved mechanical strength and different pore size were fabricated using Al₂O₃ and SiO₂ poly-hollow microspheres (PHMs) as raw materials by selective laser sintering (SLS). The effects of different contents of SiO₂ PHMs on phase compositions, microstructures, mechanical properties and pore size distribution of the prepared ceramics were investigated. It is found that moderate content of SiO₂ PHMs (≤30 wt%) could work as a sintering additive, which could enhance the bonding necks between Al₂O₃ PHMs. When the content of SiO₂ PHMs increased from 0 wt% to 30 wt%, the compressive strength of Al₂O₃-based ceramics increased from 0.3 MPa to 4.0 MPa, and the porosity decreased from 77.0% to 65.0% with open pore size decreased from 52.0 μm to 38.3 μm. However, SiO₂ PHMs could provide pores by keeping its integrity when the content of SiO₂ PHMs increased to 40 wt%, which could result in the porosity increasing to 66.8% and pore size decreasing to 30.1 μm. Selective laser sintering of different kinds of ceramic PHMs is a feasible method to fabricate porous ceramics with complex shape, controllable pore size and improved properties.     

Alkali-activated waste ceramics: Importance of precursor particle size distribution

The waste ceramics belongs to wide range of aluminosilicate materials which can be alkaline-activated to geopolymer cement – possible “green” alternative to conventional Portland cement. The studied ceramic material is generated during the size adjustment of ceramic building blocks by means of grinding. It means that most of the material is very fine, but it contains also some larger shards. This ceramic powder was used as geopolymer precursor “as received” and after removal of particles retained on 1, 0.5 and 0.125 mm sieves. These four types of precursor were activated by sodium silicate (SiO₂/Na₂O = 1) solution. The prepared mortars were tested for strength, basic physical properties, transport parameters and characterized by help of XRD and thermal analysis. It was found that the best mechanical performance provided the precursor after removal of particles retained on 0.5 mm sieve thanks to the highest geopolymerization rate. The presence of coarser particles in precursor gave rise to porosity, what consequently influenced transport parameter of geopolymers towards the lower thermal conductivity and faster moisture transport.     

Clay reactivity: Production of alkali activated cements

This study has assessed the suitability of dehydroxylated (5 h at 750 °C) red, white and ball clays for the use as prime materials in the production of alkaline cements. The analytical methodology applied to quantify their potentially reactive phases included selective chemical attack, which was also used in conjunction with subsequent ICP analysis of the resulting leachate to determine their reactive SiO₂/Al₂O₃ ratios. These results were compared with compressive strength values of the respective pastes activated with an 8-M NaOH solution and cured at 85 °C and 90% RH for 20 h. It was observed that when the reactive phase content was above 50%, the reactive SiO₂/Al₂O₃ ratio in the starting materials had a larger impact than the amount of reactive phase on the developed strength of the cement material. In this context, fly ash was used as the reference material. Finally, to verify the accuracy of the results, a binder consisting of 70 wt.% fly ash and 30 wt.% dehydroxylated clay was activated with an 8-M NaOH solution. The reactivity of this cement was determined by chemical attack with 1:20 HCl (v/v) and the reaction products were characterised by powder X-ray diffraction and ²⁹Si MAS NMR spectroscopy.     

Synthesis of ZSM-5 zeolite and silicalite from rice husk ash

Local rice husk was precleaned and properly heat treated to produce high purity amorphous SiO₂ for use in the synthesis of ZSM-5 zeolite and silicalite by hydrothermal treatment (150 °C) of the precursor gels (pH 11) under autogenous pressure in a short reaction time (4–24 h). A wide range of SiO₂/Al₂O₃ molar ratios (30–2075) and a small template content were employed to fully exploit the potential of rice husk ash (RHA). The mineralogical phases, morphology, specific surface area and pore volume of the synthesized products were investigated by XRD, FT-IR, SEM and BET analyses, respectively. Under the employed conditions, it was found that the gels with a low range of SiO₂/Al₂O₃ molar ratios (<80) produced an amorphous phase to poorly crystalline ZSM-5 zeolite; those with a medium range (80–200) favored well crystalline ZSM-5 zeolite production with a large surface area; whilst those with a high range of SiO₂/Al₂O₃ molar ratios (>200) yielded silicalite. The increase in Na₂O content, which was derived from the addition of NaAlO₂ to attain the desired SiO₂/Al₂O₃ molar ratio of the gel, did not significantly enhance the crystallization rate, crystallinity, or yield of products. On the contrary, these properties were greatly affected by the increase in the SiO₂/Al₂O₃ molar ratio.     

Enhanced electromagnetic wave absorption properties of a novel SiC nanowires reinforced SiO2/3Al2O3·2SiO2 porous ceramic

To realize the broad-bandwidth and high-efficiency absorption characteristics, a novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ porous ceramic was successfully fabricated by method of precursor infiltration pyrolysis (PIP). Polycarbosilane (PCS) and ferrocene (Fe(C₅H₅)₂) were used as the precursor and catalyst to incorporate SiC nanowires into the SiO₂/3Al₂O₃·2SiO₂ porous ceramic. The curvy SiC nanowires formed three-dimensional (3D) networks with a proper nanometer heterostructure, thereby consuming the microwave energies. The influence of SiC nanowires contents on the microwave absorption properties was investigated. The results indicate that the SiC nanowires contents can be tuned by controlling the PIP cycles, thereby modifying the dielectric properties of as-prepared composite ceramics. The dielectric and electromagnetic wave absorption performances are gradually enhanced with an increasing of SiC nanowires contents. The SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic exhibits excellent electromagnetic wave absorption abilities when the SiC nanowires content is 23.9% (PIP5). The minimum reflection coefficient (RC_min) of the composite ceramic is −30 dB at 10.0 GHz, corresponding to more than 99.9% of the electromagnetic wave consumption. The effective absorption bandwidth (EAB) can cover the frequency ranges of 8.2–12.4 GHz (the entire X-band) at the thickness of 5.0 mm. In general, the novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic can be considered as a promising electromagnetic wave absorbing material.     

Dissolution behavior of SiO2 in the molten blast furnace slags

The kinetics of SiO₂ dissolving in the molten blast furnace slags at 1743-1803 K was studied using a High Temperature Confocal Scanning Laser Microscopy (HT-CSLM), and then the effects of temperature, MgO and Al₂O₃ on the SiO₂ dissolution were clarified in this study. The experiment results showed that the dissolution process is controlled by the solute diffusion in the slag. The SiO₂ dissolution rate could be accelerated by increasing the temperature. Moreover, the SiO₂ dissolution rate is the fastest in the slag with 11.0 pct MgO when the MgO varies between 7.0 and 13.0 pct. The SiO₂ dissolution rate is the fastest in the slag with 18.0 pct Al₂O₃ when the Al₂O₃ varies between 14.0 and 20.0 pct. The effects of temperature, MgO and Al₂O₃ on the SiO₂ dissolution rate could be indicated by a simple expression (c_sat−c_b)/η that a larger of (c_sat−c_b)/η is associated with the faster SiO₂ dissolution rate, where (c_sat−c_b) is the difference between the concentration of SiO₂ in the saturated slag and in the bulk of slag, and η is the slag viscosity.     

Influence of precursor materials on the fresh state and thermo-chemo-mechanical properties of sodium-based geopolymers

Aluminosilicates are the base precursors that combined with alkali solutions manufacture geopolymers. A wide variability of aluminosilicate precursors can be found in the market worldwide, which may be an issue when proposing single designs. The goal of this study is to compare the use of different precursors in the hardening mechanisms of geopolymers. For this, two types of metakaolin (a low (MK_LR) and a high-reactive (MK_HR) one), and partial replacements made with fly-ash (FA) and blast furnace slag (BFS) are used in SiO₂/Al₂O₃ = 4.00, Na₂O/SiO₂ = 0.25, and H₂O/Na₂O = 11.00 fixed design ratios. Fresh state (viscosity and squeeze flow), transient state (Vicat needle and sonic strength), and hardening measurements (compression tests under room and high temperature conditions), were used, supported by chemical analysis (calorimetry and SAM/HCl extraction) and materials characterization (particle analysis, density, BET and XRD). In general, the reactivity, chemical composition, and morphology of each precursor, as well as solid/liquid portions of each mix were major factors influencing the hardening process. The use of MK_LR achieved shorter setting times and enhanced viscosities due to its particles larger surface area, solid/liquid ratios, and unreactive portions, reaching the highest values of strength and diminished thermomechanical performance. Partial substitutions made with FA and BFS increased the amorphous part of the binder, increasing also its flowability, setting time, and its stability to thermal exposure. The geopolymer made with MK_HR presented the lowest viscosity and longer setting time due to its almost constant dissolution rate, attributed to its enhanced reactivity from highly amorphous parts and diminished solid-to-liquid ratio mixture. Therefore, the use of varied aluminosilicates significantly modifies the materials properties, leading to different potential applications that should be considered when designing geopolymers.     

Application of an improved testing device for the study of alumina dissolution in silicate slag

This study entailed a dissolution study of alumina fine ceramics in a CaO–Al₂O₃–SiO₂–MgO silicate slag system with a CaO/SiO₂ weight ratio of 0.65. Finger-test experiments with several corrosion steps were carried out in a contemporary continuous wear testing device at 1450, 1500, and 1550 °C with 200 rpm. The corroded sample profiles were measured using a high-resolution laser scanner, and the processed measurement data were used to extract the dissolution parameters (i.e. corroded volume, surface area, mean radius, tip radius and immersion length). The diffusivity determination method using Sherwood relations was developed for the dynamic finger-test setup. The diffusivities for all corrosion steps were determined from these dissolution parameters, and those obtained from the Sherwood relations were compared with the ones received by a simulation approach that includes deviations from the cylindrical shape. The results obtained using Sherwood relations are sufficiently accurate in several cases.     

Investigation of high-temperature reactions within the ZrSiO4–Al2O3 system

Solid state reactions between ZrSiO₄ and αAl₂O₃ in powders of stoichiometric composition 3Al₂O₃·2SiO₂ were studied by X-ray diffraction and electron scanning microscopy with energy dispersive X-ray analysis (SEM + EDX). Data were obtained at temperature ranging from 1400 °C to 1600 °C for a period of time ranging from 30 min to 60 h. The results indicate that ZrSiO₄ and αAl₂O₃ react and form crystalline ZrO₂, crystalline mullite (almost 3Al₂O₃·2SiO₂ composition) and non-crystalline silicon–alumina phase (pre-mullite). At the temperature of 1600 °C the fastest stage of reaction is dissociation of ZrSiO₄. Obtained results show that dissociation of zircon is a first-order reaction. The dissolution of Al₂O₃ particles and diffusion of Al into non-crystalline phase seem to be the slowest step of the reaction.     

Fracture behavior of Al2O3–SiO2 castables by the wedge splitting test and digital image correlation technique

The fracture mechanisms are helpful for the optimization and design of toughness and microstructure of refractories. Fracture behavior of ultra-low cement bonded Al₂O₃–SiO₂ castables was researched using the wedge splitting test coupled with digital image correlation technique (WST-DIC). Flexibility of Al₂O₃–SiO₂ castables is improved by introducing andalusite aggregates into the castables. The characteristic length L_CH, a parameter used to assess flexiblity of materials, was observed to reach 287.2 mm in andalusite-containing Al₂O₃–SiO₂ castables, more than 5 times that of reference castables. Microcracks toughening is the main toughening mechanisms for flexibility improvement of the Al₂O₃–SiO₂ castables containing andalusite. Microcrack network in the Al₂O₃–SiO₂ castables could be designed by exploiting the volume expansion caused by mullitization of andalusite and the coefficient of thermal expansion (CTE) mismatch between the andalusite aggregate and the matrix. Unlike andalusite-free castables, castables containing andalusite possess a distinct fracture process zone (FPZ), the crack branching and deflection can be observed around the main crack during the fracture process, which leads to the prolong of the crack propagation path, the increase of the dissipation energy during the fracture, and the enhancement of resistance to crack propagation.     

Influence of polymer on cement hydration in SBR-modified cement pastes

The influence of styrene-butadiene rubber (SBR) latex on cement hydrates Ca(OH)₂, ettringite, C₄AH₁₃ and C-S-H gel and the degree of cement hydration is studied by means of several measure methods. The results of DSC and XRD show that the Ca(OH)₂ content in wet-cured SBR-modified cement pastes increases with polymer-cement ratio (P/C) and reaches a maximum when P/C is 5%, 10% and 10% for the pastes hydrated for 3 d, 7 d and 28 d, respectively. With wet cure, appropriate addition of SBR promotes the hydration of cement, while the effect of SBR on the content of Ca(OH)₂ and the degree of cement hydration is not remarkable in mixed-cured SBR-modified cement pastes. XRD results illustrate that SBR accelerates the reaction of calcium aluminate with gypsum, and thus enhances the formation and stability of the ettringite and inhibits the formation of C₄AH₁₃. The structure of aluminum-oxide and silicon-oxide polyhedron is characterized by ²⁷Al and ²⁹Si solid state NMR spectrum method, which shows that tetrahedron and octahedron are the main forms of aluminum-oxide polyhedrons in SBR-modified cement pastes. There are only [SiO₄]⁴⁻ tetrahedron monomer and dimer in the modified pastes hydrated for 3 d, but there appears three-tetrahedron polymer in the modified pastes hydrated for 28 d. The effect of low SBR dosage on the structure of aluminum-oxide and silicon-oxide polyhedron is slight. However, the combination of Al³⁺ with [SiO₄]⁴⁻ is restrained when P/C is above 15%, and the structure of Al³⁺ is changed obviously. Meantime, the polymerization of the [SiO₄]⁴⁻ tetrahedron in C-S-H gel is controlled.     

Compatibility of hydrogarnet,Ca3Al2(SiO4)x(OH)4(3 − x), with sulfate and carbonate-bearing cement phases: 5–85 °C

The stable existence of hydrogarnet in Portland cement compositions cured at temperatures below 55 °C has long been predicted from application of equilibrium thermodynamics. However hydrogarnet is not often reported in hydrated commercial Portland cements. The substitutions (SO₄–CO₃–OH) in AFm have previously been shown to stabilise AFm to higher temperatures and raise the temperature at which AFm converts to Si-free hydrogarnet, C₃AH₆. But unanswered question remains about the compatibility of AFm and AFm solid solutions with Si-substituted hydrogarnet, Ca₃Al₂(SiO₄)_x(OH)_4(3 − x). Phase relations of C₃AH₆ and Ca₃Al₂(SiO₄)_x(OH)_4(3 − x) at sulfate and carbonate activities conditioned respectively by (gypsum and SO₄-AFt) and (calcite and CO₃-AFt) have been determined experimentally in the range 5–85 °C. The results confirm the instability of Si-free hydrogarnet with carbonate and sulfate-bearing cement phases, but do indicate that a range of silica-substituted hydrogarnet solid solutions are stable under conditions likely to be encountered in blended cement systems.     

Wettability and interfacial reactions of a low Hf-containing nickel-based superalloy on Al2O3-based,SiO2-based,ZrSiO4, and CoAl2O4 substrates

To understand the wetting behavior and interfacial phenomena between molten superalloys and ceramic materials, the wettability and interfacial reactions of a low Hf-containing Nickel-based superalloy on the Al₂O₃-based, SiO₂-based, ZrSiO₄, and CoAl₂O₄ substrates were studied using the sessile drop method at 1773 K. The wetting angles of the alloy on the Al₂O₃-based, SiO₂-based, ZrSiO₄, and CoAl₂O₄ substrates were 141.4°, 143.5°, 135.7°, and 128.4°, respectively. This indicated that the wettability of the alloy on the Al₂O₃-based substrate was comparable to that on the SiO₂-based substrate, and the wettability of the CoAl₂O₄ system was the best among the four systems. The microstructure characteristics of the interface implied that Hf has a strong tendency to react with ceramic substrates, even at low contents. Additionally, the interfacial reactions transformed the Al₂O₃-based, SiO₂-based, ZrSiO₄, and CoAl₂O₄ ceramic substrates into (Al₂O₃ + HfO₂), (Al₂O₃ + HfO₂), (Al₂O₃ + HfO₂ + ZrO₂), and (Al₂O₃ + HfO₂ + Co), respectively, which were in contact with the alloys. The experimental results demonstrated that the wettability of the system was governed by the properties of the reaction products.     

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics was studied by nonisothermal differential scanning calorimetry (DSC). Different amorphous materials were produced by plasma spraying of near-eutectic Al₂O₃–ZrO₂–SiO₂ mixtures. Phase composition and microstructure of the amorphous materials and nanocrystalline products were analyzed. All of the investigated materials show an exothermic peak between 940 and 990 °C in the DSC experiments. The activation energies calculated from DSC traces decrease with increasing SiO₂ concentration. Values of the Avrami coefficients together with results of the microstructural observations indicate that tetragonal zirconia crystallization from materials containing more than 10 wt.% SiO₂ proceeds by a diffusion-controlled mechanism with nucleation occurring predominantly at the beginning of the process. In contrast, material with almost no SiO₂ exhibited a value of the Avrami exponent consistent with the crystal growth governed by processes at the phase boundary.     

In situ observation of the direct and indirect dissolution of MgO particles in CaO–Al2O3–SiO2-based slags

The dissolution of magnesia particles in synthetic CaO–Al₂O₃–SiO₂ (CAS)-based slags with and without MgO addition was investigated in situ with a confocal scanning laser microscope (CSLM) at 1500 and 1600 °C. The dissolution process was recorded. The effects of slag composition and temperature on the dissolution process and the time dependency of the MgO particle size during dissolution were obtained. Increasing the temperature increases the dissolution rate. However, MgO addition to the slag retards the dissolution rate significantly. The rate limiting steps are discussed. It is shown that boundary layer diffusion is responsible for the dissolution. By combining in situ observations with post mortem analyses, thermodynamic calculations of local and global equilibrium, and kinetic considerations, the conditions under which MgAl₂O₄ spinel can be formed at the particle–slag interface are clarified.     

Nanoplastic removal function and the mechanical nature of colloidal silica slurry polishing

The nanomechanical deformations on a broad range of optical material surfaces (single crystals of Al₂O₃ [sapphire], SiC, Y₃Al₅O₁₂ [YAG], CaF₂, and LiB₃O₅ [LBO]; a SiO₂–Al₂O₃–P₂O₅–Li₂O glass-ceramics [Zerodur]; and glasses of SiO₂:TiO₂ [ULE], SiO₂ [fused silica], and P₂O₅–Al₂O₃–K₂O–BaO [Phosphate]) near the elastic-plastic load boundary have been measured by nanoindentation and nanoscratching to mimic the nanoplastic removal caused by a single slurry particle during polishing. Nanoindenation in air was performed to determine the workpiece hardness at various loads using a commercial nanoindenter with a Berkovich tip. Similarly, an atomic force microscope (AFM) with a stiff diamond coated tip (150 nm radius) was used to produce nanoplastic scratches in air and aqueous environments over a range of applied loads (~20-170 μN). The resulting nanoplastic deformation of the nanoscratches were used to calculate the removal function (i.e., depth per pass) which ranged from 0.18 to 3.6 nm per pass for these materials. A linear correlation between the nanoplastic removal function and the polishing rate (using a fixed polishing process with colloidal silica slurry on a polyurethane pad) of these materials was observed implying that: (a) the polishing mechanism using colloidal silica slurry can be dominated by mechanical rather than chemical interactions; and (b) the nanoplastic removal function, as opposed to interface particle interactions, is the controlling factor for the polishing material removal rate. Furthermore, this correlation is consistent with the Ensemble Hertzian Multi-Gap (EHMG) microscopic material removal rate model described previously. The nanoplastic removal depth was also found to correlate to the measured nanoindentation hardness (H₁) of the optical material, scaling as H₁^−3.5. Two-dimensional (2D) finite element analysis simulations of nanoindentation showed a similar nonlinear dependence of plastic deformation with the workpiece material hardness. The findings of this study are used to determine an effective Preston coefficient for the material removal rate expression and enhance the predictive nature of the nanoplastic polishing rate for various materials utilizing their material properties.     

Electrospinning preparation and microstructure characterization of homogeneous diphasic mullite ceramic nanofibers

In this work, diphasic mullite (3Al₂O₃·2SiO₂) nanofibers with good homogeneity were prepared by electrospinning method. Aluminum nitrate (AN) and aluminum isopropoxide (AIP) were used as alumina sources, commercial colloidal silica as silica source, and polyvinyl alcohol (PVA) as polymer additive. Precursor nanofibers with continuous and uniform structures were acquired at mass ratio of PVA to precursor sol from 0.06 to 0.09. γ-Al₂O₃ phase was obtained at 878 ^°C and mullite phase formed at 1322 ^°C upon heating of the precursor under air atmosphere. Calcined samples suggested mullite as dominant phase at 1300 ^°C and amorphous SiO₂ could even exist at 1400 ^°C. As-prepared nanofibers possessed continuous structures with subequal average diameters at 900–1200 °C. However, such morphological characteristics were lost at temperatures above 1300 ^°C due to rapid growth of crystal grains. Al and Si elements were uniformly distributed in fibers and mixed at nanoscale, confirming homogeneity and diphasic features of nanofibers.     

Selective gas-phase conversion of maleic anhydride to propionic acid on Pt-based catalysts

Pt-based catalysts, supported on Al₂O₃, SiO₂ and SiO₂–Al₂O₃, were prepared by incipient wetness impregnation and tested in the gas phase hydrogenation of maleic anhydride at atmospheric pressure and 240 °C. In these conditions, the hydrogenolytic activity pattern was: Pt/SiO₂ > Pt/Al₂O₃ > Pt/SiO₂–Al₂O₃, which is just the opposite of the support acidity trend. These metal Pt-based catalysts showed high selectivity to propionic acid, which was always higher than 80%. The selectivity pattern to this product was: Pt/Al₂O₃ > Pt/SiO₂ > Pt/SiO₂–Al₂O₃. Both activity and selectivity patterns may be explained on the basis of metal-support interaction and support acidity.