Corundum Filler Research Articles

Development of a Porous Catalytic Converter for Dehydrogenation of Cumene to α-Methylstyrene

A porous catalytically active membrane based on α-Al2O3 was synthesized. Powdered additives of the eutectic composition of magnesium oxide and silicon carbide were added to the initial corundum filler to synthesize a membrane framework with high open porosity and physical and mechanical characteristics that was pressed at 40 – 70 MPa followed by sintering in process combustion mode. Additives of Re2O7 andWO2 were added up to 4 mass% to the initial mixture by a simple technological method to impart catalytic properties to the synthesized membrane. Scientific foundations were developed for creating a technology for one-stage production of catalytically active ultraporous membrane converters effective for dehydrogenation of cumene to α-methylstyrene.

Development of a porous catalytic converter for the dehydrogenation of cumene to α-methylstyrene

A porous catalytically active membrane based on α-Al2O3 has been synthesized. Powdered additives of the eutectic composition of magnesium oxide and silicon carbide were introduced with the initial corundum filler to synthesize the membrane frame with high open porosity and physical and mechanical characteristics. Then, pressing was carried out at a pressure of 40 to 70 MPa, followed by sintering in the process combustion mode. Additives Re2O7 and WO3 up to 4 wt. % was introduced into the initial mixture by a simple technological method to impart catalytic properties to the synthesized membrane. The scientific foundations have been developed for creating a technology for one-stage production of catalytically active ultraporous membrane converters effective for the processes of cumene dehydrogenation to α-methylstyrene.

Graphenated Ceramic Particles as Functional Fillers for Nonisocyanate Polyhydroxyurethane Composites

AbstractGraphenation of corundum and silicon carbide filler particles simultaneously improves mechanical properties and electrical conductivity of nonisocyanate polyhydroxyurethanes (NIPU) composites prepared by amine cure of polyfunctional cyclic carbonates. Typically, the ceramic fillers coated with either glucose, polydopamine, or graphite oxide (GO) are thermolyzed to produce an ultrathin graphene shell around the ceramic core, as verified by transmission electron microscopy. As compared to a blend of corundum particles with the thermally reduced graphite oxide (TRGO) nanofiller, graphenation of corundum with GO at a similar total carbon content significantly improves the Young’s modulus (7000 MPa, +184%) of trimethylolpropane glycidylether carbonate (TMPGC) cured with diethylenetriamine (DETA). Moreover, up to 30 wt% of the graphenated corundum filler is uniformly dispersed, whereas a few percent of neat TRGO account for intolerable high viscosity. Furthermore, NIPU composites containing graphenated ceramic fillers exhibit electrical conductivities of up 2.58 × 10−5 S m−1 well below the percolation threshold of neat TRGO in the same NIPU matrix. Hence, the graphenation of inorganic particles represents a facile and universal synthetic route toward tailoring functional fillers and combines the two worlds of functionalized graphene and inorganic fillers in an economic way by eliminating the tedious syntheses and handling typical for graphene nanofillers.

Influence of the Thickness of a Polymer Shell Applied to Surfaces of Submicron Filler Particles on the Properties of Polymer Compositions

The results of studies into the influence of the thickness of a polystyrene shell applied to surfaces of dispersed corundum (Al2O3) filler particles on the structure and mechanical properties of the composition of an acrylonitrile butadiene styrene plastic are presented. It is shown that the mechanical properties of the composition depend at least on two factors: the interaction between shell molecules and the polymer matrix, and the ratio of shell thickness to the average size of submicron particles of the filler. The change in the mechanical properties of the composition is explained by the decreasing mobility of polymer macromolecules near the encapsulated filler particles due to the increasing adhesion of macromolecules to the polymer shell. It was shown experimentally that the Martens hardness, elastic modulus, tensile strength, and rupture strain can be changed in some range by varying the thickness of the polymer shell on the surfaces of corundum particles.

Study of the Influence of Refractories Structure on the Thermomechanical Properties of Tunnel Kiln Equipment Lining

A study of the influence of refractories’ structure on the thermomechanical properties of the lining of the equipment of tunnel kilns has been carried out. The lining of kiln trolleys is subjected to a mechanical stress distributed evenly over the entire area and the most dangerous to brittle materials, as well as to tensile thermal stresses. The magnitude of the tensile thermal stress depends on the material and the structure of the lining. The mechanisms of destruction of products made of fireclay and liquid concrete have been studied. Mineralogical and petrographic analysis of fireclay refractories have been used, as trolley lining has established metasomatic interaction of the lining with the vapor-gas component of the kiln, as well as with the metal of the trolleys. Monolithic products, made of low-cement concrete with corundum filler, are characterized by high strength and resistance to abrasion. The total value of compression and thermal expansion stresses for them is 3.08 MPa, which is half the value of those of fireclay. When conducting the research to optimize the composition of trolley lining, a technology for manufacturing two-layer concrete blocks, combining the advantages of compositions, based on corundum and fireclay, has been developed. The chemical and granulometric composition of fireclay-based concrete in the lower thermal insulation layer and electrocorundum-based concrete in the upper reinforcing layer were selected in such a way, as to ensure similar values of linear thermal expansion coefficients and prevent possible destruction along the boundary between the layers during the operation.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 9. Physicotechnical Properties of Porous Corundum Granules and Fillers Based on Them1

Results are provided for a study of the strength properties of both individual fractions and also mixtures based upon them. It is established that in order to reduce filler electrical conductivity there should be a reduction in granule diameter or creation of denser polydispersed compositions. Introduction into a charge composition of corundum filler with a size of 60 μm increases granule thermal stability.

Effect of Pyrocatechin on the Properties of Cement-Free Refractory Concrete Mixtures Based on Silica-Containing Colloidal Binders

It is shown that the pyrocatechin (1, 2-dihydrohybezene) in an amount of 0.005 – 0.010 wt.% solid components has a pronounced plasticizing effect on mixtures of polyfraction corundum filler and colloidal SiO2-solution binder, stabilized with ammonia ions, intended for preparing cement-free refractory concrete. Self-consolidating refractory compositions are prepared with minimum water content.

Permeable Ceramic with Three-Fraction Electromelted Corundum Filler and Porcelain Binder

Porous permeable materials are prepared by selecting the grain size composition with electromelted corundum filler and porcelain mix PFL-1 binder. Specimens with an improved set of properties are prepared with addition to the composition of 5 wt.% porcelain binder (above 100% filler) after firing at 1450°C. Specimen ultimate strength in bending is 14.6 MPa, open porosity 44%, and gas permeability coefficient 0.85 μm2.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 8. Rational Drying and Firing Regimes for Crude Corundum Granules

Results of studying drying of crude corundum granules confirm the assumption that alumina-foam polystyrene mixture exhibits low sensitivity towards drying, which makes it possible to combine drying and firing in a single heating unit. Since intense liberation of foam polystyrene pyrolysis products and combustion products may lead to crude granule destruction the heating rate should be selected in order that gaseous products manage to diffuse from the material without disrupting structure continuity. A rational firing regime is proposed.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 7. Study of the Possibility of Preparing Hollow Corundum Granules1

The fraction composition of corundum granules is determined mainly by particle size analysis of a foam polystyrene nucleus, mixture moisture content, and granulation parameters. Use of high dynamic compaction loads has an unfavorable effect on product quality. Plate rotation frequency, its inclination angle, and granulation duration are established. The operating sequence for preparing hollow granules based on commercial alumina is established.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 6. Optimization of Plate Granulator Operating Regime

Mathematical planning of an experiment is used in order to reduce the amount of tests making it possible to find a collection of independent variable values determining the field of optimum target parameters: grain size composition of raw material granules, the ultimate strength in compression within a cylinder, and material bulk density after firing.

Corundum Fillers with Variable Sizes and Shapes for Epoxy Nanocomposites as High‐Performance Chemical Anchoring and Bonding Systems

AbstractHerein, the influence of corundum filler types and contents on the morphological, thermal, and mechanical properties of epoxy nanocomposites tailored for applications as chemical anchoring and bonding systems is investigated. Up to 65 wt% corundum particles with aspect ratios (AR) varying between 1 and 70, average particle sizes ranging from 500 nm to 48 µm, and nanoplatelet thickness varying from 40 to 300 nm, are uniformly dispersed in amine‐cured epoxy resins. At both 25 and 50 wt% filler content, the properties of corundum/epoxy composites are far superior to those of the corresponding benchmark epoxy composites containing a conventional filler such as cement, talcum, or sand. The incorporation of corundum nanoplatelets with AR of 50, length of 2 µm, and thickness of 40 nm, significantly improves Young's modulus (3.5–9.8 GPa) and fracture toughness KIc (0.83–1.24 MPa of epoxy nanocomposites at the expense of tensile strength (72–49 MPa). The pull‐out values of the corresponding chemical anchoring systems substantially improve with decreasing sub‐micrometer corundum particle sizes and correlate with tensile strength of the corundum/epoxy nanocomposites, but are much less dependent on corundum particle morphologies, filler aspect ratio, and Young's modulus of the corundum/epoxy composite.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 5. Effect of Molding Mixture Fineness and Moisture Content on Filler Granulation Capacity and Physicotechnical Properties1

It is established that there are three stages in molding mixture pelletization: nucleus formation, granule growth, and mass transfer between them. Addition of a surfactant improves granulation capacity and reduces molding moisture content, and increases raw granule strength. The fineness of the starting material has a significant effect on capillary reaction forces that are fundamental during molding mixture pelletization.

Highly Porous Granulated Corundum filler of Alumina-Foam Polystyrene Mixture. Part 4. Determination of Optimum Mixture Compositions1

A rational mixture composition is selected. The governing index adopted is the prescribed granule bulk density with maximum strength. It is established that object properties are considerably affected by the ratio of the main mixture components, i.e., electromelted corundum, ground technical grade alumina, and foam polystyrene, providing the greatest yield of 5 – 10 and 10 – 20 mmfraction granules.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Part 3. Theoretical Premises of Pelletizing Alumina-Polystyrene Foam Mixtures in a Granulator1

Pelletizing of alumina-foam polystyrene mixtures is determined by presence of physicomechanical and physicochemical bonds. Decisive effects in this process are molecular and capillary forces whose value is determined by the individual properties of granulated material, layer structure, and amount of moisture. The hydrophilic nature of the test system surface and its hydrodynamic tendency towards pelletizing are established.

Highly Porous Granulated Corundum Filler of Alumina-Foam Polystyrene Mixture. Parts 1 and 2

Methods available for preparing porous corundum filler have a number of marked disadvantages: significant complexity, low productivity, high energy content, and narrow fraction composition. The most promising method for preparing porous corundum fillers of three types (hollow, porous, and keramzit type) is granulation of a molding mixture based on foamed bead polystyrene (screenings). By varying granulation parameters of alumina-foam polystyrene it is possible to control end product properties.

Strengthening Binders for Porous Permeable Ceramic with Electromelted Corundum Filler

Strong porous permeable ceramic is studied, prepared by selection of grain size compositions with filler of electromelted corundum grades F600 (100 – 200 μm), F360 (40 – 60 μm), and F120 (10 – 20 μm). The strengthening binders used are very fine corundum powder (~2 μm), alloyed with 0.25 wt.% MgO; a mixture of SiC (particle size 3 – 4 μm) and MgO (particle size 1 – 2 μm) in a ratio of 2:1. Specimens in the form of bars 60 × 15 × 5.5 mm are prepared by uniaxial semidry compaction under a pressure of 50 MPa (for single fraction compositions) and 25 MPa (for three-fraction compositions). Specimens are fired in air at temperatures from 1350 to 1550°C. Specimen open porosity varies from 28 to 43%, and ultimate strength in bending from 1 to 36 MPa. The best strength is obtained using a binder in the system SiC–MgO (5 wt.% binder above 100% of filler, σben = 36 MPa, and open porosity is 30%).

Heat-Resistant Corundum Concrete Reinforced with Aluminum Oxide Fibers Synthesized Within a Matrix During Firing. Part 3. Choice of Rational Components for Preparing Corundum Concrete1

It is noted that methods for choosing the composition of refractories and structural concretes differ significantly. In choosing refractory concrete composition physicochemical processes occurring during hardening and sintering should be considered. It is established that the most complete requirements are satisfied by concretes based on high-alumina cement and corundum filler.

Formation of Material Prescribed Phase Composition from Refractory Filler Silica Powder Modified with Alkoxide and Sol-Gel Composite

Creation of ceramics and refractories with improved physicomechanical properties is possible with use of nanomaterials in their technology. Introduction of SiC nanoparticles into a ceramic material charge by using modified filler powders is proposed. Fillers modified with tetraethoxysilane during grinding leads to powder crystal structure breakdown and SiC mechanochemical synthesis. The amount of β-SiC synthesized in this way depends on the amount of modifying additive. Results are provided for modified filler phase composition before and after heat treatment at 1000°C, and mechanochemically synthesized SiC thermal stability is established. It is shown that sintering of modified electro-corundum worsens with an increase in amount of synthesized silicon carbide nanoparticles. The difference is demonstrated in phase composition formation with heat treatment of a mixture of modified and normal finely ground electrocorundum with a sol-gel binder and firing up to 1600°C. Silicon carbide nanoparticle synthesis does not exceed 3 – 7 % in both cases. Recommendations are given for use of corundum filler with a different amount of modifying additive.

Materials based on highly concentrated ceramic binding suspensions (HCBS). Corundum and corundum-mullite ceramic castables based on plasticized hcbs of bauxite

HCBS of roasted Chinese bauxite, plasticized with additives of refractory clay, and corundum or bauxite filler are used for the production of pressed ceramic castables of corundum and mullite-corundum compositions with 93–95% and 80–85% A12,O3, respectively. The optimum clay additive does not exceed 1–2%. The ceramic castables have a porosity of 15–18% and an ultimate compressive strength of 100–200 MPa after treatment at 1200–1300°C. As compared to traditional corundum refractories they are characterized by a finer capillary structure and a higher mechanical strength attained at a diminished (by a factor of 2–3) pressing pressure and a lower (by 400- 500°C) firing temperature.