Basic magnesium sulfate whisker in-situ synthesized magnesium-aluminum spinel reinforced magnesium oxide based foamed ceramic filter and preparation method thereof

Abstract

The invention discloses a basic magnesium sulfate whisker in-situ synthesized magnesium-aluminum spinel reinforced magnesium oxide based foamed ceramic filter that can realize sintering at lower temperature and has excellent chemical stability and thermal shock resistance and a preparation method thereof. The preparation method comprises the steps of: (1) by mass percentage, blending 15%-25% of nano-aluminum sol, 0.8%-1.5% of a rheological agent, and the balance magnesium oxide ceramic powder containing basic magnesium sulfate whisker, adding anhydrous ethanol, performing ball-milling and uniform mixing to obtain a ceramic slurry with a solid content of 60%-70%; (2) immersing a polyurethane foam plastic template into the ceramic slurry, extruding the polyurethane foam plastic template by aroller press to remove redundant hung slurry for making a green body, then removing an ethanol solvent in a 40DEG C-50DEG C ventilation room, and drying the green body; and (3) putting the dried green body into a sintering furnace, performing heating to 1350DEG C-1550DEG C for high temperature sintering, and conducting furnace cooling to room temperature, thus obtaining the magnesium oxide basedfoamed ceramic filter.

Description

technical field [0001] The invention relates to a magnesia-based foam ceramic filter and a preparation method thereof, in particular to a magnesia-aluminum spinel-reinforced magnesia-based foam ceramic filter synthesized in situ by basic magnesium sulfate whiskers and a preparation method thereof, belonging to metal materials and metallurgy. The filter prepared by the invention is particularly suitable for filtering and purifying magnesium and its alloy melts, and can also be used for filtering and purifying aluminum and its alloy melts. Background technique [0002] Magnesium is chemically active. During casting and processing, it is very easy to chemically react with oxygen, nitrogen and water vapor. The resulting products remain in the magnesium, affecting the internal quality of the product and deteriorating the performance of the product. According to the types and properties of inclusions in magnesium alloys, inclusions are generally divided into two categories: metal...

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Problems solved by technology

Chinese patent documents CN1011306B (pure magnesia foam ceramic filter and its preparation process), CN101138691A (preparation method of magnesia foam ceramic filter for casting), etc., prepare foam ceramics with pure magnesia as raw material, because MgO has a very high melting point and coefficient of thermal expansion (13.5×10 -6 / °C) is high, therefore, it leads to difficult sintering (sintering temperature is not lower than 0.8 times its melting point) and poor thermal shock resistance, which limits the application and development of MgO foam ceramics

add V 2 o 5 In powder form, MgO will react with V at 1190°C 2 o 5 form an approximate composition of Mg 3 V 2 o 8 The liquid phase promotes sintering and can significantly reduce the sintering temperature of MgO foam ceramics, but V 2 o 5 Harmful to the respiratory system and skin during use, and has strict restrictions on operation

with V 2 o 5 Similarly, cobalt oxide is also a good low-temperature sintering aid, but its application is limited as a highly toxic substance and rare resource

Fluoride is a strong co-solvent and mineralizer commonly used in ceramic industry sintering, Chinese patent documents CN100536986C (magnesia foam ceramic filter), CN1473947A (foam ceramic for magnesium and magnesium alloy melt purification), CN101785944B (for magnesium Fluorite (melting point 1423°C) and magnesium fluoride (melting point 1248°C) are added to the preparation method of magnesium oxide foam ceramic filter for magnesium melt filtration. The solid solution of fluoride not only increases the oxidation of the matrix during the sintering process The lattice of magnesium is distorted, and it is easy to form a low-melting liquid phase, thereby reducing the sintering temperature of magnesia ceramics; however, during the sintering process, F in fluoride combines with Si, Al, Fe, and Ca, and most (in ceramic tiles) About 70% in production) volatilization in gaseous form not only erodes the green body itself and damages the quality of sintered ceramics, but more seriously, it will cause fluoride pollution when discharged into the atmosphere. Fluoride can enter the human body through the respiratory tract, digestive tract and skin , has a toxic effect on the central nervous system and myocardium, and low-concentration fluorine pollution can lead to brittle calcification of teeth and bones. The discharge standard of fluoride must be lower than 5.0mg / m2 in the "Ceramic Industry Pollutant Discharge Standard" (GB25464-2010) 3 Therefore, using fluoride as a low-temperature sintering aid for magnesia ceramics will inevitably increase the emission of gaseous fluoride and increase the burden of environmental protection investment; in addition, fluoride ions in the residual solid-solution fluoride in ceramics exist in the form of replacing oxygen ions, resulting in crystal The chemical stability of the intergranular bonding is reduced, and it is difficult to resist the long-term erosion of flux inclusions in the magnesium melt

Water glass, silica sol and ethyl silicate are used as binders in the preparation slurry of the disclosed ceramic foam filters such as Chinese patent literature CN101138691A, and the SiO between the sintered ceramic foam particles 2 The presence of components makes it easy to react with magnesium and its alloy melts according to (4), which also reduces the chemical stability of foamed ceramics

However, diboron trioxide is easy to react with magnesium and aluminum, and is not stable in magnesium and aluminum alloy melts; at the same time, because diboron trioxide is soluble in solvents such as water and ethanol, it can strongly absorb water in the air to form boric acid. The diboron trioxide added in the preparation process of foam ceramics is dissolved in water to form a boric acid aqueous solution, which is easy to react with magnesium oxide to form magnesium borate precipitation and reduce its effect

Gallium oxide is a homogeneous oxide of diboron trioxide, which forms spinel-type MgGa with magnesium oxide at a lower temperature 2 o 4 It plays a role in reducing the sintering temperature, but the amount of gallium resources is very small (gallium is a strategic reserve metal), and the high price of gallium oxide limits its application in ordinary ceramics.

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