Properties and applications of magnesium oxide

Magnesium oxide was born in 1930s as a new material.  In the early days of the founding of the People's Republic of China, due to the increasing demand of rubber products for magnesium oxide, a number of small workshop factories first emerged in Shanghai, but the production variety is relatively single.  Until 1956 have developed light magnesium oxide and heavy magnesium oxide two specifications of varieties.  Since then, China's light magnesium oxide industry has experienced long-term upward development, light magnesium oxide products have entered the refractories, sealing materials, chemical building materials, medicine and food and other important markets.  

Magnesium oxide powder property  

Chemical properties: It can react with hot water to release hydrogen, and produce blinding white light when burning. Magnesium does not react with fluoride, hydrofluoric acid and chromic acid, nor is it corroded by caustic alkali, but it is easily dissolved in organic and inorganic acids. Magnesium can be directly combined with nitrogen, sulfur and halogen.  Organic chemicals including hydrocarbons, aldehydes, alcohols, phenols, amines, lipids, and most oils have little or no effect on magnesium.  

Physical properties: white amorphous powder.  Relative density 3.26 ~ 3.43.  Odorless, tasteless and non-toxic.  Soluble in acid and ammonium solution, insoluble in water and ethanol.  It has strong refraction in the range of visible and near ultraviolet light.  It is easy to absorb water and carbon dioxide in exposed air and gradually become basic magnesium carbonate, which is combined with water to produce magnesium hydroxide, showing a slightly alkaline reaction, and the pH of saturated aqueous solution is 10.3.  But it is very soluble in dilute acid, very slightly soluble in pure water, due to the presence of carbon dioxide increases its solubility, it is a mild catalyst.  Relative density (D254)3.58.  Melting point is 2852 ℃.  Boiling point :3600℃, after 1000℃ above high temperature burning, can be converted to crystal.  After modification, there is no agglomeration phenomenon, and it has many special functions and important application value in optics, catalysis, magnetism, mechanics, chemical industry and so on.  

Preparation method of magnesium oxide powder

Hot pressing sintering: generally hot pressing sintering and isostatic pressing sintering.  Hot pressing sintering is to apply a certain pressure (10-40 MPa) in the sintering process to accelerate the material flow, rearrangement and densification.  Continuous sintering production efficiency is high, but equipment and grinding tool cost is high, and is not conducive to sintering too thick ceramics.  

Advantages: pressure is conducive to densification, reduce sintering temperature, shorten sintering time;  The sintered ceramics have small grain size and good mechanical properties.  The porosity is close to zero and the density is close to theoretical density.  

Hot isostatic pressing: the powder is pressed into embryo or packed into a coated powder bag into a high pressure vessel, so that the powder can withstand the effect of high temperature and balanced pressure and be burned into compact parts.  Hot isostatic pressing can be done in lower sintering temperature under a lot of adverse reaction and inhibiting the heat change, no sintering additives under uniform structure, can reduce the density of sintered body can reduce or eliminate sintering residual porosity, improve the density, strength, accurate control and shape of the scale of the products, free cutting and machining processes, etc.  

Discharge plasma sintering: a new material preparation process developed in recent years, also known as pulse current sintering.  The main characteristics of the material are ultra-fast densification and density sintering by volume heating and surface activation.  

Advantages: low sintering temperature, 200-300℃ lower than HP and HIP, short sintering time (only 3min-10min), low consumption per room;  High density, fine grain, simple operation.  

Magnesium oxide powder application  

(1) coatings, plastics, rubber and other fillers: ultrafine magnesium oxide can be used as fillers of paints, paper and cosmetics, fillers and reinforcing agents of plastics and rubber and auxiliary materials of various electronic materials because of its high dispersity.  

(2) High-performance ceramics: ultrafine magnesium oxide has good sintering performance.  The high density fine crystal ceramics or multifunctional magnesium oxide films can be sintered at low temperature without the use of sintering additives, which is expected to be developed as cutting-edge materials under harsh conditions such as high temperature and high corrosion.  

(3) Absorbing materials: because of its high activity and high dispersion, ultrafine magnesium oxide is easy to be compounded with polymers or other materials.  This composite material has good microwave absorption performance, and does not reduce the strength and toughness of raw materials, and the addition of fibrous magnesium oxide has a reinforcing effect.  

(4) Adsorbent and catalyst: ultrafine magnesium oxide has a large specific surface area, which is an important raw material for the preparation of high-function fine inorganic materials, electronic components, ink and harmful gas adsorbent.  

(5) Flame retardant materials: ultrafine magnesium oxide has a good flame retardant effect, and can be used with wood chips, shavings to manufacture light, sound insulation, heat insulation, refractory fiberboard and other refractory materials and metal ceramics.  

(6) Others: fuel additives, detergents, antistatic agents and anti-corrosive agents, electrical insulating materials, manufacturing crucible, furnace, insulating tubes (tube pieces), electrode rod, electrode sheet, etc.  

(7) Cotton fabric and polyester fabric were functioned with magnesium oxide antistatic finishing agent. The test results of antistatic property showed that the finished fabric had better antistatic effect.