The difference between alumina, pseudo-boehmite and boehmite

In the world, people generally "alumina" is divided into two categories: metallurgical grade alumina and non-metallurgical grade alumina.  Non-metallurgical grade alumina is also known as multiple varieties of alumina, chemical alumina.  

Among them, pseudo-boehmite, boehmite, super fine aluminum hydroxide, activated alumina, calcined alumina and corundum are all belong to the chemical alumina this category.  

Today we are going to talk about the relationship between the chemical formula "Al2O3" and pseudo-boehmite, boehmite.  

Differences between ingredients and applications of al2o3 powder, pseudo-boehmite and boehmite

Al2O3  

At present, there are more than ten crystal types of Al2O3, such as χ, ρ, γ, κ, δ, θ and α, among which α and γ are the most widely used.  

α -al2o3 mohs hardness of about 9, melting point of 2050℃, boiling point of 2980℃, thermal conductivity of 28.88W/ (m·K), has good chemical stability, high temperature resistance and wear resistance, can be used as refractory materials, ceramics, abrasive and other basic raw materials.  Using its high thermal conductivity and good insulation, low sodium calcined alumina is used as thermal conductivity filler in electronics, information, new energy and other industries.  Low sodium alumina also has good electrical insulation performance, high refractoriness, small sintering shrinkage and other characteristics, is the manufacture of electronic substrate, spark plug and vacuum shell and other electrical components and heat resistant or wear-resistant ceramics of high quality raw materials, in addition, low sodium ultrafine alumina in recent years widely used in the production of lithium battery diaphragm material.  

γ -al2o3 has a large specific surface area, good adsorption performance, good surface acidity and other characteristics, is the application of activated alumina, can be used as dry adsorbent, fine abrasive, catalyst and catalyst carrier, used in petrochemical, gas drying, automobile exhaust and industrial organic waste gas purification treatment and other fields.  

Thin diaspore  

Boehmite, also known as boehmite and boehmite, is an important precursor of activated alumina with the molecular formula γ-AlOOH. It is a precursor of activated alumina with high order degree and complete crystallization, so it has better stability than pseudo-boehmite.  

Boehmite can withstand higher processing temperature, so boehmite can be used as a heat-resistant flame retardant for halogen-free copper clad plates, insulation products, plastic shells of devices that need to withstand higher processing temperature.  In addition, boehmite is the main raw material for the production of activated alumina catalyst for coal chemical industry, can also be used for the production of lithium battery diaphragm, sodium sulfur battery β -al2o3 raw material, calcined alumina precursor.  The low sodium ultrafine alumina prepared by the low sodium ultrafine boehmite precursor system has the characteristics of low sodium, high conversion, high insulation, good sintering performance and so on. It has been widely used in lithium battery diaphragm, microcrystalline ceramics, precision ceramics, foam ceramics, integrated circuit chips, aviation light source devices and so on.  

Pseudoboehmite  

Pseudo-boehmite is a kind of incomplete crystalline boehmite, with similar chemical composition with pseudo-boehmite, containing 1.25 ~ 2.0 crystal water, is a kind of incomplete crystalline hydrated alumina, also known as alumina monohydrate, pseudo-boehmite.  

The typical structure of pseudo-boehmite is very thin folded lamellar, which is an alumina hydrate with special spatial network structure. It has physical properties such as high specific surface area, large pore volume and chemical properties of colloidal thixotropy under acidic conditions.  These characteristics of pseudo-boehmite make it widely used in many industries, in the petroleum industry as a catalyst, carrier, binder;  Carrier coating used as catalyst for automobile exhaust treatment in automobile industry;  Used as additive of flame retardant materials in the field of fire protection;  In the paper industry used as high-grade inkjet printing paper in the ink absorbing coating;  In the environmental protection industry as a gas purification adsorbent, drinking water defluorination agent, industrial sewage color and odor elimination agent;  Used as a coating additive in the construction industry;  Reinforcing agent in ceramic composites.  

The correlation and difference between nano alumina powder, pseudo-boehmite and boehmite

Relevance

The metastable phases of χ, ρ, γ, κ, δ, θ and α can be observed during the firing of alumina hydrate.  Pseudoboehmite is a kind of boehmite with incomplete crystallization.  γ -al2o3 calcined at 400 ~ 700℃ is widely used as catalyst carrier, catalyst and adsorbent.  γ -al2o3 calcined at 1100 ~ 1200℃ is used in high grade ceramics, petrochemical and other fields.  

Pseudo-boehmite can be converted into boehmite under specific hydrothermal conditions, realizing one-way transformation between them.  In addition, both pseudo-boehmite and boehmite are precursors to alumina preparation.  

Differentiation  

Pseudoboehmite has the same molecular formula (AlOOH) as boehmite, which is a different crystal form of alumina monohydrate.  It's called a quasi thin diaspore, because the thin diaspore is a crystallization of incomplete thin diaspore, they have very similar XRD graph, the two main diffraction peak position is almost the same, the difference only lies in the intensity of the diffraction peak is different, so compared with quasi thin diaspore, thin diaspore is bigger and higher crystallinity and crystal grains more complete.  

The average grain size is the main criterion to classify boehmite and pseudo-boehmite.  The products with average grain size less than 10nm were regarded as pseudo-boehmite.  Products larger than 50nm are regarded as boehmite;  At 10-50nm, it is regarded as the intermediate product of boehmite and pseudo-boehmite, and the intermediate product can also be classified as pseudo-boehmite.  

To sum up, the differences between them are as follows:  

(1) Pseudoboehamite is an amorphous aggregation with only weak diffraction peak;  Boehmite has good crystal structure and sharp diffraction peak.  

(2) Pseudoboehmite has higher specific surface area and larger pore volume than boehmite.  The specific surface area of boehmite decreases gradually with the increase of temperature, and increases first and then decreases with the increase of temperature.