Three Typical Processes and Applicable Objects of Powder Surface Modification
The surface modification process varies according to the surface modification method, equipment and powder preparation method. At present, the surface modification processes used in industry mainly include three categories: dry process, wet process, and composite process.
1. Dry process
This is the most widely used non-metallic mineral powder surface modification process. At present, for non-metallic mineral fillers and pigments, such as heavy calcium carbonate and light calcium carbonate, kaolin and calcined kaolin, talc, wollastonite, silica micropowder, glass microspheres, aluminum hydroxide and light magnesia, clay, ceramic pigments etc., most of them adopt dry surface modification process. The reason is that the dry method has the characteristics of simple process, flexible operation, low investment and good applicability of modifiers.
(1) Intermittent dry process
The characteristic is that the time of surface modification (that is, the residence time) can be flexibly adjusted in a wide range, but it is difficult to coat the particle surface modifier uniformly, the unit product consumes more chemicals, the production efficiency is low, and the labor intensity is high. Dust pollution, difficult to adapt to large-scale industrial production, generally used in small-scale production.
(2) Continuous modification process
It is characterized by better dispersion of powder and surface modifier, more uniform particle surface coating, less modifier consumption per unit product, low labor intensity, high production efficiency, and is suitable for large-scale industrial production. The continuous dry surface modification process is often placed after the dry powder preparation process to continuously produce various non-metallic mineral active powders in large quantities, especially for inorganic materials used in polymer-based composite materials such as plastics, rubber, and adhesives. Fillers and pigments.
2. Wet process
Compared with the dry process, it has the characteristics of good surface modifier dispersion and uniform surface coating, but it needs subsequent dehydration (filtration and drying) operations. It is generally used for water-soluble or hydrolyzable organic surface modifiers and occasions where the front stage is wet powder (including wet mechanical ultrafine pulverization and chemical powder) process and the latter stage needs to be dry, such as light calcium carbonate (especially It is the surface modification of nano calcium carbonate), wet finely ground heavy calcium carbonate, ultra-fine aluminum hydroxide and magnesium hydroxide, ultra-fine silicon dioxide, etc., because the slurry generated after the chemical reaction is not wet The method surface modification also needs to be filtered and dried, and the surface modified before filtering and drying can also prevent the material from forming hard agglomerates after drying and improve its dispersibility.
Inorganic precipitation coating modification is also a wet modification process. It includes pulping, hydrolysis, precipitation reaction and subsequent washing, dehydration, calcination or roasting and other procedures or processes.
3. Composite process
(1) Mechanochemistry/Chemical Coating Composite Modification Process
It is a process of adding a surface modifier during the action of mechanical force or fine grinding and ultrafine grinding, and chemically coating and modifying the surface of the particles while reducing the particle size of the powder. The characteristic of this composite surface modification process is that it can simplify the process, and some surface modifiers also have a certain degree of grinding aid effect, which can improve the crushing efficiency to a certain extent.
The disadvantage is that the temperature is not easy to control; in addition, since the particles are continuously pulverized during the modification process, a new surface is generated, and the particle coating is difficult to be uniform. It is necessary to design the addition method of the surface modifier to ensure uniform coating and higher In addition, if the heat dissipation of the crushing equipment is not good, the local excessive temperature rise during the strong mechanical force may decompose part of the surface modifier or destroy the molecular structure.
(2) Inorganic precipitation reaction/chemical coating composite modification process
After the precipitation reaction modification, the surface chemical coating modification is essentially an inorganic/organic composite modification process. This composite modification process has been widely used in the surface modification of composite titanium dioxide, that is, on the basis of precipitation coating SiO2 or Al2O3 film, titanate, silane and other organic surface modifiers are used to treat TiO2/SiO2 or Al2O3 The surface of composite particles is modified by organic coating.
(3) Physical coating/chemical coating composite modification process
The process of surface organic chemical modification after physical coating of particles, such as metal coating or coating.
New ultra-fine powder materials, nano-calcium carbonate has great development potential
Nano-calcium carbonate, also known as ultra-fine calcium carbonate and ultra-fine calcium carbonate, belongs to a new type of ultra-fine solid powder material. Nano-calcium carbonate has the advantages of fine particle size, high whiteness, good compatibility, and good optical properties.
Nano calcium carbonate is used in a wide range of fields, including paper industry, medical and health care, rubber products, coatings and plastics. Nano-calcium carbonate accounts for a large proportion in the plastics market and can be used as a plastic regulator and reinforcing agent. Nano-calcium carbonate has excellent dispersibility, can improve the anti-aging and impact strength of plastics, and is widely used in PVC film materials.
my country's nano-calcium carbonate industry started in the 1980s and entered the stage of industrial production in the late 1980s. Non-freezing method, multi-stage spray carbonization method, intermittent carbonization method, high gravity method, internal circulation carbonization tower preparation method, jet absorption method, etc. are the main preparation methods of nano calcium carbonate in my country. The batch carbonization method can be subdivided into two types: the intermittent stirring carbonization method and the intermittent bubbling carbonization method. At present, the intermittent bubbling carbonization method is the most widely used preparation method in the world. In recent years, with the efforts of leading enterprises, some nano-calcium carbonate production technologies in my country have reached the advanced level overseas.
The raw material of nano-calcium carbonate is limestone. my country is the country with the most abundant limestone resource reserves in the world, accounting for nearly 70.0% of the world's total reserves. my country's limestone resources are concentrated in Shandong, Anhui, Henan, Hebei, Shaanxi, Gansu and other places.
But at present, functional nano-scale calcium carbonate is far from meeting market demand. Different users have different requirements for products, not only depending on particle size, but also product performance and quality. At present, there are not only calcium carbonate with various particle sizes, but also various types of calcium carbonate. There are 50-60 varieties of calcium carbonate with various functions. For example, OT calcium, which is specially used for ink, still occupies the high-end ink market in China, which is worth pondering. Researchers and manufacturers engaged in nano-scale materials should work hard on the application performance of nano-scale inorganic powder materials to develop functional and special nano-scale inorganic functional materials.
Calcination-fluorine-free and nitric acid leaching to remove impurities from quartz sand
Pickling is an important means to remove impurities in quartz, commonly used are hydrofluoric acid, nitric acid, hydrochloric acid, sulfuric acid, acetic acid and oxalic acid. When using inorganic acids for acid leaching, due to the hardness of quartz sand, the concentration of these inorganic strong acids must be very high. In many cases, the concentration of the acid is between 20-30%, and the high concentration of acid will corrode the leaching equipment. Very strong.
The commonly used organic weak acid is oxalic acid, or a combination of some weak acids is used to improve the leaching efficiency. Acetic acid is also another organic acid leaching agent, which is completely non-toxic to the environment and basically has no loss to the target product SiO2. By adding oxalic acid and acetic acid, the impurity elements in the quartz sand can be effectively removed. In contrast, oxalic acid had higher leaching and removal rates for Fe, Al, and Mg, whereas acetic acid was more efficient in removing impurity elements Ca, K, and Na.
After calcination of quartz silicon ore in a certain place, oxalic acid, acetic acid, and sulfuric acid, which is easy to treat waste liquid in the later stage, were used as leachate to remove impurities from quartz sand. The results showed that:
(1) The total amount of impurities in the quartz ore selected for the test is 514.82ppm, of which the main impurity elements are Al, Fe, Ca, Na, and the impurity minerals are mica, nepheline and iron oxides.
(2) When the quartz silica ore is calcined at 900°C for 5 hours, the removal rate of pickling impurities is the highest. Compared with uncalcined quartz ore, the surface of calcined water-quenched quartz ore has more cracks with larger width and depth, and some holes of different sizes are distributed on the surface. This is because when calcined at 573°C, quartz will undergo a phase transition from α lattice to β lattice, and the quartz matrix will expand due to the change of lattice, and the expansion rate is about 4.5%, and the volume expansion will be lead to cracks. The cracks mainly occur at the interface between the quartz matrix and the impurity inclusions, where there are many impurities. It can be inferred that the quartz ore can produce cracks after calcination and water quenching, and the cracks will expose the impurities inside the quartz sand. , can promote the effect of impurity removal by acid leaching.
(3) The calcined quartz sand is acid-leached with 0.6mol/L oxalic acid, 08mol/L acetic acid and 0.6mol/L sulfuric acid at 80°C, with a solid-to-liquid ratio of 1:5 and a stirring speed of 300r/min. Time 4h is the best condition for leaching the quartz sand. Under the optimal conditions, the best removal rates of Al, Fe, Ca and Na are 68.18%, 85.44%, 52.62% and 47.80%, respectively.
Surface modification of wollastonite and its application in natural rubber
Wollastonite is a fibrous cleaved metasilicate mineral, which has a series of excellent properties such as needle-like structure, high whiteness, low thermal expansion coefficient, excellent chemical stability and flame retardancy, and high electrical insulation. Physical and chemical properties, so wollastonite has broad application prospects.
With the development of wollastonite deep processing technology research, wollastonite has gradually become a high-quality raw material in many industrial fields such as polymer rubber and plastic industry, paint and coating industry, building material industry, ceramic metallurgy industry, and paper industry.
Using a certain wollastonite as raw material, using dodecylamine and Si-69 to carry out surface modification and filling application tests on wollastonite, discuss the process conditions of dry modification of wollastonite and the effect of modifying agents on the surface of wollastonite. mode of action, and using natural rubber as the matrix to explore the application effect of modified wollastonite, the results show that:
(1) Si-69 coupling agent can form chemical adsorption on the surface of wollastonite. The optimal conditions for modifying wollastonite are: dosage of 0.5%, modification time 60min, modification temperature 90°C. Under these conditions, the activation index of the modified wollastonite is 99.6%, and the contact angle is 110.5°.
(2) Dodecylamine exists in the form of physical adsorption such as hydrogen bond adsorption on the surface of wollastonite. The optimal conditions for modifying wollastonite are: dosage of 0.25%, modification time of 10 minutes, and modification temperature of 30°C. Under these conditions, the activation index of modified wollastonite is 85.6%, and the contact angle is 61.5°.
(3) The improvement effect of modified wollastonite on the mechanical properties of natural rubber is better than that of unmodified wollastonite, and the improvement effect of Si-69 coupling agent and dodecylamine mixed modified wollastonite on the mechanical properties of natural rubber is even greater. good.
Silica powder, why is the price of spherical powder so expensive?
Silica powder can be divided into angular silica powder and spherical silica powder according to particle shape, and angular silica powder can be divided into crystalline silica powder and fused silica powder according to different types of raw materials.
Crystalline silica powder is a silica powder material made of quartz block, quartz sand, etc., after grinding, precision grading, impurity removal and other processes. Physical properties such as linear expansion coefficient and electrical properties of the product.
Fused silica powder is made of fused silica, glass and other materials as the main raw materials, and is produced through grinding, precision grading and impurity removal processes, and its performance is significantly better than that of crystalline silica powder.
Spherical silica powder is made of selected angular silica powder as raw material and processed into spherical silica powder material by flame method. It has excellent characteristics such as good fluidity, low stress, small specific surface area and high bulk density. It is a downstream high-end product. s Choice.
As a filling material, spherical silica powder has better performance and better effect than crystalline silica powder and fused silica powder; the higher filling rate can significantly reduce the linear expansion coefficient of copper clad laminates and epoxy molding compounds, and the expansion performance is close to that of single crystalline silicon, thereby improving the reliability of electronic products; the epoxy molding compound using spherical silicon micropowder has low stress concentration and high strength, and is more suitable for semiconductor chip packaging; it has better fluidity and can significantly reduce the wear and tear on equipment and molds. Therefore, spherical silica powder is widely used in high-end PCB boards, epoxy molding compounds for large-scale integrated circuits, high-end coatings, and special ceramics.
The price of easy-to-use products is naturally high. The unit price and gross profit margin of spherical silica powder in the market are higher than those of crystalline and fused silica powder.
How is continuous basalt fiber modified?
Continuous basalt fiber is drawn from molten natural basalt at high speed at 1450°C to 1500°C. It has good mechanical and thermal properties, and is widely used because of its low price, environmental protection and pollution-free.
However, the basalt fiber has a high density and is relatively broken, and its chemical composition is mainly inorganic functional groups, which leads to the chemical inertness of the fiber surface, and because the surface of the continuous basalt fiber is very smooth, the adhesion with the resin and other substrates is poor, the sizing is difficult, and the wearability is poor, which limits the continuous basalt fiber. Direct use of basalt fibers. Therefore, it needs to be modified to increase the surface active groups, increase the adhesion with other substrates, broaden the scope of use, and give full play to the advantages of continuous basalt fiber.
1. Plasma modification
Fiber plasma modification technology is a widely used and relatively mature technology. It can act on the fiber surface through plasma, and then produce etching and form pits, etc., making the fiber surface rough and improving the smoothness of the fiber surface. Capillary effect, at the same time, by controlling the processing conditions, it basically does not damage the fiber strength. Plasma modification of basalt continuous fibers has thus attracted attention.
Sun Aigui treated the surface of continuous basalt fiber with low-temperature cold plasma with different discharge power under the condition of discharge voltage 20Pa, and found that with the increase of discharge power, the degree of surface morphology etching increased, the number of small protrusions increased, the friction factor increased, and the fiber fractured. The strength decreases, the hygroscopicity improves, and the wettability increases.
2. Coupling agent modification
The second type of better modification method of continuous basalt fiber is coupling agent modification. The chemical group on the surface of basalt fiber reacts with one end of the coupling agent, and the other end physically entangles with the polymer or The chemical reaction can strengthen the adhesion between the resin matrix and the continuous basalt fiber. Coupling agents mainly include KH550, KH560 and compound systems with other chemical substances.
3. Coating surface modification
The coating modification of continuous basalt fiber is mainly to use modifiers to coat or coat the fiber surface to improve the smoothness and chemical inertness of the fiber surface, including the coating modification using the sizing process.
4. Modification by acid-base etching method
The acid-base etching method refers to the use of acid or alkali to treat the continuous basalt fiber, the network changer (or former) in the fiber body structure is dissolved, the fiber surface is etched, grooves, protrusions, etc. are formed, and radicals such as hydroxyl groups are introduced at the same time. Group, thereby changing the roughness and smoothness of the fiber surface.
5. Modification of sizing agent
Sizing agent modification refers to improving the sizing agent in the drawing and infiltration process of producing continuous basalt fiber, so that the basalt fiber can be modified in the infiltration and drawing process, and the modified continuous basalt fiber can be produced.
Catalytic and carrier properties of non-metallic minerals and energy saving and carbon reduction
Non-metallic minerals (materials) are used as catalytic materials in industrial production processes, including chemical catalysis and photochemical catalysts or carriers, to speed up the reaction process due to their properties such as cation exchange, porosity, large surface area, and unsaturated surface chemical bonds , Improve product purity or output efficiency, etc., and achieve the purpose of saving energy, reducing consumption and reducing carbon.
For example, kaolin, zeolite, activated clay, etc. are used as catalysts and carriers; some minerals with semiconducting properties have excellent photocatalytic properties, not only have photocatalytic degradation of organic waste and antibacterial effects, but also can photocatalyze water under the action of solar energy. , CO2 into hydrogen, methane and other fuels.
Chemical catalysis uses catalysts that alter the rate of a chemical reaction during the action of reactants without appearing in the products themselves. The active component can be a single substance or a plurality of substances.
Mineral catalysts are substances that are inherently adsorptive and have certain catalytic activity. They can be used in high-temperature and high-acid-base environments, and are usually used as catalyst carriers. The common ones are kaolin, bentonite, diatomite, zeolite, attapulgite, sepiolite, etc. and their modified activation products, such as acid activated kaolin, activated clay, 4A or 5A zeolite, etc.
Photocatalytic technology is a new technology that can use solar energy for clean energy production, environmental pollution control and carbon dioxide conversion. Many fields have broad prospects. For example, in photocatalytic hydrogen production, solar energy can be used to convert water into hydrogen and oxygen; in photocatalytic synthesis, carbon dioxide can be converted into fuels such as methane and methanol; the industrial application of these two technologies can greatly reduce the consumption of energy and minerals. Utilization, thereby reducing carbon dioxide emissions, has broad application prospects in solving major problems such as global energy shortages and carbon dioxide emission reductions.
Naturally produced anatase, rutile, birnessite, hematite, goethite, etc. all have a certain photocatalytic ability, while montmorillonite, diatomite, kaolinite, mica powder, natural pumice and expansive Perlite has excellent properties such as large surface area, strong adsorption, loose and porous, high temperature resistance, acid and alkali resistance, etc., and is often used as a carrier for photocatalysts.
Using rutile as a photocatalytic material to treat wastewater containing azo dyes has both adsorption and photocatalytic degradation effects, and nano-photocatalytic active particles such as anatase TiO2, C3N4, and perovskite are loaded on montmorillonite and diatomite , mica powder, etc., not only increases the dispersion and specific surface area of active components, thereby improving photocatalytic efficiency, but also facilitates the recovery and reuse of composite photocatalysts in the process of industrial wastewater treatment.
The "mineral film" widely distributed on the top layer of the earth's land is considered to be the fourth largest circle of the earth, and it is a natural photoelectric conversion system. Rich in birnessite, hematite, goethite, anatase, rutile and other semiconductor minerals, it has good sunlight response ability, stable, sensitive and long-term photoelectric conversion performance, and converts solar energy into mineral photoelectrons under sunlight radiation Energy can not only produce oxygen and hydrogen by photocatalytically splitting water, but also promote the conversion of carbon dioxide in the atmosphere and water into carbonate minerals.
It can be seen that minerals with semiconductor properties widely exist in nature and have always played the role of photocatalysts. This not only shows the role of non-metallic minerals widely distributed on the earth's surface for carbon storage and carbon reduction, but also provides a direction for the development of new photocatalytic mineral materials.
Talc powder - the most commonly used inorganic nucleating agent for polylactic acid
Polylactic acid is a high molecular polymer obtained from renewable resources through extraction, chemical polymerization and other processes. It has biodegradability and biocompatibility. Completely decomposed into carbon dioxide and water. The use and promotion of polylactic acid can reduce the consumption of petroleum resources, and play a role in energy saving and emission reduction, which is of great significance to environmental protection.
Polylactic acid has high strength, high modulus, and good transparency and air permeability, but its crystallization rate is too slow during processing, resulting in prolonged processing cycle and poor heat resistance, which greatly limits the application fields of polylactic acid products .
At present, the most common way to improve the performance of polylactic acid is to add a nucleating agent. In actual enterprise processing applications, talc powder is the most commonly used inorganic nucleating agent for polylactic acid, which can improve the stretching, bending, etc. of polylactic acid. Mechanical properties, improve its heat resistance.
By studying the effects of different contents of talc powder on the crystallization properties and comprehensive mechanical properties of high-gloss pure polylactic acid, the results show that the crystallization peak temperature of polylactic acid increases with the increase of talc powder content, and the crystallization temperature zone continues to move to the high temperature direction, and the crystallization rate It also accelerated.
Compared with pure polylactic acid, when the mass fraction of talc powder is 10%, the comprehensive mechanical properties of polylactic acid reach the maximum, its crystallization peak temperature increases by 13.7K, the tensile strength increases from 58.6MPa to 72.0MPa, and the tensile strength at break The strain increased from 2.7% to 4.6%, the flexural strength increased from 88.9MPa to 104.0MPa, and the flexural modulus increased from 3589MPa to 4837MPa. At the same time, the addition of talcum powder will not change the polylactic acid crystal form, but will make the size of polylactic acid spherulites significantly smaller, and the crystal nucleus density will increase significantly.
Performance Characterization of Powder--Particle Size and Distribution
The characterization of powder mainly includes particle size and distribution, specific surface area, aggregate characterization, microscope structure analysis, component analysis, surface analysis, static characterization, surface wettability characterization and surface adsorption type, coating amount and coating Representation of coverage, etc. This issue briefly introduces the particle size and distribution of powder.
Powder is an aggregate of a large number of solid particles, which represents a state of existence of matter, which is neither different from gas, liquid, nor completely different from solid. Micropowder or ultrafine powder is generally a multi-particle aggregate with a particle size in the range of 100nm-10μm.
Composition characteristics of ultrafine powder:
1) Primary particles: Under the ordinary electron microscope, the magnification is increased, and only a single particle with a clear outline can be seen.
2) Secondary or high-order particles: multiple primary particles (solid or loose) aggregates (aggregates)
Particle Size (Particle Size) and Particle Size (Particle Size) Distribution
Particle diameter: Particle diameter or particle size—expressed in mm, μm, nm.
Spherical particles: the diameter of the particle is the particle diameter
Non-spherical particles: the equivalent diameter is the particle size (the particle size is when a certain physical characteristic or physical behavior of the measured particle is the closest to a homogeneous sphere (or combination) of a certain diameter, the diameter of the sphere (or combination) ) as the equivalent particle size (or particle size distribution) of the measured particles)
Preparation Technology of Clay Mineral-Metal Composite Bactericidal Material
In the new bactericidal materials prepared based on clay minerals, clay minerals themselves are mainly used as carriers for bactericidal substances (such as metals, metal oxides, organic substances), and their bactericidal ability is still limited. Modified clay minerals prepared by various methods, and composites made of clay minerals and other materials can be used as new bactericidal materials to produce bactericidal effects on various bacteria.
Clay minerals can enhance the bactericidal ability through various modification methods (including thermal modification, acid modification, inorganic modification of metals or metal oxides, organic modification and composite modification, etc.). The surface area increases, the porosity and dispersion of minerals increase, and the overall thermal stability and mechanical strength of the material are improved. The clay minerals used to modify and prepare bactericidal materials are mainly montmorillonite, kaolinite, halloysite, and vermiculite, among which montmorillonite has outstanding cation exchange capacity, large interlayer domain, specific surface area and strong It is widely used because of its adsorption capacity.
Toxic metal ions and metal oxides can be inserted into the clay mineral layer or adsorbed on its surface to prepare a composite bactericidal material. The metal ions used in the research mainly include zinc, copper, and silver (among which silver is widely used), and the metal oxides include titanium oxide, zinc oxide, copper oxide, and ferrous oxide. Clay minerals and metals or metal oxides are mainly modified through interlayer cation exchange or mineral surface adsorption. The bactericidal mechanism of this type of composite bactericidal material is related to the toxicity of metals to cells or the free radicals generated.
Clay minerals loaded with metal ions have the advantages of slow release of metals, prolonging the sterilization time, and improving the stability of sterilization materials. The slow release of metals is related to the bonding ability between hydroxyl groups on the surface of clay minerals and metals. The increased specific surface area and porosity of clay minerals help to disperse nano-metal particles, improve the contact efficiency between nano-metals and bacteria, and improve the bactericidal effect. However, considering the toxicity of metal nanoparticles, their biological toxicity needs to be considered in specific applications. However, due to the slow release of metal ions in clay minerals, metals may continue to accumulate in the body and exhibit toxicity over time.