Various changes occur in the material during the grinding process. These changes, though minor in coarse grinding, are significant in ultrafine grinding due to high grinding intensity, long grinding time, and considerable changes in material properties. This phenomenon, caused by mechanical effects during ultrafine grinding, leads to changes in the crystal structure and physicochemical properties of the material. It is called the mechanochemical effect of the grinding process.
Particle Size Changes
The most obvious change in পাউডার উপকরণ after ultrafine grinding is the reduction in particle size. Depending on the particle size, ultrafine powders are generally divided into:
- Micron scale (1–30 μm)
- Submicron scale (0.1–1 μm)
- Nanometer scale (0.001–0.1 μm)
Crystal Structure Changes
In ultrafine grinding, intense and prolonged mechanical forces cause varying degrees of lattice distortion. The grain size decreases, structures become disordered, and an amorphous or non-crystalline phase forms on the surface. Polycrystalline transformation may even occur. These changes can be detected using techniques such as X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance, electron paramagnetic resonance, and differential thermal analysis.
For example:
- Quartz: Quartz is one of the simplest silicate minerals in terms of crystal structure and chemical composition. It was one of the first minerals studied for the mechanochemical phenomena induced by mechanical energy. Studies show that when quartz is ground using a vibration mill, the grain size decreases in the initial stage. However, after prolonged grinding, the main change is amorphization due to agglomeration and recrystallization. The solubility of quartz increases in dilute alkaline solutions or water after the formation of the amorphous layer during grinding.
- কাওলিন: Layered silicate minerals such as kaolin, mica, talc, bentonite, and illite lose their ordered crystal structure and become amorphous under the mechanical activation during ultrafine grinding. Amorphization is typically associated with the loss of hydroxyl groups and a decrease in bond energy in these minerals.
- Calcite: Polycrystalline transformation is a structural change induced by mechanical forces that does not alter the chemical composition of the material. There are two forms of polycrystalline transformation:
- Double-phase transformation, usually reversible and endothermic.
- Single-phase transformation, mostly irreversible and exothermic.
Calcite transforms into rhombic aragonite during grinding. This transformation is reversible at room temperature and pressure. After prolonged grinding, the proportions of calcite and aragonite become nearly equal.
- Alumina Micro Powder: With longer grinding times, the crystal grain size of high-purity alumina decreases, while lattice strain and the effective Debye parameter increase.
Chemical Composition Changes
Due to strong mechanical activation, some materials undergo direct chemical reactions during ultrafine grinding. These reactions include decomposition, gas-solid, liquid-solid, and solid-solid reactions.
For example:
- During grinding of calcite, magnesite, iron dolomite, feldspar, and iron spinel in a vacuum mill, CO₂ is released.
- Carbonates of alkali metals, alkaline earth metals, and nickel, copper, manganese, zinc, etc., decompose during grinding.
- Zinc oxide and alumina react during grinding in a vibration ball mill to form spinels and amorphous zinc oxide powders.
Solubility Changes
When fine grinding or ultrafine grinding is applied to materials like quartz, calcite, cassiterite, corundum, bauxite, chromite, magnetite, galena, titanomagnetite, volcanic ash, and kaolin, their dissolution rate and solubility in inorganic acids increase.
Sintering Properties Changes
Changes in thermal properties due to fine or ultrafine grinding mainly include:
- With improved dispersion, solid-phase reactions become easier, lowering sintering temperatures and improving the mechanical properties of products.
- For example, after fine grinding of dolomite in a vibration mill, the sintering temperature of refractory materials decreased by 375–573K, and the material’s mechanical properties improved.
- After ultrafine grinding of quartz and feldspar, the sintering time for enamel was shortened, and the strength of ceramic products improved.
- Crystalline structure changes and amorphization shift phase transition temperatures.
- For instance, the transition temperature from α-quartz to β-quartz and quartz to cristobalite changes due to ultrafine grinding.
Cation Exchange Capacity Changes
Some silicate minerals, especially clay minerals like bentonite and kaolin, show significant changes in cation exchange capacity after fine or ultrafine grinding.
- For example, as grinding time increases, bentonite’s cation exchange capacity increases initially and then decreases. The calcium ion exchange capacity continuously decreases with longer grinding time.
- After grinding for a certain period, the cation exchange capacity and exchangeability of kaolin increase, indicating an increase in exchangeable cations.
Hydration Properties and Reactivity Changes
Fine grinding can enhance the reactivity of materials like calcium hydroxide, which is important for the preparation of building materials. Some materials are inert or insufficiently active in hydration reactions.
- For example, the hydration activity of volcanic ash and its reactivity with calcium hydroxide was almost zero initially, but after fine grinding in a ball mill or vibration mill, the activity increased to levels close to that of diatomaceous earth.
- Fine grinding can significantly improve the hydration performance of blast furnace slag. Therefore, producing cement with both high strength and a higher slag content is possible. This has great significance for the cement industry and environmental protection.
Electrical Properties Changes
Fine or ultrafine grinding also affects the surface electrical properties and dielectric performance of minerals. For instance, the isoelectric point and surface zeta potential of biotite change after impact crushing and grinding.
Density Changes
Research on grinding natural and synthetic zeolites using a planetary ball mill has shown different changes in density.
- For natural zeolite, the density decreases initially and reaches its minimum value around 120 minutes of grinding. After prolonged grinding, the density increases slightly but remains lower than the original material.
- Synthetic zeolite, after a short period of density decrease, shows an increase in density as grinding time continues. After 240 minutes of grinding, the density of the sample exceeds that of the unground material.
Properties of Clay Suspensions and Hydrogels
Wet grinding can enhance the plasticity and dry bending strength of clay. In contrast, dry grinding increases the plasticity and dry bending strength of the material in a short time, but these properties decline with prolonged grinding.
In conclusion, factors affecting the mechanochemical changes of materials include raw material properties, feed size, grinding or activation time, equipment type, grinding method, grinding environment, and additives. When studying mechanochemical effects, the comprehensive impact of these factors must be considered.
এপিক পাউডার
এপিক পাউডার, আল্ট্রাফাইন পাউডার শিল্পে ২০+ বছরের কাজের অভিজ্ঞতা। আল্ট্রাফাইন পাউডারের ক্রাশিং, গ্রাইন্ডিং, শ্রেণীবিভাগ এবং পরিবর্তন প্রক্রিয়ার উপর মনোযোগ দিয়ে, আল্ট্রাফাইন পাউডারের ভবিষ্যত উন্নয়নে সক্রিয়ভাবে প্রচার করুন। বিনামূল্যে পরামর্শ এবং কাস্টমাইজড সমাধানের জন্য আমাদের সাথে যোগাযোগ করুন! আমাদের বিশেষজ্ঞ দল আপনার পাউডার প্রক্রিয়াকরণের মূল্য সর্বাধিক করার জন্য উচ্চমানের পণ্য এবং পরিষেবা প্রদানের জন্য নিবেদিতপ্রাণ। এপিক পাউডার—আপনার বিশ্বস্ত পাউডার প্রক্রিয়াকরণ বিশেষজ্ঞ!
