Humanity has long sought to alter the properties of substances. From the ancient art of alchemy to modern variants of chemistry, science has combined with mechanics to engineer particles in such a way as to make them more useful. Particle engineering has become important in the cosmetic, food, animal feed, chemical, pharmaceutical, and other industries, seeking to alter particles' characteristics to allow businesses to deliver better products and services.
Science Behind the Particle Formation Process
To understand particle engineering, you first need to understand how particles form. Industries over time have developed specific processes and techniques to formulate materials. These include:
Fluid Bed Agglomeration
Granulating mixtures allow a substance to flow and compress while keeping particles from separating. It's a process that utilizes a specific liquid to form granules, which are then suspended through high-velocity airflow. These wet granules are then dried with hot air, with smaller particles lost due to evaporation.
Encapsulation
A standard method for forming capsules in pharmaceuticals involves spray drying, used on proteins that both attract and repel water in a suspension formula. This suspended solution is then fed into a tower usually heated to the boiling point, atomizing as it enters. As the water evaporates, starch forms a hardened shell around the material.
Blending
Sometimes blending materials becomes necessary when spray-drying particles, as is the case with formula for babies. Ingredients – such as whey proteins, milk, vegetable oil, lactose, and minerals – are homogenized, pasteurized, and spray dried to form a powder. This process distributes a uniform amount of nutrients throughout the product. Through understanding how particles form in this process, particle engineering helps create particles that are optimal sizes and shapes so that the product is the same throughout.
Micronization
This technique reduces the diameter of solid particles through mechanical means. Generally, this refers to reducing solids into micrometers, though it can also reduce particles into the nanometer range. Mechanical techniques seek to reduce particle size through crushing, grinding, and milling, using machines such as:
- Mills made from cylindrical drums cut, crush, or grind solids, using spheres within them to break down the material to the desired diameter.
- Grinding units that trap solids then rub against each other to reduce the size of particles.
This process is commonly used with food, animal feed, pharmaceutical ingredients, and various chemical compounds.
The Three Laws of Size Reduction
As with any science, some laws regulate and make sense of particle engineering. These laws apply to how particles are broken down and the amount of energy required in the process. Two of these laws even date back to the nineteenth century.
Because of the wide size and shape variation of particles, it is nearly impossible to accurately assess how much energy is needed to break down any given material. Some energy inevitably gets wasted as heat, making calculations even more difficult. As a result, the energy required can only be approximated via formulas and does not take into account mechanical losses from grinding or milling.
The three laws governing particle reduction are:
- Kick's Law states that the energy required to crush any given quantity of material to specific fractions is the same regardless of the initial size and applies to crushing solids.
- Rittinger's Law states that the energy required to reduce particle size relates directly to the increase of surface area and not length or width.
- Bond's Law, developed in 1952, looks at very large particles and predicts the energy required to crush solid materials – such as rocks or ore – to the size of material, surface area, and the formation of crack lengths.
Through experimentation in the milling process where the material is crushed, it has been found that Kick's Law reasonably estimates the energy needed for grinding abrasive particles with relatively small surface areas. For finer powders with larger surface areas, Rittinger's Law is more accurate. However, the most representative method is Bond's Law, which states that the required energy is proportional to the surface's square root compared to its volume.
Particle Engineering Applications
The industries in which particle engineering has proven beneficial are numerous. Industries analyze particle size to discover new properties for the materials they work to make those products more efficient, better, and safer.
Food Industry
Particle engineering often involves creating foods that come in the following particulate forms:
- Emulsions are combinations of either water in oil – found in spreads such as butter or margarine – or oil in water, including cream liquors, mayo, or ice cream.
- Powders made from coffee, tea, milk, and chili, along with wheat and other types of flour.
- Suspensions that include whole milk, juices, soups, pasta sauces, syrups containing fruit, some salad dressings, fruit preserves containing seeds, and yogurt with fruit bits.
How long food can be stored depends upon the size of the particles in it. Particle size in food also affects taste and smell as well as food texture.
Petroleum Industry
In the petroleum industry, the surface area of solid particles determines how quickly it reacts. The smaller the particles, the more likely a chemical reaction will occur. This includes oil, lubricants, gasoline, distillates, mixed fuels, and other petroleum products. A discovery in 1985 resulted in reducing cobalt particles' size in petroleum-based fuels, improving fuel efficiency. With petroleum utilized as a lubricant, larger particles within the fluid caused greater wear and tear, sometimes resulting in product failure.
Pharmaceutical Industry
Several factors related to particle engineering play into a drug's effectiveness when it comes to drug manufacturers.
These include:
- Drug delivery can be affected by particle size, including how quickly medicines are absorbed into the body's immune response.
- Drug design for oral or nasal sprays, in particular, need to consider particle size, as inhaled medicines with larger particulates can damage the lungs.
- Particle size and metabolism affect how quickly substances dissolve in solutions; the smaller the particles, the easier they dissolve
The particles' size is critical with inhaled pharmaceuticals, such as those used to control asthma or other pulmonary drugs that deliver medicine directly to the lungs. Larger particles will not make their way as deeply into the lungs.
Construction Industry
As with other industries, building materials tend to perform better when particle size decreases. When it comes to cement, particle size plays a significant role. Grinding particles is very energy-intensive, so finding the optimum particle size and distribution helps save both money and energy. Particle size also determines how much water you need, and when it comes to the aging process of concrete, larger particles within the mixture add to its strength and durability.
These are only a few of the applications and industries that will benefit from particle engineering in the future. Water treatment and purification, agricultural products such as pesticides, and even paint are other areas in which this technology will play a growing role.
