Metal powder is the base materials for the production of metallic component through the conventional powder metallurgy route or the emerging field of additive manufacturing. In any of these process routes, the properties of the finished product depends on the character of the base powder from which it is produced which is equally dependent on the process of production of the base powder. Therefore, there are different methods for producing metal powders with each method offering different particle morphology and purity. These methods include crushing (for brittle material), machining, mechanical pulverization, slotting, electrolysis, atomization of liquid metal using water, nitrogen, argon, or a combination of these, and reduction of metal oxides in hydrogen or using carbon. These metal oxides could be materials such as iron ore or iron oxide generated from pickling plants, in steel strip mills. Other methods include reduction of metal oxide with higher carbon containing, metal powder, chemical decomposition of metal carbonyls, and electrolytic processing of cathodic deposition from molten metal salts; and in some instances, recycling (Sharma, 2011). Each of these methods provides different particle morphology and characteristics. An illustration of typical powder shapes produced from some of these processes is shown in Figures 1 and 2.
New materials that can be tailored for individual applications are in constant demand. As the range of uses for powder metallurgy, hard metals and electronic materials expands, customer requirements are causing materials companies to come up with new products that have the necessary properties. Nickel can bring a number of benefits to these and other industries. It can improve the mechanical and fatigue properties of alloy steels, enhance conductivity and magnetic properties of electronic materials, act as a binder for holding together particulate materials and be used in filtration components in the form of high porosity products. These applications rely on high purity fine nickel powders and other special nickel forms being adapted to meet specific materials needs, for which a versatile production and processing technology is needed. The nickel carbonyl gas process fulfils these needs.
The Nickel Carbonyl Process
Nickel powder can be made by a number of different processes, including atomisation from melts or precipitation from solutions. However, these techniques tend to give relatively large particles and can be difficult to control economically at fine particle sizes. The nickel carbonyl gas process on the other hand tends to produce much finer particles, and with sufficient production know-how plus the latest computerised process controls, the particles produced can be precisely controlled to very accurate shapes and tolerances.
The nickel carbonyl gas process is used as a way of refining impure nickel. Nickel reacts with carbon monoxide to form nickel carbonyl gas (Ni(CO)4), which can be decomposed back to nickel metal at moderate temperatures with the recovery of carbon monoxide. Using thermal shock decomposition, fine or extra fine nickel powders can be made. Refineries in North America and Britain can each process up to 50,000 tonnes per year of nickel in his way, producing a wide range of different products. The use of such large volumes of carbonyl gas in the refineries allows the economic production of a range of nickel powders. New products can also be made by using the gas stream essentially as a coating medium. These new products include nickel coated graphite particulates, nickel coated carbon fibres and the large scale commercial production of high porosity nickel foam. Another benefit is that the process has no real waste products, with used gas is recycled back into the main refinery process.
Nickel Powders for Powder Metallurgy
The nickel powders produced for powder metallurgy applications have been developing step by step over recent decades as customer property specifications have become ever more stringent. Today, there are no ‘standard’ products, only certain families of powders that are based on different morphologies and subsequently fashioned for individual customer applications. Nickel powder production can now be controlled to give the powders the right particle size, density and especially particle shape to enhance the properties of low alloy steel powder metallurgy parts. Additions of nickel to the alloy typically range from 1.75-5%. Nickel-enhanced alloys are increasingly being used for making pressed and sintered parts, particularly in the automotive field.
Copper powder is produced by many processes including chemical precipitation, electrolytic deposition, oxide reduction, water atomization, gas atomization, and jet milling. Accordingly, Cu powders are commercially available in a wide range of particle shapes and sizes. Electrolytic and chemical powders exhibit poor packing and poor rheology in molding, so they have been largely unsuccessful for MIM (Wada, Kankawa, & Kaneko, 1997). Characteristics of examples of the other types are summarized in Table 20.2. Representative scanning electron micrographs are given in Fig. 20.4. These powders all have similar particle sizes but different morphologies. Typical purities reported by the manufacturers are about 99.85 wt%; however, oxygen contents can range up to 0.76 wt%. Powders are usually shipped containing desiccant and proper powder storage is essential to avoid oxidation between purchase and use.
It is important to try this experiment before doing it as a demonstration, as different samples of aluminium powder can react differently. The induction period for some samples can be quite long. However, this is an impressive and spectacular demonstration, proving that water can be a catalyst. It also shows that aluminium is a very reactive metal, and that its usual unreactive nature is due to the surface oxide layer.
The chemical properties of iodine are very similar to those of bromine and chlorine. However, its reactions are far less vigorous. It can also act as an oxidant for a number of elements such as phosphorus, aluminium, zinc and iron, although increased temperatures are generally required. Oxidation of finely dispersed aluminium with iodine can be initiated using drops of water. The reaction is strongly exothermic, and the excess iodine vaporises, forming a deep violet vapour.
Titanium powder metallurgy can produce high performance and low cost titanium parts. Compared with those by conventional processes, high performance P/M titanium parts have many advantages: excellent mechanical properties, near-net-shape and low cost, being easy to fabricate complex shape parts, full dense material, no inner defect, fine and uniform microstructure, no texture, no segregation, low internal stress, excellent stability of dimension and being easy to fabricate titanium based composite parts.
Titanium alloys parts are ideally suited for advanced aerospace systems because of their unique combination of high specific strength at both room temperature and moderately elevated temperature, in addition to excellent corrosion resistance. Despite these features, use of titanium alloys in engines and airframes is limited by cost. The alloys processing by powder metallurgy eases the obtainment of parts with complex geometry.
The metallurgy of titanium and titanium-base alloys has been intensely investigated in the last 50 years. Titanium has unique properties like its high strength-to-weight ratio, good resistance to many corrosive environments and can be used over a wide range of temperatures. Typical engineering applications of titanium alloys include the manufacture of cryogenic devices and aerospace components.
Cosmetic boron nitrides
What are these famous"white powders" that cosmetic formulators love? Why are they so addictive when you start touching them? How can they help to improve the sensoriality, even the sensuality of a cosmetic product? Which quality to choose for which application?
Here are some questions that beauty technicians have been asking themselves since the appearance and marketing of cosmetic grade boron nitride powder.
But first let's talk about the cosmetic quality of boron nitride. In space, the association of BN molecules can take two forms:
- BN hexagonal = honeycomb slats that can stack one on top of the other.
These two shapes have different properties, namely the hexagonal shape allows the sliding of the sheets, which gives it a lubricating capacity. While the cubic shape is very rigid, which gives it great hardness.
The BN cosmetic is hexagonal in shape and comes in the form of white powder with a very lubricating but non-greasy touch. Moreover, it is a material which is very resistant, inert and non-toxic and does not present any danger… neither for the consumer, nor for the formulator which must guarantee the stability of its product. It is for all these reasons that the popularity of BN is rising to the point of replacing more and more good old talc in cosmetic formulations.
The manufacturers of cosmetic raw materials have understood this well and present to date several ranges of different qualities, thus bringing many cosmetic properties to the BN : - Soft and silky touch - Slippery touch improves the spreading of the product on the skin - Light reflector for a soft focus effect - Opacity, transparency, pearly luster or even glitter depending on the crystal form - Sebum absorber - Mattifying effect - Good compaction agent - High adhesion to the skin for high hold or even non-transfer effect - High chemical stability, unaffected by pH
These powders are thus used as well for care products as make-up products and in all types of cosmetic formulations; emulsions, anhydrous casts, compact powders, even lotions where they bring several properties quoted.
Superfine powder is not just a functional material, but also established a solid foundation for the compounding and development of new functional material. The excellent performance of superfine powder exsites in its surface effect and volume effect. the smaller the size of powder, the larger the ratio between Area and volume. Because the BET (surface area) of superfine particle is large, and easy to agglomerate, so we need to do surface treatment/modify to the powder and make it easy dispersing and maximize its performance.
2.Surface modification of powder
surface modification of powder is to use inorganic substance and organic substance coating the surface of powder either by physical method or chemical process. By coating layer to the powder, the powder is recognized as composite powder that has "core" and "shell layer". and different shell layer could improve the performance of powder such as anti-corrosive, durability, light, thermal and chemical stability etc. by effecting its hydrophily,hydrophobicity,hydrophily, hydrophobicity, catalytic etc.
It is mainly applied in the production of powder metallurgy, electronic materials, friction materials, oil bearing, electrical contact materials, conductive materials, medicine, diamond products and machinery parts. In high-tech fields of petroleum catalysts, lubricants, conductive decorative coatings and electromagnetic shielding materials, the nano-copper powder is also widely used.
Processing and application technology of superfine copper powder has been a major bottleneck for development of the industry. Silty soft copper, grinding processing difficulties, easily oxidized in moist air. Water atomization high cost, low yield, non-uniform particles, and unstable quality. In addition, many newly developed production technology, part of the complex process, the electrical equipment that require high investment, low production yield, high cost, wide particle distribution, environmental pollution, energy consumption, quality instability and other issues, but also did not become a mainstream technology. Newly developed chemical reduction method can only produce nano-copper powder, and its production process is still in the laboratory research stage, secondary pollutants to deal with difficult due to the high cost of raw materials, low production yield and high cost led to products for sale The high price odd enable customers difficult to accept, in particular, is not ideal in many areas of nanoscale copper powder effect. In addition, unlike the ultra-fine copper powder metal copper, and easily oxidized to copper oxide in the air, only the protection of nitrogen, sealed package, but also affect the large-scale promotion and application of ultra-fine copper powder.
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