Search Results for sedimentation

In the handling of molten aluminum, it is fairly common to use filters as a part of the melting unit and in the gating and/or riser system. This article describes the methods of in-furnace and in-mold filtration, with an emphasis on the filtration of molten aluminum. It discusses the factors that influence the formation of inclusions. The article describes the three basic methods of mechanically removing or separating inclusions from molten metal. The methods include sedimentation, flotation, and positive filtration. The article provides a discussion on the types of molten-metal filters, including bonded-particle filters, cartridge filters, and ceramic foam filters. It lists the factors that are important in achieving optimum performance of any in-furnace filtering application. The article concludes with information on filtered metal quality and the methods of evaluation.

Particle size and size distribution have a significant effect on the behavior of metal powders during their processing. This article provides an overview of the sample preparation process for particle size measurement, which is a key step in the measurement of particle size distributions. Common particle size measuring techniques discussed in this article include sieve analysis, quantitative image analysis, laser diffraction, sedimentation methods, aerodynamic time-of-flight method, electrical zone sensing, and photon correlation spectroscopy. The advantages and disadvantages of these methods are reviewed.

The raw materials used in thermal spray processes are a critical parameter in the finished coating because the variations in their size, morphology, chemistry, and phase composition can significantly impact coating properties. Therefore, it is important to test and characterize the raw materials. This article discusses various characterization methods for powders. Topics discussed include: methods for determining particle size and/or size distribution; powder and coating stoichiometry; particle chemistry; and phase analysis by x-ray diffraction. This article discusses the characterization of thermal spray powders which involves the determination of particle size and/or size distribution and phase analysis by x-ray diffraction. It provides information on preferential volatilization and rapid solidification that influence compositional differences. Wet chemical methods, spectographic analysis, and atomic absorption spectrometry are also discussed.

Calcium phosphates react to form more stable salts in aqueous solutions. This phenomenon has been applied to the solidification process for the dental and medical cement calcium phosphate cement, which consists of multiple phases of calcium phosphates and calcium salts; solidification occurs by the formation of hydroxyapatite. Dicalcium phosphate consists of crystal water along with anhydrous and dihydrate salts. This article summarizes research achievements regarding dicalcium phosphate dihydrate (DCPD) production with controlled morphology and reactivity, including effects of an additive and of production conditions on precipitation. It also summarizes achievements made in the hybridization of nano-apatite onto DCPD particles.

Gravity has profound influences on most solidification and crystal growth processes. Modification of gravity over practical time scales for the purposes of modifying or controlling solidification proves to be a far more daunting and expensive technological challenge. This article discusses various microgravity solidification experiments that involve pure metals, alloys, and semiconductors and presents the official NASA acronyms for them. MEPHISTO, TEMPUS, the isothermal dendritic growth experiment, and advanced gradient heating facility, are also discussed.

For a wide range of new or better products, solidification processing of metallic materials from the melt is a step of uppermost importance in the industrial production chain. This article discusses the casting and solidification of molten metallic alloy along with the application of low-gravity platforms and facilities for solidification processing. It provides a description of dendritic growth studies and electromagnetic levitation. The article concludes with information on the in situ and real-time monitoring of solidification processing.

This article describes the corrosion mechanisms, challenges, and control methods in service water distribution systems. It provides a discussion on typical designs and water qualities for distribution systems used in fossil-fueled and nuclear power plants. The article also explains the techniques for controlling corrosion in service water systems.

This article explains how ceramic powders are made. It begins by briefly describing the raw materials used in structural clay products, whitewares, refractories, and advanced ceramics. It then examines various additives that promote uniformity at different stages of the process. After a description of the comminution process (wet and dry milling methods), it discusses batching and mixing operations and granulation methods. The article also deals with the effect of process variables and the steps involved in chemical synthesis, including preparation from solution and gas-phase reactions, filtration and washing, and powder recovery techniques. It concludes with a discussion on characterization, centering on size distribution analysis, specific surface area, density, porosity chemical composition, phase, and surface composition.

Computational modeling assists in addressing the issues of solid/liquid interface dynamics at the microlevel. It also helps to visualize the grain length scale, fraction of phases, or even microstructure transitions through microstructure maps. This article provides a detailed account of the general capabilities of the various models that can generate microstructure maps and thus transform the computer into a dynamic microscope. These include standard transport models, phase-field models, Monte Carlo models, and cellular automaton models.

This article focuses on microbiologically influenced corrosion (MIC) of military assets. It discusses the mechanisms of MIC in hydrocarbon fuels and atmospheric, immersion, and buried environments with specific examples. The article describes the behavior of metals and alloys, namely, copper alloy, nickel alloy, titanium and titanium alloys, aluminum alloys, stainless steels, and carbon steel in immersion environments.

Grain refinement in aluminum casting alloys tends to reduce the amount of porosity and the size of the pores and to improve mechanical properties, especially fatigue strength. This article provides information on measurement of grain size in alloys and describes the mechanisms of grain refinement in aluminum casting alloys. It reviews the use of boron and titanium as a grain refiner for aluminum casting alloys. The article discusses the best practices for grain refinement in various aluminum casting alloys. These include aluminum-silicon casting alloys, aluminum-silicon-copper casting alloys, aluminum-silicon-copper casting alloys, aluminum-zinc-magnesium casting alloys, and aluminum-magnesium casting alloys. The article also examines the benefits of grain refinement in aluminum casting alloys.

This article presents information regarding the use of protective coatings in municipal potable water systems, including raw water collection and transmission, water treatment plants, and treated water distribution. It provides useful guidance for the selection and use of protective coatings in these municipal water systems. The most commonplace corrosion-damage mechanisms are highlighted. The article describes the most common materials of construction found in municipal water systems, namely, cast iron, ductile iron, carbon steel, precast concrete cylinder pipe and reinforced concrete pipe, prestressed concrete tanks, and stainless steel. It provides information on the most common generic coating systems used for new steel tanks and water storage tanks. It concludes with a discussion of quality watch-outs when selecting or using protective coatings in municipal water systems.

Quality control of cemented carbides includes the evaluation of physical and chemical properties of constituent raw material powders, powder blends/formulations, green compacts, and fully dense finished product. This article provides a summary of the underlying principles and size ranges for the American Society for Testing and Materials (ASTM) standard methods of particle sizing and distribution. It presents the methods used to analyze the chemical composition of cemented carbide materials in a tabular form. The article also presents information on microstructural evaluation and physical and mechanical property evaluation of cemented carbides.