Search Results for chemical methods

This article provides a discussion on the process descriptions, processing conditions, and processing variables of the most common chemical methods for metal powder production. These methods include oxide reduction, precipitation from solution, and thermal decomposition. Methods such as precipitation from salt solution and gas, chemical embrittlement, hydride decomposition, and thermite reactions are also discussed. The article also discusses the methods used to produce powders electrolytically and the types of metal powders produced. The physical and chemical characteristics of these powders are also reviewed.

Various powder production processes allow precise control of the chemical composition and physical characteristics of powders and allow tailoring of specific attributes for targeted applications. Metal powders are produced by either mechanical methods or chemical methods. The commonly used mechanical methods include water and gas atomization, milling, mechanical alloying, and electrolysis. Some chemical methods include reduction of oxides. This article provides information on the reliable techniques for powder characterization and testing to evaluate the chemical and physical properties of metal powders, both as individual particles and in bulk forms.

This article focuses on wet chemical methods that have stood the test of time in laboratories around the world. It begins with a description of the appropriateness of classical wet methods. This is followed by sections on sampling procedures, basic chemical equilibria, and wet analytical chemistry. Mechanical methods and nonoxidizing acids and/or acid mixtures for dissolving solid samples for wet chemical analysis are then reviewed. Qualitative methods that are used to identify materials by wet chemical reaction are also included. The article provides information on various methods for the separation of chemical mixtures and on the types of gravimetry and titrimetry. Strategies for removing inclusions are also included to aid in their compositional understanding. The article also briefly describes the processes involved in chemical surface studies and partitioning of oxidation states. It ends by presenting some examples of the applications of classical wet methods.

This article discusses the various categories of nontraditional machining processes that are subdivided according to the form of energy being harnessed. These include mechanical, electrical, thermal, and chemical methods.

Case depth is the normal distance from the surface of the steel to the start of the core. Measurement of case depth is highly sensitive to the type of case hardening, original steel composition, quenching condition, and even to the testing method. This article describes the various methods of measuring case depth in steels, including chemical methods such as the combustion analysis and spectrographic analysis, microhardness test method, macroscopic and microscopic visual methods, and nondestructive methods. It contains a table that provides approximate equivalent hardness numbers for steel.

This article discusses the need of and the strain basis for residual stress measurements and describes the nature of residual stress fields. A generic destructive stress relief procedure is described along with the issues generally involved in each procedural step. The article presents the stress reconstruction equations to be used for computational reconstruction of the stress fields from the measured strains for the destructive methods. It provides information on the sectioning, material removal, strain measurement, and chemical methods of residual stress measurement. The article reviews the semidestructive methods of residual stress measurement: blind hole drilling and ring coring, spot annealing, and X-ray diffraction techniques. Nondestructive methods such as neutron diffraction, ultrasonic velocity, and magnetic Barkhausen noise techniques, are also discussed.

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.

Particle image analysis of metal powders can be easily performed with optical macroscopes and microscopes. This article provides examples of the particle image analysis on powders used in the powder metallurgy industry.

This article describes the eight chemical cleaning methods, namely, circulation, fill and soak, cascade, foam, vapor-phase organic, steam-injected, on-line chemical, and mechanical cleaning. It presents information on deposit types, solvents used to remove them, and construction material incompatibilities in a table. The article summarizes the uses of chemical cleaning solutions, including hydrochloric acid, phosphoric acid, and sulfamic acid, as well as the additives used to neutralize their impact on corrosion. It discusses the chemical cleaning procedures, including selection of cleaning method and solvent, documentation of cleaning, and corrosion monitoring in chemical cleaning.

This article provides an overview of the general methods of metal powder production. It details the primary methods for particle sizing used in additive manufacturing: sieving, laser diffraction and scattering, and digital image analysis. Methods of interpreting and understanding particle size distribution (PSD) data are presented, with an emphasis on the differences between count- and volume-based PSDs. The article then outlines practices for both qualitative and quantitative assessment of particle morphology.

This article provides information on basic chemical equilibria, wet analytical chemistry, and the appropriateness of classical wet methods. It focuses on nonoxidizing acids and oxidizing acids. The article includes information on the qualitative methods used to identify materials by wet chemical reaction. Gravimetry, in which a chemical species is weighed; titrimetry, which involves volume measurement of a liquid reactant; and a host of separation techniques, which require diverse forms of laboratory manipulation, are discussed. The article briefly describes the partitioning of oxidation states as well as those applications in surface studies and rapid material identification in which chemical techniques have proved useful.

Case hardening is defined as a process by which a ferrous material is hardened in such a manner that the surface layer, known as the case, becomes substantially harder than the remaining material, known as the core. This article discusses the equipment required, process variables, carbon and hardness gradients, and process procedures of different types of case hardening methods: carburizing (gas, pack, liquid, vacuum, and plasma), nitriding (gas, liquid, plasma), carbonitriding, cyaniding and ferritic nitrocarburizing. An accurate and repeatable method of measuring case depth is essential for quality control of the case hardening process and for evaluation of workpieces for conformance with specifications. The article also discusses various case depth measurement methods, including chemical, mechanical, visual, and nondestructive methods.

This article describes testing and characterization methods of ceramics for chemical analysis, phase analysis, microstructural analysis, macroscopic property characterization, strength and proof testing, thermophysical property testing, and nondestructive evaluation techniques. Chemical analysis is carried out by X-ray fluorescence spectrometry, atomic absorption spectrophotometry, and plasma-emission spectrophotometry. Phase analysis is done by X-ray diffraction, spectroscopic methods, thermal analysis, and quantitative analysis. Techniques used for microstructural analysis include reflected light microscopy using polarized light, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis of X-rays, and wavelength dispersive analysis of X-rays. Macroscopic property characterization involves measurement of porosity, density, and surface area. The article describes testing methods such as room and high-temperature strength test methods, proof testing, fracture toughness measurement, and hardness and wear testing. It also explains methods for determining thermal expansion, thermal conductivity, heat capacity, and emissivity of ceramics and glass and measurement of these properties as a function of temperature.

This article provides an overview of surface contaminants that may affect the heat treatment processes and end-product quality. It presents information on the chemicals used to clean different surface contaminants of steels. The article discusses three types of cleaning methods, namely, mechanical, chemical, and electrochemical and their effectiveness and applicability. The mechanical cleaning methods include grinding, brushing, steam or flame jet cleaning, abrasive blasting, and tumbling. Solvent cleaning, emulsion cleaning, alkaline cleaning, acid cleaning, pickling, and descaling are chemical cleaning methods. The electrochemical cleaning methods include electropolishing, electrolytic alkaline cleaning, and electrolytic pickling. The article provides information on cleanliness measurement methods such as qualitative tests and quantitative tests to ensure product quality. Health hazards that may be associated with each cleaning method and the general control measures to be used for each hazard are tabulated.

The electronic microcircuit industry has placed severe demands on metal suppliers to provide metals of the highest reproducible purity attainable as a result of the constant quest for the true values of physical and chemical properties of metals. This article describes the commonly used methods for ultrapurification of metals produced by electrolytic processes, including fractional crystallization, zone refining, vacuum melting, distillation, chemical vapor deposition, and solid state refining techniques. In addition, it describes the trace element analysis and resistance-ratio test methods used to characterize purity. Tables list the values for resistance ratios of zone-refined metals and their corresponding chemical compositions, and provide an example of the detection of impurities to concentrations in the parts per billion range, utilizing a combination of the glow discharge mass spectroscopy method and Leco combustion methods.