Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications

Free download. Book file PDF easily for everyone and every device. You can download and read online Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications file PDF Book only if you are registered here. And also you can download or read online all Book PDF file that related with Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications book. Happy reading Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications Bookeveryone. Download file Free Book PDF Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications at Complete PDF Library. This Book have some digital formats such us :paperbook, ebook, kindle, epub, fb2 and another formats. Here is The CompletePDF Book Library. It's free to register here to get Book file PDF Chemical Process in Liquid and Solid Phase: Properties, Performance and Applications Pocket Guide.

RCC is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin. After curing at high temperature in an autoclave, the laminate is pyrolized to convert the resin to carbon, impregnated with furfural alcohol in a vacuum chamber, and cured-pyrolized to convert the furfural alcohol to carbon. To provide oxidation resistance for reuse ability, the outer layers of the RCC are converted to silicon carbide. Other examples can be seen in the "plastic" casings of television sets, cell-phones and so on.

These plastic casings are usually a composite material made up of a thermoplastic matrix such as acrylonitrile butadiene styrene ABS in which calcium carbonate chalk, talc , glass fibers or carbon fibers have been added for added strength, bulk, or electrostatic dispersion. These additions may be termed reinforcing fibers, or dispersants, depending on their purpose. Polymers are chemical compounds made up of a large number of identical components linked together like chains. They are an important part of materials science. Polymers are the raw materials the resins used to make what are commonly called plastics and rubber.

Plastics and rubber are really the final product, created after one or more polymers or additives have been added to a resin during processing, which is then shaped into a final form. Plastics which have been around, and which are in current widespread use, include polyethylene , polypropylene , polyvinyl chloride PVC , polystyrene , nylons , polyesters , acrylics , polyurethanes , and polycarbonates and also rubbers which have been around are natural rubber, styrene-butadiene rubber, chloroprene , and butadiene rubber.

Plastics are generally classified as commodity , specialty and engineering plastics. Polyvinyl chloride PVC is widely used, inexpensive, and annual production quantities are large. It lends itself to a vast array of applications, from artificial leather to electrical insulation and cabling, packaging , and containers. Its fabrication and processing are simple and well-established. The versatility of PVC is due to the wide range of plasticisers and other additives that it accepts. The term "additives" in polymer science refers to the chemicals and compounds added to the polymer base to modify its material properties.

Such plastics are valued for their superior strengths and other special material properties. They are usually not used for disposable applications, unlike commodity plastics. Specialty plastics are materials with unique characteristics, such as ultra-high strength, electrical conductivity, electro-fluorescence, high thermal stability, etc.

The dividing lines between the various types of plastics is not based on material but rather on their properties and applications. For example, polyethylene PE is a cheap, low friction polymer commonly used to make disposable bags for shopping and trash, and is considered a commodity plastic, whereas medium-density polyethylene MDPE is used for underground gas and water pipes, and another variety called ultra-high-molecular-weight polyethylene UHMWPE is an engineering plastic which is used extensively as the glide rails for industrial equipment and the low-friction socket in implanted hip joints.

The study of metal alloys is a significant part of materials science. Of all the metallic alloys in use today, the alloys of iron steel , stainless steel , cast iron , tool steel , alloy steels make up the largest proportion both by quantity and commercial value. Iron alloyed with various proportions of carbon gives low, mid and high carbon steels.

LIQUID CRYSTAL IN URDU:FSc Chemistry Book1 -Properties & Types of Liquid Crystal and their uses

An iron-carbon alloy is only considered steel if the carbon level is between 0. For the steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. Heat treatment processes such as quenching and tempering can significantly change these properties, however. Cast Iron is defined as an iron—carbon alloy with more than 2. Nickel and Molybdenum are typically also found in stainless steels. Other significant metallic alloys are those of aluminium , titanium , copper and magnesium.

Copper alloys have been known for a long time since the Bronze Age , while the alloys of the other three metals have been relatively recently developed. Due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. The alloys of aluminium, titanium and magnesium are also known and valued for their high strength-to-weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. These materials are ideal for situations where high strength-to-weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications.

The study of semiconductors is a significant part of materials science. A semiconductor is a material that has a resistivity between a metal and insulator. Its electronic properties can be greatly altered through intentionally introducing impurities or doping. From these semiconductor materials, things such as diodes , transistors , light-emitting diodes LEDs , and analog and digital electric circuits can be built, making them materials of interest in industry. Semiconductor devices have replaced thermionic devices vacuum tubes in most applications. Semiconductor devices are manufactured both as single discrete devices and as integrated circuits ICs , which consist of a number—from a few to millions—of devices manufactured and interconnected on a single semiconductor substrate.

Of all the semiconductors in use today, silicon makes up the largest portion both by quantity and commercial value. Monocrystalline silicon is used to produce wafers used in the semiconductor and electronics industry. Second to silicon, gallium arsenide GaAs is the second most popular semiconductor used. Due to its higher electron mobility and saturation velocity compared to silicon, it is a material of choice for high-speed electronics applications. These superior properties are compelling reasons to use GaAs circuitry in mobile phones, satellite communications, microwave point-to-point links and higher frequency radar systems.

Other semiconductor materials include germanium , silicon carbide , and gallium nitride and have various applications. Materials science evolved—starting from the s—because it was recognized that to create, discover and design new materials, one had to approach it in a unified manner. The field thus maintains close relationships with these fields. Also, many physicists, chemists and engineers also find themselves working in materials science. The field of materials science and engineering is important both from a scientific perspective, as well as from an engineering one.

When discovering new materials, one encounters new phenomena that may not have been observed before. Hence, there is a lot of science to be discovered when working with materials. Materials science also provides a test for theories in condensed matter physics.

Materials are of the utmost importance for engineers, as the usage of the appropriate materials is crucial when designing systems. As a result, materials science is an increasingly important part of an engineer's education. From Wikipedia, the free encyclopedia. Main article: History of materials science.

Main article: Nanostructure. Main article: Microstructure. Main article: Crystallography. Main article: Chemical bonding. Main article: List of materials properties. Main article: Thermodynamics. Main article: Chemical kinetics. Main article: Nanomaterials. Main article: Biomaterial. Main article: Ceramic. Main article: Composite material. Main article: Polymer.

Main article: Alloy. Science portal Engineering portal. Archived from the original on A Search for Structure. MIT Press. August Retrieved 3 August Physics in Perspective. Bibcode : PhP John Wiley and Sons, pp. Materials Science and Engineering — An Introduction 8th ed.

  • An Angle of Light;
  • How to Beat the Casino: Humorous Systems Revealed.
  • The Suprise of Love (Oberon Classics).
  • Cold Altar: An Alex Bourque Mystery (Small Town PI series)?
  • Mechanism of drying.
  • Boomtown Saloons: Archaeology And History In Virginia City (Shepperson Series in Nevada History).

Navrotsky Applied Physics Letters. Bibcode : ApPhL.. Archived from the original PDF on June 18, Physical Review Letters. Bibcode : PhRvL.. Archived from the original PDF on Retrieved Construction Digital. Archived from the original on 31 December Retrieved 18 November BBC Click. The Guardian. Archived from the original on 2 September BBC News.

  • Liquid Chromatography - Chemistry LibreTexts.
  • Leaving Love (Georgia Low Country Fiction Book 4)!
  • The Action Research Planner: Doing Critical Participatory Action Research.
  • Managing Aid: Practices of DAC Member Countries?
  • Materials science - Wikipedia.
  • The Boss;
  • Recommended for You;

Retrieved 27 April Kraft [ ] used an optimization algorithm for compaction and LPS to predict and minimize the distortion as a result of inhomogeneous density distributions in the green body. The model captured qualitatively the important phenomenon in LPS, such as wetting and microstructure behavior, including deformation, coalescence, pore migration, and pore elimination.

Examples of FEM simulations of 3D components. The version given in a is based on the European Powder Metallurgy Association inverted T distortion test geometry with actual shape after LPS for comparison and b is based on a test geometry where the simulation predicts spreading of the free standing fingers. The simulations correspond to W—8. FEM proves most useful. The approach relies on a database of measured material properties for input.

Simulation of the final component size and shape, properties, and defects are fast using personal computer resources. The reduction of the time and cost needed to obtain material properties to feed the FEM simulations is an area of current research, since experimental testing for each system is quite expensive. The hope is that such synthesis of material properties might be possible based on material informatics using existing databases or new techniques such as data mining and computer thinking algorithms.

Multiscale modeling is now applied to solid-state sintering. The extension to LPS is still pending. Two cases have been reported; one goes from DEM for mesoscale to macroscale continuum mechanics [ ] and the other goes from MC simulation for microscale to FEM for macroscale [ ]. Successful development of these methods will undoubtedly require large research investments. However, much benefit might be possible if more efficient processes can be developed, with better optimization and time reduction routines applicable to LPS. Liquid phase sintering emerged from an empirical origin that started in the s.

Since the s, there has been progress in the quantitative treatment of LPS to the point of effective computer simulations that predict microstructure, component size, and component shape. The scientific principles have advanced to include many processing factors and provide a platform for the identification of new systems.

Summary sketch of the divergence in initial structure when the melt forms in LPS, where swelling is associated with melt solvation into the solid and densification is associated with solid solvation into the liquid. Example phase diagram for LPS where the ideal combination of composition and temperature gives solid solubility in the liquid eutectic liquid in this case with a low solubility of the liquid in the solid.

The melting temperature decrease gives a processing temperature benefit. A schematic of the overlapping events in LPS; densification is very rapid at short times where chemical diffusion is initially rapid, and as liquid forms and solution-reprecipitation occurs the densification slows. Final sintering of the solid skeleton can be a slow process. As the particle size, liquid content, and other factors are adjusted the shape and placement of this curve will change.

A schematic map illustrating density versus the liquid volume behavior. With a low liquid content the bulk of densification will be by slow solid phase sintering, while with a high-liquid content it is possible to reach full density during heating to the liquid formation temperature. Most LPS compositions require several cooperating mechanisms, with solution-reprecipitation being most important. During solution-reprecipitation LPS, the rate of grain growth depends on the solid—liquid contact area.

Hence, as illustrated here the grain growth rate constant depends on the liquid content to the inverse two-thirds power. Shown here are data from several LPS studies [ 15 , ]. There is much about LPS that is in need of research attention. From an industrial view, the most pressing needs relate to dimensional control. Because of tight industrial tolerances, many LPS materials are machined or ground after sintering. These post-sintering dimensional adjustments are costly. How can LPS be used to give the final size and shape?

What factors, beside green density gradients, contribute to distortion during LPS? How might nonuniform sintering shrinkage be minimized? Can changes in the starting microstructure for example, via particle size, mixing technology, or compaction conditions be used to minimize distortion? Efforts focused on these areas show LPS systems often distort shortly after the liquid forms and continue to distort with a viscous flow or creep behavior.

Is it possible to separate densification events from distortion to improve sintered tolerances? Possibly there are gains from idealized cycles, such as by slow heating. Modeling efforts in LPS have included most of the key concepts. The initial chemical gradients associated with coated or mixed powder are important to the initial sintering trajectory, as is the green body density homogeneity. Recent efforts have made good progress using integral work concepts to explain LPS densification, distortion, and coarsening [ , , ]. Next will be integration of these ideas to include particle size and solubility effects so the models can be generated with minimum experimentation.

In turn, constitutive equations derived from simple relations will enable accurate computer simulations of the size, shape, density, microstructure, properties, and performance. The authors are most thankful to Wei Li for his great care in reviewing the manuscript. Skip to main content Skip to sections.

Advertisement Hide. Download PDF. Review: liquid phase sintering. Open Access. First Online: 01 January Introduction Packed particles heated near their melting temperature bond together by sintering. From these efforts emerge a conceptual view of the events taking place, as sketched in Fig. The solid grains undergo solid-state sintering during heating. Depending on the solid—liquid solubility relations, different microstructure evolution pathways are possible. The common situation is for the liquid to wet the solid.

In this case, the newly formed liquid penetrates between the solid grains, dissolves the sinter bonds, and induces grain rearrangement. Further, because of solid solubility in the liquid, the liquid improves transport rates responsible for grain coarsening and densification.

Chemical Process in Liquid and Solid Phase

The surface energy associated with pores leads to their annihilation, while there is progressive microstructure coarsening and bonding to increase rigidity. Open image in new window. The LPS microstructure is constantly evolving. After an initial transient, the overall scale of the microstructure increases with time, while the relations between phases vary only by a time-dependent scaling parameter. With prolonged sintering, the terminal condition would consist of a single grain with an associated liquid, such as illustrated in Fig.

Prior to reaching this terminal condition, the LPS microstructure is characterized by porosity, pore size, grain size, and distributions in most features. However, years are required to transform micrometer-sized particles into millimeter-sized grains, times much longer than used in practice. Even so, during a typical LPS cycle, hundreds to thousands of initial particles coalesce to form each final grain. After LPS, the microstructure consists of the solid grains with a solidified liquid network, and possibly residual pores. In some cases, the pores are retained for lubrication, frangibility, or filtration attributes.

Thus, liquid phase sintered microstructures exist in several variants, as illustrated in Fig. Accordingly, substantial performance differences result, especially in properties such as hardness, strength, and elastic modulus. This is especially true for the WC—Co cemented carbides [ 16 , 17 ]. Each phase in the LPS microstructure is characterized by shape and size distributions, and variations in the degree of connection.

The greatest attention is devoted to the solid grain size. Coarsening gives a steady-state morphology that changes length scale as time progresses, as illustrated in Fig. The structures appear similar except for the difference in magnification. When the liquid forms in LPS, the microstructure consists of solid, liquid, and vapor.

1st Edition

Liquid spreading on the solid replaces solid—vapor interfaces with liquid—solid and liquid—vapor interfaces. As shown in Fig. A low-contact angle induces liquid spreading over the solid grains, providing a capillary attraction that helps densify the system. For small grains, contact stress can rival that seen in pressure-assisted sintering techniques, such as hot isostatic pressing [ 31 ]. In practice, a broad range of capillary conditions exist, since the microstructure is composed of a range of grain sizes, grain shapes, pore sizes, and pore shapes, each with a different capillary condition.

A wetting liquid moves to occupy the lowest energy configuration, so it preferentially flows to the smaller grains and pores.

Solid-phase extraction columns in the analysis of lipids

This gives rise to rearrangement densification [ 32 ]. Rearrangement takes a few minutes, since heat flow from the furnace determines the rate of melt formation, and compacted powders are poor thermal conductors [ 33 ]. A high-contact angle indicates poor wetting, so the liquid retreats from the solid. This results in compact swelling and liquid exuding from pores, as evident in Fig. Thus, depending on the contact angle, liquid formation causes either densification or swelling. The magnitude of the capillary effect depends on the amount of liquid, particle size, and contact angle [ 31 ].

The solid—vapor dihedral angle is observed where a grain boundary intersects the vapor phase, but in LPS more concern is given to the intersection of the grain—grain contacts with the liquid phase, as illustrated in Fig. Using Eq. The relative change in dihedral angle is proportional to the solid—liquid surface energy change associated with solvation of the solid into the liquid.

Small changes in the solid—liquid surface energy are sufficient to give liquid penetration of grain boundaries. Newly formed wetting liquid spread to fill small pores and preferentially penetrate grain boundaries [ 34 ]. Dissolution reactions during spreading decrease the solid—liquid interfacial energy below the equilibrium value [ 35 ]. This causes a dihedral angle variation as illustrated in Fig. After liquid formation and spreading, the solid—liquid system approaches equilibrium. With a low liquid content, the liquid fills pockets between grains, as illustrated in Fig.

However, during the liquid flow the reduction in skeletal strength leads to component distortion [ 37 ]. In some cases, the liquid forms lenticular islands on the grain boundaries to give a necklace microstructure, as shown in Fig. Parameters such as the dihedral angle have a natural distribution that reflects the grain boundary energy variation between different grain—grain contacts. The dihedral angle distribution tends to stabilize eventually. It is common to report typical values, such as the mean or median.


The grains are less spherical with more solid—solid contacts at the higher solid contents. The conceptual lowest value is 20 vol. Assuming the solid is denser than the liquid, gravity causes the solid volume fraction to increase with depth in the body. The lowest solid contents are created using free-settling solid grains. This is illustrated in Fig. In most situations, it is assumed the pores are smaller than the grains, as evident in Fig.

Pores collect between the grains and are wetted by the liquid. Capillarity drives the liquid to preferentially fill smaller pores [ 58 ]. As the smaller pores fill, the mean pore size increases while the porosity and number of pores decrease. Further, because of pore buoyancy, there is progressive migration of the pores to the top of the component. Beere [ 59 ] describes the idealized microstructure based on surface energies; but inhomogeneities cause nonuniform liquid formation and spreading in the component [ 60 ].

Large melt-forming particles generate pores when they form a liquid [ 61 ]. In cases where the melt-forming particles are large and the compact has a low porosity, this spreading leads to swelling, but densification still occurs at longer times [ 62 ]. Large pores can be filled over time by meniscus growth if there is no trapped gas in the pores [ 71 , 72 ]. These large pores are stable up to a critical size. Trapped gas in the pores acts to inhibit final densification [ 73 ]. Initially the pores are irregular in shape. Later they form a rounded network of connected pores.

Unfortunately, several LPS systems exhibit delayed pore generation where a high-temperature reaction produces an insoluble gas [ 70 , 73 ]. An example is shown in Fig. Grain shape depends on the volume fraction of solid, dihedral angle, and surface energy anisotropy. Contacts between neighboring grains cause the grains to flatten. The effect is most pronounced at low liquid contents.

Beere [ 59 ] solved for the equilibrium grain shape under various assumed conditions. In a complimentary view, Fig. The liquid shape and grain shape are related. Wray [ 77 ] isolated the six structures shown in Fig. These correspond to the six regions on the dihedral angle—volume fraction liquid map in that figure. A dihedral angle below The liquid forms discrete pockets for low liquid contents and large dihedral angles, independent of grain size. Calculations for grain shape have been extended to gradient compositions [ 79 ].

As part of pore elimination, the grains undergo both size and shape changes by solid dissolution into the liquid, diffusion of that dissolved solid through the liquid, followed by reprecipitation of dissolved solid onto lower energy solid surfaces. This process is called solution-reprecipitation. This process allows the larger grains to grow at the expense of the smaller grains. Accordingly, the dissolving small grains are spherical [ 80 ], while the growing large grains are flat faced [ 81 ].

Warren [ 82 ] determined how grain shape varied due to anisotropic solid—liquid surface energy. The grain shape changes to a flat-faced structure with a relatively small change in orientation-dependent surface energy. The micrograph in Fig. Chemical additives segregated to the interface provide one means to adjust either grain size or shape in the sintered product [ 83 ]. Grain size in LPS materials is usually reported as the mean intercept length.

Other measures include the number of grains per unit area or the diameter of a grain with equivalent projected area. Models for the LPS grain size distribution predict the 3D sizes while most experimental data give the 2D random intercepts. Two transformations are required to go from the 2D random intercepts to true grain sizes; the first transforms the intercepts into equivalent circles, and the second transforms the circles into equivalent spheres.

Due to the randomness of the section plane with the grain, few grains are sliced at their largest diameter. Even for the case of monosized spheres, the 2D grain size is smaller than the actual size. Further, most models assume isolated spheres while the actual microstructures consist of connected nonspherical grains [ 84 ]. Grain agglomeration is inherent to LPS, even in dilute systems [ 85 ]. Accordingly, coalescence must be included in the grain size distribution models [ 86 ]. Another problem relates to the assumed diffusion field around each grain [ 87 ].

Observations show each grain exhibits a growth or shrinkage trajectory that depends on its local environment, not on the mean field [ 88 ]. In spite of these several difficulties, LPS grain size converges to a self-similar distribution, independent of the starting particle size distribution [ 89 ]. A two-way mathematical technique allows extraction of the 3D grain size distribution [ 90 ].

The cumulative 3D distribution gives a form similar to Eq. The grain separation is important to mechanical behavior, since often the matrix phase resists crack propagation. The grain separation depends on grain size, liquid content, and dihedral angle [ 23 , 82 , 93 ].

The contact between grains is not always circular, as seen in Fig. There are instances where very different contact shapes are evident, including half-moon and doughnut shapes. Many solid—solid contacts involve grains of differing sizes. In such cases the grain boundary is curved and favors grain coalescence, with the large grains absorbing the small grains, often evident as elongated grains in the microstructure. The grain coordination is the number of touching grains it has in three dimensions. Three-dimensional grain coordination is hard to measure, so the convention is to use 2D measures such as contiguity or connectivity.

Contiguity C SS is the relative solid—solid interface area in the microstructure. Contiguity initially varies in LPS due to liquid penetration of the grain boundary followed by subsequent neck growth between contacting grains. After a few minutes, it tends to stabilize at a value that depends on the solid volume fraction and dihedral angle, independent of the grain size. For monosized spherical grains, Fig. The VC—Co system has a low dihedral angle, so it has a lower contiguity trace.

This relation is less accurate at high-solid contents since it does not include a grain shape effect. For nonspherical grains, the grain contacts are variable in size and shape, but contiguity exhibits a similar variation with solid content [ 17 , 97 ]. Connectivity is a related parameter based on the average number of grain—grain connections per grain as observed on a random 2D cross-section. It is effective in explaining the resistance to distortion during LPS [ 98 ].

Early in LPS the bonds between solid grains grow so contiguity increases over time. Any change in interfacial energies changes the dihedral angle and contiguity [ 39 ]; thus, contiguity drops on first melt formation, with a subsequent time-dependent behavior, as illustrated in Fig. Liquid phase sintering is a normalization process. Although the starting point in LPS depends on the green body porosity, particle size, and homogeneity, still the microstructure converges to a common evolution pathway.

During LPS, porosity is usually decreasing, but since smaller pores are annihilated first the mean pore size increases while the grain size is increasing.

  1. Siddur Bayit The Believers Hebrew Prayer Companion.
  3. About For Books Chemical Process in Liquid and Solid Phase: Properties, Performance and?
  4. General Scheme!
  5. Letterboxed: The Evolution of Widescreen Cinema.
  6. Looking for other ways to read this?!
  7. Further, the dihedral angle and contiguity vary dramatically when the liquid first forms. After the transients, the microstructure takes on a self-similar aspect that largely varies with grain size. Thus, microstructures from many different materials look similar in spite of chemical differences.

    Examples from semisolid processing and geological materials exhibit these same characteristics [ , ]. System wt. Chemical interactions Mixed powders with different compositions represent a nonequilibrium condition. This microstructure continues to be out of equilibrium during the preliquid stage of sintering. Even so, equilibrium thermodynamics provides a good indicator of the sintering behavior, with solubility being a dominant factor.

    In the simplest case, the binary phase diagram provides a first estimate of the potential for densification of the mixed phases. In LPS, particle size is important because it determines the curvatures, contact stress, and capillarity, thereby easing densification. A high green density results in a higher-sintered density, but in mixed powder systems the behavior depends on the solubility.

    Solubility between the two powders determines the tendency toward swelling. Microstructure changes such as densification, grain bonding, and grain growth occur before the liquid forms. Initially grain growth is restrained by pore drag, so grain growth accelerates as full density is reached. During liquid formation the grain size goes through a rapid change. In turn, a larger grain size leads to longer diffusion distances and a reduced rate of densification. Depending on the grain size and solubility, near full densification is possible before liquid formation, while in the absence of solid solubility in the liquid, both densification and grain growth are retarded.

    Phase diagrams help explain the interactions observed in LPS. Wetting has a significant effect and traces to solubility relations evident in the phase diagram. Wetting systems have solid solubility in the liquid that induces liquid spreading to fill pores. Systems such as W—Cu and Al 2 O 3 —Ni have low mutual solubility, so there is little sintering due to chemical gradients prior to liquid formation. A low-contact angle gives grain rearrangement and densification due to the capillary force exerted by the wetting liquid.

    Densification occurs within seconds after liquid formation [ 32 , 33 ]. The capillary force arises from the liquid—vapor surface tension as shown in Fig. Interacting systems have solubility relations that create intense diffusion fluxes during the early portion of LPS. A persistent liquid phase is most common, where there the amount of liquid exceeds its solubility in the solid. A wetting liquid penetrates grain boundaries to give densification by rearrangement, solution-reprecipitation, and solid-state sintering.

    A high-solubility ratio is ideal for LPS. In many instances, the mixed powders form a eutectic liquid that corresponds to a high-solubility ratio. In many cases, near full densification occurs with a small quantity of liquid. This is evident in Fig. These micrographs were taken just prior to and just after liquid formation.

    Note the material is almost dense prior to liquid formation, but substantial change occurs when the liquid forms. Similar behavior is seen in liquid metal embrittlement [ ], reactive wetting [ ], and diffusion induced grain boundary migration [ ]. In LPS, liquid penetration of grain boundaries occurs because the initial melt is undersaturated with solid.

    The rapid dissolution of solid into the newly formed liquid dissolves the interface to momentarily lower the surface energy. As a consequence, the newly formed liquid is chemically aggressive and penetrates the solid—solid interfaces, reducing the dihedral angle below the equilibrium value. The penetration rate depends on the reactivity of the liquid, its viscosity, and the contact angle. Liquid penetration of the grain boundaries causes grain separation and a swelling on liquid formation as the dihedral angle changes.

    This is documented in the Fe—Cu system, where carbon additions increase the dihedral angle, leading to less swelling, as shown in Fig. In this case, the iron particles were large so the swelling event far offset any sintering shrinkage. Had the experiment been performed with a micrometer-sized iron powder, then substantial densification would have followed the swelling event. Neighboring grains bond together after the first melt spreads between the solid grains [ ]. A solid skeletal microstructure slows densification, since the system strengthens with neck growth.

    If there is insufficient liquid to fill all pores, then continued densification relies on solid diffusion through the liquid. If the solid is not soluble in the liquid, then densification occurs by the relatively slower solid-state skeletal densification [ 27 , ]. However, solution-reprecipitation is dominant when the solid is soluble in the liquid. It occurs in three steps: 1 solid dissolution into the liquid, preferentially from higher energy regions, including asperities, convex points in the microstructure, areas under compression, and small grains,.

    Pore elimination and microstructure coarsening are key features of solution-reprecipitation controlled densification. Both depend on the same diffusion steps, as do grain shape changes and the growth of intergrain bonds. For example, Fig. Solution-reprecipitation produces simultaneous changes in density, grain size, grain shape, and neck growth. Conceptual models of solution-reprecipitation are shown in Fig. Grain shape accommodation via solution-reprecipitation improves grain packing, releasing liquid to fill pores. Grain shape accommodation is favorable because the overall interfacial energy is reduced.

    The vapor interface energy reduction is greater than the penalty from an extended solid—liquid interface [ , ]. Contact flattening is the first mechanism and it is sketched in Fig. Routledge eBooks are available through VitalSource. An eBook version of this title already exists in your shopping cart. If you would like to replace it with a different purchasing option please remove the current eBook option from your cart. Hardback : Add to Wish List. Description Contents Subjects.

    Description This new book offers research and updates on the chemical process in liquid and solid phases.