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By Roger C. Urquhart

Copper-nickel-sulphide ores mined in the Rustenburg district of South Africa are generally smelted in electric furnaces because of the high-temperature slag produced, the availability of cheap electric power, and the smaller pollution problems. Apart from melting, the functions of the electric furnace are to recover most of the matte content in the converter slag by physical and chemical interaction with the furnace bath and to provide adequate time for the optimum separation of matte and slag. Smooth, efficient operation will denend on fluid slags for settling, balanced by high resistivities to obtain adequate concentration and distribution of power by way of current heating. To obtain a greater understanding of the processes involved, an investigation was undertaken at Rustenburg Platinum Mines on the smelting of copper-nickel concentrates in a 19.5 MVA furnace with six in-line electrodes. The matte- and slag-tapping temperatures, slag temperatures, slag analyses, electrical data, and electrode position were measured. Radioactive tracers were introduced into the slag, and quantitative results relating to the flow pattern within the furnace were obtained. These studies were augmented by scaled laboratory investigations relating to the determination of cell constants and current distribution within the furnace. Instantaneous field and power distribution plots were determined by use of an on-line mini-computer. The applicability of these results to furnace operation is discussed.

Jan 1, 1976

By Zhang-Guang Gao, Ming-Mei Zhu, Rui-Rui Zhao, Chao Jiang

This paper focuses on the CaO-SiO2-FeO-MgO-MnO-P2O5 slag system that represents the major components of dephosphorization slag in BOF. Phosphorus distribution between 2CaOSiO2-3CaOP2O5 Solid Solution and Liquid Slag were analyzed by FactSage. The effects of slag content, basicity on the distribution ratio of P between the solid solution phase and the liquid phase (LP) and the percentage content of P in solid solution phase and liquid phase have been discussed. The results show that, with the increase of basicity, LP (wt%) decreases until the basicity reaches 1.9, then it turns to increase. LP (wt%) increases gradually with the increasing amount of FeO or P2O5.

Mar 1, 2017

By Fiseha Tesfaye, Pekka Taskinen

"Thermodynamics of the equilibrium phase assemblage Ago_9Cul.lS-Cu2-xS-CuS have been studied by an EMF -method. The ternary phase was synthesized from the pure Cu2S and Ag2S in vacuum furnace at high-temperature and mixed with appropriate compositions of Cu2S and CuS to form the cathode electrode. The EMF-measurements were made on the solid-state galvanic cell Pt(-) I Ag I RbAg,ils I Ago9Cu1.1S-Cu2-xS-CuS I Pt(+), in a temperature range from 316 K to 498K.Based on the measured EMF vs. T relations, thermodynamic functions (?fG° , ?fS and ?fH°) of stromeyerite (Ag0.9Cu1.1S) in equilibrium with Cu2-xS and CuS have been determined. The obtained experimental values have been compared with the available literature values. New experimentally determined thermodynamic properties of the solid solution (Ag,Cu)2Sss were determined.IntroductionDue to intense mining of high grade sulfide ore minerals in the past, recently, the available sulfide ores are poor in metals and becoming increasingly complex; such that, the production of high grade metals by the conventional pyrometallurgical processes is compromised. Consequently, smelters are in need to modify their operating flow sheets and strategies for processing more complex feed materials economically, while meeting the strict environmental regulations. To make the appropriate modifications, accurate thermochemical data of phases and phase assemblages which exist in these complex ore minerals are essential.Silver-bearing sulfosalts are encountered in ore minerals for the production of base metals and are common sources of silver. Among the silver-based sulfosalts, stromeyerite (Ag0_9Cu1.1S) is relatively common ore mineral in most hydrothermal vein and replacement deposits [1]. Recently, the ternary chalcogenide compound Ago0.93Cu1,07S has been studied, intensively, due to its high ionic conductivity and gradual disorder in the sequential phase transitions [2]. Therefore, accurate knowledge of the thermodynamic properties of stromeyerite has considerable fundamental and practical interest in many aspects of extractive, chemical and physical metallurgy."

Jan 1, 2014

By Donghai Li, Cheng Pan, Xuewei Lv, Mei Liu, Enguang Guo

"Phosphorite is the main raw material for the production of phosphorus in chemical industry. More attentions have been drawn to the phosphorite concentrate beneficiated from low-grade phosphorite due to the decrease of high-grade phosphorite. For another, the agglomeration process is necessary for the phosphorite concentrate after beneficiation process. The mineralogy and sintering process of the phosphorite from Leshan, China were studied in this work. The result shows that the main phases in the phosphorite are fluorapatite (Ca3(P04)3F), hydroxylapatite (Cas(P04)3(0H)), quartz (Si02) and dolomite (CaMg(C03)2). The yield of the sinter increases with increasing the carbon dosage to 7%, and then decreases when it continuously increases. Similar regularities were found for the strength and the content of P20s of the sinter. The best strength of the sinter as well as its P205 content were discovered when the carbon dosage is 7%. Fluorapatite ((Ca5(P04)3)F) is the main phase in the sinter while fuggerite (Ca2MgSiz01) is the main binder phase.IntroductionPhosphorus is an important foundation industrial raw material of national defense industry, food industry and chemical industry, where it is used to produce red phosphorus, phosphonium hydroxide, phosphorus pentasulfide and phosphoric anhydride[l-2]."

Jan 1, 2013

By G. O. Onyedika, M. U. Obidiegwu, G. C. Onuegbu

The effect of kolanut (KN) filler and compatibilizer (maleic anhydride) contents on the transport of toluene through low density polyethylene (LDPE) and low density polyethylene composite were studied at the temperatures 40, 60 and 80 °C.The kolanut powder used was ground to 25 μm particle size. In preparation of composite 0–5 wt% of kolanut powder and 0–2.5 wt% of the compatibilizer were mixed with 200 g of low density polyethylene in an injection moulding machine. The injected polyethylene and polyethylene/kolanut composites (LDPE/KN) were taken for sorption test. The sorption data obtained for low density polyethylene and kolanut powder filled low density polyethylene at the different temperature investigated were expressed as the molar percentage uptake (% Qt) of toluene per gram of the kola nut composites. Results show that the uptake of toluene at the five filler content (0–5 wt%) generally increased with increase in sorption temperature but decreased with increase in compatibilizer and filler contents. This can be seen at 80 °C and 0, 1, 1.5 and 2.5 wt% of compatibilizer respectively. The molar percentage uptake of toluene at 1 wt% of filler yielded the following values; 8.6789, 8.4768, 8.3476 and 8.2679 respectively. At 2 wt% it yielded 8.6224, 8.1333, 7.9525 and 7.9042 respectively, at 3 wt% it gave 8.4336, 7.9450,7.8900 and 7.7823 respectively, at 4 wt% it yielded 8.0263,7.9614,7.8218 and 7.6800 respectively and at 5 wt% it gave 7.9635, 7.8630, 7.6256 and 7.5013 respectively.

Mar 1, 2017

By W. Y. Kim, K. H. Song, K. Nakata

"The present study was carried out to evaluate the mechanical properties of friction stir welded Inconel 600/SS 400 lap joints. In this process, friction stir welding (FSW) was performed at a tool rotation speed of 200 rpm and welding speed of 100 mm1min, and argon gas was utilized to prevent surface oxidation during the welding. Application of FSW notably decreases the grain size of Inconel 600 alloy from 20 µm in the base material to 8 ~ in the stir zone. However, the grain size of SS 400 in the weld zone was slightly coarsened, when compared to the base material. Also, the hooking in the advancing side and the intermetal1ic compounds (M7C3) in the weld interface between Incone1 600 and SS 400 were well formed. These intermetallic compounds and hooking were effective to increase in mechanical properties such as tensile and peel strengths.IntroductionFriction stir welding (FSW), applicable welding process at solid state, has several advantages in defect suppression such as blow hole, segregation and cracking which mainly occurs in fusion welding [1, 2]. Notable grain refinement in the stir zone due to FSW can expect the outstanding increase in mechanical properties of the welds. In constructing the chemical and power plants, Ni base superal10ys have been used in many parts, moreover, fusion welding as construct method, such as gas tungsten arc welding, electron beam welding and laser welding, has been mainly used [3-5]. However, fusion welding has a limit in an increase in chemical and mechanical properties in the welds. Lately, Ni base superalloys to which FSW applied have been reported with notable enhancement in mechanical properties, which resulted from refined grains in the welds [6-10]. These researches showed the possibility in applying the FSW, directly."

Jan 1, 2012

By J. K. Brimacombe

Plant trials have been conducted at the Tacoma Smelter of ASARCO to assess the effect on tuyere blockage and refractory erosion at the tuyere line, of increasing the injection pressure of air into a Peirce-Smith con¬verter. Four tuyeres each having an ID of 19.1 mm (3/4 in) were installed toward one end of the tuyere line of the No. 4 Converter. Air and oxygen-enriched air were injected at 414 kPag (60 psig) through these tuyeres and at the usual 83 kPag (12 psig) through the remainder of the tuyeres in an otherwise normal converter campaign. The test campaign consisted of 88 charges and lasted for 89 days. During this period, punching of the high-pressure tuyeres was found to-be unnecessary; and when, as a precaution, the tuyeres were cleaned by hand at the end of a charge, they were always open. Also it was observed that the flow of high-pressure air remained constant. Accretion formation around the tip of the high-pressure tuyeres varied from charge to charge and was influenced by the matte grade and the level of oxygen enrichment.

Jan 1, 1983

By D. J. Senor

Closed chamber incineration (CCI) is a novel technique by which irradiated nuclear graphite may be destroyed without the risk of radioactive cation release into the environment. The process utilizes an enclosed combustion chamber coupled with molten carbonate fuel cells (MCFCs). The transport of cations is intrinsically suppressed by the MCFCs, such that only the combustion gases are conducted through for release to the environment. An example CCI design was developed which had as its goal the destruction of graphite fuel elements from the Fort St. Vrain reactor (FSVR). By employing CCI, the volume of high level waste from the FSVR will be reduced by approximately 87 percent. Additionally, the incineration process will convert the Sic coating on the FSVR fuel particles to SiO2, thus creating a form potentially suitable for direct incorporation in a vitrification process stream. The design is compact, efficient, and makes use of currently available technology.

Jan 1, 1994

By John J. Dunkley

Recent years have seen the increased use of hydrometallurgy in the smelting and refining of metals. However this is often used as a final refining step, following an initial pyrometallurgical smelting process. Huge amounts of material are produced as melts which have to be cast, comminuted, and taken up into solution or leached. A common method is to granulate the melt and then grind it. In the case of metallic melts this can be difficult or unfeasible due to the ductility of the granulated particles. Water atomisation is capable of replacing the granulation and grinding stages with a single process step that can process in excess of 30tlhour of melt into particles as fine as 50 microns. Applications in operation in Co, Cu, Ni, Ag, Au, Pt and Rh refining are discussed together with potential applications in copper smelting.

Jan 1, 2003

By Hiroaki Kawamura, Takeshi Yoshikawa, Kazuki Morita, Yutaka Yanaba

"To develop an alternative metallurgical process for phosphorus removal in the production of solar-grade silicon (SOG-Si), slag treatment of metallurgical-grade silicon (MG-Si) was conducted, followed by acid leaching. Phosphorus-doped silicon alloy or MG-Si containing certain amounts of phosphorus and calcium was reacted at 1723 K and 1773 K with CaO--CaF2 of several compositions. Phosphorus removal from the molten silicon into the slag phase was confirmed by reduction to phosphide ions, P3-, and phosphate ions, P3-. These ions were separately determined using a wet chemical analysis method developed by ourselves. The highest phosphorus distribution ratio obtained was 2. 7 after reaction for 18 h with 17.5 mass% CaO--CaF2 slag. We then conducted acid leaching of the silicon and achieved removal of a large fraction (over 90 % ) of the phosphorus, which was much higher than that obtained by ordinary oxidizing slag treatment.IntroductionIn recent years, the production of solar cells has been increasing rapidly. Because of this, the demand for solar-grade silicon (SOG-Si) has also been growing rapidly. The development of lower-cost mass production processes is therefore needed to provide silicon feedstock. Phosphorus is one of the impurities in metallurgical-grade silicon (MG-Si). Because of its large segregation coefficient (kp = 0.35) [l ], it is difficult to remove phosphorus using a solidification refining process. Vacuum melting is considered to be a promising method for removing phosphorous from MG-Si [2], but the issues of high cost and large energy consumption have still to be resolved.Slag treatment is often used to remove impurity elements by oxidizing reactions during general oxidation refining processes. For example, phosphorus in molten steel is removed into a slag phase as phosphate ions, PO4 3-l-, by the following reaction:"

Jan 1, 2013

By Y. K. Rao

Relatively pure crystalline lead sulfate (PbSO4) can be produced by chemical vapor transport from an impure source such as the lead-acid battery paste or the roast-ore-leach-residue from a hy¬drometallurgical process-route. In a closed-reactor, transport of matter is induced by a tempera¬ture-gradient and the steady-state transfer rate can be calculated using the data on the standard free energies of formation for the species present and the pertinent binary diffusion coefficients. The present work focusses on chemical vapor transport in a tubular reactor (1.4-cm inner diameter x 10-cm long) with the source- and deposition-ends held at 850°C (T,) and 750°C (Td), respectively; PbC12(g) is the 'solvent' or 'transport agent' and NiSO4(s) placed in the source-zone -serves to maintain a sufficiently high S0,-potential such that the stability of the lead sulfate species is ensured. For the purposes of analysis, the gas-phase in the reactor is assumed to consist of eight species: H2O, PbC12, SO3, SO2. O2 HO, C12, and PbC14. The reaction between C12(g) and PbSO4(s) in the high-temperature source-zone produces PbCl2, SO2, and 02; four more reaction-equilibria in the same zone yield other species. In the low-temperature deposition-zone, reaction equilibrium involving PbC12, H2O, and SO, leads to the nucleation and growth of PbSO4 crystals; three other reaction-equilibria occur in this zone. By employing the virtual equilibrium state for the end-zones and coupling it to the Stefan-Maxwell diffusion equations for each of the gas species, the respective partial pressures for these, in the source- and deposition-zones, are computed at steady-state. From these data, the molar fluxes of PbCl2. PbCl4, and so forth, are determined. Allowing for the transport-enhancing effects of thermal convection, the net transport rate of lead (or PbSO4) is duly calculated for specified initial conditions. The predicted rates show very good agreement with measured rate data reported in the literature [ V. Plies, T. Kohlmann and R. Gruehn: Z. anorg. allg. Chem, 568, 62 (1989)

Jan 1, 1995

By Masahiro Yoshimura, Sergiy Korablov

"Hydi-othermal corrosion ofTiN, TlAlN and CrN PVD films (3 µm thick) deposited on SUS-304 substrate was studied in 100MPa water in 20-950°C temperature range up , to 750h. The beginning temperature of their reaction was determined as 200°c for TiN and TiAlN and 500°C for CrN films, which are quite low in comparison with that of air oxidation of those powders. Very thin oxide scales. of TinO; n-I homologous series phases were formed above 300°C. TiO2 anatare. is observed for TIN and TiAlN films at 400°C. The· feature of hydrothermal corrosion of CrN films seems to be CrNxOy phase formation.Distinguishable weight changes were observed at higher temperature than 700°C for TiN, 750°C for· TiAlN and 800°C for CrN respectively. Hydrothermal corrosion kinetics .was constructed to calculate the activation energy of hydrothermal corrosions. On the base of obtained data, hydrothermal corrosion resistance was as follows: TiN – TiAlN - CrN. Facetted oxide crystals were formed at higher temperature than 500°C for TiN, TiAlN and 850°C forCrN.IntroductionThe metallic nitride (TiN; TiAlN, CrN) PVD films have high hardness, strength and wear resistance. Therefore these films are widely used in industry for wear resistij.nce application such as cutting tools and die molds. Their performances depend on not only the mechanical properties but also corrosion resistance of coated films. High temperature oxidation of metalliq nitride and nitride films was well studied [1-5]. However there are no reliable data concerning the .corrosion resistance of coated nitride materials. In high-temperature and high-pressure water. There are a few reports on hydrothermal corrosion of nitride films [6,7]. The increase of corrosion resistance of CVD films was observed in following succession TiC - TiCNO - TiCN - TiN at 300-680°C temperature interval and I 00 MPa pressure water according to data of the first report. Kawana et al. [7] have reported about excellent corrosion resistance of CrN films under 290°C and 8, 6 MPa water during I 000 h in the circulating type experimental loop. The films thickness was about 7-10 µm in both cases. However it remains unclear the chemical state of the surface species and especially in-depth distribution, oxide scale thickness and its growth, and defects formation in the oxide film."

Jan 1, 2000

By R. Boom, B. Kraaijveld, H. Kuntzel, Y. Meteleva-Fischer

"Alloying refining with rare earth elements followed by acid leaching was examined for the potential of upgrading of metallurgical grade silicon. Microstructure study of silicon alloyed with small additions of rare earths showed behavior relatively similar to the influence of calcium addition. After alloying with neodymium the phosphorus content was detected in various intermetallic silicides containing neodymium and iron. The content of lanthanum and neodymium in refined silicon was by several times lower than that of aluminium and calcium. Alloying with lanthanum and neodymium at smaller additions than calcium reduced the phosphorus content down to the same level. The efficiency of lanthanum and neodymium in removal of boron and phosphorus at the 1-2 wt% of their additions and their low solubility in silicon make the alloying with these metals followed by acid leaching an attractive option for the refining route of metallurgical grade silicon up to solar grade.IntroductionA striving for a cheap ""green"" energy directs the research interests in silicon solar cells towards new efficient refining routes for metallurgical grade silicon (MG-Si, -98% purity). The silicon price determines up to high extent the solar module's price, so that cheap and efficient metallurgical process is awaited. The research challenge is to fulfil the purity requirements of solar grade silicon (SoG-Si, 6N) by competing with the energy-consuming and environmentally unfriendly Siemens process. Most difficult impurities to remove are boron and phosphorus, so technologies dedicated to their efficient removal attract an attention of industry and academia.Alloying refining (also known as solvent refining) is one of the most promising refining options, which is based on a principle of solid-liquid extraction using limited solubility of impurity elements in solid silicon [ 1]. Various elements were proposed for alloying refining: aluminium [2], calcium [3], tin [4], iron [5], copper [6] etc. The attractiveness of the alloying refining is in decreasing a melting point of the metal mixture and an affinity of the alloying element to the most harmful impurities, especially to boron and phosphorus. However, the difficulties are still faced due to self-solubility of the alloying elements, their low affinity to boron and/or phosphorus, silicon losses and necessity of removal of the silicide impurity phases in an additional step, using acid leaching [7], fractional melting [ 8] etc."

Jan 1, 2013

By Baozhong Ma, Qian Li, Yonggang Wei, Shiwei Zhou, Bo Li, Chengyan Wang, Hua Wang

The magnesium-rich nickel oxide ore (w (Ni) =1.09 %, w (MgO)=29.08 %) mixed with 6 % and 8 % anthracite were roasted at different temperatures. XRD and SEM/EDS techniques were utilized to characterize the phase and microstructure transformation of the ores. The results show that lizardite and chrysotile of raw ore were converted into forsterite and enstatite during reduction roasting process. Simultaneously, iron and nickel oxide were reduced and migrated from the initial magnesium silicate. Fe3Si were formed when the roasting temperature went up to 1300 ℃ and 1350 ℃, and a small amount of Ni was observed in it. Temperatures got too high were not benefit to the polymerization of ferronickel.

Jan 1, 2015

By Trevor Saldanha, Nawshad Haque, Will Sikora

This study reported life cycle assessment (LCA) of six copper mines in Australia, Papua New Guinea and Portugal. Inventory data was sourced from published papers, sustainability reports by mining companies, independent technical reports and previous CSIRO studies. Sima Pro software and various databases were used to evaluate life cycle based environmental impacts. The impact indicators were: global warming potential (GWP), acidification potential, water footprint, ecotoxicity potential, ozone depletion potential and human toxicity potential (carcinogenic and non-carcinogenic), abiotic resource depletion potential (minerals and fossil fuels), particulate matter and ionizing radiation. Generally, open pit mines were found to have a GWP of approximately 1.0 t CO2-eq/t Cu concentrate while underground mines had approximately 1.3 to 1.8 t CO2-eq/t Cu concentrate. Environmental impacts varied between mines considerably due to several factors, most notably: ore grade, mining method, flowsheets and ore mineralogy. Energy consumption and sources were significant contributors to most impact categories.

Mar 1, 2018

By D. G. Hattingh, A Els-Botes

"Considerable information is available on the factors influencing the iron-zinc reaction rate at 450° C of low carbon steels, in comparison there is a scarcity _of similar fundamental information of spheroidal graphite irons. This can be attributed to the more complex microstructure and ferrous alloy chemical analysis of spheroidal graphite irons. Hot-dip galvanizers have identified the complexity in controlling and predicting the thickness of the galvanized coating formed on commercial cast irons, which has serious financial implications for both the galvanizer and customer.Commercial hot-dip galvanizing has been in use for over 160 years and yet an elementary understanding of the dynamics associated with the hot-dip galvanizing of spheroidal graphite cast iron is still insufficient. To allow the. process to become a modem surface engineering technology, the fundamental aspects of the process must be thoroughly understood.When a clean iron or steel article is dipped into the molten zinc, zinc initially solidifies around the steel or iron. As heat is transferred to the article form the bath, this initial solidified zinc layer remelts and a series of iron-zinc alloy is formed by the reaction of the zinc with the surface of the article; on removal from the bath, some of the molten zinc is taken out on top of the alloy layers. At normal galvanizing temperature (450 °C), the reaction between iron and zinc is usually parabolic with time. The rate of reaction is rapid at first but then slows down and the coating thickness does not increase greatly if the article is immersed in the bath for longer times(1)."

Jan 1, 2000

By J. Jakumelt

The coupled simulation of mold filling and solidification for an investment casting process presents difficult. This is due to the complexity of the carious physical process and the geometry, To achieve this task in a precise way, the CFD program FLUENT and the casting simulation tool CASTS were closely coupled. Any physical quantity, such as velocities or temperatures, can be exchanged via files after each time step of the simulation. The communication and operating sequence of the programs is controlled by PERL-scripts. This enables the expertise of FLU ENT for flow simulation and the strength of CASTS, for casting simulation to be combined. The coupled simulation was successful applied to an aerospace investment casting. Several physical models were tested for correct treatment of the casting filters, the porosity of the mold and the viscosity of the liquid metal. The results demonstrate that even complex investment casting geometries can be investigated using CASTS-FLUENT.

Jan 1, 2003

By I. Gaballah

Decontamination of synthetic solutions of PbC12 containing 10, 100 and 1000 ppm of lead, using chemically treated barks had been studied. The percentage of !cad cations' removal from solutions depends upon the pH and the initial concentration. About 99 % of the initial lead content can be removed at pH of about 3.5, 5.5 and 6.5 for initial concentrations of 10, 100 and 1000 ppm respectively. The maximum retention capacity of the treated bark is about 83 mg of lead per gram of modified bark. Bark loaded with lead had been analyzed by Infra Red spectroscopy. It seems that lead reacts with hydroxyl groups of the phenolic constituents of the bark. On the other hand, the removal of a lead cation by the bark leads to the release of two H+. This seems to show that the removal of lead could be interpreted as an ion exchange with hydrogen belonging to the hydroxyl groups of the modified bark.

Jan 1, 1994

By R. M. Sweetin

Detailed descriptions by operating area of the Kidd copper smelter are presented, together with accounts of complement staffing, training, and preparation activities for smelter start-up in June 1981. Concentrate tonnages smelted in the first twelve months of operation were constrained by the capacity of the furnace off-gas system. However, modifications designed and introduced over that period, plus sustained efforts by operations and maintenance personnel have resulted in stepwise improvements in smelter performance.. Consistent operation at design feed rates has been well demonstrated over the third and fourth smelter campaigns and efforts continue on further improving the continuous smelter on-line times and increasing campaign life. In November 1982., following a seventeen month preproduction period, the Kidd smelter attained full operating status.

Jan 1, 1983

By F. J. J. van Loo, A. A. Kodentsov, J. A. van Beek, M. R. Rijnders

"A periodic layered morphology of the reaction zone has been observed in several annealed solid/solid diffusion couples, including metal/metal and metal/ceramic couples. This morphology is characterized by a regular array of alternating layers, which are either single-phase layers or bands of particles embedded in an intermetallic matrix phase. A description of several systems showing periodic layer formation is given. It is shown that the periodic layered structure with the single phase layers and the one with the bands of particles have a different mechanism of formation.IntroductionSolid state reactions in ternary systems can produce a variety of reaction zone morphologies if there are two or more reaction products. Three types of morphology have been described in detail: 1) simple layered; 2) isolated precipitates in a singlephase layer; 3) interpenetrating columnar (lamellar) or interwoven structure. Understanding the factors that govern the formation of different morphologies is of importance in many fields of engineering. For solid state displacement reactions the conditions governing the formation of these morphologies are well understood [1-4]. For example, the development of a layered or aggregate reaction zone depends on the relative diffusivities of the components through the reaction products.This paper is concerned with the periodic layered morphology which has been observed in various solid state systems. We consider this to be a fourth type of reaction layer morphology. Two manifestations of periodic layered morphology may be distinguished. One form consists of regularly spaced layers of particles of one reaction product embedded in a matrix phase (another reaction product). The other form consists of single-phase layers embedded in a matrix phase. It will be shown that each manifestation has its own mechanism of formation. In section A we consider a system (Ag/Ti-foil/Si) in which periodic layer formation will be explained as a special case of the Liesegang phenomenon. In section B we consider systems where the periodic layered structure has a different origin."

Jan 1, 1996