Acidic Slurry Research Articles

Surface Chemistry Studies of Copper Chemical Mechanical Planarization

Surface chemistry studies of the chemical mechanical planarization (CMP) of copper are presented in this paper. Blanket copper samples were polished with an acidic alumina-based slurry which contains an organic acid salt (phthalic acid salt) and an oxidizer Surface studies using X-ray photoelectron spectroscopy (XPS) were performed on copper samples after chemical etching or CMP in order to determine the effect that different polishing parameters (i.e., pH and oxidizer concentration) have on the copper surface. XPS studies were also done on samples that were passively soaked in an acidic slurry mixture containing different concentrations of to determine how the chemical action alone affects the removal of copper. The etching results revealed that a cuprous oxide forms on the surface of etched metal while polished samples showed CuO and The effect of these copper oxide films on the removal of copper in passive etching and chemical mechanical polishing is discussed. © 2001 The Electrochemical Society. All rights reserved.

γ-Radiolytic desulphurisation of some high-sulphur Indian coals catalytically accelerated by MnO 2

γ-Radiolysis of acidic aqueous coal slurries is a novel and effective method for the simultaneous oxidative desulphurisation and demineralisation of high-sulphur coals. This method is capable to selectively remove the inorganic and organic forms of sulphur simultaneously through the in situ-generated H 2O 2 and other radiolytic products. In effect, there is neither any appreciable degradation of coal matrix nor any loss in the caking property and volatile matter content of the coals after the removal of sulphur. However, significant removals of sulphur and mineral matter are effected at rather high γ-dose (175×10 4 Gy or so). Therefore, for the process to be economically viable and commercially adaptable, the applied γ-dose needs to be somehow substantially brought down, at which the same level of desulphurisation could be achieved. Catalytically, accelerating the radiolysis process is one such possibility to effect the desulphurisation step at a low γ-dose. Reported in this paper are the results of investigations on the desulphurisation and demineralisation of high-sulphur (sulphur content in the range 3–5.5%) Churphy, Chalang and Bapung coals of Meghalaya by γ-radiolytic process catalysed by MnO 2. The maximum removal of total sulphur (15.6%, 30.0% and 29.8%) at 30×10 4 Gy in the presence of MnO 2 and the simultaneous removal of mineral matter (20.0% and 18.5% from Churphy and Chalang coals at 30×10 4 Gy and 12.0% from Bapung coal at 45×10 4 Gy) are at par with removals at 175×10 4 Gy without MnO 2, which has been attributed to MnO 2 catalytically accelerating the radiolytic process via the formation of highly reactive MnO under the action of γ-rays. All the other features of non-catalysed radiolytic desulphurisation such as stabilisation of the slurry and coal not becoming radioactive during irradiation, increase in the heating value, improvement in the caking property, no appreciable degradation of coal matrix after removal of sulphur from the coals remain the same.

Effect of zirconium acetate on the fluidity of acidic aqueous alumina slurries with high solids loading

Effect of zirconium acetate on the fluidity of acidic aqueous alumina slurries with high solids loading

Extraction of lanthanides from the phosphoric acid production process to gain a purified gypsum and a valuable lanthanide by-product

In the HemiDiHydrate (HDH) phosphoric acid production processes, calcium sulfate hemihydrate (HH) is formed from the reaction of fluoroapatite ore with sulfuric acid, after which it is recrystallized into calcium sulfate dihydrate (DH, gypsum). Some impurities from the feedstock are incorporated in the HH during the first reaction and finally end up mainly in the sparingly soluble gypsum. By introducing ion exchange resin during the phosphoric acid-mediated recrystallization, lanthanides that are dissolved from the HH can be removed from the acid before they become incorporated again in the gypsum. With 250 g resin/kg phosphoric acid slurry, lanthanides were removed to up to 53% of the input. The resulting decrease of the lanthanide concentration in the gypsum is lower, up to 34%. The extraction efficiency is influenced by the recrystallization reaction. Lanthanides that are most readily taken up by the gypsum are extracted least. Although the sulfonic acid resin has a preference for the trivalent lanthanides, calcium ions are also extracted.

Beneficial effect of oxygen-active elements on the resistance of aluminide coatings to corrosive erosion and dry erosion

Oxygen-active elements such as yttrium and cerium are often used to improve the performance of high-temperature alloys. Recent studies demonstrate that the oxygen-active elements are also beneficial to the wear resistance of materials in corrosive environments or at elevated temperatures. In this work, the effect of yttrium and cerium on the corrosive erosion of an aluminide coating on 1030 steel at ambient temperature, in sulfuric and salty slurries, respectively, were investigated. The microstructure of the aluminide coatings was investigated using optical microscopy and transmission electron microscopy (TEM). The distribution of yttrium or cerium in the diffusion layer was analyzed using energy-dispersive spectroscopy (EDS), and the microhardness of the coating also was determined. The corrosion rate, polarization behavior and corrosive erosion of the Y/Ce-containing aluminide coatings, as well as their dry sand erosion at different temperatures from 30 to 190°C were evaluated. The results showed that the oxygen-active elements significantly increased the resistance of the aluminide coatings to corrosive erosion in silica-containing sulfuric acid slurry and silica-containing salt slurry, respectively. The modified aluminide coating also manifested a higher resistance to corrosion at ambient temperature, as well as to dry sand erosion at different temperatures.

Dependency of dishing on polish time and slurry chemistry in Cu CMP

In this paper the influences of slurry chemistry and thickness of the copper layer on dishing will be discussed. The dishing is studied for different patterns and variable polishing times. We found that the concentration of the oxidiser and the thickness of copper layer have a strong impact on dishing. The larger Cu features develop dishing at a higher rate than smaller structures during overpolishing. The experimental results lead to the following hypothesis for the Cu removal and surface passivation. The oxidizer (H 2O 2) reacts with Cu in an acidic slurry (pH 4) and Cu 2+ ions are formed. The anions of the carboxylic acid react with Cu 2+ ions and form an insoluble salt (R(COO) 2Cu) which passivates the surface. This passivation layer is removed in protruding areas by mechanical abrasion. Once removed from the surface, the ‘metallic soap’ particles are swept away by the turbulent motion in the slurry.

Slurry erosion properties of ceramic coatings

The effectiveness of ceramic coatings on pump impellers used in the acidic gypsum-fly ash slurry environments in desulphurisers was assessed by using two kinds of slurry erosion tester. The experimental results from the two testers did not always coincide, although in general they did. The possible reasons and the implications of this distinction between the two testers were discussed, and the following conclusions were reached: (1) Generally, although ceramic coatings, in particular Cr 2O 3 and Al 2O 3, have much improved slurry erosion resistance, the resistance of ceramic coatings to slurry-erosion is closely related to the techniques of plasma spraying. At optimum manufacturing conditions, ceramic coatings are about two times as resistant as the base metal (SUS329J1); (2) Vicker's hardness ( H v) is an effective parameter for the assessment of slurry erosion properties of ceramic coatings, as well as bulk ceramics; (3) The most deleterious environment for slurry pumps used in desulphurisers is pure fly ash, therefore, fly ash should be removed as much as possible before desulphurising in thermal power plants.

Erosion–corrosion of thermal-sprayed nylon coatings

Thermal-sprayed coatings nylon1010, SiCw-nylon1010 and Al 2O 3 p-nylon1010 were deposited on 16Mn steel. Erosion–corrosion tests were conducted using an erosion–corrosion tester in pH 1–12 sand slurry with impact velocities from 2.1 m/s to 5.6 m/s. The effects of pH value and impact velocity on the coatings were discussed. The results showed that the coatings presented good erosion–corrosion resistance except both in strong acid and in alkaline slurries. It was found that both SiC whisker and Al 2O 3 particles added into nylon increased the erosion–corrosion resistance of the nylon coating because they resisted the impact of sand particles. The Al 2O 3p-nylon1010 coating had the lowest erosion–corrosion loss rate at low velocity. However, at higher velocity its erosion–corrosion loss rate increased due to the spalling of Al 2O 3 particles. At all test conditions, the plastic deformation, tearing and the dissolve swelling and hydrolysis of nylon matrix were dominant mechanisms. At higher velocities the partial spalling of Al 2O 3 particles occurred so that they could not play a reinforcement role. In strong acid or alkaline slurry, the erosion–corrosion resistance of the coatings depended not only on the properties of nylon and reinforcements as well as their bonding but also on the synergetic effects between erosion and corrosion.

An assessment of ways to abate ammonia emissions from UK livestock buildings and waste stores. Part 1: ranking exercise

The options for abating ammonia emissions from livestock buildings and waste stores under UK conditions have been assessed. There is increasing interest in reducing such emissions, which contribute to long-range atmospheric pollution problems, and which, via subsequent deposition, can also harm sensitive ecosystems. A literature review was first carried out, and a “brainstorm” idea-generating session was held, together leading to lists of feasible abatement approaches: one for each of a range of types of livestock buildings and waste stores. A ranking exercise was then conducted. A set of aspects of each application of each feasible abatement approach was drawn up: the aspects considered included not only capital costs and running costs but also such others as animal welfare, stage of development and knock-on effects. Each aspect of each application of each approach was given a ranking of between 1 (very poor) and 5 (very good). When the aspects of “potential abatement” and “achievable abatement now”, as well as either “capital costs” or “animal welfare”, were weighted by a factor of 5, the “best bet” abatement approaches for livestock buildings were identified as (a) dietary manipulation (for all types), (b) raising the C/N ratio by generous use of bedding (for any buildings based on solid manure), (c) exhaust air cleaning, especially by bioscrubbers (for force-ventilated pig and poultry buildings), (d) oil layers or (e) fixing with acid (for slurry-based piggeries) and (f) drying by ventilation of muck (for any poultry building). For waste stores, the “best bet” abatement approaches were identified as (g) replacing storage with industrial scale processing or (h) with land filling (niche solutions only), (i) dietary manipulation, (j) fixing with acid (slurries only), (k) increasing the surface's resistance to ammonia volatilisation (by crusts for cattle slurry, but by floating granules for pig slurry), (l) minimising surface area by heap shape (solid manures), and (m) cover sheets (solid manures). For stored poultry manure, the low moisture content allowed good showings by the additional options of (n) drying, and, in the case of poultry manure with litter in certain parts of the UK, (p) sale for combustion in a Non-Fossil Fuel Obligation (NOFFO) power station, the electricity from which commands a higher price than that from a conventional power station. A closer look at the economic consequences of different abatement approaches was taken by means of a mathematical model: this work is reported in a companion paper.

Alum Mud: Phase Identification and Catalytic Potential for Aqueous-Phase Decomposition of Hydrogen Peroxide

Alum mud (AM), a solid residue, is generated during the manufacture of alum from bauxite ore by digesting with H2SO 4. Because of the use of different bauxite ores and different operating conditions, the chemical and mineralogical composition of AM varies. In general, AM can be characterized as an acidic slurry of very fine particles of aluminum oxide, iron oxide, silica, titanium dioxide, etc. and/or a mineralogy of different phases like biotite, mullite, quartz, hematite, futile, etc. The disposal of high volume-solidwastes like AM, red mud, and fly ash is currently a pressing issue. With the amount of landfill space declining, utilization as a form of disposal is quickly becoming a necessity rather than a choice. Many research groups are working on various productive-use applications of such solid wastes. Though considerable work was done both on fly ash and red mud (Klopries et al., 1990; Emasiri et al., 1992; Daniels et al., 1993; Weng and Hung, 1994; Batabyal et al., 1995; Sur et al., 1996), very little attention was given to AM. Hydrogen peroxide, an eco-friendly oxidant, was used for years in waste treatment to detoxify a wide range of aqueous and gaseous pollutants in the presence of various catalysts (Borup and Ashcroff, 1992; Murakoshi et al., 1992; Lother and Walton, 1993) which are generally present in AM, fly ash, and red mud. The use of mineral-catalyzed peroxide treatment based on 1-I202 has recently received increased attention in remediation of contaminated soil containing various chlorinated compounds, pesticides, etc. where bioremediation may not be effective for high biorefractory contaminants (Watts et al., 1990; Tyre et al.,

A novel technique to determine organic processes in pig wastes

Complex processes concerning declining concentration of organic matter within pig wastes have been investigated using deuterated phenol (d5) and acetic acid (d 4) over a ten day period. Decomposition rates of products responsible for odours and pollution were also quantified. These products included the volatile fatty acids, phenols and indoles as well as gaseous methane and carbon dioxide. The last two were quantified in the headspace flow to assess methanogenesis and the activity of bacteria. The relative rates of emission, production and bio-decay were calculated as exponential curves showing that acetic acid was lost through emission and bio-decay with half lives of 158 h and 95 h, respectively. Bio-production of acetic acid was very low. The emission rate of methane was 4.0 g m −3 d−1. The ratio of methane generated to the bio-decay of acetic acid concentration was 1: 66. The decline of acetic acid in slurry was shown to be a concentration-dependent process. Other volatile fatty acids demonstrated similar declining concentration characteristics but at a lesser rate. This was also the case for 4-methyl phenol with a half life of 495 h. However phenol demonstrated different declining concentration and production characteristics with a maximum concentration of 85 mg l−1 at 175 h. Carbon dioxide was produced at a greater rate than acetic acid was lost from the slurry (a ratio of 1.88: 1.0). Ammonia was emitted at a rate of 4.7 g m−2 d−1. © 1999 Society of Chemical Industry

Modification of the Preston equation for the chemical–mechanical polishing of copper

Chemical-mechanical polishing (CMP) of copper was conducted in two acidic (pH 1.3 and 3.8) slurries and one alkaline pH (10∼12) slurry with alumina particles as the abrasives. In acidic media with 0.1 M Fe(NO 3) 3 as a copper etchant and [1]H-benzotriazole (BTA) as an inhibitor, copper polish rate increases linearly with solids concentration in the polishing slurry. The polish rate increased linearly with increasing downward pressure and rotational speed with all of the above slurries. However, the Preston equation does not represent the polish rate data. Inclusion of an additional velocity term, representing the greater dependence of removal rate on the velocity and a constant, representing the purely chemical reactivity of the slurry which is, in general, higher than the static dip rate in the Preston equation, provided a more satisfactory representation of the data. The effect of the concentration of various slurry chemicals on the added constant term was investigated using a bench-top Struers DAP-V polisher. As expected, addition of BTA significantly reduces the value of this constant. Also some data on polish selectivity and the effect of alumina morphology are presented.

The interaction between different barrier metals and the copper surface during the chemical-mechanical polishing

The copper polishing rate in a weak acid slurry with H 2O 2 as a oxidizing agent is determined by a two-step process of the formation of copper oxides followed by its mechanical abrasion. The electrochemical potential is a criterion for the driving force of oxidation-reductions reactions that occur during the Cu dissolution process. Using the experiment a corrosion potential ( E corr) was determined. It depends on the potential of the cathodic reaction, the Tafel slopes of each reaction and the control of the reaction by Tafel kinetics or concentration polarisation. Potentiodynamic measurements were performed with different H 2O 2 contents in the slurry. The dissolution current density ( i corr) is correlated to the oxidation-reduction reaction rate. In the presence of a barrier metal, such as WTi, the dissolution rates were influenced by galvanic effects. W and Ti and their compounds were dissolved in the slurry by the complexing ability of H 2O 2. There is an increase in the barrier wet etch rate when copper is present. In the case of polishing both TiW and Cu simultaneously a dramatic increase of the barrier polish rate was observed. The acceleration of the W or Ti polish rate can be explained by the galvanic coupling between Cu and the barrier metal. By the use of TiN as a barrier metal no galvanic interaction has been observed. The removal rates of TiN have not been influenced by the presence of Cu.

Laser cladding coating against erosion-corrosion wear and its application to mining machine parts

Erosion-corrosion wear is a common failure type for many mining machine parts. This paper introduces the erosion-corrosion wear resistant, nickel based alloy coating, which is manufactured onto AISI 1045 steel by laser cladding technology. X-ray diffraction, scanning electron microscopy (SEM) and microhardness testing were used to investigate the microstructure and hardness of the coaring. After that, erosion-corrosion wear experiments were carried out on an MSH type erosion-corrosion wear tester to study the erosion-corrosion wear characteristics of the laser clad coating. 420 stainless steel was also tested under the same conditions as a contrast specimen. The slurry was made up of water and quartz, while sulphuric acid was added to create corrosive condition. Experiments were arranged to test the relation between erosion-corrosion wear rate, the acid concentration and slurry erosion speed. Finally this paper introduces the application of laser cladding technology to balance plates of slurry pumps used in underground mining.

Chemical-Mechanical Polishing of Copper in Glycerol Based Slurries

AbstractThe development of a reliable/reproducible chemical-mechanical polishing (CMP) process to planarize and define copper using a dual damascene approach is essential for introducing copper as the interconnection metal. In this paper we present results of a new polishing slurry containing glycerol and Al2O3 abrasive. The slurry is a near-neutral medium and does not have the effect of acidic or basic slurries on copper. The effect of glycerol concentration and the abrasive size on the CMP behavior is investigated. The changes in the slurry temperature, pH, viscosity, dielectric constant and surface tension were examined as a function of the glycerol concentration. The results, indicating a strong dependence on both the glycerol concentration and the abrasive size, are explained on the basis of viscosity and dielectric constant of the solution and the van der waal forces and the electrostatic repulsion between the particles.

Mechanisms of copper removal during chemical mechanical polishing

Schemes using chemical mechanical polishing of copper have been proposed for the patterning of interconnections in copper multilevel metallization. In this article, the phenomena involved in the removal of copper during copper chemical mechanical polishing are investigated. The concentration of chemical etchant in the polish slurry is varied to investigate the chemical component, and the applied pressure is varied to investigate the mechanical component. Two slurries, an ammonium hydroxide plus ferricyanide slurry and a nitric acid slurry, are used to polish both copper and Cu2O thin films. Removal of copper or Cu2O is hypothesized to be a result of mechanical abrasion, while the role of the chemical etchant is to dissolve the material abraded from the surface rather than to etch the material directly from the surface.

The influence of applied potential on the erosion-corrosion behavior of AISI321 stainless steel in acidic slurry medium

The influence of applied potential on the erosion-corrosion (E-C) behavior of AISI321 stainless steel in 10% H 2SO 4 + 15% corundum sand (60 mesh) acidic slurry was investigated using a modified slurry pot apparatus. The surface morphologies of E-C specimens at various applied potentials were observed by scanning electron microscopy. The results showed that cathodic protection could significantly decrease E-C rate, and the cathodic protection efficiency could be 73.6%. The influence of applied anodic potentials on the E-C behaviors could be classified as the following three types: 1. A. The E-C rate increased sharply in region I (a little more positive than free-corrosion potential); 2. B. The E-C rate decreased significantly in region II (stable passive region), and the anodic protection efficiency could be 64.5%; 3. C. The E-C rate increased again in region III (transpassive region) because of intergranular corrosion. The appropriate potential range of anodic protection is 0-0.8 V (SCE).

The influence of corrosion on the erosion of aluminium by aqueous silica slurries

The slurry erosion-corrosion behaviour of aluminium in aqueous silica slurries containing 0.5 M NaCl, acetic acid and 0.1 M Na 2CO 3 at open circuit has been investigated using a modified slurry erosion rig. The erosion rates of aluminium in the NaCl and acetic acid slurries were much higher than those in an aqueous slurry without electrolyte additives even though the pure corrosion component was very small. Eroded specimens were examined by scanning electron and optical microscopy. In pure aqueous slurry erosion, the basic mechanism leading to mass loss was the ductile fracture of flakes formed on the eroded surface. In corrosive slurries, however, the mass loss was enhanced by cracking of the flakes induced by stress and corrosion.

Kinetics of sulfur dioxide oxidation in slurries of activated carbon and concentrated sulfuric acid

The oxidation of sulfur dioxide (SO 2) in the presence of activated carbon particles has been studied experimentally in slurries of both pure water and sulfuric acid solutions. In the water slurries, the oxidation of absorbed molecular SO 2 is accompanied by parallel oxidation of HSO 3 − ions produced by SO 2 dissociation. In acid slurries of pH less than one, the dissociation of molecular SO 2 is inhibited and only direct oxidation of molecular SO 2 is observed. Experiments in up to 35 wt% sulfuric acid solutions were carried out in slurries of fine coconut activated carbon particles. The rate of molecular SO 2 oxidation has been correlated both to an empirical power-law model and to a heterogeneous Langmuir-Hinshelwood type model: R pl = 0.21 m 1 0.69m 2 0.19 m 3 0.72 , R in = 3.81 10 8m 1m 2 2 (1 + 8.46 10 3m 1 + 4.53 10 3m 2 + 1.20m 3) 3 The Langmuir-Hinshelwood model corresponds to a kinetic mechanism limited by the surface reaction between adsorbed, non-dissociated O 2 and two adsorbed molecular SO 2 molecules.

95/00826 Consumers more satisfied with coal

Slurry (coal refuse), which contains pyritic materials, produces sulfuric acid when wetted and oxidized. The acidity, together with droughtiness and high surface temperatures, create a complex problem for revegetation. Four grasses, orchardgrass (Dactylis glomerata L.), redtop (Agrostis alba L.), reed canarygrass (Phalaris arundinacea L.) and tall fescue (Festuca arundinacea Shreb.), were planted on an acid slurry site at Captain Mine, Arch of Illinois Inc., Perry County, IL, USA, to evaluate the effects of soil amendments. Organic material from composted garbage (0, 112, 224 and 336 Mg ha-1), limestone (0, 45, 90 and 135 Mg ha-1) and a mixture of organic material and limestone (56/22.5, 112/45 and 168/67.5 Mg ha-1) were incorporated into the slurry. All the grasses established successfully and persisted best on treatments involving the addition of limestone. Tall fescue and reed canarygrass were the grasses best suited for the revegetation of the acid slurry impoundments. The grasses did not accumulate heavy metals to levels considered potentially toxic to livestock. The application of limestone with or without organic material appears to be a possible alternative method for revegetating acid slurry without the addition of a soil cover.