Acidic Slurry Research Articles

Investigations Of The Chemical-Mechanical Polishing Of Polymer Films For ILD Applications

AbstractLow dielectric constant films are being investigated as the interlayer dielectric (ILD) in a multilevel interconnection scheme for advanced ULSI circuits. In such applications they will be subjected to planarization processes using chemical-mechanical polishing (CMP), either directly during dielectric planarization or indirectly in the final stages of metal patterning using the Damascene process. In this paper we report the results of our initial investigations of the CMP of three different polymers, all with dielectric constant in the range of 2.3 – 2.7 and with different mechanical and chemical properties. The CMP was carried out using alumina as the abrasive in basic and acidic pH slurries. The effect of preannealing the polymer on the CMP behavior was also investigated

Post-CMP Cleaning of W and SiO2: A Model Study

ABSTRACTChemical-Mechanical Planarization (CMP) of SiO2 is performed using alkaline silica slurries while CMP of tungsten (W) utilizes acidic slurries with alumina as the abrasive. Proposed mechanisms for the two CMP processes, with more emphasis on SiO2-CMP, have been discussed in literature. However, much less is known about the removal mechanism of residual slurry particles from the planarized surfaces - a crucial step for subsequent device processing. We discuss the chemical and physical basis of post-CMP cleaning by double-side scrubbing using polyvinyl alcohol (PVA) brushes and show how the interactions between the wafer surface, slurry, and the brush material affect the overall cleaning efficiency. Using the zeta potential concept the common features for cleaning surfaces after SiO2-CMP and W-CMP are established and the differences between these two systems are highlighted. We present surface particle levels for two model systems as a function of cleaning chemistries and discuss their influence on post-CMP surface metal levels.

Monitoring and Analysis of Gravel-Packing Procedures To Explain Well Performance

Gravel-packed gas wells completed in the Gulf of Mexico since 1980 were reviewed to build a selective database for a completion-effectiveness study. Gas wells with clean, uniform sands were selected for analysis. Significant monitoring data identified were injectivity tests at different points during the completion and fluid loss rates (barrels per hour). Injectivity before gravel pacing and productivity after gravel pacing were classified according to sidewall-core permeabilities. Different gravel-pack preparation and execution techniques were reviewed. Fluid-loss-control pills were identified as the greatest source of damage restricting gravel-packed well productivity. Injectivity tests and sidewall-core permeabilities provide valuable information for monitoring well completion procedures.

Flow injection flame atomic absorption analysis of Fe and Mn in cement samples

A new procedure has been developed for the determination of Fe and Mn in cements. It consists in dispersing 50 mg of the solid sample in 25 ml of 0.15 mol/l HNO3 and 0.12 mol/l HCl solution. Acid slurries are heated at 50°C for 10 min and then different volumes of the slurry are injected into a water carrier stream. This previous acid treatment leaches the elements to be determined and permits the use of acid solutions as standards. For the Mn determination, the use of a single line flow injection manifold provides a limit of detection of 0.03 mgl−1 and a dynamic range up to 6 mgl−1. For the determination of Fe, the on-line dispersion of samples, using a well stirred mixing chamber, increases the dynamic range up to a concentration of 125 mgl−1 and provides a limit of detection of 1 mgl−1. The procedure has been applied to the analysis of real cement samples and a certified reference material. Results were in agreement with those obtained by a reference procedure involving the alkaline fusion of samples and batch analysis by flame atomic absorption spectrometry.

Lethal and sub-lethal effects of acid, aluminium and lime on Gammarus pulex during repeated simulated episodes in a Welsh stream

SUMMARY. 1. A soft-water stream in upland mid-Wales was dosed with sulphuric acid, aluminium sulphate and limestone slurry to produce a zone of aluminium at low pH. and one of aluminium, low pH and added lime. 2. Three episodes of 24-h duration were induced, each separated by a 12-h inter-dosing period, and the responses of the crustacean Gammarus pulex monitored throughout. 3. G. pulex parasitized by the acanthocephalan Pomphorhynchus laevis were significantly more sensitive than unparasitized individuals. 4. Liming significantly reduced mortality during dosing but postexposure deaths were greatest for animals which had been exposed in the time zone. 5. The disruption of precopulalory behaviour in G. pulex was rapid and liming did not mitigate this response.

Reclamation of acid coal refuse

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.

Radiolytic desulphurization of high-sulphur coals

Gamma-ray-induced radiolysis of aqueous or acidic aqueous coal slurries is an effective method of desulphurization of some high-sulphur (2–8 wt%) Indian coals; not only the inorganic and organic sulphur but also the mineral matter are oxidatively removed without seemingly affecting the coal matrix. This novel radiolytic process has potential for the simultaneous desulphurization and demineralization of coal slurries prior to pipeline transportation, being technologically feasible and economically viable.

Electrochemical oxidation of acidic Alberta coal slurries

The electrochemical oxidation of four different types of Alberta coals of bituminous and subbituminous rank have been studied in 1 M H2SO4 slurries at 90°C under potentiostatic conditions at an applied potential of 1.0 V with respect to RHE. Two particle sizes (>200 and <60 mesh) were used to determine the rate constant for the electrochemical oxidation of coal mediated by Fe3+. Two rate constants,k c.1, andk c.2, representing initial (0-∼6 h) and subsequent (∼6–24 h) stages of electrochemical oxidation of coal, respectively, were observed. A correlation between the rate constants and the fixed carbon content (rank) of the coals was drawn. Gas chromatographic analysis of the gaseous oxidation products indicated the production of carbon dioxide. The rate and current efficiency for this production was determined as a function of electrolysis time with the rate of production reaching a steady-state level after a few hours of electrolysis. Possible mechanisms, for the oxidation of coal are discussed, based on structural and functional group models.

A Kinetic Study of the Electrochemical Oxidation of Alberta Coal Slurries

The kinetics of the Fe3+‐mediated electrochemical oxidation of four types of Alberta coals in acidic slurries have been investigated. A critical examination of the previously reported mechanisms and kinetic treatments for the electrochemical oxidation of coal slurries is provided. In this work, a new approach was developed to analyze and to determine the rate constant of the electrochemical oxidation of coal, shown here to be an irreversible process. Two second‐order rate constants, and , representing the initial (0 to ca. 6h) and subsequent (ca. 6 to 24h) stages of electrochemical oxidation, respectively, were obtained from this approach. A correlation between these rate constants and the fixed carbon content (rank) was observed for the coals studied.

Oxydesulphurization of Turkish lignites in acidic and basic slurries

Powdered Turkish lignites from Can, Beypazari and Elbistan areas were desulphurized by leaching in a small, stirred autoclave with aqueous alkaline (0.2 M Na 2CO 3, pH = 11.5) and acidic (pH = 1.3) solutions under oxygen partial pressures of 10–15 atm and at 125–175 °C. The sulphur contents of these lignites were mostly organic and the Oxydesulphurization process was not significantly effective. The total sulphur removal was slightly better under acidic conditions and pyritic sulphur removal had an optimum temperature of about 150 °C. Organic sulphur removal would increase with increased temperatures, but this would be at the expense of losses in the heating values (which was insignificant for mild conditions of this study), The treatment with any alkaline solution does not seem to be appropriate for Elbistan lignites, since a significant proportion of it (about 45 wt%) is dissolved in 0.2 M Na 2CO 3 solution.

Mediator-Assisted Electrochemical Desulfurization of Coal

A bituminous coal from Illinois (Colchester No. 2) in acid slurry was electrolyzed anodically at 1.2–1.3 V versus SCE (saturated calomel electrode) and 65–75°C. Hydrogen gas was observed to evolve at the cathode with almost 100 percent Faradaic current efficiencies, while simultaneous desulfurization of coal was noted in the anode compartment. In order to enhance sulfur removal, the cations of Ce (IV) and Fe (III) were added to coal slurries. Up to 80 percent reduction in sulfur content of the coal was observed.

KINETICS OF COAL SLURRY ELECTROXIDATION

Expressions for limiting currents are obtained to describe the heterogeneous electroxidation of a suspended solid particle in a stirred electrolyte. The electrochemical reaction involves oxidation of a dissolved cation (mediator) in the electrolyte followed by oxidation of the solid coal particle by the cation via an irreversible pseudo first order chemical reaction. This model is applied to bulk electrolysis of the acidic coal slurries containing dissolved Fe(II), and the observed limiting currents permit evaluation of the chemical rate constant of coal oxidation. In addition to Fe(III), multivalent cation of Cu(II) was found to enhance the rates of electrochemical oxidation of coal.

Electrochemical oxidation of coals: Voltammetry and mass spectrometry

The anodic oxidation of sulphuric acid slurries of lignite, bituminous, and anthracite coals; a high-yield extract of coal; and carbon black, has been investigated voltammetrically and with simultaneous m.s. monitoring of evolved gases. The previously reported evolution of carbon dioxide at very low voltages was shown to be chemically released from minerals. The low rank coals and the asphaltite did show considerable electrochemical activity near to 1.0–1.2 V, mainly from the conversion of leached ferrous ion to the ferric form. Further activity near 1.4–1.5 V arose from the oxidation to CO 2 of leached organic matter. For well-washed low rank coals, the coal extract and the anthracite, CO 2 release was only observed at high (>2.8V) anode voltages, with simultaneous release of oxygen. Electrochemical gasification of coal via anodic oxidation of macromolecules at low voltages did not occur.

Pyrite-assisted water electrolysis

Anodic oxidation of acidic pyrite slurries stirred on platinum electrodes was studied at applied potentials of 0.5–1.0 V, SCE (standard calomel electrode). Hydrogen evolution with Faraday current efficiencies of over 95% was observed at the cathode at potentials as low as 0.6 V, SCE. Pyrite was found to dissolve in the electrolyte forming sulfate anions. X-ray diffraction spectroscopy of samples after 6 h of electrolysis indicated no free sulfur formation on the surface of the pyrites used. The electrochemical evolution of oxygen is replaced by the anodic oxidation of pyrite. Since the oxidation of pyrite occurs at potentials lower than that required for evolution of oxygen in an ordinary water electrolysis cell, the overall potential required for water electrolysis is diminished. The result is lowered consumption of energy and the production of hydrogen, sulfuric acid and ferric sulfate. The effect of temperature, pyrite slurry concentration and electrode potential on the rates of reaction has been investigated and reported.

Sulphur removal from coal by electrolysis

Anodic oxidation of acidic coal slurries at potentials of 0.8–1.0 V, on the NHE scale, causes pyrite present in coal to react and dissolve while H 2 is produced simultaneously at the cathode. If coal is filtered from unelectrolysed coal slurries, the filtrates show similar electrochemical reactivity. Cyclic voltammetry applied to either slurry orfiltrate indicates that the reversible, one-electron oxidation of Fe(II) to Fe(III) is a major reaction, but chemical assays reveal that sulphide also is oxidized, to S ° and SO 4 2−.The electrochemical reactions may involve direct oxidation of pyrite when coal particles strike the anode; it is likely, in addition, that dissolved ionic Fe may act as an electron shuttle between solid pyrite and the anode. Other experiments without coal also indicate that Fe(III) (which can be produced from Fe(II) at the anode) can oxidize pyrite and thiophene. Preliminary experiments with lignite and a bituminous coal suggest that up to 40% of the total sulphur can be removed from coal by slurry electrolysis in acidic electrolyte with either platinum or graphite electrodes.

Near-u.v.-light-induced competitive hydroxyl radical reactions in aqueous slurries of titanium dioxide

Photolysis of oxygenated benzoic acid and sodium benzoate aqueous slurries of titanium dioxide (anatase) with near-u.v. light gives hydroxybenzoic acids; hydroxyl radicals are shown to be involved.

Phytic acid removal from soybeans by a lipid protein concentrate process

AbstractOver 90% of phytic acid has been removed from full‐fat soy flour by a lipid‐protein concentrate process previously reported in 1974 by the Northern Regional Research Center. In the current study, parameters for optimizing phytic acid removal were evaluated. By changing both the molar concentration of the calcium chloride solution used and the pH of the initial acid slurry, various amounts of phytic acid and mineral elements were recovered in the acid‐precipitated curd. A mathematical treatment of the data using multiple regression analusis showed phytic acid removal possible from 10 to 90%, zinc recovery from 10 to 90%, and calcium concentrations equalling twice that of the original starting flour. All variable conditions introduced into the process had no effect on protein (90–93%), fat (98–100%), and iron (94–96%) recoveries. The results presented in this report can be applied to a large number of processes now being used for making edible soy proteins, and thereby low phytin‐containing products can be acheived.

Composition of the product of algal culture in the liquid phase of animal slurry

AbstractThe composition of the product of algal culture in the liquid phase of slurry has been examined. The material consists of cells of the cultured alga (Chlorella vulgaris) together with those of the endogenous microbial community, and contains approximately 42% true protein, 23% carbohydrate, 16% lipid and 9% nucleic acid. The protein is deficient in the sulphur amino acids but rich in lysine. The latter feature appears to be related to the presence of hexanoic acid in slurry. The endogenous microorganisms do not make a significant direct contribution to the composition of material harvested after algal culture. Light and temperature have only slight effects upon composition of the harvested material.

The use of potentiostatic techniques in the development of improved stainless steels for chemical plant

AbstractIt is possible by potentiostatic methods to exactly forecast the behaviour of unusual material/corrodent systems; such methods may, consequently, be used for the development of corrosion resistant alloys. A new alloy on iron base (with, %, 25 Cr, 5.5 Ni, 3.0 Cu, 2.5 Mo) combines very good mechanical properties with resistance to general corrosion, pitting and crevice corrosion. Industrial applications include impellers for pumps operating in acid slurries (30% P2O5, 30% CaSO4 as solids, 2% H2SO4, HF, H2SiF6; 60–80°C, three years without corrosion); pump impeller for sulfuric acid and other corrosive products shipped in tank ships; impeller for a sea water pump (no corrosion after 4 years' operation).

Decomposition of Nitrate in Mixtures of Minced Grass and Water

THE addition of various substances, such as amino-acids, has a temporary inhibitory effect on the formation of lactic acid in slurries made from minced grass and water1. Among the substances tested in this connexion was potassium nitrate, and it was found, in preliminary tests, that the inhibition was due to the partial formation of nitrite from the nitrate, the former then being decomposed to nitric oxide. The reaction nitrate → nitrite only inhibits the formation of lactic acid temporarily, and when the lactic fermentation reaches a reasonable level, as measured by the fall in pH of the mixtures, the second reaction nitrite → nitric oxide takes place.