Hot Acid Solution Research Articles

Ion-chromatographic determination of inorganic anions and cations in some reagents used in the electronics industry

In the electronics industry, wafer cleaning is usually performed by means of hot ammoniacal or acidic hydrogen peroxide solutions, which remove organic surface films by oxidative breakdown and dissolution to expose the substrate surface for concurrent and/or subsequent decontamination reactions. It is difficult to establish the optimum renewal cycle of the cleaning solutions to avoid economic as well as pollution problems. The present work deals with the application of ion chromatography to the determination of anionic as well as cationic impurities in hydrogen peroxide and ammonia, which are extensively used in wafer cleaning technology. As these two reagents cannot be injected directly into the separator column, methods are suggested for the pretreatment of the samples. Hydrogen peroxide was subjected to UV photolysis for about 30 min in an UV digestor at 85 ± 5°C. Though ammonia could also be treated in the same manner, simply heating it at 85 ± 5°C for 45 min in a dust-free cell, to expel most of the ammonia as gas, was found to be satisfactory. The samples were then analysed by ion chromatography and were found to contain chloride, phosphate, sulphate, copper, zinc, iron and manganese as impurities in variable amounts, when analysed at different stages of the wafer cleaning operation (20–1000 μg/l).

Models for the interactions between pectin molecules and other cell-wall constituents in vegetable tissues

In experiments to study the relationships between textural change and chemical changes in pectins of vegetables after different cooking treatments, pectins in the alcohol-insoluble solids (AIS) of the vegetables were fractionated into four groups according to their solubility in different extractants, and their yields were correlated with the firmness of the tissues. Based on the correlations observed for various vegetables, a simple model consisting of five types of basic pectin interactions in the tissues was proposed first. It includes S-type pectin extractable with cold water, A-type pectin extractable with cold chelating-agent solutions, B-type pectin extractable with hot water, C-type pectin extractable with hot chelating-agent solutions, and P-type pectin extractable with hot dilute acid or alkali solutions, among which C-type pectin was obtained by calculation rather than direct determination. It was found later that, in some cases, the amount of C-type pectin thus obtained came out as a negative value, which is apparently unreasonable. We therefore proposed, by speculation, an elaborate model consisting of twelve sub-types of complicated pectin interactions, which are based on the simple model, in order to explain the unreasonable situation resulting from the calculated value of C-type pectin content. Using snap-bean pods as sample, we now present several experiments to support the real existence of some of the complicated pectin interactions previously proposed. The supporting data came from the analysis and comparison of the amounts of bound calcium in the pectin fractions extracted and from the measurement and comparison of the size of pectin molecules extracted before and after further treatment by either heating or calcium removal.

Corrosion inhibition of carbon and low alloy steels in hot hydrochloric acid solutions

Abstract A study has been made of the resistance to corrosion of one carbon steel and two low alloy steels in 2M HCl solutions at temperatures between 60 and 90°C and of the effectiveness of some organic compounds used as corrosion inhibitors under the same experimental conditions. Weight loss results, spectrophotometric analysis for the determination of the Fe2+ ion concentration, and electrochemical data suggest that the level of inhibition and the various effects of the examined inhibitors on the behaviour of carbon and low alloy steels can be explained by the specific mechanisms of the action of each of the inhibitors.

Preliminary studies on the insecticidal activity and wash‐fastness of twelve pyrethroid treatments impregnated into bednetting assayed against mosquitoes

AbstractThe insecticidal properties of twelve pyrethroid preparations impregnated into polyester netting were compared, before and after washing, with a view to assessing their suitability for treating bednets (mosquito nets) in the field. Bioassays were carried out by exposing the mosquitoes, Anopheles gambiae Giles sensu stricto andAedes aegypti L. to netting with two concentrations of insecticide, on washed and unwashed samples, for 30 s and 3 min at different times after impregnation. Mortality was recorded after 24 h. Permethrin applied at 97°C at pH 3.4 resulted in increased uptake by polyester fibres. The performance of most insecticides on unwashed netting had not declined appreciably 12 weeks after impregnation. However, all the insecticides were depleted by washing. The treatments with best insecticidal activity after washing were cypermethrin, lambda‐cyhalothrin applied at ambient temperature and normal pH and permethrin applied in a hot acid solution.

ChemInform Abstract: The Evolution of Silicon Wafer Cleaning Technology

The purity of wafer surfaces is an essential requisite for the successful fabrication of VLSI and ULSI silicon circuits. Wafer cleaning chemistry has remained essentially unchanged in the past 25 years and is based on hot alkaline and acidic hydrogen peroxide solutions, a process known as RCA Standard Clean. This is still the primary method used in the industry. What has changed is its implementation with optimized equipment: from simple immersion to centrifugal spraying, megasonic techniques, and enclosed system processing that allow simultaneous removal of both contaminant films and particles. Improvements in wafer drying by use of isopropanol vapor or by slow‐pull out of hot deionized water are being investigated. Several alternative cleaning methods are also being tested, including choline solutions, chemical vapor etching, and UV/ozone treatments. The evolution of silicon wafer cleaning processes and technology is traced and reviewed from the 1950s to August 1989.

The Evolution of Silicon Wafer Cleaning Technology

The purity of wafer surfaces is an essential requisite for the successful fabrication of VLSI and ULSI silicon circuits. Wafer cleaning chemistry has remained essentially unchanged in the past 25 years and is based on hot alkaline and acidic hydrogen peroxide solutions, a process known as “RCA Standard Clean.” This is still the primary method used in the industry. What has changed is its implementation with optimized equipment: from simple immersion to centrifugal spraying, megasonic techniques, and enclosed system processing that allow simultaneous removal of both contaminant films and particles. Improvements in wafer drying by use of isopropanol vapor or by “slow‐pull” out of hot deionized water are being investigated. Several alternative cleaning methods are also being tested, including choline solutions, chemical vapor etching, and UV/ozone treatments. The evolution of silicon wafer cleaning processes and technology is traced and reviewed from the 1950s to August 1989.

無水クロム酸熱傷による急性クロム中毒の１例

A 20-year-old male plating worker was accidentally immersed up to his lower thorax in a vat of hot chromic acid solution. The patient sustained third degree burns over 60% of the lower body surface area. Blood and urine concentrations of chromium were 740μg/dl and 1, 550μg/l, respectively. The initial course was characterized by hypotension, hypoglycemia, acute renal failure, hepatic damage, and thrombocytopenia. Continuous hemodiafiltration between Day 3 and Day 28 after the exposure resulted in recovery from renal failure. Although he underwent debridement and epidermization twice, candidiasis of the burned surface led to candidemia. After a second skin grafting on Day 50, his condition deteriorated, with azotemia again and hyperbilirubinemia. General convulsions occurred after Day 55, and he died on Day 66. The autopsy revealed tubular necrosis of the kidneys, a markedly enlarged liver (5, 700g), with severe fatty infiltration and a slightly atrophic brain without microscopical abnormality. The 21 cases of acute chromium intoxication previously reported are reviewed and recommendations for the management of such patients are presented.

Adsorption of methylcarbamate by montmorillonite

Adsorption of methylcarbamate by Na-, Mg-, Al- and Cu-montmorillonite has been studied by infrared spectroscopy and X-ray diffraction. The methylcarbamate is adsorbed on all homoionic clays studied by an ion-dipole interaction, between CO group and the exchangeable cations. On Cu-montmorillonite, the oxygen atom of the ester group is also coordinated with the exchangeable cation. This latter coordination is promoted by partial dehydration of the montmorillonite. Also, the NH 2 group is coordinated with the exchangeable cation by a water bridge. All homoionic montmorillonite complexes were decomposed to NH 3 (retained on the clay mineral as NH 4 +), CO 2 and CH 3OH, when equilibrated at room temperature and at 100% relative humidity for 12 h. By contrast, the methylcarbamate-clay complexes were stable on heating at 80°C for 12 h. Evidently, the urethanes are hydrolyzed in hot acidic and alkaline aqueous solution to CO 2, NH 3 and alcohol. X-ray diffraction patterns showed that the methylcarbamate was able to penetrate into the interlayer space of the montmorillonites.

ChemInform Abstract: Stability of Synthetic Zeolite ZSM‐5 to Dealumination with Chromium(III) Salt Solutions.

AbstractIt is found that the synthetic zeolite ZSM‐5 undergoes less than 10% dealumination in hot acidic (pH ∼ 1.4) CrCl3 solutions.

Inhibition of Corrosion resistant alloys in hot hydrochloric acid solutions

AbstractWeight loss measurements were performed in 20% and 28% hydrochloric acid at 90 °C on carbon steel, 22Cr5Ni duplex stainless steel, and two superaustenitic steels – 27Cr31Ni3Mo and 19Cr25Ni4Mo –, in presence of organic substances used singly or mixed. The organic substances examined were quaternary ammonium salts (1–4‐pyridyl)‐pyridinium chloride hydrochloride, dodecylpy‐ridiniumchloride, benzyldimethylstearylammonium chloride, and (dodecyltrimethylammonium bromide), alkynols (1‐octyn‐3‐ol, propargyl alcohol) and trans‐cinnamaldehyde. The synergistic effect of potassium iodide on the inhibitive efficiency of the organic substances was studied.The variations of corrosion rate during the test time (normally six hours) were recorded by means of polarization resistance measurements. Polarization curves were also recorded.The results showed that the corrosion rates of the four steels examined can be reduced to less than 1 mg/cm2 · h using ternary inhibitor mixtures containing quaternary ammonium salts, trans‐cinnamaldehyde and potassium iodide (0.2% of each component).Electrochemical tests gave useful indications on the action mechanism of the inhibitors studied.

Extraction-Spectrophotometric Determination of Ruthenium(III) with O,O’-Diethyl Dithiophosphate

Ruthenium(III) reacted with O, O′-diethyl dithiophosphate(dtp-) in a hot hydrochloric acid solution and gave a red complex, [Ru(dtp)3], which could be extracted into chloroform. The spectrum of the extracted complex was affected by experimental conditions such as reaction temperature, reaction time, hydrochloric acid concentration and dtp- concentration. The calibration graph for ruthenium(III) was linear over the range of (0.17-5.2)×10-4mol dm-3 ruthenium(III) under the condition of 6mol dm-3 hydrochloric acid, 0.1mol dm-3 dtp- and heating at 60°C for 15min. The molar absorptivity at 510nm was 2.18×103cm-1 mol-1 dm3 and the relative standard deviation was 1.5% (12runs) for 3.5×10-4mol dm-3 ruthenium. The ions which interfered severely were Mo(VI), Cu(II), Pb(II), Bi(III), Tl(I), In(III), Te(IV), Cd(II), V(V), Hg(II), Ag(I), Co(II) and NO2-.

Chemisorption mechanism and effect of polyacrylic acid on the improvement in bond durability of zinc phosphate-to-polymer adhesive joints

It has been found that the outermost surface sites of polyacrylic acid-complexed crystalline zinc phosphate layers precipitated on cold-rolled steel surfaces act significantly to promote interfacial adhesive bonding to polymeric topcoats. This is the result of electrostatic internal diffusion and segmental chemisorption mechanisms of polyelectrolyte macromolecules either on newly precipitated crystal nuclei or on crystal growth sites during the primary zinc phosphate conversion process. The nature of the polymer-to-polymer chemical bond produced at the polymer-to-complex zinc phosphate precoat interfacial joints plays the key role in the achievement of long-term bond durability upon exposure to chemically corrosive environments. The locus of adhesive loss at the polymer-to-complex zinc phosphate joints after exposure to a hot acid solution was clearly identified to be cohesive failure in the crystalline precoat layers. A stable bond resulted from the formation of an interfacially produced hydrophobic structure by interactions between the polymer and the functional organic species existing on the complex precoat surfaces. The chemisorbed polyelectrolytes also served chemically to couple the organic coating and the inorganic zinc phosphate conversion layer.

Role of Acid Concentration in Leaching of Cordierite and Alkali Borosilicate Glass

The leaching rates of both cordierite and heat‐treated alkali borosilicate glass were studied in hot nitric acid solutions ranging from ∼0.1 to ∼16N. Weight loss and penetration measurements of the specimens showed that the reaction rates go through a maximum with acid concentration. The data indicate that the rate of leaching, which involves ion‐exchange and hydration reactions, is controlled not only by acid strength, but also by water activity.

New Aspects in Thiourea Leaching of Precious Metals

High reagent consumption and low efficiencies are the main obstacles against common use of thiourea for the leaching of precious metals. A new technique of universal application has been developed by which reagent consumption is depressed to about 0.5 kg/t while high metal yields are achieved and passivation of feed material is avoided. The basic principle is the selective reduction of formamidine disulfide to thiourea during leaching, maintaining the oxidized part of the initial thiourea to about 50%. This prevents the generation of passivating sulfur and enables high redox potentials of above 400 mV for rapid metal dissolution at low thiourea concentration. Pulp processes with activated carbon or resins as adsorbents can be applied. Stripping of precious metals is achieved with hot thiourea or acid solutions.

Título en español

Un estudio se llevó a cabo para determinar la viabilidad de enlatar guineos verdes acidulándolos para bajar su pH a menos de 4.6, de modo que los envases se pudiesen esterilizar a presión atmosférica en agua hirviendo. Se ensayaron tres métodos de acidulación: inmersión de rodajas de guineos en soluciones de los ácidos acético y cítrico a temperatura ambiente; escaldado en soluciones de estos ácidos y luego envasados en una salmuera acidulada; y acidulación en la misma lata usando salmueras aciduladas con ácido cítrico. En todos los experimentos de acidulación, los guineos se prepararon en la misma forma: la fruta verde se sumergió en agua a 200° F (93° C) por 30 minutos para inactivar su sistema enzimático y facilitar el mondarlos. Se pelaron a mano y la fruta se cortó en pedazos de alrededor de 1 pulgada (2.5 cm) de largo. El procedimiento de enlatar fue el siguiente: la fruta ya acidulada parcialmente o sin acidular se envasó a mano en latas 303 ó 211 x 304, a razón de 9 onzas (270 g) y onzas (150 g), respectivamente. Se añadió la salmuera hirviendo manteniendo las latas por 5 minutos en un tunel de vapor antes de cerrarlas. Las latas luego se mantuvieron en agua hirviendo por 30 minutos y luego se enfriaron a temperatura ambiente antes de almacenarlas. Se probó que la acidulación de los guineos verdes por inmersión a temperatura ambiente tanto en una solución de ácido acético al 2, 4 y 6% y de ácido cítrico al 1 y 2% no fue práctica, pues requeria un tiempo de inmersión demasiado largo para bajar el pH de la fruta a menos de 4.6. Sin embargo, la escaldadura probó ser un método eficaz de acidulación, pudiéndose bajar el pH de la fruta en pocos minutos a temperatura que fluctuó entre 160 a 190° F (71-88° C) en soluciones de ácido acético al 4 y 6% de ácido cítrico al 3 y 4%. Los cambios en el pH de la fruta durante este tratamiento fueron menos pronunciados al acercarse el pH a 4.0, lo que se atribuyó a que a este pH la fruta presenta una acción amortiguadora. El guineo verde acidulado por una escaldadura de 5 minutos a 180° F (82° C) en una solución de ácido acético al 4% y luego envasado en salmuera de un 2% de sal y 0.5% de HAc resultó con un pH de estabilización de 4.1 , el cual no sufrió cambios apreciables durante dos meses de almacenamiento a temperatura ambiente. Cuando los guineos verdes se escaldaron en soluciones de ácido cítrico al 1 y 2% y luego se enlataran en salmuera al 2% de sal y .3% de ácido cítrico, se obtuvo un producto enlatado con un pH de estabilización de alrededor de 4.1 . Cuando se bajó la acidez de la salmuera a menos de .3%, el pH del producto enlatado resultó ser más alto de lo deseable, aproximándose a 4.6. Los estudios de almacenamiento a temperatura ambiente con fruta acidulada por adición al envase de salmuera acidulada demonstraron que durante un período de almacenamiento de un año ocurrieron pocos cambios en el pH de estabilización, en el pH de la fruta y en el pH de la porción líquida. El pH de la fruta acidulada resultó ser siempre más alto que el de estabilización de la porción líquida durante el período de almacenamiento estudiado. El almacenamiento de este producto a una temperatura de 45° F (7 .2° C) resultó en valores pH de estabilización y de la fruta más altos que en los lotes similares que se almacenaron a 85° F (29.4° C). La acidez de la fruta fresca indicó una correlación significativa con el pH de la fruta enlatada, aumentándolo al aumentar la acidez de la fruta. El uso de sal en la salmuera causó una reducción en el pH del producto enlatado y aumentó significativamente la acidez. La fruta enlatada sin sal resultó con un pH más alto y una acidez más baja.

The inhibition of the intergranular corrosion of a sensitized stainless steel in hot acidic solutions

The inhibition of the intergranular corrosion of a sensitized stainless steel in hot acidic solutions

The inhibition of the intergranular corrosion of a sensitized stainless steel in hot acidic solutions

The inhibition of the intergranular corrosion of a sensitized stainless steel in hot acidic solutions

HNbO 3 and HTaO 3: New cubic perovskites prepared from LiNbO 3 and LiTaO 3 via ion exchange

The synthesis of HNbO 3 and HTaO 3 from LiNbO 3 and LiTaO 3 via ion exchange in hot aqueous acid solutions is reported. This reaction is accompanied by a topotactic structural transformation from the rhombohedral LiNbO 3 structure to the cubic perovskite structure; cell constants are a = 3.822(1) Å for HNbO 3 and 3.810(2) Å for HTaO 3. These new compounds have been characterized by powder X-ray diffraction, thermogravimetric analysis, and solid-state NMR. They are electronic insulators and have low ionic conductivity. Evidence of partially proton-exchanged phases Li 1− x H x MO 3 was also seen. The possible significance of this ion exchange reaction for devices using LiNbO 3 or LiTaO 3 is discussed.

最近の表面分析機器による表面解析と表面改善 (II)

This article reviews the application of surface analytical techniques by which convenient information has been obtained on the surface layer of container materials. Included are the application for tinplate, TFS (Tin free steel) and Aluminum. By use of these techniques, the thickness and the composition of the surface layer, which significantly affect the corrosion resistance and lacquer adhesion, can be determined and provide us with some aspects to improve the performance.The corrosion resistance of tinplate depends on the surface nature of steel substrate. The surface enriched constituents, which could not be completely removed in the preparation section of electrolytic tinning line, act to turnish the apearence and also result in high ISV (Iron solution) and ATC (Alloy-tin couple) value. Concerning the passivation film on tinplate, the thickness and composition of surface oxide film have a correlation to the lacquer adhesion. The nature of hydrated chromic oxide on TFS, which correlates to the deterioration of lacquer adhesion in a hot citric acid solution, has also been proposed from a new aspect. Analysis of the stained layer on aluminum reveals that the layer is contaminated by iron and other elements originated from city water and that iron plays an important role in staining.

Synthesis and characterization of poly(m‐and p‐phenylene carboxylates) and corresponding copolyesters, 2

AbstractPoly(phenylene carboxylate) and the corresponding copolyesters were prepared respectively by homopolycondensation of m‐ and p‐hydroxybenzoyl chlorides and by condensation of a mixture of acid chlorides of ortho‐ and para‐hydroxy benzoic acids. These polyesters which did not undergo Fries rearrangement were hydroyzed to acid monomers on treatment with hot aqueous acid solution. The copolyesters were characterized and compared with the corresponding homopolyesters.