Lead Monoxide Research Articles

Vaporization of Lead Zirconate‐Lead Titanate Materials: II, Hot‐Pressed Compositions at Near Theoretical Density*

The vaporization of lead monoxide from lead zirconate‐lead titanate materials was studied by thermogravimetric techniques in vacuum with hot‐pressed pellets of near theoretical density. The initial step of the complex, two‐step vaporization observed in cold‐pressed pellets in an earlier investigation is absent. The rate‐determining step for both the porous, cold‐pressed, and pore‐free, hot‐pressed materials is the bulk diffusion of lead across a thickening lead‐depleted layer at the surface of the pellet and results in a parabolic time dependence. Although parabolic rate constants are slightly lower overall for the dense materials, the activation energies for the weight loss process remain approximately 38.5 and 35 kcal/mole for the pure and Bi‐doped Pb(Zr0.65Ti0.35)O3 compositions, respectively. Vaporization mechanisms and rates were unchanged under nitrogen or oxygen pressures up to 50 torr at 1000°C. Alumina Knudsen cells were used to study the equilibrium vapor above a powdered, hot‐pressed Pb(Zr0.65.Ti0.35)O3 composition. Mass spectrometric analysis of the vapor at 950°C showed that the vapor species and their relative abundances were the same as the equilibrium vapor species above pure lead monoxide. Continuous weight loss data from these cells gave an apparent vapor pressure that was 2% of the vapor pressure of pure lead monoxide at a given temperature, but gave the same second law enthalpy of vaporization. The overall vaporization process can be represented by the reversible equilibria: the diffusion of Pb2+ and O2‐ to the surface through a lead‐depleted region whose phases and compositions are determined by the subsolidus phase relations in the PbO‐ZrO2‐TiO2 ternary system, the reaction at or near the surface to form PbO, and the subsequent vaporization of PbO.

Some molten ionic oxides as chemical reagents

AbstractMolten ionic oxides possess important desirable properties: thermal stability, and useful chemical properties resulting from their acid or basic behaviour, i.e., from their capacity to accept or donate an oxygen ion, and, in several cases, relatively low melting points, well below 1000°c.Bismuth trioxide was found to effect a two‐temperature decomposition of ammonium chloride, yielding ammonia and hydrogen chloride. Molten antimony trioxide was found to attack rock phosphate and convert part of the phosphate to a water‐soluble form. Molten lead monoxide was found to dissolve calcium oxide readily, to dissolve chromic sesquioxide, to decompose chromite ore and to permit an extraction of iron‐free lead chromate into an upper layer of molten alkali chloride. Addition of lead sulphide to a lead monoxide melt caused formation of elemental lead and lead sulphate.Vanadium pentoxide was found to decompose ammonium chloride, yielding first, hydrogen chloride and then, ammonia. The reaction of a vanadium pentoxide melt with rock phosphate, studied in some detail, resulted in water‐solubilisation of the phosphate. The product formed in the melt is probably a calcium phosphate vanadate, from the aqueous solution of which calcium can be precipitated by ammonium carbonate; the ensuing ammonium phosphate and vanadate solution can be separated by known methods, permitting recovery of the vanadium pentoxide, and yielding ammonium phosphate.

Action of lead monoxide as an inorganic photosensitizer

Action of lead monoxide as an inorganic photosensitizer

Determination of Lead in Lead Crystal by Atomic Absorption Spectrometry

The use of spectrochemical techniques in the quantitative analysis of lead crystal has been described. The U. S. Customs Service has a unique interest in glassware which contains lead. Glassware containing more than 24% lead monoxide is dutiable at a different rate than glassware containing 24% or less. The existing procedures for the determination of the lead content of glassware are time-consuming in comparison to the rapidity with which atomic-absorption values can be determined.

Polymorphism, optical and photoelectrical properties of lead monoxide thin single crystals

AbstractThe optical and photoelectric properties of the hybridal polymorphic lead monoxide single crystals have been studied. The crystals core is of orthorhombic structure, and tetragonal monoxide is present in the surface layer. The spontaneous and artificial enantiotrophical transformation of orthorhombic to hybridal single crystals results in: 1) appearing of additional absorption band; 2) activation of photoelectric sensity \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{\Delta I}}{{I_D }} \approx 10^5 {\raise0.7ex\hbox{${\rm o}$} \!\mathord{\left/ {\vphantom {{\rm o} {\rm o}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\rm o}$}}} \right) $\end{document}; 3) the spectral response shows the form characteristic for the case of high surface recombination velocity with maximum photocurrent about ∼615 nm. The activation of the photoelectric sensity is explained by the formation of the tetragonal (red) monoxide.

Hydrothermal growth of single crystals and phase width of tetragonal lead monoxide

Single crystals of the red, tetragonal modification of lead-monoxide were grown under hydrothermal conditions. Solutions of lithium hydroxide proved to be superior for growth to the commonly used sodium hydroxide solutions. Conventional Morey-type vessels were employed. The width of the existence region on the oxygen-rich side of this binary compound was investigated by growing the crystals with or without Pb 3O 4 present in the starting material. Subsequent chemical analysis showed the composition to vary from the stoichiometric composition to PbO 1.001. These differences were also reflected in a variation of the temperature of the transition from the tetragonal to the orthorhombic modification.

Mechanism of action of lead monoxide on combustion: Interaction between lead monoxide and oxygen derivatives of hydrocarbons

A better understanding of the mechanism of catalytic action of lead monoxides on combustion is provided by studies showing that the lead oxides react with carbonyl and hydroxyl derivatives of hydrocarbons (whose combustion they promote), but not with ethers and hydrocarbons (whose combustion they inhibit). The principal products of reaction of lead monoxides with acetone, acetaldehyde, methanol, methyl acetate, acetic acid and acetic anhydride were analysed. The effect of metallic lead on these organic compounds was also studied.

Effect of lead monoxide on the combustion behaviour of oxygen derivatives of hydrocarbons

In contrast to its inhibiting effect or the combustion of hydrocarbons, lead monoxide strongly promotes the combustion of oxygen derivatives of hydrocarbons which contain carbonyl and/or hydroxyl groups. It markedly lowers the temperature at which oxidation commences, greatly increases the extent of reaction, and causes carbon dioxide to form in far greater amounts than carbon monoxide. Whereas lead monoxide undergoes hardly any change in the course of its inhibiting effect, during promotion it is reduced to lead in the combustion of acetic acid, acetic anhydride and formaldehyde. However, it is not reduced in the course of its prompting effect on acetone and methyl acetate where instead it glows and sinters. With methanol both these effects occur concurrently, a faint glow appears on the surface of the lead oxide and some reduction occurs beneath the surface. The observations throw fresh light on the mechanism of anti-knock and pro-knock effects of lead alkyls in gasoline engines. Mechanisms are proposed to explain the results.

Catalytic oxidation of propylene, isobutene, and benzene over lead monoxide

The catalytic oxidation of propylene, isobutene, and benzene has been studied over a lead monoxide catalyst in the general temperature range 230–310 °C. The catalyst was prepared by evaporation to give a thin layer upon which electrical conductance measurements were also made, and the electrical conductance was used to give information about the nature of the adsorbed species and of the nonstoichiometry of the oxide. It is concluded that propylene adsorption was accompanied by electron donation to the catalyst and that under catalytic conditions the oxide was p-type. In all cases the reaction proceeded entirely to give carbon dioxide and water vapor, and the reaction was shown to be first order in oxygen pressure and zero order in hydrocarbon pressure, with activation energies of 26, 28, and 30 kcal mole −1 for propylene, isobutene, and benzene, respectively. It is concluded from the pressure dependence data that reaction involves only physically adsorbed molecular oxygen. Using radiation in the near-UV and visible regions, a search was made for photoadsorption and photocatalysis, but no such effects could be detected.

Optical absorption coefficients of lead monoxide single crystal of the yellow modification

Single crystals of the yellow modification of lead monoxide were grown from the melt. The crystallographic axes could be determined easily from the configuration of the etch pits obtained by thermal etching or from the directions of streaks in the c plane. Optical absorption coefficients were determined in the fundamental absorption edge (380mμ–470mμ) for crystals cleaved in the c plane. They are a maximum when the electric field is parallel to the crystallographic b axis and a minimum parallel to the a axis. The temperature coefficient of the optical band gap is 1.0×10 −3eV/deg.

ゴム用不溶性いおう/ゴム用塩化いおう/ゴム用リサージ(一酸化鉛)/ゴム用水酸化カルシウム(消石灰)

ゴム用不溶性いおう/ゴム用塩化いおう/ゴム用リサージ(一酸化鉛)/ゴム用水酸化カルシウム(消石灰)

Influence of impurities on the formation of red and yellow PbO

The influence of silica and other impurities, as well as of reactant concentrations, upon the course of the reaction between lead acetate and ammonium hydroxide, and upon the identity of the reaction products, are described. The immediate reaction product is a white precipitate consisting of either Pb(CH 3COO) 2·2Pb(OH) 2, or Pb(OH) 2, or a mixture of these compounds, depending upon the presence or absence of impurities, and upon reactant concentrations. In contact with the supernatant liquid the basic acetate or hydroxide converts spontaneously into a green precipitate which has the orthorhombic structure of yellow lead oxide. After decantation and drying the result is red, tetragonal lead oxide if certain impurities are absent. The elements Si, Ge, P, As, Sb, Se, Te, Mo and W, when present in the precipitation solution as anions at concentrations as low as 10–100 ppm prevent the transformation of the orthorhombic into the tetragonal structure. The result is then yellow orthorhombic lead oxide. By application of these findings, it is possible to prepare ultra-pure red oxide, or the yellow oxide only slightly contaminated with one of the specified elements, as desired.

The non-stoicheiometry of lead monoxide

The non-stoicheiometry of lead monoxide

Photoconductivity in Tetragonal and Orthorhombic Lead Monoxide Layers

The photoconductive behavior of evaporated layers of lead monoxide in both the tetragonal and orthorhombic crystalline modifications has been investigated. Stoichiometry was controlled on a relative scale by controlling the oxygen pressure during sample preparation, yielding both n- and p-type material. Current—voltage characteristics, optical absorption, and variation of photocurrent with (1) wavelength, (2) applied field, and (3) light intensity are presented and discussed for the two forms. Energy band gaps of 2.0 eV for the tetragonal form and 2.6 eV for the orthorhombic form are indicated. A maximum resistivity of 3×1011Ω·cm with a μτ product of 4×10−7 cm2/V was measured for the tetragonal phase. The corresponding values for the orthorhombic phase were 1×1013Ω·cm and 1×10−9 cm2/V. Whereas in earlier pictures photosensitivity was explained as a contact phenomenon, the present data demand a model such as impurity sensitization or interparticle barrier modulation to explain the observed bulk photosensitivity.

Physical interpretation of a PbO-photodetector

The photosensitivity of a tetragonal lead monoxide crystal with one electolytic and one metallic contact is described with a simplified theory. From the wavelength dependence of the photocurrent the conclusion is drawn that essentially only the depletion layer near the illuminated contact (thickness about 1 μ) contributes to the photosensitivity. The absolute quantum efficiency of the excitation process in unity in the 3300–5500 Å wavelength region, the product of hole mobility and recombination lifetime is estimated to be about 2 x 10 -9 cm 2/V.

The preparation of lead dioxide for X‐ray diffraction studies

AbstractLead dioxide is the active constituent of the positive electrode in the lead‐acid battery. Both the α‐ and the β‐modifications are present in battery electrodes and X‐ray diffraction techniques must be used to differentiate the role of each in the reactions occurring in the lead‐acid battery system. Standard samples of the two forms of lead dioxide are necessary for this purpose, and samples prepared by various methods have been studied. Powder patterns of electrodeposited samples of both α‐ and β‐lead dioxide showed preferred orientation effects which could not be removed by grinding. Chemically prepared samples of the two forms were well crystallised and did not produce preferred orientation effects. α‐Lead dioxide prepared by the oxidation of yellow lead monoxide (using a fused mixture of sodium chlorate and sodium nitrate) and β‐lead dioxide prepared by hydrolysis of lead tetra‐acetate were chosen as standard samples for X‐ray studies and their diffraction patterns have been recorded. A mechanism of nucleation has been proposed for the formation of α‐lead dioxide in alkaline and neutral media, and the β‐form in acid media.

Cerebral biopsy in the investigation of presenile dementia. I. Clinical aspects.

In most instances presenile dementia is based on well-defined organic diseases and it is not necessary to resort to cerebral biopsy to establish a diagnosis. These organic disorders cover a wide spectrum and include cerebro-vascular disease, tumours, trauma and well-defined degenerative states such as Huntington's chorea, vitamin deficiencies, endocrine disturbances, infections (bacterial and viral) and poisons such as alcohol, lead, barbiturates, bromides and carbon monoxide. The effects of liver and kidney failure as well as the hypercapnia of pulmonary insufficiency account for others.

Studies relating to the mechanism of antiknock action of tetraethyl lead

The lead compounds formed during the combustion in glass apparatus of hydrocarbons containing tetraethyl lead (TEL) are mainly orthorhombic and tetragonal polymorphs of lead monoxide. Their relative proportions vary with temperature and with the nature of the base fuel. The oxidative degradation of the organic part of TEL promotes combustion. Combustion inhibition by TEL is entirely due to the lead monoxides formed, both types having similar effects although that of the tetragonal form is the greater. Lead monoxide of either type introduced as a coating on the walls of the reaction vessel is not as effective as lead monoxide formed directly by vapour phase oxidation of TEL. The effect of lead monoxides on combustion intermediates is to destroy peroxides completely, to decrease the concentration of carbonylic compounds and to increase that of hydrocarbons. The relative proportions of the different carbonylic compounds, and also those of hydrocarbon intermediates, remain almost unchanged. Mechanisms have been proposed to account for these effects.

The bonding in the yellow form of lead monoxide

The bonding in yellow PbO, which exists in infinite zig-zag chains along the a-axis of the unit cell, is analysed and the following scheme is proposed. The oxygen electrons are used to form the PbO chain and to hold these chains together in layers perpendicular to the c-axis of the unit cell. To do this, oxygen is hybridised either completely sp 3, or sp 2 in the chain bonds and sp 2 ± p in the interchain intralayer bonds. In the chain, lead uses two 6p atomic orbitals to form bonds with two of the oxygen hybrid orbitals, and binds the chains together by 6d z 2 ± 6p z hybrid orbitals which overlap with the remaining two oxygen hybrid orbitals. Interlayer bonding is van der Waals bonding between the filled 6s orbitals on adjacent lead atoms. The peculiar geometry in the crystal structure of yellow PbO is accounted for successfully. The bonding model is consistent with the lake character and the extremely low conductivity observed for yellow PbO.

Mass-spectrometric study of the vaporization of lead monoxide. Dissociation energy of PbO

Mass-spectrometric study of the vaporization of lead monoxide. Dissociation energy of PbO