Decreasing Surface Coverage Research Articles

Electrochemical Anodic Dissolution Kinetics of Titanium in Fluoride-Containing Perchloric Acid Solutions at Open-Circuit Potentials

The influence of fluoride on the anodic dissolution kinetics of titanium was studied by several electrochemical techniques at steady-state open-circuit potentials in 1.0 M containing fluoride with various concentrations ranging from 0 to 0.1 M. The promoting effect of fluoride (especially when ) on the anodic dissolution behavior of titanium was characterized and discussed by taking into account the changes in the estimated electrochemical and kinetic parameters. The faradaic impedance for the anodic dissolution of titanium was analyzed both by fitting based on an equivalent electrical circuit model and by theoretical derivation based on a two-step mechanism involving one adsorbed intermediate species. By correlating the faradaic impedance expression derived from the dissolution mechanism with that deduced from the equivalent electrical circuit model, some important kinetic parameters (such as the apparent rate constants and and the surface coverage ) could be estimated from the equivalent circuit elemental parameters (such as , , and ). The charge-transfer reaction was the rate-determining step at lower fluoride concentrations of , leading to a high surface coverage of , while the chemical dissolution reaction is the rate-determining step at higher fluoride concentrations of , leading to a decreased surface coverage of .

Application of atomic force microscopy to the study of natural and model soil particles

The structure and surface chemistry of soil particles has extensive impact on many bulk scale properties and processes of soil systems and consequently the environments that they support. There are a number of physiochemical mechanisms that operate at the nanoscale which affect the soil's capability to maintain native vegetation and crops; this includes soil hydrophobicity and the soil's capacity to hold water and nutrients. The present study used atomic force microscopy in a novel approach to provide unique insight into the nanoscale properties of natural soil particles that control the physiochemical interaction of material within the soil column. There have been few atomic force microscopy studies of soil, perhaps a reflection of the heterogeneous nature of the system. The present study adopted an imaging and force measurement research strategy that accounted for the heterogeneity and used model systems to aid interpretation. The surface roughness of natural soil particles increased with depth in the soil column a consequence of the attachment of organic material within the crevices of the soil particles. The roughness root mean square calculated from ten 25 microm(2) images for five different soil particles from a Netherlands soil was 53.0 nm, 68.0 nm, 92.2 nm and 106.4 nm for the respective soil depths of 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm. A novel analysis method of atomic force microscopy phase images based on phase angle distribution across a surface was used to interpret the nanoscale distribution of organic material attached to natural and model soil particles. Phase angle distributions obtained from phase images of model surfaces were found to be bimodal, indicating multiple layers of material, which changed with the concentration of adsorbed humic acid. Phase angle distributions obtained from phase images of natural soil particles indicated a trend of decreasing surface coverage with increasing depth in the soil column. This was consistent with previous macroscopic determination of the proportions of organic material chemically extracted from bulk samples of the soils from which specimen particles were drawn. Interaction forces were measured between atomic force microscopy cantilever tips (Si(3)N(4)) and natural soil and model surfaces. Adhesion forces at humic acid free specimen surfaces (Av. 20.0 nN), which are primarily hydrophilic and whose interactions are subject to a significant contribution from the capillary forces, were found to be larger than those of specimen surfaces with adsorbed humic acid (Av. 6.5 nN). This suggests that adsorbed humic acid increased surface hydrophobicity. The magnitude and distribution of adhesion forces between atomic force microscopy tips and the natural particle surfaces was affected by both local surface roughness and the presence of adsorbed organic material. The present study has correlated nanoscale measurements with established macroscale methods of soil study. Thus, the research demonstrates that atomic force microscopy is an important addition to soil science that permits a multiscale analysis of the multifactorial phenomena of soil hydrophobicity and wetting.

Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy

We present a new technique of broad-band heterodyne-detected sum frequency generation (HD-SFG) spectroscopy and demonstrate its high sensitivity allowing surface-selective measurements of vibrational spectra at submonolayer surface coverage, as low as a few percent of a monolayer. This was achieved without the help of surface enhancement phenomena, on a transparent dielectric substrate (water), and without introducing fluorescent labels, in fact, without utilizing any electronic resonances. Only the intrinsic vibrational transitions were employed for the detection of the analyte molecules (1-octanol). Unlike conventional (homodyne-detected) SFG spectroscopy, where the signal intensity decreases quadratically with decreasing surface coverage, in HD-SFG, the scaling is linear, and the signal is amplified by interference with a reference beam, significantly improving sensitivity and detection limits. At the same time, HD-SFG provides the phase as well as the amplitude of the signal and thus allows accurate subtraction of the non-resonant background--a common problem for surfaces with low concentrations of analyte molecules (i.e., weak resonant signals).

Conduction Band Mediated Electron Transfer Across Nanocrystalline TiO2 Surfaces†

Mesoporous thin films comprised of interconnected nanocrystalline (anatase, 20 nm) TiO2 particles were functionalized with [Ru(bpy)2(deebq)](PF6)2, where bpy is 2,2'-bipyridine and deebq is 4,4'-diethylester-2,2'-biquinoline, or iron(III) protoporphyrin IX chloride (hemin). These compounds bind to TiO2 with saturation surface coverages of 8 (+/-2)x10(-8) mol/cm2. Electrochemical measurements show that the compounds first reduction occurs prior to or commensurate with the reduction of the TiO2 electrode. Apparent diffusion constants, Dapp, abstracted from chronoabsorption data measured in acetonitrile were found to be dependent on the applied potential and the electrolyte used. The Dapp values for reduction of Ru(dcbq)(bpy)2/TiO2, where dcbq is 4,4'-(COO-)2-2,2'-biquinoline, increased with decreasing surface coverage. At near saturation surface coverage, the apparent diffusion constant was 9.0 x 10(-12) m2/s after a potential step from -0.61 to -1.31 vs Fc+/0. The Dapp varied by over a factor of six with applied potential for the oxidation of [Ru(dcbq-)(bpy)2]-/TiO2 to Ru(dcbq)(bpy)2/TiO2. Complete reduction of hemin/TiO2 to heme/TiO2 was observed under conditions where the heme surface coverage was about 1/100 of that expected for monolayer surface coverage. The hemin reduction rates were strongly dependent on the final applied potential. The rates for heme to hemin oxidation were less than or equal to the hemin to heme rates in the presence and absence of pyridine. This behavior was opposite to that observed with Ru(dcbq)(bpy)2/TiO2 where reduction was slower than oxidation. A Gerischer-type model was proposed to rationalize the rectifying properties of the interface.

Evaluation of new prosthetic meshes for ventral hernia repair

In hernia repair, particularly laparoscopic hernia repair, direct contact between mesh and abdominal organs cannot always be avoided. Several mesh materials and composite meshes have been developed to decrease subsequent adhesion formation. Recently, new meshes have been introduced. In an experimental rat study, their value was established and compared with that of meshes already available on the market. In 200 rats, eight different meshes were placed intraperitoneally and in direct contact with abdominal viscera. The following meshes were tested: polypropylene (Prolene), e-PTFE (Dualmesh), polypropylene- polyglecaprone composite (Ultrapro), titanium-polypropylene composite (Timesh), polypropylene with carboxymethylcellulose-sodium hyaluronate coating (Sepramesh), polyester with collagen-polyethylene glycol-glycerol coating (Parietex Composite), polypropylene-polydioxanone composite with oxidized cellulose coating (Proceed), and bovine pericardium (Tutomesh). At 7 and then at 30 days postoperatively, adhesion formation, mesh incorporation, tensile strength, shrinkage, and infection were scored by two independent observers. Parietex Composite, Sepramesh, and Tutomesh resulted in decreased surface coverage with adhesions, whereas Prolene, Dualmesh, Ultrapro, Timesh, and Proceed resulted in increased adhesion coverage. Parietex Composite, Prolene, Ultrapro, and Sepramesh resulted in the most mesh incorporation. Dualmesh and Tutomesh resulted in significantly increased shrinkage. There were no differences in mesh infection. Parietex Composite and Dualmesh resulted in a moderate inflammatory reaction, as compared with the mild reaction the other meshes exhibited. Parietex Composite and Sepramesh combine minimal adhesion formation with maximum mesh incorporation and tensile strength. The authors recommend the use of these meshes for hernia repair in which direct contact with the abdominal viscera cannot be avoided.

The corrosion inhibition of steel with Schiff base compounds in 2 M HCl

The inhibitor effect of N,N′-bis(salicylidene)-2-hydroxy-1,3-propanediamine (LOH) and N,N′-bis(2-hydroxyacetophenylidene)-2-hydroxy-1,3-propanediamine (LACOH) in 2moldm−3 HCl medium on mild steel with known compound has been investigated at 303K. It has been determined using weight loss, polarization and impedance methods (EIS) that the corrosion rates decrease and percentage inhibition efficiencies and surface coverage degrees increase with increasing additive concentration. The inhibitors appear to function through the Langmuir adsorption isotherm. Results show LACOH to have the highest inhibition efficiency among the two compounds studied.

Structures and Properties of Self-Assembled Monolayers of Bistable [2]Rotaxanes on Au (111) Surfaces from Molecular Dynamics Simulations Validated with Experiment

Bistable [2]rotaxanes display controllable switching properties in solution, on surfaces, and in devices. These phenomena are based on the electrochemically and electrically driven mechanical shuttling motion of the ring-shaped component, cyclobis(paraquat-p-phenylene) (CBPQT(4+)) (denoted as the ring), between a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) ring system located along a dumbbell component. When the ring is encircling the TTF unit, this co-conformation of the rotaxane is the most stable and thus designated the ground-state co-conformer (GSCC), whereas the other co-conformation with the ring surrounding the DNP ring system is less favored and so designated the metastable-state co-conformer (MSCC). We report here the structure and properties of self-assembled monolayers (SAMs) of a bistable [2]rotaxane on Au (111) surfaces as a function of surface coverage based on atomistic molecular dynamics (MD) studies with a force field optimized from DFT calculations and we report several experiments that validate the predictions. On the basis of both the total energy per rotaxane and the calculated stress that is parallel to the surface, we find that the optimal packing density of the SAM corresponds to a surface coverage of 115 A(2)/molecule (one molecule per 4 x 4 grid of surface Au atoms) for both the GSCC and MSCC, and that the former is more stable than the latter by 14 kcal/mol at the optimum packing density. We find that the SAM retains hexagonal packing, except for the case at twice the optimum packing density (65 A(2)/molecule, the 3 x 3 grid). For the GSCC and MSCC, investigated at the optimum coverage, the tilt of the ring with respect to the normal is theta = 39 degrees and 61 degrees, respectively, while the tilt angle of the entire rotaxane is psi = 41 degrees and 46 degrees , respectively. Although the tilt angle of the ring decreases with decreasing surface coverage, the tilt angle of the rotaxane has a maximum at 144 A(2)/molecule (the 4 x 5 grid/molecule) of 50 degrees and 51 degrees for the GSCC and MSCC, respectively. The hexafluorophosphate counterions (PF(6)(-)) stay localized around the ring during the 2 ns MD simulation. On the basis of the calculated density profile, we find that the thickness of the SAM is 40.5 A at the optimum coverage for the GSCC and 40.0 A for MSCC, and that the thicknesses become less with decreasing surface coverage. The calculated surface tension at the optimal packing density is 45 and 65 dyn/cm for the GSCC and MSCC, respectively. This difference suggests that the water contact angle for the GSCC is larger than for the MSCC, a prediction that is verified by experiments on Langmuir-Blodgett monolayers of amphiphilic [2]rotaxanes.

Studies on the effect of vanillin and protocatechualdehyde on the corrosion of steel in hydrochloric acid

The inhibitor effect of vanillin (4-hydroxy-3-methoxy-benzaldehyde) and protocatechualdehyde (3,4-dihydroxy-benzaldehyde) in hydrochloric acid medium on steel with known composition has been investigated. It has been determined using, weight loss, polarization and impedance methods that the corrosion rates decrease and percentage inhibition efficiencies and surface coverage degrees increase with increasing additive concentration. On the other hand inhibition efficiencies are seen to increase with decreasing in temperature. The inhibitors appear to function through the Langmuir adsorption isotherm. Polarisation studies indicate the compounds studied to be mixed inhibitors. All the methods employed are in reasonable agreement.

Cytoplasmic regions of the β3 subunit of integrin αIIbβ3 involved in platelet adhesion on fibrinogen under flow conditions

Platelet adhesion to surface-bound fibrinogen depends on integrin alphaIIbbeta3. In the present study, we investigated the role of the regions 749EATSTFT756N and 755TNITYRG762T of the beta3 cytoplasmic tail in the regulation of platelet adhesion under flow conditions, by introducing peptide mimetics in platelets. Introduction of peptide EATSTFTN (E-N) increased surface coverage by 35%, an effect caused by 25% more adhesion. In contrast, peptide TNITYRGT (T-T) decreased surface coverage by 16%, as a result of 25% less adhesion. An S-->P substitution in the E-N peptide, thereby mimicking a mutation in Glanzmann's thrombasthenia, abolished the effect of E-N. A suboptimal concentration of cytochalasin D is known to enhance ligand binding to alphaIIbbeta3 in platelet suspensions. Under flow, cytochalasin D (1 micro mol L-1) induced 50% more platelet adhesion, with a strong reduction in platelet spreading. Both peptides opposed the increase in adhesion by cytochalasin D and partly (E-N) and completely (T-T) restored platelet spreading. Thus, the 749EATSTFT756N and 755TNITYRG762T regions of beta3 contribute to the regulation of alphaIIbbeta3 anchorage to the cytoskeleton and platelet spreading to an adhesive surface.

Structure−Function Relationships in High-Density Octadecylsilane Stationary Phases by Raman Spectroscopy. 3. Effects of Self-Associating Solvents

Raman spectroscopy is used to examine the subtle effects of polar, hydrogen-bonding solvents; temperature; and the surface grafting method (surface- or solution-polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2. Rotational and conformational order is assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequencies at which these Raman bands are observed. Alkyl rotational and conformational order decreases with decreasing surface coverage in these polar solvents, consistent with the behavior of these materials in air. For homogeneously distributed, high surface coverage materials, these polar solvents induce rotational ordering that is proposed to be due to the self-association of these solvents through hydrogen bonding or other dipole interactions at the alkylsilane-solvent interface. From these observations, molecular pictures of these solvent-stationary-phase interfaces are proposed in which solvent interaction with the stationary phase occurs primarily at the distal methyl group of the alkyl chains.

Structure-function relationships in high-density octadecylsilane stationary phases by Raman spectroscopy. 4. Effects of neutral and basic aromatic compounds.

The effects of aromatic compounds (toluene, benzene, p-xylene, anisole, aniline, and pyridine), temperature, and surface grafting method (surface- or solution-polymerized) on alkyl chain rotational and conformational order in a series of high-density octadecylsilane stationary phases ranging in surface coverage from 3.09 to 6.45 micromol/m2 are examined by Raman spectroscopy. Rotational and conformational order are assessed using the intensity ratio of the antisymmetric to symmetric v(CH2) modes as well as the frequency at which the symmetric v(CH2) band is observed. Alkyl rotational and conformational order decrease with decreasing surface coverage in these aromatic compounds, which is consistent with the behavior of these materials in air and in other solvents. In addition, order of the alkyl chains is dependent on solvent hydrophobicity, hydrogen-bonding ability, and basicity. The most hydrophobic compounds impart disorder to the stationary phase; the hydrogen-bonding aromatics increase the rotational order of homogeneously distributed, high-surface-coverage materials; and basic aromatic compounds increase the conformational order of high- and low-coverage materials as the basic compounds undergo silanophilic interactions with exposed surface silanols. From these observations, molecular pictures of the chromatographic interface that display interactions between the alkyl chains and these aromatic compounds are proposed.

Thermal Stability of Au/NbOx/Nb and Au/Nb2O5/W Model Catalysts Studied by Angle-Resolved X-Ray Photoelectron Spectroscopy

The thermal stability of gold deposited on Nb2O5/W, Nb2O5/Nb and NbO/Nb substrates was investigated by angle-resolved X-ray photoelectron spectroscopy. Gold in amounts 0.1-1.2 monolayer was vapour-deposited on an oxide substrate under ultrahigh vacuum. A shift of the Au (4f) core level towards higher binding energies and an increase in the line width with decreasing surface coverage by Au were observed for all supports and explained by final state effects in the photoemission process. The lower magnitude of the shift observed in the case of Au/NbO/Nb was attributed to better screening of the core hole by electrons of the metallic NbO phase. The results present evidence that on heating of the Au/Nb2O5/W system up to 550 °C only agglomeration occurred without significant diffusion of Au into the oxide substrate. Annealing of the Au/Nb2O5/Nb model catalyst above 350 °C resulted in reduction of Nb2O5 to suboxides and inward diffusion of Au. Diffusion into the substrate above 350 °C has also been observed for the Au/NbO/Nb sample. The distribution of Au within the surface layers of substrate has been estimated by analysis of Au (4f) and Nb (3d) angle-resolved spectra. The inward diffusion of Au on annealing observed for the Nb2O5/Nb and NbO/Nb substrates is facilitated by a high density of defects in NbO. Besides information on the particular Au/Nb2O5/W, Au/Nb2O5/Nb and Au/NbO/Nb systems, our results demonstrated potentials of angle-resolved photoelectron spectroscopy for determination of the distribution of a metal in annealed model catalysts and for study of extended interfaces.

ROSAT all-sky survey of W Ursae Majoris stars and the problem of supersaturation

From ROSAT all-sky survey (RASS) data we obtained X-ray fluxes for 57 W UMa type contact systems. In our sample we detected three stars which are the shortest period main sequence binaries ever found as X-ray sources. For stars with (B V )0 0:6 a plateau is reached, similar to the saturation level observed for single, rapidly rotating stars. The X-ray flux of W UMa stars is about 4{5 times weaker than that of the fastest rotating single stars. Because early type, low activity variables have longer periods, an apparent period-activity relation is seen among our stars, while cool stars with (B V )0 > 0:6 and rotation periods between 0.23 and 0.45 days do not show any such relation. The lower X-ray emission of the single, ultra fast rotators (UFRs) and W UMa stars is interpreted as the result of a decreased coronal lling factor. The physical mechanisms responsible for the decreased surface coverage diers for UFRs and W UMa systems. For UFRs we propose strong polar updrafts within a convection zone, driven by nonuniform heating from below. The updrafts should be accompanied by large scale poleward flows near the bottom of the convective layer and equatorward flows in the surface layers. The flows drag dynamo generated elds toward the poles and create a eld-free equatorial region with a width depending on the stellar rotation rate. For W UMa stars we propose that a large scale horizontal flow embracing both stars will prevent the magnetic eld from producing long-lived structures lled with hot X-ray emitting plasma. The decreased activity of the fastest rotating UFRs increases the angular momentum loss time scale of stars in a supersaturated state. Thus the existence of a period cuto and a limiting mass of W UMa stars can be naturally explained.

A study of the energetics of the Cl2/MgO(001) interface using correlation corrected periodic Hartree–Fock theory

The energetics of the Cl2/MgO(001) interface were investigated using the ab initio periodic Hartree–Fock (PHF) method and local density functional correlation corrections to PHF theory, as implemented in the program CRYSTAL92. Estimates of the correlation corrected PHF energies are made by post-SCF evaluations of three gradient corrected functionals. The correlation energy is calculated from the fully converged ground state PHF charge density and added to the PHF total energy. This is the first study of interfacial energetics using the correlation corrected PHF theory. PHF and correlation corrected molecule/surface binding energies are reported for seven orientations of the adsorbate with respect to the surface plane. Three of the configurations align the intramolecular axes along the surface normal and the remaining geometries arrange the molecules heat-to-tail, parallel to the surface plane. The most favorable interaction occurs when chlorine approaches a surface oxygen along the normal direction. This site preference is consistent with a classical electrostatic description of the physisorption process. The binding energy increases with decreasing surface coverage. At the most dilute coverage studied (1:8) the PHF binding energy was 4.1 kcal/mol and the correlation corrected binding energies ranged from 9.2 to 10.3 kcal/mol. All three functionals tended to increase the molecule/surface attractions, shorten the molecule/surface equilibrium distance, increase the curvature of the molecule/surface potential energy surface near equilibrium, and reduce the molecule/molecule repulsions.

From the Understanding of the Reaction Mechanism Towards Optimizing the Deposition Rate and Optoelectronic Properties of a-Si:H

ABSTRACTWe present new results of kinetic studies of the deposition of high quality a-Si:H which strongly support the reaction mechanism suggested in our earlier papers: 1. SiH4 → SiH2; 2. SiH2 + SiS4 → Si2H6 (SiH2 + Si2H6 → Si3H6); 3. Si2H6 → 2a-Si:H (Si3H8 → 3a-Si:H). The “SiH3 mechanism”, as promoted by several workers, is in contradiction with these experimental facts.The di- and trisilane, which have a much higher reactive sticking coefficient than monosilane, play the role of reactive intermediates which facilitate the heterogeneous decomposition of silicon carrying species at the surface of the growing film. The values of the reactive sticking coefficient of Si2H6 and Si3H8 depend on the surface coverage by chemisorbed hydrogen; they increase with decreasing surface coverage. Under the conditions of the growth of high quality a-Si:H films the reactive sticking coefficient of disilane amounts to 10−4 to 10−2 which is in a good agreement with recent data of other authors.The rate determining step of the growth of high quality a-Si:H films is the desorption of hydrogen from the surface of the growing film. This can be strongly enhanced by ion bombardment at impact energy of <100 eV. In this way, homogeneous, good quality films were deposited at rates up to 1800 Angströms/min, and there is a well justified hope that this rate can be further increased.

Determination of CO adsorption heats from kinetic data for CO hydrogenation over metals

Studies of catalytic CO hydrogenation following the Langmuir-Hinshelwood mechanism indicate that the observed decrease in the activation energy with increasing temperature is due to the decreased surface coverage with reactants. The relationships obtained permit to carry out approximate estimates for the adsorption heat of CO.

X-ray photoelectron spectroscopy of supported metal particles

Small silver and palladium particles supported on carbon, alumina and silica substrates were studied by X-ray photoelectron spectroscopy. With decreasing surface coverage 3d core levels of metal shift toward higher binding energies. Comparable shifts are found for several transition and noble metals deposited on a clean carbon surface, indicating that they have their origin in the final state effects. The magnitude of the shift is considerably influenced by the substrate surface state. On Al2O3 and SiO2 substrates the sign of the metal line-shift is positive for Pd but negative for Ag. This difference is interpreted as a consequence of the different nucleation and growth mechanisms of the two metals.

Kinetics of desorption of water from the rutile surface

The rate of desorption of water from the rutile TiO 2 surface was measured at 25°, 40°, 60°, 80°, and 100°C. by means of a quartz reed microbalance. The Elovich equation was modified so that the rate of desorption approached zero as the reversible water on the surface approached zero. By analogy to classical first-order kinetics, a rate coefficient k was developed in terms of two constants, m and P, and the surface concentration, A: k = m/ A[exp ( PA) − 1]. Application of the modified Elovich equation to the rate data showed that one set of constants was sufficient to describe the rate process, as opposed to the Elovich equation, which required at least two sets of constants. The Arrhenius equation was applied to calculated values of the rate coefficient at different temperatures and at constant surface coverage in order to obtain the heat of desorption, qd. The heat of desorption varied from 8.0 to 5.9 kcal./mole with decreasing surface coverage.

The role of the ionic double layer in processes occurring upon illumination of the germanium/solution interface

Results of the photoelectrochemical process on germanium cathodes in alkaline solution are reported. It is shown that the stationary photopotential is determined mainly by the charge transfer through the ionic double layer. The phenomenon is described as decreasing surface coverage of the germanium cathode by adsorbed hydrogen upon illumination. The mechanism of the phenomenon is discussed.

Effect of thermal treatment of various carbons on the adsorption of vapors

1. Adsorption isotherms have been determined and compared for the vapors of water, methanol, and benzene on a number of carbon blacks which had been subjected to different thermal treatments. With increasing treatment temperature, there were decreases in both the amount of surface oxygen, capable of exchange reaction with aqueous NaOH, and in surface roughness of the blacks. The surface of the blacks became much more uniform after treatment in a hydrogen stream at 1700°. 2. Adsorption of water vapor fell rapidly with increasing graphitization, mainly as the result of removal of surface oxides. With blacks graphitized in a hydrogen stream at 1700°, water vapor adsorption was very small, even in the region of high pressure ratios. 3. Adsorption of methanol vapor on graphitized blacks dropped markedly in the region of low pressure ratios, as the result of destruction of surface oxides. In this case, decrease in surface roughness played a secondary role. 4. Adsorption of benzene vapor on graphitized blacks decreased, with decreasing surface roughness and surface coverage with chemical compounds, in the region of low surface coverage. 5. The surface properties of blacks of different origin were very similar after graphitization in a hydrogen stream at 1700δ.