Excess CH4 Research Articles

In situ decarboxylation of acetic and formic acids in aqueous inclusions as a possible way to produce excess CH4

AbstractAccurate reconstruction of diagenetic P‐T conditions in petroleum reservoirs from fluid inclusion data relies on valid measurements of methane concentration in aqueous inclusions. Techniques have been developed (Raman spectrometry) to provide sufficiently accurate data, assuming measured methane concentration has not been modified after aqueous inclusion entrapment. This study investigates the likelihood that organic acids derived from petroleum fluids and dissolved in formation water might suffer decarboxylation upon postentrapment heating within the fluid inclusion chamber, thereby generating excess CH4 in the inclusions. Four different experiments were conducted in fused silica capillary capsules (FSCCs), mimicking fluid inclusions. The capsules were loaded with acetic (CH3COOH) or formic (HCOOH) acid solution and were heated to 250°C for short durations (<72 h) in closed‐system conditions, with or without applying a fixed PH2. Reaction products were characterized by Raman and FT‐IR spectrometry. Results indicate that decarboxylation reactions did take place, at variable degrees of progress, and that measurable excess CH4 was produced in one experiment using acetic acid. This suggests that methane may be produced from dissolved organic acids in natural aqueous inclusions in specific situations, possibly inducing errors in the thermodynamic interpretation.

Seepage of methane at Jaco Scar, a slide caused by seamount subduction offshore Costa Rica

Methane (CH4) concentrations and CH4 stable carbon isotopic composition (d13CCH4 ) were investigated in the water column within Jaco Scar. It is one of several scars formed by massive slides resulting from the subduction of seamounts offshore Costa Rica, a process that can open up structural and stratigraphical pathways for migrating CH4. The release of large amounts of CH4 into the adjacent water column was discovered at the outcropping lowermost sedimentary sequence of the hanging wall in the northwest corner of Jaco Scar, where concentrations reached up to 1,500 nmol L-1. There CH4-rich fluids seeping from the sedimentary sequence stimulate both growth and activity of a dense chemosynthetic community. Additional point sources supplying CH4 at lower concentrations were identified in density layers above and below the main plume from light carbon isotope ratios. The injected CH4 is most likely a mixture of microbial and thermogenic CH4 as suggested by d13CCH4 values between -50 and -62 % Vienna Pee Dee Belemnite. This CH4 spreads along isopycnal surfaces throughout the whole area of the scar, and the concentrations decrease due to mixing with ocean water and microbial oxidation. The supply of CH4 appears to be persistent as repeatedly high CH4 concentrations were found within the scar over 6 years. The maximum CH4 concentration and average excess CH4 concentration at Jaco Scar indicate that CH4 seepage from scars might be as significant as seepage from other tectonic structures in the marine realm. Hence, taking into account the global abundance of scars, such structures might constitute a substantial, hitherto unconsidered contribution to natural CH4 sources at the seafloor.

Estimating greenhouse gas emissions from soil following liquid manure applications using a unit response curve method

Quantitative information is critical in policy making related to the roles of agriculture in greenhouse gas (GHG) emissions. A Unit Response (UR) curve method was developed in this study for modeling GHG emissions from soil after liquid manure applications. The emission sources (soils and liquid manures) are conceptualized as a set of linear cascaded chambers with equal storage-release coefficients, or two sets of cascaded chambers in parallel, each set having equal storage-release coefficients. The model is based on a two-parameter gamma distribution. Three parameters in this model denote the number of cascaded chambers, the storage-release coefficient, and the multiplier (referring to the total net emissions) added to the gamma distribution function. These parameters can be expressed as functions of site-specific background fluxes without applications of manure/fertilizer. The method was assessed with emissions data from five fields in Washington State. The results showed that at the WSU and Lynden sites, the average excess CH4 emissions due to manure applications were 0.39 and 0.17kg CH4–Cha−1, respectively; the average excess CO2 emissions were 216.50 and 25.20kg CO2–Cha−1, respectively; and the average excess N2O were 0.37 and 0.03kg N2O–Nha−1, respectively. The UR method may fill the gaps between field measurements, simple emission factor (EF) method, and complex process-oriented models. This method has the potential to be used for estimating additional GHG emissions due to manure/fertilizer applications.

Pd/γ-Al2O3 monolithic catalysts for NOx reduction with CH4 in excess of O2: Effect of precursor salt

Palladium monolithic catalysts based on γ-Al 2 O 3 were developed and their activities and selectivities for the selective catalytic reduction of nitrogen oxides employing methane as the reducing agent in oxygen excess (CH 4 -SCR) for use at pilot plant scale, were determined. The alumina monoliths were sulphated to increase the activity of the support and subsequently impregnated with one of three precursor salts: palladium chloride, nitrate or acetate, respectively. The catalysts were characterised by XRF, XRD, TGA–DTA, H 2 -TPR, N 2 ad/desorption and MIP. Significant differences in the catalytic activities, selectivity and stabilities were found. In the case of nitrate and acetate palladium precursors, multilayer sulphates for both and Al 2 (SO 4 ) phase for the latter were observed that may inhibit the interaction of the reactants with the active phase, leading to catalysts with reduced activity. Palladium chloride was the most efficient precursor for NO x abatement, not only due to the stability of the surface sulphates that hinder the competitive CH 4 oxidation reaction but also to the presence of Cl − ions that seem to play an important role in the reaction. This catalyst had the lowest tendency for the competing hydrocarbon oxidation reaction and also demonstrated the highest stability after 40 h of reaction in the chosen operating conditions.

Aqueous and isotope geochemistry of mineral springs along the southern margin of the Tibetan plateau: Implications for fluid sources and regional degassing of CO2

Springs issuing from different faults and shear zones along the crest of the Himalayas tap three different levels of crust beneath the Tibetan Plateau. From structurally highest to lowest these are the Tingri Graben, the South Tibetan Detachment System (STDS), and the Ama Drime massif (ADM). The aqueous chemistry reflects water‐rock interactions along faults and is consistent with mapped rock types. Major ion chemistry and calculated temperatures indicate that spring waters have circulated to greater depths along the N‐S trending faults that bound the Tingri Graben and Ama Drime detachment (ADD) compared to the STDS, suggesting that these structures penetrate to greater depths. Springs have excess CO2, N2, He, and CH4 compared to meteoric water values, implying addition from crustal sources. The 3He/4He ratios range from 0.018 to 0.063 RA and are consistent with a crustal source for He. The δ13C values of dissolved inorganic carbon (DIC) and CO2 gas range from −5.5 to +3.8‰ and −13.1 to −0.3‰ versus Peedee belemnite, respectively. Sources of carbon are evaluated by calculating isotopic trajectories associated with near‐surface effervescence of CO2. Positive δ13C values of the Tingri graben and STDS springs are consistent with decarbonation of marine carbonates as the source of CO2. Negative values for the ADD springs overlap with mantle values but are best explained by metamorphic devolatilization of reduced sedimentary carbon. The δ15N values of N2 range from −2.2 to +2.1‰ (versus AIR) and are explained by mixtures of air‐derived nitrogen, metamorphic devolatilization of sedimentary nitrogen, and nitrogen from near‐surface biogenic processes. CO2 flux is estimated by scaling from individual springs (∼105 mol a−1 per spring) to extensional structures across the southern limit of the Tibetan Plateau and likely contributes between 108 and 1011 mol a−1 (up to 10%) to the global carbon budget.

Carbon isotopic characterization for the origin of excess methane in subsurface seawater

We collected samples of seawater, zooplankton, and sinking particles in the northwestern North Pacific to determine the source of excess CH4 over the saturation value in equilibrium with the atmospheric CH4 in the oxygenated open ocean, using stable carbon isotope as a tracer. We found that subsurface (∼100 m depth) seawater is supersaturated (up to 12%) with 13C‐enriched CH4 (up to −33.1‰) relative to surface seawater in equilibrium with the atmosphere (−47‰), suggesting that in situ addition of 13C‐enriched CH4 must be responsible for CH4 enrichment at depth. The δ13C of CH4 emitted from sinking particles (from −36.7 ± 1.2‰ to +5.9 ± 7.5‰) is within the range of that of excess CH4 in seawater, suggesting that the major source of subsurface excess CH4 is sinking particles. The unusually 13C‐enriched δ13C composition of CH4 emitted from sinking particles suggests that active microbial CH4 oxidation occurs within the oxic/anoxic boundary of these particles. On the basis of the Rayleigh equation, we estimated that at least 62% of CH4 produced within the anoxic center of sinking particles is oxidized within 100 m of the surface.

Microorganisms Metabolizing on Clay Grains in 3-Km-Deep Greenland Basal Ice

We have discovered > 10(8) microbial cells/cm3 attached to clay grains in the bottom 13 m of the GISP2 (Greenland Ice Sheet Project) ice core. Their concentration correlates with huge excesses of CO2 and CH4. We show that Fe-reducing bacteria produce most of the excess CO2 and methanogenic archaea produce the excess CH4. The number of attached cells per clay grain is proportional to grain perimeter rather than to area, which implies that nutrients are accessed at grain edges. We conclude that Fe-reducing microbes immobilized on clay surfaces metabolize via "shuttle" molecules that transport electrons to grain edges, where they reduce Fe(III) ions at edges to Fe(II) while organic acid ions are oxidized to CO2. Driven by the concentration gradient, electrons on Fe(II) ions at grain edges "hop" to Fe(III) ions inward in the same edges and oxidize them. The original Fe(III) ions can then attach new electrons from shuttle molecules at the edges. Our mechanism explains how Fe-reducers can reduce essentially all Fe(III) in clay minerals. We estimate that the Fe(III) in clay grains in the GISP2 silty ice can sustain Fe-reducing bacteria at the ambient temperature of -9 degrees C for approximately 10(6) years. F420 autofluorescence imaging shows that > 2.4% of the cells are methanogens, which account for the excess methane.

C1 oxidative coupling via bromine activation and tandem catalytic condensation and neutralization over CaO/zeolite compositesII. Product distribution variation and full bromine confinement

We describe a three-step bromine-mediated process for oxidative coupling of methane using O2 as oxidant. In the first step, a supported metal bromide solid is treated with O2 to generate Br2 and supported metal oxide. The Br2 thus formed reacts with excess CH4, giving a mixture of CH4, bromomethanes, and HBr. This mixture is passed over a CaO/zeolite composite which condenses bromocarbons with 100% conversion to products, and neutralizes HBr to reform the metal bromide. The resulting product contains higher hydrocarbons, excess CH4, and water. Once the HBr neutralizing capacity of the CaO is spent, the supported CaBr2/ZSM-5 may also serve as catalyst for methyl bromide coupling. The effect of temperature, pressure, and reaction time on the intermediate methane bromination as well as on the overall partial oxidation product distribution is discussed. Incorporation of this scheme into a reactor into which only methane and O2 are fed is described.

Recent Decline of Atmospheric Concentration and Emission of Methane in Nagoya Metropolitan Area

Abstract Anthropogenic emissions of methane (CH4) from major sources such as landfills, automobiles, and rice paddy fields in the Nagoya metropolitan area were estimated using several emission process parameters such as emission factors and activity data for the decade from 1988 to 1997. The sum of CH4 amounts emitted from these three major sources was calculated to be 4.93 Gg of CH4 in 1988 and 5.19 Gg of CH4 in 1997. Methane emissions from the 12 landfill sites located around the Nagoya metropolitan area gradually increased until 1996 and then decreased in 1997, while those from automobiles and rice paddy fields continuously declined for the same decade. The total amount of CH4 emitted from the 12 landfills was much larger than those from other two sources. In 1993, for example, the amount was estimated as 3.26 Gg of CH4, 58% of which was generated from the largest landfill site. The excess CH4 concentration in the urban atmosphere, which was estimated from the difference between the CH4 concentration at the urban site and the background CH4 concentration at the Mauna Loa observatory, Hawaii, USA, showed the long-term trends similar to the CH4 emission from the largest landfill site. As a result, we conclude that the CH4 emission from the largest landfill dominantly impacted on the excess CH4 concentration due to the major sources in the Nagoya metropolitan area.

CH 4 -based dry etching of high Q InP microdisks

CH 4 -based InP dry etching techniques have been investigated by using electron cyclotron resonance etching and reactive ion etching (RIE) methods to obtain microdisk and ring structures having smooth, vertical sidewalls, and specular etched surfaces. The RIE method is chosen for the device etch process owing to the higher perfection of the surfaces generated by this process. Excess CH4 introduced in the InP RIE process was found to generate excessive polymers and resulted in sloped, rough sidewalls. A multistep RIE process involving a high-pressure (75 mTorr) condition, followed by a lower pressure (15 mTorr) etching to the completion of the structure was developed that leads to very smooth sidewalls. This process was successfully utilized in the fabrication of vertically coupled microdisk resonators.

Noble gas constraints on hydrocarbon accumulation and groundwater flow in the central area of Western Sichuan Basin

The noble gas concentrations and isotope ratios of seven natural gas samples from the central area of the Western Sichuan Basin were measured. The samples all have40Ar/36Ar ratios greater than the atmospheric values, and the3He/4He ratios (RIR a ) are entirely consistent with the crustal radiogenic He values. The vertical variation of the calculated Ch4/36Ar ratios with depth clearly indicates that the CH4 and36Ar are intimately associated, indicating a common reservoir intermediate to the sampled reservoirs, where they are well mixed and stored together prior to entrapment into gas reservoirs. Meanwhile, the calculated CH4/36Ar ratios range between 8×106 and 64×106 very much greater than the CH4/36Ar values for pure water and 5 mol/L NaCl brine at low temperature and hydrostatic conditions, reflecting the presence of “excess” thermogenic CH4 over that supplied by a CH4-saturated groundwater at low temperature, and the excess CH4 saturation and dissolution to be at depth greater than the sampled reservoirs. This conclusion is consistent with the δ13C(CH4) and δ13C(C2H6) values. In addition, the4He/36Ar ratio is correlated with depth, showing that the crustal radiogenic4He are well mixed with the atomosphere-derived36Ar before introducing into gas reservoirs. The4He/36Ar ratio vertical variation with depth can be attributed to the preferential transport of4He relative to36Ar in fluxes from lower aquifers through water-filled pores into the upper one. The increasing4He/40Ar ratios with decreasing depth, from 1.3 times to 29 times greater than the crustal production ratio, are also assumed to be the results of preferential transport4He relative to40Ar from the production site into groundwater.

Quantifying Methane Oxidation from Landfills Using Stable Isotope Analysis of Downwind Plumes

Landfills are major contributors to the atmospheric CH4 budget. A major uncertainty in estimating CH4 flux from landfills is determining the attenuation of CH4 emission by methanotrophic bacteria in the aerobic outer portions of the cover soil. These bacteria intercept the gas as it migrates toward the atmosphere. To estimate cover soil oxidation, we made seasonal measurements of the difference in the δ13C of CH4 within the anoxic zone and CH4 released from landfills and captured downwind at two landfills in the Northeastern United States. Anoxic zone CH4 at the Nashua Landfill averaged −54.6 ± 0.7‰, n = 205, and displayed no significant seasonal pattern. Methane was in excess over ambient air concentrations in the downwind plume ranging from 2.13 to 3.41 ppmv. The δ13C of excess CH4, as determined by mass balance with correction for ambient air CH4, varied from −49.35 to −54.28‰. We used these values to calculate soil CH4 oxidation, which ranged from 0 to 23.6%. Oxidation was greatest in the summer and in the fall, with an annual value of 12 ± 8%. At a second landfill, plume CH4 ranged from 1.96 to 2.92 ppmv with excess δ13C values of −52.17 to −58.06‰. Oxidation at this landfill ranged from 0 to 14%.

Non-automotive sources of carbon monoxide in urban areas

Measurements of carbon monoxide were taken for two years at several locations in Portland, Oregon. There is a residual CO that is not accounted for by automobile emissions and the background concentrations. The ratio of excess CH4 (above background) to the residual CO is close to direct measurements of the emission factor of CH4/CO from biomass burning which supports the idea that the residual CO, observed in our study, is from biomass burning. Biomass burning sources consist of agricultural burning in the surrounding areas and wood burning for heat. The diurnal and seasonal timing of the residual CO is consistent with our knowledge of these sources. We found that in Portland, during Fall and Winter, biomass burning contributes 20–40% of the carbon monoxide excess over background levels.

Formation of Nonplanar CuI(CO)3Tricarbonyls on CuI–ZSM-5:An FTIR Study at 80 K

The selective catalytic reduction of N2O with CH4 in the presence of excess O2 (CH4-SCRN2O) and CH4 + O2 reaction were studied on Ni-MOR, Co-MOR and Fe-MOR, prepared from H-MOR or Na-MOR, by ion-exchange or CVD.FTIR showed that transition metal ions (tmi) were well dispersed, mainly isolated with at least two coordinative vacancies. For CH4-SCRN2O, irrespective of Brønsted acid site and Na+ amount, catalysts were active in the order Fe-MOR > Ni-MOR > Co-MOR. Using a methane-poor mixture, on all samples CH4-SCRN2O consisted of two nearly independent reactions: CH4 + N2O and CH4 + O2. Using a methane-rich mixture, CH4-SCRN2O consisted of a CH4 + N2O + O2 reaction, whose stoichiometric ratios depended on the tmi. Whereas on Ni-MOR methane combustion occurred as side reaction, on Co-MOR and Fe-MOR no side reactions occurred. Accordingly, for CH4 + O2 Co-MOR and Fe-MOR were poorly active, whereas Ni-MOR were highly active.We conclude that in CH4-SCRN2O a monoatomic oxygen form activates methane on Co-MOR and Fe-MOR catalysts, whereas both a monoatomic oxygen form and a molecular oxygen form activate methane on Ni-MOR. Being active for the CH4-SCRN2O and CH4-SCRNOx and forming CO only in traces, Ni-MOR are promising catalysts for the simultaneous SCR of N2O and NOx using CH4 as reducing agent.

Chemical characteristics of continental outflow from Asia to the troposphere over the western Pacific Ocean during September–October 1991: Results from PEM‐West A

An important objective of the Pacific Exploratory Mission‐West A (PEM‐West A) was the chemical characterization of the outflow of tropospheric trace gases and aerosol particles from the Asian continent over the western Pacific Ocean. This paper summarizes the chemistry of this outflow during the period September – October 1991. The vertical distributions of CO, C2H6, and NOx showed regions of outflow at altitudes below 2 km and from 8 to 12 km. Mixing ratios of CO were ≈130 parts per billion by volume (ppbv), ≈1000 parts per trillion by volume (pptv) for C2H6, and ≈100 pptv for NOx in both of these regions. Direct outflow of Asian industrial materials was clearly evident at altitudes below 2 km, where halocarbon tracer compounds such as CH3CCl3 and C2Cl4 were enhanced about threefold compared to aged Pacific air. The source attribution of species outflowing from Asia to the Pacific at 8–12 km altitude was not straightforward. Above 10 km altitude there were substantial enhancements of NOy, O3, CO, CH4 SO2, C2H6, C3H8, C2H2, and aerosol 210Pb but not halocarbon industrial tracers. These air masses were rich in nitrogen relative to sulfur and contained ratios of C2H2/CO and C3H8/C2H6 (≈1.5 and 0.1 respectively) indicative of several‐day‐old combustion emissions. It is unclear if these emissions were of Asian origin, or if they were rapidly transported to this region from Europe by the high wind speeds in this tropospheric region (60 – 70 m s−1). The significant cyclonic activity over Asia at this time could have transported to the upper troposphere emissions from biomass burning in Southeast Asia or emissions from the extensive use of various biomass materials for cooking and space heating. Apparently, the emissions in the upper troposphere were brought there by wet convective systems since water‐soluble gases and aerosols were depleted in these air masses. Near 9 km altitude there was a distinct regional outflow that appeared to be heavily influenced by biogenic processes on the Asian continent, especially from the southeastern area. These air masses contained CH4 in excess of 1800 ppbv, while CO2 and OCS were significantly depleted (349 – 352 ppmv and 450 – 500 pptv, respectively). This signature seemingly reflected CH4 emissions from wetlands and rice paddies with coincident biospheric uptake of tropospheric CO2 and OCS.

Assimilation of inorganic nitrogen by seep mytilid Ia, an undescribed deep-sea mussel containing methanotrophic endosymbionts:fate of assimilated nitrogen and the relation between methane and nitrogen assimilation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 123:137-148 (1995) - doi:10.3354/meps123137 Assimilation of inorganic nitrogen by seep mytilid Ia, an undescribed deep-sea mussel containing methanotrophic endosymbionts: fate of assimilated nitrogen and the relation between methane and nitrogen assimilation Lee RW, Childress JJ Undescribed deep-sea mussels containing methanotrophic endosymbionts (seep mytilid Ia) are found at high densities around hydrocarbon seeps of the Gulf of Mexico where methane, nitrate and ammonium are present at high concentrations. In this study we investigated assimilation of ammonium, nitrate, glycine and methane using 15N- and 13C-labelled tracers to determine sites of assimilation, rates of assimilation, and the chemical form in which assimilated C and N appears. We then investigated the interaction between inorganic nitrogen assimilation and methane assimilation to assess whether they are directly dependent on each other. 15NO3-, 15NH3 and 13CH4 were assimilated primarily into the gills where the bacteria are located, with negligible incorporation into symbiont-free tissue. In contrast,13C15N-glycine was assimilated equally into gill and symbiont-free tissue. These results indicate that inorganic N is assimilated in the gill tissue. The bulk of 13C and 15N label from methane and ammonium incubations was in the 80% EtOH soluble fraction, suggesting that the primary assimilation product was low-molecular-weight metabolites. Some 13C was incorporated into carbon storage products. Mussels that assimilated excess 13CH4 converted 35% of 13CH4 into an EtOH insoluble form. Negligible 15N label was observed in this fraction. Inorganic N assimilation and methane assimilation were not tightly coupled. N assimilation was not affected by absence of methane or inhibition of methanotrophy. Methane assimilation was not stimulated by increased N assimilation. Seep mytilids were capable of luxury consumption of inorganic N, i.e. C/N assimilation ratios below the average C/N ratio of mussel tissues (4.2). We believe that luxury consumption is supported by C reserves resulting in part from methanotrophy. From relations between CH4 and N source concentration and assimilation rate, we estimated the environmental conditions that result in balanced C/N assimilation. From this analysis we predict that at environmentally realistic methane and inorganic N concentrations seep mytilids assimilate excess CH4. Seep mytilid Ia . Methanotrophy . Chemoautotrophy . Nitrogen assimilation . Ammonium . Nitrate . Methane . Hydrocarbon seep Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 123. Publication date: July 20, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

In situ ellipsometric study of a palladium catalyst during the oxidation of methane

Ellipsometry is used to follow the growth of a PdO layer on the surface of a thick Pd-film catalyst during methane oxidation at ∼ 500°C. The oxide layer that develops under rich conditions (excess CH4) is quite porous and roughens with time. Little CO is formed during this period, but the CO2 formation rate increases until spontaneous oscillations develop, which correlate with changes in the ellipsometric data. These changes indicate that the porous oxide rapidly converts to a metal-rich state, which has decreased catalytic activity, and then slowly reoxidizes.

Urban Atmospheric 14CO and 14CH4 Measurements by Accelerator Mass Spectrometry

Atmospheric gas samples (0.1m3) were collected at ground level during January/February 1984 in Las Vegas, Nevada for 14C/13C accelerator mass spectrometry and total abundance measurements of CO and CH4. During winter months in this locale, CO concentrations can occur at 10 to 100 times background, occasionally exceeding the National Ambient Air Quality Standard (NAAQS). Methane concentrations show a slight enhancement (∼24%) above the background (non-urban troposphere) level. A comparison of CO and CH4 concentrations shows a good linear correlation which may indicate a common source. Preliminary 14C/13C results of the two species suggest that fossil emissions are the predominant source of excess CO and CH4 in the samples taken. Estimates of anthropogenic CO and CH4 are important for source apportionment of combustion emissions. In addition, this information is valuable for understanding the global CO and CH4 cycles and, therefore, human impact on climate and the stratospheric ozone layer.

GaAs METAL ORGANICS VAPOUR PHASE EPITAXY : RESIDUAL CARBON

GaAs grown from trimethylgallium (TMG) and arsine (AsH3) countaing residual carbon C. It is mostly incorporated essentialy as acceptor. Photoluminescence spectra exhibit besides the usual features a peak at 1.477 eV the higher the greater the ratio As/Ga. Annealing under H2 + AsH3 enhances the intensity of this peak. GaAs layers were grown with excess CH4. This gives highly compensated layers ; the 1.477 eV peak appears in all these samples. The kinetics of growth is drastically changed by the excess CH4.

Chemicothermal treatment at the volga automobile factory

1. In continuous muffle-free furnaces with no distinct separation of the saturation and diffusion zones it is possible to create different carbon and nitrogen potentials in various zones of the furnace by supplying the necessary quantities of natural gas and ammonia. 2. To exclude structural defects of the carbonitride case the carbon potential in the saturation zone is maintained within limits of 0.9–1.0%, and 0.7–0.8% in the diffusion zone, with ammonia supplied in the diffusion zone. The flow of the atmosphere is toward the latter zone, which prevents ammonia from entering the diffusion zone. 3. The necessary condition for high quality of machine parts is automatic control of the carbon potential of the furnace and strict control of the quantity of ammonia supplied to the furnace. The carbon potential is monitored and controlled by means of the concentration of excess CH4 in the saturation zone and CO2 in the last zone of the furnace before quenching.