Amorphous Grains Research Articles

The Formation of Crystalline Dust in AGB Winds from Binary-induced Spiral Shocks

As stars evolve along the asymptotic giant branch (AGB), strong winds are driven from the outer envelope. These winds form a shell, which may ultimately become a planetary nebula. Many planetary nebulae are highly asymmetric, hinting at the presence of a binary companion. Some post-AGB objects are surrounded by tori of crystalline dust, but there is no generally accepted mechanism for annealing the amorphous grains in the wind to crystals. Here, we show that the shaping of an AGB wind by a binary companion provides a possible mechanism for forming crystalline dust in the orbital plane.

CdSe thin film growth: Primarily amorphous nanograins to self-assembled nanowires

We demonstrated that electrodeposition can be used in CdSe thin film growth from primarily amorphous grains to self-assembled crystalline nanowires. CdSe films grown on indium tin oxide (ITO) coated glass substrates were characterized for their structural, morphological, compositional, optical, and photoelectrochemical properties. Depending on deposition time the films were found to form amorphous and crystalline. In addition, the morphology changes from spherical grains to web-like and then to nanowires as the deposition time increases from 500 to 1000 and then to 1500 s, respectively. The CdSe films composed of different structures and morphologies show different physicochemical properties. Herein, the results of this comprehensive study are described and discussed.

The mineralogy of cosmic dust: astromineralogy

Stardust is newly-formed in the ejected shells of gas that surround stars towards the end of their lives. Observations of the thermal emission from this dust, which is at relatively low temperatures ( T = 50–200 K), in the circumstellar shells around these stars indicate that the dust consists of both amorphous and crystalline materials. The observed solid phases include: almost pure crystalline Mg-rich silicates (forsterite and clinoenstatite), amorphous silicates, diopside, spinel, oxides (corundum and Fe 0.9 Mg 0.1 O), and also carbon-rich solids such as: (hydrogenated) amorphous carbons, aromatic hydrocarbons and silicon carbide. Crystalline grains with isotopic signatures that indicate that they formed around evolved stars, and that therefore pre-date the formation of the solar system ( e.g. , the pre-solar silicate, nanodiamond, silicon carbide, graphite, corundum, spinel, hibonite, titanium carbide and silicon nitride grains), have now been extracted from primitive meteorites. Pre-solar forsterite and amorphous silicate grains have also been extracted from interplanetary dust particles. The dust formed around evolved stars is ejected into the surrounding interstellar medium by the relatively benign effects of stellar winds, where it is subject to stochastic and violent processing in fast supernova-generated shock waves. In this medium between the stars all the silicate dust appears to be completely amorphous and it is generally thought that dust processing, via ion irradiation/implantation in shocks and/or by cosmic rays, leads to the amorphisation of the crystalline silicate grains that were formed around the evolved stars. The formation of the dust, in circumstellar environments and subsequently ejected into the interstellar medium, is thus balanced by destructive processes that erode and eventually destroy it. This paper introduces the subject of interstellar, circumstellar and pre-solar dust composition (Astromineralogy), discusses where the dust comes from, how it evolves and what its eventual fate might be.

Analysis of Molecular Hydrogen Formation on Low-Temperature Surfaces in Temperature Programmed Desorption Experiments

The study of the formation of molecular hydrogen on low-temperature surfaces is of interest both because it enables the exploration of elementary steps in the heterogeneous catalysis of a simple molecule and because of its applications in astrochemistry. Here, we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments, beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations, and the energy barriers of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results are used in order to evaluate the formation rate of H2 on dust grains under the actual conditions present in interstellar clouds. It is found that, under typical conditions in diffuse interstellar clouds, amorphous silicate grains are efficient catalysts of H2 formation when the grain temperatures are between 9 and 14 K. This temperature window is within the typical range of grain temperatures in diffuse clouds. It is thus concluded that amorphous silicates are good candidates to be efficient catalysts of H2 formation in diffuse clouds.

Various nano-size iron oxide polymorphs on mesoporous supports I: New mesoporous catalyst supports synthesized in acidic and alkaline media

A fairly large number (altogether 12) of new mesoporous silica catalyst supports have been synthesized mainly in alkaline media using ionic (CTAB) and non-ionic Aldrich-type triblock poly(alkylene oxide) copolymers and polyglycol mixtures. Preference was given to water–glass as the silicon source. This study was aiming at setting up an own catalyst carrier repertory to be able to select supports with “good” characteristics for the investigation of deconvoluted Mössbauer and EPR spectra. This task could not be carried out on compact oxides. The physical characterization (N 2 adsorption, XRD, SEM, HRTEM, SAED, Mössbauer, EPR and 29Si-NMR spectroscopy) was supplemented by activity testing, as well, in the N 2O-mediated selective oxidation of benzene and synthesis of (carbon) nanotubes at very high temperature. The first part of the planned two publications deals with the description of various synthesis recipes of silica carriers and a few novel observations obtained during their characterization. It seems to be important to know that the so called amorphous silicas are not always and never fully amorphous. Their structure consists of crystalline SiO 2 polymorph grains (β-tridymite or quartz) embedded and randomly oriented in the agglomeration of amorphous silica particles of similar (15–20 nm) size. This final state of genesis is preceded during the synthesis by the separation of viscous, tacky liquid droplets from the aqueous phase when the “surfactant + silicate” complex becomes insoluble in the slurry. Later on the droplets solidify as such or experience a slight deformation if the ordering continues even after their separation. The amorphous silica grains have no hexagonal pore structure, thus, pore walls either. Their extreme heat– and hydrothermal stability is due to this fact. They can be synthesized from water–glass in a wide range of specific surface areas and pore diameters, and in the possession of activity testing data and information obtained from the respective deconvoluted EPR and Mössbauer spectra, the selection of a “good” carrier from the literature or rather from an own carrier repertory seems to be a promising perspective.

Exothermic Chemical Reactions Can Drive Nonthermal Crystallization of Amorphous Silicate Grains

To explain how cometary silicates crystallize yet still preserve volatile interstellar ices in their parent comets, we experimentally demonstrate the possibility of chemical-reaction-driven crystallization, which is called nonthermal crystallization, using laboratory-synthesized amorphous Mg-bearing silicate grains. Analog silicate grains ~50-100 nm in diameter covered with a carbonaceous layer consisting of amorphous carbon, CH 4, and other organics to a thickness of ~10-30 nm were used as models. The analog silicate grains crystallized via the direct flow of surface reaction energy, which is produced by the graphitization of the carbonaceous layer due to oxidation at room temperature in air, into the silicates. The experimental results imply that amorphous silicates are transformed into crystalline silicates as the grains leave the comet's surface, rather than as the comet was accreted 4.5 billion years ago. Thus, primordial ices and amorphous silicate grains are predicted to reside in most comets until they approach the Sun.

Mössbauer effect studies of sputter-deposited tin–cobalt and tin–cobalt–carbon alloys

Sn–Co–C alloys are now used as negative electrodes in the latest generation of Li-ion batteries, although not much is known about the phases present in the materials, their micro or nanostructure nor their physical properties. Here, sputtered combinatorial libraries of Sn 1− x Co x (0 < x < 0.6) and [Sn 0.63Co 0.37] 1− y C y (0.1 < y < 0.5) were studied by 119Sn Mössbauer effect spectroscopy and X-ray diffraction to learn their phase content and micro or nanostructure. The sputtered Sn 1− x Co x films showed the presence of crystalline β-Sn, a new metastable cubic Sn–Co phase, an amorphous Sn 1− x Co x (0.26 < x < 0.45) phase and Co 3Sn 2 as x, or the Co content, increased. The sputtered [Sn 0.63Co 0.37] 1− y C y (0.1 < y < 0.5) materials consist of amorphous grains of Sn 0.63Co 0.37 separated by a carbon matrix. The impact of this nanostructure on the utility of these materials as negative electrodes in Li-ion batteries is discussed.

Abundant Crystalline Silicates in the Disk of a Very Low Mass Star

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the `Cores to Disks' Spitzer Legacy Program from mid-, near-infrared and optical data, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5 to 35 micron spectrum taken with the IRS and it shows strong 10 and 20 micron silicate features with high feature to continuum ratios and clear crystalline features out to 33 micron. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot (~ 300 K) dust responsible for the 10 micron feature consists of a roughly equal mix of small (~ 0.1 micron) and large (~ 1.5 micron) grains, whereas the cold (~ 70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (> 1 micron). Since the cold dust emission arises from deeper layers in the inner (< 3 AU) disk as well as from the surface layers of the outer (3-5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms.

Molecular Hydrogen Formation on Amorphous Silicates under Interstellar Conditions

Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented for the first time and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained earlier for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers, we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H2 formation within a temperature range that is relevant to diffuse interstellar clouds. The results also indicate that the hydrogen molecules are thermalized with the surface and desorb with low kinetic energy. Thus, they are unlikely to occupy highly excited states.

Synthesis and characterization of alumina- and zirconia-based powders obtained by the ultrasonic spray pyrolysis

The ultrasonic spray pyrolysis (USP) technique was used for synthesis of alumina- and zirconia-based powders. The starting agents were aqueous solutions, atomized by the ultrasonic spray generator and pyrolized in the furnace under the open-air conditions. The powders prepared by USP were in the form of solid and hollow aggregates (spheres) consisted of nanosize amorphous grains as determined by the microscopy and the X-ray diffraction techniques. The alumina-based powders were consolidated by the pulse plasma sintering resulting in single-phase materials. Different behavior of solid and hollow particles during the isostatic sintering is found; a higher degree of deformation of spheres is observed in the second case.

Infrared Emission from Interstellar Dust. IV. The Silicate‐Graphite‐PAH Model in the Post‐SpitzerEra

IR emission spectra are calculated for dust heated by starlight, for mixtures of amorphous silicate and graphitic grains, including varying amounts of PAH particles. The models are constrained to reproduce the average Milky Way extinction curve. The calculations include the effects of single-photon heating. Updated IR absorption properties for the PAHs are presented that are consistent with observed emission spectra, including those newly obtained by Spitzer. We find a size distribution for the PAHs giving emission band ratios consistent with the observed spectra of the Milky Way and other galaxies. Emission spectra are presented for a wide range of starlight intensities. We calculate how the efficiency of emission into different IR bands depends on PAH size; the strong 7.7 μm emission feature is produced mainly by PAH particles containing Umin. We present graphical procedures using Spitzer IRAC and MIPS photometry to estimate the parameters qPAH, Umin, and γ, the fraction fPDR of the dust luminosity coming from photodissociation regions with U > 100, and the total dust mass Mdust.

Dust yields in clumpy supernova shells: SN 1987A revisited

We present a study of the effects of clumping on the emergent spectral energy distribution (SED) from dusty supernova (SN) shells illuminated by a diffuse radiation source distributed throughout the medium. These models are appropriate for Type II SNe older than a few hundred days, when the energy input is dominated by γ-rays from 56 Co decay. The fully 3D radiation transport problem is solved using a Monte Carlo code, MOCASSIN, and we present a set of models aimed at investigating the sensitivity of the SEDs to various ·clumping parameters. We find that, contrary to the predictions of analytical prescriptions, the combination of an optical and infrared (IR) observational data set is sufficient to constrain dust masses even in the case where optically thick clumps are present. Using both smoothly varying and clumped grain density distributions, we obtain new estimates for the mass of dust condensed by the Type II SN 1987A by fitting the optical and IR spectrophotometric data of Wooden et al. at two epochs (day 615 and day 775). When using amorphous carbon grains, our best fits to the observational data imply that about 2.0 x 10 -4 M O of dust had condensed in the envelope of SN 1987A by day 615 and between 2.0 x 10 -4 and 4.2 x 10 -3 M ⊙ by day 775. We find that the absence of a silicate emission or absorption feature in the observed mid-IR spectra implies that no more than 15 per cent of the dust formed around SN 1987A can have been in the form of silicate particles. Our models require larger dust masses for the case of graphite grains, namely between 4.2 x 10 -4 and 6.6 x 10 -4 M ⊙ at day 615 and between 4.5 x 10 -4 and 7.5 x 10 -4 M ⊙ at day 775. From our numerical models, we derive dust masses for SN 1987A that are comparable to previous analytic clumped graphite grain mass estimates, and at least two orders of magnitude below the 0.1-0.3 M ⊙ that have been predicted to condense as dust grains in primordial core-collapse SN ejecta. This low condensation efficiency for SN 1987A is in contrast to the case of SN 2003gd, for which a dust condensation efficiency as large as 0.12 has recently been estimated.

D.C. conductivity and thermal aging of conducting zeolite/polyaniline and zeolite/polypyrrole blends

Abstract The d.c. conductivity σ of zeolite/polyaniline (PANI) and zeolite/polypyrrole (PPy) blends of various concentrations in zeolite was measured from 80 to 320 K. Moreover, the thermal degradation of σ was studied by heating the blends at 70 °C under environmental conditions for times between 0 and 600 h approximately. The experimental results indicate a structure of the granular metal type, in which conductive grains are randomly distributed in an insulating matrix and thermal degradation is due to the shrinking of them. As the zeolite content increases in the zeolite/PPy blends, the separation between the conductive grains decreases, the conductivity increases and the thermal stability of the blends improves. On the contrary, the behaviour of the zeolite/PANI samples is almost independent from the zeolite content. An explanation of this difference is proposed based on the crystalline character of the conductive grains in PANI in contrast to the amorphous grains of PPy.

Look into the Seeds of Time

![Figure][1] CREDIT: NASA Comets are failed harbingers of doom, but many of us will remember more fondly the peaceful visits of comets Hayakutake and Hale-Bopp to our skies in 1996 and 1997. These wanderers of our solar system spend most of their time in its cold outer reaches, only occasionally venturing near Earth's orbit. As they veer close to the Sun, ice and dust from their small nuclei are swept out by the radiation and solar wind into a fuzzy halo, or coma, and a long tail. Comets are thought to harbor relatively pristine detritus from the rubble disk out of which the planets grew. In just over a year, two space missions have given us a close look at the materials that make up different comets. First, Deep Impact fired a projectile into the nucleus of comet 9P/Tempel 1, ejecting a huge plume that was studied remotely (see Science , 14 October 2005). Now, as described in this issue, Stardust has retrieved direct samples of the coma of comet 81P/Wild 2. Comet Wild 2 originally hails from the Kuiper belt, beyond Neptune, but was recently perturbed into an orbit between Mars and Jupiter that is within the reach of spacecraft. After its launch in 1999, Stardust sneaked up on the comet in 2004, then returned its precious cargo to Earth in a capsule on 15 January 2006. Bringing back materials from a known extraterrestrial source, as with the Apollo samples from the Moon, is critical for deciphering the history of our solar system and interpreting our other extraterrestrial samples: meteorites and cosmic dust particles. Stardust's goal rested largely on two technical achievements. First the spacecraft had to be slowed so that it could engage with the comet. A clever trajectory enabled it to pass within 240 km of the nucleus at a speed of just 6 km/s, albeit six times faster than a bullet. To catch the comet particles, a special lightweight material called aerogel was developed and molded into a detector grid. Aerogel, the lightest solid known, is a foamed glass that has the density of air (see the cover). Particles were gently brought to a standstill as they tunneled through it without much heating or alteration, leaving carrot-shaped tracks. Thousands of tiny particles were trapped, most of them smaller than a micrometer in size. Analysis of the tiny samples by many international teams shows that many particles are mixtures of minerals, mostly silicates. The lack of amorphous grains is one surprise, because such materials are seen in interstellar space. Isotopically, the comet specks resemble rocks from the inner solar system; virtually no grains that pre-date the Sun were seen. A single grain contains minerals produced at high temperatures, in a region close to the Sun, and with isotope ratios similar to those of some meteorites. Thus, material has been mixed across the solar system, from the innermost portion to the outer regions of the Kuiper belt where this comet originated. Although this mixing makes it difficult to explain comet histories, it also means that the Stardust samples might tell us much more about how planets formed. The first rock samples brought back to Earth from anywhere beyond the Moon, the tiny Stardust grains may contain the building blocks of the entire solar system. [1]: pending:yes

ASpitzerStudy of Comets 2P/Encke, 67P/Churyumov‐Gerasimenko, and C/2001 HT50 (LINEAR‐NEAT)

We present infrared images and spectra of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger program to observe comets inside of 5 AU from the Sun with the Spitzer Space Telescope. The nucleus of comet 2P/Encke was observed at two vastly different phase angles (20° and 63°). Model fits to the spectral energy distributions of the nucleus suggest that comet Encke's infrared beaming parameter derived from the near-Earth asteroid thermal model may have a phase angle dependence. The observed emission from comet Encke's dust coma is best modeled using predominately amorphous carbon grains with a grain size distribution that peaks near 0.4 μm, and the silicate contribution by mass to the submicron dust coma is constrained to <31%. Comet 67P/Churyumov-Gerasimenko was observed with distinct coma emission in excess of a model nucleus at a heliocentric distance of 5.0 AU. The coma detection suggests that sublimation processes are still active or grains from recent activity remain near the nucleus. Comet C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the spectrum obtained at 3.2 AU, and we derive a silicate-to-carbon dust ratio of 0.6. The ratio is an order of magnitude lower than that derived for comets 9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).

Deep metastable eutectic condensation in Al-Fe-SiO-H2-O2 vapors: Implications for natural Fe-aluminosilicates

Vapors of Al-Fe-SiO-O2-H2 having two different compositions produced ferroaluminosilica grains as a function of agglomeration and fusion along mixing lines in the Al2O3-FeO-SiO2 system that are defined by the predictable, deep metastable eutectic (DME) compositions of the smallest condensate grains. Disorder of these amorphous grains is higher than in quenched glass of identical composition, which is the very property of dissipative structures (Prigogine 1978, 1979) that are states of organization of matter where disequilibrium becomes a source of order. Iron-oxidation states control ferrosilica condensate compositions. We present the first magnetic measurements showing a high Fe3+ content in condensed ferrosilica grains. The Fe-cordierite grain composition is primarily the result of predictable non-equilibrium condensation, not the bulk gas phase composition. Natural terrestrial and anthropogenic (e.g., smelters, coal fly ash) Fe-cordierite might well be a metastable phase due to kinetically controlled processes. Amorphous Mg,Fe-bearing aluminosilica dust in chondritic interplanetary dust aggregates and (rare) Mg,Fe-aluminosilicates in meteorites might have condensed via similar processes.

Preliminary investigations by Raman microscopy of prehistoric pigments in the wall‐painted cave at Roucadour, Quercy, France

AbstractRaman microscopy (RM) was applied to an ongoing study of prehistoric pigments employed in Palaeolithic wall paintings in the Roucadour Cave (France). Micro‐samplings were carried out on parts of red or black painted figures representing animals and also negative human hands.These first analyses showed that in all the red micro‐samples, the main pigment is haematite. Where the tone was dark red, well‐formed crystals of haematite were identified, but magnetite, Mn oxide and carbon grains were also found. An intermediate mineral phase structurally in‐between goethite and haematite was also identified. In red samples, the yellowish hydrated species goethite was also detected. A great quantity of white, greyish‐white and yellowish‐white crystals were present in the pigment, and many of them were identified as calcite or quartz.The black pigments were constituted of well‐formed crystals of Mn oxyhydroxide in some black micro‐samples. Suggestions are made for the identification of some mineral species (bixbyite, hollandite, nsutite) but there is still much uncertainty on this topic. In others, amorphous carbon grains were utilised as the main pigment. This distinction is important for orienting the research towards a subsequent investigation by radiocarbon dating.Traces of anatase were found in black pigments, as were traces of rutile and gypsum in red pigments. It is interesting that haematite occurs in all the black pigments, black because of the great content of C or of Mn oxyhydroxide, and that several red pigments contain minor carbon, such that each pigment is a mixture with at least five different species in most micro‐samples. These data are compatible with the possibility that the prehistoric artists used naturally‐occurring impure geological materials (e.g. (Fe,Mn)‐ochre rocks) and natural biological materials (e.g. wood or oil to make charcoal or soot), but it cannot exclude the fact that they may have treated the raw materials and/or manufactured mixtures of purer materials. Copyright © 2006 John Wiley &amp; Sons, Ltd.

SpitzerIRS Observations of FU Orionis Objects

We present 5-35 $\mu$m spectra, taken with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope, of five FU Orionis objects: FU Ori, V1515 Cyg, V1057 Cyg, BBW 76, and V346 Nor. All but V346 Nor reveal amorphous silicate grains in emission at 10 $\mu$m and 20 $\mu$m, and show water-vapor absorption bands at 5.8 and 6.8 $\mu$m and SiO or possibly methane absorption at 8 $\mu$m. These absorption features closely match these bands in model stellar photospheres -- signs of the gaseous photospheres of the inner regions of these objects' accretion disks. The continuum emission at 5-8 $\mu$m is also consistent with such disks, and, for FU Orionis and BBW 76, longer-wavelength emission may be fit by a model which includes moderate disk flaring. V1057 Cyg and V1515 Cyg have much more emission at longer wavelengths than the others, perhaps evidence of substantial remnant of their natal, infalling envelopes.

The 10 μm Infrared Band of Silicate Dust: A Laboratory Study Comparing the Aerosol and KBr Pellet Techniques

The profile of the silicate 10 μm IR band contains important information about the evolutional stage of dust in circumstellar environments and the possible ongoing process of planetesimal formation. In order to extract this information, the observed band profiles are compared with calculated or laboratory-measured absorption cross sections of amorphous and crystalline grains with different sizes and compositions. We present in this study the first laboratory measurements of the 10 μm band profiles of nonembedded, i.e., free-flying, particles of amorphous and crystalline Mg2SiO4 (with two different particle shapes), amorphous and crystalline MgSiO3, and crystalline olivine. We compare the spectra with those measured on embedded grains and discuss the potential of the new experimental method for comparison with observed spectra, as well as for future studies of agglomeration and surface manipulation of the grains.

Cavitation erosion characteristics of a Fe–Cr–Si–B–Mn coating fabricated by high velocity oxy-fuel (HVOF) thermal spray

A Fe–Cr–Si–B–Mn coating was prepared by high velocity oxy-fuel (HVOF) thermal spray on the surface of 1Cr18Ni9Ti stainless steel. Microstructures of the coating were investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning election microscopy (SEM), and the cavitation erosion resistance of the coating was evaluated using a GB6383-86 standard method in fresh water and compared with hydro-machine material ZG06Cr13Ni5Mo martensite stainless steel. The coating consisted of a Fe–Cr-rich matrix and several kinds of borides, the former comprised both amorphous phase and nanocrystalline grains. The nanocrystalline grains with a size about 10–50 nm further formed into an agglomerate-like structure with an average size of 100–500 nm. The coating had a significantly higher microhardness (HV 0.21008) than the comparing material ZG06Cr13Ni5Mo (HV 0.2260), which resulted in greater weight losses of ZG06Cr13Ni5Mo at the whole cavitation erosion process. It was found that the mass loss began at the edges of the pores or the interface between un-melted or half-melted particles and the matrix in the coating, while the mass loss was initiated at the lath interface of martensite in the ZG06Cr13Ni5Mo. The experimental results indicate that the HVOF thermal spray is a promising method to prepare the cavitation resistance coating.