Deposition Of Mg Research Articles

Ga-polar GaN Camel diode enabled by a low-cost Mg-diffusion process

In this letter, we show that low-cost physical vapor deposition of Mg followed by a thermal diffusion annealing process increases the effective barrier height at the metal/Ga-polar GaN Schottky interface. Thus, for the first time, GaN Camel diodes with improved barrier height and turn-on voltage were realized compared to regular GaN Schottky barrier diodes. Temperature-dependent current–voltage characteristics indicated a near-homogeneous and near-ideal behavior of the GaN Camel diode. The analysis performed in this work is thought to be promising for improving the performance of future GaN-based unipolar diodes.

Multifunctional poly(allylamine hydrochloride)/bioactive glass layer by layer surface coating on magnesium alloy for biomedical applications

The present study reports on a novel multilayer coating for biodegradable magnesium (Mg) alloy substrates. This coating contains soy protein hydrolysate (SPH), poly(allylamine hydrochloride) (PAH), and folic acid (FA) templated bioactive glass (BG) nano particles. The multilayer, designated as SPH/(PAH/BG)n, was coated onto an alkaline-treated Mg alloy surface (AMgS) through a dip-coating process with various numbers of cycles (n = 5and 7) using a layer-by-layer (LbL) assembly. The BG particles had an average diameter of 12.53 ± 2.22 nm and were embedded with therapeutic FA molecules. Scratch testing, wettability, and roughness tests showed excellent adherence of the SPH/(PAH/BG)7 coating on AMgS, making it suitable for cell attachment. Electrochemical measurements in Hanks balanced salt solution (HBSS) demonstrated that the SPH/(PAH/BG)7 coating improved the corrosion resistance of the Mg alloy. SPH/(PAH/BG)7 coated substrate showed a maximum protective efficacy of 98.4041 %, thanks to the bioactive nature of BG. High-resolution XPS and XRD analyses on SPH/(PAH/BG)7/AMgS confirmed the corrosion deposition of Mg(OH)2, MgHPO4.H2O, CaHPO4.H2O, SiO2, MgCO3 and CaCO3 on the substrate surface after immersion in HBSS for 10 d at 37 °C. The LbL coated Mg substrate also showed excellent cytocompatibility by hemolysis assay These results suggest that the SPH/(PAH/BG)7/AMgS material has multifunctional properties and can be a possible alternative for biomedical applications of Mg alloys.

Zein-Bioactive Glass nanocomposite Coating on Magnesium Alloy Substrate for Orthopedic Applications

Excellent mechanical strength and biodegradable characteristics of magnesium alloys have sparked considerable interest in orthopedic applications. The utilization of magnesium alloys in orthopedic applications has been restricted due to their brittleness caused by high corrosion rate in biological environments. One of the best techniques for increasing corrosion resistance of these alloys is surface coating. For the first time, the present work aims to dip-coat zein-bioactive glass (BG) nanocomposite on AZ31B magnesium alloy. The alloy surface was also coated by native zein as a control coating. BG nanoparticles required for zein and BG (zein_BG) composite were synthesized by a bio-inspired method using cetyltrimethylammonium bromide (CTAB) as a template. The formation of BG particles was affirmed by FTIR showing characteristic Si-O-Si and Si-O– peaks. Nano-size of BG particles with an average diameter of 6.67 ± 0.06 nm was reported by TEM. SEM micrographs revealed successful deposition of zein and zein_BG coatings on the magnesium alloy surfaces. High-resolution XPS analysis on zein_BG-coated Mg alloy immersed in HBSS revealed the corrosion deposition of Mg(OH)2, MgHPO4.H2O, CaHPO4.H2O, SiO2, MgCO3, and CaCO3 on the substrate surface. More than twofold wettability, 95% adhesion strength and 14-fold increase in surface roughness were reported for zein_BG-coated magnesium alloy compared to the bare surface. Measurements of weight loss in zein and zein_BG-coated alloy substrates in Hanks Balanced Salt Solution (HBSS) for 10 d at 37°C showed a drastic decrease in weight loss of substrates after coating. As a result, zein_BG-coated substrate was observed to possess the maximum protective efficacy (95.99%) against corrosion. Interestingly, electrochemical measurements revealed a vast decrease in corrosion current density (2.41 E−6 A.cm−2) of zein_BG-coated substrate compared to the uncoated substrate (3.04 E−4 A.cm−2). Electrochemical impedance spectra (EIS) confirmed capacitive behavior of zein_BG-coated alloy substrate. These findings demonstrated that simple zein_BG composite dip coating was a successful corrosion-resistant implant coating on magnesium alloy surface for orthopedic applications.

Thick p-type Mg2Si film on Si: Growth, structure and transport properties

A ∼ 0.8–0.9 µm thick Mg2Si film was grown by pulsed deposition of Mg on Si(111) at 340 °C in UHV. The X-Ray Diffraction (XRD) and cross-sectional High-resolution Transmission Electron Microscopy (x-HRTEM) data demonstrate the high crystal quality and nearly 100% texture of the film. Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) depth profiling show that the synthesized Mg2Si contains some oxygen. Hall measurements reveal the p-type conductivity of 130 S/cm and carrier concentration of 6 × 1018 cm−3 at room temperature (RT), the acceptor concentration of ∼ 1.4 × 1018 cm−3 at 190 K, hole activation energy Ea ≈ 26 meV, mobility μ∼5050 cm2/V∙s at 75 K and μ∼134 cm2/V∙s at RT. The p-type conductivity is related to either unintentional doping with oxygen or/and Mg vacancies occurred during the non-equilibrium process of silicide ultra-fast formation. The outstanding transport parameters of the film are explained by its high crystal quality and texture. The films with such thickness and transport properties are suitable for photovoltaic and thermoelectric applications.

Heterogeneously Catalyzed Selective Acceptorless Dehydrogenative Aromatization to Primary Anilines from Ammonia via Concerted Catalysis and Adsorption Control.

Although catalytic dehydrogenative aromatization from cyclohexanones and NH3 is an attractive synthetic method for primary anilines, using a hydrogen acceptor was indispensable to achieve satisfactory levels of selectivity in liquid-phase organic synthetic systems without photoirradiation. In this study, we developed a highly selective synthesis of primary anilines from cyclohexanones and NH3 via efficient acceptorless dehydrogenative aromatization heterogeneously catalyzed by an Mg(OH)2-supported Pd nanoparticle catalyst in which Mg(OH)2 species are also deposited on the Pd surface. The basic sites of the Mg(OH)2 support effectively accelerate the acceptorless dehydrogenative aromatization via concerted catalysis, suppressing the formation of secondary amine byproducts. In addition, the deposition of Mg(OH)2 species inhibits the adsorption of cyclohexanones on the Pd nanoparticles to suppress phenol formation, achieving the desired primary anilines with high selectivity.

Characterization of AZ31/HA Biodegradable Metal Matrix Composites Manufactured by Rapid Microwave Sintering

This study reports the development of magnesium alloy/hydroxyapatite-based biodegradable metal matrix composites (BMMCs) through rapid microwave sintering. Magnesium alloy (AZ31) and hydroxyapatite powder were used in four compositions 0, 10, 15 and 20% by weight. Developed BMMCs were characterized to evaluate physical, microstructural, mechanical and biodegradation characteristics. XRD results show Mg and HA as major phases and MgO as a minor phase. SEM results correlate with the XRD findings by identifying the presence of Mg, HA and MgO. The addition of HA powder particles reduced density and increased the microhardness of BMMCs. The compressive strength and Young's modulus increased with increasing HA up to 15 wt.%. AZ31-15HA exhibited the highest corrosion resistance and lowest relative weight loss in the immersion test for 24 h and weight gain after 72 and 168 h due to the deposition of Mg(OH)2 and Ca(OH)2 layers at the sample surface. XRD analysis of the AZ31-15HA sintered sample after an immersion test was carried out and these results revealed the presence of new phases Mg(OH)2 and Ca(OH)2 that could be the reason for enhancing the corrosion resistance. SEM elemental mapping result also confirmed the formation of Mg(OH)2 and Ca(OH)2 at the sample surface, which acted as protective layers and prevented the sample from further corrosion. It showed that the elements were uniformly distributed over the sample surface. In addition, these microwave-sintered BMMCs showed similar properties to the human cortical bone and help bone growth by depositing apatite layers at the surface of the sample. Furthermore, this apatite layer can enhance osteoblast formation due to the porous structure type, which was observed in the BMMCs. Therefore, it is indicative that developed BMMCs can be an artificial biodegradable composite for orthopedic applications.

Preliminary study for deposition of Mg<sub>2</sub>Si thin films with high-power impulse magnetron sputtering

We report the preliminary results of the deposition of Mg2Si thin films using high-power impulse magnetron sputtering (HiPIMS). HiPIMS operates using deposition equipment similar to DC magnetron sputtering but with repetitive electric current pulses to achieve higher current densities, generating ionized sputtered particles. The HiPIMS method was used to deposit Mg2Si thin films on unheated silicon and sapphire substrates using a Mg2Si sintered target, which were subjected to SEM-EDS characterization. The peak power density was evaluated to be 0.5 kW/cm2 or less, which was considered to exceed the DC sputtering regime. The film thickness was evaluated to be approximately 200 nm after 30 min of deposition. The composition ratio of Mg to Si on the film was approximately 2:1, which was close to that of the target. A crack-free surface morphology was achieved by applying a substrate bias voltage of 200 V.

Recycled Aluminium Alloys and their Models: Role and Behaviour of Alloying Elements during Alkaline Etching

Alkaline etching is a common pretreatment for aluminum surfaces. Etching behavior was compared between an alloy based on post-consumer scrap (PCS) and several model alloys of rolled AA3005 and extruded AA6060 with systematically varied amounts of Mn, Cu and Ni. Analysis of concentrations of alloy elements in the etching solution by inductively coupled plasma mass spectrometry (ICP-MS) shows that significant fractions of the investigated elements Cu, Fe, Mg, Mn, Ni, and Zn dissolve. Surface analysis of samples in different stages of the etching process show (i) an increase in oxide layer thickness with etching time, (ii) an enrichment of important alloy elements and impurities (Cr, Cu, Fe, Mg, Mn, Si) near the metal/oxide interface, and (iii) the deposition of Mg, Fe, Si-containing aluminum hydroxide on the surface. A comparison with open circuit potential measurements and time-resolved electrochemical polarization resistance measurements enables a detailed analysis of the etching mechanism. The aluminum dissolution rate during etching is limited by the transport of species through the oxide precursor layer, thus is potential-independent. Differences in etching rates between different alloy classes, evidenced by mass loss measurements, are related to differences in the cathodic or anodic reaction mechanisms (hydrogen evolution or metal dissolution) during etching.

Variously Prepared Zeolite Y as a Modifier of ANFO.

In the presented research, we investigated Ammonium Nitrate Fuel Oil (ANFO), with the addition of variously modified zeolite Y as an attractive explosive. Analysis of both blasting tests and thermodynamic models of blasting properties led to the conclusion that the addition of zeolite Y enhanced the detonation properties of such prepared ANFO via the growth of the detonation pressure, temperature, compression energy, and heat of the explosion. Generally, the modification of ANFO with variously prepared zeolite Y also reduced the volume of (COx + NOx) post-blast fumes. Furthermore, it was found that the ANFO’s velocity of detonation (VOD) could be controlled by the choice of the way of zeolite Y modification. Namely, for zeolite Y without Mg, as well as Mg-Y prepared via the impregnation method, the VOD rose. The opposite effect was observed when ANFO was modified with Mg-Y, obtained from the deposition of Mg over zeolite Y via the ultrasonic-assisted procedure.

A promising experimental paradigm and mechanism of Mg2Si UHV growth on a non-uniformly heated Si(111) sample

The processes involved in the Mg2Si film growth on the Si(111) surface at different temperatures in UHV were studied in a single experiment with a sample whose surface had the wedge-shaped temperature distribution within the range of 360–510 °C. The Mg2Si film was grown by a pulsed deposition of Mg at the rate of up to ∼104 nm/s. The Raman spectroscopy data show that Mg2Si formed only on the colder sample area, but for T > 484 °C it was not observed. The mean residence time of a Mg atom on Si(111) at 480 °C is estimated as ∼ 10−6 s. The paradigm of experiments with non-uniformly heated samples is briefly considered. While studying various temperature-dependent processes, the necessary number of experiments can be radically reduced by creating temperature distribution on the sample surface.

Ultrathin (In, Mg) films on Si(111): A nearly freestanding double-layer metal

We report on the formation of triple-atomic-layer metal films on Si(111) by deposition of Mg onto In double-layer films. The deposited Mg atoms are intercalated between the In layers and Si substrate and form a buffer layer with $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ periodicity on an unreconstructed Si(111) surface. Two metal layers with nearly hexagonal close-packed arrangement are stacked in an ABC sequence on the buffer layer. The (In, Mg) triple-layer phase shows free-electron-like electronic structure with circular Fermi surface. Unlike the single Fermi circle of the In double layers, the Fermi surface of the (In, Mg) triple layers is composed of two circles with different radii. The larger and smaller Fermi circles are found to come from bonding and antibonding states between the top and middle layers of the three layers. The bottom layer acts as a buffer layer to saturate the Si dangling bonds and realize a nearly freestanding double-layer metal.

Synchrotron X-ray Spectroscopic Investigations of In-Situ-Formed Alloy Anodes for Magnesium Batteries.

Magnesium batteries present high volumetric energy density and dendrite-free deposition of Mg, drawing wide attention in energy-storage devices. However, their further development remains stagnated due to relevant interfacial issues between the Mg anode and the electrolyte and sluggish solid-state diffusion kinetics of Mg2+ ions. Herein, an in situ conversion chemistry to construct a nanostructured Bi anode from bismuth selenide driven by Li+ is proposed. Through the combination of operando synchrotron X-ray diffraction, ex situ synchrotron X-ray absorption spectroscopy, and comprehensive electrochemical tests, it is demonstrated that the nanosize of the in-situ-formed Bi crystals contributes to the fast Mg2+ diffusion kinetics and highly efficient Mg-Bi alloingy/de-alloying. The resultant Bi anodes exhibit superior long-term cycling stability with over 600 cycles under a high current density of 1.0 A g-1 . This work provides a new approach to construct alloy anode and paves the way for exploring novel electrode materials for magnesium batteries.

Kinetics and mechanism of MgH2 hydrolysis in MgCl2 solutions

In the present work we systematically studied the hydrolysis of magnesium hydride in MgCl2 aqueous solutions, which was used as a process promotor. The initial hydrolysis rate, the pH of the reaction mixture, and the overall reaction yield are all found to be linearly dependent of the logarithm of MgCl2 concentration. The phase-structural and elemental compositions of the formed precipitates showed that they do not contain chlorine ions and solely consist of Mg(OH)2. The size of the Mg(OH)2 crystallites increased with increasing content of MgCl2 in the aqueous solution.The best agreement between the observed and modelled hydrolysis kinetics was achieved by applying a pseudo-homogeneous model that describes the process rate as increasing with H+ ions concentration. The deposition of Mg(OH)2 which is impermeable to water and blocks the surface of the remaining MgH2 however simultaneously and partially suspends this reaction. We therefore propose a mechanism of MgH2 hydrolysis in the presence of MgCl2 that is based on the comparison of the kinetic dependencies, variations of solutions pH and the structural and elemental analysis data for the solid deposits formed during the interaction. We furthermore define the kinetic model of the process, and the equation that describes the variation in pH of solutions containing chloride salts. Hydrolysis efficiency increased with increased relative MgCl2 amount; the best performance being achieved for the stoichiometric ratio MgH2+0.7MgCl2 (MgCl2/MgH2 weight ratio of 12.75/100). This provided a hydrogen yield of 1025 mL (H2)/g MgH2. Maximum hydrogen yield peaked at 89% of the theoretical H2 generation capacity, and was achieved within 150 min of hydrolysis start, 35% of hydrogen being released in the first 10 min after start, the hydrogen generation rate being as high as 800 mL min−1·g−1 MgH2.

Mg-modified CoMo/Al2O3 with enhanced catalytic activity for the hydrodesulfurization of 4, 6-dimethyldibenzothiophene

Hydrodesulfurization of 4, 6-dimethyldibenzothiophene is of great significance for emission reduction and environmental protection. Herein, the effects of Mg addition on CoMo/Al2O3 were systematically studied for the hydrodesulfurization of 4, 6-dimethyldibenzothiophene. The CoMo/Mg-Al2O3 was formed by incorporating Mg in the alumina lattice and showed excellent hydrodesulfurization performance compared to CoMo/Mg/Al2O3 formed after deposition of Mg on the alumina surface and to CoMo/Al2O3 without introducing Mg. Experimental characterization and theoretical calculations showed that the introduction of Mg is beneficial to the formation of β-CoMoO4, which significantly promoted the production of CoMoS active sites. Meanwhile, the introduction of Mg mainly improved the medium-strong surface basic sites.

Analysis of Mg(OH)2 Deposition for Magnesium Air Fuel Cell (MAFC) by Saline Water

Magnesium air fuel cell (MAFC) systems are eco-friendly fuel cells that use electrolytes of saltwater and oxygen from the air to produce power. However, MAFC cells face a critical problem, which is the deposition of side products on the surface of the Mg anode plate and the cathode electrode. Therefore, this study will focus on the analysis of factor on Mg(OH)2 deposition by identifying the optimal seawater, Mg alloy, and surface roughness and additives solution. Magnesium plates AZ31 are used as the anode, and air electrode as the cathode. This study also considers physical characteristics such as SEM, EDX and corrosion test while chemical characterization by performance test with difference electrolyte, anode, and roughness. Catechol-3,5-disulfonic acid disodium salt (tiron) as anti-deposition used to reduce the deposition of Mg(OH)2 on the anode and cathode surfaces and thus improve the performance of MAFC. From the performance study, the MAFC able to produce a power density of 27.54 mW/cm2 which is high compare to the MAFC without tiron. Therefore, with the active area by 110.25 cm2, the MAFC generates 2.93 W. The deposition of Mg(OH)2 reduces the active area of magnesium oxidation, thus, reduce the electricity generation. With the knowledge of optimal seawater concentration and improvement of a single fuel cell system, this study is expecting to assist the fisheries and aquaculture sector as well as the coastal communities in terms of providing a better, safer, and cheaper alternative source of electricity.

Synthesis of crystalline Mg2Si films by ultrafast deposition of Mg on Si(111) and Si(001) at high temperatures. Mg/Si intermixing and reaction mechanisms

Mg2Si films have been grown on Si(111) and Si(001) surfaces at ~ 387–477 °C by ultra-fast deposition in vacuum. The original pulse-type evaporator used allows Mg deposition rates of ~103–104 nm/s which provide effective accumulation of Mg on hot Si surfaces despite its fast re-evaporation. The silicide films at different stages of formation and growth have been obtained by varying the pulse duration, Mg deposit amounts and substrate temperatures. The local structure and crystal quality of the obtained Mg2Si films have been studied. The mechanism of the Mg2Si film formation and growth process is considered. The role of high temperatures in the formation of film texture is demonstrated. The existing to date experimental data on Mg–Si intermixing and Mg2Si formation are explained. Technologies of Si/Mg2Si solar cells can be based on these results.

Pseudocapacitive Ti-Doped Niobium Pentoxide Nanoflake Structure Design for a Fast Kinetics Anode toward a High-Performance Mg-Ion-Based Dual-Ion Battery.

Magnesium-ion batteries (MIBs) have received increasing attention for next-generation energy storage recently because of the natural abundance, high capacity, and dendrite-free deposition of Mg. However, their applications are hindered by irreversible Mg anode plating in conventional electrolytes and the lack of cathode materials, demonstrating high working voltage, satisfactory Mg2+ diffusivity, and long cycling life. In this work, we first developed a novel magnesium-ion based dual-ion battery (Mg-DIB) by utilizing expanded graphite as the cathode and Ti-doped niobium pentoxide nanoflakes (Ti-Nb2O5 NFs) as the anode. The Ti-Nb2O5 NFs showed hierarchical structures of microspheres with diameters of 4-5 μm assembled by nanoflakes. For the first time, the Mg-ion storage mechanism in Ti-Nb2O5 NFs was investigated. Benefiting from the hierarchical structure design and pseudocapacitive intercalation behavior of Mg ions, the Ti-Nb2O5 NF anode exhibited fast Mg-ion diffusion. Consequently, the Mg-DIB exhibited a high discharge capacity of 93 mA h g-1 at 1 C (1 C corresponding to 100 mA g-1), along with good long-term cycling performance with a capacity retention of 79% at 3 C after 500 cycles. The Mg-DIB also demonstrated a capacity retention of 77% at 5C, indicating its good rate performance. Moreover, the Mg-DIB exhibited a high discharge medium voltage of ∼1.83 V, thus enabling a high energy density of 174 W h kg-1 at 183 W kg-1 and 122 W h kg-1 at a high power density of 845 W kg-1, among the best of the reported magnesium-ion full batteries. Our work provides a new strategy to improve the performance of MIBs and other rechargeable batteries.

Electrostatic Shielding Guides Lateral Deposition for Stable Interphase toward Reversible Magnesium Metal Anodes.

Compared with lithium, magnesium shows a low propensity toward dendritic deposition due to its low surface self-diffusion barriers. However, due to the intrinsic surface roughness of the metal and the nonuniformity of the formed solid-electrolyte interphase, uneven deposition of Mg still happens, which brings about high local current density and continuous proliferation of the interphase, greatly exacerbating the passivation. Unfortunately, little attention has been paid to the deposition uniformity and the interfacial stability of Mg metal anodes, which result in a potential penalty. Herein, we modify the electrolyte with cathodically stable cations to guide smooth deposition via an electrostatic shielding strategy. The cations adsorbed on the initial protuberances effectively homogenize the charge flux by repulsing the incoming Mg2+ away from the tips. Importantly, we prove the lateral growth can benefit the interphase stability and electrochemical reversibility.

Top-Gate Amorphous Indium-Gallium-Zinc-OxideThin-Film Transistors With Magnesium Metallized Source/Drain Regions

Magnesium (Mg)-induced metallization of amorphous indium-gallium-zinc-oxide (a-IGZO) films is investigated to develop a self-aligned (SA) top-gate (SATG) a-IGZO thin-film transistor (TFT) technology. The high-conductive and SA a-IGZO source/drain (S/D) regions are well realized by a short time of sputtered deposition of Mg onto the a-IGZO film on a heated substrate, followed by the removal of the spare Mg on the surface in hot water. It is shown that the resistivity of the a-IGZO films is lowered to about $4 \times 10^{-{3}}\,\,\Omega $ cm from over $10^{{4}}~\Omega $ cm with a 36-s Mg deposition at $300~^{\circ }\text{C}$ . The metallization effect is believed to be the consequence of a large number of donor-like defects (oxygen vacancies) generated by oxidation–reduction reaction at the interface between the Mg and a-IGZO films. The SATG a-IGZO TFTs fabricated by the proposed technology show excellent electrical characteristics, such as a field-effect mobility of 19.5 cm $^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ , a subthreshold swing of 0.19 V/dec, an ON-/ OFF-current ratio of over $10^{{9}}$ , a low S/D series resistance of $2.1~\Omega $ cm, a small channel length shrinking of around $0.1~\mu \text{m}$ , and a high stability against electrical stresses.

Viscosity modification enhanced the migration and distribution of colloidal Mg(OH)2 in aquifers contaminated by heavy metals

Mg(OH)2 is extensively considered as an potential material for groundwater remediation because its injection could provide a long-term pH buffering system. In this study, colloidal Mg(OH)2 was regarded as an alternative reagent for the in-situ remediation of heavy metal polluted groundwater. However, experiments demonstrated that the transport performance of colloidal Mg(OH)2 in groundwater was depressed by the contamination of heavy metals and its stabilization performance for heavy metals was deteriorated. To solve these difficulties, the transport properties of colloidal Mg(OH)2 was enhanced by viscosity modification by adding xanthan gum (XG). Column tests were conducted to investigate the transport performance of colloidal Mg(OH)2 with and without viscosity modification, and to evaluate its stabilization effect for Pb and Cd polluted aquifer. Experimental results indicate that although the injection pressure increased during the migration of colloidal Mg(OH)2, the increased viscosity effectively could decrease the intensity of Brownian motion of Mg(OH)2 particles and reduce the collision efficiency between colloidal particles and aquifer media. Thus, deposition of Mg(OH)2 particles on aquifer media significantly reduced after viscosity modification, and its migration performance in groundwater was effectively enhanced. In contrast, the distribution of colloidal Mg(OH)2 was more uniform after viscosity modification, and immobilization of heavy metals in contaminated aquifer was noticeably improved, furthermore the exchangeable fraction of Pb and Cd is significantly reduced.