Chemical Changes at the Interface Between Low Carbon Steel and an Al-Si Alloy During Solution Heat Treatment

The aim of this work was to characterize the chemical changes during solid state solution heat treatment of a metallurgically bonded steel/Al-Si interface. For this purpose, low carbon steel plates covered with the A-S7G03 aluminium alloy (7 wt.% Si, 0.3 wt.% Mg analogous to A356) were prepared by dip coating, water-quenching to room temperature and reheating in the solid state at 480-560 °C for 3-160 h. Upon reheating at 535 °C, a reaction layer was observed to grow at the interface between steel and the iron-saturated Al-Si alloy. As long as an intimate contact could be maintained, the total thickness, x, of the reaction layer increased with time, t, according to a nearly parabolic growth law x ² = K·t − b. At 535 °C, the value of the growth constant was K = 4.045 × 10⁻¹⁴ m² s⁻¹. This constant was found to be thermally activated [K = K ₀ exp(−Q/RT)] with K ₀ = 4.37 × 10⁻⁴ m² s⁻¹ and Q = 153 kJ mol⁻¹. The whole chemical interaction process was controlled by solid state volume diffusion and the reaction layer sequence corresponded to a diffusion path in the Al-Fe-Si phase diagram. A striking feature of the reaction process is the unbalanced diffusion of aluminium atoms through the reaction zone which rapidly results in the formation of Kirkendall voids. As these voids coalesce, solid state diffusion becomes more and more difficult and the steel/alloy bond gets weakened. Oxidation appears to be an aggravating factor, where applicable.     

Density of liquid gold measured by a non-contact technique

Electrostatic levitation together with multi-beam laser heating and ultraviolet imaging made possible to handle a sample of liquid gold, without any contamination, and to determine its density over a large temperature range. Over the 1337–1800 K interval, the density of Au was measured as ρ(T)=1.74× 10⁴−1.44 (T−T_m) kg·m⁻³, where Tm, the melting temperature, was 1337 K. These data yield a calculated volume expansion coefficient of 8.3×10⁻⁵ K⁻¹. The values agree well with the literature values.     

Effects of Sc doping on electrical conductivity of BaZrO<Subscript>3</Subscript> protonic conductors

BaZr1-xScxO3-0.5x (x=0.07,0.10,0.13,0.16) powders were prepared by solid-state reaction method,and ZnO was used as sintering aid.Samples with different amount of ZnO additive were sintered at 1450 ℃ for 6 h in air.Single cubic perovskite phase proton conductors were obtained.Conductivity was measured by electrochemical workstation.It was shown that Sc doping could increase conductivity through enhancing the carrier concentration in the material,but excessive Sc content might decrease the carrier concentration because of its charge compensation.ZnO had an influence on carrier concentration and mobility and affected the electrical conductivity.2 mol％ ZnO and 13 mol％ ScO1.5 doped sample showed the highest DC conductivity of 3.6 × 10-3 S·cm-1 tested at 800 ℃ in wet hydrogen atmosphere.     

Effect of plasma oxidation time and annealing condition on the temperature dependence of tunneling magnetoresistance

We have investigated the temperature dependence of tunneling magnetoresistance, (TMR) on plasma oxidation time und annealing temperature. Magnetic tunnel junctions comprising Si/SiO₂/Ta/CoFe/TrMn/CoFe5/All.6 (oxidized)/CoFe5/Ta (in nm) were sputter-deposited. Thin tunnel barriers were formed by oxidizing Al layers under oxygen plasma for 30–70 sec. When needed, post-deposition annealing was carried out at 450–500 K for 20 min under 500 Oe of external magnetic field. The temperature dependence of such samples was measured between 10 K and 300 K using a cryogenic MR tester. The spin polarization behavior was represented asP(T)-P ₀(1-αT ^1.5), whereP ₀ and α are spin polarization value and spin wave parameter, respectively. Ti uppared that there was an optimum oxidation condition that resulted in the highestP ₀ (40.3%) and the lowest α((10±4.742)×10⁻⁶ K^1.5). At this condition, the tunnel barrier is thought to possess the least amount of residual A1 or magnetic dead layers at the barrier/ferromagnet interface. The sample that underwent 450 K annealing resulted in a slight enhancement in spin polarization.     

Oxidation Behavior of TiAl<Subscript>3</Subscript>/Al Composite Coating on Orthorhombic-Ti<Subscript>2</Subscript>AlNb Based Alloy at Different Temperatures

This paper reports the oxidation behavior of TiAl₃/Al composite coating deposited by cold spray. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The oxidation kinetics of the coating was tested at 650, 800, and 950 °C, respectively. The parabolic rate constant for the coating oxidized at 650 °C was k _p = 7.2 × 10⁻² mg·cm⁻²·h^−1/2 for the tested 1200 h. For the coating oxidized at 800 °C, the oxidation kinetics could be separated into two stages with k _p value of 39.8 × 10⁻² mg·cm⁻²·h^−1/2 for the initial 910 h and 17.7 × 10⁻² mg·cm⁻²·h^−1/2 for the stage thereafter. For the coating oxidized at 950 °C, the oxidation kinetics can be separated into three stages with k _p of 136.9 × 10⁻² mg·cm⁻²·h^−1/2 in the first 100 h, followed by 26.9 × 10⁻² mg·cm⁻²·h^−1/2 from 100 to 310 h, and 11.8 × 10⁻² mg·cm⁻²·h^−1/2 from 310 to 1098 h. XRD, SEM, and EPMA were used to study the microstructure of the coating. The results indicated that the oxidation took place throughout the entire coating instead of only at the surface. The aluminum phase in the composite coating was soon oxidized to Al₂O₃ in all tested cases. The aluminum in TiAl₃ phase was depleted gradually and oxidized to Al₂O₃ along with the degradation of TiAl₃ to TiAl₂ and TiAl as the temperature increased and time proceeded. AlTi₂N was also a typical oxidation product at temperature higher than 800 °C. The experimental results also indicated that the protection of the coating was attributed greatly to the interlayer formed between the coating and the substrate.     

Investigation on Oxygen Chemical Diffusion Properties of Perovskite Oxides (La1?x Pr x )0.6Sr0.4Co0.8Fe0.2O3?δ

Perovskite oxide samples of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (x = 0.2, 0.4, 0.6, 0.8) are obtained by solid-state reaction method. The oxygen chemical diffusion properties of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ are determined by electrical conductivity relaxation technique. The results show that the conductivity of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ increases with the increase of oxygen partial pressure. The (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ samples have a high oxygen chemical diffusion coefficient, which decreases linearly with a decrease in temperature and an increase in Pr content. The oxygen chemical diffusion coefficient D _chem remains fairly constant at high PO₂. The oxygen chemical diffusion coefficient is the highest for (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ with x = 0.2, and attains a value of 9.41 × 10⁻⁵ cm² s⁻¹ at 600 °C. This shows the material’s promise as a cathode material for intermediate temperature solid oxide fuel cells.     

Orientation control of a lamellar microstructure in a Ti−Al intermetallic compound by high-temperature compression in an alpha single-phase and/or in a two-phase region and the alpha re-heat treatment

In order to control the spatial Ti−Al distribution of the α₂+γ γ lamellar microstructure in Ti−Al alloys, processes consisting of a high-temperature deformation in an alpha single-phase region, and an annealing and deformation in the α₂+γ ψ region were examined. The compression deformation temperatures and strain rates were from 1573 to 1623 K and from 1.0×10⁻⁴ to 5.0×10⁻³ s⁻¹, respectively. Dynamic recrystallization occurred during the compressive deformation in the alpha single-phase region. The uniaxial compression resulted in the formation of a fiber texture. It was found that more than half of the lamellar microstructure can be arranged within 30 degrees from the specimen surface by these processes. It was also shown that the orientation control of the lamellar microstructure in a polycrystalline Ti−Al intermetallic compound is effective in improving the creep resistance of this material.     

The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Alloys with composition Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe₂Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27 °C (300 K) to 1277 °C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe₂Al revealed that Fe atoms occupy the 8c site in space group Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe₂Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn₂-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn₂-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe₂Al is 1.4552 × 10⁻⁵ K⁻¹.     

Thermodynamic Calculation of HfB<Subscript>2</Subscript> Volatility Diagram

The thermodynamics of the oxidation of HfB₂ at temperatures of 1000, 1500, 2000, and 2500 K have been studied using volatility diagrams. Both the equilibrium oxygen partial pressure ( P_\textO2 P_{{{\text{O}}_{2} }} ) for the HfB₂(s) to HfO₂(s) plus B₂O₃(l) and the partial pressures of B-O vapor species formed due to B₂O₃(l) volatilization increase with increasing temperature. Vapor pressures of the predominant gaseous species also increase with P_\textO2 P_{{{\text{O}}_{2} }} . At 1000 K, the predominant vapor transition sequence is predicted be BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g) with increasing P_\textO2 P_{{{\text{O}}_{2} }} , and the predominant gas is BO₂(g) with a pressure of 1.27 × 10⁻⁶ Pa under the condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa. At higher temperatures of 1500, 2000, and 2500 K, the system undergoes vapor transitions in the same sequence of B(g) → BO(g) → B₂O₂(g) → B₂O₃(g) → BO₂(g). Under the same condition of P_\textO2 P_{{{\text{O}}_{2} }}  = 20 kPa, the predominant vapor species is B₂O₃(g) with pressures of 2.38, 4.49 × 10³, and 3.55 × 10⁵ Pa, respectively. Volatilization of B₂O₃(l) may produce porous HfO₂ scale, which is consistent with the experimental observations of HfB₂ oxidation in air. The present volatility diagram of HfB₂ shows that HfB₂ exhibits oxidation behavior similar to ZrB₂, and factors other than volatility of gaseous species affect the oxidation rate.     

Physicochemical study of the nanodiamond surface

Suspensions of five types of ultrafine diamond of a detonation synthesis in distilled water and 0.9 mol/l NaCl solution were found to have pHs in the range of 3–6, which results from the intrinsic acidity of their surfaces. The possibility of quantitatively determining the protogenic groups of a surface is found using the pH-potentiometric method. The data on the kinetics of the varying pH of suspensions in water and 0.9 mol/l NaCl solution and the data on the curves of the alkali titration of the suspensions of nanodiamond in the indicated systems make it possible to infer the presence of one or two types of acid groups on the surface of a diamond. The constants of dissociation (pK ₁) of these groups on the assumption of their single-base nature are estimated. From 1 × 10⁻³−5 × 10⁻² mol/l chloride solutions of H[AuCl₄] and RhCl₃ on the surface of diamond, gold(III) and rhodium(III) are found to be adsorbed; the adsorption of methylene blue from its 2.5 × 10⁻⁴−5 × 10⁻⁴ mol/l solutions reaches more than 90% (upon adsorption from 5 ml of the initial solution by a 0.05-g nanodiamond).     

Tie-lines and mixing properties of solid solutions in the system CaO-SrO-PbO-O at 1100 K

Phase relations in the system CaO-SrO-PbO-O₂ at 1100 K have been determined by equilibrating samples with different compositions in air, oxygen, or evacuated ampoules for 7 days and characterizing quenched specimens by optical and scanning electron microscopy, energy-dispersive analysis of x-rays (EDX), and x-ray diffraction (XRD). There is a solid-state miscibility gap in the pseudo-binary system CaO-SrO, and continuous solid solubility between Ca₂PbO₄ and Sr₂PbO₄ at 1100 K. Substitution of Ca for Sr occurs only to a limited extent (∼2 mol.%) in SrPbO₃. The calcium-rich solid solutions (Ca_1−y Sr _y )₂PbO₄ characterized by y≤0.255 are in equilibrium with PbO in air; compositions with y≥0.255 coexist with (Ca_1−z Sr _z )PbO₃. There is a three-phase region involving the two monoxide solid solutions (Ca_1−x Sr _x )O on either side of the miscibility gap with x=0.24 and 0.71 and (Ca_1−y Sr _y )₂PbO₄ with y=0.96. Accurately determined are the locations of tie-lines between the solid solutions. Attainment of equilibrium was checked by the conventional tie-line rotation technique. The excess Gibbs energy of mixing of the solid solution with orthorhombic structure is obtained by an analysis of tie-line data; for the mixing of one mole of Ca and Sr represented by (Ca_1−y Sr _y )Pb_0.5O₂, ΔG ^E =y(1−y) [15,840−2950 y] J/mol. The thermodynamic properties suggest the onset of immiscibility in this solid solution below 884 (±5) K. The miscibility gap is asymmetric with a critical composition at y=0.43 (±0.02). Inside the triangle (Ca_1−y Sr _y )Pb_0.5O₂−(Ca_1−z Sr _z )PbO₃−PbO, a small liquid-phase region is present close to the PbO corner, surrounded by three two-phase fields. Each corner of the approximately triangular liquid-phase region is associated with a three-phase field.     

Tie-lines and mixing properties of solid solutions in the system CaO-SrO-PbO-O at 1100 K

Phase relations in the system CaO-SrO-PbO-O₂ at 1100 K have been determined by equilibrating samples with different compositions in air, oxygen, or evacuated ampoules for 7 days and characterizing quenched specimens by optical and scanning electron microscopy, energy-dispersive analysis of x-rays (EDX), and x-ray diffraction (XRD). There is a solid-state miscibility gap in the pseudo-binary system CaO-SrO, and continuous solid solubility between Ca₂PbO₄ and Sr₂PbO₄ at 1100 K. Substitution of Ca for Sr occurs only to a limited extent (∼2 mol.%) in SrPbO₃. The calcium-rich solid solutions (Ca_1−y Sr _y )₂PbO₄ characterized by y≤0.255 are in equilibrium with PbO in air; compositions with y≥0.255 coexist with (Ca_1−z Sr _z )PbO₃. There is a three-phase region involving the two monoxide solid solutions (Ca_1−x Sr _x )O on either side of the miscibility gap with x=0.24 and 0.71 and (Ca_1−y Sr _y )₂PbO₄ with y=0.96. Accurately determined are the locations of tie-lines between the solid solutions. Attainment of equilibrium was checked by the conventional tie-line rotation technique. The excess Gibbs energy of mixing of the solid solution with orthorhombic structure is obtained by an analysis of tie-line data; for the mixing of one mole of Ca and Sr represented by (Ca_1−y Sr _y )Pb_0.5O₂, ΔG ^E =y(1−y) [15,840−2950 y] J/mol. The thermodynamic properties suggest the onset of immiscibility in this solid solution below 884 (±5) K. The miscibility gap is asymmetric with a critical composition at y=0.43 (±0.02). Inside the triangle (Ca_1−y Sr _y )Pb_0.5O₂−(Ca_1−z Sr _z )PbO₃−PbO, a small liquid-phase region is present close to the PbO corner, surrounded by three two-phase fields. Each corner of the approximately triangular liquid-phase region is associated with a three-phase field.     

Thermal expansion of the W5Si3 and T2 phases of the W–Si–B system investigated by high-temperature X-ray diffraction

The coefficients of thermal expansion (CTE) of the W₅Si₃ and T₂ phases of the W–Si–B system were determined using high-temperature X-ray diffraction in the 298–1273 K temperature interval. Alloys with nominal compositions 62.5W37.5Si (at%) and 58W21Si21B (at%) were prepared from high-purity materials through arc melting followed by heat treatment at 2073 K for 12 h under argon atmosphere. The highly different thermal expansion coefficients of W₅Si₃ along the a (5.0 × 10⁻⁶ K⁻¹) and c (16.3 × 10⁻⁶ K⁻¹) axes lead to a high thermal expansion anisotropy (α_c/α_a ≅ 3.3). On the other hand, the T₂-phase exhibits similar thermal expansion coefficients along the a (6.9 × 10⁻⁶ K⁻¹) and c (7.6 × 10⁻⁶ K⁻¹) axes, indicating a behavior close to isotropic (α_c/α_a ≅ 1.1).     

Thermal expansion of the V5Si3 and T2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V₅Si₃ and T₂-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V_62.5Si_37.5 (V₅Si₃ phase) and V₆₃Si₁₂B₂₅ (T₂-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V₅Si₃ phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10^?6 K^?1 and 11.7 × 10^?6 K^?1, respectively. Similarly, the thermal expansion anisotropy value of the T₂-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10^?6 K^?1 and 8.3 × 10^?6 K^?1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti₅Si₃ phase, the V₅Si₃ phase presents lower thermal expansion anisotropy. The T₂-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T₂-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.     

Electron Temperature and Density of the Plasma Measured by Optical Emission Spectroscopy in VLPPS Conditions

Measurements of electron temperature and electron density have been carried out on a plasma plume under very low pressure conditions (P = 1 mbar) using optical emission spectroscopy. The plasma torch was operated at a power level of 20-55 kW corresponding to an Ar/H₂ flow rate of 40/0 to 40/8 L/min and current intensity variation from 500 to 700 A. The electron temperature (T _e) was determined based on the calculation of the relative intensity of two spectral lines, H_α and H_β. It was found that T _e decreased from 0.2 to 0.9 eV with increasing detection distance from the nozzle exit from 40 to 60 cm. Changes in the current and the flow rate of H₂ also had a significant impact on it. There are significant fluctuations in the hydrogen emission intensity when using current intensity of 700 A or with increasing hydrogen fraction in the mixture. However, it seemed that there was no evident change in T _e when different powder sizes were injected. Correspondingly, electron densities ranged from 0.76 × 10¹⁴ to 1.41 × 10¹⁵ cm⁻³ and were obtained using Stark-effect broadening of the H_β (486 nm) line under the assumption of local thermodynamic equilibrium (LTE).     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

Reactive Diffusion in Ni-Si Bulk Diffusion Couples

Reactive diffusion in the Ni-Si system has been studied using bulk polycrystalline Ni/Si wafer diffusion couples in the temperature range from 450 to 700 °C and with annealing times of up to 32 h. For all diffusion couples, three phases were detected Ni₂Si, Ni₃Si₂, and NiSi. The thickness e of the reaction product is not homogeneous; its global growth kinetics satisfies the parabolic law and the total growth coefficient k ² (e ² = k ² t) is found to be expressed by: k ² = 2.5 × 10⁻⁴ exp (−160 kJ/RT), in m²/s. The Ni₂Si layer is homogeneous in thickness, and the value of its growth coefficient obtained by extrapolation at lower temperatures is more than two orders of magnitude smaller than the values obtained in thin-film experiments.     

Superplastic Behavior of Al-4.5Mg-0.46Mn-0.44Sc Alloy Sheet Produced by a Conventional Rolling Process

This article describes the superplastic behavior of the Al-4.5Mg-0.46Mn-0.44Sc alloy. The investigated alloy was produced by casting and was conventionally processed to form a sheet with a thickness of 1.9 mm and an average grain size of 11 μm. The superplastic properties of the alloy were investigated using a uniaxial tensile testing with a constant cross-head speed and with a constant strain rate in the range 1 × 10⁻⁴ to 5 × 10⁻² s⁻¹ at temperatures from 390 to 550 °C. The investigations included determinations of the true-stress, true-strain characteristics, the maximum elongations to failure, the strain-rate sensitivity index m, and the microstructure of the alloy. The m-values determined with the strain-rate jump test varied from 0.35 to 0.70 in the temperature interval from 390 to 550°C and strain rates up to 2 × 10⁻² s⁻¹. The m-values decreased with increased strain during pulling. The elongations to failure were in accordance with the m-values. They increased with the temperature and were over 1000%, up to 1 × 10⁻³ s⁻¹ at 480 °C and up to 1 × 10⁻² s⁻¹ at 550 °C. A maximum elongation of 1969% was achieved at an initial strain rate of 5 × 10⁻³ s⁻¹ and 550 °C. The results show that the addition of about 0.4 wt.% of Sc to the standard Al-Mg-Mn alloy, fabricated by a conventional manufacturing route, including hot and cold rolling with subsequent recrystallization annealing, results in good superplastic ductility.     

Synthesis and electrochemical characteristics of Fe-P alloy prepared by electrothermal reduction method

Microscale Fe-P alloy was prepared using Ca₃(PO₄)₂ and Fe₂O₃ in an electrothermal reduction process, and the electrochemical performance was investigated in detail. The initial discharge capacity could reach ∼566.8 mAh/g at 0.3 C rate, and the fade trend was so slight that the normalized capacities from 1.0 to 2.0 C rate were adjacent. The energy density and the power density could reach ∼1133.6 Wh/kg and ∼912.4 W/kg, respectively. The rate capability and the cycle performance were comparable to those of the Fe-P alloy synthesized using zerovalent iron and phosphorus. At 0.5 mV/s scan rate, the oxidation peak and the reduction peak for the reaction of lithium ions with P were positioned at ∼1.3 and ∼0.5 V, respectively. The reaction occurred under diffusion control, and the lithium ion diffusion efficient was ∼1.5×10⁻⁹ cm²/s.     

Effects of porous carbon on sintered Al-Si-Mg matrix composites

The influence of microporous particulate carbon char on the mechanical, thermal, and tribological properties of wear-resistant Al-13.5Si-2.5Mg alloy composites was studied. Large increases in surface area due to the formation of micropores in coconut shell chars were achieved by high-temperature activation under CO₂ gas flow. Activated char particles at 0.02 V _f were used to reinforce the alloy. The composites were fabricated via a double-compaction reaction sintering technique under vacuum at a compaction pressure of 250 MPa and sintering temperature of 600 °C. At more than 35% burn-off of the carbon chars at the temperature of activation, 915 °C, the total surface area remained virtually unaffected. The ultimate tensile strength and hardness decreased by 23% and 6 %, respectively; with increasing surface area of the reinforcement from 123 to 821 m²g⁻¹. The yield strength and the percentage of elongation decreased by a factor of 2 and 5, respectively. No significant change in sliding wear rate was observed but the coefficient of friction increased by 13 % (0.61 to 0.69). The coefficient of linear thermal expansion was reduced by 16 % (11.7 × 10⁻⁶ to 9.8 × 10⁻⁶ °C⁻¹), and remained unaffected at more than 35 % burn-off. Energy-dispersive spectrometry of the particles of the activated chars showed that oxides of potassium and copper coated the open surfaces. Failure at the matrix-char interface was observed, and this was attributed to localized presence of oxides at the interfaces as identified by electron probe microanalysis. Poor wetting of the oxides by magnesium at the sintering conditions resulted in formation of weak matrix-char interface bonds. J.U. Ejiofor, formerly of the Department of Metallurgical and Materials Engineering, The University of Alabama