The effect of particle size on the maximum permissible oxygen concentration to prevent dust explosions

The oxygen concentration in the gas phase at the boundary between an explosion and no explosion in a dust cloud, y_o^b, has been investigated for several particle sizes and for mixtures of coarse and fine dusts of the same material. The maximum permissible oxygen concentration, y_o^m, at which no explosion is obtained has also been determined. Measurements for several type of materials were made in the modified version of the standard small vertical tube apparatus. Nitrogen was used as the inert gas and a train of sparks as the source of ignition. The results obtained indicated that the oxygen concentration is dependent on the particle size, that is, values of y_o^m decrease with a decrease in the size of the particles. Below 100 μm, values of y_o^m become almost constant. Admixture of fine dust as low as 5% to coarse dusts is sufficient to reduce the y_o^m values severely.     

Re-explosion hazard potential of solid residues and gaseous products of coal dust explosion

In the present work, solid residues and gaseous products after the initial explosion of coal dust were collected by self-made devices, respectively, and their explosiveness was further studied to assess the re-explosion hazard. The results show that the solid residue can explode again, and its explosion pressure (P_ex) and pressure rise rate ((dP/dt)_ex) both increase gradually as dust concentration and ignition energy increase, but decrease with the larger particle size. Solid residue is characterized by a lower deflagration index (K_st) than raw lignite dust, but it can produce greater severity than some raw high-rank coal dust in some cases. The gaseous products of coal dust explosion are mainly composed of CO, H₂ and CH₄, and some trace gases. The volume fraction of CO and H₂ in the gaseous products rises in proportion to the concentration of coal dust. For coal dust explosion with a concentration >200 g/m³, the gaseous products collected are flammable and have a wider explosion limit and a lower limited oxygen content. This research provides valuable information and reference for future prevention and control of secondary explosion disasters in coal mines.     

Research on law and mechanism of dust explosion in bag type dust collector

The bag type dust collector will accumulate dust during long-term operation, and the high temperature during operation will cause dust explosion. In this paper, with the dust removal system involved in the “8·2” Kunshan dust explosion accident taken as the research background, the minimum ignition temperature and lower explosion limit experiments are carried out on aluminum powder with different particle sizes (10–60 μm) by using the lowest ignition temperature test device and the 20 L near-spherical explosive device. The dust concentration distribution and temperature field in the bag type dust collector are analyzed through the CFD-FLUENT software. Through the analysis of the experimental results, it is found that when the particle size of aluminum powder is 19 μm, the minimum ignition temperature is 585 °C, and the lower explosion limit of concentration is 0.04 kg/m³. The simulation results indicate that the dust particles gather in the dust collecting bucket, and the aluminothermic reaction occurs in the dust collecting bucket. The temperature of the upper and right parts in the dust collecting bucket is above 600 °C, which exceeds the minimum ignition temperature. At the interface between the dust hopper and the dust collecting bucket, the concentration of aluminum powder reaches 0.126 kg/m³, which exceeds the lower explosion limit of aluminum powder.     

Investigation of lag on ignition of coal dust clouds under varied experimental conditions

Lag on ignition (LOI) of coal dust cloud greatly influences the initiation and propagation of coal dust explosion. This paper investigates the effects of coal dust particle size, dust concentration, ignition temperature, and dust dispersion pressure on LOI of coal dust clouds using Godbert-Greenwald furnace along with a high-speed camera. LOI of coal dust cloud significantly decreased by 1/13 times from 959 to 77 ms with increase in the ignition temperature from 600 to 1000 °C, demonstrating greatest influence of ignition temperature on LOI. LOI increased by 60% with increase in dust concentration from 500 to 4000 g/m³. Optimum dust dispersion pressure at which LOI was found minimum is determined 70 kPa. Empirical relations are established between LOI of coal dust cloud and particle size, ignition temperature, dust concentration, and dispersion pressure. The results are analysed in terms of the occurring physical processes, which led to a better understanding of the variation of LOI, ignition behavior, and explosion propagation of coal dust clouds at varied experimental conditions.     

Combustion synthesis of TiNi intermetallic compounds

The synthesis of the TiNi intermetallic compound using the thermal explosion mode of the combustion synthesis technique has been used to determine the heat of fusion, ΔH _m (7.77 kcal mol⁻¹), of the TiNi intermetallic and the heat capacity,C _p1 (17.96 cal mol⁻¹ K⁻¹), of the liquid-phase TiNi. The effect of heating rate and degree of dilution of the Ti + Ni powder compact reactants with previously synthesized TiNi on the ignition,T _ig, and combustion,T _c, temperatures in an argon atmosphere have been determined. It was found thatT _c was dependent on heating rate and dilution with TiNi, whereasT _ig remained unchanged with respect to these two process variables.     

The effect of strontium (Sr) on the ignition temperature of magnesium (Mg): a look at the pre-ignition stage of Mg–6 wt% Sr

The effect of strontium (Sr) addition on the ignition and oxidation behavior of magnesium has been investigated. Continuous heating experiments carried out in dry air-flow reveal that the ignition temperature (T _i) is raised from 640 °C (of pure Mg) to up to 854 °C at 6 wt% Sr addition. The oxidation behavior of Sr containing alloys was investigated during (i) isothermal oxidation experiments above the liquidus temperature (~640 °C) and (ii) during pre-ignition heating to 700 °C. The change in the ignition temperature of various alloy compositions is related to the amount of Sr that can be segregated to the surface and to the activity of the elements in the surface in the stages prior to ignition.     

Generation of thermal strains in carbon fibre-reinforced bismaleimide (PMR-15) composites: Part 1: The determination of residual thermal strains in cross-ply laminates

The level of residual thermal strain which develops in PMR-15 cross-ply laminates has been determined from the curvature of unbalanced 0°/90° beams. The hysteresis in the temperature dependence of the beam deflection has been attributed to the plasticizing effect of entrapped curing volatiles (mainly water and methanol). Vacuum drying has been shown to remove the hysteresis but increase the magnitude of the residual thermal strain. The latter appears to result from a complex interaction between the enhancement in matrix expansion coefficient, a reduction in transverse modulus and the strain-free temperature (T₁). Since T₁ is in the region of 300°C it has not proved possible to demonstrate its reduction directly. These values of thermal strain have been compared with predictions obtained from measured transverse and matrix expansion coefficients (α_t, α_m). The presence of residual volatiles also appears to be responsible for some variability in the temperature dependence of the matrix-dominated expansion coefficients. Post-curing at higher temperatures gives rise to better reproducibility in the values of α_m, α_t and ϵ_{t 1}^th. The role of these volatiles is discussed further in Parts 2 and 3.     

Partial inhibition of acrylonitrile–butadiene–styrene dust explosion by sodium bicarbonate

During acrylonitrile–butadiene–styrene (ABS) plastic processing, dust explosions could occur in production and transportation. In this paper, the explosion properties and pyrolysis mechanism of ABS dust were studied. The inhibition effects of sodium bicarbonate (NaHCO₃) on ABS dust were investigated using the 20-L explosion chamber, Hartmann tube, and G-G furnace. The results demonstrated that NaHCO₃ effectively decreased both the ignition sensitivity and the explosion severity of ABS dust explosion by increasing the mass fraction of the inhibitor. Adding 50 wt% NaHCO₃ could reduce the explosion hazard to an acceptable level. Combined with an analysis of gas phase products and thermal decomposition behaviour, it was discovered that incorporating NaHCO₃ enhanced the heat stability of ABS dust. The decomposition of added NaHCO₃ produced a substantial quantity of CO₂, consuming many free radicals especially OH• and H•, which further reduced the decomposition temperature of ABS. The inhibitor effectively interrupted the combustion chain reaction and inhibited the propagation of the explosion. The results establish a scientific and operational basis for the prevention and management of dust explosion hazards in the ABS processing field.     

Magnetoresistance and Irreversibility Fields of Bismuth-Based 1G Tape

The magnetoresistance and irreversibility fields of commercial bismuth-based 1G tape were studied on the basis of the temperature dependencies of the magnetoresistance at the two relative orientations of magnetic field and superconductor plane. The critical temperatures of this tape are the following: T _{c50 %} = 110.3 K and T _c0 = 109.9 K, and the width of superconducting transition is ΔT = 0.5 K. The widths of the transition to the superconducting state versus applied magnetic fields were derived for both orientations. The experimental data were fitted using the formula ΔT = C H ^m + ΔT ₀. The irreversibility field values were obtained and successfully fitted as a function of temperature. At 77 K, they were found to amount to H _{i r r} = 72.8 kOe and H _{i r r} = 5.5 kOe for the parallel and perpendicular directions, respectively.     

A study on the dust control effect of the dust extraction system in TBM construction tunnels based on CFD computer simulation technology

In order to control dust in a tunnel boring machine (TBM) construction tunnels, this paper, in combination with field measurements, applies CFD computer simulation technology to study the dust control effect of TBM construction tunnels under different dust extraction flow rates. Firstly, the dust extraction system is closed, and the result of the simulation show that the dust diffuses to the entire TBM working area within 181 s, indicating the necessity of having a dust extraction system in the tunnel. Secondly, the dust extraction system is open and under the original dust extraction flow rate of Q_e = 8 m³/s, the overall dust diffuses to the entire working area L_o = 130 m, and the full-face dust diffusion distance is L_f = 47.54 m. Then the study was carried out with the setting of 2 m³/s ≤ Q_e ≤ 14 m³/s. The results show that: when Q_e ≤ 8 m³/s, the full-face dust diffuses to 47.54–71.84 m; when Q_e > 8 m³/s, the full-face dust can be controlled at 42.81–46.34 m; and when Q_e = 8 m³/s, the full-face dust control effect is better, and the average dust concentration in the tunnel is as low as 12.25 mg/m³, indicating that the original dust extraction system has a better design. The field measurement results verify that the CFD computer simulation results are accurate.     

Extension of Lindemann’s Formula to Study the Pressure Dependence of Melting Temperature

Lindamann’s formula is extended to investigate the pressure dependence of the melting temperature, T _m(P). The important ingredient is the pressure dependence of the Debye temperature which has been determined from the measured data of acoustic longitudinal and transverse waves velocities. It is shown that Lindemann’s type relation can be utilized to obtain an empirical relation for T _m(P) in terms of the Grüneisen parameter and the bulk modulus. Computed values of T _m(P) for alumina, Heusler alloy, and gabbro (an igneous rock) are presented.     

Constant-Volume Gas Thermometry with Different Helium-3 Gas Densities at NMIJ/AIST

Constant-volume gas thermometer (CVGT) measurements are conducted using ³He of three different densities as the working gas to obtain the thermodynamic temperature T _CVGT and the second virial coefficient of ³He, B, at temperatures down to 3 K, using the triple point of Ne as a reference temperature. Densities of 127 mol ?? m^?3 and 278 mol ?? m^?3 are used in addition to the density of 168 mol ?? m^?3 used in the measurement reported previously, where T _CVGT was obtained using the virial coefficient adopted by the International Temperature Scale of 1990 (ITS-90), B _ITS-90. T _CVGT is obtained by two methods, by the single- and multi-isotherm fitting of B to the three densities and by the method used in the previous work using one of the three densities and B _ITS-90. B obtained from the isotherm fitting agrees with B _ITS-90 within the uncertainty of the data used to derive B _ITS-90. Moreover, B obtained from a multi-isotherm fit agrees with that of recent theoretical ab initio calculations within 0.05?cm³ ?? mol^?1 at 5 K and above, and within 0.3?cm³ ?? mol^?1 down to 3 K. The values of T _CVGT obtained from the multi-isotherm fits assuming different forms for the temperature dependence of B agree with each other within 0.1?mK. T _CVGT obtained from the multi-isotherm fitting agrees with that obtained from the method in the previous report within 0.22?mK. The tendency of the difference between T _CVGT and the ITS-90 temperature reported in the previous work is confirmed in the present work.     

Use of the linear heat flow for poor conductors and its application to the thermal conductivity of nylon

Thermal conductivity measurements have been carried out on Polypenco 101 and Comco brands of nylon 66 (polyhexamethylene adiapamide) rods along the direction of extrusion. The temperature range covered was 1.2 to 350 K, Below 20 K our date (estimated uncertainty ± 2%), together with all known published data, conforms to the expression λ = 0.00193T^1.30Wm^?1K^?1 to within 10%. Radiative effects above 100 K were demonstrated by performing measurements with and without batting; at 300 K there was a 50% difference between the two sets of data. It is concluded that other radiative effects are present besides direct losses of heat. An increase in the slope of the conductivity versus temperature curve was observed for both samples at the brittleness temperature (T_B = 188 K) and a value of λ_max = 0.371 Wm^?1K^?1 was obtained at the glass transition temperature $\text{T}{}_{\mathrm{g}}\text{? 330 K}$. Above 200 K, λ is nearly independent of temperature. A value of 0.365 W m^?1 K^?1 ±3% was found at 300 K, which is about 25% greater than values obtained previously by radial measurements. Anisotropy is a probable cause of this difference. Thermal conductivity integrals have been constructed from the data.     

Copper-based materials formed by high rate sputtering

This paper presents the results of microstructure and property determinations made on pure and alloyed copper sputter deposited at rates of 20–25 nm s^-1. For each material, the effects of substrate temperature and post-deposition annealing on the grain size and tensile properties were investigated. Fully dense coherent structures were obtained at all substrate temperatures. The absence of the porous poorly bonded structures obtained at temperatures in the range 0.1–0.2T_m by other workers is attributed to the low gas pressure, the normal incidence adatoms and the polished substrates used in the present study.All materials exhibited high tensile strenghts when deposited at 0.2T_m Values of 700 MPa were observed with pure copper, while precipitation-hardening and dispersion-hardening alloys produced values of 1000MPa. The principal difference between these materials was in the stability of their as-deposited structure and their strength during post-deposition annealing. For example, pure copper was unstable to recrystallization at room temperature (0.2T_m), while the dispersion- strengthened alloys exhibited only minor softening at 0.8T_m and very little grain growth at 0.95T_m. The mechanical properties are discussed in relation to the microstructure produced by high rate deposition.     

Tensile creep study of copper with alumina dispersions prepared by high rate physical vapour deposition

Mott has suggested that the ideal creep-resistant material will be one with a fine grain size in which the grain boundaries are filled with some substance, say a refractory oxide, to inhibit the motion of grain boundaries. Such a system, alumina-dispersed copper, was prepared by high rate physical vapour deposition. The process parameters and their effect on structure and texture have been studied. The room temperature mechanical properties have also been reported. This paper deals with a high temperature mechanical property, i.e. tensile creep. Tests were made on a constant-stress vacuum creep rig with a Ferrometic feedthrough to ensure a zero leakage rotary seal. A vacuum of 1.33 X 10^?3 Pa was maintained. The test temperatures were 500°C (0.57T_m) and 700°C (0.72T_m). The stresses applied were 2.07, 3.45, 4.14 and 6.89 X 10⁷ Nm^?2. Tests were made on as-deposited films and on cold-rolled condensates.Minimum creep rate curves showed the effect of the alumina content in raising the creep resistance of copper. Cold rolling also reduced the minimum creep rate markedly. Varying the temperature and stress affected the shape of these curves. Stress-rupture plots were used to summarize the data.Grain refinement together with a fine stable dispersion seem to give improved creep strength. The critical barrier of the Orowan stress was noted. The stress exponent for a low alumina deposit (0.21 vol.%) was about 8, and the apparent activation energy for creep was about 202 kJ mol^?1 (0.13 vol.%). There was an inverse relationship between the rupture life and the minimum creep rate, their product being constant (about 0.2).     

Equilibrium vacancy parameters and limit temperature of nonequilibrium melting in osmium

For osmium, based on experimental data on enthalpy and the averaged heat capacity obtained by the method of mixing within the temperature range of 1150?C2960 K, for the first time the parameters of the equilibrium vacancies for this metal have been determined: the vacancy formation energy E = 1.8 eV, the vacancy concentration at melting c = 3.3%, and the vacancy formation entropy S = 25.6 J/(mol K). The limit temperature of the onset of nonequilibrium melting of osmium T _m = 4256 K and its relative value T _lim/T _m = 1.30 has been calculated.     

Superconductivity and Ferromagnetism of the Ru-1232 Compounds in the (Ru1−x Nb x )Sr2(GdCe1.8Sr0.2)Cu2O z System

The Ru-1232 compounds have been synthesized in the (Ru_1?xNb _x )Sr₂(GdCe_1.8Sr_0.2)Cu₂O _z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T _c ^l and T _c ^h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T _c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T _m is about 90 K. This study also shows that both of the values of T _c and T _m become low with increasing x from 0.0 to 0.3.     

Effect of Al-ion substitution on structural and magnetic properties of Co–Ni ferrites nanoparticles prepared via citrate precursor method

Nanocrystalline Co_0.8Ni_0.2Al_yFe_2−yO₄ (y = 0.00, 0.15, 0.30, 0.45, 0.60, 0.75) powders have been synthesized by the citrate precursor auto-combustion method. The effect of the nonmagnetic aluminum ion substitution on the structural and magnetic properties has been studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy revealed that the obtained powders have a single phase of cubic spinel structure. The crystallite sizes estimated from XRD data have been confirmed using high-resolution transmission electron microscopy (HRTEM). Photographs showed powders consisting of nanosized grains with an average size ranging from 10 to 45 nm, depending on the Al content. Magnetic hysteresis loops were traced at room temperature using vibrating sample magnetometer (VSM). It was found that, due to the aluminum substitution, the values of magnetic losses and saturation and remanent magnetization were decreased, indicating a reduction in the ferrimagnetic behavior. This reduction of magnetization, compared to the undoped sample, was attributed to the increase of spin noncollinearity with increasing Al content. Samples with toroidal forms were used to measure both the initial permeability (μ_i) and Curie temperature (T_C). The obtained results showed a decrease in the values of both μ_i and T_C as the Al content increases. This behavior was explained in view of the weakness in the interaction of A and B sublattices with increasing Al³⁺ ion concentration.     

Solid-Liquid Interface Motion of 4He in an Acoustic Field

When acoustic waves were applied to the solid-liquid interface of ⁴He perpendicularly, from the solid side, the solid was megted at high temperatures and grown at low temperatures. This means that the direction of the force on the interface was inverted at an inversion temperature, T _i. We attributed this effect to the acoustic radiation pressure, which induced crystallization and megting [Phys. Rev. Lett. 90, 075301, (2003)]. Temperature dependence of the interface motion by acoustic waves was investigated in several surface orientations. Anisotropy of T _i was found and T _i was lower on a vicinal surface than on a rough surface.