Suppression method of industrial Al alloy powder explosion in dry and humid environment: A low-cost intrinsic safety technology

During the production and processing of Al alloy, a large number of small particle size powders will be produced. If the concentration of these Al alloy dust is too high under dry conditions, it will lead to dry powder explosion, and if hydrogen is produced in contact with water under wet conditions, it will lead to hydrogen explosion. This work is intended to develop a simple, cost effective technology that inerts waste Al alloy dust and minimizes its explosion hazards in different environments. Dihydrogen phosphates (KH₂PO₄, NH₄H₂PO₄, Ca(H₂PO₄)₂) are used to test the explosion flame propagation, explosion pressure, and hydrogen evolution, of waste Al alloy dust. The results show that dihydrogen phosphate can significantly reduce the flame propagation distance, speed, explosion pressure and hydrogen evolution performance of Al alloy dust, and inhibit the explosion of Al alloy dust in dry and humid environment to varying degrees. In different experiments, Ca(H₂PO₄)₂ has the best inerting effect, low cost and simple operation, which realizes the intrinsic safety of metal dust processing process. The phosphating film on the surface of Al alloy particles blocks the generation of Al(OH)₃ and retains the metal body to the greatest extent, which provides a possibility for the recycling of waste metal dust.     

Inhibition characteristics of coal dust explosion at the gasification atmosphere

The risk of coal dust explosion threatens the safety of coal gasification process. To reveal the inhibition of carrageenan dry-water material (CDM) on coal dust explosion, a 20 L spherical explosive device was adopted to compare with SiO₂ and NH₄H₂PO₄ at the atmosphere of coal gasification. The thermal decomposition behavior and chemical structures of the explosion residues were characterized by synchronous thermal analyzer, X-ray photoelectron spectroscopy and FTIR. The results indicate that the CDM showed the optimal inhibiting effect on 300 mesh and the maximum explosion pressure of anthracite coal dust was reduced to 0.02 MPa with the percentage of 97.53%. At the same concentration, the inhibiting effect of CDM on the coal dust explosion was better than that of SiO₂ and weaker than that of NH₄H₂PO₄. Through the residues analysis, the CDM mainly prevented the volatilization of C-H and consumption of oxygen-containing groups and sulfur-containing groups contributing to the inhibition of coal dust explosion.     

Study on mechanism and dynamics of inert powder explosion inhibitor inhibiting aluminum powder explosion

In order to study the suppression performance and action mechanism of inert powder on aluminum powder explosion flame, using the dust explosion flame propagation test system, five kinds of common inert powder and two kinds of aluminum dust with different particle sizes were selected for explosion flame suppression and overpressure suppression experiments. Combined with the thermal characteristic curve of inert powder, the inhibition performance and action mechanism of inert powder on aluminum powder explosion were systematically studied. The results show that the inhibition effect of MPP dry powder on aluminum dust is better than that of NaHCO₃, CaCO₃, Al(OH)₃ and NH₄H₂PO₄; The inhibition mechanism model of inert powder on aluminum powder explosion flame is established, and the action mechanism is analyzed. The oxidation process of aluminum dust with and without MPP dry powder was analyzed by Coats Redfern (C-R) method, and the activation energy and kinetic models of different stages were obtained. The results were verified by Flynn Wall Ozawa (FWO) and Kissinger Akahira Sunose (KAS) methods. The research results can provide a theoretical basis and basis for the explosion suppression design of aluminum dust and the development of explosion suppression powder.     

The effect of modification of KH2PO4 hardening liquid with H3PO4 and chitosan on setting reactions and compressive strength of calcium phosphate cement

The setting processes and mechanical properties of tetracalcium phosphate (TTCP) -monetite cements with H₃PO₄ and chitosan modified KH₂PO₄ hardening liquid have been studied. From XRD phase analysis, it was found that brushite was created in the first stage of the setting process by the interaction between phosphate compounds in hardening liquids and TTCP. Calcium deficient hydroxyapatite was the final product of the hardening process. The orthophosphoric acid addition to KH₂PO₄ hardening liquid caused lowering resistance to disintegration and an increase in the setting times of cements which allows the possibility for their control. Cement with pure KH₂PO₄ hardening liquid was resistant to wash-out immediately after mixing. Chitosan addition to KH₂PO₄ + H₃PO₄ hardening liquid of an amount around 1 wt.% did not affect change of setting time or improvement of disintegration behaviour of cement. Compressive strengths were around 80–100 MPa in cements soaked in SBF without an chitosan addition and chitosan caused an approximately 15% decrease in compressive strength. The compressive strength of calcium phosphate cements is more influenced by the hydroxyapatite particle morphology than their crystallinity.     

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.     

Transport properties and modification of potassium dihydrogen orthophosphate

We have studied the thermal behavior, proton conductivity, and structural properties of composite proton electrolytes based on KH₂PO₄, the mixed salt K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03, and silicon dioxide with a pore size of 70 Å in a wide composition range. The results demonstrate that the proton conductivity of the (1–x)KH₂PO_4–xSiO₂ (x = 0.1–0.5) composite systems increases by more than two orders of magnitude, reaching 3 × 10^–3 S/cm at a temperature of 225°C. The increase in conductivity is due to the formation of a disordered amorphous state of the salts as a result of partial KH₂PO₄ dehydration and the formation of K₄H₆(PO₄)₂P₂O₇ as an intermediate product. In the composites based on the highly conductive, disordered K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03 mixed salt, close in composition to KH₂PO₄, heterogeneous doping causes no increase in conductivity, and the conductivity decreases with increasing doping level, which is caused by dispersion of the salt and the dehydration process, leading to the formation of K₄H₆(PO₄)₂P₂O₇ and KPO₃.     

Synthesis of biopolymeric particles loaded with phosphorus and potassium: characterisation and release tests

The authors synthesised nanoparticles (NPs) loaded with P and K from KH₂ PO₄ using gelatin type‐A and type‐B, and sodium alginate as carriers. Using type‐A and type‐B gelatin, quasi‐spherical particles were obtained, with average sizes of 682 and 856 nm, respectively; with sodium alginate, the resulting NPs exhibited spherical shapes and 600 nm particle average size. The authors found an interaction between KH₂ PO₄ and alginate via the hydrogen bonds existent among the carboxylic groups of the carbohydrate and the OH‐groups of the H₂ PO₄ ‐; interactions among gelatin types with the OH‐groups and the H₂ PO₄ ‐ion were also observed. Adding trypsin to the distilled water solutions of the NPs coated with type‐A gelatin increased the concentration of P in the solution by threefold, while increasing that of K increased by 2.6‐fold. Conversely, adding α ‐amylase to the water solutions with sodium alginate increased the P and K concentrations in the solution by nearly 1.3‐ and 1.1‐fold, respectively. Thus, sodium alginate resulted in NPs with smaller sizes and better spherical formations, though with a high polydispersity index and lower release rate of P and K. This low release rate represents an advantage since plants demand nutrients for long periods, and conventional fertilisers display low use efficiency.Inspec keywords: nanofabrication, nanoparticles, hydrogen bonds, gelatin, biomedical materials, particle size, enzymes, molecular biophysics, biochemistry, nanobiotechnology, polymer films, potassium compoundsOther keywords: sodium alginate, biopolymeric particles, release tests, type‐B gelatin, spherical shapes, carboxylic groups, OH‐groups, distilled water solutions, type‐A gelatin, quasi‐spherical particles, particle average size, hydrogen bonds, trypsin, spherical formations, high polydispersity index, plants, α‐amylase, size 682.0 nm, size 856.0 nm, size 600.0 nm, H₂ PO₄ , KH₂ PO₄      

Industrial Application of a Deep Purification Technology for Flue Gas Involving Phase-Transition Agglomeration and Dehumidification

A moist plume forms when the flue gas emitted from wet desulfurization equipment exits into the ambient air, resulting in a waste of water resources and visual pollution. In addition, sulfur trioxide (SO₃), water with dissolved salts, and particles in the wet flue gas form secondary pollution in the surrounding atmosphere. In this study, a deep purification technology for flue gas involving phase-transition agglomeration and dehumidification (PAD) is proposed. This deep purification technology includes two technical routes: the integrated technology of phase-transition agglomeration and a wet electrostatic precipitator (PAW); and the integrated technology of phase-transition agglomeration and a mist eliminator (PAM). Industrial applications of PAW and PAM were carried out on 630 and 1000 MW coal-fired units, respectively. The results show that the average amount of recycled water obtained from wet flue gas by means of PAD is more than 4 g·(kg·°C)⁻¹. Decreasing the wet flue gas temperature by 1.5–5.3 °C allows 5%–20% of the moisture in the flue gas to be recycled; therefore, this process could effectively save water resources and significantly reduce water vapor emissions. In addition, the moist plume is effectively eliminated. With the use of this process, the ion concentration in droplets of flue gas is decreased by more than 65%, the SO₃ removal efficiency from flue gas is greater than 75%, and the removal efficiency of particulate matter is 92.53%.     

空间粉尘对航天器高温热管撞击效应的研究

本文利用爆炸式和电磁式加速器模拟研究空间粉尘粒子对高温热管的碰撞损伤效应.研究表明,微米级粉尘粒子难以击穿航天器高温热管管壁,但对热管表面的热控涂层光学性能变化有较大影响.亚毫米级粉尘粒子取决于速度的不同,高温热管由表面热控涂层光学性能下降一直到被击穿发生载热体的泄漏现象.针对高温热管在高速粉尘粒子撞击下的运行密封性和辐射功率等问题进行了试验研究及理论分析.测量结果表明,高温热管在工作温度T=900K时,被粉尘粒子击穿的速度由常温下的5.3 km/s降为4.8 km/s.     

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.     

Humidity sensors using KH2PO4-doped porous (Pb,La)(Zr,Ti)O3

Humidity sensing devices were prepared by using fine porous (Pb, La)(Zr, Ti)O₃ (PLZT) particles with ferroelectricity instead of insulating metal oxides such as alumina and zircon. The impedance of PLZT with 1 wt %. KH₂PO₄ was 10⁶ and lower than that of zircon with 3.8 wt % KH₂PO₄ by a factor of 10² in a dry atmosphere. In addition, the impedance in a humid atmosphere was controlled by the adding of potassium dihydrogen phosphate and changed by about four orders of magnitude in the humidity region 0 to 90% relative humidity at 1 kHz for samples burnt at 700° C. The humidity dependence of impedance is mainly governed by the change of coverage of adsorbed water. The hydrophilicity is affected by the burning temperature and lanthanum content of PLZT used as starting particle for porous PLZT ceramics burnt with KH₂PO₄. From complex impedance analysis it is confirmed that the resistive component inserted in parallel with the capacitive component decreases steeply with an increase in humidity, while the capacitive component is poorly dependent on the humidity.     

A pulsed optical absorption spectroscopy study of wide band-gap optical materials

The paper presents the results of a study on the formation and evolution of short-lived radiation-induced defects in wide band-gap optical materials with the mobile cations. The spectra and decay kinetics of transient optical absorption (TOA) of radiation defects in crystals of potassium and ammonium dihydro phosphates (KH₂PO₄ and NH₄H₂PO₄) were studied by means of the method of pulsed optical absorption spectroscopy with the nanosecond time resolution under excitation with an electron-beam (250 keV, 10 ns). A model of electron tunneling between the electron and hole centers under conditions of the thermally stimulated mobility of one of the recombination process partners was developed. The model describes all the features of the induced optical density relaxation kinetics observed in nonlinear optical crystals KH₂PO₄ and NH₄H₂PO₄ in a broad decay-time range of 10 ns–10 s after the pulse of radiation exposure. The paper discusses the origin of radiation defects that determine the TOA, as well as the dependence of the decay kinetics of the TOA on the temperature, excitation power and other experimental conditions.     

Dilatometric and dielectric studies on phase transition of potassium dihydrogen phosphate-boric acid binary system

Linear thermal expansion coefficient, dielectric data and transition temperature of KH₂PO₄-H₃BO₃ binary are reported. The transition temperature obtained from differential scanning calorimetry (DSC) is in concurrence with the dielectric and thermal expansion data. Further, this transition is classified as first order. Thermal expansion coefficients and enthalpy values of the binary are reported and compared with the data of pure KH₂PO₄.     

An investigation on the aluminum dustexplosion suppression efficiency and mechanism of a NaHCO3/DE composite powder

A NaHCO₃/diatomaceous earth (DE) composite powder suppressant with unique clustered structures is prepared by high-pressure impact method, using DE as the carrier and NaHCO₃ as the loaded chemical suppressant. The purpose is to obtain affordable, environmentally friendly, high-efficiency power explosion suppression materials. The suppression efficiencies of the NaHCO₃/DE composite powder suppressant on aluminum dust propagation and explosion pressure are tested. The results show that as the content of the NaHCO₃/DE composite powder suppressant increases, the maximum flame length gradually reduces and the suppression efficiency gradually increases. Addition of 60 wt% of the NaHCO₃/DE composite powder suppressant suppress aluminum dust flame propagation and addition of 100 wt% of the NaHCO₃/DE composite powder suppressant can fully suppress aluminum dust explosion. Comparison with pure NaHCO₃ and pure DE reveals that NaHCO₃/DE composite powder suppressant is more effective in suppressing aluminum dust flame propagation and aluminum dust explosion pressure than either of the two powders alone. The suppression mechanism of the NaHCO₃/DE composite powder suppressant is established: On the one hand, reaction is suppressed by the decomposition of NaHCO₃ and the product of this decomposition; on the other hand, as DE is rich in porous structures, when the loaded NaHCO₃ powder separates from DE, the porous structures will not only limit flame propagation, but will also well adsorb the substances generated from explosion reaction.     

Cryogenic Drilling of Ti–6Al–4V Alloy Under Liquid Nitrogen Cooling

This article is focused on experimental study of the effects of cryogenic liquid nitrogen (LN₂) coolant during drilling of Ti–6Al–4V alloy material with three different levels of cutting speed (V_c) and feed rate (f) at a constant depth. Cutting temperature (T), thrust force (F_z), torque (M_z), surface roughness (R_a), and hole quality are the output responses investigated by using cryogenic LN₂ coolant compared with a wet coolant. Tool wear and chip morphology were examined with the changes in cryogenic LN₂ coolant. It is found that cryogenic LN₂ coolant results in lowering cutting zone temperature which helps more removal of heat from the cutting zone. Lower thrust forces and surface roughness were observed due to less friction and better chip breaking in cryogenic LN₂ condition. Also better chipping results in improvement in hole quality, viz., circularity and cylindricity in cryogenic LN₂ condition. Less serration and uniform segmentation results in better chip morphology and no damage to the cutting inserts resulted in improved tool life in cryogenic LN₂ condition. The main application of cryogenic LN₂ coolant in the cutting zone provides better lubrication and is more effective than wet coolant. The effects of this investigation show that cryogenic LN₂ coolant is an alternative approach for a wet coolant in the drilling process.     

密闭空间煤粉爆炸特性的实验研究

为了探明煤粉在密闭空间中的爆炸特性参数,利用20 L球形爆炸装置进行实验测试,实验研究了不同点火能量对煤粉爆炸行为的影响,对比CaCO_3和Al(OH)_3两种惰性介质的抑爆效果及惰性介质的抑爆效力随点火能量的变化规律进行了重点探讨。结果表明:随着点火能量的增加,爆炸压力随着煤粉浓度的增加呈现先上升后下降的趋势,在同一浓度下,粉尘最大爆炸压力和最大升压速率呈线性上升,在高浓度下,粉尘爆炸压力受点火能量的影响更显著;添加CaCO_3和Al(OH)_3能够降低煤粉的爆炸压力,相对于CaCO_3的物理抑爆而言,Al(OH)_3的物理-化学抑爆效果更佳;惰性介质抑爆效力随点火能量增加而下降,建议采用5~10 k J点火能量考察惰性介质对煤粉爆炸的抑制效力。     

Growth and electro-optic studies in mixed (NH4) x K1−x H2PO4 single crystals

Single crystals and mixed crystals of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) were grown with different dopant concentrations of NH₄H₂PO₄ in KH₂PO₄ in solution by Holden’s rotary crystallizer technique. The effect of additives like Borax (Na₂B₄O₇·10H₂O), seed crystal rotation rate and qualities of the crystals were studied. The half-wave voltages (in longitudinal mode) for KDP mixed with 1% ADP (by weight) were found and hence the unclamped (low frequency) electro-optic coefficients (r ₆₃) were calculated for various wavelengths in the visible region of the spectrum. It was noted that the half-wave voltage increases with increase in wavelength and temperature.     

Preparation of Cu–Al–Ni shape memory alloy strips by spray deposition-hot rolling route

The present work describes the preparation of near-full density Cu–Al–Ni shape memory alloy (SMA) strips via a novel processing route consisting of ‘spray deposition’ of atomised liquid Cu–Al–Ni alloy with a jet of argon gas followed by hot-rolling densification of the deposited preform. The subsequent homogenisation of the hot rolled Cu–Al–Ni strips resulted in complete martensitic structure in the finished strip, consisting of self-accommodated plates of β₁′ and γ₁′ martensites. The characteristic transformation temperatures and shape memory effects of Cu–Al–Ni strips were studied. It has been demonstrated that the Cu–Al–Ni SMA strips, prepared in the present work, resulted in relatively finer grain size with better combination of strength and ductility compared to other techniques based on conventional casting method.     

Crystal structure studies of mixed system of NaH2PO4 and KH2PO4 with H3BO3

X-ray powder analysis of solid solution of NaH₂PO₄ and KH₂PO₄ with H₃BO₃ was carried out. Both the systems were observed to be tetragonal. The crystallographic data are reported.     

Conversion of the Echinoderm Mellita eduardobarrosoi Calcite Skeleton into Porous Hydroxyapatite by Treatment with Phosphated Boiling Solutions

The influence of the boiling solution technique (a nonhydrothermal wet treatment) in the formation of hydroxyapatite (HA) from a novel source, an echinoderm known as Mellita eduardobarrosoi, whose skeleton contains calcite as an inorganic constituent, was investigated. The experimental plan explores the conversion using a batch boiling system composed of KH₂PO₄ + KOH aqueous solutions at initial pH's of 8, 9, 10, 11, and 12, where granules of skeleton were dispersed to yield PO₄/CaCO₃ ratios of 1.0, 1.5, and 2.0. Chemical and X-ray diffraction analysis of the resulting material showed that the conversion of calcite by this technique is almost always higher than 70%, pH's 10 and 11 yielding the highest conversion. Depending on the operating conditions, the obtained material is a mixture of the original calcite and HA of varying stoichiometry and composition. Nevertheless, the interconnected porosity is preserved.