Hydrothermal Hot-pressing Research Articles

Hydrothermal Hot Isostatic Pressing (HHIP)-Experimental Proof of Concept.

A new hydrothermal hot isostatic pressing (HHIP) approach, involving hydrothermal water conditions and no usage of inert gas, was hypothesized and tested on 3D-printed Al-10%Si-0.3%Mg (%Wt) parts. The aluminum-based metal was practically inert at the applied HHIPing conditions of 300-350 MPa and 250-350 °C, which enabled the employment of a long (6-24 h) HHIP treatment with hardly any loss of material (the overall loss due to corrosion was mostly <0.5% w/w). Applying the new approach on the above-mentioned samples resulted in an 85.7% reduction in the AM micro-pores, along with a 90.8% reduction in the pores' surface area at a temperature of 350 °C, which is much lower than the 500-520 °C applied in common argon-based aluminum HIPing treatments, while practically maintaining the as-recieved microstructure. These results show that better mechanical properties can be expected when using the suggested treatment without affecting the material fatigue resistance due to grain growth. The proof of concept presented in this work can pave the way to applying the new HHIPing approach to other AM metal parts.

Processing of highly porous bioglass monoliths by hydrothermal hot pressing

Porous bioglass monoliths have been processed by hydrothermal hot pressing (HyHP) from sol-gel and melt-derived bioglass powders of composition (in mol %): SiO2–CaO–P2O5 (55.0-40.0-5.0) and SiO2–CaO–Na2O–P2O5 (47.2-26.4-23.8-2.6), respectively. An open porosity of >70% ever reached in 3D structures is reported for monoliths issued from sol-gel powders. Dissolution studies were performed in simulated body fluid (SBF) for 1–30 days. The monoliths were analysed using X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to observe the formation of an apatite-like layer and elemental concentration of SBF was evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). A higher kinetics in the development of apatite layer was observed for sol-gel derived monoliths. This result is explained by the high surface areas of the nanosized sol-gel powders and the possibility of HyHP to create large porosity (mesoporous monoliths) and retain large surface areas. HyHP is also effective in processing 3D-bioglass structures with porosity gradient by co-sintering powders of different size.

Enhanced sodium ion conduction of highly dense bulk zeolite X prepared by hydrothermal hot-pressing

Highly dense bulk zeolite X with translucency was successfully fabricated by hydrothermal hot-pressing of zeolite powder at 150 °C. Densification was achieved by addition of a small amount of distilled water or a 1 mol/L NaOH solution. Enhanced sodium ion conduction was observed for the densified bulk ceramic bodies. The ion conductivities obtained were beyond 0.001 S/cm, and are comparable to those of practical solid electrolytes applied in electrochemical devices such as batteries and chemical sensors.

Microstructural development of MnCO3 microsphere compacts through hydrothermal hot-pressing

Low-temperature sintering is a highly effective method for solidifying powders of thermally degradable materials, such as carbonates and hydroxides. Hydrothermal hot-pressing (HHP) is a low-temperature sintering method that uses a dissolution-precipitation reaction to water under hydrothermal conditions. Most sintering techniques, including HHP, were devised to fabricate high-density compacts; hence, varying the internal microstructure during solidification is challenging. The present study focuses on the microstructural development of MnCO3 microsphere compacts through HHP. Depending on the HHP process temperature, the formation of MnOOH fibers and Mn3O4 nanoparticles within the MnCO3 compacts or hollowing of the microspheres during the compaction was observed. The direct production of microstructure-controlled compacts by HHP will contribute to new structural designs and add functionalities to existing applications.

Hydrothermal Hot Pressing of CaCO3‐Chitosan Composites with High CaCO3 Content

In this study, a hydrothermal hot pressing (HHP) method was used for the preparation of molded composites with high CaCO3 content. Specifically, composites consisting of chemically synthesized CaCO3 and chitosan and scallop shells milled with a ball mill were molded by the HHP method; the structures, mechanical properties, and vibration absorption characteristics of the resulting disc‐shaped molded composites were investigated. All the composites had high CaCO3 contents (93%); flexural strengths (several megapascals) comparable to those of limestone and cement; and vibration absorption characteristics (logarithmic attenuation factors of 0.07–0.18) superior to those of aluminum alloys, stainless steel, and ceramics (which have logarithmic attenuation factors of &lt;0.01). The composites prepared from the CaCO3‐chitosan composites can be expected to find application as light‐control materials, as materials for controlling the propagation of light, sound, and vibration waves including vibration‐isolating materials and as CO2‐fixation materials.

Synthesis of HA/β-TCP combined artificial bone filling material by Hydrothermal Hot-Pressing and influence of α-TCP on the mechanical property

Synthesis of HA/β-TCP combined artificial bone filling material by Hydrothermal Hot-Pressing and influence of α-TCP on the mechanical property

Improvements of porosity and strength by hydrothermal hot press synthesis of TCP combined HA composite bone filling material

Improvements of porosity and strength by hydrothermal hot press synthesis of TCP combined HA composite bone filling material

CaCO3–Polymer Nanocomposite Prepared with Supercritical CO2

A novel process for generation of a CaCO3–polymer nanocomposite with a controlled three-dimensional shape was developed. Specifically, a nanocomposite with a high CaCO3 content was produced by introducing supercritical CO2 into a polymer matrix containing Ca ions. A mixture of poly(vinyl alcohol), Ca acetate, and poly(acrylic acid) was poured into a mold, the mold was placed in an autoclave, and CO2 was introduced to precipitate CaCO3 within the polymer matrix. Laser Raman spectroscopy and transmission electron microscopy showed that this process produced a nanocomposite containing highly dispersed CaCO3 (aragonite) nanoparticles. The flexural strength of the nanocomposite was larger than the flexural strengths of limestone and CaCO3 produced by hydrothermal hot pressing. The use of supercritical CO2 facilitated CO2 dissolution, which resulted in rapid precipitation of CaCO3 in the polymer matrix. The above-described process has potential utility for fixation of CO2.

Heavy metal fixing and heat resistance abilities of coal fly ash-waste glass based geopolymers by hydrothermal hot pressing

Hydrothermal hot pressing (HHP) was used to prepare high compressive strength fly ash-wasted glasses based geopolymers, which was subject to thermal analysis and the test of heat resistance as well as heavy metal solidification. Results showed that the geopolymers had good efficiency of encapsulating and fixing heavy metals. As for heavy metal element like Cu, Zn, Cd and Pb, the fixed efficiency reach at least 95%. Heat resistance test showed that the most mass-loss ratio of geopolymers was below 11.04% and the compressive strength was more than 55.27 MPa when it was calcined at 200–1000 °C for 2 h. During the calcining, geopolymers had gone through several main processes, including the evaporation of the free water, the bound water and constitutional water, the decomposition of carbonate, combustion of carbon, and crystallization reaction. XRD and FT-IR analysis showed that when calcined at 1000 °C, there produced several new crystallization phases with good heat resistance, including nepheline, kyanite, sillimanite. The improvement of this work does not only reflect that the hydrothermal hot pressing is featured by simple procedures, easy automation, timesaving and low cost, and also provide a long-term goal project, which could meet both demands: utilizing solid waste, saving resources and protecting the environment.

Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

Abstract Densification of calcium hydroxyapatite fine powders doped with different concentrations of Mg (2, 4 and 6 mol% Mg, MgHA) was successfully achieved for the first time in a nearly fully dense state using the hydrothermal hot pressing (HHP) technique at low temperatures. Consolidation of MgHA powders was studied under different temperatures (150–240 °C), reaction times (1–6 h), and powder particle size (20 nm–1.5 µm). X-Ray diffraction analyses indicated that the particle densification under HHP conditions proceeded without any variation in the crystalline structure and regardless of the Mg content. The results from this work showed that an increase in temperature accelerates the reaction between MgHA particles and water (solvent) mixed during the hydrothermal treatment. Particle packing associated with bulk densification was achieved through a massive dissolution-recrystallisation mechanism, which induced the formation of small particles that rapidly crystallised on the surface of the partially dissolved original MgHA particles. The optimum conditions to obtain pellets with a high apparent density of 3.0758 ± 0.001 g/cm3 and tensile strength value of 12.6 ± 0.6 MPa were 10 wt% of water at a temperature of 240 °C with a 6 h reaction time and 6 mol% of Mg (MgHA3). The use of the HHP technique coupled with the fine particle size and reactivity of the MgHA precursor powders with water allowed us to produce disks that were compacted to a nearly full dense state with a low content of open porosity of 2.0%.

Properties of binderless coal slime briquette via hydrothermal hot pressing dewatering

ABSTRACTDewatering and binderless briquetting of Liulin coal slime by hydrothermal hot pressing (HHP) method were studied under a wide range of process conditions. Fourier transform infrared spectroscopy and XRD were used for characterization. Results indicated that the optimal conditions were a pressure at 4.2 Mpa, a temperature of 150℃, and additive NaOH at 3.0%. The increase of temperature caused the loss of absorbed water in clay minerals and also some organic species having functional groups, such as -CH3 and -CH2. The alkalinity caused the loss of oxygen functional groups and the formation of hydroxysodalite, which reduced the water storage capacity and promoted coal particles agglomeration.

High-Strength Solidification of Fly Ash/Carbide Slag and Its Fixing Ability for Heavy Metals

Hydrothermal hot-pressing will occur between silica in fly ash and calcium in carbide slag and give rise to high-strength hydrates. High-strength solidified specimens were prepared with fly ash and carbide slag via hydrothermal hot-pressing at 200°C and 7 MPa. The effect of concentration of activator and content of carbide slag on compressive strength of the specimens was analyzed. It was found that when the mass ratio of fly ash to carbide slag was 1:1 and 20% 5 mol/L NaOH solution was added, the solidified specimens contained a large amount of cross-linked fibrous tobermorite with compressive strength of 70.93 MPa. The solidified specimens had a good fixation effect on such heavy metals as Cu, Zn, Cd and Pb. Hydrothermal hot-pressing, featured by simple procedures, easy automation and low cost, is an ideal potential way of utilizing fly ash and carbide slag and fixation of heavy metals.

Bioceramics and Biocomposites from Marine Sources

Advanced technologies and biocomplexity offer new dimensions for the development of novel medical products obtained from marine resources. Because several biomaterials can be derived from synthetic or natural sources, this area offers a very large variety of natural species that may be used for biomedical applications, including tissue engineering, drug delivery and surgery. The marine environment is a natural collector of porous materials the porosity of which varies from submicron to millimeter. The production of hydroxyapatite from synthetic chemicals can sometimes lead to a costly work and sea creatures may represent an alternative way to produce very fine and even nano-structured biomaterials. Rapana venosa is, in this sense, a study marine organism because its shell is made of aragonite that can be converted into bioceramic powder, which can subsequently be used for biomedical applications. The indirect use of marine organisms was tackled according to different routes: synthetic precursor casts using biomorphic moulds, chemical conversion of the inorganic marine matrix into a biomorphic substitute, and self-assembly of nanoparticles via chemical and molecular interactions. The chemical conversion is the most developed practice to obtain biomaterials for bone regeneration. It can be realized by hydrothermal synthesis or hydrothermal hot pressing. Both methods suppose a pre-treatment to remove the organic matrix of the skeleton. Hydrothermal synthesis involves heating the marine skeletons under alkaline conditions at a specific temperature pressure in either a reaction vessel or an autoclave. The temperature and pressure have an important significance concerning material structure properties of final product in terms of degree of crystallinity, grain size, and specific surface area. The temperature has an importance on the crystallite size (50-150 nm), and in general, the optimal temperature ranges between 200-250°C. Hydrothermal hot pressing is the process used in the fabrication of some commercial bone substitutes from coral sources and involves the solidification of synthetic hydroxyapatite powder. Some experimental results related to the processing of Rapana venosa snail shell in order to obtain hydroxyapatite for medical applications are presented at the end. In conclusion, preliminary results obtained by us show that this snail shell appears to be suitable to be used as raw material for obtaining hydroxyapatite.

Low temperature preparation of porous materials from TV panel glass compacted via hydrothermal hot pressing

The influence of aqueous solutions (deionized water or Na2CO3 solutions, 0.1–0.5M) and other processing parameters such as temperature (150–250°C) for preparing hydrothermal hot-pressed TV panel waste glass compacts was investigated to produce porous glass specimens. Waste powdered glass (5g) from old analog Philips television panels (Mexico) with particle sizes of <38µm was mixed with various amounts of the selected aqueous solution (5–20wt%). The TV glass panel particles dissolved in all of the mineralizer solution that were employed, and the behavior was controlled by the amount of aqueous solution added to the glass powder densification stage. The reactions of the glass particles with water or Na2CO3 solutions produced a solid glass phase that included water molecules or Na+ and CO3−2 ions, respectively. The hydrothermal hot press (HHP)-treated glass compacts prepared at 200°C for 2h at a constant loading pressure of 20MPa exhibited a marked expansion after heat treatment conducted at 700°C for 1h in an air atmosphere. The expansion of the HHP compacted TV panel glass specimens was further increased for the samples prepared with 0.5M Na2CO3 solution; these foamed glasses exhibited the lowest apparent densities that varied from 0.309 to 0.319g/cm3.

Synthesis and Characterization of Dense Mesoporous Alumina

Dense mesoporous alumina bulks were successfully synthesized by a hydrothermal hot-pressing (HHP) method for mesoporous alumina powders prepared as starting material with a high BET surface area and narrow pore size distribution. As a result, mesoporous alumina HHP bulks had high density with uniformity pore size distribution and a high specific surface area. Their microstructural features for dense mesoporous alumina bulks were observed by SEM. The characterization of mesopores was examined.

Synthesis of bulk lanthanum polyphosphate and other rare earth phosphates through hydrothermal hot-pressing

Bulk samples of lanthanum polyphosphate were synthesized through a hydrothermal hot-pressing (HHP) process. In this process, pressing temperature, pressure and volume of water were varied in order to improve the density and strength of the resulting materials. The strength of the bulk samples was estimated through drilling and ultrasonic treatments. In order to improve the strength of the materials, the use of microwave irradiation was examined. Lanthanum polyphosphate formed porous bulk samples with a filling factor of approximately 70%, which was calculated from real and theoretical densities. With respect to machinable strength, a drilled hole greater than 7.0 mm in diameter was obtained on some bulk samples, and the diameter of the samples was 14 mm. The HHP process is a useful method for obtaining bulk samples of lanthanum polyphosphate. Bulk lanthanum polyphosphate containing water crumbled easily to a powder form upon ultrasonication. However, these bulk samples retained their shape upon ultrasonication, despite containing water, after exposure to microwave irradiation, and also experienced minimal weight loss. Furthermore, to study the effect of microwave heating, bulk lanthanum orthophosphate, yttrium orthophosphate and polyphosphate were also examined.

Novel low temperature processing techniques for apatite ceramics and chitosan polymer composite bulk materials and its mechanical properties

A co-precipitation method was used for processing chitosan (CHI)/calcium hydrogen phosphate dehydrate (DCPD) hybrid material. CHI solution was mixed into 1.0-M calcium nitrate solution. CHI/DCPD hybrid material was prepared by the above explained addition of CHI and Ca ion source to 1.0-M diammonium hydrogen phosphate solution. It was observed by transmission electron microscopy that CHI and DCPD were mixed within submicron meter scale. CHI/HA bulk materials derived from the CHI/DCPD hybrid materials were obtained by using a hydrothermal hot-pressing (HHP) method. A pressure of 40MPa was initially applied to the sample. An HHP autoclave was heated up to 150°C for 2h. Modified 3-point bending tests were conducted to obtain an easy estimate of the fracture toughness for the CHI/HA bulk materials made with the HHP method. The critical stress intensity factor Kc of the fabricated CHI/HA bulk materials was enhanced from 0.30 to 0.40MPam1/2 by the hybridization of CHI into DCPD.

Zeolite Y deposition on aluminum substrate without structure directing agents (SDAs)

Zeolite Y was deposited on an aluminum substrate without using structure directing agents (SDAs) (e. g. tetrapropyl-ammonium hydroxide: TPAOH). Zeolite Y powder that contained NaOH solution and an Al disk are pressed at 40 MPa uniaxially and heated up to 130 °C for 1 h through an autoclave for hydrothermal hot-pressing (HHP). Solidification of zeolite Y powder and deposition on Al substrate have been achieved simultaneously through the above shown treatment. The deposited zeolite Y has no secondary phase by pyrolytic decomposition and a dense structure. No other oxide layer generates at interface between the deposited zeolite Y and Al substrate. The interface has good adhesive property and high contact area. It is firstly demonstrated that the simple heat and pressing treatment is useful for zeolite Y deposition on Al substrate without using SDA.

Effects of SnO&lt;sub&gt;2&lt;/sub&gt; Doping on the Performance of ZnO Porous Thick Film Gas Sensors

By using a unique hydrothermal hot-press (HHP) technique, ZnO and ZnO/SnO2composite porous nanosolids (the content of SnO2is 0, 1, 5 and 10 wt.%, respectively) were prepared. Furthermore, four kinds of gas sensors were fabricated by using ZnO (the sensor denoted as ZS0) and ZnO/SnO2composite (denoted as ZS1, ZS5 and ZS10 respectively) porous nanosolids. The intrinsic resistance and gas sensing performance of sensors ZS0, ZS1, ZS5 and ZS10 to ethanol and acetone were tested. By comparing with that of ZS0, the sensors ZS1, ZS5 and ZS10 have obviously lower intrinsic resistance and working temperature, and their selectivity to ethanol was also improved. The reason for above results has been analyzed on the basis of micro-morphology observations.

Preparation of γ-Al2O3 porous nanosolid/fluorescein fluorescent nanocomposites by a simple method

Abstract γ-Al2O3 porous nanosolid has been successfully prepared by a hydrothermal hot-press method, using γ-Al2O3 nanoparticles as the raw material. Furthermore, an orange-red compound, C20H12O5, that exhibits intense fluorescence in alkaline solution, fluorescein was assembled into the pores of γ-Al2O3 porous nanosolids by a simple method, thus a γ-Al2O3/fluorescein nanocomposite was obtained. Because of the interaction between fluorescein molecules and the surface atoms of pores of γ-Al2O3 porous nanosolid, a photoluminescent enhancement was observed in γ-Al2O3/fluorescein nanocomposite by comparing with that of fluorescein. In addition, the effect of the fluorescein concentrations on the photoluminescence of the nanocomposites was also investigated.