Two-step Pretreatment Process Research Articles

Integrated biorefinery of Mucor circinelloides biomass and sugarcane bagasse for application of high-value biopolymers

The replacement of expensive components in microbial growth media with pretreated lignocellulosic waste component to increase the product spectrum and add value to the bioproducts has been encouraged to achieve sustainable and feasible utilization of waste biomass as per the biorefinery approach. This study demonstrates an integrated biorefinery approach towards utilization of sugarcane bagasse and biomass of Mucor circinelloides ZSKP. A maximum reducing sugar recovery of 80.67 g/l was achieved after combining pretreatment with saccharification. A low temperature, glycerol, and ammonium phosphate pretreatment method was established, where glycerol pretreatment conditions were reduced from 250 to 150 °C and from 120 to 45 min. The ammonium phosphate-containing hydrolysate yielded 12.89 g/l of fungal biomass after fermentation to add to 20.8 g lignin from the delignification step. The biomass production was further improved to 17.69 g/l after supplementation with corn steep solids and mineral salts. The fermentation process also yielded 2.36 g/l chitosan and 4.9 g/l of lipids after extraction from the oleaginous fungus. The lignin infused glycerol plasticized chitosan biocomposite plastic had a 100% improvement in thermogravimetric properties with almost 50% more energy needed to increase the temperature of the material when compared to glycerol only plasticized biocomposite. The fungal chitosan showed antimicrobial properties and was effective as a preservative spray for fresh tomatoes and apples extending their shelf life to at least 14 and 18 days, respectively. This study therefore demonstrated that a novel two-step pretreatment process could be environmentally beneficial and yielded multiple products for biotechnological applications.

Two-step pretreatment for improving enzymatic hydrolysis of spent coffee grounds

Spent coffee ground has attracted increasing attentions since it contains many useful components such as polysaccharides, protein, lipid and bioactive compounds. The aim of this research is to enhance the enzymatic hydrolysis to release important sugars in spent coffee ground using different pretreatment methods. Spent coffee grounds were pretreated by alkali pretreatment, organosolv pretreatment and the combined process. The pretreated material was hydrolyzed by different commercial enzymes including Cellulast, Pectinex, Ultraflomax and Viscozyme. Monosaccharides, total phenolic content and antioxidant activity in the hydrolysate were measured and evaluated. The use of Viscozyme achieved the highest reducing sugar yield and showed the significant difference from other enzymes. Alkali and organosolv pretreatment demonstrated to improve the production of sugars. The alkali pretreatment followed by organosolv treatment effectively removed lignin, resulting in only 14% lignin in the pretreated sample. The maximum reducing sugar concentration reached 6120 mg/L through two-step pretreatment and subsequent enzymatic hydrolysis, corresponding to a yield of 161 mg sugar/g substrate. The spent coffee ground hydrolysate contained 2917 mg/L mannose, 1633 mg/L glucose and 957 mg/L galactose. Phenolic compounds were observed to be released during the enzymatic hydrolysis, giving a total phenolic content of 174.4 mg GAE/L and the SCG hydrolysate also showed an antioxidant capacity equivalent to 263.2 mg/L ascorbic acid after 120 h hydrolysis. This study demonstrated a scalable two-step pretreatment process to obtain important sugars including mannose, glucose, and galactose along with phenolic compounds for further industrial uses.

Exploring optimal strategies for aquatic macrophyte pre-treatment: Sustainable feedstock for biohydrogen production

Aquatic macrophytes; Water hyacinth (Eichhornia crassipes) and Azolla, biomass have certain advantages over terrestrial plant biomass to use as non-edible feed for 2nd generation bioenergy production. This is mainly due to the lower lignin content and higher productivity of aquatic macrophytes. These macrophytes do not require arable land. Present study explored on development of factorial approach based optimal pretreatment process for mild acid hydrolysis of Eichhornia crassipes and Azolla microphylla biomass for conversion to fermentable sugars. The simpler structure of aquatic plants translates to higher sugar recovery using milder pretreatment conditions compared to terrestrial plants. H2SO4 & HCl used in mild concentrations for acid hydrolysis experiments. Approximately, 20% of the dry biomass was recovered as fermentable sugar (mainly xylose) upon treatment with dilute sulphuric acid (0.5–1.5% v/v) or hydrochloric acid (2–4% v/v) at 100–120 °C for 30–60 min. Within this range of parameters, sugar yield followed a simple additive model, implying that a decrease in sugar yield is due to reduction of one parameter. This provides a choice between high temperature short time (HTST) and low temperature long time (LTLT) treatments. HTST requires sophisticated pressure vessels and correspondingly higher capital investment for the advantage of a higher throughput. LTLT treatments can be performed in cost economy manner using relatively simple equipment. For economic, environmental and technical reasons, acid addition should be kept to a minimum, which is possible by a choice of higher temperature and longer treatment time. Such pretreatment may be employed as the first step of a two-step pretreatment process prior to enzymatic saccharification of cellulosic fraction. The acid pre-treated hydrolysate of water hyacinth and Azolla microphylla explored for hydrogen production through dark fermentation process through employment of C5 & C6 sugar utilizing microbe Enterobacter cloacae DT-1 strain.

Valorization of food waste: Extraction of cellulose, lignin and their application in energy use and water treatment

The study focuses on the isolation of the two important macromolecules of plant, lignin, and cellulose microcrystals (CMC) from agro-waste (peanut shell) and evaluates their potential application in biofuel production and wastewater treatment. The extraction of CMC was a two-step pretreatment process carried out by utilizing Sodium hydroxide followed by bleaching with Sodium Hypochlorite. The result showed that about 0.39 g/g of cellulose (dry wt%) was extracted from peanut shell waste. Scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction were considered for the characterization of cellulose and lignin. Also, besides, the saccharification and fermentation process was optimized. The maximum yield of reducing sugar was 3.16 mg/ml at pH (7) utilizing cellulose (5gm). A significant difference in bioethanol yield was observed between Zymomonas mobilis and Saccharomyces cerevisiae producing (0.471 g/g) and (0.637 g/g) bioethanol respectively. The Kraft lignin (1.5 mg/ml) and cellulose left after bioethanol extraction (CLA) were further used for crystal violet dye removal. The maximum adsorption capacity shown by lignin was about 87.64% followed by cellulose with 69% removal, whereas for CLA the removal capacity was highest to 98.21%. The finding demonstrates the potential of extracted cellulose for bioethanol production, and the challenges of utilizing CLA and lignin in wastewater treatment.

Deposition of mirror-like surface finish ultrananocrystalline diamond films on tungsten carbide by optimizing the substrate pretreatment

In this study, we successfully fabricated ultrananocrystalline diamond (UNCD) films on tungsten carbide with mirror-like surface finish (Ra < 40 nm), strong adhesion, and exceptional tribological performance by adopting the optimized two-step pretreatment process. It was found that the ultrasonication in Murakami reagent will substantially increase the substrate surface roughness even with short duration, which is less controllable compared with that of immersion in Murakami reagent. Besides, the surface roughness is strongly affected by acid etching when the substrate is firstly ultrasonicated in Murakami reagent. However, it is much less influenced for the immersion pretreatment. With the UNCD film, a decrease in the surface roughness up to 72% can be realized compared with the as-pretreated substrate. The Rockwell indentation tests demonstrate that the adhesive strength of the UNCD film deposited with the optimized pretreatment is comparable to that of MCD and NCD films as reported in other studies. Ball-on-plate tribotests with Si3N4 counterpart balls reveal that the coefficient of friction (COF) of the UNCD film is 0.07–0.12, which is 76.6% and 41.6% lower compared with that of the MCD and NCD film. The wear rate of the UCND film is 0.708–1.844 × 10−7 mm3/(N·m), close to that of the MCD and NCD film. The results reported in study provide significant insights into the scientific and industrial research of diamond-coated WC-Co cutting tools.

Fractionation of corn stover by two-step pretreatment for production of ethanol, furfural, and lignin

The comprehensive utilization of lignocellulose is great importance for improving the economic feasibility of biomass refining industry. Here, we established a two-step pretreatment process for fractionation and production of multiple products (furfural, ethanol, and lignin) from corn stover (CS). In the first step, H2SO4 pretreatment was used to remove hemicellulose and the effect of solid/liquid ratio (SLR) was investigated. The hemicellulose containing washing liquor was treated for furfural production without any additional catalyst and the maximum furfural yield (46.5%) was obtained at 210 °C for 20 min. It was found that the physical barrier of lignin was its mainly inhibition mechanism that limited the enzymatic digestibility of H2SO4 pretreated solid. The following NaOH pretreatment removed 90.8% of lignin and resulted in excellent glucan enzymatic conversion (98.6%). A large amount of acid insoluble lignin (AIL, 17.0 g/100 g CS), p-coumaric acid (1416.9 mg/100 g CS) and ferulic acid (249.4 mg/100 g CS) were observed in NaOH pretreatment liquor. The two-step pretreated CS produced up to 115.3 g/L of ethanol during simultaneous saccharification and fermentation (SSF) at 25% (w/w) solid loading. These results demonstrated that the successive H2SO4 and NaOH pretreatment was an efficient method for fractionation and integrative utilization of CS.

Improving enzymatic hydrolysis efficiency of wheat straw through sequential autohydrolysis and alkaline post-extraction

In this work, a two-step pretreatment process of wheat straw was established by combining autohydrolysis pretreatment and alkaline post-extraction. The results showed that employing alkaline post-extraction to autohydrolyzed wheat straw could significantly improve its enzymatic hydrolysis efficiency from 36.0% to 83.7%. Alkaline post-extraction lead to the changes of the structure characteristics of autohydrolyzed wheat straw. Associations between enzymatic hydrolysis efficiency and structure characteristics were also studied. The results showed that the factors of structure characteristics such as delignification, xylan removal yield, crystallinity, accessibility and hydrophobicity are positively related to enzymatic hydrolysis efficiency within a certain range for alkaline post-extracted wheat straw. The results demonstrated that autohydrolysis coupled with alkaline post-extraction is an effective and promising method to gain fermentable sugars from biomass.

A Sequential Steam Explosion and Reactive Extrusion Pretreatment for Lignocellulosic Biomass Conversion within a Fermentation-Based Biorefinery Perspective

The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation of the collected lignin-rich liquid fraction yielded a solid residue with high lignin content, offering possibilities for subsequent applications. Moreover, hydrolysability tests showed almost complete saccharification of the pretreated solid residue, which when combined with the low concentration of the generated inhibitory compounds, is representative of a good pretreatment approach. Scheffersomyces stipitis was capable of fermenting all of the glucose and xylose from the non-diluted hemicellulose fraction, resulting in an ethanol concentration of 17.5 g/L with 0.34 g/g yields. Similarly, Saccharomyces cerevisiae produced about 4% (v/v) ethanol concentration with 0.40 g/g yields, during simultaneous saccharification and fermentation (SSF) of the two-step pretreated solid residue at 10% (w/w) consistency. These results increased the overall conversion yields from a one-step steam explosion pretreatment by 1.4-fold, showing the effectiveness of including an extrusion step to enhance overall biomass fractionation and carbohydrates conversion via microbial fermentation processes.

High sensitive detection of penicillin G residues in milk by surface-enhanced Raman scattering

The antibiotic residue in animal source foods (milk, meat, etc.) is threatening people's health due to its abusing in livestock breeding more and more seriously. In this study, a simple and sensitive SERS method coupled with a two-step pretreatment process of sample was proposed for the residue detection of penicillin G (PENG) in real milk sample. It can be found that the two-step pretreatment process of sample is an essential procedure for the successful detection of PENG residue in milk, which can effectively avoid interference from other components in the sample and achieve the trace-level detection of PENG residue by SERS. Under the optimal test conditions, the limit of detection of PENG residue is 2.54×10−9mol/L (equal to 0.85μg/kg), which is lower than the standard of the European Union (4μg/kg). And, there is a good linear relationship (R2=0.9902) in the concentration range of 1.0×10−8~1.0×10−3mol/L. By this method, the recovery of PENG residue ranges from 76% to 97% with relative standard deviation between 4.8% and 2.1%. The proposed SERS method can be effectively applied for determination of PENG residue in milk.

Fermentable sugars from Eucalyptus globulus: Process optimization

Abstract In the last years, bioethanol production from lignocellulosic materials is receiving more attention from researchers since it is an abundant raw material in certain regions, it is cheaper, does not compete with foods like sugarcane or corn, and can reduce up to 86% of carbon dioxide emissions when compared with gasoline. However, the process economy is linked to the pretreatment needed to make the cellulose accessible for further steps of enzymatic hydrolysis and fermentation. Then, the motivation of this work is to propose a MILP model to perform an optimal synthesis of the pretreatment for obtaining fermentable sugars from the Eucalyptus globulus specie. For this purpose, a General Disjunctive Program (GDP) is formulated. The obtained results suggest that there is a small difference between a two-step pretreatment process (pretreatment with posthydrolysis) and one-step pretreatment of diluted acid process.

Pretreatment of rice straw for ethanol production by a two-step process using dilute sulfuric acid and sulfomethylation reagent

Abstract Ethanol is now one of the most widely used transport bio-fuels and production of ethanol from rice straw (RS) is an effective RS utilization way. This work investigated a novel two-step RS pretreatment process with the goal of decreasing the ethanol production cost through complete utilization of its components. In the process, RS was first treated with dilute sulfuric acid to remove the hemicellulose and recover the xylose from its hydrolyzate as a feedstock for xylitol production, and then the residue was treated with the standard sulfomethylation reagent to remove the lignin and recover its hydrolyzate containing the lignosulfonate as a cement water reducer. Among tested conditions, the best acid treatment (AT) conditions were 100 °C, 1.0 wt% sulfuric acid, 10% (w/v) RS and 2 h, and the hydrolyzate recycled 5 times. After AT, the xylose was recovered from its hydrolyzate with 83.2% yield. The best sulfomethylation treatment (ST) conditions were 160 °C, 15% (w/v) acid treated RS, and 5 h using the standard sulfomethylation reagent. After ST, its hydrolyzate containing 5.0% lignosulfonate was directly recovered as a cement water reducer. Under the above best two-step treatment conditions, 94% hemicellulose and 92% lignin in the origin RS were removed, but cellulose had almost no loss. After the simultaneous saccharification and fermentation of the two-step treated RS (100 g L − 1 ) for 72 h, the ethanol concentration and its yield reached 40.6 g L − 1 and 86.4% respectively. It suggests the two-step pretreatment process was an efficient RS pretreatment method for its ethanol production. This process can be an example of RS bio-refinery for bio-fuel production.

Al Dur SWRO plant: a double challenge for pre- and post-treatments

The Al Dur Power & Water Company is a 2.1 billion USD gas-fired greenfield power generation and seawater reverse osmosis desalination plant that is located on the southeast coast of Bahrain. The company Degrémont has been selected to design and build the Reverse Osmosis (RO) desalination plant, for a drinking water production capacity of 218,000 m3/day. The plant design had to answer to particularly challenging requirements, both for the pre-treatment and for the post-treatment steps. The pre-treatment step is one of the key factors for the success of desalination using the reverse osmosis process. Its purpose is to remove the major foulants, which can be found in the seawater to allow for a reliable operation of the reverse osmosis units. It is even more essential within the Gulf area, where the seawater contains high concentrations of organics and is subject to algal blooms. Al Dur RO plant was thus designed with an efficient two-step pre-treatment process: a flotation step, including an enhanced coagulation stage, and a filtration step. In parallel, to assess the seawater variability and demonstrate the performances of the selected pre-treatment line, a pilot study was carried out on-site during one year. Al Dur drinking water objectives were particularly challenging and the design had to incorporate unusual guarantees such as a Silt Density Index below 3.0%/min, a turbidity below 0.2 NTU and a Langelier Saturation Index between 0.1 and 0.3. As a consequence, to comply with both the Bahraini drinking water standards and the tender specifications, the Al Dur mineralization unit design included a high velocity lime water saturator and a lime water filtration unit. The present paper describes the pre- and post-treatment performances based on the initial project design, the pilot study and the on-site results during the commissioning and the first few months of operation.

Ethanol production from corn stover pretreated by electrolyzed water and a two-step pretreatment method

Pretreatment is one of the most important unit operations for ethanol production from biomass feedstocks. In this study, corn stover was used as a feedstock to examine the effectiveness of two pretreatments: electrolyzed water pretreatment and a two-step pretreatment. Electrolyzed water was employed as a catalyst to conduct one-step pretreatment of corn stover at three temperatures (165, 180 and 195°C) and three treatment times (10, 20 and 30 min). During the two-step pretreatment process, an organic alkaline solution of 1% (w/w) NaOH in 70% (w/w) ethanol was used for lignin removal in the first step, followed by a second step using hot water. No furfural or 5-hydroxymethyl furfural was detected in the hydrolysates from both pretreatment methods when the detection limit of the HPLC was 0.2 g/L. The highest glucan conversion yields were 83% obtained at 195°C for 30 min with acidic electrolyzed water and 83% by the two-step process, where the second step of the pretreatment was at 135°C for 30 min. The hydrolyzates from the two pretreatment methods showed good performance in Saccharomyces cerevisiae fermentation tests. The two new methods may provide promising alternatives for the pretreatment of biomass for ethanol production.

Effects of Two-Step DC Electrochemical Pretreatment of Fine Grinding WC-Co Tool Surface on Morphology and Quality of Diamond Coatings

In the present investigation, diamond coating was deposited on fine grinding cemented carbide substrate by direct current arc discharge chemical vapor deposition. The effect of electrolytic etching time in the two-step electrochemical pretreatment process (firstly using electrolytic etching, and then using acid etching) on morphology and quality of the diamond coating were systemically studied. The surface morphology feature and quality of diamond coatings were characterized by means of Scanning Electron Microscope (SEM), laser Raman spectrometer respectively. The results showed that the electrolytic etching duration has distinctly effect on the quality and crystal features such as morphology, crystal type and grain size of diamond coating. It showed that as electrolytic current is direct current 3A, electrolytic etching time altering from 0.5 min to 7.5min, the surface morphology of diamond films gradually transition from microcrystalline cubic-octahedron to cauliflower type nanocluster, and further increase the electrolytic etching time, will lead to several negative effects on the quality and nucleation of the coatings which is not only retard the diamond nucleation, but also promote the formation of graphite.

Comparative Studies of Biodiesel Production from Rubber Seed Oil, Coconut Oil, and Palm Oil Including Thermogravimetric Analysis

High viscosity and low volatility of vegetable oils compared to diesel lead to injector fouling and carbon deposits in engine cylinders while using them directly in engines. Biodiesel from the vegetable oils produced by a transesterification process could reduce viscosity considerably and improve the volatility. The properties of methyl esters produced from rubber seed oil, coconut oil, and palm kernel oil, which are locally available, especially in Kerala (India), are presented here. The viscosity of methyl esters of these oils is found to be comparable with diesel fuel as per ASTM D6751-02. Biodiesel from rubber seed oil (with high FFA) was produced by employing a two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mgKOH/g with 0.40 and 0.35 v/v methanol-oil ratio and 1.0% v/v H2SO4 as catalyst at a temperature of 63(±2)°C with 1 h reaction time followed by transesterification using a methanol-oil ratio of 0.30 v/v, 0.5 w/v KOH as an alkaline catalyst at 55(±2)°C with 40 min reaction time to yield 98–99% biodiesel. Coconut oil and palm oil, being edible oils and having similarities in fatty acid composition, transesterification with 0.25 v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 58(±2)°C, 20 min reaction time for coconut oil and 0.25% v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 60(±2)°C for palm kernel oil converted them to 98–99% biodiesel. The viscosity of coconut biodiesel was more comparable to diesel fuel than that of other biodiesels, such as rubber seed oil biodiesel and palm oil biodiesel. Furthermore, thermogravimeric analysis indicated that coconut oil biodiesel is more volatile than other biodiesels and the volatility is nearer to diesel fuel.

A comparative study of vegetable oil methyl esters (biodiesels)

In the present study, rubber seed oil, coconut oil and palm kernel oil, which are locally available especially in Kerala (India), are chosen and their transesterification processes have been investigated. The various process variables like temperature, catalyst concentration, amount of methanol and reaction time were optimized. Biodiesel from rubber seed oil (with high free fatty acid) was produced by employing two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mg KOH/g with 0.40 and 0.35 v/v methanol–oil ratio and 1.0% v/v H 2SO 4 as catalyst at a temperature of 63(±2) °C with 1 h reaction time followed by transesterification using methanol–oil ratio of 0.30 v/v, 0.5 w/v KOH as alkaline catalyst at 55(±2) °C with 40 min reaction time to yield 98–99% biodiesel. Coconut oil and palm oil, being edible oils, transesterification with 0.25 v/v methanol–oil ratio, 0.50% w/v KOH as at 58(±2) °C, 20 min reaction time for coconut oil and 0.25% v/v methanol–oil ratio, 0.50% w/v KOH as alkaline catalyst at 60(±2) °C for palm kernel oil will convert them to 98–99% biodiesel. The brake thermal efficiency of palm oil biodiesel was higher with lower brake specific fuel consumption, but rubber seed oil biodiesel(ROB) showed less emission (CO and NO x ) compared to other biodiesels.

Methyl Ester Production from Rubber Seed oil Using Two-Step Pretreatment Process

Vegetable oil methyl ester is a very suitable substitute to diesel fuel as green energy or renewable energy in CI engines. A method has been developed to form methyl ester from rubber seed oil, by reducing the acid value of the oil having about 24% free fatty acids (FFAs) to 2 mg KOH/g by a two-stage pretreatment process. The first stage requires about 0.4 v/v of methanol–oil ratio and the second stage 0.35 v/v of methanol, in the presence of an acid catalyst, 1% v/v H2SO4, with continuous stirring at a temperature of 63(±2)°C. The mixture is provided one hour settling time to form the top layer as methanol–water mixture, which is removed. The bottom layer is subjected to transesterification with 0.3 v/v of methanol–oil ratio in the presence of 0.5 w/v KOH as alkaline catalyst to produce rubber seed oil methyl ester. The properties of rubber seed oil methyl ester are comparable with diesel fuel as per the ASTM D6751.

Effect of acidic etching and fluoride treatment on corrosion performance in Mg alloy AZ91D (MgAlZn)

Fluoride activation of Mg AZ91D die-cast alloy surfaces by ammonium fluoride pre-treatment is an important procedure in industry. The procedure forms a fluoride rich layer on the surface enabling the formation of coatings in a uniform manner during further treatments. The present study explores the time dependence of the sequential two-step pre-treatment process – acid etching in H 2SO 4 (first step) and steeping in NH 4F (second step) – on the corrosion properties of AZ91D alloy. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) show the α phase to be selectively etched via a “peeling-off” mechanism that eventually leads to the undercutting and undermining of the β-phase network. After ammonium fluoride treatment, variations in structure and chemical composition of the fluoride rich layer were shown to depend on the underlying phase of the alloy surface by SEM and time-of-flight secondary-ion-mass-spectroscopy (ToF-SIMS). After step 1 (acid etching), electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution indicates greater charge transfer resistance ( R t ) for samples of greater exposed β surface area. This greater R t increases after step 2 (NH 4F steeping). Furthermore, the corrosion protection properties of F-coated AZ91D can be significantly enhanced by optimizing the durations of the two pre-treatment steps. Indeed, over extension of the duration of either step 1 or step 2 leads to deterioration of the overall corrosion resistance.

Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids

A technique to produce biodiesel from crude Jatropha curcas seed oil (CJCO) having high free fatty acids (15%FFA) has been developed. The high FFA level of JCJO was reduced to less than 1% by a two-step pretreatment process. The first step was carried out with 0.60 w/w methanol-to-oil ratio in the presence of 1% w/w H 2SO 4 as an acid catalyst in 1-h reaction at 50 °C. After the reaction, the mixture was allowed to settle for 2 h and the methanol–water mixture separated at the top layer was removed. The second step was transesterified using 0.24 w/w methanol to oil and 1.4% w/w NaOH to oil as alkaline catalyst to produce biodiesel at 65 °C. The final yield for methyl esters of fatty acids was achieved ca. 90% in 2 h.

Fracture strength of two-step pretreated and diamond coated cemented carbide microdrills

Experiments were undertaken to evaluate effects of conventional two-step pretreatment process and diamond coatings on fracture strength of cemented carbide microdrills. For the pretreatment of the samples, the often used Murakami solution (10 g KOH + 10 g K 3 [Fe(CN) 6 ] + 100 gH 2 O) and an acid solution of hydrogen peroxide (10 ml 98 wt% H 2 SO 4 + 100 ml 38%H 2 O 2 ) were used. Diamond coatings were deposited using a coaxial excited microwave plasma system. The experimental results reveal that for small sized tools, the pretreatment will bring about negative effect on the fracture strength of the microdrills and among the two steps in the etching process, the acid etching is more harmful because it will create a porous surface layer to the tools. Therefore, the conventional pretreatment process is not suitable for the treatment of small sized tools; even it could improve effectively adhesion of diamond coatings to the cemented carbide substrates.